Mark S. Rzchowski - US grants

0210449
Eom

This proposal was received in response to the Nanoscale Science and Engineering Initiative, Program Solicitation NSF 01-157, in the NIRT category. The proposal focuses on understanding intrinsic phenomena governing spin transport at the nanoscale, and the development of new methods for its manipulation for future spin-controlled, magneto-electronic, devices. It addresses one of the most exciting aspects of current research on next-generation electronic devices: the manipulation of spin, rather than only electrical charge. The advantages of these magnetoelectronic devices include nonvolatility, faster switching in static memory elements, and higher density due to a simpler device structure. These issues become even more important as technology drives device sizes toward the nanoscale, where new fundamental physical effects emerge that alter spin transport, as well as high-frequency dynamics and switching times.
An understanding of these issues at the nanoscale requires single-crystal magnetic heterostructures with atomically-sharp interfaces, patterned to nanometer dimensions. This proposal probes nanoscale spin transport phenomena in epitaxial magnetic oxide nanostructures grown with atomic-layer control, whose magnetic, electronic, and interfacial properties are tuned at will. Layers with defined electronic, magnetic, and morphological characteristics positioned with atomic-layer control in epitaxial systems are used to address crucial fundamental questions in magnetic nanostructures.
This research program consists of 1) design, growth, and characterization of epitaxial magnetic oxide heterostructures with atomic layer control by pulsed laser deposition with in-situ real-time structural analysis 2) high-resolution and analytical TEM to determine atomic structure and electronic properties of the interfaces; 3) nanoscale patterning of novel magnetic heterostructures below 50 nm; 4) scanning probe measurements of topography and local electronic properties; 5) education and outreach efforts with a focus on introducing young people to modern, multidisciplinary science and technology, using the research direction as a vehicle.
The multidisciplinary, multiuniversity/industry team consists of members working in Materials Science, Physics, Electrical Engineering, and device development. Research, education, and outreach all follow the theme of nanoscale structures, novel phenomena, and spin transport control. This work will build a scientific foundation for the understanding of new phenomena in nanoscale spin-controlled devices. The PIs industrial and multidisciplinary interactions will be very beneficial in advancing research as well as in educating students. This study will also provide fundamental guidelines in the atomic-scale control of nanoscale systems such as ferroelectrics and oxide-semiconductor integration that are important for next-generation technology.

