Qian Niu - US grants

9705406 Plummer This FRG proposal addresses, experimentally and theoretically, basic materials science issues in a collaborative program involving researchers at four universities and ORNL, combining expertise and facilities to explore a new concept in epitaxy, an "electronic growth" mechanism. Within this mechanism the critical thickness for the formation of an atomically flat film corresponds to the thickness where the two-dimensional electronic system can be confined in a potential well between the vacuum and the substrate. This magic film thickness depends on the nature of quantum well states, that is, the overall arrangement of atoms is dictated by the preference of electrons to occupy certain quantum-mechanical states. Special resources made available jointly for this project include high resolution photo-emission, surface x-ray scattering, scanning probe microscopy, high resolution inelastic electron scattering, and super computing equipment. The proposed research emphasizes understanding of fundamental mechanisms and processes through a combination of theoretical and experimental studies. %%% The project addresses forefront materials science research issues in a topical area of materials science having high technological relevance. The research will contribute basic materials science knowledge at a fundamental level to important aspects of metal-semiconductor interfaces critical to electronic/photonic devices and integrated circuitry, in general. Additionally, the fundamental knowledge and understanding gained from the research is expected to contribute to improving the performance of advanced devices and circuits by providing a fundamental understanding and a basis for designing and producing improved materials and structures for the quantum mechanical devices of the future. The research program may lead to a new paradigm for metal heteroepitaxy, which is of significance in the fabrication of electronic devices and microelectronics circuitry. ***

This research project focuses on the study, both experimentally and theoretically, of quantum transport of ultra-cold atoms in optical lattices, in particular, in mixed phase space, in billiards, and in quasi-periodic lattices, as well as the effects of many body interactions and decoherence. Some of the projects include probing: 1) quantum chaos in time-dependent potentials in a regime of mixed phase space, 2) quantum chaos in the quantum billiard, 3) transport in quasi-periodic lattices in one and two dimensions, 4) breakdown of adiabaticity in the region of strong interactions, and 5) the sensitivity to noise and dissipation for local structures in classical phase space.

This project addresses effects of quantum confinement on epitaxial growth of metal/semiconductor thin films and nanostructures. The approach is a combined theory/experiment collaborative activity among researchers at U. Tx/Austin and ORNL, and is aimed at greater understanding and utilization of an "electronic growth" concept. To date, the main findings of the "electronic growth" model are that a competition between quantum confinement, charge spilling, and interface-induced electron density os-cillations can make a flat ultrathin metal film critically, magically, marginally stable, or totally unstable against morphological roughening. For Ag on GaAs and other III-V semiconductor substrates, the electronic growth mechanism leads to the existence of a critical thickness for the formation of an atomically flat film. Theoretical studies also showed the existence of magic thicknesses for other metal/semiconductor systems, and the possibility of oscillatory metal-nonmetal transitions. The theo-retical and experimental scope of this project will include quantum effects in both the vertical and lat-eral directions and the interplay between thermodynamic and kinetic factors. The goal is to gain a deeper understanding of the pathways of the electronic mechanism for film growth, and to achieve controlled formation of lower-dimensional structures. The possibility of using electronic energetics as-sociated with quantum states and charge quantization to influence geometric ordering and size selec-tion of quantum dot arrays will also be explored. Theoretical predictions of critical/magic thicknesses and oscillatory metal-nonmetal transitions in a variety of systems will be studied experimentally.
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The project addresses basic research issues in a topical area of materials science with high technologi-cal relevance. The basic knowledge and understanding gained from the research is expected to contrib-ute to next generation electronic/photonic materials. An important feature of the program is the inte-gration of research and education through the training of students in a fundamentally and technologi-cally significant area. The project is co-supported by the DMR/EM and DMR/MET programs.

