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Events


CNS Seminar Series, Spring 2012



Prof. Kimani Toussaint, Jr.

University of Illinois, Urbana-Champaign

"Photonics Research for Bio/nano Environments:
Applications to Nanophotonics and Biophotonics"


Friday, March 2, 2012

12:15,  700 Clark Hall
Lunch at Noon

Abstract: The application of photonics to help solve problems in biology and nanotechnology has become increasingly popular because of the importance of these areas to society. Research carried out at the laboratory for Photonics Research of Bio/nano Environments (PROBE) at the University of Illinois at Urbana-Champaign focuses on developing technologies that would be useful in the areas of nanophotonics and biophotonics. This talk will highlight the major projects pursued by our group in each of these areas.

The nanophotonics research pursued by PROBE lab primarily pertains to both characterization and application of plasmonic nanoantenna arrays. There is burgeoning interest in exploiting the potentially high local field enhancements that these structures provide, particularly for applications in light harvesting and for near-field control of optical forces. To this end, we will discuss how the optical parameter space, namely, input optical power, wavelength, and polarization along with the geometry of gold bowtie nanoantenna arrays (BNAs) can be tuned for a relatively broad and enhanced nonlinear optical response ranging from second-harmonic generation and two-photon photoluminescence to continuum generation. We will also discuss how the aforementioned optical and geometric parameters can enable very efficient particle manipulation using low input power and low-numerical aperture (NA) focusing. In this case, for a fixed BNA geometric condition, various particle manipulation regimes are obtained, and trapping efficiencies up to 20x greater than what is obtained using conventional high-NA optical traps are observed.

With regards to the biophotonics research, we will discuss Fourier transform-secondharmonic generation (FT-SHG) microscopy, which combines the nonlinear imaging technique of SHG with spatial harmonic analysis to quantitatively image the structure and organization of fibrillar collagen-based tissues. In addition, we use the fact that SHG is a coherent process to determine the polarization-dependent normalized tensor components of the 2nd-order scattering coefficient. We show that this latter parameter could be useful for quantitative assessment of molecular changes to collagen fibers.





CNS Seminar Series, Fall 2011

Prof. Nader Engheta

University of Pennsylvania

"Of Light, Electrons, and Metamaterials"

Thursday, November 3, 2011

12:15,  700 Clark Hall
Lunch at Noon

Abstract: In my group we have been developing the concept of “optical metatronics”, i.e. metamaterial-inspired optical nanocircuitry, in which the three fields of “electronics”, “photonics” and “magnetics” can be merged together.  In such a paradigm, the concept of metamaterials and plasmonics optics can be exploited to bridge the gaps among these fields, to modularize, standardize, and parametrize some of the optical and electronic phenomena, and to transplant concepts from one field into another.  In this unified platform of optical metatronics, the nanostructures with specific values of permittivity and permeability may act as the optical lumped circuit elements at the nanoscale, analogous to the circuit elements in RF electronics.  Nonlinearity in metatronics can also provide us with novel optical nonlinear lumped elements.  Optical nanoantennas can link the “macroworld” with such “nanoworld” in optical metatronics.  We have investigated the concept of metatronics through extensive analytical and numerical studies, computer simulations, and recently in a set of experiments at the IR wavelengths.  We have also been exploring how metamaterials can also be exploited to control the flow of photons, analogous to what semiconductors do for electrons, providing the possibility of one-way flow of photons, photon diodes, and photon capacitors.  We are now extending the concept of metatronics to other platforms such as graphene as a new paradigm for metatronic circuitry and also as one-atom-thick metamaterials and one-atom-thick transformation optical devices.  I will present an overview of our most recent results in these topics and discuss future directions and potentials.




CNS Seminar Series, Spring 2011


Prof. Roel Baets

Ghent University and IMEC

"Silicon photonics: the integration of light sources"

Friday, May 20, 2011

Noon, 700 Clark Hall
Lunch at 11:45am

Abstract: In this seminar I will discuss research at Ghent University - IMEC on integrated light sources in the context of a silicon photonics platform.  Two distinct approaches will be covered.  The first is the "hybrid silicon laser".  It relies on the bonding of think InP-InGaAsP epi-layers on patterened silicon photonics wafers and subsequent processing into electrically driven microlasers.  We are working on a who zoo of different hybrid lasers for different applications.  The second approach is based on four-wave-mixing in silicon and allows to generate new optical frequencies on the basis of optical pumping.  Our progress in this area both at telecom and longer wavelengths will be discussed, both for crystalline and amorphous silicon-on-insulator.



Prof. Lincoln Lauhon

Department of Materials Science and Eng.
Northwestern University

"Functional Imaging of Nanowires"

Tuesday, April 5, 2011
1:30pm, 700 Clark Hall



CNS Seminar Series, Fall 2010

"Phase transition in nanowires and on carbon nanotubes"

Abstract: Because of the latent heat, need for nucleation, and change in density, first-order phase transitions tend to be very sensitive to inhomogeneities and difficult to study and control in bulk material. Advantages can be gained by working with nanoscale systems which are small compared with the scale of inhomogeneities and domain structure. For example, we are investigating the formation and behavior of monolayers of gases physisorbed on individual single-walled carbon nanotubes. The quantity adsorbed is indicated by the downshifts of the vibrational resonance frequencies of the nanotube in the presence of vapor at controlled pressure and temperature.

Electrical measurements can be done simultaneously. To begin with, we are concentrating on the simplest substances, the noble gases. We find that their binding to nanotubes is, unsurprisingly, smaller than to graphite. For Kr in some cases we see sharp phase transitions within a monolayer, indicating that the nanotube surface is a near-perfect substrate. For Kr and Ar we see changes in the nanotube conductance as a monolayer forms and as phase transitions occur. For He we see possible signs of quantum effects.

Some observations remain to be understood.

Prof. David Cobden

Department of Physics

Friday, October 8, 2010
12:15pm, 700 Clark Hall

_________________________________________________________

 

"Integrated Quatum Photonics"

Abstract: Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [3]), measurement (eg. [4]) and other quantum technologies [5]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [6]. Here we report high-fidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [7]. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [8]. We have used this architecture to implement a small-scale compiled version of Shors quantum factoring algorithm [9] and demonstrated heralded generation of tunable four photon entangled states from a six photon input [10]. We have combined waveguide photonic circuits with superconducting single photon detectors [11]. We have also demonstrated how quantum process discrimination can be implemented with photonic circuits [12].  Finally, we describe our most recent results on complex quantum interference behavior in multi-mode interference devices with up to eight inputs and outputs, quantum walks of correlated particles in arrays of coupled waveguides (Fig. 1), the development and implementation of a scheme that dramatically improves implementation of quantum logic circuits by harnessing entanglement on non-computational degrees of freedom, and strongly enhanced photon collection from diamond color centers under micro-fabricated integrated solid immersion lenses [13].

REFERENCES
[1] T. D. Ladd, F. Jelezko, R. Laflamme, Y. Nakamura, C. Monroe, and J. L. OBrien, Nature 464, 45 (2010).
[2] J. L. O’Brien, Science 318, 1567 (2007).
[3] T. Nagata, R. Okamoto, J. L. O’Brien, K. Sasaki, and S. Takeuchi, Science 316, 726 (2007).
[4] R. Okamoto, J. L. O’Brien, H. F. Hofmann, T. Nagata, K. Sasaki, and S. Takeuchi, Science 323, 483 (2009).
[5] J. L. O’Brien, A. Furusawa, and J. Vu?ckovi´c, Nature Photon. 3, 687 (2009).
[6] A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L.O’Brien, Science 320, 646 (2008).
[7] A. Laing, A. Peruzzo, A. Politi, M. R. Verde, M. Halder, T. C. Ralph, M. G. Thompson, and J. L. O’Brien, arXiv:1004.0326 .
[8] J. C. F. Matthews, A. Politi, A. Stefanov, and J. L. O’Brien, Nature Photon. 3, 346 (2009).
[9] A. Politi, J. C. F. Matthews, and J. L. O’Brien, Science 325, 1221 (2009).
[10] J. C. F. Matthews, A. Peruzzo, D. Bonneau, and J. L. O’Brien, arXiv:1005.5119
[11] C. M. Natarajan, A. Peruzzo, S. Miki, M. Sasaki,Z. Wang, B. Baek, S. Nam, R. H. Hadfield, and J. L. O’Brien, Appl. Phys. Lett. 96, 211101 (2010).
[12] A. Laing, T. Rudolph, and J. L. O’Brien, Phys. Rev. Lett. 102, 160502 (2009).
[13] J. P. Hadden, J. P. Harrison, A. C. Stanley-Clarke, L. Marseglia, Y.-L. D. Ho, B. R. Patton, J. L. OBrien, and J. G. Rarity, arXiv:1006.2093.

Prof. Jeremy O'Brien

Centre for Quantum Photonics, H. H. Wills Physics Laboratory
and Department of Electrical and Electronic Engineering
University of Bristol

Thursday, September 9, 2010
12:15pm, 700 Clark Hall

 

CNS Seminar Series, Spring 2010

"Quantum Opto-Electronics with Semiconducting Nanowires and Carbon Nanotubes"

Abstract: We are interested in quantum controlling the optical and electronic behavior of solid state nanostructures. We are working towards an interface, based on pn-junctions, for transferring electronic quantum states coherently into photonic states. Our systems of choice are (InAsP) semiconducting nanowires and carbon nanotubes. Both systems have been cleaned up such that we can control individual electrons and holes, study their hyperfine and spin-orbit interactions, control spin quibits and discover properties of mechanics at the nanoscale. The quantum behavior is measured both in electrical and optical properties.

 

Prof. Leo Kouwenhoven

Quantum Transport Group
Kavli Institute of Nanoscience
Delft University of Technology

Tuesday, May 18, 2010
12:15 p.m., 122 Rockefeller Hall

 

_______________________________________________________

“Optical Nanostructures for Advanced Communication Systems”

 

Abstract: Wavelength-scale optical resonators can enable on-chip manipulation of photons, and will be important building blocks for optical- and quantum-communication systems. We recently demonstrated photonic crystal nanobeam cavity1,2 , fabricated in silicon, that supports modes with quality factor Q~106. Furthermore, by taking advantage of mechanical degrees of freedom of two coupled-nanobeam cavities3, we demonstrated reconfigurable optical filters4 that could be dynamically and reversibly tuned. In our structure, that combines NEMS with nanophotonics, an external bias voltage controls the separation (<100nm) between the nanobeams via the electrostatic force, which in turn has a strong effect on the resonant wavelength of the structure.  We demonstrate tunable filters with a tuning range of ~10nm, using less than 6V of external bias and negligible steady-state power consumption4.

Bright single-photon source based on diamond nanowire5, that we recently discovered, is another example of novel functionalities enabled by nanostructuring. Nitrogen vacancy (NV) color center in diamond has emerged as promising quantum emitter that combines the key advantages of isolated atomic systems with solid-state integration. In order to further improve the efficiency of NV-based quantum-emitters, it is important to enhance the collection efficiency of emitted photons.  We achieved this using nanowire-antenna approach, and demonstrated an order of magnitude larger collection efficiency over devices based on bulk diamond crystals.

