Ivan K. Schuller - US grants

This award supports a cooperative research program involving Professor Ivan K. Schuller of the University of California, San Diego, and Professor Ricardo Ramirez of the Pontifical Catholic University of Chile, in Santiago. The project involves use of modern computational techniques to study a variety of problems in the fields of thin film and surface physics, including the epitaxial growth of different crystal types (face centered cubic (fcc) and body centered cubic (bcc)), and the energetics and kinetics of hydrogen absorption on the surfaces of transition metals. The equation of motion of the surface of an epitaxially growing system will be solved using the computational technique of Molecular Dynamics (MD). The epitaxial system will consist of a literal model of the top few atomic layers of a bcc substrate and the related potential distributions, combined with a model of the growing fcc layers. Particular attention will be paid to the effect of the starting orientation on the final results. The hydrogen-surface behavior problem will be approached by setting up a model of a stable fcc crystal which will be given a surface potential distribution approximating that of nickel. A single hydrogen atom will then be allowed to interact with this crystal via a suitably chosen potential and the MD of the combined system will be analyzed to study diffusion properties, the energy distributions at subsurface sites, and kinetics. This study represents an application of computer modeling, in particular the Molecular Dynamics method, to a class of important problems in condensed matter physics. The simulation of epitaxial crystal growth could have important implications, for example, in the production of new semiconductor materials and devices, yet theoretical approaches to this problem have been sparse. Each of the investigators brings complementary strength to this research, with experimental and simulation expertise from the U.S. and theoretical expertise from Chile. Numerical calculations will be performed in both the U.S. and Chile, with elements of computer codes developed jointly. The problems to be studied are of considerable scientific and technological importance, and the simulation results should be useful as tests for theories and guidelines for future experimentation.

A multisource sputtering system with in-situ characterization capabilities useful for the preparation of thin films and superlattices will be acquired. Some of the problems to be studied with this apparatus are; basic processes important in thin films growth including the study of the effect of growth parameters on the structure and physical properties of thin films and superlattices; effects of controlled roughness on the structure of thin films and superlattices; a variety of superconducting problems, including dimensional studies and development of ultrahigh critical field materials; magnetism, especially studies related to magnetic anisotropy, DC magnetization and ferromagnetic resonance; transport properties both in the perpendicular and parallel direction and development and study of the optical properties of multilayers in the soft x-ray range. This type of an instrument is a must for any of the studies here. The principal investigator is well known for his research in the preparation of thin films and multilayered materials while at Argonne National Laboratory

Professor Schuller will study the properties of thin superconducting films to better understand the superconducting mechanisms and to provide for improvement of these properties. The experiments will use the sputtering and molecular beam epitaxy (MBE) techniques to grow polycrystalline, textured, and epitaxial films of high temperature oxide superconductors. The composition, compositional uniformity, and structure will be determined using a number of surface techniques including ion milling, Auger, x-ray photoelectron, and ion scattering spectroscopies. Physical properties such as magnetotransport, superconducting temperature, critical currents, and magnetic field response on isolated high temperature superconducting films and films in proximity with other materials will be examined. Special care will be taken in the preparation of the materials with regard to choice of substrate, post-preparation heat and oxygen treatment.

With the advent of modern computers it is possible to tackle the numerical simulation of condensed matter physics problems using realistic models. Molecular Dynamics (MD) is a computational technique which allows the study of the statistical mechanics of and transport in many.body systems by solving simultaneously the classical equations of motion of N particles, where N is a large number. From the experimental point of view, much effort has been invested to prepare thin films and novel materials using vapor phase deposition techniques. In spite of the considerable importance that the growth of thin films has in basic and applied condensed matter physics, only limited effort has been dedicated to its theoretical understanding. Most of the work to date relies on phenomenological models relying on a variety of parameters which are hard to determine experimentally. Some limited amount of numerical simulation has also been performed mostly using Monte Carlo (MC) methods. For the growth of thin films however dynamics is of key importance and MC methods are not well suited to study the dynamical behavior. It is therefore of importance to perform MD studies in order to understand the role dynamics has in thin film growth. In many cases, numerical simulation can also provide a guide to experimental studies. The reason for this is that in numerical studies it is possible to change parameters independently so that the relative importance of one parameter with respect to others can be ascertained. Here they propose to use MD to stimulate and study a variety of problems regarding the vapor phase growth of thin films as well as a variety of surface related problems.

