Alex De Lozanne - US grants

This Equipment Grant is provided to build a facility for the synthesis of thin films of new oxide superconductors. Two major problems in the synthesis of thin films are: the ability to control the stoichiometry of the film, and the ability to incorporate enough oxygen. So far thin films have been synthesized by using a large oxygen background pressure in conventional e-beam and sputtering chambers. All these films require a high temperature oxygen anneal, hence, making them less practical for applications requiring compatibility with other thin film devices. This thin film facility is designed to provide a large rate of oxygen arrival at the substrate, preferably in an atomic state, while maintaining the metal sources and their rate monitors at low pressures. This makes the deposition rates more stable and reproducible, and extends the lifetime of the sources. This facility will be used to produce high quality films at the lowest process temperatures, and the films will be used for tunneling, transport measurements and devices.

9704222 Erskine This award partially supports the development of unique instrumentation for synthesizing laterally constrained thin film and multilayer magnetic materials and microstructures and for studying novel magnetic phenomena in the structures The new instrument incorporates state-of-the-art thin film growth and characterization capabilities, contact mask and focused ion beam technology capable of creating submicron structures in the films, and complementary high spatial resolution magnetic sensitive spectroscopy/microscopy probes The new instrumentation adds important capabilities to existing research programs of several faculty at The University of Texas which explore thin film magnetism, mesoscopic physics, micromagnetics and magneto-transport phenomena. Scientific issues to be explored based on new capabilities of the instrument include 1) micromagnetic phenomena including properties of magnetic domains in ultrathin films and patterned micron-scale ultrathin film structures; 2) the effects of deliberately induced substrate roughness (atomic steps) and film thickness variations on magnetic domains and related properties including coercive forces and anisotropy of thin films and thin film based microstructures; 3) finite size scaling effects, critical behavior, exchange coupling and dynamical properties of well characterized multilayer and microstructured magnetic systems, and 4) magneto-transport and related magnetic phenomena associated with multilayer films and multilayer- based microstructures. An important feature of the instrument design is the unique combination of materials growth and microstructure fabrication capabilities, materials characterization tools and magnetic sensitive probes which can be used separately or as an integrated system. The instrument consists of three coupled subsystems 1) a thin film growth and characterization chamber incorporating multicell molecular beam epitaxy (MBE) with real-time growth monitoring tools inclu ding Reflection High Energy Electron Diffraction (RHEED) and Auger Electron Spectroscopy (AES); Low Energy Electron Diffraction (LEED) including high resolution spot profile analysis capability; 2) a Magneto-Optic Kerr Effect (MOKE) polarimeter set up for high spatial resolution scanning measurements as well as analysis of hysteresis dynamics; and 3) a high resolution Scanning Electron Microscope with Spin Polarization Analysis (SEMPA) instrument. The SEM/SEMPA instrument is configured to accept a Focused Ion Beam (FIB) column to mill microstructures while viewing the process using SEM. The system is integrated with gate valves and air lock chambers permitting the SEMPA/MOKE subsystem or the MOKE/film growth subsystem to be used independently. %%% This instrumentation has the potential to advance the fundamental knowledge and understanding of thin-film magnetic structure. Such structures have great potential for device applications, which can produce breakthroughs in magnetic device technology.

In this project a two-tip scanning tunneling microscope (STM) of a new design, never considered before, will be developed. In this design the two tips probe a very thin sample from opposite sides. In addition, another two-tip STM will be designed in which the two tips probe the sample in a more conventional geometry, with both tips on the same side of the sample. Nanotube tips recently developed by the investigator enable these designs. Nanotube tips may be ideal for spin-polarized tunneling, as well as for a host of scientific and practical applications that can benefit from a coherent point source of spin-polarized electrons. The two-tip STM will make possible new experiments that will probe the Green function of the sample material, so that one can get detailed information on semiconducting or metallic samples such as mean free path, the phase and energy dependence of scattering from impurities, details of the band structure, and the transition from the ballistic to diffusive transport. This instrument can also probe the symmetry of the order parameter in a superconductor, so that refinements of the current d-wave picture can be obtained for high temperature superconductivity. Graduate and undergraduate students will participate in this project. They will benefit from training in advanced instrumentation and techniques, in the development of the novel STM instrument, and from using it to probe the behavior of electrons in the most detailed fashion yet available.