1P. B. Deotare, M. W. McCutcheon, I. W. Frank, M. Khan, and M. Loncar, APL, 94, 121106 (2009)
2M. W. McCutcheon and M. Loncar, Optics Express, 16, 19136 (2008)
3 P. B. Deotare, M. W. McCutcheon, I. W. Frank, M. Khan, and M. Loncar, APL, 95, 031102 (2009)
4 I.W. Frank, P.B. Deotare, M.W. McCutcheon, Marko Loncar, arXiv:0909.2278
5 T.M. Babinec, B.M. Hausmann, M. Khan, Y. Zhang, J. Maze, P.R. Hemmer, M. Loncar, Nature Nanotechnology (March 2010),  arXiv: 0908.0233

Marko Loncar is Assistant Professor of Electrical Engineering at Harvard’s School of Engineering and Applied Sciences. He received his Diploma (1997) from University of Belgrade (Republic of Serbia) and his MS (1998) and PhD (2003) degrees from California Institute of Technology, all in electrical engineering. His expertise is in nanophotonics and nanofabrication. His recent research interests include optical nanocavities, nanoscale optomechanics, diamond nanophotonics and quantum optics, and cavity-enhanced nonlinear optics. Dr. Loncar has co-authored more than 50 journal articles and has given more than 50 invited talks and seminars. He is recipient of NSF CAREER Award in 2009, and Alfred P. Sloan Fellowship in 2010.

Prof. Marko Loncar

School of Engineerig and Applied Sciences
Harvard University

Thursday, March 11, 2010
12:15 p.m., 700 Clark Hall

_________________________________________

" Nanosilicon Photonics "

Abstract: Silicon Photonics is no more an emerging field of research and technology but it is a present reality with commerical products available on the market, where low dimensional silicon (nanosilicon or nano-Si) can play a fundamental role. After a review of the field, the optical properties of silicon reduced to nanometric demensions are introduced. The use of nano-Si, in the form of Si nanocrystals, in the main building blocks of Silicon Photonics (waveguides, modulators, sources and detectors) is reviewed and discussed. Recent advances of nano-Si devices such as waveguides, optical resonators (linear, rings, and diesks) are treated. The development of high efficiency light emitting diodes for interchip bidirectional optical interconnects is presented as well as the recent progresses to exploit nano-Si for solar cells. In addition, non-linear optical effects which enable fast all-optical switches are described.

References

Silicon Nanocrystals; Fundamentals, Synthesis and Applications edited by L. Pavesi and R. Turan (Wiley-VCH Verlag GmbH, Berlin 2010) ISBN: 978-3-527-32160-5 Hardcover 688 pages March 2010

Silicon photonics II edited by D. Lockwood and L. Pavesi Topics in Applied Physics (Springer Verlag 2010)

 

Prof. Lorenzo Pavesi

Nanoscience Laboratory, Department of Physics
University of Trento

Thursday, March 18, 2010
12:15 p.m., 700 Clark Hall

_________________________________________

""Graphene-based materials and their potential for applications"

Abstract: Thermal chemical vapor deposition has been used to grow graphene on copper substrates [1] and isotopic labeling (13C vs 12C [2]) was used to study how graphene grows on Cu [3]. We will also discuss graphene’s potential as a transparent electrically conductive thin film [4a, b, c] and for electrical energy storage (e.g.,,graphene-based ultracapacitors [5]).  Our top-down approaches [6,7] were the first to target obtaining individual layers of graphite obtained by micromechanical exfoliation. Another productive direction has been to convert graphite to graphite oxide (GO), generate aqueous colloidal suspensions containing individual layers of GO (we call them ‘graphene oxide’), and to use these ‘graphene oxide platelets in a variety of ways, such as for making composites with polymers [8], silica [9], and ‘paper-like’ materials [10].Time permitting, I will revisit our pioneering contributions in the use of such chemically modified graphenes in large quantities, which depend on preparing chemically modified graphenes as colloids [11].

Support of our work by DARPA, the state of Texas, UT Austin, and prior support by NASA and the NSF, is appreciated.  Recent support on graphene-based ultracapacitors (NSF, DoE-SISGR, Graphene Energy Inc) as well as on graphene-based transparent conductive films (DARPA) is appreciated. Ruoff Group publications are at http://bucky-central.me.utexas.edu/publications.htm .

1. Xuesong Li, Weiwei Cai, Jinho An, Seyoung Kim, Junghyo Nah, Dongxing Yang, Richard Piner, Aruna Velamakanni, Inhwa Jung, Emanuel Tutuc, Sanjay K. Banerjee, Luigi Colombo, Rodney S. Ruoff, Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils, Science (2009), 324, 1312-1314.
2. Cai, Weiwei; Piner, Richard D.; Stadermann, Frank J.; Park, Sungjin; Shaibat, Medhat A.; Ishii, Yoshitaka; Yang, Dongxing; Velamakanni, Aruna; An, Sung Jin; Stoller, Meryl; An, Jinho; Chen, Dongmin; Ruoff, Rodney S.Synthesis and Solid-State NMR Structural Characterization of 13C-Labeled Graphite Oxide. Science (2008), 321(5897),1815-1817
3.Xuesong Li; Weiwei Cai; Luigi Colombo; Rodney S. Ruoff. Evolution of Graphene Growth on Ni and Cu by    Carbon Isotope Labeling. Nano Letters (2009).Meryl D. Stoller; Sungjin Park; Yanwu Zhu; Jinho An; Rodney S. Ruoff.
4. (a). X. S. Li, Y. W. Zhu, W. W. Cai, M. Borysiak, B. Y. Han, D. Chen, R. D. Piner, L. Colombo, R. S. Ruoff,      Transfer of large-area graphene films for high-performance transparent conductive electrodes, Nano Letters,  ASAP, DOI: 10.1021/nl902623y (2009).  (b). Weiwei Cai, Yanwu Zhu, Xuesong Li, Richard D. Piner, and          Rodney S. Ruoff. Large area few-layer graphene/graphite films as transparent thin conducting electrodes.     Applied Physics Letters (2009), 95, 123115; (c). Yanwu Zhu, Weiwei Cai, Richard D. Piner, Aruna Velamakanni, and Rodney S. Ruoff. Transparent self-assembled films of reduced graphene oxide platelets.   Applied Physics Letters (2009), 95, 103104.
5. Meryl D. Stoller; Sungjin Park; Yanwu Zhu; Jinho An; Rodney S. Ruoff. Graphene-Based Ultracapacitors.    Nano Letters (2008), 8 (10), 3498-3502.
6. Lu XK, Yu MF, Huang H, and Ruoff RS, Tailoring graphite with the goal of achieving single sheets, Nanotechnology, 10, 269-272 (1999).
7. Lu XK, Huang H, Nemchuk N, and Ruoff RS, Patterning of highly oriented pyrolytic graphite by oxygen plasma etching, Applied Physics Letters, 75, 193-195 (1999).
8. Sasha Stankovich, Dmitriy A. Dikin, Geoffrey H. B. Dommett, Kevin M. Kohlhaas, Eric J. Zimney, Eric A. Stach, Richard D. Piner, SonBinh T. Nguyen and Rodney S. Ruoff, Graphene-based composite materials, Nature 442 (2006) 282-285.
9. Supinda Watcharotone, Dimitry A. Dikin, Sasha Stankovich, Richard Piner, Inhwa Jung, Geoffrey H. B. Dommett, Guennadi Evmenenko, Shang-En Wu, Shu-Fang Chen, Chuan-Pu Liu, SonBinh T. Nguyen, Rodney S. Ruoff. Graphene-Silica Composite Thin Films as Transparent Conductors. Nano Letters, 7(7), (2007), 1888-1892.
10. Dmitriy, A. Dikin, Sasha Stankovich, Eric J. Zimney, Richard D. Piner, Geoffrey H. B. Dommett, Guennadi Evmenenko, SonBinh T. Nguyen, Rodney S. Ruoff. Preparation and characterization of graphene oxide paper. Nature, 448, (2007), 457-460.
11. Park, Sungjin; Ruoff, Rodney S. Chemical methods for the production of graphenes. Nature Nanotechnology (2009), 4, 217-224.

Biography:
Prior to joining The University of Texas at Austin as a Cockrell Family Regents Chair in Mechanical Engineering and Materials Science and Engineering, Prof. Rod Ruoff served as Director of the Biologically Inspired Materials Institute at Northwestern University. He has been a ‘Visiting Chair Professor’ at Sungkyunkwan University in South Korea. He received his B.S. in Chemistry from the U. of Texas (Austin) and Ph.D. from the University of Illinois-Urbana. He was a Fulbright Fellow at the Max Planck Institute-Goettingen, Germany.  From ‘89-’90, he was a Postdoctoral Fellow at the IBM T. J. Watson Research Center in New York. Prior to joining Northwestern in 2000, he was a Staff Scientist at the Molecular Physics Laboratory of SRI International and Associate Professor of Physics at Washington University. His research interests and activities include global environment and energy-related issues; synthesis and physical/chemical properties of nanostructures and composites; technology development, and developing new tools for biomedical research. Prof. Ruoff has published 215 refereed journal articles in the fields of chemistry, physics, mechanics, & materials science.  He is a co-founder of Graphene Energy, Inc., and the founder of Nanode, Inc.

 

 

Prof. Rod Ruoff

University of Texas, Austin

Wednesday, January 27, 2010
12:15 p.m., 700 Clark Hall

 

CNS Seminar Series, Fall 2009

" Gallium-arsenide deep-center laser "

Abstract:

The ongoing quest for semiconductor lasers with low threshold current has led to the development of new materials (e.g., quantum wells, wires, and dots) and new optical resonators (e.g., microdisks and photonic bandgap crystals).  In a novel approach to ``thresholdless" lasers, we have developed a new growth technique for self-assembled deep-centers in the technologically important
semiconductor gallium-arsenide.  We recently demonstrated the first gallium-arsenide deep-center laser.  These lasers, which intentionally utilize gallium-arsenide deep-center transitions, exhibit a threshold current density of less than 2A/cm2 in continuous-wave mode at room temperature at the important 1.54um fiber-optic wavelength.  The significance is that this threshold is much lower than for bandgap transitions in conventional bulk semiconductors.   Moreover, in contrast to conventional semiconductor devices,
whose operating wavelengths are fixed by the bandgap energy, the
room-temperature stimulated-emission from gallium-arsenide deep-centers can be tuned very widely from the bandgap (about 900nm) to half-the-bandgap (1600nm). We demonstrated laser action at many wavelengths between 1.2um and 1.6um, which includes fiber-optic wavelengths.  The significance is that it has been a long-sought goal to tune the stimulated-emission from the same semiconductor over a wide wavelength range.  At present, wide tunability of the laser operating wavelength can be obtained from optically-pumped dye-lasers, titanium-sapphire lasers, and free-electron lasers.  A semiconductor source of tunable coherent infrared radiation would have many applications, such as fiber-optics, spectroscopy, lab-on-a-chip, chemical species identification,
medicine, and dentistry.  Our demonstration of broad-area laser action was accomplished with electrical injection, and not merely optical pumping.