This proposal is for the acquisition of an X-Ray powder-diffractometer for the characterization of intermetallic compounds, thin film and superlattices. The diffractometer will be used in research related to high temperature and field superconductivity, the coexistence of superconductivity and magnetism, reentrant superconductivity, oscillatory magnetic states that co-exist with super conductivity magnetic field induced superconductivity, epitaxial growth, superlattices and ceramic thin films. In addition, this instrument will be operated as a facility to support a variety of other research efforts within the University.

We believe that the physical properties of artificially-prepared thin films are strongly affected by the synthesis and processing methods employed and therefore structural and chemical characterization must play a key role in all research performed on such films. We plan to synthesize novel magnetic thin films using state-of-the-art techniques such as sputtering and molecular-beam epitaxy, then characterize the structure and chemical composition using a wide variety of methods. Growth and characterization studies will be correlated with physical properties, especially magnetotransport and magnetization. The studies will relate to the magnetism of superlattices and interfaces with two problems - giant magneto-resistance and exchange bias - receiving particular attention.

9317748 Schuller Technical abstract: This proposal relates to the growth, characterization, and modeling of the physical properties of strongly correlated electron systems of varying dimensionality. The systems to be studied are mostly prepared using state-of-the-art thin film deposition and electron beam and scanning tunneling lithography techniques. The condensed matter problems studied include dimensional transitions from zero to one, one to two, and two to three dimensions in superconductivity and magnetism. A crucial and essential ingredient proposed here is the structural and chemical characterization of the artificial structures used in these studies. The materials will be grown using sputtering and molecular beam epitaxi. The growth techniques will be correlated with in situ and ex situ structural characterization techniques combined with simulation and refinement methods developed in the principal investigator's laboratory. Non-technical abstract: The study of novel materials in restricted geometries provides the basic research basis and is directly related to applications in the field of microelectronics, including the development of novel sensors, devices and recording media. The condensed matter problems studied include dimensional transitions from zero to one to two and three dimensions in superconductivity and magnetism. A crucial and essential ingredient proposed here is the structural and chemical characterization of the artificial structures used in these studies. The materials will be grown using a variety of growth techniques. The growth techniques will be correlated with structural characterization techniques developed in the principal investigator's laboratory. ***

9400310 Schuller This Americas Program award will support Dr. Ivan Schuller of the University of California, San Diego, in a theoretical-experimental collaboration in the field of magnetic thin films, with Prof. Ricardo Ramirez of the Universidad Catolica, Santiago, Chile. The studies proposed are geared towards understanding thin film growth in a quantitative fashion. From the experimental point of view thin films and interfaces will be characterized using several growth techniques and a large variety of structural and chemical characterization techniques. Prof.Ramirez has been conducting theoretical studies of thin film growth in Chile, while Dr. Schuller has an experimental program in the same field underway in the U.S. This award will allow coupling of both programs. The area is of importance to researchers working in technologies requiring thin films and multilayer film metallic growth and characterization. These include the magnetic recording industry, sensor technology, and new technologies growing out of giant magneto- resistance phenomena. ***

This three-year award will support U.S.-France cooperative research in condensed matter physics between Ivan K. Schuller of the University o California San Diego, and Alain Gilabert of the University of Nice. The objective of their research is to investigate the properties of superconducting layers with an insulating layer between them. They will study the coupling of vortices, using an intervening medium, in order to develop and characterize new superconding devices. The U.S. investigator brings to this collaboration his expertise in sample preparation and growth and characterization of high quality multilayer superconducting and magnetic materials. This is complemented by the French investigator's abilities in theory and experiment. The calculations for the devices and the testing of the new material will occur in France. Studies of superconducting vortices are important to both basic and applied research. This will advance our knowledge of a novel state of matter and could lead to improved performance of superconducting devices in a magnetic field.

