No abstract

By combining ab initio molecular dynamics simulations and many-body perturbation theory calculations of electronic energy levels, we determined the band edge positions of functionalized Si(111) surfaces in the presence of liquid water, with respect to vacuum and to water redox potentials. We considered surface terminations commonly used for Si photoelectrodes in water splitting experiments. We found that, when exposed to water, the semiconductor band edges were shifted by approximately 0.5 eV in the case of hydrophobic surfaces, irrespective of the termination. The effect of the liquid on band edge positions of hydrophilic surfaces was much more significant and determined by a complex combination of structural and electronic effects. These include structural rearrangements of the semiconductor surfaces in the presence of water, changes in the orientation of interfacial water molecules with respect to the bulk liquid, and charge transfer at the interfaces, between the solid and the liquid. Our results showed that the use of many-body perturbation theory is key to obtain results in agreement with experiments; they also showed that the use of simple computational schemes that neglect the detailed microscopic structure of the solid-liquid interface may lead to substantial errors in predicting the alignment between the solid band edges and water redox potentials.

Effective methods for decoupling superconducting qubits (SQs) from parasitic environmental noise sources are critical for increasing their lifetime and phase fidelity. While considerable progress has been made in this area, the microscopic origin of noise remains largely unknown. In this work, first principles density functional theory calculations are employed to identify the microscopic origins of magnetic noise sources in SQs on an α-Al2O3 substrate. The results indicate that it is unlikely that the existence of intrinsic point defects and defect complexes in the substrate are responsible for low frequency noise in these systems. Rather, a comprehensive analysis of extrinsic defects shows that surface aluminum ions interacting with ambient molecules will form a bath of magnetic moments that can couple to the SQ paramagnetically. The microscopic origin of this magnetic noise source is discussed and strategies for ameliorating the effects of these magnetic defects are proposed.

Hydrogen dopant is injected into interstitial sites rather than into substitutional sites (e.g., W, Nb in VO 2 lattice [5,6] ) without destroying the framework of the lattice. In this way, electrons (one per hydrogen) are effectively and reversibly supplied to the correlated oxide lattice. [12] Because hydrogen-induced carrier doping minimizes the dopant-induced disorder, the use of hydrogen is close to mimicking pure band-filling control of correlated systems. The charge carriers supplied by hydrogen are expected to cause large changes in electrical resistivity and optical transmission across the hydrogen-induced phase transition. These changes would make the correlated materials useful in "ionotronic" devices. [12,13,16,17] Recently, it was demonstrated that up to one electron can be introduced into each VO 2 chemical unit by hydrogen spillover method. [12] Hydrogen diffuses along the empty [001] R channel in the lattice and forms thermodynamically stable hydrogenated VO 2 [11,18,19] (HVO 2 ). The electron doping by hydrogen allows dynamic band filling of VO 2 and achieves a two-step phase transition from insulator (VO 2 , 3d 1 ) to metal (H x VO 2 ; 0 < x < 1) to insulator (HVO 2 , 3d 2 ) during interinteger d-band filling. These changes are accompanied by expansion of out-of-plane lattice parameters in an epitaxial (100) R -faceted VO 2 thin film. An important question is whether a new insulating phase universally emerges near-integer band filling of d regardless of facet orientation and how crystal facet orientation influences the stability and kinetics of the hydrogenated-insulating HVO 2 epilayer with 3d 2 configuration.Here, we demonstrate universal and distinct characteristics on the reversible injection of hydrogen dopants to, and release of hydrogen dopants from, (001) R -VO 2 epitaxial films, as well as (100) R -VO 2 epitaxial films. The doping caused remarkable expansion in the out-of-plane lattice parameter (a-axis in (100) R -faceted HVO 2 films; c-axis in (001) R -faceted HVO 2 films), and stabilized the hydrogenated-insulating phase at the highest hydrogen contents. These results suggest that metal-insulator transition induced by electron doping is universal in H x VO 2 regardless of the facet direction. Contrary to universal phase transition to HVO 2 , transition rates and the degree of lattice expansion were controlled by facet orientation: because of anisotropic diffusion of hydrogen in the rutile lattice, the transition to (001) R -HVO 2 that has a surface-exposed oxygen channel was faster than the transition to (100) R -HVO 2 . Moreover, as a result of the Unlike the substitutional dopants, interstitial hydrogen effectively supplies significant amount of carriers in the empty narrow d band in correlated electronic systems by reversibly adding it into interstitial sites. Here, it is demonstrated that hydrogenated VO 2 , a heavily hydrogenated correlated insulating phase with 3d 2 electronic configuration, can be thermodynamically stabilized by topotactically preserving its lattice framework r...

Caught in the light: The fulvalene diruthenium complex shown on the left side of the picture captures sun light, causing initial Ru-Ru bond rupture to furnish a long-lived triplet biradical of syn configuration. This species requires thermal activation to reach a crossing point (middle) into the singlet manifold on route to its thermal storage isomer on the right through the anti biradical.