Anomalous Resolutions in Scanning Thermal Microscopy of Graphite

The local thermal conductivity of various kinds of graphite surfaces has been investigated by scanning thermal microscopy (SThM) on a scale comparable to the size of a SThM probe. SThM operates under a constant force feedback and scans a sample surface with a resistive wire which makes direct contact with the surface. The probe consists of a bent platinum wire of 5 μm in diameter. The surface topography of the same sample is also studied by atomic force microscopy (AFM) using silicon cantilevers. Highly oriented pyrolytic graphite shows large flat terraces by AFM and large areas of uniform conductivity by SThM. Various graphite films made by chemical vapor deposition exhibit different AFM images unique to each sample but contain a stack of flat graphite plates as a common element. The overall features of SThM images agree with those of the AFM images of the corresponding sample. In addition to this similarity on the micrometer scale, SThM shows complex fine structures as small as 50 nm wide, which are not detected by AFM. We propose that a complex SThM feature results from a depth-probing characteristic of SThM and that the anomalous high resolution is due to contamination-assisted sharpening of the probe.