William D. Nix, Ph.D. - US grants

An investigation of time-dependent deformation employing both computer modelling and experiments will be conducted on pure metals and the intermetallic compound, nickel aluminide (Ni 3AL). The research will include studies of the cell structures developed during deformation in terms of the elastic properties of individual dislocations and the development of a constitutive model for plastic flow, including flow kinetics, strain hardening, static and dynamic recovery. The overall aim of this work is to develop a model which is capable of describing the basic characteristics of both low and high temperature deformation.

This award will support collaborative research between U.S. and French material scientists on the topic of ion-assisted coating of stainless steel. The U.S. investigators, all from Stanford University, are: Dr. Robert Sinclair, Dr. William Nix and Dr. David Stevenson. The French counterpart is Professor P. Moine, Laboratoire de Metallurgie Physique, University of Poitiers. Ion-implementation has become over the past decade a versatile and effective method for the modification of materials properties, including those of metals,semi-conductors, ceramics, composites and polymers. In this project the investigators will carry out a scientific investigation of the ion-assisted coating of stainless steel. The technical goal is to realize a low friction coefficient, high wear and corrosion resistant surface, by using amorphous TiNi combined with BN. The scientific issues addressed will be: 1. The relationship of the coating microstructure with ion-beam processing conditions, by carrying out thorough material characterization on a wide variety of samples. 2. Correlation of the surface properties with the microstructure, with particular attention to adhesion, nano-hardness, friction, wear and corrosion. The Poitiers laboratory is well-equipped for the ion-implantation, secondary ion-mass spectrometry and x-ray characterization, and the tribological property studies. The Stanford group has much experience with cross-section transmission electron microscopy, mechanical properties of thin films and electrochemical corrosion studies. Results of this research should provide 1) new knowledge about the structure, properties and formation mechanisms of novel and promising coatings of stainless steel and 2) improved understanding of ion-assisted coating technology.

The aim of the proposal is to explore the potential of multilayer structures by studying their synthesis by sputter deposition with in-situ characterization as well as measurement of their mechanical properties. Grazing incidence X-ray scattering is used to examine the surface and interfaces during deposition. The films are synthesized with alternating face-centered cubic and body-centered cubic metal pairs. These films offer the opportunity to study strengthening by finely spaced obstacles that inhibit dislocation motion and relating this strengthening to film epitaxy, film thickness and misfit strains. A strength in the program is the use of an in-situ analysis technique, which could lead to new understanding of film growth.

9408552 Clemens The purpose of this research is to investigate and optimize the strengthening mechanisms in epitaxial metal multilayers. A previous grant developed the capability for growing and structurally characterizing epitaxial (001) oriented FCC/BCC superlattices by sputter deposition. Hardnesses of these materials were investigated and enhancements nearly 300% found over the rule of mixtures. This remarkable phenomenon is the subject of this continued program. Using singly-oriented, epitaxial films, both the mismatch and relative thickness of layers are varied to deduce plastic flow mechanisms. Structural characterization involves high resolution cross-section transmission electron microscopy of as-deposited and deformed materials so that the atomic scale defects responsible for deformation can be identified. This information is incorporated into the modeling component of the program, which utilizes both continuum and atomistic approaches. %%% One result of this program will be metal films of unusually high hardness. These films could find applications in semiconductor, information storage, and coatings technologies. In addition, this program should develop fundamental understanding about plastic deformation in layered materials and ultra-thin films. ***

The McCullough building, erected in the 1960's, is the home for materials research at Stanford University. Currently the building houses the Center for Materials Research, an NSF Material Research Laboratory. It is the goal of the Center to created a new Laboratory for Advanced Materials that will bring 15 faculty from Applied Physics, Materials Science and Engineering, Electrical Engineering, Physics and the Stanford Synchrotron Radiation Laboratory to form a multidisciplinary advanced materials research and education community. However, present infrastructural conditions within the building have created an unsafe facility that lacks proper ventilation, electrical, plumbing and air conditioning systems. The building is not in compliance with existing codes for the type of research activities it currently houses nor the for the planned program activities in advance materials. ARI funds will provide support to assist Stanford in its efforts to renovate laboratory research space in McCullough, specifically, the HVAC, electrical and plumbing systems. The major objective is to ensure that the building is upgraded to occupancy code to accommodate the research and research training activities required in the facility. The project is critical to the long-range plans of Stanford in the area of materials research, a research area of national importance. New renovated space for advanced materials will be dedicated to research in the synthesis, understanding and application of advanced materials, and to the education of students from various science and engineering disciplines in the multidisciplinary style essential in materials research.

