AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP28
Structure of the (0001) Surface of Hafnium and Hafnium Diboride and of Epitaxial Thin Films of Hafnium Diboride Grown on Hafnium

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: R. Singh, University of Illinois, Chicago
Authors: R. Singh, University of Illinois, Chicago
C.L. Perkins, University of Illinois, Chicago
M. Belyansky, University of Illinois, Chicago
M. Trenary, University of Illinois, Chicago
Correspondent: Click to Email
Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED) have been used to investigate the surface structure of single crystals of Hf, HfB@sub 2@, and epitaxial thin films of HfB@sub 2@ grown on a Hf substrate through the thermal decomposition of diborane. A comparison of the properties of HfB@sub 2@(0001) and Hf(0001) is of interest because the topmost atomic layer of both surfaces consists of a close-packed two-dimensional array of Hf atoms with lattice constants that differ by only 1.7%. In the bulk structure of HfB@sub 2@, the (0001) Hf atom planes are hexagonal close-packed and are separated by 0.348 nm. A graphite-like honeycomb lattice of boron atoms lies between the Hf planes. A clean well-annealed HfB@sub 2@(0001) surface is found to consist of Hf-terminated terraces separated by 0.35 nm with no boron layers exposed. When the HfB@sub 2@ sample is not well-annealed or when contamination is present, reconstructed surfaces are observed with both LEED and STM, including a (3x3) structure induced by carbon. The Hf(0001) surface consists of flat (0001) terraces separated by monoatomic steps 0.25 nm in height. The high reactivity of the group IV metals is reflected in the difficulty in obtaining contamination free images of the Hf surface. From the determination of the basic structural features of the HfB@sub 2@ and Hf surfaces by STM, patches of Hf and HfB@sub 2@ can be clearly distinguished in STM images acquired during different stages in the growth of epitaxial thin films of HfB@sub 2@ on a Hf substrate. The thin film growth mechanism can thereby be inferred from such images.