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Microscopes with ever increasing ability to probe small details have been major instruments in advancing our understanding of the microscopic structures and behaviors of materials. Scanning tunneling microscopes (STMs) are the latest types of such instruments that now allow the probing of materials at the atomic level of dimensions. In this project, a new type of STM, based on the use of two, rather than one, probe tips will be developed. One version will have the two tips on opposite sides of a very thin sample, a geometry that has never before been even contemplated. A second version of the two-tip STM will be of a more conventional geometry, in which the two tips are on the same side of the sample. Both versions can be realized on the basis of probe tips, which are atomically sharp needles (carbon nanotubes), that were recently developed in the investigator's laboratory. Such two-tip STMs will allow a new set of investigations of the properties of materials, including high temperature superconducting compounds that will result in a better understanding of their structure and behavior. These results will ultimately be of use and benefit to technology. This project will involve the participation of graduate and undergraduate students. They will thereby acquire knowledge and skills in a very active contemporary area of condensed matter physics and materials science. These will enable them to be productive members of the scientific/technological workforce of the next few decades of this century.

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This project develops new tools and methodology to study properties of magnetic microstructures. A broad range of technology-enabling magnetic phenomena is emerging from research on thin films and thin-film based structures. The novel magnetic effects associated with engineered materials now provide the basis for a broad range of new magnetic devices including magnetic sensors that improve hard-disk performance in computers (giant-magnetoresistance read heads) and permit magnetic-materials-based random access memory (MRAM) to be developed. In order to optimize the performance of the new magnetic materials and explore new device architecture that exploits the new magnetic phenomena, precise understanding and control of the magnetic effects are required. The new instrumentation to be developed from this NSF award and the research to be carried out using it will advance our understanding of magnetic phenomena that enables new technological applications. The research will study factors that govern critical magnetic properties such as magnetic switching thresholds, the speed at which information can be stored and retrieved, and factors that govern how magnetic materials growth and microstructure fabrication affect the properties. The research is likely to result in discovery of new magnetic effects as well as deeper understanding of novel magnetic phenomena that have already been discovered. The research will provide rigorous training for graduate students in the important fields of condensed matter physics and materials technology that is essential for the United States to maintain a leading position in science and technology.


This project develops new tools and methodology to study properties of magnetic microstructures. A broad range of technology-enabling magnetic phenomena is emerging from research on thin films and thin-film based structures. The novel magnetic effects associated with engineered materials now provide the basis for a broad range of new magnetic devices including magnetic sensors that improve hard-disk performance in computers (giant-magnetoresistance read heads) and permit magnetic-materials-based random access memory (MRAM) to be developed. In order to optimize the performance of the new magnetic materials and explore new device architecture that exploits the new magnetic phenomena, precise understanding and control of the magnetic effects are required. The new instrumentation to be developed from this NSF award and the research to be carried out using it will advance our understanding of magnetic phenomena that enables new technological applications. The research will study factors that govern critical magnetic properties such as magnetic switching thresholds, the speed at which information can be stored and retrieved, and factors that govern how magnetic materials growth and microstructure fabrication affect the properties. The research is likely to result in discovery of new magnetic effects as well as deeper understanding of novel magnetic phenomena that have already been discovered. The research will provide rigorous training for graduate students in the important fields of condensed matter physics and materials technology that is essential for the United States to maintain a leading position in science and technology.

A fundamental competition between order and disorder lies at the heart of materials science and technology. Interactions between atoms or electrons spaced sub nanometer apart can lead to collective organization into states with long-range order. Order in electronic states gives rise to physical consequences such as magnetism, ferroelectricity and superconductivity. In bulk materials, the collective electronic properties exhibit a characteristic length scale called the coherence length, which corresponds to the minimum grain size in superconductors, and in ferromagnets the domain wall width. These length scales generally exceed or are comparable to geometrical parameters of nanostructured materials. For these reasons nanostructured materials represent an important new frontier for the study of collective electronic behavior. This interdisciplinary research team will study the physical consequences of nanometer-size dimensions on collective and independent electron properties in individual nanocrystals and in controlled nanocrystal arrays. It is unique in the combination of expertise in materials synthesis, materials characterizations and theory that has been brought together at a single institution. It also forges a close partnership with one leading company in information technology and two foreign institutions. Educationally, this NIRT will help lead the campus-wide initiative at UT Austin for training the next generation of scientists in nanoscience through the integration of research and education and a strong partnership with the newly established Center of Nano- and Molecular Science and Techology. It integrates diversity by actively recruiting graduate students in minority groups. It further reaches out to K-12 education in the Austin area.




