A pre-time-zero spatiotemporal microscopy technique for the ultrasensitive determination of the thermal diffusivity of thin films

Abstract

Diffusion is one of the most ubiquitous transport phenomena in nature. Experimentally, it can be tracked by following point spreading in space and time. Here, we introduce a spatiotemporal pump-probe microscopy technique that exploits the residual spatial temperature profile obtained through the transient reflectivity when probe pulses arrive before pump pulses. This corresponds to an effective pump-probe time delay of 13 ns, determined by the repetition rate of our laser system (76 MHz). This pre-time-zero technique enables probing the diffusion of long-lived excitations created by previous pump pulses with nanometer accuracy, and is particularly powerful for following in-plane heat diffusion in thin films. In contrast to existing techniques for quantifying thermal transport it does not require any material input parameters or strong heating. We demonstrate the direct determination of the thermal diffusivities of the layered materials MoSe${}_2$ (0.18 cm${}^2$/s), WSe${}_2$ (0.20 cm${}^2$/s), MoS${}_2$ (0.35 cm${}^2$/s), and WS${}_2$ (0.59 cm${}^2$/s). This technique paves the way for observing novel nanoscale thermal transport phenomena and tracking diffusion of a broad range of species.

References in corpus (11)

• Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2
• Extraordinary room-temperature photoluminescence in WS2 monolayers
• Length-dependent thermal conductivity in suspended single-layer graphene
• Excitonic linewidth and coherence lifetime in monolayer transition metal dichalcogenides
• Optical Limiting and Theoretical Modelling of Layered Transition Metal Dichalcogenide Nanosheets
• Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2
• Exciton diffusion in two-dimensional metal-halide perovskites
• Tracking ultrafast hot-electron diffusion in space and time by ultrafast thermo-modulation microscopy
• Thermal expansion and transport in van der Waals solids from first-principles calculations
• Ambipolar diffusion of photo-excited carriers in bulk GaAs
• Observation of giant and tuneable thermal diffusivity of Dirac fluid at room temperature

Cited by in corpus (1)

• Detecting, distinguishing, and spatiotemporally tracking photogenerated charge and heat at the nanoscale