l w c

9ally mounted on a micro cantilever of an atomic force microscope ~AFM! probe so that tip-sample constant contact force is main-tained by the force feedback loop of the AFM. While the tip scans on a sample, tip-sample heat transfer changes the tip temperature, which is measured and used to calculate the temperature or ther-mal properties of the sample at the tip-sample contact. SThM has been used to locate ‘‘hot spots’ ’ in electronic devices and to image contrast in thermal properties of composite thin film materials @3#. In both cases, qualitative rather than quantitative results have been obtained. To accurately interpret a temperature map or a thermal property image obtained by SThM, a thorough understanding of heat transfer mechanisms at the tip-sample con-tact is required. The knowledge of heat transfer at micro or nano-scale contacts is, however, still limited @3,7,8#. Figure 1 shows the schematic diagram of a SThM tip in contact with a sample sur-face. Also shown are the various heat transfer mechanisms. The temperature sensor is a thin-film metal thermocouple junction fab-ricated at the end of the tip. The various tip-sample heat transfer mechanisms include solid-solid conduction at the contact, conduc-interpreting the thermal imaging results and for further improving the technique. In the following sections, we will ~i! present several experiments for characterizing the heat transfer mechanisms at the nanoscale tip-sample point contact; ~ii! describe a model consid-ering various microscale heat transfer mechanisms for extracting point contact thermal resistance from the experimental data; and ~iii! discuss the relative contribution of various conduction mecha-nisms under different conditions. Experiments Figure 2 shows the cross section and scanning electron micro-graphs of one of the thermal probes that we have thermally-designed and batch-fabricate