Charles Masamed Marcus - US grants

Technical abstract: An experimental investigation will be carried out of low temperature transport in mesoscopic semiconductor structures. Particular attention will be placed on exploring the connection between randomness in quantum transport and quantum signatures of classical chaos. Applications include the use of feedback control of phase-coherent transport for the purpose of developing semiconductor quantum dots to operate as low-noise magnetometers. Nontechnical abstract: The focus of the research is to understand the physics which governs the motion of electrons in ultrasmall devices. Recent results indicate that when the electrons can travel distances larger than the device dimension without appreciable scattering by impurities and other defects then the geometry of the device becomes a significant factor in determining the electron's motion. This sensitivity to geometry can be a useful tool to study the underlying mechanisms of chaotic motion and to ultimately design new devices. The proposed research will be carried out at low cryogenic temperatures and in very high quality semiconductor structures to increase the mobility of the electrons. :

w:\awards\awards96\num.doc 9629180 Marcus This experimental project will advance the fundamental understanding of the mesoscopic scale behavior of matter, and particularly the appearance of quantum-mechanical chaotic behavior. The experimental research entails fabrication of semiconductor microstructures, in the form of wires and dots, and the measurement of their electronic properties at millikelvin temperatures. Universal statistics of conductance fluctuations are connected to quantum manifestations of chaos. The educational components of the project involve finding successful ways to use advanced textbooks in the teaching of freshman physics, and the integration of undergraduate students in laboratory research. %%% The research carried out searches for understanding of changes in the performance of semiconductor microelectronic devices that eventually will result from making the devices ever smaller. Smaller devices are desirable in improving the speed and complexity of computer chips such as the Pentium chip, but it is expected further advances in the speed and complexity of computer chips will eventually be limited by the onset of different physical rules for electron behavior. The present research will contribute to our understanding of this transition in behavior. The work may also suggest new device designs which may be superior in the desirable limit of extremely small device size and high device density. The educational components of the project relate to novel methods in teaching elementary college physics and in giving undergraduate science students an earlier exposure to laboratory research. ***

9871947
Dai
Carbon nanotube research has been an extremely active field over the past years.
Nanotube materials have unique structural, electrical and mechanical properties, which makes them promising for a range of projected scientific and technological applications. However, significant future efforts are required in order to realize these promises. This research proposes obtaining large-scale arrayed nanotube probe tips and sensors with advanced functions for scanning probe microscopy applications. We also propose obtaining electrical circuits based on arrayed nanotubes networks. The overall motivation is to enable a series of novel nanotube devices useful for scientific and technological applications.

The immediate research goals and activities of this proposed research will include
(1) developing controlled chemical vapor deposition methods to synthesize high quality and yield carbon nanotubes materials. (2) Synthesizing nanotubes directly into probe tips and cantilevers for scanning probe microscopy applications. Our approaches will involve combining chemical synthesis (CVD) with top-down nanofabrication methods (such as ebeam lithography). The integration of carbon nanotube tips into arrayed AFM cantilevers could enable a powerful parallel AFM imaging and nanofabrication system. (3) Fabrication and characterization of A-FM cantilevers using individual carbon nanotubes. A defect free carbon nanotube is a perfect one-dimensional crystal that has the highest Young's Modulus among all materials. There is no intrinsic structural mechanism expected in nanotubes for mechanical energy dissipation. Therefore, a nanotube can be utilized as a cantilever to measure extremely small forces. Methods for fabrication and mechanical characterizations of nanotube based cantilevers are proposed. (4) The physics of carbon nanotube electronic devices will be studied. We will start the construction of nanotube electrical circuits at the nanotube synthesis stage. Improving electrical contacts to individual nanotubes by chemical means will be a major focus in this proposed research.

