  This work combines the principles of the heat spreader method and imaging
capability of the thermoreflectance measurements to measure the in-plane
thermal conductivity of thin-films without the requirement of film suspension
or multiple thermometer deposition. We refer to this hybrid technique as heat
diffusion imaging. The thermoreflectance imaging system provides a temperature
distribution map across the film surface. The in-plane thermal conductivity can
be extracted from the temperature decay profile. By coupling the system with a
cryostat, we were able to conduct measurements from 40 K to 400 K. Silicon thin
film samples with and without periodic holes were measured and compared with
in-plane time-domain thermoreflectance (TDTR) measurement and literature data
as validation for heat diffusion imaging.