Biography:

At Yale University, Dr. Janet Pan has been a winner of the NSF Career, ONR Young Investigator, and Sheffield Teaching Awards.  Dr. Pan has been an Invited Speaker at the March Meeting of the APS, the International Conference on the Physics of Semiconductors, and Photonics West.   Dr. Pan received all her
degrees from the Massachusetts Institute of Technology.  While at MIT, she won the Hertz, NSF, and Rockwell International Graduate Student Fellowships.  She was also a winner of the Associate of MIT Alumnae Highest Academic Achievement Award for best female undergraduate student.

Prof. Janet Pan

Yale University

Wednesday, November 18, 2009
12:15 p.m., 700 Clark Hall

_________________________________________

" Engineering a Quantum Information Processor "

Abstract:

Fundamental advantage of utilizing quantum resources for computation and communication has been discovered in the last fifteen years, and experimental demonstration of representing and manipulating quantum bits in physical systems and simple quantum algorithms followed. While the experimental research in this field has progressed at a rapid pace, the notion of a practical information processor based on quantum physics still faces tremendous amount of challenges. Construction of a scalable quantum information processor is a system design challenge that
requires cutting-edge technology guided by engineering principles. The task requires expertise in quantum physics, computer architectures and integrated microsystems technology, and presents a truly multidisciplinary challenge. In this talk, I will discuss the issues associated with designing and constructing a realistic quantum information processor, and some of the technology progress made to date. I will present micro-electromechanical systems (MEMS), micro-optics and photonics technology applied to integration of qubits represented by atomic ions trapped in a ultra-high vacuum chamber.

Bio: Prof. Jungsang Kim received his Ph.D. degree in Physics from
Stanford University in 1999, where he demonstrated the first semiconductor-based single photon sources, and advanced single photon detectors for quantum optics experiments. Prior to joining Duke University in 2004, he was a Technical Manager at Bell Laboratories, Lucent Technologies, where he worked on MEMS technologies applied to optical communication systems, and advanced basestation architectures for wireless communications. At Duke University, he leads several research projects related to multi-functional integrated systems, including scalable quantum information processing based on trapped ions, MEMS technology for atom-based quantum information processing, and advanced photon detectors for quantum communications.

Prof. Jungsang Kim

Duke University

Wednesday, November 11, 2009
12:15 p.m., 700 Clark Hall

CNS Seminar Series, Summer 2009

"Low frequency noise in graphene: Influence of disorder and band structure "

Abstract:

One of the main applications of Graphene is expected to be as active elements in electronics. While there are advantages in the form of high carrier mobility, robustness, and miniaturization, there are several technical issues that limit the performance of a graphene-based transistor. In particular, one needs to understand the sources and influence of disorder in graphene quantitatively not only to accelerate its application in electronics, but also to realize many of the exotic physics of Dirac Fermions. In this talk I shall present some recent experiments with low-frequency electrical noise to understand disorder in exfoliated mono- and bi-layers of Graphene, which seems to arise primarily from the underlying substrate. I shall also discuss how this could actually reflect the band properties of graphene with increasing number of layers.

Ref:

1. A. N. Pal & A. Ghosh, Phys. Rev. Lett. 102, 126805 (2009)

2. A. N. Pal & A. Ghosh, Appl. Phys. Lett. (in press); cond-mat/0905.4485

 

Prof. Arindam Ghosh

IISC, Bangalore, India

Wednesday, Juluy 29, 2009
12:15 p.m., 700 Clark Hall

CNS Seminar Series, Spring 2009

"Geometry, light and a wee bit of magic"

Abstract:

Many mass-produced everyday products of modern technology would appear to be completely magical to our ancestors: mobile phones, television, computers, electric light, cars, etc. Some devices that are still perceived as magical or mysterious are about to appear in the laboratory and are not so mysterious after all. For example, the first prototypes of cloaking devices have been recently made at Duke University, Berkeley and here at Cornell. At Harvard University, first vital steps towards levitating objects on the forces of the quantum vacuum have been made. At St Andrews, we observed first indications of artificial black holes in the laboratory, using extremely short light pulses in photonic-crystal fibres. Invisibility devices, quantum forces and optical black holes have two things in common: they represent applications of Einstein’s general relativity in Maxwell’s electromagnetism and their practical demonstrations are made possible by modern metamaterials. I will try to elucidate the scientific principles acing behind the scenes of such "pure and applied magic".

Prof. Ulf Leonhardt

University of St Andrews, Scotland

Wednesday, June 10, 2009
12:15 p.m., 700 Clark Hall

_____________________________________________

" Probing Polymer Photovoltaics: Nanoscale
Morphology to
Nanoscale Photonics "

Abstract:

Organic semiconductors are potentially attractive materials for use in low-cost solar cells and energy efficient lighting and displays. However, we lack a fundamental understanding of many basic physical processes in these heterogeneous materials. This talk will discuss our work ranging from the use of nanopatterned surface chemistry to the development and application time-resolved Electrostatic Force Microscopy (trEFM), and photoconductive Atomic Force Microscopy (pcAFM). These techniques allow us to measure charge generation, collection, and trapping with sub-100 nm resolution so we can correlate variations in performance directly with variations in local film structure. The observed current and photocurrent distributions have implications for optimization of film processing, selection of materials for buried polymer/anode contacts, and design of organic tandem cells. Finally, we discuss the spectral properties of plasmonic near-field excitation enhancements near colloidal nanoparticles, which might find use in applications with extremely thin light absorbing layers.

Prof. David Ginger

Department of Chemistry

University of Washington

Wednesday, April 1, 2009
12:15 p.m., 700 Clark Hall

_____________________________________________

"Nanomechanics of nano-carbon"

Abstract:

This talk will describe our work toward fundamental understanding of the mechanical properties of carbon nanotubes and graphene, and their application in nano-electromechanical devices (NEMS).  This includes recently-published measurements of the mechanical stiffness[1] and electromechanical response[2] of carbon nanotubes of known chirality, and measurement of the stiffness and ultimate strength of single graphene sheets[3].  More recent work includes analysis of the Raman spectrum of graphene under uniaxial strain; measurement of thickness-dependent friction in graphene; and electrical readout and mass sensing properties of graphene nanomechanical resonators.

James Hone is currently Associate Professor of Mechanical Engineering at Columbia University.  He received his PhD in experimental condensed matter physics from UC Berkeley in 1998, and did postdoctoral work at the University of Pennsylvania and Caltech, where he was a Millikan Fellow.  He joined the Columbia faculty in 2003.  

His current research interests include synthesis, characterization, manipulation, and applications of carbon nanotubes; graphene; nanomechanical devices; and nano-biology.

1. Yang Wu, Mingyuan Huang, Feng Wang, Henry X. M. Huang, Sami Rosenblatt, Limin Huang, Hugen Yan, Stephen P. O’Brien, J. Hone, and Tony F. Heinz, “Determination of the Young’s Modulus of Structurally Defined Single-Walled Carbon Nanotubes,” Nano Letters 8, 4158 (2008)

2. Mingyuan Huang, Yang Wu, Bhupesh Chandra, Hugen Yan, Yuyao Shan, Tony F. Heinz, J. Hone, “Direct Measurement of Strain-induced Changes in the Band Structure of Carbon Nanotubes,” Phys. Rev. Lett. 100, 136803 (2008).

3. Changgu Lee, Xiaoding Wei, Jeffrey Kysar, J. Hone, “Measured elastic properties and ultimate strength of monolayer graphene,” Science 321, 385 (2008)

Prof. James Hone

Department of Mechanical Engineering and NSEC

Columbia University

Thursday, February 26 , 2009
12:15 p.m., 700 Clark Hall

CNS Seminar Series, Fall 2008

"Terahertz Studies of Nanobolometers, and of
One-Dimensional
Conduction in Carbon Nanotubes "

Abstract:

We have conducted studies of very small, absorbing nanostructures that have signature excitations in the Terahertz (1012 Hz) range, or can provide new, ultrasensitive detection in that frequency range. Single-wall metallic carbon nanotubes display novel effects of one-dimensional electron physics. They should display many significant predictions of the Luttinger liquid model. We describe experiments that are underway at Yale to probe these predictions, and compare these to recent measurements at Cornell. As an introduction, we describe how the Fourier-transform spectrometer we have developed can be used also to test ultrasensitive superconducting nanobolmeters. These bolometers are predicted to be ultrasensitive energy detectors, and can detect single Terahertz photons, of energy 10-21 J or less.

Bio:  Prof. Prober’s research is in superconductivity and quantum devices.  He received a PhD in Physics from Harvard in 1975, and joined the Yale faculty that year as an Assistant Professor.  He is also appointed in the Department of Physics.  He is a Fellow of the American Physical Society and a member of the Connecticut Academy of Science.  He has been awarded two Fulbright Faculty Fellowships, and has been a Visiting Professor at Tel Aviv University and the Weizmann Institute of Science.  Dr. Prober is the chair of the Department of Applied Physics and also Director of Graduate Admissions for the School of Engineering. 

 

Prof. Daniel Prober

School of Engineering and Applied Science

Yale University

Wednesday, November 19, 2008
12:15 p.m., 700 Clark Hall


 

 

"Mimicing the Eye: Imagers Based on Hemispherical
Focal Plane Arrays Using Organic Photodiodes"

Abstract:

The human eye provides an example of an ideal imaging system: it is compact and lightweight while having a very wide field of view without image distortion, a very low f/number (and hence high sensitivity in low light), and has a very simple lens system. The architecture is made particularly simple since the image is formed on a nearly hemispherical surface, thereby matching the curved focal plane of the lens. Achieving this imaging system in modern cameras has been difficult since the “film plane” must be flat if conventional, brittle semiconductor sensor arrays are used. Indeed, formation of high performance organic electronic devices on three dimensionally deformed surfaces is severely constrained by the tensile stresses and shear slip that are introduced during the deformation process. Here, we demonstrate the direct transfer of metals via cold welding onto preformed, 1.0 cm radius plastic hemispheres with micrometer scale feature resolutions to realize 100x100 organic photodetector focal plane arrays that mimic the architecture of the human eye [1]. This demonstration significantly extends the ability of direct transfer patterning, previously only demonstrated on planar substrates, to advanced optical and electronic applications. The passive matrix focal plane array consists of high performance, (40µm)2 organic double heterojunction photodetectors with response extending across the visible spectrum. The dark current density of a typical detector is 2.5±­0.1 µA/cm2 at -1V bias, and with a peak external quantum efficiency reaching 12.6±0.3% at a wavelength of 640nm. The photodetector impulse response was 20ns, making the array suitable for video recording applications.

Dr. Stephen Forrest

Departments of EECS, Physics and Materials Science and Engineering
University of Michigan

Thursday, October 2, 2008
12:15 p.m., 700 Clark Hall

Dr. Forrest

 

 


"Nanostructure Architectures for Next Generation Solar Cells "

Abstract: Environmentally friendly energy resources are needed to meet our clean energy demand. Semiconductor nanoparticle and nanotube assemblies provide new ways to develop next generation solar cells.[1-4].  Of particular interest is the nanowire/nanotube architecture which can significantly improve the efficiency of nanostructure based solar cells.  We have now developed quantum dot solar cells by assembling different size CdSe quantum dots on TiO2 films composed of particle and nanotube morphologies (Scheme 1).  Upon bandgap excitation, CdSe quantum dots inject electrons into TiO2 nanoparticles and nanotubes, thus enabling the generation of photocurrent in a photoelectrochemical solar cell.  These composite semiconductor nanostructures can be tailored to tune the photoelectrochemical response via size control of CdSe quantum dots and improve the photoconversion efficiency by facilitating the charge transport through TiO2 nanotube architecture. Ways to improve power conversion efficiency and maximize the light harvesting capability through the construction of a rainbow solar cell and carbon nanotube-semiconductor hybrid assemblies will be presented. The salient features of carbon nanotube and graphene scaffolds[5, 6] for facilitating charge collection and charge transport will also be discussed.

