Effect of diamond surface orientation on the thermal boundary conductance between diamond and aluminum

[100] and [111] oriented diamond substrates were treated using Ar:H and Ar:O plasma treatments, and 1:1 HNO3:H2SO4 heated at 200 °C. Subsequent to these treatments, an aluminum layer was either evaporated or sputteredon the substrates. The thermal boundary conductance (TBC) as well as the interfacial acoustical reflection coefficient between this layer and the diamond substrate was then measured using a Time Domain ThermoReflectance (TDTR) experiment. For the Ar:H plasma treated surfaces the [111] oriented faces exhibited conductances 40% lower than the [100] oriented ones with the lowest measured TBC at 32 ± 5 MWm− 2 K− 1. The treatments that led to oxygen-terminated diamond surfaces (extiti.e. acid or Ar:O plasma treatments) showed no TBC anisotropy and the highest measured value was 230 ± 25 MWm− 2 K− 1 for samples treated with Ar:O plasma with a sputtered Al layer on top. Sputtered layers on oxygen-terminated surfaces showed systematically higher TBC than their evaporated counterparts. The interfacial acoustic reflection coefficient correlated qualitatively with TBC when comparing samples with the same type of surface terminations (O or H) but this correlation failed when comparing H and O terminated interfaces with each other.