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±0.1 Å, wherein changes as small as 0.1 Å 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.
This work was done in collaboration with researchers from the Saykally group at UCB, LBNL, UC San Diego, SLAC, and FERMI. The experiments were conducted at the free-electron laser facility FERMI in Italy.
Our paper was now published in Physical Review Letters:
In this work, we utilize XUV-SHG spectroscopy to investigate the polar metal phase of LiOsO3, where the coexistence of polarity and metallicity is unexpected since the itinerant conducting electrons in metals are expected to screen out long-range electrostatic forces that typically stabilize a permanent polarization. This is one of the first uses of nonlinear X-ray spectroscopy to investigate a material across a phase transition. A sensitivity to broken inversion symmetry appears above the Li K-edge, with theory showing how the spectrally-resolved SHG varies with Li-displacement. As the first demonstration of XUV-SHG spectroscopy around a phase transition, these results pave the way for using nonlinear XUV methods to investigate broken symmetry from an element-specific perspective.
Congratulations to Emma for her first author paper, and Angelique and Can for their first paper in the group. Also, we are excited for Clarisse’ first paper, who contributed to this work during her NSF-REU visit last summer.
This work was done in collaboration with researchers from LBNL, UC San Diego, Argonne National Laboratory, Penn State, and the University of Tokio. The experiments were conducted at the free-electron laser facility SACLA in Japan.
Our paper appeared in Nano Letters (open access) and was selected as cover featured article:
College of Chemistry news release:
We had our first retreat as a group and went hiking two days in Yosemite National Park. Giant Sequoias, Glacier Point and several waterfalls were explored. Despite 103 degrees, it has been a very memorable retreat.