Prof. Prashant V. Kamat

Department of Chemistry and Biochemistry, Department of Chemical and Biomolecular Engineering
University of Notre Dame

Thursday, September 18, 2008
12:15 p.m., 700 Clark Hall

Prashant V. Kamat


"Spintronics: Nanoscience and Nanoelectronics "

Abstract: Manipulation of spins in condensed matter is a frontier in physics and nanoelectronics. By the use of spin current, we can electrically control magnetization, through which the interaction between carrier spins and localized spins is elucidated and the magnetization direction is reversed. Here, I discuss two areas of research we are currently involved. One is the electrical manipulation of magnetization, ranging from electric-field control of magnetization direction [1] to domain wall manipulation by spin-polarized current in ferromagnetic semiconductors [2]. The other is giant tunnel-magnetoresistance and current-induced magnetization switching in MgO-barrier magnetic tunnel junctions [3]. I will also discuss about the impact of MgO-barrier magnetic tunnel junction on logic circuits [4]. This work was supported by the "Research and Development for Next-Generation Information Technology" program from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

 

Prof. Hideo Ohno

Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication
Tohoku University

Friday, August 15 , 2008
12:15 p.m., 700 Clark Hall

Hideo Ohno


CNS Seminar Series, Spring 2008

"Photosynthetic Architectures and Materials
for Organic Solar Cells"

Abstract: Organic solar cells use semiconducting thin films of molecules or polymers to replace the inorganic semiconductors found in more conventional solar cells. The motivation is the promise of lower costs. But to date, the efficiency and stability of organic solar cells remains uncompetitive with inorganic devices. This performance contrasts with that other molecular approach to solar energy conversion, photosynthesis – a self sustaining process that dominates the globe and fixes more than 100 Gtons of carbon annually at an equivalent power of 100 TW.

In this talk, we report the exploitation of photosynthetic materials and device architectures in organic solar cells.

The culmination of the work is an ‘organic solar concentrator’ (OSC), which adopts the photosynthetic architecture by separating the functions of light absorption and charge generation. We demonstrate OSCs based on both synthetic dyes and phycobilisomes - highly efficient light gathering structures evolved by algae. We report efficiencies of up to 6.8% at 1 sun. OSCs are a flexible new solar technology that can be used in concert with existing inorganic solar cells.  Like other organic semiconductor devices, OSCs are compatible with low cost manufacturing and are expected to be inexpensive.

Prof. Marc Baldo

Dept. of Electrical Engineering and Computer Science
M.I.T.

Thursday, Arpil 24, 2008
12:15 p.m., 700 Clark Hall

Marc Baldo


CNS Seminar Series, Fall 2007

"Spin Transport in Ferromagnet
Semiconductor Heterostructures "

Abstract: A longstanding goal of research in semiconductor spintronics is the ability to inject, modulate, and detect electron spin in a single device.   I will discuss recent progress in the study of spin transport in ferromagnet-semiconductor heterostructures, including the electrical detection of spin accumulation and the observation of spin precession in transport.  The focus of our work is on epitaxial Fe/GaAs (100) heterostructures comprising a heavily doped Schottky barrier on an n-doped channel (n = 2x10^16 – 1x10^17 cm^-3).  A non-equilibrium spin polarization is injected into the channel by tunneling through the Fe/GaAs Schottky barrier.  Electrical spin detection is accomplished by measuring the electrochemical potential at a non-local detection contact.  In this manner, a spin-valve signal which decays with increasing separation of the source and detector is observed.  More importantly, the spin detection signal can be modulated by precession of the spin in the channel of the device.  In a sufficiently large transverse field, the spin valve effect is completely suppressed by dephasing in the GaAs channel.  This experimental approach allows for a direct comparison with optical measurements of spin polarization in the channel as well as a simple drift-diffusion model for the spin transport.  The devices allow us to probe quantitatively the spin lifetime and diffusion constant as well as hyperfine fields that influence spin precession and dephasing.  We show that the magnitude and sign of the accumulated polarization depend strongly on the bias voltage across the injector, although the details of this behavior are not understood.  This work was supported by ONR, the NSF MRSEC, NNIN, and IGERT programs, and the Los Alamos LDRD program.


Spin Polarized Image

Prof. Paul Crowell

School of Physics and Astronomy
University of Minnesota

Thursday, November 29, 2007
12:15 p.m., 700 Clark Hall

Prof. Crowell


"The Coupling of Mechanical and Magnetic Degrees of Freedom in Magneto Electromechanical Systems "

Abstract: The dynamics of small magnetic cantilevers is affected by the coupling between the mechanical and magnetic degrees of freedom Magnetization reversal is facilitated by torsional motion of the cantilever and magnetomechanical torques can be detected as line splittings in current-induced ferromagnetic resonance spectra.

We study theoretically the possible utilization of electric current-induced mechanical torques in ferromagnetic-normal-metal heterostructures generated by spin-flip scattering [4-6] or the absorption of transverse spin currents by a ferromagnet as discussed above. We propose a concept for a spin-transfer-driven electric nanomotor based on integrating metallic nanowires with carbon nanotubes, in which the current-induced mechanical torques drive a rotary motion.

Dr. Gerrit Bauer

Theoretical Physics Group
Kavli Institute of NanoScience
Delft University

Tuesday, October 30, 2007
12:15 p.m., 700 Clark Hall

Dr. Bauer


"Active Photonic nanomaterials: from disordered to periodic"

Abstract: Active photonic nanomaterials, which have high gain or large nonlinearity, are essential to the development of nanophotonic devices and circuits. In this talk, I will provide a review of our recent research activities related to the fabrication of active photonic nanomaterials and the development of photonic devices based on such materials. In particular, we focus on a wide bandgap semiconductor zinc oxide and fabricate a broad range of structures, from disordered to periodic, with various nanofabrication techniques. Lasing in the near-ultraviolet frequency has been realized in both periodic and random structures at room temperature under optical pumping.

Prof. Hui Cao

Department of Physics and Astronomy
Northwestern University

Thursday, October 11, 2007
12:15 p.m., 700 Clark Hall

Hui Cao Research Laboratory


"Multiple Exciton Generation in Semiconductor Quantum Dots and Novel Molecules: Applications to Third Generation Solar Photon Conversion "

Abstract: In order to utilize solar power for the production of electricity and fuel on a massive scale, it will be necessary to develop solar photon conversion systems that have an appropriate combination of high efficiency (delivered watts/m2) and low capital cost ($/m2).  One potential, long-term approach to high efficiency is to utilize the unique properties of quantum dot nanostructures to control the relaxation dynamics of photogenerated carriers to produce either enhanced photocurrent through efficient photogenerated electron-hole pair multiplication or enhanced photopotential through hot electron transport and transfer processes.  To achieve these desirable effects it is necessary to understand and control the dynamics of hot electron and hole relaxation, cooling, charge transport, and interfacial charge transfer of the photogenerated carriers with femtosecond (fs) to ns time resolution.  At NREL, we have been studying these fundamental dynamics in various bulk and nanoscale semiconductors (quantum dots (QDs), quantum rods/wires, and quantum wells) for many years using fs transient absorption, photoluminescence, and THz spectroscopy. Recently, we predicted that the generation of more than one electron-hole pair (which exist as excitons in QDs) per absorbed photon would be an efficient process in QDs . This prediction has been confirmed over the past 2 years in several classes of QDs.  We have observed very efficient and ultrafast  multiple exciton generation (MEG) from absorbed single high energy photons in Group IV-VI and recently in Si QDs.  Efficient MEG has the potential to greatly enhance the conversion efficiency of solar cells that incorporate QDs for both solar electricity and solar fuel (i.e. H2) production. Selected aspects of this work will be summarized and recent advances will be discussed; a unique quantum mechanical model to explain efficient and ultrafast MEG based on the coherent superposition of multiple excitonic states (in collaboration with Al. L. Efros and A. Shabaev at NRL) will also be discussed. Various possible configurations for quantum dot solar cells that could produce ultrahigh conversion efficiencies for the production of electricity and solar fuels (e.g. H2 from H2O) will be presented, along with progress in developing such new types of solar cells.  Finally, we have also predicted an analogous MEG effect in molecules (called singlet fission) that could be used in molecular chromophore-sensitized nanocrystalline TiO2 solar cells and new preliminary evidence for this effect will also be presented. .

Prof. Arthur Nozik

Center for Basic Sciences
National Renewable Energy Laboratory
Golden, CO 80401
and
Department of Chemistry
University of Colorado, Boulder

Thursday, September 27, 2007
12:15 p.m., 700 Clark Hall

Arthur Nozik

CNS Seminar Series,Spring 2007

"Nanowire Building Blocks for Photonics & Electronics "

Abstract: Nanowires are of both fundamental and technological interest. They represent the critical components in the potential nanoscale electronic and photonic device applications. Achieving high level of synthetic control over nanowire growth allows us to explore some of their very unique and exciting physical properties. For example, semiconductor nanowires can function as self-contained nanoscale lasers, sub-wavelength optical waveguides, frequency converters and photodetectors. It was also discovered that the thermoconductivity of the silicon nanowires can be significantly reduced when the nanowire size in the 20 nm region, pointing to a very promising approach to design better thermoelectrical materials for energy conversion. In this talk, I will outline our recent efforts in the direction of using nanowires for photonics, electronics and energy conversion applications.

Prof. Peidong Yang

Department of Chemistry
University of Califonia at Berkeley

Thursday, April 5, 2007
12:15 p.m., 700 Clark Hall

Peidong Yang Group



"Chirality-resolved single-walled carbon nanotubes"

Abstract: The utilization of single-walled carbon nanotubes (SWNTs) in large quantities for molecular electronics, optoelectronics, biosensors, and medical applications will require SWNTs of the same physical structure, electronic type, and band gap.  Since current methods of synthesis produce mixtures of nanotubes with different physical structures and electrical properties, the development of strategies for the post-production separation of these one-dimensional materials is highly desirable.  In this work, we demonstrate a scalable method for separating SWNTs by their diameter and electronic type (i.e., semiconducting versus metallic) using density gradient ultracentrifugation (DGU).  Since DGU is a technique commonly utilized to separate and isolate different sub-cellular components, DNA from RNA, and even different sequences of DNA by their compositions, we initially focused on the bulk sorting of DNA wrapped SWNTs in aqueous density gradients [1].  This process led to enrichment of SWNTs by diameter – especially in the small diameter regime (i.e., SWNT diameter = 0.7 – 1.0 nm).  However, DNA wrapping possessed several undesirable characteristics including prohibitive expense in large scale production, irreversible wrapping, and inefficient wrapping for SWNTs with diameters exceeding 1 nm.  Consequently, subsequent work has focused on DGU of surfactant encapsulated SWNTs [2].  In particular, bile salt surfactants, such as sodium cholate (SC), have overcome the drawbacks of DNA.  Furthermore, additional control over the density-structure relationship has been achieved by using co-surfactant mixtures of SC and sodium dodecyl sulfate (SDS).  For example, highly efficient metal versus semiconductor separation has been achieved with SDS:SC co-surfactant ratios ranging from 1:4 to 3:2.  Characterization of the resulting sorted SWNT samples includes optical absorption spectroscopy, photoluminescence spectroscopy, atomic force microscopy, and direct charge transport measurements.  Since DGU produces relatively large quantities of monodisperse SWNTs, this talk will conclude with our most recent efforts to realize enhanced performance in SWNT devices, such as thin-film field effect transistors, using SWNTs sorted by DGU.


