研究目的
Investigating the electronic and lattice contributions to picosecond time-resolved X-ray absorption spectra of CuO at the oxygen K-edge, and analyzing the effects of laser excitation on lattice temperature dynamics.
研究成果
Photoinduced changes in CuO XAS spectra beyond 150 ps are dominated by lattice heating effects. The thermal dynamics are well described by a one-dimensional diffusion model for 532 nm excitation, yielding a thermal conductivity of (1.3±0.4) W m–1 K–1, similar to CuO powder. The findings emphasize the importance of understanding depth-dependent profiles for accurate thermal modeling in trXAS experiments, with implications for mitigating thermal effects in future high-repetition-rate XFEL studies.
研究不足
For 355 nm excitation, large temperature gradients within the probed volume hinder quantitative analysis. The thermal conductivity values may be affected by sample morphology and extrapolation uncertainties. The study is limited to CuO films and specific excitation conditions.
1：Experimental Design and Method Selection:
The study uses optical-pump – X-ray-probe picosecond trXAS setup at beamline 8 of the Advanced Light Source (ALS). Pump-probe experiments are performed at two different photon energies (355 nm and 532 nm) with varying fluences. Steady-state temperature-dependent XAS measurements complement the trXAS data. A one-dimensional thermal diffusion model is employed to analyze heat transport.
2：Sample Selection and Data Sources:
CuO films are generated by thermal surface oxidation of copper sheets. Samples are raster-scanned to mediate damage. Data include trXAS spectra at multiple time delays and XAStemp spectra at temperatures from 22°C to 145°C.
3：List of Experimental Equipment and Materials:
Equipment includes a mobile laser-pump – X-ray-probe setup, ALS beamlines (8.0.1.2 and 11.0.2), laser system with 10 ps FWHM pulses at 355 nm and 532 nm, time-sensitive micro-channel plate detector, photodiode with Al filter, button heater stage, thermocouple. Materials include CuO samples, oxygen gas at 3 mTorr.
4：2 and 2), laser system with 10 ps FWHM pulses at 355 nm and 532 nm, time-sensitive micro-channel plate detector, photodiode with Al filter, button heater stage, thermocouple. Materials include CuO samples, oxygen gas at 3 mTorr.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Samples are excited with laser pulses and probed with X-ray pulses. Time-dependent oxygen K-edge absorption spectra are recorded in total fluorescence yield mode. Difference spectra ΔtrXAS and ΔXAStemp are calculated. Data are analyzed using convolution methods and thermal diffusion simulations.
5：Data Analysis Methods:
Data analysis involves energy resolution matching via Gaussian convolution, linear interpolation and extrapolation of XAStemp spectra, and fitting procedures (homogeneous and inhomogeneous models) to derive temperature profiles and thermal conductivity. Statistical techniques include minimization of residuals.
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