  Precise measurement of temperature distribution and thermal behavior in
microscopic regions is critical in many research fields. We demonstrate lock-in
thermography using nitrogen-vacancy centers in diamond nanoparticles. We
successfully visualize thermal diffusion in glass coverslip and Teflon with
micrometer resolution and deduce their thermal diffusivity. By spreading
diamond nanoparticles over the sample surface, temperature variation can be
measured directly without any physical contact, such as lead wires, making it
possible to visualize the micrometer-scale thermal behavior of various
materials.
