The origin of the almost unique combination of optical transparency and the ability to bipolar dope tin monoxide is explained using a combination of soft and hard Xray photoemission spectroscopy, O K-edge X-ray emission and absorption spectroscopy, and density functional theory calculations incorporating van der Waals corrections. We reveal that the origin of the high hole mobility, bipolar ability, and transparency is a result of (i) significant Sn 5s character at the valence band maximum (due to O 2p−Sn 5s antibonding character associated with the lone pair distortion), (ii) the combination of a small indirect band gap of ∼0.7 eV (Γ−M) and a much larger direct band gap of 2.6−2.7 eV, and (iii) the location of both band edges with respect to the vacuum level. This work supports Sn 2+ -based oxides as a paradigm for nextgeneration transparent semiconducting oxides.

Despite mounting evidence that materials imperfections are a major obstacle to practical applications of superconducting qubits, connections between microscopic material properties and qubit coherence are poorly understood. Here, we combine measurements of transmon qubit relaxation times (T1) with spectroscopy and microscopy of the polycrystalline niobium films used in qubit fabrication. By comparing films deposited using three different techniques, we reveal correlations between T1 and intrinsic film properties such as grain size, enhanced oxygen diffusion along grain boundaries, and the concentration of suboxides near the surface. Qubit and resonator measurements show signatures of two-level system defects, which we propose to be hosted in the grain boundaries and surface oxides. We also show that the residual resistance ratio of the polycrystalline niobium films can be used as a figure of merit for qubit lifetime. This comprehensive approach to understanding qubit decoherence charts a pathway for materials-driven improvements of superconducting qubit performance.

We determined the shifts in the energy levels of approximately 15 nm thick poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] films deposited on various substrates including self-assembled monolayer (SAM) modified Au surfaces using photoelectron spectroscopy. As the unmodified substrates included Au, indium tin oxide, Si (with native oxide), and Al (with native oxide), a systematic shift in the detected energy levels of the organic semiconductor was observed to follow the work function values of the substrates. Furthermore, we used polar SAMs to alter the work function of the Au substrates. This suggests the opportunity to control the energy level positions of the organic semiconductor with respect to the electrode Fermi level. Photoelectron spectroscopy results showed that, by introducing SAMs on the Au surface, we successfully increased and decreased the effective work function of Au surface. We found that in this case, the change in the effective work function of the metal surface was not reflected as a shift in the energy levels of the organic semiconductor, as opposed to the results achieved with different substrate materials. Our study showed that when a substrate is modified by SAMs (or similarly by any adsorbed molecules), a new effective work function value is achieved; however, it does not necessarily imply that the new modified surface will behave similar to a different metal where the work function is equal to the effective work function of the modified surface. Various models and their possible contribution to this result are discussed.

We find a new 5 eV satellite in the Ti 1s photoelectron spectrum of the transition-metal oxide SrTiO 3 . This satellite appears in addition to the well-studied 13 eV structure that is typically associated with the Ti 2p core line. We give direct experimental evidence that the presence of two satellites is due to the crystal-field splitting of the metal 3d orbitals. They originate from ligand 2p t 2g → metal 3d t 2g and ligand 2p e g → metal 3d e g monopole charge-transfer excitations within the sudden approximation of quantum mechanics. This assignment is made by the energetics of the resonant and high-energy threshold behaviors of the Ti K-L 2 L 3 Auger decay that follows Ti 1s photo-ionization.