w:\awards\awards96\*.doc 9801921 Schuller This experimental research project is concerned with vortex pinning in thin film superconductors by controlled pinning structures. It is a joint experimental/theoretical study of the physics of vortices in low and high Tc thin films subject to artificial pinning. The pinning structure is engineered using state-or-the-art lithography processes. Pinning structures under study include regular and weakly disordered arrays of "holes", and/or "stripes" made of normal or magnetic materials. The pinning characteristics of these arrays over a wide range of temperature, field and materials parameters will be characterized by transport, noise, and direct imaging measurements. Novel pinning patterns will be used to expand the pinned phase to a broad range of magnetic fields, beyond the nominal matching field, to enhance vortex pinning. They also provide new "media" in which a variety of new and interesting vortex phenomena can be studied. Theory is an inherent part of the project. New fabrication methods and devices will be developed using state of the art thin film techniques together with forefront lithography processes. This research program is interdisciplinary in nature and involves several pre- and post-graduate researchers in its activities. They will become familiar with research equipment and methods applicable to condensed matter physics, microelectronics, magnetic recording and sensors, and superconducitng devices. Their training will be excellent preparation for careers in industry, government laboratories or academia. %%% This experimental basic research project is concerned with increasing the current carrying capacity of superconducting thin films. The "critical" current of a superconductor in the presence of a magnetic field is influenced by "pinning centers" which act as anchors fo r the magnetic flux lines (vortices) which penetrate the thin film. The critical current can be increased by increasing the pinning. This study investigates vortex pinning in thin film superconductors by controlled pinning structures. It is a joint experimental/theoretical study of the physics of vortices in low and high Tc thin films subject to artificial pinning. The pinning structure is engineered using state-or-the-art lithography processes. Pinning structures under study include regular and weakly disordered arrays of "holes", and/or "stripes" made of normal or magnetic materials. The pinning characteristics of these arrays over a wide range of temperature, field and materials parameters will be characterized by transport, noise, and direct imaging measurements. Novel pinning patterns will be used to expand the pinned phase to a broad range of magnetic fields, beyond the nominal matching field, to enhance vortex pinning. They also provide new "media" in which a variety of new and interesting vortex phenomena can be studied. Theory is an inherent part of the project. New fabrication methods and devices will be developed using state of the art thin film techniques together with forefront lithography processes. This research program is interdisciplinary in nature and involves several pre- and post-graduate researchers in its activities. They will become familiar with research equipment and methods applicable to condensed matter physics, microelectronics, magnetic recording and sensors, and superconducitng devices. Their training will be excellent preparation for careers in industry, government laboratories or academia. ***

9724808 Schuller This Americas Program award will support travel and related expenses for six senior researchers and six young investigators, to participate in two workshops on research of current interest in the fields of solid state physics and materials science. These workshops will be held concurrently with a Latin American Symposium of Solid State Physics (SLAFES), in Oaxaca, Mexico, January 11-16, 1998. The topics to be discussed in the two workshops will be the physical properties of heterostructures and the magnetic properties of low dimensional systems. Organizers are Dr. Ivan Schuller, University of California, San Diego, and Dr. Jose Luis Moran Lopez, Universidad Autonoma de San Luis Potosi. The physics and materials science of low dimensional systems is an important current subject of research worldwide, but much of the research is performed by small groups in many institutions. Therefore, there is a strong need to bring together this small group of researchers for open discussions of past research and future directions. The two workshops will meet this need, especially with the opportunity of holding them concurrently with the Latin American Symposium, which has had US participation since its inception and has played an important role for the development of American collaboration for many years. ***