Prof. Mark Hersam

Materials Science and Engineering Dept ,
Northwestern University

Thursday, March 29, 2007
12:15 p.m., 700 Clark Hall

Hersam Group


"Cold molecules - the new frontier in the ultacold world "

Dr. Jun Ye

JILA and the National Institute of Standards and Technology

Thursday, February 22, 2007
12:15 p.m., 700 Clark Hall

Jun Ye



 

CNS Seminar Series, Fall 2006

"Electrical Soliton Modelocking - Taming Electrical Solitons"

Abstract: Solitons are a unique class of nonlinear pulse waves that have captivated scientists for over a century. Electrical solitons, which are created on nonlinear transmission lines (electromagnetic waveguides whose dielectric constant changes with the electric field applied), are especially interesting as they allow the use of the fascinating physics of solitons in a medium that touches our everyday lives, modern electronics.

In this talk, I will describe the first electrical soliton oscillator (electrical soliton modelocked system) that my research group has recently developed. Made by looping a nonlinear transmission line around an amplifier, the soliton oscillator self-generates a stable train of electrical solitons, initially growing them from background noise. By nature, solitons are unruly, and solitons circulating in an oscillatory loop tend towards chaos. The key to our success in building the stable oscillator was finding a way to tame the unruly behaviors and realizing it in the amplifier. The successful soliton control shown in this work with the latest prototype in a tiny silicon microchip may herald widespread use of solitons in electronics, especially in all-electronic ps-resolved time-domain metrology & in wireless system applications.

(Co-workers) David Ricketts and Xiaofeng Li

 

Prof. Donhee Ham

Electrical Engineering,
Harvard University

Thursday, November 30, 2006
12:15 p.m., 700 Clark Hall

Harvard Electronics & IC Research Laboratory


 

"Recent Developments in Mid-infrared Quantum Cascade Lasers"

Abstract: Quantum Cascade (QC) lasers are a rapidly evolving mid-infrared semiconductor laser technology based on intersubband transitions in multiple coupled quantum wells. The lasers’ key strengths are their considerable wavelength tailorability, high power and high-speed operation, and fascinating design potential.

We will first give an overview of QC lasers followed by a discussion of several recent highlights. In particular, we will discuss QC lasers with active region cascades that are “multi-functional”; i.e. they are capable of multiple-wavelength or broadband emission, or also incorporate quantum wells with resonant intersubband optical nonlinearities. As an example for the latter, a QC laser with active regions specially designed to incorporate a giant optical nonlinearity emitted light at pump and second harmonic wavelengths of 9.1 and 4.55µm, respectively, with up to few milliwatts of second harmonic power and a nonlinear power conversion efficiency of up to 36 mW/W2.

We will conclude with a short review on the state of the art of QC laser performance and applications, especially in trace gas sensing. An outlook at the challenges and promises ahead in the QC laser area will close the talk.

 

Prof. Claire Gmachl

Electrical Engineering,
Princeton University

Thursday, November 16, 2006
12:15 p.m., 700 Clark Hall

cgmachl(at)princeton.edu


 

"Quantum Interference Control of Charge and Spin in Semiconductors"

Abstract: Optical phase is not often considered as a control parameter in semiconductor photonics.  However, when two light beams with different wavelengths or polarizations couple valence and conduction band states, quantum interference of the absorption pathways permits generation and phase control of charge and spin currents. I will review some of our recent work on quantum interference control of currents in GaAs and Si, including optical control of the spin Hall effect.

 

Prof. Henry van Driel

Dept. of Physics and Institute for Optical Sciences
University of Toronto

Thursday, November 2, 2006
12:15 p.m., 700 Clark Hall

Institute for Optical Sciences


"Electron transport across single σ-bonded Molecular Monolayers:
Are we asking the relevant questions?"

Abstract:  We study the title question with semiconductor/alkyl monolayers/metal structures, by combining transport and photoemission (Kahn, Ueno, Umbach, Naaman) measurements with theoretical (DFT) calculations (Kronik). Our results lead to questions, such as what is the relevance of the HOMO/LUMO concept for these systems, is there a well-defined transport barrier and width, and, more trivial(?), what are the contact areas in molecular electronics? I will try to present a semi-coherent picture of this on-going study.

Prof. David Cahen

The Rowland and Sylvia Schaefer Chair in Energy Research
Weizmann Institute

Thursday, October 26, 2006
12:15 p.m., 700 Clark Hall

Optoelectronic Materials Group


"Well-Defined Single Molecule Circuits::
Structure-Conductance Relationships Using Amine-Gold Linkages"

Abstract:  We recently demonstrated that the conductance of single molecule junctions formed by breaking Au point contacts in an environment of molecules with amine linkages can be measured reliably and reproducibly1. We have now studied junctions formed by approximately 30 different amine terminated molecules, allowing systematic study of the correlation between molecular properties and single molecule junction conductance. This talk will focus on the relation between molecular conductance and molecule conformation for the simple case of a biphenyl, two benzene rings linked together by a single C-C bond. Our results from a series of seven biphenyl derivatives show that the molecular junction conductance depends on the twist angle. Specifically, we find that the planar molecule has the highest conductance, and the conductance for the series decreases with increasing twist angle, consistent with a cosine squared relation predicted theoretically2.

  1. L. Venkataraman, J.E. Klare, I.W. Tam, C. Nuckolls, M.S Hybertsen and M. Steigerwald, Nano Letters, vol. 5, pp. 458-462, 2006.
  2. L. Venkataraman, J.E. Klare, C. Nuckolls, M.S Hybertsen and M. Steigerwald, Nature, vol. 442, pp. 904-907, 2006.

Dr. Latha Venkataram

Department of Physics
Center for Electron Transport in Molecular Nanostructures
Columbia University

Thursday, October 19, 2006
12:15 p.m., 700 Clark Hall

lv2117(at)columbia.edu


"Towards nanocrystal electronics: high-resolution device
fabrication and controlled particle assembly"

Abstract:  Nanocrystals are tunable crystals a few nanometers in size, exhibiting a range of quantum phenomena at room temperature.  Efforts to explore nanocrystals unite the frontiers of chemistry, physics and engineering, and open up new applications ranging from electronics to biology.  In this talk, I will discuss the assembly of spherical and rod-like CdSe and PbSe semiconductor nanocrystals into electronic devices, their electronic properties and the basic mechanisms of charge transport, both in the limit of large arrays and the limit of only a few quantum dots. I will show how local charge transport behavior can be directly imaged by electrostatic-force microscopy and correlated to nanopatterns observed with transmission electron microscopy.

I will also describe transmission electron beam ablation lithography (TEBAL); a new and highly flexible top-down technique for fabricating device components roughly one order of magnitude smaller than what is possible with other top-down techniques.  TEBAL is based on ablation of atoms from a continuous metal film with the ~ 5 Å diameter imaging beam of a high-resolution transmission electron microscope (HRTEM).   Arbitrary patterns (nanogaps, nanorings, curved nanowires, etc.) may be “carved out” with sub-nanometer accuracy at precise locations.  Because TEBAL is performed inside a HRTEM, atomic resolution in situ imaging of the ablation action is easily obtained and allows for real-time feedback control.

Prof. Marija Drndic


Department of Physics and Astronomy
University of Pennsylvania

Thursday, October 5, 2006
12:15 p.m., 700 Clark Hall

Drndic Lab


"Photonic Crystal deviced and circuits for classical and
quantum information processing"

CANCELLED

Abstract: We have recently demonstrated a number of classical and quantum information processing devices enabled by strong light-matter interaction in photonic crystals, including a quantum dot-photonic crystal cavity single photon source and an ultrafast nanocavity laser with low threshold. I will describe these devices, their efficient design and fabrication methods we have developed, as well as our recent success in combining them into small quantum networks on a chip.

Prof. Jelena Vuckovic


Electrical Engineering
Stanford University

Thursday, September 7, 2006
12:15 p.m., 700 Clark Hall

Vuckovic Research Group
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CNS Seminar Series, Spring 2006


"Silicon Lasers"

Abstract: Silicon, the wonder material of the 20th century, appears to have one more trick up its sleeve. After dominating the digital electronic industry, the bedrock of the digital world, it is now being considered as a platform of choice for building optoelectronic devices. Today, most of the building blocks that make up an optical communication system are already available in silicon. A silicon laser would complete the highly anticipated silicon photonics tool box. But, conventional wisdom holds that silicon cannot lase because of its indirect bandgap. Taking this axiom as a motivation rather than a deterrent, researchers have been rushing to prove their predecessors wrong and to unleash the mighty silicon laser.

This talk will begin with a tutorial on why lasing is not possible in bulk silicon showing that while the indirect bandgap plays a role, it’s the absorption by free carriers that prevents optical amplification, the prerequisite to lasing. It will then review the recent breakthroughs based on nanophotonics as well as Raman Effect. The talk will conclude by arguing that silicon is the ideal Raman medium for mid wave IR (MWIR) wavelengths where high power sources of coherent radiation are needed for biochemical detection, infrared counter measure and other pressing applications.

Prof. Bahram Jalali

Electrical Engineering,
UCLA

Thursday, April 27, 2006
12:15 p.m., 700 Clark Hall

Optoelectronics Circuits and Systems Laboratory



"Synthesis of Micro- and Nanoscale Hydrogel Structures"

Abstract: Poly (N-isopropylacrylamide) (PNIPAm) belongs to the class of crosslinked polymer networks called hydrogels, which can respond to an external stimulus with a change in their size and shape. External stimulus can be a change in any ambient parameter such as temperature, pH, electrical or magnetic field. Due to their stimuli-responsive nature, micropatterned hydrogels are increasingly finding applications as flow valves in microfluidics, cell and tissue scaffolds, targeted drug delivery, controlled release etc. By using higher resolution lithographic techniques, one may also pattern hydrogels at nanoscale. Compared to their micropatterned counterparts, nanopatterned hydrogels would possess faster response to external stimulus due to their small size and high surface-to-volume ratio.

N-isopropylacrylamide is known to undergo crosslinking in bulk, when irradiated with gamma rays, x-rays and e-beam. PNIPAm hydrogels can be patterned using x-ray and electron beam lithography to address the question “how small can a hydrogel structure be and still retain its stimuli-response behavior?” Fabricating nanopatterned hydrogels by direct e-beam writing also provides the unique possibility to tailor their stimuli-response properties by creating artificial network morphologies. These fabrication techniques are also amenable for direct integration of such functional patterned hydrogels into NEMS and BioMEMS devices.

