Saturable Absorption of Free-Electron Laser Radiation by Graphite near the Carbon K-Edge
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Engineering topics
Principi, Emiliano
Publications and source records attributed to Principi, Emiliano.
Angstrom-Resolved Interfacial Structure in Buried Organic-Inorganic Junctions
Charge transport processes at interfaces which are governed by complex interfacial electronic structure play a crucial role in catalytic reactions, energy storage, photovoltaics, and many biological processes. Here, the first soft X-ray second harmonic generation (SXR-SHG) interfacial spectrum of a buried interface (boron/Parylene-N) is reported. SXR-SHG shows distinct spectral features that are not observed in X-ray absorption spectra, demonstrating its extraordinary interfacial sensitivity. Comparison to electronic structure calculations indicates a boron-organic separation distance of 1.9 {\AA}, wherein changes as small as 0.1 {\AA} result in easily detectable SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast and sensitive to individual atomic layers, it creates the possibility to study a variety of interfacial processes, e.g. catalysis, with ultrafast time resolution and bond specificity.
74 ATOMIC AND MOLECULAR PHYSICS↗
Free Electron Laser Measurement of Liquid Carbon Reflectivity in the Extreme Ultraviolet
Ultrafast time-resolved extreme ultraviolet (EUV) reflectivity measurements of optically pumped amorphous carbon (a-C) have been performed with the FERMI free electron laser (FEL). This work extends the energy range used in previous reflectivity studies and adds polarization dependence. The EUV probe is known to be sensitive to lattice dynamics, since in this range the reflectivity is essentially unaffected by the photo-excited surface plasma. The exploitation of both s- and p-polarized EUV radiation permits variation of the penetration depth of the probe; a significant increase in the characteristic time is observed upon increasing the probing depth (1 vs. 5 ps) due to hydrodynamic expansion and consequent destruction of the excited region, implying that there is only a short window during which the probed region is in the isochoric regime. A weak wavelength dependence of the reflectivity is found, consistent with previous measurements and implying a maximum electronic temperature of 0.8 eV ± 0.4.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