This individual investigator award is to a senior professor for a project dedicated to a comprehensive study of the phenomenon of "exchange bias." The project consists of state of the art growth, structural, chemical and magnetic characterization, and measurement of physical properties using a broad range of techniques. The aim is to develop an increased understanding of the phenomenon that occurs when two dissimilar magnetic materials are placed in contact with each other. The exchange bias forms the basis for a number of applications that use the so called "spin valve" technology for magnetic storage and sensors. Although the phenomenon is used in many applications, a basic understanding is lacking. Issues that will be addressed by this research include, the influence of structural and magnetic parameters, and the effect of interfacial parameters such as roughness and interdiffusion. Through a thorough experimental attack, a better understanding of the phenomenon should be obtained. This will have a direct impact on related technologies. Students and postdocs working on this project will acquire technical and fundamental knowledge and skills that can be lead to careers in basic or applied research in academia, industry, or government laboratories.
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This individual investigator award is to a senior professor for a project dedicated to the study of a phenomenon known as "exchange bias", which occurs when two dissimilar magnetic materials are in contact with each other. This phenomenon appears in a variety of material configurations (i.e. thin films, small particles, etc.) and is an important ingredient in a number of sensor applications. Although the phenomenon is used in a 55 billion dollars industry, there is little basic understanding of its origin. Basic research along these lines may have an important effect on the development of novel sensors and improved magnetic storage. Graduate students and postdoctoral fellows are essential collaborators in this work. They will not only help in advancing our understanding of this important phenomenon, but will also acquire a broad range of technical skills that will serve them whether they are interested in careers in academia or the sensor and storage industries. This is an ideal area of research in which basic research can have a direct, relevant impact on industries and technology of crucial importance to the nation.

This grant supports the purchase of a low temperature scanning tunneling microscope (STM) that will be used for investigations of defects and bonding sites in electronic and sensor materials. The low temperature STM provides a zero drift environment in which isolated molecules do not diffuse. In this quiet, stationary environment, the local electronic structure of single defects or bonding sites can be determined using current-voltage (dI/dV) measurements. The specific systems that will be studied with this instrument include: (a) defects at the semiconductor/gate oxide interface; (b) polysilole-based nanowire sensors; (c) halogen reactions with aluminum; (d) mixed, asymmetric metal phthalocyanine-based chemical sensors; and (e) fabrication of ordered arrays of single macromolecular assemblies. With the advent of commercial software (VASP) for calculating the electronic structures of molecules on surfaces, low temperature STM and STS studies can be directly compared to both simulated STM images and the partial density of states on single atoms. This comparison provides critical insights into the control of electronic structure on surfaces.

This instrument will have impact on a broad audience at the university. (a) The San Diego Fellowship program for entering graduate students: UCSD is donating 3 months of support for 4 entering graduate students. These fellowships will be used to support graduate students to increase the diversity of the chemistry and physics graduate programs. (b) Undergraduate research: Undergraduate students will be involved in the proposed research via the Howard Hughes Undergraduate Enrichment Program (HHUEP) and the UCSD Office of Academic Enrichment. (c) UCSD-TV and webcasts: Lectures that are appropriate for high school and college students will be recorded for both broadcast and webcast by the UCSD-TV education outreach program. (d) Teacher training: The funds support one high school science teacher per summer to work in a research laboratory at UCSD. The teacher will have the opportunity to learn how to use the telemetry system developed at the UCSD National Center for Microscopy and Imaging Research (NCMIR). The NCMIR facilities house an electron microscope that can be remotely controlled via the web, enabling teachers and students to use the SEM directly from their classrooms. (e) Industrial collaborations: The low temperature STM will be used in collaborative research projects that focus on device and sensor development and involve Motorola, Microsense, and IBM.

This is an international collaborative research project that was submitted in response to NSF Solicitation NSF 02-135. This international collaboration focuses on pinning of vortices at state-of-the-art lithographically defined pinning structures. The vortex state will be studied in both low and high Tc materials. The collaboration joins a scientists at the UC San Diego and Universidad Complutense, Madrid, Spain. Both laboratories will be involved with the lithographic structures and with transport and other measurements. The research should shed light on limitations to current transport in superconducting materials and is of interest from both fundamental and technical viewpoints. Students will participate in international research activities, along with traditional and cutting edge training that will prepare them for careers in academe, industry or government.

Non Technical Abstract

Vortices are prevalent in nature all the way from the atmosphere, charge and uncharged plasmas, magnetic and superconducting materials. An important issue in this field is the way to anchor these vortices, the so called "pinning" because physical properties are modified in fundamental ways if vortices are pinned. A particularly interesting physical situations arises in superconductors where the magnetic field penetrates the material by the formation of arrays of superconducting vortices. These vortices can be pinned by artificially prepared pinning arrays which can be produced using novel lithographic techniques. This project is dedicated to the study of fundamental issue which arise when superconducting vortices interact with nanostructured arrays. Issues such as the effect of the array geometry, materials, shape of the pinning sites will be studied.In addition to its basic research interest, these studies may lead to schemes for reducing spontaneous noise and enhancing the superconducting properties of the material.