This Focused Research Group (FRG) project the topic of length scales and dimensionality cross-over in nanoscience and technology. The project aims to bridge the gap between the nanoscopic world of atoms and the mesoscopic world of materials and devices, by integrating quantum growth with more traditional growth concepts, addressing a spectrum of fundamental issues in condensed matter- and materials sciences. The project addresses the size effect on (i) Cooper pair formation and order parameter in superconductivity; (ii) magnetic anisotropy and ordering tem-peratures in magnetic quantum dots; and (iii) the interplay between free carriers and magnetic moments in artificially-structured dilute magnetic semiconductors. The FRG involves researchers with complementary expertise and capabilities in quantum growth and manipulation schemes for metallic nanostructures, interface engineering, transport measurements on surface systems and ultrathin films, and theory of nucleation and growth, mesoscopic physics, transport, and magnet-ism. The project includes collaborative partnerships between the university investigators and the Center for Nanophase Materials Sciences (CNMS) at Oak Ridge National Laboratory (ORNL).
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This project addresses basic research issues in a topical area of materials science with significant technological relevance, and places emphasis on the integration of research and education. The proposed program embodies development for a new partnership between the Center for Nano-phase Materials Sciences (CNMS) at Oak Ridge National Laboratory (ORNL) and the academic institutions represented in this proposal. The proposed science and supporting infrastructure pro-vide an excellent setting for the education and training of internationally competitive students and postdocs. They can access some of the world's most advanced facilities for nanoscale sci-ence and ultrafast computing at UT-Austin, UT-Knoxville, and ORNL. The educational outreach effort will focus on the development of a new curriculum for nanoscale science and technology, in partnership with the Center of Nano- and Molecular Science and Technology at the University of Texas. The curriculum will be aimed at bridging the departmental boundaries and traditional research disciplines, which is expected to foster a collaborative atmosphere of excitement and discovery. The research integrates materials synthesis and characterization, and shows how the-ory and experiment can work hand-in-hand to push the frontier of nanoscale science and technol-ogy. The project will enlarge the pool of young scientists who have collaborative research ex-perience and who will be ready to take their place in the highly-skilled workforce that continues to drive today's high-tech society.
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This proposal aims to continue a research program on quantum transport of ultra-cold atoms. The PI will investigate quantum structure and dynamics of ultra-cold atoms in optical billiards and to measure quantum transport of ultra-cold atoms and condensates in two-dimensional optical lattices, with the focus on the transport in real space. In addition, experiments will be performed on the extraction of single atoms from a Bose-Einstein condensate with very high fidelity, with the atoms remaining in the ground state of a potential well (a quantum tweezer). Finally the project will implement multi-particle interferometry with atoms. On the broader impact of the research, the preparation of single atoms in a specified quantum state is the basis for several different schemes for quantum computation and quantum information processing.

This proposal was received in response to Nanoscale Science and Engineering initiative NSF-03-043, category NIRT. The effort involves a team of materials scientists with complementary expertise in magnetic thin film growth, nanostructure fabrication, mesoscopic physics and magnetic materials. The scientific objective of the research program is to advance the fundamental understanding of spin distributions and spin dynamics, including damping, in nanostructured magnetic materials on picosecond time scales. The development of high-performance ultrahigh-frequency magnetic materials will require new tools for probing and accurately modeling spin distributions on a nanometer spatial scale and spin dynamics on a sub-picosecond time scale. The current research combines technique development (spin-polarized electron scanning tunneling microscopy and femtosecond laser-based spin-dynamics), and novel materials synthesis (self-assembly and template growth) with multi-scale multi-phenomena theory and modeling. Integrated with this are outreach (NSF/UT Austin Research Experience for Undergraduates program) and educational components (new courses in nanotechnology and mesoscopic physics) that will provide new materials and trained personnel required for continued technological advances in magnetic materials.

This proposal was received in response to Nanoscale Science and Engineering initiative NSF-03-043 category NIRT. The team consists of materials scientists with complementary expertise in magnetic thin film growth, nanostructure fabrication, theoretical materials physics, and magnetic materials characterization to address new scientific and technological issues that arise in submicrometer scale magnetic structures. The objective is to advance fundamental understanding of relationships between materials properties and magnetic response in microfabricated magnetic materials. Scientific and technological relationships between dimensionality, shape, and structure of nanoparticles and their magnetic properties will be investigated. The effort combines technique development (new high-speed high-spatial resolution probes of magnetic response) with new methods of producing sub-micron magnetic structures (atomic self-assembly), and powerful numerical/theoretical methods for simulating and understanding magnetic response. The research may lead to new magnetic materials with applications using currently unused high-frequency bands in radar, telecommunications, radio astronomy, spectroscopy and imaging. The research is integrated with educational and outreach activities including new graduate level courses covering magnetic nanostructures and technology and undergraduate research experience activities. The program is designed to attract and train the next generation of scientists and engineers required for continued scientific and technological advances in the application of magnetic materials.

