J. S. Bow

Thin film Ti/6H-SiC interfacial reaction : high spatial resolution electron microscopy study

Abstract The structure and chemistry of thin Ti films on Si-terminated vicinal (0001) α-SiC substrates was investigated by high-resolution imaging and high-spatial-resolution nanospectroscopy. The Ti was deposited on in-situ cleaned SiC substrates under UHV conditions by evaporation; subsequent post-deposition heat treatments were also performed under UHV conditions. Examination of as-deposited interfaces showed that Ti deposited epitaxially with basal plane/close-packed direction alignment on the substrate. No reaction zone was visible and the interface was chemically sharp. Lattice misfit was accomodated by interface dislocations. Post-deposition heat treatment at 700°C caused formation of Ti5Si3 and TiC reaction products at the Ti/SiC interface. The reaction product morphology was complex and dependent on reaction time. For short times (≈ 20 min) parabolic rate kinetics were obeyed, but for longer times (≈ 60 min) formation of Ti5Si3 dominated and the rate decreased. HREM image contrast of SiC, Ti5Si3 and TiC varied with position near the interfaces. Preliminary theoretical calculations indicated these apparent changes in structure resulted from local changes in orientation and thickness.

Chemical Widths at Composite Interfaces: Relationships to Structural Widths and Methods for Measurement.

Energy selected imaging with a Zeiss 912 {Omega}-filter TEM was used to examine grain boundary solute distributions in an Si{sub 3}N{sub 4}/SiC(w) ceramic densified with Y{sub 2}O{sub 3} + Al{sub 2}O{sub 3} sintering aid. These results are compared to boundary region solute distributions in the same materials determined by field emission small probe electron energy loss spectroscopy and related methods. The intrinsic higher incident flux of the FEG small probe methods renders them the most useful for high spatial resolution local chemical width measurement. Energy selected imaging is fast and relatively simple for determining elemental distributions in boundaries at low magnifications. The methods are complementary.