Technical Abstract

The study of vortex pinning in superconductors is an interesting basic research area, with implications for the fabrication of high critical current tapes and low noise superconducting devices. The interaction between artificially prepared pinning arrays and the superconducting vortex lattice leads to quantum matching phenomena which manifest as enhanced critical currents and decreased resistance at particular fields. This research project, will be dedicated to (a) finding the type of pinning structure which individually provides strong pinning of vortices, and (b) introducing appropriate "defects" within the periodic array of pins, such as stripes and/or random fluctuations on the pinning site positions. (a) will increase the domain wall energy for the periodic point pins and increase the magnetic field width for the periodic stripe pins, thereby reducing thermal fluctuations, while (b) can change the universality class of the commensurate phase, thereby suppressing thermal fluctuations in fundamental ways. The issues concerning (a) are mostly material-specific, involving the microscopic mechanism of individual vortex-pin interaction. The issues concerning (b) are statistical in nature, having to do with the collective interaction of the vortex lattice with the array of pins. Both of these issues will be investigate systematically, and through extensive experimental collaborations and interactions with theoretical groups active in the field.

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


Abstract
The objective of this research is to study fundamental electronic, photonic, chemical, and bio-logical behaviors of nanoscale structures relevant to future applications in next generation storage, energy harvesting, communications and computing, quantum communication and information proc-essing, superconductivity, and biomedical and biochemical sensing. The approach is to utilize nano-scale e-beam lithography in conjunction with other nanomanufacturing technologies to fabricate and characterize nanometer scale metamaterials, devices, and subsystems in which these new behaviors are expected to manifest themselves most clearly and can be exploited.
Intellectual merit: The proposed acquisition will enable investigation of smaller structures, finer features, and larger patterns than can be experimentally accessed today. Electronic and spin dif-fusion, a variety of magnetic behaviors, structural and chemical changes, superconducting decoher-ence, and many other phenomena that occur at nanometric length scales in common materials will be explored. Research projects are also planned in the areas of nanophotonics, metamaterials, quantum optics, quantum information, and nanomedicine.
Broader Impact: The creation of wealth through advances in nanoscale science and technol-ogy is at the heart of the 21st century economy. The impacts span multiple technical fields, including information systems, health care, energy, pollution monitoring, and chemical threat and explosive detection for homeland security applications. The UCSD Nano3 facility is serving a wide area of Southern California, and the proposed tool will benefit users throughout this geographic area. The project will also play a significant role in promoting education and development of human resources in science and engineering at the graduate and undergraduate levels, diversity and outreach.

Non-technical
This research is in the field of organic materials and low-dimensional systems. It consists of the fabrication of ultra-short chains of 7 to 200 atoms in length, to test theoretical models and explore the emergence of new magnetic properties. This study provides a broader and deeper understanding of the magnetic behavior of low-dimensional systems and may have a direct impact on the development of a new generation of spintronic devices. This research has an active educational component. The project involves two graduate students who perform research for their Ph.D. thesis topic and two physics undergraduate students per semester. During these activities, students receive training at first synchrotron and neutron facilities and are exposed to state of the art advanced experimental techniques. Community outreach efforts associated with this project involve a partnership with high schools in San Antonio school districts and the production of short videos on different topics related to nanotechnology using a comical approach. These efforts are aimed to increase scientific knowledge in high school students and provide tools for science educators across the United States.