TECHNICAL: Supported by NSF, which began in 1998, this FRG program developed a novel 'electronic growth' concept, stressing the vital importance of quantum size effects of the itinerant electrons in defining the stability as well as the likely growth mode of metallic thin films on semiconductor substrates. This new concept adds a substantial new facet to the phrase 'quantum engineering', in that quantum effects can now be exploited to precisely control the formation of metallic structures in the quantum regime. Capitalizing on PI's strengths and conceptual advances achieved so far in the broad areas of metallic and magnetic nanostructures, this project aims at pushing the research objectives in three new frontiers: (a) One-dimensional (1D) Electronic Growth and 1D Quantum Structures; (b) Subsurfactant Epitaxy and Quantum Growth of Hybrid Quantum Structures; and (c) Adsorption Energetics, Surface Mobility, and Chemical Reactivity on Quantum Films. In area (a), as 1D electronic systems exhibit sharp spikes in the density of states (DOS), as opposed to the staircase DOS of 2D systems, one expects much stronger quantum size effects. This can potentially be exploited for controlling the formation of 1D quantum structures. The interplay between the spin-resolved DOS and 1D quantum growth will be investigated. In addition, 1D superconductivity will be pushed toward the clean limit and thoroughly explored. In area (b), by integrating the concepts of 'subsurfactant epitaxy' and 'electronic growth', the PIs will fabricate hybrid quantum structures involving superconductors and dilute magnetic semiconductors. Success here will allow to explore the novel concept of charge and spin manipulation in such hybrid systems. In area (c) the PIs will investigate how the quantum stability influences three intimately related surface phenomena: adsorption energetics of atoms and molecules, their surface migration rates, and chemical reactivity on selected catalytic metal films. NON-TECHNICAL: Artificially engineered electronic systems in reduced dimensions occupy a central part in modern materials research. By developing advanced synthesis techniques, materials scientists strive to tailor novel electronic materials through dimensional control with the ultimate atomic precision. The driving force is the realization that, in reduced dimensions, quantum effects are bound to be more pronounced, and may result in intriguing new physical properties of technological significance. The educational goals are manifold. The first is to prepare the next generation of materials scientists in nanoscience and nanotechnology through research training involving postdoctoral researchers, graduate students, and undergraduates. Undergraduate students are recruited through the REU programs in our institutions. The next goal is to provide broader education through the development of a new curriculum and new courses in nanoscience and technology at the graduate and undergraduate levels at both institutions. This educational goal has been achieved successfully and will continue to be pushed to new fronts. Finally, in terms of K-12 nanoscience education, the PIs will recruit high school science teachers through the UTEACH program at Univ. of Texas. In addition, to introduce the concept of nanoscience at the most basic level the PIs also foster a partnership with the Austin Children's Museum to develop demonstration kits for nanoscience education for young children from K-5. Similar efforts have been and will continue to be made at the University of Tennessee. As a specific example, one PI, Zhang, has served as a volunteer science instructor in a local primary school for years and will continue on such efforts.

TECHNICAL SUMMARY:

Elegantly fabricated functional materials with reduced dimensions occupy a central stage of modern materials research. By uncovering fundamental enabling concepts in growth science and developing advanced synthesis techniques, materials scientists strive to tailor novel materials through dimensional control with the ultimate atomic precision. This scientific enterprise is driven by the realization that, by reducing the dimensionality of the systems, quantum effects within the systems are tuned to be more pronounced, potentially resulting in emergent physical properties of technological significance. This FRG program pioneered in the formulation and development of an innovative concept, termed "electronic growth", stressing the vital importance of quantum mechanically confined motion of the itinerant electrons in defining the overall stability as well as the preferred growth mode of a variety of metal films and nanostructures on different substrates. The far-reaching impact of this new concept lies in its enabling role: It provides the basis on which quantum size effects can be exploited to precisely control the formation of metallic structures; such structures formed in the quantum regime, in turn, are bound to serve as appealing platforms for elucidating intriguing quantum properties. The proposed research emphasis in the new phase will focus on exploration of new frontiers of quantum growth. The central objectives will be to gain property tunability of the metal systems tailored in the quantum regime, developed around three thrusts, each of profound fundamental and practical importance: (a) Superconductivity in Low Dimensional Electron Systems; (b) Tuning Plasmonic Properties in the in the Quantum Regime; and (c) Formation and Catalytic Properties of Quantum Metal Alloys.

NON-TECHNICAL SUMMARY:

This proposal is aimed at creating an inter-disciplinary research program focusing on the research area of metallic nanostructures where the physical properties are dominated by quantum size effects. The ultimate research goals are to use atomic scale control of materials synthesis to tune the physical properties in the quantum regime. The proposal focuses on the integration research and education to train internationally competitive students and postdocs. This setting is provided through the unique partnership of this FRG team with the Oak Ridge National Laboratory (ORNL). Together, UT-Austin, UT-Knoxville, and ORNL provide a closely collaborative, inter-disciplinary research/educational platform for next generation of US leaders in materials research. The investigators are also committed to educational outreach to a broader audience at all levels. This will be accomplished with multi-prone approaches including (a) offering special topic courses which enrich the curriculum in Nanoscience and Technology that are also accessible to broader undergraduate students, (b) enhancing the outreach program of Summer Academy of Nanoscience and Nanotechnology for State-wide high school teachers and students in Texas, and (c) targeting high school students who are participating in the Tennessee Governor's school for the Sciences and Engineering by offering them research training. Finally, this program is fully committed to broadening participation of under-represented groups in graduate research with specific goals of increasing the percentage of graduate students that are woman or/and of Hispanic background.