The presentation will be prefaced with a brief introduction to the Center for Nanoscale Materials at Argonne National Laboratory.

Acknowledgment: This work has been supported in part by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under contract No. W-31-109-Eng-38

Derrick Mancini

Project Manager, Argonne National Laboratory

Thursday, April 13, 2006
12:15 p.m., 700 Clark Hall

mancini (at) anl.gov



"What's new in Nanoscale Structures? -- Fluctuations and Transformations"

Abstract: The nanoscale world is not a scaled-down version of the macroscopic world. Nanoscale structures have special properties by virtue of their smallness alone, which yields quantum confinement, high surface-to-volume ratio and susceptibility to fluctuations. Direct imaging at the atomic scale using scanned probe techniques allows the latter effect, fluctuations, to be observed and quantified. Quantitative characterization of these fluctuations using the tools of statistical mechanics yields correlation functions as well as more direct measures of stochastic behavior such as first-passage properties

The stochastic vs. deterministic factors in the behavior of individual nanoscale structures will be illustrated for the case of supported lead crystallites. silver structures decorated with fullerenes, and metallic and semiconducting electrical conductors.

Acknowledgment: Different aspects of this work have been supported by the NSF-MRSEC, LPS and the DCI post-doc program.

Prof. Ellen Williams

Materials Research Science and Engineering Center
University of Maryland College Park

Thursday, March 30, 2006
12:15 p.m., 700 Clark Hall

The Williams Lab


"Electromagnetic Field Enhancement near Ag Nanocrystals: Single Molecule Raman Spectroscopy, Optical Forces, and Surface Photochemistry"

Abstract: Two 30nm Ag nanocrystals exhibit junction a junction "hot spot" in their local electromagnetic field enhancement when separated by a few nm. If the a molecule is chemisorbed in the junction and also electronically resonant with the laser, this enhancement is sufficient to enable single molecule Raman spectroscopy. The laser-induced ac polarization in the Ag which creates the "hot spot" also creates a very strong attractive potential between the nanocrystals that squeezes the junction. We calculate these optical forces by integration of the Maxwell stress tensor. The Ag local field enhancement can also be used for photochemistry, to control the shape of Ag nanocrystals growing via surface photoreduction of Ag ion.

Prof. Louis Brus

Chemistry Department
Columbia University

Thursday, March 2, 2006
12:15 p.m., 700 Clark Hall

Brus Group



"Silicon-chip-based optical resonators with Q factor > 100 million "

Abstract: A novel processing method has been applied to create optical micro-resonators having Q factors as high as 500 million on silicon wafers.  These devices open up many new applications for lab-on-a-chip experimental work. After describing the processing and passive optical properties of these devices, the consequences of resonant energy buildup in a microscale, ultra-high-Q system will be described.   Demonstrations of micro Raman and micro OPO lasers based on these cavity structures will be reviewed. Finally, radiation confined within a vessel exerts pressure upon its walls. If the vessel is a high-Q micro-cavity, then a weak power level, coupled to the cavity, can exert a substantial, resonantly-enhanced pressure on the internal micro-cavity walls. Such a pressure will deform the cavity structure and change the resonant condition. This effect has been theorized to produce a parametric oscillation in the mechanical modes of the optical resonator. The first observation of this effect will be described.

 

Radiation pressure induced mechanical oscillation in a whispering gallery micro-toroid (below threshold left; above threshold right)

 

Prof. Kerry Vahala

Applied Physics
California Institute of Technology

Thursday, February 23, 2006
12:15 p.m., 700 Clark Hall

Vahala Research Group

 

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CNS Seminar Series, Fall 2005



"Plasmonics: A Route to Nanoscale Optical Devices"

Abstract: Since the development of the light microscope in the 16th century, optical device size and performance has been limited by diffraction. Photonic devices of today are composed of dielectric materials with modest dielectric constants, and are much bigger than the smallest electronic devices for this reason. However subwavelength spatial confinement of light at dimensions down to less than 10% of the free-space wavelength is possible using plasmonic components.   Ultimately it may be possible to employ plasmonic components to form the building blocks of a chip-based optical device technology that is scaleable to molecular dimensions, with potential imaging, spectroscopy and interconnection applications in computing, communication and chemical/biological detection.

In this talk I will describe recent opportunities presented by plasmonics for chip-scale integration of photonic and electronic devices, including i)design of metal-insulator-metal plasmon waveguides that optimize the trade-off between mode localization and propagation loss in the visible and near-infrared ii) on-chip Si CMOS compatible light near-infrared light sources for coupling into plasmonic networks iii) plasmon-enhanced emission from quantum dots, and iv) opportunities for active plasmonic devices based on electro-optic and all-optical modulation of plasmon propagation.

Prof. Harry A. Atwater

Thomas J Watson Laboratory of Applied Physics
California Institute of Technology

Thursday, November 10, 2005
12:15 p.m., 700 Clark Hall

haa(at)its.caltech.edu



"Taking a Picture of Disorder Inside Semiconductors "

Abstract:  In normal metals electrons travel only very short distances, on the order of Angstroms, before they are scattered. In contrast, in specially engineered semiconductor materials disorder can be reduced to an exceptionally low level, allowing electrons to travel distances a million times longer, up to nearly a millimeter, before scattering. Despite this remarkable achievement, the influence of disorder in these materials is very important and not well understood. The technique described in this talk takes advantage of a special property of two-dimensional electronic systems. In large magnetic fields, a 2D layer of electrons has a very peculiar behavior: small changes in the local electron density can cause a patch of electrons to change from being a metal to an insulator. Applying voltages to a metal scanning probe tip modifies the local electron density to create a ring-shaped region of insulating electrons centered at the position of the tip. Not all patches of insulating electrons are created equal: in some cases, the inherent disorder in the sample can creates small islands inside the insulating ring. Single electron resonant tunneling through these islands can allow electrons to traverse the insulating ring. The results show that transport through insulating regions of this 2D quantum Hall system is strongly affected by these islands, and they act as stepping stones for transporting electrons through the frozen background. The images thereby provide a direct view of disorder in very clean samples.

Prof. Raymond Ashoori

Physics
M.I.T.

Thursday, October 13, 2005
12:15 p.m., 700 Clark Hall

http://rleweb.mit.edu/rlestaff/p-asho.htm



"The Excited-State Properties of Single-Wall Carbon Nanotubes"

Abstract:  Single-wall carbon nanotubes provide a model system to investigate the nature of electrons confined in a 1-dimensional system.  The ground-state properties and unique electronic transport properties have extensively studied.  The nature of the excited states, as revealed in the optical measurements, is, however, less understood.  Recently there have been several important advances in this regard, including the observation of nanotube luminescence and electro-luminescence.

In this talk we will describe measurements of the properties and dynamics of nanotube luminescence and its relation to the fundamental photophysics of carbon nanotubes. Using the distinctive selection rules of nonlinear spectroscopy, we also demonstrate the excitonic nature of the optical transitions in carbon nanotubes.  Finally we present recent results in which electronic transitions of individual single-wall nanotubes have been investigated by resonant Rayleigh scattering.  This method provides new possibilities for the investigation of environmental effects and tube-tube interactions at the single nanotube level.

Prof. Tony Heinz

Physics
Columbia University

Thursday, September 29, 2005
12:15 p.m., 700 Clark Hall

tfh3@columbia.edu



" Resonances in Photonic Crystals and Nanophotonic Structures"

Abstract: The developments of photonic crystals and nanophotonic devices allow unprecedented control over the behavior of light. In particular, the resonant states in these structures that are on the wavelength or even sub-wavelength scales can be used as a basic building block to create new optical physics and devices. In this talk, we give examples on non-reciprocal resonators; on coherent stopping, storage and time-reversal of light; and on new meta-materials with geometrically controlled dielectric constants.

Prof. Shanhui Fan

Electrical Engineering
Stanford University

Thursday, September 15, 2005
12:15 p.m., 700 Clark Hall

shanhui@stanford.edu


" Charged colloidal quantum dots:color, conductivity,
luminescence and carrier dynamics"

Abstract:  Colloidal nanoparticles can potentially be used to create materials with optimized or novel functions.  Semiconductor quantum dots are one such promising building block where a few electrons dramatically modify their properties.  Injecting charges in films of colloidal quantum dots can be achieved by using optical excitation, reducing species, electrochemical or solid state gating.  In particular, electrochemical gating coupled with optical spectroscopy has allowed a detailed and quantitative study of the influence of charges on transport.  Low-temperature measurements show the films to conduct via variable range hopping and this model also explain the 150% positive magnetoresistance that appears at very low temperature.  n-type dots should also display different luminescent properties and this is indeed observed, with significantly reduced lasing threshold for charged films.  Finally, n-type dots allowed to study the electron intraband relaxation in the absence of  the electron-hole Auger processes, and it has been found that intraband relaxation is then likely induced by coupling to molecular vibrations of the surface ligands.

Prof. Philippe Guyot-Sionnest

Physical Chemistry
University of Chicago

Thursday, September 1, 2005
12:15 p.m., 700 Clark Hall

http://chemistry.uchicago.edu/fac/guyot-sionnest.shtml


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CNS Seminar Series, Spring 2005


" Optical Control in Semiconductor Dots for Quantum Operations "

Abstract: Semiconductor quantum dots have optical properties similar to simple atomic systems, unlike higher dimensional semiconductor structures that are dominated by manybody physics associated with the continuum states. They also provide a potentially ideal electronic structure appropriate for quantum computing.  We will present data showing that these structures can be coherently controlled on a time scale short compared to the quantum decoherence time and that entangled states of qubits (represented by exciton optical Bloch vectors) can be created.  The system is remarkably robust against pure dephasing and we have been able to demonstrate a simple conditional quantum logic device involving multiple Rabi flops of the exciton and biexciton.

The future of this work lies in coherence engineering of the materials to provide longer coherence times for the qubits.  To this end, our group is now working on single electron doped quantum dots where the spin, with long coherence time, is the qubit.  Measurements show that we can coherently control the spin state of a single electron.

This work done in collaboration with Dan Gammon (NRL) and L.J. Sham (UC-SD) with support from AFOSR, ARO/ARDA/NSA, ONR and NSF.

Prof. Duncan Steel

The Harrison M. Randall Laboratory, FOCUS Center
University of Michigan

Thursday, May 5, 2005
12:15 p.m., 700 Clark Hall

dst@eecs.umich.edu



"Molecular Nanostructures: Modeling Assembly, Transport, Hysteresis And Switching"

Abstract: Molecular nanoscience poses challenges first in understanding structure, and next in mastering properties.  In the first part of the talk, we will utilize a combination of non-equilibrium Greens functions and polaron theory to discuss transport, hysteresis and switching in molecular current transport junctions. The effectiveness of relatively simple models in understanding (at least on a semi-quantitative basis) complex transport structures will be emphasized, and some conclusions will be drawn concerning the appropriate limits in which simple pictures can be recovered.

