Roy Clarke - US grants

The use of materials in metastable states is becoming very pervasive in many technological applications. Very often the atomic arrangements in such cases have intermediate-range order somewhat characteristic of crystalline structure but they are not in true thermodynamic equilibrium. The kinetic behavior of metastable structures, and especially their relation to the equilibrium long-range ordered state, is quite poorly understood at present. There has been substantial progress in the theory of non-equilibrium processes using the concepts of kinetic critical phenomena, but little experimental work which probes directly the microscopic mechanisms. We propose a thorough study of this area utilizing powerful ne techniques in time-resolved x-ray diffuse scattering. The research exploits the recent developments in x-ray sources (very brightness synchrotron radiation) and detectors (fast two- dimensional CCDs) which are expected to revolutionize time- resolved studies. The goal of the research is to identify universal features of the kinetics which can be incorporated into a general quantitative description of non-equilibrium structural processes. Two model systems have been chosen for these studies; the research will focus on the rapid thermal annealing of thin- film heterostructures which have important optoelectronic applications, and the growth and relaxation mechanisms of electrochemically deposited dendrites and thin film structures.

This research deals with the growth mechanisms, structure, and physical properties of incommensurate molecular beam epitaxy (MBE) heteroepitaxy of metal and semiconductor overlayers. The heterostructures will include Ta-Nb and Co-Au superlattices. These overlayers will be deposited on III-V semiconductors as well as sapphire and silicon substrates. Part of the work will address growth processes encountered in migration enhanced epitaxial deposition.

We are to developing a number of new experiments for the senior-year undergraduate Solid State Physics Laboratory course with the transmission electron microscope (TEM) they have acquired with ILI grant funds. Such an instrument did not previously exist in the Physics Department and this did not permit the inclusion of microstructural studies in the teaching laboratory curriculum. The provision of the TEM allows laboratory instructors to emphasize the importance of the relationship between lattice structure and electronic properties in the solid state of matter. The experiments demonstrate a number of important phenomena in modern solid state physics including atomic lattice imaging, quantum interference of electrons, charge density waves, and quasi- crystal diffraction. The instrument is being used in both imaging and reciprocal space modes and is available also for Modern Physics course demonstrations of the wave nature of electrons and atomic structure. The equipment, in addition, is available for undergraduate research projects in solid state physics. A laboratory manual and resource book is being written to make the new experiments accessible to other undergraduate programs.

This undulator beamline will be developed, instrumentated, and operated at the Advanced Photon Source (APS) under the auspices of the Michigan/AT&T Collaborative Access Team (MATT-CAT). The APS represents a very significant step forward for the future of materials research: for the first time it will be possible to carry out time-resolved studies of materials under real dynamic conditions. MATT-CAT is conceived as a center for real-time x-ray studies which will operate as a joint university-industry initiative bringing together faculty and students at the University of Michigan, and research staff at AT&T Bell Laboratories, to focus on the kinetic behavior of materials. MATT-CAT's goal is to establish a center of excellence devoted to the structural kinetics of materials which will benefit from the interaction of physicists, chemists, materials scientists and engineers. To accommodate this goal, two fully instrumented beam lines will be developed, one will have an undulator source, and the other a bending magnet. The undulator beam line is designed to achieve high resolution and will consist of a back-reflection monochromator, situated in the rear hutch, with the monochromated beam transported to a forward hutch. Here, high-resolution analyzers and fast array detectors currently under development will be available for time- resolved scattering studies. The extremely high brightness, collimation, and stability of the undulator beam will be exploited for new kinds of coherent spectroscopic measurements of non-hydrodynamic modes in solids and complex fluids. This beam line will be available to the MATT-CAT members 75-80% of the time, with the remaining time allocated to general users. Technical staff will be employed in the construction of the beam lines, the day-to-day operation and upkeep of the instruments, and will assist users.

A new Graduate Traineeship Program in Ultrafast Optical Sciences will be established. The specific focus of the five traineeships will be on the University of Michigan's newly created Center for Ultrafast Optical Science (CUOS), an NSF Science and Technology Center created to enhance the nation's competitiveness in high-speed photonics and pulsed laser optics. This is a field where a well-documented demand exists for highly trained personnel who will lead the burgeoning revolution in optical science and technology. CUOS is inherently interdisciplinary in scope and draws on faculty and resources in several departments: Applied Physics, Electrical Engineering, Physics, and Chemistry. These multidisciplinary components are integrated via a common emphasis on the utilization of high peak power lasers for new areas of fundamental science, and for technological applications that exploit the special characteristics of ultrafast light pulses. This comprehensive and innovative program addresses several crucial needs in graduate education: it aims to increase the number of American undergraduates going on to PhD studies in areas of national importance, it actively engages and nurtures underrepresented groups in the research of the Center, via a novel outreach initiative funded by University matching funds, and it addresses important issues of retention and time-to- degree by providing pre-enrollment summer research internships.

