Thermal transport from nanostructured heat sources on diamond probed using coherent extreme ultraviolet beams*

Nanostructured materials can exhibit properties unattainable in bulk materials, with applications in next-generation energy efficient devices. However, macroscopic, diffusive transport models break down at length scales comparable to the mean free path of a material’s dominant heat carriers. Moreover, there are few characterization techniques that can probe functional nanosystems. Here, we use short wavelength (~30nm), ultrafast (~10fs) extreme ultraviolet (EUV) beams to nondestructively probe thermal transport away from nanoscale heat sources on diamond. Diamond is a promising material for diodes, high strength coatings, and integrated circuits—and is of special interest for quantum communication and memory. We impulsively heat nickel nano-gratings fabricated on a diamond substrate with an infrared pump laser and quantify the heat transport efficiency by monitoring the surface deformation using a time-delayed EUV probe. We use our experimental results to develop and validate a predictive hydrodynamic transport model and investigate the respective roles played by diamond’s intrinsic scattering environment and the nickel-diamond interface. Additionally, we spatially analyze non-diffusive cooling processes using individual diffracted orders in the scattered EUV probe.