This Nanoscale Exploratory Research (NER) proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF 02-148). The project undertakes an exploratory study of spin injection and transport in organic and polymeric conductors. The approach is to fabricate organic heterostructures, employing solid-state magnetic electrodes as a source of spin polarized carriers, and manipulate the nanoscale interfacial properties using molecular self-assembly and related techniques. Spin will be injected into semiconducting and conducting polymer/organic thin films. Several specific systems consistent with "exploratory" time scales and support levels, including the organic analog of giant magnetoresistance, spin-injected organic/polymer light-emitting diodes, and tunneling from magnetic nanocrystals through organic layers will be addressed. In these systems, the interface is judged to be of critical importance since it controls injection characteristics through the electronic barrier height in the case of electronic charge, and spin-scattering characteristics in terms of magnetic electrodes. It is anticipated that interfacial control will be afforded by organic systems to manipulate spin-injection properties through the use of interfacial self-assembled monolayers, and surface doping of the barrier polymer by chemical or electrochemical means.
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The project addresses basic exploratory research issues in a topical area of materials science with high technological relevance; it is considered a high risk/high pay-off activity. Conducting polymers and molecular organics are rapidly becoming technologically important materials because of their unique fusion of semiconducting electronic properties with the flexibility of organic/polymeric materials. A wide variety of electronic devices have been demonstrated with organic materials, such as light-emitting diodes, laser diodes, and field-effect transistors. The advantages of resulting 'plastic' electronic devices include ease of fabrication, scalability, and molecular-level control of interfacial morphology and electronic characteristics. The project encompasses the research and education theme of Nanoscale Structures, Novel Phenomena, and Quantum Control. 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 is expected to have broad impact by providing unique educational opportunities and basic knowledge critical to potential development of organic spintronic devices having advantages of both organic electronics and solid-state spintronics. The project is jointly supported by the MPS/DMR/EM and MPS/DMR/POL programs.
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***NON-TECHNICAL ABSTRACT***
Superconductors are essentially frictionless conductors of electricity. Thus, they avoid the heating effects that occur even in very high-conductivity copper wires. High magnetic field devices, impossible to make with copper, therefore become a possibility. Unfortunately superconductivity occurs only at rather low temperatures. There was great excitement when MgB2, an apparently simple superconductor made from inexpensive raw materials, was recently discovered to be superconducting at twice the temperature of any other simple superconductor. The electronic characteristics of MgB2 provide unique opportunities to explore the possibility of improving the material's properties to make them superior to those of any present superconductor. This Focused Research Group (FRG) award provides support for an inter-institutional collaboration between groups at the U. of Wisconsin-Madison (UW), Arizona State U. (ASU), Pennsylvania State U. (PSU), and the U. of Puerto Rico-Mayaguez (UPRM). The project seeks to understand how to make MgB2 attractive for applications. The team has already demonstrated that MgB2 remains superconducting in higher magnetic fields than materials based on Nb. More than 99% of all current superconducting magnets are made from Nb based materials. Superconductivity is vital to many aspects of technology, especially to Magnetic Resonance Imaging (MRI). General Electric, one of the world's largest manufacturers of MRI machines will collaborate on this study. This effort will be implemented by research carried out by graduate research students and amplified by collaboration with the developing materials science program at UPRM and by outreach at the K-12 level to Native American and Hispanic communities in Arizona. The project is supported by the Condensed Matter Physics, Ceramics, and MRSEC programs in the Division of Materials Research, as well as by the Office of Multidisciplinary Activities.


***TECHNICAL ABSTRACT***
Magnesium diboride is a hexagonal layered compound recently found to have a 40K superconducting transition temperature, almost twice as high as any other electron-phonon superconductor. Even more interesting is that MgB2 contains two distinct superconducting gaps that are only weakly coupled to each other. The larger sigma gap is formed by in-plane sigma boron bonds, whereas the smaller pi gap results from pi boron bonds between the Mg and B planes. This inter-institutional Focused Research Group (FRG), consisting of groups at the U. of Wisconsin-Madison (UW), Arizona State U. (ASU), Pennsylvania State U. (PSU), and the U. of Puerto Rico-Mayaguez (UPRM), will address fundamental physics and materials science issues of MgB2 alloys, concentrating on bulk-form samples and damage studies that have great potential for MgB2 technology. The project seeks to understand how the upper critical field is affected by scattering in and perhaps between the sigma and pi bands of MgB2 and how the scattering changes as MgB2 is alloyed or ion irradiated. Bulk form samples will be the primary thrust of the studies at UW and UPRM; transmission electron microscopy will be performed at UW. Researchers at PSU will concentrate on modeling of the alloying process. Ion irradiation and connectivity effects will be the focus of research at ASU. The broader impacts are both technological and educational. The superconducting magnet user community is excited by recent demonstrations that Hc2 of alloyed MgB2 can exceed Hc2 of the Nb-based superconductors, from which virtually all superconducting magnets are presently made. US industry and national laboratories, as well as international academic collaborators, will work with the FRG to explore the full potential of MgB2 for cryocooled magnets in the 10-30K range, as well as ultra high-field magnets beyond the reach of any Nb-based material. Outreach collaborations in research through a recently started UW-UPRM NSF-PREM at UPRM will be further developed and K-12 outreach will start at ASU to Hispanic and Native American communities in Arizona. The project is supported by several programs in the Division of Materials Research, as well as by the Office of Multidisciplinary Activities.