This grant provides support for the acquisition of a focused ion beam (FIB) workstation for multidisciplinary materials research at the University of Michigan. The FIB is an essential tool for the removal and addition of precisely controlled quantities of material from or to a wide variety of structures and devices at the micrometer and nanometer length scale. The FIB has enabled the development of innovative applications in the studies of ceramics, semiconductors, nano-composites, metals, catalysts, earth materials and biological materials. The FIB will be housed in a University-wide, centralized
user facility and will be made available to all research groups on campus, other university researchers and to industry. Immediate uses for the new dual-beam FIB include: 1) novel nano-scale engineering applications, patterning, fabrication and machining; 2) sectioning, high-resolution SEM imaging and 3D reconstruction of microstructures, site-specific specimen preparation for in-situ scanning and ex-situ transmission electron microscopy; and 3) individual, device-level modifications of semiconductor devices.

In the past ten years, over 125 research groups, from the University of Michigan, other nearby universities and industry have made use of the University materials characterization facilities. This multidisciplinary research has resulted in more than 3550 publications. Over 1100 graduate students have used the facilities for a major portion of their thesis research. Currently, 42 graduate and 16 undergraduate students are actively involved in research that will make use of the new FIB. The FIB instrument will allow the research community to more effectively pursue their studies of materials at the nanoscale, while also promoting the teaching, training and learning of the graduate and undergraduate students. Students support by the Undergraduate Research Opportunities Program (UROP) and Research Experience for Undergraduates (REU) programs are actively working on the characterization of materials. The instrument will also be used in summer research projects for minority high school students, high school teachers and young women. Once installed, the FIB will be available to a number of students in the NASA Summer High School Apprenticeship Program (SHARP) for under-represented groups.

Technical: The goal of this project is to achieve greater understanding of epitaxial growth conditions and processes associated with the synthesis of no-common-atom short period superlattices (SPS) with well-defined interfaces-the constituent layers of such superlattices do not share a common element. No-Common-Atom systems, e.g., InAs/GaSb, have attracted interest for potential applications in infrared optoelectronics technology through the possibility of tuning electronic band structure by manipulating low-symmetry interface structures. The approach includes identification, understanding, and control over atomistic mechanisms of interface formation. Atomic resolution characterization is an essential element of the approach. A direct method to image buried interfaces using x-ray synchrotron radiation will be studied. This technique, COBRA, is capable of providing, non-destructively, a three-dimensional map of epitaxial thin-film structures with sub-Angstrom resolution of atomic positions. COBRA maps will be a key to achieving detailed structural and compositional information useful for understanding and controlling growth conditions for achieving interface structures having desired optoelectronic properties. Theoretical predictions of interface composition distributions will be compared with experimentally determined interface structures, and used to guide experiments.
Non-Technical: The project addresses basic 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 new understanding and capabilities in electronic/photonic devices. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. The project provides excellent research opportunities for graduate training, including experience at national facilities (Advanced Photon Source), and also for more junior students to become interested in science and engineering. Working with high school students and undergraduates, the PIs have devised a program of research activities which are integrated with research, but which are also accessible to less experienced students. The PI's will also organize an innovative Summer Camp to interest middle school girls in science and engineering.

Technical

This program funds a new advanced, spherical aberration-corrected high-resolution transmission electron microscope, which will be situated in the University of Michigan North Campus Electron Microbeam Analysis Laboratory. The instrument will have a resolution of 0.8 angstroms in the scanning transmission mode. It will enable researchers to determine chemistry, atomic structure, bonding characteristics, and three-dimensional imaging of materials at the true atomic level. Although it will be a critical instrument in the support of the wide range of nano-technology and energy research programs at the university, it will also operate as a resource for research institutions, both in industry and academia, in southeastern Michigan and the surrounding states. The instrument will have a 300 kV monochromated field emission gun and will have spherical aberration correction of the probe forming system. The imaging system will allow both scanning imaging and static beam imaging. In scanning imaging with a high angle annual dark field detector this microscope will allow atomic resolution imaging with atomic number contrast. Chemical analysis will be conducted by high-resolution electron energy loss spectroscopy, convergent beam electron diffraction and energy dispersive X-ray spectrometry.


