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Materials Science and Engineering: Nanoscience and Technology
^ High-Speed, Monolayer-Sensitivity Scanning Microcalorimetry for Solid-Solid Interface and Surface Studies
L. H. Allen,* G. Ramanath, S. Lai
National Science Foundation, DMR 94-19604

(Conducted in the Coordinated Science Laboratory)

Researchers are developing a new technique that is potentially a very powerful method for directly obtaining quantitative values for small enthalpy of reactions at interfaces, surfaces, and near surface regions. This microcalorimeter is expected to have high sensitivity, capable of measuring extremely small amounts of heat generated during solid/solid reactions and surface processes as well as low enthalpy of internal microcrystalline processes. This technique will be useful for measuring the kinetics of interface reactions, such as the nucleation of silicides at buried interfaces, and the study of near-surface processes, such as point-defect annihilation and coalescence of vacancies in Si following ion implantation.

^ Materials Processes Far from Equilibrium
R. S. Averback*
U.S. Department of Energy, DE-FG02-91ER45439

(In cooperation with the Frederick Seitz Materials Research Laboratory)

Fundamental aspects of properties of materials driven far from equilibrium by high energy methods are investigated. These studies include the processing of nanocomposite materials for high strength magnets. Ion beam processing is employed for thin film magnets and mechanical milling is used for bulk nanocomposite magnets. Ion beams are also employed for nanopatterning thin metal films on dielectric substrates for catalysis, magnetic, and optical applications. The work combines computer simulation and in situ experimentation using a scanning probe method and electron microscopy.

^ Kinetic Processes on TiN Surfaces
D. G. Cahill,* J. E. Greene,* M. Wall
U.S. Department of Energy, DE-FG02-91ER45439

TiN is a critical thin-film material in the microelectronics and cutting tool industries. Researchers use reactive magnetron sputtering to deposit epitaxial TiN on lattice matched MgO substrates and apply scanning tunneling microscopy to measure fundamental aspects of the surface kinetics (the diffusion of adatoms, the nucleation of new terraces, the stability of small clusters, and asymmetries in the attachment of adatoms at ascending versus descending steps). These data are then used to understand more complex issues in the growth of polycrystalline films, such as the selection of preferred orientation and competitive grain growth.

^ Laser Modification of Surface Morphology
D. G. Cahill,* T. Schwarz-Selinger, J. Serrano
U.S. Department of Energy, DE-FG02-91ER45439

Researchers are studying the mechanisms of laser texturing of semiconductor crystals. Tightly focused, single pulses from a passively Q-switched microchip laser are used to produce laser dimples with a radius of ~ 2mm and a depth that can be varied over a range of 10–500 nm. The strong temperature gradient produces a gradient in the surface tension that drives fluid flow in the laser melt. Si wafers modified by laser texturing are then applied in experiments on the nucleation of epitaxial nanostructures and fundamental studies of mass transport and step motion using low-energy electron microscopy (LEEM).

^ Nanostructures by Ion-Beam Induced Dewetting
D. G. Cahill,* R. S. Averback,* X. Hu
U.S. Department of Energy, DE-FG02-91ER45439

A planar metal film prepared on a dielectric substrate is typically metastable and will dewet from the substrate at elevated temperatures. Researchers use energetic heavy ions (800 keV Kr+) as a novel means of producing localized melting of nanometer-thick metal films deposited on silica and sapphire. A nanostructured film results from the short time scale and length scale of the ion-beam induced thermal spikes. Researchers are investigating the mechanisms that control the rate of dewetting, the in-plane length scale of the pattern formation, and the eventual sinking of metal nanoparticles into an amorphous substrate due to viscous flow.

^ Nanoscale Cluster Assembly on Compliant Substrates: A New Route to Epitaxy and Nanostructure Synthesis
J. H. Weaver,* C. Haley, D. Xu
U.S. Department of Energy, DE-FG02-91ER45439

This project focuses on the intrinsic properties of three-dimensional nanostructures and on their behavior when they come in contact with other materials. It exploits a unique soft-landing cluster deposition technique that the research team developed to synthesize nanostructures, deliver them to atomically clean surfaces, and explore fundamental issues related to stability, wetting, interface reactions, and passivation. Investigations like these are critical if we are to understand processes associated with nanostructure integration into mesoscopic structures. While the growth process has been demonstrated in this project, researchers have just begun to exploit its capabilities. Through this project, researchers are now concentrating on structural aspects associated with cluster assembly, as probed with scanning tunneling microscopy and electron microscopy.

^ Controlled Growth of Nanostructures in a UHV Transmission Electron Microscope
J. M. Zuo,* B. Q. Li, Y. F. Shi
U.S. Department of Energy, DE-FG02-91ER45439; University of Illinois

(In cooperation with the Frederick Seitz Materials Research Laboratory)

Researchers use a specially built UHV transmission electron microscope to study the growth conditions and substrate effects on nanostructure formations grown by molecular beam epitaxy, or gas reaction. In-situ real-time electron imaging and electron diffraction are used to extract structural information or examine structural morphology.

^ Nanodiffraction and Nanocrystallography
J. M. Zuo,* R. D. Twesten, I. Petrov
U.S. Department of Energy, DE-FG02-91ER45439

(In cooperation with the Frederick Seitz Materials Research Laboratory)

Nanoscience requires nano-characterization. Most conventional characterization techniques are sensitive to either large surface areas or bulk volumes. The challenge is how to determine individual nanostructure that could be significantly different from each other. To face this challenge, researchers are developing new electron beam characterization techniques that take advantage of the nanometer sized electron probe and the strong interaction of electrons with matter that would enable determination of structure, composition, and electronic states of individual nanostructures. The project is based on a newly installed, state-of-the-art field emission gun electron microscope, JEOL2010F, in collaboration with the DOE Center for Microanalysis of Materials (CMM).


Summary of Engineering Research