Jia Lu, MSc - US grants

This Nanoscale Interdisciplinary Research Team brings together expertise in state-of-the-art spin-tunneling science with proven success in fabrication and characterization of single-electron transistors. The goal here is to understand science in spin-based nano-fabricated structures by probing the quantum states and dynamics of spins on nano-sized islands, laying the foundation for a new generation of ultra-fast and non-volatile electronics. This program begins with the fabrication of simple nanostructures based on proven single-electron transistor architecture and processing, with ferromagnetic electrode(s) to inject polarized spins. These new nanoscale hybrid structures will be used to test various theoretically predicted phenomena such as enhanced magnetoresistance, single-electron charging effects, conductance oscillations, and spin diffusion. One of the novel features of this effort is to inject fully polarized spins into nonmagnetic materials such as carbon nanotubes, nonmagnetic metals, and superconductors, by spin filtering through the use of a magnetic semiconductor. Ultimately, the localization of a single-electron of controlled spin in a highly sensitive nanostructure will enable novel and more versatile spin-based devices, which so far is being pursued based on the behavior of large numbers of spin-polarized electrons. This program represents an excellent opportunity for the students (of all levels) involved being educated in the nanoscience; participate in a true team effort with complementary and collective goals. The students will work in multidisciplinary areas - physics, materials science, and nano-devices, getting trained and educated in the spin-based research laying the foundation for future technology, which is already in short supply in the U.S.
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The recognition of electron spin as a binary variable analogous to its charge as currently used in semiconductors, opened new fields of science and technology that have already led to commercial devices, called spin electronics. This interdisciplinary team will address the underlying fundamental science and engineering research issues that are critical to the emerging field of nanoscale spin electronics (also called as spintronics). In spite of the recent progress and potentially promising for applications, the field of spintronics just beginning to unravel, (remains largely unexplored) and requires extensive research efforts. The proposed research (elucidating spin transport including spin tunneling and injection from a ferromagnet into a nonmagnetic metal, superconductor or a semiconductor) holds great promise for nanoscale science and future information technology. This aim is supported by the investigation of promising new materials combinations for spin transport and the development of powerful, innovative probes of spin dynamics in nanostructures. This team, with complementary knowledge and expertise - of physicists, material scientists and electrical engineers, will efficiently address all the issues from the conceptual level to the near-device stage. The proposed program will ultimately lead to novel spin electronic devices that meet the criteria for low power, broadband, and ultra high density including extremely powerful computers. Many PhD students, and importantly undergraduates and high school students will take part in this program under the guidance of the PIs and postdoctoral fellows. The training will generate future scientists and engineers in high demands in the area of nano-science and spin-based information technology to maintain the future technological prowess of the country, critically necessary for the national security.
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This four-year Nanoscale Interdisciplinary Research Team (NIRT) project at Washington University, with Professor William E. Buhro as principal investigator, pursues a new family of one-dimensional nanostructures form elemental boron and metal-borides. These nanomaterials are expected to posses mechanical strengths, chemical and thermal stabilities, and electrical (metallic) conductivities comparable to or even surpassing those of carbon nanotubes. Boron and metal-boride nanostructures will be ideal candidates for nanoscale electrical interconnects and semi-conducting components in nanoelectronic and nano-electrochemical devices. Synthetic methods to be employed include catalyzed chemical vapor deposition (CVD), and plasma techniques. Mechanical properties of nanotubes and nanowhiskers will be measured on mechanical-testing stages of scanning transmission electron microscope. Electrical-transport properties will be studied using the nanoelectronic-testing stage developed at Washington University.

Proposal Title: PECASE: Single Spin Transistors - Science, Application and Education
Institution: University of California-Irvine

This is a proposal aimed at exploring the spin properties, both from the fundamental physics point of view as well as from their relevance to the recent technologically important area of spintronics. The PI proposes to combine the recent experimental developments of single-electron transistors and magnetic tunnel junctions to fabricate new spin electronics devices, which we call single spin transistors based on the controllability and manipulability of single-electron spins.
This proposal aims to fabricate and characterize single spin transistors which use the carbon nanotube as the nano-sized island. It will reveal new physical aspects of the quantum states and dynamic behavior of single electron spins in the one dimensional system. This device is based on the proven single electron transistor architecture and processing, with the island weakly coupled to ferromagnetic electrodes to inject and detect polarized spins. These nanoscale hybrid structures will be used to test various theoretically predicted phenomena such as enhanced magnetoresistance, single electron charging effects, conductance oscillations, and spin diffusion. One of the novel features of this effort is to inject fully polarized spins into the one dimensional carbon nanotubes, by spin filtering through the use of a magnetic semiconductor. Ultimately, the localization of a single electron of controlled spin in a highly sensitive nanostructure will enable novel and more versatile spin electronic devices, which so far is being pursued based on the behavior of large numbers of spin-polarized electrons. The proposed research will be critical to extremely high-density magnetic information storage, electron-spin-based quantum computing, magneto-electronic sensors, and perhaps future spin electronic devices and systems yet to be imagined. To continue the education and training of students, graduate students, undergraduates and high school students, especially from the underrepresented groups, will be recruited to participate in the proposed research. This program represents an excellent opportunity for the students (of all levels) involved being educated in the nanoscience. They will work in multidisciplinary areas - physics, materials science, and nanoelectronics, the future trend in science and technology. These highly educated and trained people will become either future educators or the technical backbone of spin based information storage technology, which is already in short supply in the U.S.