The proposed research will be highly interdisciplinary involving synergetic groups at Stanford University (in Chemistry, Physics and Applied Physics, Electrical and Mechanical Engineering). We will also be interacting closely with our collaborators at NASA Ames Research Center, KLA-Tencor, Park Scientific and other industrial companies. This collaboration has already been initiated recently and some promising results are being generated. The results include (1) the demonstration that carbon nanotube tips provide a solution to the long-standing tip-wear problem in A-FM based nanolithography. (2) Synthesis of bulk single-walled nanotube materials using new chemical vapor deposition (CVD) approaches. And (3) CVD synthesis of nanotubes on flat surfaces containing catalytic particles patterned by nanofabrication techniques. Our collaboration will represent an ideal opportunity to bring together scientists and engineers in different disciplines and institutions; to merge bottom-up chemical synthesis with topdown nanofabrication; and to allow students in different departments to work together and receive broader academic and research training. Thus, the proposed research will be of fundamental and practical significance and will accelerate the impact of nanostructures on real-world problems.
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With this award from the Instrumentation for Materials Research Program, the Department of Chemistry and Chemical Biology at Harvard University will acquire a Variable-Temperature Scanning Probe Microscope bolt-on module from Omicron Instruments. This instrument will facilitate research in a number of areas, including a) the phase transitions of individual nanocrystals, b) the electron transport through individual molecules, nanocrystals and their arrays and c) the electron transport through individual carbon nanotubes and nanorods. The VT-SPM system will serve as a major piece of infrastructure for building present and future efforts in investigating nanostructures and materials at Harvard University and it will serve as a locus for new collaborative efforts to fabricate and manipulate nanometer-scale materials and to investigate their physical and chemical properties in unprecedented detail.
A scanning probe microscope (SPM) coupled with a variable-temperature stage allows atomic-resolution imaging of both conductive and nonconductive surfaces as well as a variety of chemically derived nanostructures at controlled sample temperature. This ability of SPM to image and manipulate nanometer-scale structures as a function of temperature opens up many new research fronts in chemistry, physics and related interdisciplinary areas of science since it allows physical and chemical investigations of nanometer-sized materials as a function of the most important thermodynamic variable, temperature. Using the SPM will expose students to a central tool for surface science, materials science and the emerging field of nanoscience.
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With this award from the Instrumentation for Materials Research Program, the Department of Chemistry and Chemical Biology at Harvard University will acquire a Variable-Temperature Scanning Probe Microscope bolt-on module from Omicron Instruments. This instrument will facilitate research in a number of areas, including a) the phase transitions of individual nanocrystals, b) the electron transport through individual molecules, nanocrystals and their arrays and c) the electron transport through individual carbon nanotubes and nanorods. The VT-SPM system will serve as a major piece of infrastructure for building present and future efforts in investigating nanostructures and materials at Harvard University and it will serve as a locus for new collaborative efforts to fabricate and manipulate nanometer-scale materials and to investigate their physical and chemical properties in unprecedented detail. Using the SPM will expose students to a central tool for surface science, materials science and the emerging field of nanoscience.
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This research is an experimental study of dynamic mesoscopic transport phenomena in semiconductor microstructures and hybrid metals/superconductor systems. The unifying theme is the interplay between three elements: quantum coherence, disorder or chaos, and dynamics in the form of a time-dependent potential. The proposed experiments also have in common the theme of dc pumping of charge using cyclic oscillating potentials, extending recent work on adiabatic quantum pumping to include the role of decoherence, dissipation, and nonadiabatic time dependence. Besides shape-deformable quantum dots, two novel pumping devices are proposed: a pump that operates in the fractional quantum Hall regime, allowing a pumping of fractionally charged quasiparticles, and a hybrid metal-superconductor that uses the ac Josephson effect to produce a cycling time evolution of boundary conditions. This research will be carried out in a new laboratory at Harvard University. The project will support a graduate student as well as materials and supplies needed for the experiments. Other students on these projects will be supported by independent fellowships. The students will be trained in state-of-the-art nanoelectronics techniques and will be well prepared for careers in academe, industry or government.
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Trends in microelectronics have two clear directions, smaller and faster. The study of quantum mechanical effects in electronic devices-particularly disorder or chaotic systems-is known as mesoscopic physics, where "meso" indicates intermediate in size between atoms (where quantum physics is well understood) and the realm of large, classical electronics, governed by Ohm's law and other familiar classical laws. Mesoscopic physics has seen rapid development in the last decade, predominantly as a result of advances in the fabrication of clean semiconductors devices. By comparison, little work has been done on the high-speed side, and most of what is known about quantum-coherent devices is restricted to dc. The proposed experimental work aims to investigate quantum coherent electronic devices fabricated from semiconductors and hybrid metal/superconductor devices, at high frequencies, when effects of time evolution can lead to the destruction of quantum coherence effects, but can also lead to new effects such as the pumping of electrons due to cyclic, periodic changes in the effective shape of the device. These results will impact our understanding and development of high-speed nanoelectronics. The project will support one graduate student as well as provide materials and supplies for the project. Other students working on these experiments will have outside funding from the NSF and other sources. The students will be trained in state-of-the-art nanoelectronics techniques and will be well prepared for careers in academe, industry or government.

