A new nanofabrication procedure has been developed for making thermocouple probes for high-resolution scanning thermal microscopy. Thermocouple junctions were placed at the end of SiN x cantilever probe tips and were typically 100-500 nm in diameter. Cantilever bending due to thermal expansion mismatch was minimized for Au-Ni, Au-Pt, and Au-Pd thermocouples, by carefully choosing thermal probe materials, film thicknesses, and deposition conditions. A spatial resolution of 24 nm was demonstrated for thermal microscopy although the noise-equivalent limit of 10 nm was estimated from experimental data. Using thermopower measurements, a simple model was developed to calculate the tip-sample thermal resistance. Model-based calculations, correlations between topographical and thermal features, as well as experiments in different gaseous and humidity environments indicate that the dominant tipsurface heat conduction is most likely through a liquid film bridging the tip and the sample surface, and not through the surrounding gas, solid-solid point contact, or near-field radiation. Dynamic measurements within a 100 kHz bandwidth showed a time constant of about 0.15Ϯ0.02 ms which was attributed to the thermal time constant of the whole cantilever. Calculations suggested the RC electrical time constant and the thermal time constant of the thermocouple junction to be on the order of 10 ns which, however, could not be experimentally probed.

No abstract

Heat conduction between two parallel solid walls separated by liquid argon is investigated using three-dimensional molecular dynamics (MD) simulations. Liquid argon molecules confined in silver and graphite nano-channels are examined separately. Heat flux and temperature distribution within the nano-channels are calculated by maintaining a fixed temperature difference between the two solid surfaces. Temperature profiles are linear sufficiently away from the walls, and heat transfer in liquid argon obeys the Fourier law. Temperature jump due to the interface thermal resistance (i.e., Kapitza length) is characterized as a function of the wall temperature. MD results enabled development of a phenomenological model for the Kapitza length, which is utilized as the coefficient of a Navier-type temperature jump boundary condition using continuum heat conduction equation. Analytical solution of this model results in successful predictions of temperature distribution in liquid-argon confined in silver and graphite nano-channels as thin as 7 nm and 3.57 nm, respectively.