This award supports Professors William Nix and John Bravman, plus two graduate students, all from Stanford University, to collaborate in studies of failures in electronic materials with Professor Eduard Arzt and his research group of the Institute for Metallurgy of the University of Stuttgart, Germany. Professor Arzt and his students have pioneered the study of `interface controlled` deformation processes, and they have developed a new technique for studying electromigration failure. The U.S. group led by Professor Nix has developed models to describe the flow and accumulation of ions in conductor lines and the initial stages of void formation. They also have specialized equipment for studying the formation and propagation of voids in metal lines. Advances in miniaturization of integrated circuits have exposed the metallic conductor lines to increasingly severe operating conditions. The aim of this research collaboration is to develop a better understanding of the microstructural and alloying effects that control the reliability of conductor lines in integrated circuits. These lines typically carry very high current densities which causes atoms to migrate from one place to another creating damage sites. This leads to the formation of voids and cracks in the surrounding materials, which is the cause of major reliability problems for miniaturized electronic devices. Joining the complementary expertise of these U.S. and German research groups will accelerate progress in understanding such critical electromigration phenomena in conductor lines.

0085569
Gao

Computational nano-engineering is an emerging field of research aimed at developing nanoscale modeling and simulation methods to enable and accelerate the design and development of functional nanometer-scale devices and systems. Just as microfabrication has led to microelectronics revolution in the 20th century, nano-precision engineering will be a key to the nanotechnology revolution in the 21st century. A major challenge in this technology is to fabricate patterned nanostructures. The objective of the proposed research is to develop multiscale modeling and simulation methods for nanopatterning. As a prototype example with comprehensive industrial impact, we will focus our efforts on nanopatterning of magnetic nanostructures for high-density information storage device applications where the control of grain size distribution is becoming increasingly important, and the drive for decreased media noise and increased storage density is pushing the grain size below the 10 nm regime.

We propose a systematic study of the mechanisms that control the grain size and grain size distribution in magnetic thin films. We will use continuum theories to model the length scales determined by competing mechanisms of epitaxy, surface stress, surface energy, strain energy, compositional free energy and quantum energy. We will develop kinetic Monte Carlo and quantum simulations to simulate nanoscale self-organization for creating magnetic thin film media with ultra-fine grain sizes and ultra-narrow grain size distributions. The simulation tools will allow us to quantitatively investigate nanofabrication processes, and in particular, to predict the grain size and grain size distribution in magnetic nanostructures.

The proposed project will have immediate impact on the magnetic information storage nanotechnology by providing industry with the first theoretical tool to analyze nanofabrication processes based on the state-of-the-art knowledge of nanoscale modeling and simulation. This project will allow engineers to reduce or eliminate costly and slow processes of developing new nanostructured materials. Through the proposed research, we will develop the framework of computational nanopatterning technology which will benefit the whole spectrum of current nanotechnology challenges. This project will lead to better understanding of the basic mechanisms that control the structuring of materials at the nanometer scale. The Kinetic Monte-Carlo simulation and quantum simulation methods developed under this project will have far-reaching significance for the design and manufacturing of nanodevices.

This FRG/GOALI project is a collaborative effort between researchers at Stanford U., Lehigh U., and Applied Materials, Santa Clara, CA. The project addresses microstructural stability, micromechanics, and electrical properties of materials used in the fabrication of on-chip capacitors incorporating dielectrics such as BaxSr1-xTiO3 (BST) and PbZrxTi1-xO3 (PZT). The aim is to improve understanding of thin film micromechanics, on-chip capacitor electrical performance, and how both electrical and mechanical properties may be modified through thin film microstructural control. Emphasis is on development of a mechanistic understanding of stress relaxation, surface roughening, and film debonding processes occurring during processing of thin film electrodes and diffusion barriers for high-K capacitor applications. Degradation of interfacial contact resistivity and dielectric reliability using patterned capacitor test structures will also be studied. Thermal stress relaxation of electrodes, which affects both adhesion and roughness, will be modified by alloying electrode layers and producing two phase microstructures through internal oxidation. It is anticipated that the research will lead to new strategies for improving the reliability and processing stability of on-chip capacitors that use perovskite-structure high permittivity dielectrics. Research will be performed by a multi-disciplinary, multi-investigator team at Stanford University and Lehigh University. Students and faculty will collaborate with materials researchers and process-integration specialists at Applied Materials, Inc. Joint research activities with AMAT will include sharing of research resources and samples, joint planning of experiments and regular meetings to review progress, visits by students to Applied Materials' laboratories, and mentorship of students by AMAT personnel.
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The project addresses basic research issues in a topical area of materials science with high technological relevance. The basic knowledge and understanding gained from the research is expected to contribute to improving electronic materials performance in current and future device and circuit applications. 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 multidisciplinary (materials science, electrical engineering) and industrially-connected nature of this FRG/GOALI program offers unique educational opportunities for students to experience a teamwork-oriented research environment from both academic and industrial perspectives. The project is co-funded by the Electronic Materials(EM) and Metals(MET) programs in DMR, the Mechanics And Structures of Materials program in ENG/CMS, and the ENG GOALI office.
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TECHNICAL EXPLANATION This collaborative award is made in response to proposals submitted to the FY05 NSF-EC Cooperative Activity in Computational Materials Research. The project involves the Ohio State University, Stanford University and Los Alamos National Laboratory in the US and collaborating institutions in Switzerland, Germany and the Netherlands. The aim of this cooperative activity is to develop and validate a computational approach to understand and predict unique plasticity phenomena at the nano and sub-micron scales. In recent years, a combination of advances in synthesis, characterization, and computational techniques has revealed striking plasticity phenomena that are not explained by traditional crystal plasticity theories or even more recent strain gradient theories. These phenomena are associated with shrinking sample size to the sub-micron regime and decreasing structural length scales such as grain size to the nano-scale regime. An exciting prospect is that new deformation regimes have been identified which, if understood, could enable the development of materials with unrivaled strength. Thus, the primary impact of the proposed work is an understanding of material strength at length scales not addressed by current plasticity theories. Such an activity is expected to impact our understanding of strength and work hardening in thin films and guide our understanding of appropriate material parameters for small-scale devices used in MEMS.