This proposal was received in response to the NSF Spin Electronics for the 21st Century Initiative, Program Solicitation NSF 02-036. The proposal focuses on investigation of techniques to locally induce, control, and detect electron spin in semiconductor microstructures by using properly located electrostatic gate voltages. Electrostatic gates are easily defined on a submicron scale and should provide switching and manipulations of spin currents. A variety of approaches to this goal will be pursued, including (i) gate-programmable nuclear polarization applied to single and double quantum dots, and the transfer of nuclear spin from dot to dot, (ii) gate-controlled spin-polarization in high-mobility GaAs/AlAs epitaxial layers; and (iii) electron-spin-resonance {ESR) measurements in AlAs.

Combining state-of-the-art fabrication technology, careful measurements, and theoretical analysis, the proposed research is highly interdisciplinary. It relies on expertise of three experimentalists and one theorist in engineering and physics. It also entails the full participation of graduate and undergraduate students, who will gain invaluable experience and knowledge in cutting edge materials science and engineering, with a focus on the emerging and potentially rewarding field of spin electronics.

The work will be centered at Princeton University with one investigator at Harvard University. Existing facilities at Princeton and Harvard will be adequate to carry out all the proposed work. The majority of requested funding will be used to support graduate students. Workshops at Princeton are planned to insure a focused research effort and to enhance interaction among students working on the common research goals.

The objective of this proposal is to investigate a new approach for fabricating nanoscale electronic circuits. The approach is to selectively deposit, then lithographically pattern, layers of graphitic carbon on substrates of TiC or Pt, then induce the patterned layers to roll up into small-diameter tubes by heating. This approach allows complex and massively integrated circuits, including branching elements, with controlled chirality of the constituent tube-like elements.
The ability to pattern complex circuits of nanotubes, control chirality by setting the direction of individual components based on orientation, and to form complex circuit topologies would constitute a revolution in electronics, and would therefore have a broad societal impact. Arguably, without a breakthrough of this sort, nanotubes will not be useful for electronics. Our educational objective is to provide an exciting research environment and opportunities for career advancement for young scientists. The cross-disciplinary nature of the research will provide them with exposure to different disciplines, including Physics, Materials Science, Chemistry, and Engineering. All three participating groups have strong track records of emphasizing undergraduate research. Overall, this project has the potential to yield a breakthrough in the nanofabrication of circuits. In concert, we will train young scientists in an exciting field that emphasizes collaborative and cross-disciplinary research.

*****NON-TECHNICAL ABSTRACT*****
Spin, as the name suggests, is a fundamental property of electrons describing their angular momentum (as if they were spinning) and associated magnetic properties. While modern electronics predominantly use the charge of the electron to encode information, electron spin is also working for us, notably in hard drives, credit card strips, and any other magnetic storage medium. However, spin offers a much more powerful application-one that has yet to appear in any technology, but which theory has shown could lead to revolutionary improvements in computation and communication by tapping the laws of quantum mechanics. This project aims to study experimentally how information about spin orientation is conveyed between electrons in an intrinsically quantum mechanical way. Rather than investigating electrons in their natural environment, e.g., in a metal (which is difficult to probe and control), this project will fabricate artificial electronic systems from nanoscale semiconductors devices known as quantum dots, allowing far greater control over individual electrons. In quantum dots, spins can be coupled and uncoupled with the turn of a knob, as in a transistor. By constructing artificial electronic systems and investigating how spin information is communicated, the project aims to learn the limits of how long-range coupling can be used for future technologies in which programmed information is encoded in electron spin. The students working on these projects will learn skills that will enable them to become productive members of the academic or industrial communities.