0708759
Chang-Beom Eom
University of Wisconsin-Madison
Active Nanostructures with Giant Piezo-response


Intellectual Merit: Major challenges are emerging as electromechanical systems move to the nano-scale (nanoelectromechanical systems, or NEMS), with an integration density that demands faster and larger relative motion range. Our recently developed giant piezoelectric epitaxial thin-films directly on silicon can drastically increase the motion range and speed, with even potentially greater response by using engineered nanoscale strain distributions and domain structures. We will integrate epitaxial thin film heterostructures of giant piezoelectric materials directly on silicon to make hyper-active nano-electromechanical systems. These heterostructures are compatible with silicon nanofabrication processes, can be integrated with silicon-based electronics, and have large enough response to revolutionize active NEMS actuators. This research will develop a fundamental scientific understanding of nanoscale piezoelectric phenomena in active nanoscale electromechanical devices, with applications in high performance signal processing, communications, sensors, and nano-positioning actuators. The relationship between piezo-response and nanoscale strain and domain configurations developed here can be applied to multifunctional materials to develop new NEMS devices.

Broader Impacts: This research will resolve the fundamental issues that control nanoscale performance of piezoelectric materials in NEMS devices. Future generations of NEMS devices enabled by this research are likely to find wide-ranging applications and bring technological advances to many parts of society. Our Education goal is a broad experience for all students. This includes first-year student rotation through research groups, working in international and industrial laboratories, research interactions with individuals of diverse backgrounds, and participating in outreach programs. In Outreach, secondary school science teachers from Mayaguez, Puerto Rico will be brought to UW-Madison each summer for a nanotechnology learning/research experience. They will develop classroom material in both English and Spanish, and put in place programs for implementation secondary schools across the country. Graduate students will be involved as mentors to the teachers.

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."
Technical. The goal of this focused research group (FRG) proposal is to achieve an atomic-level understanding of the growth and novel properties of switchable oxide hetero-interfaces, with advanced properties and new functionalities. The idea is to create new 2D interfacial materials, switched by external stimuli, whose electronic, magnetic, optical, and transport properties depend critically on atomic-scale materials characteristics. Switchable interface materials with, spatially modulated conductance, tunable by an applied electric field, and spin-polarized interface materials responding to magnetic fields will be explored. The focus is on identification and understanding of atomic level mechanisms and electrical transport associated with atomic layer-by-layer synthesis. It is anticipated that functionalizing 2DEGs at oxide interfaces may be transformative, in that it could lead to new research fields where interplay between ferroelectricity and 2D transport reveals unexplored properties important for device applications. Logic devices with switchable electron and/or spin current based on 2D interface materials are envisioned. The approach involves a collaborative coordinated effort to explore materials science issues of growth and novel properties of switchable oxide hetero-interfaces. Specific tasks are (1) theoretical exploration of the dependence of interfacial properties on materials characteristics; (2) atomic layer epitaxial growth and characterization of switchable two-dimensional oxide hetero-interface materials; (3) electrical transport and magnetic characterization of interfacial electronic properties.
Non-Technical. The project addresses fundamental research issues in a topical area of electronic/photonic materials science having technological relevance. This research is expected to identify and resolve fundamental materials science issues in switchable 2D interfacial oxide heterostructures; prototype electronic devices fabricated from these interfacial materials may find new and wide-ranging applications. Education and outreach activities will be integrated with the research. The education goal is to provide a broad interdisciplinary experience for all students. This includes first-year student rotation through research groups, working in an international institution and the Argonne National Laboratory, research interactions with individuals of diverse backgrounds, and participating in outreach programs. Students from underrepresented groups will be actively recruited through collaboration with U. Puerto Rico-Mayagüez. Secondary school teachers will come from Puerto Rico to the U. WI for a nanoscience learning/research experience. They will develop classroom material, and put in place programs for implementation at their schools in Puerto Rico. Graduate students will be involved as mentors to the teachers. The results of the program will be widely disseminated through teacher presentations at schools and at education conferences, and through published articles.

