RESISTANCE BEHAVIOR OF ZINC-SULFIDE, ALUMINUM-NITRIDE, SILICON-CARBIDE AND POLYMETHYL METHACRYLATE UNDER ULTRAHIGH PRESSURE.

摘要

The single crystal diamond spherically-tipped indentor-flat anvil ultrahigh pressure generating systems was used to seek to observe insulator-to-metal transitions in ZnS, AlN, SiC and PMMA. ZnS was studied by a new non-shorting electrical resistance monitoring technique using the interdigitated electrodes. A metallic transition was observed at 14.0 (+OR-) 0.6 GPa, very close to existing reported values and thus demonstrating the feasibility of the new technique. Interdigitated electrodes with finger widths and spacings (both of d) of 12.5 (mu)m, 6 (mu)m and 3 (mu)m were used in the ZnS work. Electrodes with d = 0.5 (mu)m fabricated by electron beam lithography using PMMA as resist were used to seek to observe the metallic transition in AlN, theoretically predicted at 90 Gpa. Premature cracking of the r.f. reactive sputter deposited, brittle AlN films under moderate pressure broke the electrodes thus preventing meaningful resistance measurements at higher pressure. However, the coated method where thin metal films were deposited on both the indentor and the flat anvil to act as electrodes produced evidence that AlN remained insulating up to at least 59 GPa. Studies on detached thin films of SiC in the multilayer configuration with the coated method indicated that SiC remained an excellent insulator up to a least 72 GPa. Studies at higher pressures were prohibited by the fracture of the brittle film resulting in electrical shorts. Interdigitated electrodes with a d = 1.25 (mu)m were also used in the SiC work. This indicated that SiC was insulating up to at least 63 GPa. Pressurization of PMMA showed that PMMA remained highly insulating up to 100 GPa.