Technical
This research is aimed to study three fundamental problems in magnetic 1D chains: 1) the determination of the extent and persistence of short- and long-range magnetic interactions as a function of the chain's length and defects, 2) the control and modulation of the spin along the chains, and 3) the exploration of proximity effects in varying composition magnetic/non-magnetic metal chains. To achieve these objectives, the PIs have developed a method for the fabrication of macroscopic arrays of 1D chains that allow precise control of their length, composition, and spin. Specifically, this research focuses on the ultra-short (and poorly explored) chain of ~7 to 200 atoms long. Monoatomic and varying composition chains are grown by Organic Molecular Beam Epitaxy (OMBE) using metallo-phthalocyanine (MPc) superlattices (SLs). MPcs are a family of planar organic molecules with one metal atom located in the molecule's center surrounded by organic support. Many metal ions (Fe, Ni, Cu, Co, and Mn) can be substituted into the MPc giving rise to many isostructural compounds with different electronic (spin) configurations and physical properties. These molecules stack face-to-face giving rise to 1D metal chains when grown by OMBE. The orientation of the chain and its length can be controlled by substrate choice and thickness of the deposited MPc layer respectively. Moreover, using a SL structure, the chain composition, and spin can be varied by intercalating other magnetic and non-magnetic MPc layers. This project includes structural characterization (XRD and HRTEM) and magnetic measurements (SQUID, VSM, and AC susceptibility) in a broad temperature/field. Synchrotron techniques such as XMCD are used to obtain element-selective magnetic measurements and electronic configuration of the metals ions forming the varying composition chains. NEXAFS and DFT calculations allow determining the spin configuration of these elements.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

NON-TECHNICAL SUMMARY

Recent research has outlined a possible pathway to room-temperature superconductivity based on hydrogen-rich materials exposed to very high pressures, which would be a transformative technological development. The required high pressures (similar to those at the Earth’s core) present major technical challenges for practical use and applications. In this project, a new approach is proposed in which hydrogen-rich “quantum” materials are designed which could exhibit high-temperature superconductivity without the application of pressure. This project, supported by the NSF’s Division of Materials Research, is to synthesize multi layers of a quantum material, a photosensitive material, and a hydrogen-rich material, which under the right conditions would favor high-temperature superconductivity. From an educational standpoint, this project exposes students to modern condensed matter physics, to state-of-the-art experimental and calculational tools, to materials synthesis and characterization techniques, and to the scientific research process. The research team assembled here has a long-standing interest and record of outreach activities that showcase the beauty and importance of quantum materials, superconductivity and modern solid-state physics. The PIs, two of which are Hispanics, are engaged in fostering diversity and inclusion in the technological work force and also in encouraging underrepresented groups to pursue careers in physics and STEM disciplines. From the societal standpoint, this research contributes important clues about the mechanism of high-temperature superconductivity and its potential applications. A better understanding of this phenomenon may lead to materials with higher superconducting transition temperatures, which would yield important technological benefits to the nation. This would substantially improve the transference and storage of energy, create new forms of environmentally friendly transportation systems, and provide a new platform for novel computational schemes.

TECHNICAL SUMMARY

This project, supported by the Division of Materials Research, outlines a new approach in the search for new superconductors based on hydrogen-rich materials. Prior research has claimed the discovery of near-room-temperature superconductivity under very high pressures in hydrogen-rich materials or at very short timescales in photo-excited quantum materials and heterostructures. This project aims to develop high-temperature superconducting heterostructures which are stable at ambient pressure by combining a quantum material (Q-material) with a material which contains a high concentration of hydrogen (H-material). This way, the Q-material contains the charge carriers and the H-material provides the coupling for superconductivity. This judiciously designed heterostructure combines the favorable properties of both ingredients and may exhibit novel properties as a whole or at the interface. In addition, to boost the superconducting properties such as the charge carrier doping, a hybrid heterostructure containing a photoconducting material subject to the appropriate electromagnetic radiation will be used. The combination of these thoroughly investigated individual materials and phenomena provide a potential path towards room temperature superconductivity at ambient pressure. From an educational standpoint, this project exposes students to many aspects of modern condensed matter physics, to state-of-the-art experimental and calculation tools, to materials synthesis and characterization techniques, and to the process of scientific research and publication. The research team assembled here has a long-standing interest and record of involvement in various outreach activities that showcase the beauty and importance of quantum materials, superconductivity and modern solid-state physics. The PIs, two of which are Hispanics, are engaged in fostering diversity and inclusion in the technological work force and also in encouraging underrepresented groups to pursue careers in physics and STEM disciplines. From the societal standpoint, this research contributes important clues about the mechanism of high-temperature superconductivity and its potential applications. A better understanding of this phenomenon will lead to materials with higher superconducting transition temperatures, which, along with other technological applications, would substantially impact the transport and storage of energy.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.