The high intellectual merit of this project derives from a goal to address the fundamental nature of plasticity posed by sub-micron and nano-scale samples, and from the creative process by which ab initio, atomistic, and Peierls approaches to computational materials science are used to support a direct comparison between dislocation dynamics level modeling and novel micro-pillar and in-situ x-ray diffraction verification techniques. The inadequacies of current plasticity theories, including strain gradient formulations, will be addressed via a systematic approach in which the kinetics of cross slip and role of free surfaces and grain boundaries as sources and sinks will be systematically studied. An exciting premise in this investigation is that sub-micron and nano-scale samples may derive extraordinary strength from "dislocation-starvation." A principle outcome is that the proposed, focused interaction among several computational techniques will provide the basis for a new plasticity theory for sub-micron and nano-scale components.

The broader impact of the project draws from the current industrial and scientific thrusts to understand the properties of small devices. The research is aimed at enabling small mechanical device design and development, by providing a computational tool base with which to predict the mechanical properties of components as size and structure are diminished to the sub-micron and nano-scale. Our computational and experimental findings will be packaged into an open web site for use by the academic and industrial communities - particularly those in the US and EC - and will set a precedent for comprehensive, accessible computational materials results at the sub-micron scale.

The educational impact will be enhanced by investigators who are commited to participation from under-represented groups, the unique educational exchange offered by an international collaboration, and a proposed series of web-based lectures to teach the basis of each of the computational materials methods to be used in this program.
NON-TECHNICAL EXPLANATION
This collaborative award is made in response to proposals submitted to the FY05 NSF-EC Cooperative Activity in Computational Materials Research. The project involves the Ohio State University, Stanford University and Los Alamos National Laboratory in the US and collaborating institutions in Switzerland, Germany and the Netherlands. The aim of this cooperative activity is to develop and validate a computational approach to understand and predict unique plasticity phenomena at the nano and sub-micron scales. In recent years, a combination of advances in synthesis, characterization, and computational techniques has revealed striking plasticity phenomena that are not explained by traditional crystal plasticity theories or even more recent strain gradient theories. These phenomena are associated with shrinking sample size to the sub-micron regime and decreasing structural length scales such as grain size to the nano-scale regime. An exciting prospect is that new deformation regimes have been identified which, if understood, could enable the development of materials with unrivaled strength. Thus, the primary impact of the proposed work is an understanding of material strength at length scales not addressed by current plasticity theories. Such an activity is expected to impact our understanding of strength and work hardening in thin films and guide our understanding of appropriate material parameters for small-scale devices used in MEMS.

The high intellectual merit of this project derives from a goal to address the fundamental nature of plasticity posed by sub-micron and nano-scale samples, and from the creative process by which ab initio, atomistic, and Peierls approaches to computational materials science are used to support a direct comparison between dislocation dynamics level modeling and novel micro-pillar and in-situ x-ray diffraction verification techniques. The inadequacies of current plasticity theories, including strain gradient formulations, will be addressed via a systematic approach in which the kinetics of cross slip and role of free surfaces and grain boundaries as sources and sinks will be systematically studied. An exciting premise in this investigation is that sub-micron and nano-scale samples may derive extraordinary strength from "dislocation-starvation." A principle outcome is that the proposed, focused interaction among several computational techniques will provide the basis for a new plasticity theory for sub-micron and nano-scale components.

The broader impact of the project draws from the current industrial and scientific thrusts to understand the properties of small devices. The research is aimed at enabling small mechanical device design and development, by providing a computational tool base with which to predict the mechanical properties of components as size and structure are diminished to the sub-micron and nano-scale. Our computational and experimental findings will be packaged into an open web site for use by the academic and industrial communities - particularly those in the US and EC - and will set a precedent for comprehensive, accessible computational materials results at the sub-micron scale.

The educational impact will be enhanced by investigators who are commited to participation from under-represented groups, the unique educational exchange offered by an international collaboration, and a proposed series of web-based lectures to teach the basis of each of the computational materials methods to be used in this program.