Quantification of atomic force microscopy tip and sample thermal contact

A thermal conduction measurement device was fabricated, consisting of a silicon dioxide membrane with integrated thermal sensors (Pt resistance heater/thermometer and Pt–Au thermocouples) using MEMS technology. Heat transfer between the heated device and a number of unused atomic force microscope and scanning thermal microscope probes was measured. Changes in thermal conduction related to changes in the tip shape resulting from initial contact were observed. The sensors were fabricated by electron beam lithography and lift-off followed by local subtractive processing of a Pt–Au multilayer to form Pt heater–resistance thermometer elements and Pt–Au thermocouples. Thermal isolation from the silicon substrate was provided by dry release of the supporting 50 nm thick SiO₂ membrane using an isotropic SF6 inductively coupled plasma etch. The high thermal isolation of the sample combined with the sensitivity of the temperature sensors used allowed the detection of thermal conduction between the tip and the sample with high precision. The measured temperature range of the Pt resistor was 293–643 K. The measured thermal resistance of the membrane was 3 × 10⁵ K/W in air and 1.44 × 10⁶ K/W in vacuum. The tip contact resistance was measured with a noise level of 0.3g₀ T at room temperature, where g₀ is the thermal resistance quantum.