This interdisciplinary program brings together expertise in advanced synthesis of metal and semiconductor nanostructures, expertise in nanoscale characterizations of structural, electronic, transport, optical and magnetic properties, and expertise in mesoscopic and many-body condensed matter theory, working together in a single institution to explore the physical consequences of nanometer-size dimensions on collective and independent electron properties in individual nanocrystals and in controlled nanocrystal arrays. Of particular interests are ferromagnetic, superconducting, and normal metal nanocrystals, and ferromagnetic, semimagnetic, and normal semiconductor quantum dots. In ferromagnetic and superconducting systems the emphasis to date has been on the collective properties that underlie, for example, the use of ferromagnets for information storage and the potential use of small superconductors as quantum-bits. As these particles become smaller, the physics of the magnetic anisotropy barriers essential for information storage will be altered, and superconductivity will be destroyed, respectively. This regime is a frontier for fundamental physics and for materials physics and chemistry, and will be the focus of this research program. This research team also forges a close partnership with one leading company in information technology and two foreign institutions. It will strengthen educational and training efforts at UT Austin in nanoscience and nanotechnology by designing a new curriculum that removes barriers between current disciplinary specialization in different majors and provides an excellent training ground for the future generation of scientists in nanoscale science and technology.

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.

Interfaces and defects have played the most important roles in determining the performance of modern electronics. The rapid progress of nanoscience and technology further amplifies the critical roles of interfaces/defects since, in nanostructures, the volume ratio of interfaces and defects grows significantly with the size reduction. This IGERT proposal establishes an interdisciplinary doctoral training program on Atomic and Molecular Imaging of Interfaces/defects in Nanostructured Materials. This program integrates nanostructure fabrications, atomic scale characterizations, and materials theory into a comprehensive education and research training program for graduate students, including six different departments in the colleges of Natural Sciences and Engineering at the University of Texas at Austin. The underlying research goal is to obtain atomic level understanding of how interfaces and defects impact the local electronic structure and functionality of nanoscale electronic, spintronic, and organic/inorganic materials, and how they impact the performance of devices based on these materials. Students trained in this research program will be provided great breadth in their perspectives toward solving important scientific problems, a key and necessary characteristic for the future generation of leaders in nanoscience and technology. The key education and training features include development of a nanoscience and technology core curriculum with a seamless transition to interdisciplinary research programs. Career development opportunities for students will be provided through internships at high-tech industry and national labs. The community educational outreach program is aimed at enhancing nanoscience education at all levels, from pre-K to high school. In addition, by partnering with the International Center for Nanotechnology and Advanced Materials (ICNAM) at the University of Texas, this program is aimed at increasing the participation of under-representated groups, especially Hispanic students, in graduate education. IGERT is an NSF-wide program intended to meet the challenges of educating U.S. Ph.D. scientists and engineers with the interdisciplinary background, deep knowledge in a chosen discipline, and the technical, professional, and personal skills needed for the career demands of the future. The program is intended to catalyze a cultural change in graduate education by establishing innovative new models for graduate education and training in a fertile environment for collaborative research that transcends traditional disciplinary boundaries.

****NON-TECHNICAL ABSTRACT****
Nanotechnology is well known as an important part of the economy, both present and future, but most people do not realize that for ages mankind has made materials with certain desirable properties by controlling the nanostructure of the material. In this sense nanotechnology has been around for a few millennia. What has changed dramatically in the last few decades is our ability to characterize what we make, which has greatly improved our synthesis techniques. Microscopy has been an important component of this recent revolution in nanocharacterization. This project is based on the simple idea of rastering a nano-sized sensor over the sample to measure different properties, such as magnetism and superconductivity. The research team working on this involves young men and women, many of Hispanic background, from the High School to the Ph.D. level.

****TECHNICAL ABSTRACT****
This project emphasizes the development of novel scanning probe techniques that operate at low temperatures, with the goal of studying new materials. Recent examples include the study of colossal magnetoresistive materials, manganites in particular, by tunneling microscopy and spectroscopy, magnetic force microscopy (MFM) and contact atomic force microscopy. Another example is the study of multiferroic materials with Kelvin force microscopy and MFM. The most recent technique is based on a microscopic Hall sensor, which has been used to study a dilute magnetic semiconductor (Ga0.94Mn0.06As). These techniques will provide a better understanding at the nanoscale of the electronic, magnetic, and transport properties of new materials.

