MEASURING LOCAL THERMAL-CONDUCTIVITY IN POLYCRYSTALLINE DIAMOND WITH A HIGH-RESOLUTION PHOTOTHERMAL MICROSCOPE

A photothermal microscope that provides micrometer lateral and submicr ometer depth resolution was designed. Thermal conductivity measurement s with modulation frequencies up to 12 MHz on single grains in polycry stalline diamond demonstrate its lateral resolution power even for a h ighly conducting material. Measured conductivities strongly depend on the averaged volume and values up to 2200 W/mK are found in the high f requency limit where: the properties inside a grain are sampled. The c apability of the instrument to measure thermal parameters on thin film s is demonstrated for gold films evaporated on quartz with a thickness ranging from 20 to 1500 nm. Measurements reveal a strong thickness de pendence for both thin film conductivity and the contact resistance be tween film and substrate. Thermal conductivity decreases monotonically from 230 to 30 W/mK whereas the contact resistance rises from 2 x 10( -7) to 8 x 10(-6) m(2)K/W with decreasing film thickness. (C) 1997 Ame rican Institute of Physics.