# Transient heating of Pd nanoparticles studied by x-ray diffraction with time of arrival photon detection

## TL;DR

Researchers used x-ray diffraction to study how Pd nanoparticles heat up and cool down rapidly when exposed to laser pulses.

## Contribution

The study introduces a novel time-of-arrival photon detection method for measuring transient heating in nanoparticles without scanning pump-probe delays.

## Key findings

- Pd nanoparticles heat up by at least 100 K within nanoseconds of laser excitation.
- Cooling of the nanoparticles occurs over 90 ns, slower than expected due to the low thermal conductivity of the oxide support.
- The experimental setup achieved a time resolution of 15 ± 5 ns, closely matching the laser pulse duration.

## Abstract

Pulsed laser heating of an ensemble of Pd nanoparticles, supported by a MgO substrate, is studied by x-ray diffraction. By time-resolved Bragg peak shift measurements due to thermal lattice expansion, the transient temperature of the Pd nanoparticles is determined, which quickly rises by at least 100 K upon laser excitation and then decays within 90 ns. The diffraction experiments were carried out using a Cu x-ray tube, giving continuous radiation, and the hybrid pixel detector Timepix3 operating with single photon counting in a time-of-arrival mode. This type of detection scheme does not require time-consuming scanning of the pump-probe delay. The experimental time resolution is estimated at 15 ± 5 ns, which is very close to the detector's limit and matches with the 7 ns laser pulse duration. Compared to bulk metal single crystals, it is discussed that the maximum temperature reached by the Pd nanoparticles is higher and their cooling rate is lower. These effects are explained by the oxide support having a lower heat conductivity.