Non-Technical

This program funds a new high resolution transmission electron microscope, an instrument that images extremely fine structure of material and is critical to successful nanotechnology and energy research in the University of Michigan and other research institutions in southeastern Michigan. In lieu of light, the transmission electron microscope uses a very high energy beam of electrons (300,000 volts) to probe the thin foils or particles of materials. The samples are so thin that 250 of them would be required to match the thickness of the average human hair. The imaging resolution of the new microscope will be higher than any previously located in Michigan. It will, for example, be able to image individual impurity atoms in the atomic lattices of silicon devices. The instrument will also be capable of performing chemical analyses of these samples, using what are known as spectroscopic techniques. Spectroscopy involves measuring the energy range of electrons or X-rays emitted by the sample when the high energy electron beam interacts with it. The instrument will allow researchers in the region to compete globally in research in nanotechnology, energy related materials and biological technologies. It will mean that research requiring materials characterization in Michigan will remain at the leading edge.

Technical: This project seeks fundamental understanding of the evolution of epitaxial quantum dot nanostructures. It is anticipated that the outcome of this research will provide insights on what controls the shape, strain, and chemical composition profile in the dot and its vicinity; what factors drive the evolution of quantum dots under different thermodynamic and kinetic conditions; and how directed-assembly, by patterning, can alter the properties of these structures. This study will benefit from new developments demonstrating that direct x-ray phase retrieval methods can non-destructively probe the 3D structure, chemical and strain distributions of epitaxial quantum dots. The plan is to apply Coherent Bragg Rod Analysis (COBRA) mapping techniques to a variety of quantum dot systems, including self-assembly by Stransky-Krastanov growth and droplet epitaxy, as well as novel site directed assembly methods. In-depth x-ray synchrotron studies of patterned dot arrays will be achieved by Focused Ion Beam patterning as well as nanostructure growth on patterned templates made by electron-beam lithography. Site directed deposition of quantum dots has the potential to greatly improve the compositional and geometrical uniformity of quantum confined materials, compared to self assembled dots?this limitation has been holding back widespread implementation of quantum dots for applications. The combination of state-of- the-art materials growth and deposition with advanced x-ray phase reconstruction techniques is expected to provide the means to control critical growth parameters, quantitatively measure their effects on quantum dot structures, and use this information to engineer desirable properties.
Non-Technical: The project addresses basic 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 new understanding and capabilities for semiconductor quantum dot systems of interest for improving existing semiconductor device technologies, such as lasers, and detectors, especially for telecommunications and solar applications. Quantum dot systems may also be an enabling technology for future areas of application such as quantum computing and single electron devices. The project offers research opportunities for graduate training, including experience at national facilities (Advanced Photon Source), and also for more junior students and under-represented groups to develop their interests in science and engineering. The PIs are heavily involved in outreach activities, from junior high through undergraduate research opportunities. They have integrated hands-on activities which resonate with societal needs; for example, they have planned new curriculum on alternate energy applications, and are working with innovative data sharing informatics.

Dr, Roy Clarke started the Applied Physics Program at the University of Michigan in 1987 with the recognition that the existing Physics Program was not equipped to address the needs of students who wanted to pursue research in areas outside of the traditional physics boundaries including many students from groups underrepresented in science, engineering and mathematics. The Applied Physics Program soon became a transformative model for other graduate programs that are committed to enhancing the diversity of their cohorts and for more effectively utilizing the benefits of the interdisciplinary environment that is the hallmark of large research universities in the 21st century. The program has graduated a significant fraction of all physics Ph.D.s awarded in the past ten years to students from underrepresented groups. Dr. Clarke was awarded the first Imes and Moore Faculty Award for excellence in mentoring in 2006 and was recognized by the Sloan Foundation as an Outstanding Mentor in 2008.

This project plans to combine two capabilities, the tunable atom-like electronic quantum states of nanostructured materials and ultrashort-pulsed laser sources based on fiber-optics, to provide a route to making nanostructure materials economically and efficiently. The versatility of this approach is a major driver of the project: condensation of nanoparticles from a femtosecond laser-generated plasma can produce nanoparticles of essentially any material deposited as a thin film, including semiconductors and different kinds of metals that are useful for energy-critical applications. This versatility is the key to developing a wide range of applications for a variety of users.

This research may provide a new route to achieving the goal of inexpensively fabricating nanopartical films in sufficient density and quantity or industrial-scale applications. Sustainable, environmentally friendly, affordable, energy supply is challenge facing today's society. New materials development can be essential to this task; for example, efficient solar energy harvesting, by catalytic splitting of water molecules or by photovoltaic power generation could benefit greatly from cost-effective materials for utilizing renewable energy. Research conducted through this project may serve as the basis for a scalable technological solution to the need for energy-critical materials.