Probing Nanoscale Heat Transport in Liquid Environments—Contact and Non-Contact Immersion Scanning Thermal Microscopy (iSThM)

Operation of Scanning Thermal Microscopy (SThM) [1] in liquid environment probing thermal phenomena with nanoscale resolution could open unique opportunities for studies of biological materials, processes in the rechargeable energy storage and catalysis. Until recently such SThM operation would be deemed fully impossible, due to dominating heat dissipation from the heated probe into the surrounding liquid that thought to drastically deteriorate both the sensitivity of the probe and its spatial resolution. Nevertheless, Tovee and Kolosov [2] showed that such immersions SThM, or iSThM, is not only possible for the certain widely used type of the probe (Kelvin Nanotechnology, Scotland), but also opens the possibility to make nanoscale mapping of the heat transport with the near-field operation of SThM. Here we show that the presence of liquid provides highly stable thermal contact between the probe tip and the sample eliminating one of the major drawbacks of the ambient or vacuum SThM’s – variability of such contact. iSThM can effectively observe the semiconductor devices and 2D materials with the resolution of few tens of nanometres, providing new tool for exploring thermal effects of chemical reactions and biological processes with nanoscale resolution. Using finite element modeling analysis we show that selecting suitable thermal conductivity of the liquid allows to to significantly enhance contrast of iSThM for the particular material. We also experimentally demonstrate that by applying of the ultrasonic vibration to the probe and by detecting a shear response of the probe it is possible to achieve near – non-contact iSThM paving the way for efficient zero-damage nanoscale thermal probing