Gerd Duscher - US grants

This is a collaborative project between participating groups in Germany, Sweden, and the US. The project addresses fundamental materials science issues in silicon-on-insulator (SOI) structures of particular technological relevance to realization of advanced device performance. The approach involves determination of the distribution and segregation of dopants within deca-nanometer SOI structures utilizing theoretical and experimental tools to gain greater understanding of processes leading to dose-loss and segregation to both oxide interfaces in nanoscale-device structures. Experimental methods will include atomic resolution TEM-based Z-contrast and electron energy-loss spectroscopy. Modeling will consist of atomistic ab initio calculations and process modeling. The core issue of segregation studies is that the atomic structure of silicon/oxide interfaces remains elusive in spite of intensive research. The model dependence of segregation energy in ab initio materials simulations is commonly considered to be a disadvantage. It is planned to exploit this model dependence by combining it with analytical TEM to transform a disadvantage into a powerful characterization tool, called AIDA-TEM (Ab initio Interface Dopant Analysis by Transmission Electron Microscopy). Since the predicted segregation sites of many impurities and dopants are heavily dependent on the atomic structure model of the interface, segregation sites of a number of impurities will first be determined experimentally. Then, which atomic interface model is in agreement with these experimental findings will be determined. In this way, AIDA-TEM helps to determine interface structure, dopant segregation behavior, and (from the ab initio calculations) electronic properties, which can then be used to predict device characteristics. Process modeling, based on experiments and ab initio calculations, is expected to lead to an understanding of dopant redistribution and dose loss mechanisms. And knowledge of structure-property relationships, dependent on dopants and annealing conditions, will allow determination of more optimum device processing parameters.
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The project addresses fundamental research issues associated with materials having technological relevance in nanoelectronics. An important feature of the project is the strong emphasis on education, with emphasis on integration of research and education, and an international collaboration providing both scientific and educational benefits. Staff and student exchanges will supplement electronic communications between the participating groups. Undergraduate and graduate students involved in the project will be exposed to international and world-class science and technology. Young scientists and students greatly benefit from these kinds of projects, to learn the basics of nanoscience and to become motivated to pursue new ideas of their own. This NSF project is co-funded by the Division of Materials Research (Electronic Materials and Ceramics Programs), and the International Office (Western Europe) as a Cooperative Activity in Materials Research between the NSF and Europe (NSF 02-135). The project is being carried out in collaboration with participating groups in Germany (Heiner Ryssel Professor at the Electrical and Electronic Engineering Department, University of Erlangen-Nurnberg, Germany and Director of the Fraunhofer Institute of Integrated Circuits, Erlangen, Germany), and Sweden (Mikael Ostling Professor, Head of Department, Department of Microelectronics and Information Technology, Laboratory of Solid State Devices, KTH, Royal Institute of Technology).

The SiWEDS Center works closely with the industry member scientists and engineers, carries out a unique multi-university program of research in silicon materials. They provide critical materials physics and chemistry solutions that increase the yield, performance, and reliability of silicon materials and devices used for Giga Scale Integrated Circuits. The SiWEDS targets areas with great potential for true long-term breakthrough on the one hand, coupled with near term payoffs on the other. This multi-university I/UCRC is led by North Carolina State University and involves the University of California-Berkeley, Arizona State University, University of Arizona, University of South Florida, University of Washington, MIT, and Stanford University.

This proposal formally establishs a multi-university Silicon Solar Consortium (SiSoC) as part of NSF?s Industry/University Cooperative Research Center (I/UCRC) program. The Georgia Institute of Technology and North Carolina State University (the lead institution) will maintain research sites to collaborate on research, fabrication, and characterization of advanced photovoltaic (PV) materials and devices.

The proposed center's goal is to help reestablish a global leadership role for the U.S. Silicon PV industry by having government together with the solar-electric power industry jointly stimulate high quality university level research and education, while developing an expanded and skilled workforce. The Center will collaborate with other university and government agencies bringing together the leading academic institutions currently involved in PV research and development. Research emphasizes materials characterization leading to a fundamental understanding of impact of defects/impurities/mechanical behavior of solar cell materials to accommodate various needs of both single- and multi-crystalline Si wafers, thin films and nanoscale PV science and technology. Results will create strategies for processing advanced silicon PV structures and devices. Research will also focus on reducing the cost of PV generated electricity and designing and fabricating high efficiency solar cells.

SiSoC will help develop a skilled workforce in a much needed area. This will be enabled by having NSF and other government agencies, together with the solar-electric power industry jointly stimulating high quality university level research and education. Research activity will also be strengthened through student internships at industry member locations. This center will also be used to compliment efforts for outreach and improve opportunities for underrepresented minorities/women to participate in PV materials research through such programs as the Research Experiences for Undergraduates.