*****TECHNICAL ABSTRACT*****
This project will explore non-local spin-spin interactions, analogs of the well-studied Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins in metals, in an artificially fabricated spin system based on gate-defined GaAs quantum dots. Particular experiments will (1) investigate the competition between RKKY and Kondo effects, aiming to shed light on less controllable counterparts of this competition in strongly correlated electronic materials, (2) explore RKKY interactions mediated by ballistic electrons or a small confined fermi sea, and (3) to observe the dephasing effects of spin coupling on the electron sea itself through weak localization measurements. A second main goal of the project is to explore the use of spin as a holder of quantum information. Because the RKKY interaction conveys spin information nonlocally it is an interesting candidate to mediate the long-range transfer of spin information for spin-based quantum information processing. However, the coupling of spins to an electron sea presumably leads to losses of quantum coherence analogous to Korringa relaxation. Experimental techniques developed in this project will determine if long-range communication of spin information using RKKY interactions are possible for future technologies. The students involved with this research will obtain the knowledge and skills necessary for future careers in academe or in industrial or national laboratories.

This award supports an international collaboration for research and education among Harvard University and University of Florida (UF) in the USA, University of Basel and ETH (Zurich) in Switzerland, and University of Regensburg in Germany. The main goal of the project is to understand, control, and utilize the hyperfine interaction of electron spins, confined in low-dimensional condensed matter systems, with the nuclear spins of the host lattice. Four emerging themes in condensed matter physics draw particular attention to this topic, making a Network-scale activity timely. Those themes are: i) advances in nanoscale control of matter, e.g. , quantum dots, where electrons interact with far fewer nuclear spins thereby greatly enhancing the effectiveness of hyperfine coupling; ii) emergence of spintronics devices employing the electron's spin rather than charge for future prospects of quantum repeaters, quantum computers, and quantum memory for secure communication and enhanced computation, iii) engineered interactions in novel materials, such as gating and tailoring of band structure, and iv) availability of high-quality fabrication facilities. There are three main thrusts in this Network: i) control of spin and electron-nuclear interaction in III-V semiconductor quantum dots [experiment: Harvard; theory: Harvard, Basel]; ii) coupling of nuclear spins via itinerant carriers (RKKY interaction) and nuclear magnetism in p-doped heterostructures [experiment: ETH, Regensburg; theory: UF, Basel, Harvard]; and iii) electron-nuclear interactions in 13C-enriched nanotubes [experiment: Harvard, theory: Harvard, Basel, UF]. By investigating the interface between fundamental and applied problems in an international environment, this Network contributes to the kind of cross-training of graduate students that is needed for the next generation of device engineers and scientists, perhaps working with quantum-coherent devices. Exchange of students between experimental groups at Harvard and ETH and between theoretical groups at Harvard, Basel, and UF will take place over the course of the project

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Marcus

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."

