  Nanoscale thermal properties are becoming of extreme importance for modern
electronic circuits that dissipate increasing power on the length scale of few
tens of nanometers, and for chemical and physical properties sensors and
biosensors using nanoscale sized features. While Scanning Thermal Microscopy
(SThM) is known for its ability to probe thermal properties and heat generation
with nanoscale resolution, until today it was perceived impossible to use it in
the liquid environment due to dominating direct heat exchange between
microfabricated thermal probe and surrounding liquid that would deteriorate
spatial resolution. Nonetheless, our theoretical analysis of SThM in liquids
showed that for certain design of SThM probe with resistive heater located near
the probe tip, their thermal signal is only moderately affected, by less than
half on immersion in a dodecane environment. More significantly, its spatial
resolution, surprisingly, would remain practically unaffected, and the thermal
contact between the tip apex and the studied sample would be beneficially
improved. Our experimental trials of such immersion SThM, or iSThM, were fully
successful and here we report for the first time nanoscale SThM measurements of
thermal conductivity of Ultra Large Scale Integration polymerceramic metal
interconnects with the spatial thermal resolution down to 50 nm. Further
studies of heat transport in nanoscale graphite flakes in iSThM suggested, in
particular, that highly anisotropic thermal conductivity in graphene layers may
play significant role in the nanoscale thermal transport in liquid environment.
New iSThM opens a wide range of applications from noncontact measurements of
thermal transport in semiconductor devices to exploring graphene energy
storage, catalytic reactions and heat generation in biological systems.