Living organs respond to mechanical load not only by deformation, but also by growth, resorption and structural remodeling. While the elasticity of soft tissues is relatively well-studied, the interaction between mechanical factors and adaptive growth remains poorly understood. The goal of the project is to gain understanding of coupled stress-growth motion through (1) developing and evaluating biomechanics models for stress-regulated growth and remodeling in vascular system; (2) developing finite element formulations for the simulation of coupled stress-growth motion; and (3) investigating the mechanical aspect of aneurysm growth and remodeling. The research will bring new dimensions into the biomechanical analysis of soft tissues. A better understanding of tissue adaptive behavior and the relation to physiological functions is expected to be obtained out of this research. The project plans to incorporate the research results into classroom teaching by introducing new teaching modules for continuum mechanics, computational mechanics and vascular mechanics courses. It also offers educational opportunities for graduate and undergraduate students to work on leading edge research projects.

The objective of this research is to determine the feasibility of using a biological system for templating particles into well-ordered two- and three-dimensional assemblies, with the vision toward new applications in nanoscale optoelectronic devices and high temperature electrochemical systems. The approach is to attach inorganic nanoparticles to protein templates to form highly-ordered two-dimensional arrays, characterize the spatial and optical properties of these protein-nanoparticle assemblies, and use layer-by-layer assembly to build three-dimensional protein-nanoparticle hybrid materials.

Intellectual Merit:
This research will develop a new strategy to construct nanostructured materials. The ability to fabricate assemblies comprising small inorganic nanoparticles into arrays of predetermined spacing and arrangement is currently not feasible. By enabling lattice parameter manipulation and ordered layer-by-layer assembly, arrays that consist of particles exhibiting the quantum size effect may reveal new properties. This, in turn, could enable the design of novel devices in areas such as optoelectronic technologies and fuel cells.

Broader Impact:
The program is necessarily a multidisciplinary endeavor, and it therefore represents an excellent opportunity for students to participate in a collaborative team effort and be trained to work with team members of diverse backgrounds. Under this proposed project, students at all educational levels (graduate, undergraduate, and high school) will be actively recruited. The results of this proposed work will also be integrated into topics presented in graduate-level courses.

This award supports a two-day conference for undergraduate women in physics that focuses on the critical transition from undergraduate to graduate study. On January 19-20, 2008, the University of Michigan, the University of Southern California (USC) and Yale University will each host a Conference for Undergraduate Women in Physics (CUWP). The unifying aim of the three conferences is to encourage young women to apply to graduate school by providing a stimulating and supportive venue for them to learn about the exciting possibilities presented by advanced careers in physics. Towards this goal, the conference objectives are that participants leave with:
. Increased awareness of current research and career options in physics.
. Greater familiarity with the graduate school experience.
. Resources for applying to and being successful in graduate school as well as
general resources for women in physics.
. A network of women in physics.
The two-day event will bring together female undergraduate students in physics from
across the US to learn about current research and career opportunities in physics, the
graduate school application process and experience, and resources for women in physics.
Women attending the conferences will have the opportunity to present original research,
discuss physics topics with other students, and meet other successful women with more advanced careers in physics.

Intellectual merit of the proposed activity:
The project aims to study spin transfer torques driven by electric and thermal spin currents by utilizing ordered arrays of self-assembled ferromagnetic nanowires, and to investigate the nonlinear magnetization dynamics in these closely packed spin torque oscillator arrays. The objectives of this collaborative research are: (i)to study electric and thermal spin torques generated by a ferromagnetic nanowire in response to electric potential and temperature gradients; (ii) to study nonlinear collective magnetization dynamics in the hexagonally packed two dimensional arrays of strongly coupled spin transfer torque oscillators; and(iii)to develop a high-power microwave voltage controlled oscillator based on an array of phase locked spin torque oscillators.

The proposed array of spin torque oscillators consist of hexagonally ordered cobalt nanowires electrodeposited in anodized alumina template. These nanowires will serve as spin current injectors into a thin ferromagnetic film common to all injectors. Spin currents will be generated by either voltages or thermal gradients applied across the nanowires. Coupling among the individual spin torque oscillators will be facilitated by spin waves propagating in the common ferromagnetic layer. Ultrafast electrical detection of magneto-dynamics, broadband ferromagnetic resonance and magnetic force microscopy will be used to characterize the nonlinear magnetization dynamics in the array of spin torque oscillators. The proposed research will advance the understanding of the large-amplitude magnetization dynamics driven by electric and spin currents, which is important for the development of the next generation ultrafast and non-volatile magneto-electronic devices such as hard drive read heads and wireless communication systems. This research program will also benchmark the relative strength of thermally driven spin currents against the more common spin-polarized electric currents in the same system.

Broader impact of the proposed activity:
The microwave voltage controlled oscillator developed in this research will have a significant technological impact on information storage and telecommunication industries. PhD students, as well as undergraduates and high school students will take part in this program under the guidance of the investigators. The practical training in nanofabrication and unique measurement techniques offered by this program will prepare specialists for the USA magneto-electronics industry that are currently undergoing a rapid transition from micro- to nano-scale. The PIs will continue to attract underrepresented students from minority-serving institutions, such as California State Universities, as well as local K-12 students to participate in the research projects. In the education curriculum, all investigators have developed courses on nanoscience and nanotechnology with a series of demonstrations for graduate and undergraduate students.

This project is jointly funded by the Electronics, Photonics, and Magnetic Devices Program (EPMD) in the Division of Electrical, Communications and Cyber Systems (ECCS) and by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR).