GOALI: Phase Stabilities of Rare Earth Metal Silicides and the Growth of Silicide Nanowires

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

This GOALI project is a study of the phase stabilities of rare earth metal silicides and the growth of nanowires on preferred directions along a silicon substrate. Many rare earth metals react with silicon to form disilicides exhibiting the same crystal structure as that of erbium disilicide. The < 0211 > direction of the silicides often has a negative lattice mismatch with one of the <110> directions of the Si. Disilicides of Er, Ho and Dy have such a lattice mismatch. Other rare metal disilicides, such as disilicides of Sm, Gd, and Tb, exhibit a positive lattice mismatch. The mismatch along the c-axis of these disilicides with the perpendicular <110> direction of Si is always positive. This project examines the compositional stabilities of ternary rare earth metal silicides in the solid state at 650C by determining ternary phase relationships. Taking advantage of the chemical similarity of the rare earth metals, an efficient approach is outlined for determining the ternary phase equilibria, including the compositional stability of the disilicides. Since nanowire growth takes place at high temperatures and the coefficients of thermal expansion of these silicides are expected to be different from that of Si, the coefficients of thermal expansion of these disilicides are measured as a function of temperature and alloy composition by high-temperature x-ray diffraction. These investigations are carried out at UW-Madison. Each year of the grant, two or more of the researchers working at UW-Madison will spend time at Hewlett-Packard Laboratory to carry out nanowire growth and characterization with access to HP's expertise and facilities. On the basis of this combined study, appropriate conditions for growing ternary silicide nanowires with optimal lattice mismatch will be determined. %%% The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to important fabrication aspects of electronic/photonic devices. An important feature of the program is the integration of research and education through graduate student and post doctoral training in a fundamentally and technologically significant area. A post doctoral research associate and a graduate student will spend time each year of the project working on site at Hewlett-Packard Laboratory benefitting from the Industrial collaboration staff expertise and facilities and instrumentation available at HP. The availability of unique instrumentation and facilities, and direct intellectual interaction with HP staff provides invaluable educational opportunities and perspectives, and fosters the integration of research and education. The project is co-supported by the DMR/Metals and Electronic Materials programs and the MPS OMA(Office of Multidisciplinary Activities). ***