RESUMO
Progress in superconducting device and detector technologies over the past decade has realized practical applications in quantum computers, detectors for far-infrared telescopes, and optical communications. Superconducting thin-film materials, however, have remained largely unchanged, with aluminum still being the material of choice for superconducting qubits and niobium compounds for high-frequency/high kinetic inductance devices. Magnesium diboride (MgB2), known for its highest transition temperature (Tc = 39 K) among metallic superconductors, is a viable material for elevated temperature and higher frequency superconducting devices moving toward THz frequencies. However, difficulty in synthesizing wafer-scale thin films has prevented implementation of MgB2 devices into the application base of superconducting electronics. Here, we report ultrasmooth (<0.5 nm root-mean-square roughness) and uniform MgB2 thin (<100 nm) films over 100 mm in diameter and present prototype devices fabricated with these films demonstrating key superconducting properties including an internal quality factor over 104 at 4.5 K and high tunable kinetic inductance in the order of tens of pH/sq in a 40 nm thick film. This advancement will enable development of elevated temperature, high-frequency superconducting quantum circuits, and devices.
RESUMO
Manganese antimonate (MnySb1-yOx) electrocatalysts for the oxygen-evolution reaction (OER) were synthesized via chemical vapor deposition. Mn-rich rutile Mn0.63Sb0.37Ox catalysts on fluorine-doped tin oxide (FTO) supports drove the OER for 168 h (7 days) at 10 mA cm-2 with a time-averaged overpotential of 687 ± 9 mV and with >97% Faradaic efficiency. Time-dependent anolyte composition analysis revealed the steady dissolution of Mn and Sb. Extended durability analysis confirmed that Mn-rich MnySb1-yOx materials are more active but dissolve at a faster rate than previously reported Sb-rich MnySb1-yOx alloys.
RESUMO
Transient extreme ultraviolet (XUV) spectroscopy is becoming a valuable tool for characterizing solar energy materials because it can separate photoexcited electron and hole dynamics with element specificity. Here, we use surface-sensitive femtosecond XUV reflection spectroscopy to separately measure photoexcited electron, hole, and band gap dynamics of ZnTe, a promising photocathode for CO2 reduction. We develop an ab initio theoretical framework based on density functional theory and the Bethe-Salpeter equation to robustly assign the complex transient XUV spectra to the material's electronic states. Applying this framework, we identify the relaxation pathways and quantify their time scales in photoexcited ZnTe, including subpicosecond hot electron and hole thermalization, surface carrier diffusion, ultrafast band gap renormalization, and evidence of acoustic phonon oscillations.
RESUMO
There is increasing demand for tailored molecular inks that produce phase-pure solution-processed semiconductor films. Within the Cu-Sn-S phase space, Cu2SnS3 belongs to the I2-IV-VI3 class of semiconductors that crystallizes in several different polymorphs. We report the ability of thiol-amine solvent mixtures to dissolve inexpensive bulk Cu2S and SnO precursors to generate free-flowing molecular inks. Upon mild annealing, polymorphic control over phase-pure tetragonal (I4Ì 2m) and orthorhombic (Cmc21) Cu2SnS3 films was realized simply by switching the identity of the thiol (i.e., 1,2-ethanedithiol vs 2-mercaptoethanol, respectively). Polymorph control is dictated by differences in the resulting molecular metal-thiolate complexes and their subsequent decomposition profiles, which likely seed distinct Cu2-x S phases that template the ternary sulfide sublattice. The p-type tetragonal and orthorhombic Cu2SnS3 films possess similar experimental direct optical band gaps of 0.94 and 0.88 eV, respectively, and strong photoelectrochemical current responses. Understanding how ink formulation dictates polymorph choice should inform the development of other thiol-amine inks for solution-processed films.