The volume and variability of water flowing through rivers and streams are primary regulators of freshwater biodiversity, particularly for fishes. This regulation is partially due to energetic constraints imposed by particular flow conditions. For example, some species are better adapted to fast currents for food resource acquisition, while others require slower currents. In addition to energetic constraints, species are also influenced by biological interactions such as predation and competition with ecologically similar species. Consequently, fish populations will persist given suitable amounts of food resources and reasonable levels of interactions with other species, two factors which are also regulated by flow conditions. Nevertheless, the combined effects of flow characteristics and biological interactions in determining fish species diversity are not well understood. This project addresses this issue by collecting food web data from multiple sites in the Meramec River system in southeastern Missouri and relating these measurements to stream flow characteristics. Investigating factors influencing food web structure in the context of various flow regimes will provide novel information on the primary factors regulating biodiversity in freshwater stream ecosystems.

The Meramec River watershed is located in the Ozark Highlands and represents a freshwater biodiversity hotspot in North America. Over 120 species of fishes are found in the Meramec River and its tributaries. At the same time, the Meramec River supplies drinking water to approximately 250,000 people. Although the drainage area remains relatively pristine, some stream sections are experiencing ongoing degradation due to human modifications of the landscape. Consequently, the Meramec River watershed is a primary focus of collaborative conservation efforts by the Missouri Department of Conservation and The Nature Conservancy due to its biological importance and the dependence of humans on the water resources in the drainage. Results from this research will be of practical use for these conservation agencies during their attempts to balance human activities and the conservation of biodiversity in this unique aquatic ecosystem. In addition, several undergraduate students will be trained in research techniques as well as exposed to issues focused on the conservation of aquatic resources.

This project investigates novel ways to transport, guide and direct thermal energy (heat) based on the new paradigm of topological thermal transport. Through this paradigm, heat can be guided to flow only along the boundary of a material while avoiding its interior, as well as in a highly directional ways that are also robust to material disorder and other defects. To achieve this, the team will harness and engineer special topological properties of materials and devices involving various heat carriers including electrons, phonons (crystal lattice vibrations) or light. Discoveries and innovations from this project could impact many technological areas involving the control and transport of thermal energy, such as on-chip heat management and cooling in modern electronic and photonic systems, as well as energy generation, conversion and harvesting through thermoelectrics and photothermovoltaics. The project could also lead to new schemes for thermal management such as thermal insulation, ?cloaking? and directed thermal flow. The research team will contribute to an online forum called ?Thermal Hub? within NSF-funded NanoHub that counts millions of subscribers and users. The forum is expected to facilitate sharing and exchange of information in the emerging field of ?topological thermal transport?, and benefit research and development in nanoscale thermal engineering in general. Both graduate and undergraduate students will be actively involved in the research and learning activities of the program. Particular attention will be placed on broadening the participation of women & minority students via various diversity and outreach activities by the team. The project will leverage several existing programs at their institutions and partnerships with several undergraduate and minority colleges.

Topological states of electrons such as quantum Hall effect (QHE) and topological insulators (TI) are some of the most important developments in contemporary condensed matter physics. Such topological electronic states feature topologically-protected electronic transport along the boundary of an insulating bulk sample that is immune to scattering by various impurities. This project will pursue topological concepts in the so-far-unexplored realm of thermal transport. The proposed approach will harness or engineer topological properties of three different types of heat carriers ? electrons, phonons and phonon-polaritons, to realize topologically guided and protected thermal transport that can be further controlled by external forces and fields. The first theme of the program will explore high-quality electronic topological insulators with insulating bulk and conducting topological surface states of spin-helical Dirac electrons to demonstrate optically and magnetically controlled, and non-reciprocal electronic thermal conduction, and other novel thermal transport carried by such topological surface electrons. The second and third themes of the project will focus on the extension and analogs of several key physical mechanisms underlying the electronic topological states --- such as spin-momentum coupling/locking, chirality/valley states, and spin/valley Hall effects --- to phonons and hybrid phonon-photon polaritons, toward realizing various topological phononic states and phonon/thermal transport.