Thermal analysis of submicron nanocrystalline diamond films

•A strategy to analyze NCD anisotropic thermal properties by SThM is proposed.•We examine thermal conductivity variations with thickness in columnar NCD films.•High thermal conductivities may be reached already in the submicron range.•The columnar structure enhances vertical transport compared to the lateral.

The thermal properties of sub-μm nanocrystalline diamond films in the range of 0.37–1.1 μm grown by hot filament CVD, initiated by bias enhanced nucleation on a nm-thin Si-nucleation layer on various substrates, have been characterized by scanning thermal microscopy. After coalescence, the films have been outgrown with a columnar grain structure. The results indicate that even in the sub-μm range, the average thermal conductivity of these NCD films approaches 400 W m− 1 K− 1. By patterning the films into membranes and step-like mesas, the lateral component and the vertical component of the thermal conductivity, klateral and kvertical, have been isolated showing an anisotropy between vertical conduction along the columns, with kvertical ≈ 1000 W m− 1 K− 1, and a weaker lateral conduction across the columns, with klateral ≈ 300 W m− 1 K− 1.