Technical Description: Complex oxides have been fertile ground for new discoveries, due particularly to their wide-ranging electronic, optical, and magnetic properties. Interfaces between complex oxides and related materials create juxtapositions between different symmetries and ordered states, and it has become clear that these interfaces are new materials in their own right and lead to dramatically different properties from those in bulk. This project focuses on an iterative cooperation between forefront theory and experiment that determines the fundamental principles controlling new physical phenomena at oxide interfaces, uses these principles to design couplings between multiple orders at interfaces to generate new functionalities, and experimentally synthesizes and investigates designed interfacial materials for novel electronic devices. These atomic-scale interfacial materials can lead to, for example, new classes of electric-field controllable electronic and magnetic phenomena, and enable the development of new technologically important devices that exploit these couplings. Using a predictive theory and modeling, and feedback to theory from experiments, the research team aims to design, understand, and synthesize novel oxide hetero-interfaces that have unique properties not presently available.

Non-technical Description: New approaches to the discovery of materials displaying novel properties are critical for the continued scientific progress in condensed matter science and applications. This project addresses this need with a focus on "oxide interfacial materials," those formed at and near the atomically abrupt boundary between two oxygen-based materials, each of which can exhibit a stunning array of phenomena such as magnetism, piezoelectric behavior, superconductivity, and structural ordering. At the interface, interactions between these functionalities give rise to unexplored nanoscale behaviors. These new interfacial materials are some of the most promising in which to realize new phenomena that will challenge our current understanding, and that will develop new electronic device directions to address our society's technology needs. The project brings a broad educational experience to all students, interacting with faculty members of this research team at five universities, working with scientists at National Laboratories and international institutions, and participating in outreach activities. The faculty and graduate students work with secondary school teachers from the US and Puerto Rico to develop classroom material based on their materials genome learning/research experience.

NON-TECHNICAL DESCRIPTION: Materials with a particular crystalline arrangement of atoms, known as perovskite, have played important roles in applications ranging from electronic and magnetic devices to micro-machined actuators and sensors. Some of the most interesting phenomena arise at interfaces between these and other materials, where the atomic and structural aspects combine to form new materials in their own right. The main goal of this research is the discovery of a new class of interface materials based on antiperovskites. These antiperovskites exchange the atomic positions of the more common perovskites, creating unique, wide-ranging properties different from the parent materials. Interfaces between these two 'anti'-structures create unexplored fundamental opportunities for materials design. This research will discover the fundamental principles controlling these new materials systems, develop atomic-scale design principles, and create and explore these interfaces for potential applications in electronic, magnetic, and quantum-controlled devices.

TECHNICAL DESCRIPTION: Complex perovskite materials have been fertile ground for new discoveries, due particularly to their wide-ranging structural, electronic, optical, and magnetic properties. Interfaces between perovskites create juxtapositions between different symmetries and ordered states, and it has become clear that these interfaces are new materials in their own right, with inherently multiple length-scale distortions near the interface that lead to rotations, deformations, and electronic and structural orderings dramatically different from those in bulk. The main goal of this research is the discovery of a new class of interface materials based on antiperovskites. Antiperovskites have the perovskite structure, but cation and anion positions are interchanged, resulting in unique, wide-ranging properties different from perovskites. Interfaces between these two 'anti'-structures create unexplored fundamental opportunities for materials design. The fundamental principles controlling new physical phenomena at these interfaces will be determined, and the principles used to design couplings between multiple orders at interfaces to generate new functionalities. This research is aimed at developing atomic scale design principles for antiperovskite heterointerfaces, constructing databases of the stable interface structures, and developing antiperovskite heterostructures with scientifically important and technologically transformative structural, electronic, and magnetic properties. The project implements an integrated effort of theory, materials synthesis, structural, electronic, and magnetic characterization. The research will use an iterative approach, where feedback from experimental measurements of interfacial structure and electric and magnetic order is used to refine theoretical parameters and approximations. This iterative approach will develop a fundamental understanding of the interface atomic structure and bonding between disparate materials, and how it creates new interfacial spin order and electronic configurations. These atomic-scale interface materials will lead to new classes of controllable electronic and magnetic phenomena, and new growth approaches that will make possible heteroepitaxy of other materials systems with large disparity in structure and chemical bonding. The predictive theory and modeling, with feedback to theory from materials growth, and from structural, electronic, and transport characterization, will produce hetero-interfaces that have unique properties not presently available.