NON-TECHNICAL ABSTRACT
Silicon-based electronic devices are the main component in virtually all microelectronic applications, e.g., computers and computer chips that are everywhere in cars, appliances, etc. For high-power and high-temperature uses, however, e.g., on-engine chips, power grid controls, etc. Si-based electronics are either inefficient or not usable at all. Silicon carbide is the most promising alternative, but, despite major advances in the last decade, including breakthroughs by the present team, difficult technical problems remain to be resolved. The proposed research addresses these issues with a mix of experimental and theoretical techniques. At the heart of the difficulties is the interface between silicon carbide and its native oxide, namely silicon dioxide, and the impact of the oxidation process on the underlying crystalline material. The expected results will be relevant to the broader field of the oxidation of diverse materials. Educational outreach projects will highlight to high school teachers and students the special needs of high-power, high-temperature electronics and the impact of research advances in important applications.

TECHNICAL ABSTRACT
Silicon carbide is a promising alternative to Si for high-temperature, high-power electronics because of its larger energy gap and heat-conduction coefficient, but also because its native oxide is silicon dioxide. The SiC/SiO2 interface, however, is more complex that the Si/SiO2 interface, which is at the heart of Si-based electronics. The main problem is that oxidation releases C atoms, some of which are stuck at the interface as defects. Despite major advances in passivating defects at the SiC/SiO2 by N and H, including breakthroughs by the present team, electron mobility remains lower than desirable for applications. Recent evidence points to subtle changes in the underlying SiC substrate. The proposed research will combine state-of-the-art microscopy, electrical measurements, and theory to elucidate the oxidation process at the atomic scale, identify the origins of undesirable effects and defects, and identify new design specifications to improve carrier mobilities. Extensive education outreach will make advances accessible to high schools and the community.

Technical summary: Transition metal-oxides are highly promising materials in modern technology because they are stable at high temperatures and in corrosive environments, and because their physical and chemical properties are highly tunable. The design of metal oxides for technological applications such as electronics, photovoltaics, and catalysis necessitates a thorough understanding of the physical complexity that lies beneath the broad functionality of these materials. This project involves the acquisition of a molecular beam epitaxy apparatus with an in-situ low-temperature scanning probe microscope for the synthesis and atomic-scale characterization of novel artificially-structured oxide materials. Molecular beam epitaxy offers unique capabilities of creating atomic arrangements with atomically precise control of thickness and composition, which will be utilized to systematically tune the properties of oxide thin films and interfaces with special emphasis on clean energy applications. This special instrument for epitaxial synthesis and characterization will be an important nucleus of the educational and training activities at the Joint Institute for Advanced Materials, which is a newly-established umbrella organization at The University of Tennessee and Oak Ridge National Laboratory, fostering interdisciplinary research, education, and partnership for the development of advanced materials in East Tennessee.



Layman summary: Metal oxides are highly promising materials for electronic and clean energy applications, including photocatalysis, where light-activated catalysts are used, for example, to split water into pure oxygen and hydrogen; and photovoltaics, which convert solar radiation into direct electric current. Nearly all such applications involve processes that take place at the surfaces or interfaces of these oxide materials. Fundamental understanding and better control of these processes would greatly benefit from the capability of producing well-defined surfaces, interfaces, and thin film materials, as well as from the capability to systematically alter and characterize the structural and electronic properties of these materials with precision down to the atomic level. The project involves the acquisition of a molecular beam epitaxy apparatus for the synthesis of artificially-structured metal-oxide materials, with special emphasis on clean energy applications, along with a scanning probe microscope for imaging individual atoms and mapping the nanoscale properties of these materials. Molecular beam epitaxy offers researchers the extraordinary capability of constructing novel materials from atomic "Lego principles," guided by theoretical calculations or predictions. This special instrument for epitaxial synthesis and characterization will be an important nucleus of the educational and training activities at the Joint Institute for Advanced Materials, which is a newly-established umbrella organization at The University of Tennessee and Oak Ridge National Laboratory, fostering interdisciplinary research, education, and partnership for the development of advanced materials in East Tennessee.

PROGRAM DIRECTOR'S RECOMMENDATION

IIP 1238288
University of Tennessee Knoxville (UTK)
Duscher

The University of Tennessee Knoxville is planning to join the Industry/University Cooperative Research Center (I/UCRC) entitled Center for Next Generation Photovoltaics which is a multi-university center comprised of the University of Texas-Austin (UTA) and the Colorado State University (CSU). The existing Center focuses on the advancement of CdTe & CIGS thin films, thermal process modeling, imaging, and nanocrystal systems.

The goal of this proposal is to seek NSF funding to for a planning meeting to allow the University of Tennessee Knoxville to recruit industry support to allow it to join an existing I/UCRC Center focused on Next-Generation Photovoltaics (NGP). Participation by UTK will expand the scope of the existing I/UCRC to include research on organic materials, thin-film silicon materials and artificial photosynthesis.