The second part of this discussion will focus on use of agent-based ideas to analyze assemblies comprising molecular subunits.   This algorithmic approach has real promise for understanding the complex behavior of molecular nanostructure assembly.

Prof. Mark Ratner

Chemistry Department
Northwestern University

Thursday, April 21, 2005
12:15 p.m., 700 Clark Hall

ratner@chem.northwestern.edu



"Watering Silicon Nanograss: How to Get Droplets to Roll or Stick on Demand"

Abstract: An ability to manipulate microscopic volumes of liquids with the high precision becomes increasingly important with the recent progress in micro- and nanofluidics and its rapid penetration in various industrial applications. Dynamic control over the interaction of liquids with the solid substrate constitutes a very important aspect of this problem. Nanostructured solid surfaces offer a promising way to achieve this goal. In this talk we discuss recently demonstrated dynamically tunable nanostructured surfaces. The behavior of these surfaces can be reversibly switched between superhydrophobic and hydrophilic states by the application of electrical voltage and current. The proposed approach potentially allows novel methods of manipulating microscopically small volumes of liquids. This includes almost frictionless liquid transport, the ability to selectively immobilize the droplets at any given time or position, as well as dynamic control over the penetration on liquids through the nanostructured layer.  The obtained results potentially open new and exciting opportunities in microfluidics, optics, thermal management of microelectronics, chemical microreactors, bio/chemical detection, and many other areas.

Dr. Tom Krupenkin

Lucent Technologies

Thursday, April 7, 2005
12:15 p.m., 700 Clark Hall

tnk@lucent.com


"Quantum Control and Nano-Photonics in Quantum Information Science"

Abstract: New challenges from quantum information processing and quantum metrology provide compelling motivation for interdisciplinary research that draws together wide-ranging areas of science and engineering.  In this talk I will describe two ongoing projects that pursue novel integrations of control theory and nanotechnology with atomic physics.  In the first, we are utilizing tools from control theory to develop novel approaches to feedback-stabilized quantum state preparation and robust sub-shotnoise magnetometry with atoms.  In the second, we are attempting to develop "integrated quantum nodes" for a quantum communication network that will combine chip-scale atom traps with photonic bandgap structures.

Prof. Hideo Mabuchi

Caltech

Thursday, March 17, 2005
12:15 p.m., 700 Clark Hall

http://minty.caltech.edu/hmabuchi/


"Oxide-Semiconductor Materials for Quantum Computation "

Abstract:  Quantum computers, as yet undeveloped, are believed to be able to solve certain problems exponentially faster than ordinary computers. One of these problems, number factorization, can be used to defeat public key encryption schemes like RSA, which is widely used in the internet. The potential of these and other applications has led to a worldwide race to build the first working quantum computer. The state of experimental quantum computation is primitive--neither quantum bits (qubits) nor quantum gates (qugates) have been demonstrated in a scalable form. In this talk, I will describe a proposal to create a quantum processor using ferroelectrically coupled electron spins in Silicon. Quantum information is stored in the spin of electrons, which form a conveninent two-level system. The electrons are confined in the semiconductor (Si) using the static polarization from an epitaxial ferroelectric. Fast optical gating occurs using the nonlinear process of optical rectification. Ge quantum dots are used as "windows" that allow light to initialize or "boot" the quantum computer. Initial steps toward the development of quantum information technology using ferroelectric/semiconductor heterostructures will be presented.

Prof. Jeremy Levy

University of Pittsburgh

Thursday, March 10, 2005
12:15 p.m., 700 Clark Hall

http://cosmqc.net/epsilon


"Silicon Photonic Crystals and Photonic Wires Circuits"

Integration of optics at the chip scale is seen as key to significantly reducing the cost of optical components. Silicon or more specifically silicon on insulator is an attractive platform for integration owing to its high refractive index that offers strong light confinement and therefore ultra-compact devices. By adopting a substrate material that is CMOS compatible, decades of materials and process knowledge can be leveraged. Feasibly both passive and active optical elements could be combined with electronics on a single chip to achieve monolithic optoelectronic integration.

Single-mode strip waveguide and W1 photonic crystal waveguide fabricated on SOI wafer.

We performed detailed experimental study of transmission properties of PhC-based and photonic wire-based components as sharp bends, wide-angle Y-splitters, and more complicated devices as Mach-Zehnder modulators and compare their performance in terms of losses, bandwidth and dispersion. We will discuss how the unique properties of photonic crystals may be incorporated into photonic integrated circuits and what improvement in functionality they might provide.

Dr. Yurii Vlasov

IBM T.J. Watson Research Center
Yortown Heights, NY

Thursday, February 10, 2005
12:15 p.m., 700 Clark Hall

yvlasov@us.ibm.com



"
Precision Radiofrequency Measurements of Nanomechanical Systems "

Abstract: There is much interest in the fabrication and properties, both static and dynamic, of nanoscale systems. At UC Santa Barbara we have been developing top-down lithographic approaches to fabricating highly integrated electromechanical systems, that include electronic means for monitoring the motion, and other degrees of freedom, of these systems. In this talk I will briefly described some approaches that we have explored, and discuss in somewhat more detail recent measurements on nonlinear mechanical resonators, in which an interesting measurement scheme that relies on the nonlinear behavior allows precision determination of the resonator parameters.


Prof. Andrew Cleland

University of California
Santa Barbara

Thursday, January 27, 2005
12:15 p.m., 700 Clark Hall

http://www.cnsi.ucla.edu/faculty/cleland_a.html


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CNS Seminar Series, Fall 2004


"
Plastic Solar Cells: Promise and Progress "

Abstract: In a world where energy demands are soaring and oil supplies are peaking, research on renewable energy sources is gaining increasing attention. Among renewable energy sources, solar energy production is growing fast with an annual growth rate of 35%. Fifty years after the invention of the first crystalline silicon solar cell, worldwide photovoltaic sales are still based on bulk high-purity crystalline silicon. However, some new technologies based on thin films are on the threshold of commercialization and others are near the horizon. Organic semiconductors that can be printed over large-area, light-weight substrates show great potential for photovoltaic technologies.

In this talk, we will discuss the challenges that need to be overcome before plastic solar cells can fulfill their true promise. We will show that their performance is very sensitive to the ability to control the electronic and optical properties of the organic materials at the nanoscale. Charge transport properties will be discussed in particular for a variety of different materials with morphologies ranging from amorphous to polycrystalline, to liquid crystalline. Recent progress in the fabrication, modeling and optimization of organic multilayer thin-film devices will be presented.

Prof. Bernard Kippelen

School of Electrical and Computer Engineering
Georgia Tech

Thursday, December 2, 2004
12:15 p.m., 700 Clark Hall

kippelen@ece.gatech.edu



"
Feeling the magnetism of individual spins:
recent results from magnetic resonance force microscopy
"

Abstract: Is it possible to build a microscope that can look below surfaces and image molecules and materials with atomic resolution in three dimensions? Such a microscope would revolutionize structural molecular biology and be an important tool for nanoscale science and technology. Magnetic resonance force microscopy (MRFM) is an attempt to address this "holy grail" of microscopy.

In this talk, we describe the basic principles of MRFM and discuss recent results that demonstrate the detection of an individual electron spin buried within a silica sample. We review various innovations that set the  stage for single spin detection, including attonewton force detection using  ultrathin silicon cantilevers. We also discuss spin manipulation techniques, including using MRFM for real-time control of spin fluctuations. Finally, we consider some of the challenges remaining before 3D atomic imaging and real-time quantum state readout can be realized.

Magnetic Resonance Force Microscopy Rugar
                          IBM

Dr. Daniel Rugar

IBM Research Division
Almaden research Center

Thursday, November 4, 2004
12:15 p.m., 700 Clark Hall

rugar@almaden.ibm.com


" Geometry and Scale in Photonics"

Abstract: The scaling of optoelectronics devices to smaller and smaller spatial dimensions results, at least theoretically, in an increased device density and reduced optical systems size. Additionally, and perhaps more importantly, there is also a corresponding increase in the strength of light-matter interactions with reduced size scale, an effect which can dramatically alter the power, speed, and efficiency of an optical device. Geometry below or at the wavelength scale also plays an intricate role in optics, as demonstrated recently in the work on engineered photonic crystals and so-called "left-handed" materials. In this talk I will discuss the application of geometry and scale in optical structures to several different areas of our own current research: chip-scale atom-cavity QED, microcavity surface -emitting Quantum Cascade Lasers, and silicon microphotonics.

Prof. Oskar Painter

Applied Physics
California Institute of Technology

Thursday, September 30, 2004
12:15 p.m., 700 Clark Hall

http://copilot.caltech.edu/


" Functional Nanocrystal-Quantum-Dot Assemblies:
Putting Dots to Work
"

Abstract: Using modern colloidal chemistry, semiconductor nanocrystals (NCs), known also as NC quantum dots, can be fabricated with nearly atomic precision in a wide range of sizes and shapes. They exhibit high photoluminescence quantum yields and narrow, size-controlled emission lines, and they can easily be manipulated into complex two-dimensional (2D) and 3D assemblies. All of these properties make NCs ideally suited for studies of size/ structure-dependent quantum mechanical interactions as well as ideal building blocks for nanoscale engineering. This presentation focuses on light emitting properties of semiconductor NCs in the regimes of both optical and electrical pumping. By using shape-controlled NCs or multi-shell NC heterostructures, we can almost independently manipulate carrier confinement energies (i.e., emission wavelengths) and their relaxation dynamics [1, 2]. This capability is particularly useful for achieving the optical amplification/lasing regime. We use different types of "engineered" II-VI and IV-VI nanocrystals to demonstrate amplified spontaneous emission with colors tunable from the near infrared to the blue [3, 4]. We also develop and study novel types of hybrid epitaxial/colloidal nanostructures, which allow efficient electrical pumping of NC emitters via either "noncontact" exciton transfer [5] or direct charge injection from epitaxial layers of wide gap semiconductors.

1. H. Htoon, J.A. Hollingsworth, R. Dickerson, and V.I. Klimov, Phys. Rev. Lett 91,    227401 (2003).

2. V. Klimov, A. Mihkailovsky, D. McBranch, C. Leatherdale, and M. Bawendi, Science 287, 1011 (2000).

3. V. Klimov, A. Mikhailovsky, S. Xu, A. Malko, J. Hollingsworth, C. Leatherdale, and M. Bawendi, Science 290, 314 (2000).

4. R.D. Schaller, M.A. Petruska, and V.I. Klimov, J. Phys. Chem. B 107, 13765 (2003).

5. M. Achermann, M.A. Petruska, S. Kos, D. Smith, D.D. Koleske, and V.I. Klimov, Nature 429, 642 (2004).

Dr. Victor I. Klimov

Los Alamos National Laboratory
Chemistry Division, C-PCS

Thursday, September 16, 2004
12:15 p.m., 700 Clark Hall

http://quantumdot.lanl.gov


" Engineering Ferroelectrics Using Strain"

Abstract: Molecular beam epitaxy (MBE) has achieved unparalleled control in the customization of semiconductors at the nanometer level; its use for the customization of ferroelectric oxides with similar nanoscale customization appears promising. This talk will describe the use of reactive MBE to synthesize dielectric and ferroelectric perovskite oxides, including new compounds and metastable superlattices, whose structures are engineered using epitaxy.