The overall goal of the proposed research is to functionalize Si nanoparticles to target common cancers, enhance the NMR signal of these particles using dynamic nuclear polarization (DNP), and characterize the hyperpolarized particles in vitro. These are vital steps toward our overall objective of developing a novel molecular imaging probe based on MRI of hyperpolarized silicon nanoparticles, to provide a novel tool for measuring and imaging biological processes in health and disease. The use of hyperpolarized noble gases for lung imaging has clearly demonstrated the benefits of imaging hyperpolarized agents, providing both dramatically increased detection sensitivity as well as eliminating all background signals. Recently, 13C imaging of 13C-hyperpolarized metabolites has provided a method for rapid metabolic profiling. However, the very short nuclear relaxation times of hyperpolarized agents used, typically less than 60 s for most 13C agents, is much too short for the imaging of targeted molecular probes that require several hours to both reach and bind their targets. The investigators have demonstrated that Si nanoparticles can be surface-coated, have their polarization enhanced by over three of orders of magnitude compared to room temperature Boltzmann polarization, and that the 29Si nanoparticle spins can exhibit nuclear relaxation times >500 s. Investigators have also shown that this relaxation time can be tailored for the application by modifying particle size. The present proposal focuses on functionalization of the nanoparticles to target common cancer cells and efforts to maximize and retain the hyperpolarization of the Si nanoparticles during delivery. Such 29Sibased imaging agents will provide powerful and much needed new tools for targeted molecular imaging, cell tracking and the detection of tumors. The proposal consists of three specific aims. The first aim is to develop targetable Si nanoparticles that can be hyperpolarized; the second aim is to develop high efficiency dynamic nuclear polarization; the third aim is to perform standard NMR and MRI on the functionalized nanoparticles, before and after hyperpolarization.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

This award will provide partial support for the completion of Harvard's helium recovery and reliquefaction infrastructure . The project includes helium gas recovery piping from a multi-user nuclear magnetic resonance facility and from the labs of 15 faculty members (8 physics, 3 engineering, and 4 chemistry), and the fixed equipment to collect, liquefy, and dispense the recovered helium. The project would also include HVAC, electrical, and control infrastructure required for operation.

Helium is used extensively in physics, engineering, chemistry, and biology research whenever cold environments are needed for experiments or detectors. Current and future research activities include making accurate measurement of the electron magnetic moment and the fine structure constant, and the most stringent test of charge-parity-time symmetry with leptons; using helium as a buffer gas to cool new atoms and molecules into Bose-Einstein condensates and quantum Fermionic systems; providing cooling for studies of the electronic orders in exotic correlated electron materials such as high-Tc superconductors and graphene; allowing access to the quantized energy levels in nanostructures fabricated from materials such as GaAs, carbon nanotubes, graphene, and diamond; and permitting diagnostics such as nuclear magnetic resonance, Mossbauer spectroscopy, and scanning tunneling spectroscopy of newly synthesized molecules and catalysts.

Each year, over 300 students and postdocs will be working on research projects in physics, chemistry, and materials science that involve liquid helium. The liquefier would conserve helium, a precious nonrenewable resource, and would consume approximately one-fifth the electricity of alternative technologies such as pulse tube refrigerators.

Underlying the global economy is the ability to process information quickly and cheaply. The field of quantum information processing, which harnesses the unusual features of quantum physics, offers a novel approach to rapid encoding and manipulation of information. In this project, researchers from Middlebury College, Harvard, and University of Copenhagen create and investigate quantum bits (qubits) "the fundamental building blocks of quantum computation" formed from carbon nanotubes. The team of researchers exploits the unique properties of carbon nanotubes to manipulate and interrogate the qubits, with the goal of demonstrating coherent control of the fragile quantum states. The key properties of nanotubes that make them well suited for quantum information processing are themselves newly understood, and are a forefront area of fundamental physics. Those properties include spin-orbit coupling associated with circumferential motion around the nanotube, electron-nuclear coupling and the ability to control dephasing of electron spin. The project is a good balance between future potential applications in the exciting area of quantum information, and condensed matter physics in nanoscale electronics, as fundamental physics. Students involved in the project particularly appreciate the connection between fundamental and applied components of the activity.

The subject of the project "quantum information processing" is inherently revolutionary. In addition, the project is designed to build on the exceptional strengths of liberal arts colleges and research universities in educating students and conducting research. Undergraduates perform a significant portion of the research, providing invaluable training for careers in physics. Research conducted at Harvard during the summer feeds directly into the curriculum at the PI's institution, Middlebury College, as students work in parallel on credit-bearing projects and senior theses and interact with their peers at Harvard. The aim is to foster a critical mass of students who are deeply engaged in all aspects of research, from collecting and analyzing data to presenting results, and who have the training and expertise necessary to excel in physics.