0923231
de Lozanne
U. Texas Austin

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

Technical Summary: The development of a low temperature scanning tunneling microscope with spin-polarized and spectroscopic capabilities is proposed (SP-STM). While a handful of similar instruments are operating in Europe and Japan, so far there are only two in the US. The proposed instrument will have three features that are designed to increase its productivity compared to existing facilities: the tip will be characterized with in-situ field ion microscopy, in-situ scanning electron microscopy, and with a secondary in-situ room temperature STM. The new instrument will have a superconducting magnet to provide sufficient field to manipulate the magnetic moment of the tip and the sample. This instrument will benefit the research programs of 12 faculty on our campus and will strengthen existing collaborations amongst this group and with researchers world-wide. The initial experiments will include studies of multiferroic and manganite materials. This is timely since a new MBE facility for oxide growth has just arrived. We will also study the behavior of triangular arrays of self-assembled magnetic nanoplatelets, which is a promising realization of the elusive frustrated Ising model. Spin-torque effects will be studied and used to manipulate the magnetization of individual nanoplatelets. All these studies will be complemented by existing capabilities in low temperature magnetic force microscopy and Hall Probe microscopy. The PI?s are already committed to the training of a diverse community of scientists, both individually as well as collectively through their participation in programs such as REU, IGERT, and outreach to High Schools.



Layman Summary: "The nation that controls magnetism will control the universe," predicted Dick Tracy, the comic book hero debuted in 1931. The creator of this character would probably not believe to what extent this has become a reality: most of our financial, medical, and government records are now stored on magnetic media with ever increasing information density. While information storage technology has already benefitted from basic discoveries made in the past decade or two, the most recent developments are even more impressive, such as the detection of the magnetic spin of a single electron. The scanning tunneling microscope, known for its ability to image atoms on surfaces, is blind to the magnetic properties of the sample. Fortunately this microscope can be fitted with spin-polarized ?glasses? that allow us to look at the magnetic landscape at the atomic scale. Unfortunately this is not easy, and European labs have taken the lead in this important technique. Only two labs in the US have developed spin-sensitive tunneling microscopes. The PI and his group have developed similar microscopes for 27 years and propose to use their expertise to build a new generation of spin-sensitive microscopes that can make this powerful technique more widely available in the US. The team that will work on this is unusually diverse, because half of the doctoral students are female and more than half of the team is Hispanic. During the summer the team also has a few high school students, with strong emphasis on the participation of young women.

Non-technical Abstract:
The spin of an electron is a simple quantum mechanical property when the electron is isolated, but when electron spins interact inside a solid a large variety of wonderful phenomena can be observed. Magnetism and superconductivity are two major examples where spins play a seminal role. The PI and his team have developed microscopes based on the idea of scanning a nanoscale sensor over the sample in order to probe the charge and spin properties down to the atomic scale. They use these techniques to study new manganese oxides that have unusual magnetic and electrical properties, and superconducting copper oxides that can produce regular patterns in their charge and spin distributions. These studies are important in order to understand the role of spin in complex magnetic and superconducting oxides, which will serve to improve current materials and will help in the design of new materials for future applications.

Technical Abstract:
In this proposal, experiments to be performed on interesting oxides with a new low temperature spin polarized scanning tunneling microscope (SP-STM) are highlighted. While there has been much progress in the understanding of the phase diagram for high temperature superconductors, there are still fundamental questions about the nature of the superconducting phase, the presence and properties of other phases, and whether all these order parameters compete or coexist at the microscopic level. All these issues are particularly important in the pseudogap region of the phase diagram, an area that extends to lower doping and higher temperatures than superconductivity, and the topic of intense debate. Charge and spin density waves (CDW, SDW) have been reported to exist in this region, but so far most measurements are done with bulk probes that provide average properties. The SP-STM is particularly well suited to provide microscopic information down to the atomic scale. Other scanning probes are also used to improve our understanding of these materials and phenomena. This proposal focuses on two newer oxides with the 327 crystal structure: one is a superconducting cuprate [(LaSrCa)3Cu2O6+d] and the other a magnetic manganite [La2-2xSr1+2xMn2O7]. These materials were chosen because their structure promotes excellent cleaving characteristics that are essential to produce a clean, ordered surface for STM studies, and because they allow the study of fundamental questions on the role of antiferromagnetic interactions and CDW/SDW in the cuprates, and charge, spin, and orbital ordering in the manganites.