Low-cost, reliable photovoltaics would lead to widespread adoption of solar energy as a renewable energy source. Solar energy utilization is critically important to the future of the planet. It is also an excellent training arena for future scientists and engineers because it is highly interdisciplinary, necessitating communication and interaction across disciplines. The I/UCRC efforts will also be interfaced with key educational programs at UTK, CSU, and UTA, as well as leveraging capabilities at the Oak Ridge National Laboratory. The industrial partnerships in the I/UCRC will be vital to the success of this program. The Center will have a team of faculty and students that is diverse in gender, race and ethnicity.

Non-technical Description: Nanoscience and nanotechnology often involve materials of reduced dimensionality, such as one-dimensional (1D) nanotubes and nanowires as well as 2D sheet materials. Reduced dimensionality frequently leads to new phenomena not observed in their 3D counterparts. This research project aims to synthesize two different 2D materials joined together to form a plane of single atomic-layer thickness. The constituent 2D materials in such an in-plane heterostructure are crystalline, and the atomic order is not disturbed crossing the sharp interfaces of the different materials. Due to these traits similar to those of epitaxial heterostructures in 3D, the synthesis of the in-plane heterostructures is called "epitaxy in 2D." Successful synthesis of such structures enables the investigation of the associated new physics, which is expected to lead to novel electronic, photonic, and magnetic devices. The new knowledge generated during the course of the research is passed directly to students by integrating research into teaching, not only to convey excitement of new discoveries but also to stimulate curiosity. This project also impacts K-12 STEM education through outreach activities. In addition, the team participates in a National Public Radio (NPR) program to educate the public on science and technology.

Technical Description: This research project focuses on the synthesis and characterization of two-dimensional (2D) heterostructures. The long-term goals of the research are: 1) To establish the growth science of 2D heterostructures; 2) To reveal the very rich and often exotic physics of these structures; and 3) To develop novel electronic, photonic, and magnetic device concepts based on the novel physics. Specifically, the scope of this project includes: 1) Perfection of the zigzag boundary of the graphene-hexagonal boron nitride (graphene-hBN) in-plane heterostructure. This involves the elimination of antiphase disorders by growing the nonpolar graphene onto the edges of polar hBN in a well-controlled environment to overcome the chemical factors preventing this growth sequence. The interface is characterized by atomic resolution, element-contrast imaging to investigate the obtainability of a truly atomically sharp boundary. 2) Synthesis of complex in-plane heterostructures comprising multiple graphene-hBN junctions. Besides bottom-up growth, top-down control is incorporated when necessary. 3) Initial investigation of the novel physics, such as tunneling between localized boundary states and spin polarization of the boundaries, of these heterostructures. Dichroism in electron energy loss spectroscopy is the method of choice for the initial experimental probing of the spin polarization of the atomic-scale of the boundary states.

Non-technical description:
When a strong interaction between light and matter occurs, new phenomena (entangled quantum states) arise, which are generally not observed in nature. This quantum entanglement can potentially be harnessed for quantum information technologies with drastically improved data acquisition and processing. In this project, the research team uses semiconductor nanowires, which are surrounded by metal nanoparticles to investigate the interaction between light (in the form of plasmons) and semiconductor (in the form of excitons). To achieve strong coupling and quantum entanglement, the morphology of this nanostructure is modified by laser processing inside a transmission electron microscope. The light-matter coupling is investigated with optical methods and electron microscopy along with theoretical modelling. This project opens new prospects for designing novel quantum materials with significant impact in the areas of quantum information and quantum science. The project fully integrates education and training of graduate and undergraduate students with an emphasis on recruitment from underrepresented groups. The training prepares the students for a wide range of careers. Outreach to the public includes contributions to local STEM programs and organized lab-tours of the electron microscopy facilities for high-school students.

Technical description:
Entanglement and strong coupling are the basis for quantum computing and quantum sensing. As a model system to study these quantum effects the research team is using an open cavity semiconductor nanowire-metal nanoparticle system in which excitons and plasmons can interact in regimes ranging from weak to strong coupling. Ultrafast optical spectroscopy and electron energy-loss spectroscopy are uniquely combined to study the energy transfer and many-emitter entanglement with high temporal and high spatial resolution. Laser processing of these plasmonic nanostructures inside the transmission electron microscope allows modifications of the morphology during atomic resolution imaging providing a system to achieve and to control quantum entanglement. The central thrusts in this project are to synthesize nano-morphologically controlled metal/organic/semiconductor nanowires and to study the coupling of excitons and plasmons. Both the change in the nanostructure morphology and the inserted organic modulator critically modify the coupling strength in this quantum system. The calculated dielectric response function connects the loss function obtained from the electron energy-loss spectroscopy measurements with the optical measurements. Complementary theoretical modelling provides a fundamental understanding of these light-matter interactions. The investigations of the research team open new prospects for designing novel quantum materials to exploit strong coupling and many-emitter entanglement with significant impact in the areas of quantum ?information, -chemistry and -biology.

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.