Prof. Darrell G. Schlom

Dept. of Materials Science & Engineering
Penn State University

Thursday, September 2, 2004
12:15 p.m., 700 Clark Hall

http://www.ems.psu.edu/~schlom/


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CNS Seminar Series, Spring 2004


" Molecular Materials and Devices "

Abstract: Efforts to fabricate devices based on active molecular components have been driven by both the fundamental interest in using chemistry to build function at the molecular level and the looming technological expectation of the end of Moore 's law. In this talk, we describe the directed assembly of organic and metal-metal bonded supramolecular systems that are interesting materials for potential electronic and memory device applications. Molecules are chosen with head groups that bind to metal or oxide surfaces and tail groups that bind to metal electrodes or that template the growth of the particular molecular system. Optical spectroscopy, scanning probe microscopy, and electrochemistry are used to characterize the chemistry and physics of molecular assemblies. We incorporate these molecular systems in nanometer scale device "test" structures aimed at understanding the electronic characteristics of two- and three-terminal molecular devices.

Dr. Cherie Kagan

IBM
T.J. Watson Research Center

Thursday, April 29, 2004
12:15 p.m., 700 Clark Hall

http://www.research.ibm.com/


" Circuit Quantum Electrodynamics:
Observing Strong Coupling Between a Superconducting Qubit and a Photon
"

Abstract: I will describe recent experiments in which the strong coupling limit of cavity quantum electrodynamics has been realized for the first time using superconducting circuits. In our approach, we use a Cooper pair box acting as an artificial atom coupled to a transmission line resonator forming a one-dimensional cavity. The strong coupling limit is reached as the vacuum Rabi frequency for the coupling of cavity photons to quantized excitations of the qubit exceeds the damping rates of both the cavity and the qubit. When the qubit is detuned from the cavity resonance frequency a high-fidelity dispersive quantum non-demolition read-out of the qubit state is achieved. Using this read-out technique we have characterized the qubit properties spectroscopically and attained coherence times greater than 100 ns, indicating that this architecture is extremely attractive for quantum computing and control.

Prof. Rob Schoelkopf

Departments of Applied Physics and Physics
Yale University

Thursday, April 15, 2004
12:15 p.m., 700 Clark Hall

http://www.eng.yale.edu/rslab

 

" Lead-Salt Nanocrystals: Strong Quantum Confinement of Electrons "

Abstract: I will introduce the basic properties of semiconductor quantum dots, and then focus on the properties of lead-salt (PbS, PbSe, PbTe) nanocrystals.  These structures are ideal for studies of strong confinement of charge carriers and investigations of the vibrational modes of nanocrystals. They are also technologically relevant, because they are among the few material systems that can produce strongly size-quantized optical transitions at infrared wavelengths between one and three microns.  Examples of established properties will be presented along with open questions that are the subject of current research.

Prof. Frank Wise

Applied and Engineering Physics

Cornell University

Thursday, April 01, 2004
12:15 p.m., 700 Clark Hall

http://people.ccmr.cornell.edu/~fwise/


"Magnetic Quantum Tunneling in Single Molecule Magnets"

Abstract: Single molecule magnets (SMMs) are magnetic nanostructures that consist of a core of strongly exchange-coupled transition metal ions with a large collective magnetic moment per molecule, thus far up to 26 Bohr magnetons, and a predominantly uniaxial magnetic anisotropy. Their molecular nature enables experimental studies of nearly monodisperse ensembles of nanomagnets with well-defined size, shape, chemical composition, and magnetic anisotropy. This talk will present experiments that address the origin of magnetic quantum tunneling (MQT) in the prototype SMM Mn 12 -acetate and, in particular, the nature of the transverse interactions that produce quantum tunneling. Recent experiments that employ microwave fields to modulate MQT and characterize quantum superpositions states of "up" and "down" spin-projections will also be described.

Prof. Andrew Kent

Department of Physics
New York University

Thursday, March 04, 2004
12:15 p.m., 700 Clark Hall


"Current-induced transverse spin wave instability in a thin nanomagnet "

Abstract:It has been experimentally verified that a spin polarized electric current incident on a thin ferromagnet can change the orientation of the magnetization via a mechanism known as "spin transfer". We show that an unpolarized electric current incident on a thin ferromagnet can excite a spin-wave instability transverse to the current direction if source and drain contacts are not symmetric, although it can not change the over-all magnetization direction.

Prof. Piet Brouwer

Physics
Cornell University

Thursday, February 19, 2004
12:15 p.m., 700 Clark Hall


" Optics on the Nanometer Scale "

Abstract: Nano-optics is motivated by the rapid advance of nanoscience and nanotechnology. It aims at exploring optical phenomena and techniques beyond the diffraction limit of light. Among the applications are high-resolution microscopy and spectroscopy, nanolithography, and nanomanipulation. In this seminar I will discuss the main ideas behind nano-optics and I will give an overview of topics pursued in the nano-optics group at the University of Rochester.

(a) Confocal and (b) near-field Raman scattering images of the same area of a carbon nanotubesample acquired at 2615 cm^-1 (G'-band). Near-field Raman imaging increases spatialresolution by a factor 10-20.

(c) Raman scattering spectrum recorded on an individual single-walled carbon nanotube. The spectrum uniquely identifies the chemical nature of the sample.

Prof. Lukas Novotny

The Insitute of Optics
University of Rochester

Thursday, February 5, 2004
12:15 p.m., 700 Clark Hall

The Nano-Optics Home Page


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CNS Seminar Series, Fall 2003


"
The Structure and Growth of Single-
and Double-Walled Carbon Nanotubes
"

Abstract: Single- and double-walled carbon nanotubes have potential applications for future electronics and nanomachines. However, as-grown carbon nanotubes have a dispersion of structures, which differ in both diameter and chirality, and electric and mechanical properties. Characterization of these nanotubes has been a challenge. Recently, we developed a coherent electron diffraction/imaging technique by forming a nanometer-sized parallel beam of electrons that can be used to record diffraction patterns from individual nanotubes. Furthermore, the combination of coherence and high angular resolution allows the over-sampling of diffraction pattern and solution of phase problem by ab-initio phase retrieval, thus, imaging of carbon nanotubes (Ref 1) . Using this technique, we have investigated a large number of single- and double-walled carbon nanotubes. We found that neither zig-zag nor arm-chair tubes is preferred for growth. Double-walled carbon nanotubes are generally incommensurate and there is a peaked distribution of spacings between two tubes. The implication of these findings will be discussed based on the growth mechanism of carbon nanotubes. The technique of coherent electron nanodiffraction and diffractive imaging by the solution of the phase problem is general and applicable to other nanostructures.


Prof. Jian-Min (Jim) Zuo*


Department of Materials Science and Engineering and

F. Seitz Materials Research Laboratory

University of Illinois , Urbana-Champaign

Thursday, December 4, 2003
12:15 p.m., 700 Clark Hall

*In collaboration with J. Tao, J. Bording, Boquan Li, M. Gao,
R.Twesten and I. Petrov

Ref 1. See, e.g., J.M. Zuo, I. Vartanyants, M. Gao, R. Zhang and L.A. Nagahara, "Atomic Resolution Imaging of A Single Double-Wall Carbon Nanotube From Diffraction Intensities," Science, 300, 1419-1421 (2003).

Group Web Page


"Soft Materials and Nanopatterning Techniques for Electronics"

Abstract: Organic materials have a strong potential to play important roles in future electronic and photonic systems. Additive printing and lamination techniques can be used directly with these classes of soft materials to build unusual devices with dimensions deep into the sub-micron regime. This talk describes the operational aspects of transistors and light emitting diodes that are fabricated with these techniques using small molecule organics, polymers and carbon nanotubes as the active components. it provides examples of working prototypes, such as flexible paperlike displays, that demonstrate some promising applications.

Dr. John Rogers


Department of Materials Science and Engineering
University of Illinois at Urbana

Thursday, November 20, 2003
12:15 p.m., 700 Clark Hall


" Exploring surfaces and cavities in nanotubulites with a sub-nm electron beam "

Abstract: Since their discovery by Iijima, the specific morphology of nanotubes with an empty cylindrical core space and the presence of large surface areas on both outer and inner sides of the walls, has captured the interest of many researchers who have demonstrated quite diversified types of fillings with gases, molecules or solid compounds. In particular, new families of nano-objects have been identified, such as nanowires, nanocontainers, peapods. They offer strong potentialities for exhibiting novel properties and for developing new applications as transport components, storage devices or reaction chambers. On the other hand, the combination of intense electron probes of near-atomic dimension (in a STEM microscope) with highly efficient 2D detectors for recording electron energy-loss spectra (EELS) within a few milliseconds, has provided quite powerful tools to explore individual nanostructures with unprecedented spatial (sub-nm) and energy (sub-eV) resolutions. In particular, following the demonstration of the identification of single atoms encaged in fullerene molecules along peapods structures , we have further used this technique for analyzing the presence of trapped molecules within SWNTs or for detecting the presence of thin layers, acting as potential wetting agents, at the interfaces between the encapsulating nanotube and its filling. Beyond performing sub-nm elemental analysis on such hybrid nano-objects, the EELS technique has also been used to locally investigate their electronic states and dynamics. We can either measure the unoccupied density of states accessible through the EELS fine structures observed on core edges or the collective behavior of the electron population deduced from the bulk and surface plasmon modes of excitation, investigated with the primary electron probe in an intersecting or a grazing incidence. New examples related to the exploration of clean or activated surfaces will be presented.

Prof. Christian Colliex


Universite Paris Sud

Monday, November 17, 2003
3 :30 p.m., 700 Clark Hall


"Gaining Control in the Synthesis of Single Walled Carbon Nanotubes"

Dr. L . Liu

Department of Chemistry
Duke University

Thursday, October 23
12:15 p.m., 700 Clark Hall


"Imaging the atomic-scale chemistry and electronic structure inside nanodevices"

Prof. David Muller


Applied and Engineering Physics

Cornell University

Thursday, October 9
12:15 p.m., 700 Clark Hall


"Taking nuclear magnetic resonance to the nanoscale using cantilevers"

Prof. John Marohn


Department of Chemistry and Chemical Biology

Cornell University

Thursday, September 25
12:15 p.m. , 700 Clark Hall


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CNS Seminar Series, Spring 2003

"Localized Charge Properties of Individual Semiconductor Quantum Rods"

Dr. Todd Krauss


University of Rochester

Thursday, May 1
12:15 PM, Clark Hall 700


"Magnetic Memory, Spintronics, and Magnetic Nanostructures"

Dr. Jonathan Sun


IBM
T. J. Watson Research Center, Yorktown Heights, NY

Thursday, April 17
12:15 PM, Clark Hall 700


"Metal Nanocrystal Nonvolatile Memories"

Prof. Edwin Kan


Electrical and Computing Engineeering

Cornell University

Thursday, March 27
12:15 PM, Clark Hall 700


"30 nm Channel Length Pentacene Transistors"

Prof. George Malliaras


Materials Science & Engineeering

Cornell University

Thursday, March 13, 2003
12:15 PM, Clark Hall 700

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