Orbital-selective confinement effect of Ru 4d4d orbitals in SrRuO3_3 ultrathin film

The electronic structure of SrRuO$_3$ thin film with thickness from 50 to 1 unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering (RIXS) technique at the O K-edge to unravel the intriguing interplay of orbital and charge degrees of freedom. We found that orbital-selective quantum confinement effect (QCE) induces the splitting of Ru $4d$ orbitals. At the same time, we observed a clear suppression of the electron-hole continuum across the metal-to-insulator transition (MIT) occurring at the 4 u.c. sample. From these two clear observations we conclude that QCE gives rise to a Mott insulating phase in ultrathin SrRuO$_3$ films. Our interpretation of the RIXS spectra is supported by the configuration interaction calculations of RuO$_6$ clusters.Comment: 7 pages, 7 figure

Nanotextured Morphology of Poly(methyl methacrylate) and Ultraviolet Curable Poly(urethane acrylate) Blends via Phase Separation

Domain structures of spin-coated immiscible poly(methyl methacrylate) (PMMA) and ultraviolet (UV) curable poly(urethane acrylate) (PUA) blends were studied using atomic force microscopy (AFM). Spin casting the PMMA/PUA blends in propylene glycol monomethyl ether acetate (PGMEA) was accompanied with phase separation, and PUA was subsequently cross-linked under UV radiation. Selective dissolution of PMMA in the phase-separated films was feasible using tetrahydrofuran (THF) solvent after the UV curing process, because the cured PUA material is highly stable against THF. Morphology of phase-separated structure, including domain size and height, could be controlled by varying total concentration of the blended solution, and various nanoscale features such as island-like and hole-like structures were achieved by changing weight ratio of the two immiscible polymers

Oxygen radical-mediated oxidation reactions of an alanine peptide motif - density functional theory and transition state theory study

<p>Abstract</p> <p>Background</p> <p>Oxygen-base (O-base) oxidation in protein backbone is important in the protein backbone fragmentation due to the attack from reactive oxygen species (ROS). In this study, an alanine peptide was used model system to investigate this O-base oxidation by employing density functional theory (DFT) calculations combining with continuum solvent model. Detailed reaction steps were analyzed along with their reaction rate constants.</p> <p>Results</p> <p>Most of the O-base oxidation reactions for this alanine peptide are exothermic except for the bond-breakage of the C_α-N bond to form hydroperoxy alanine radical. Among the reactions investigated in this study, the activated energy of OH α-H abstraction is the lowest one, while the generation of alkylperoxy peptide radical must overcome the highest energy barrier. The aqueous situation facilitates the oxidation reactions to generate hydroxyl alanine peptide derivatives except for the fragmentations of alkoxyl alanine peptide radical. The C_α-C_βbond of the alkoxyl alanine peptide radical is more labile than the peptide bond.</p> <p>Conclusion</p> <p>the rate-determining step of oxidation in protein backbone is the generation of hydroperoxy peptide radical via the reaction of alkylperoxy peptide radical with HO₂. The stabilities of alkylperoxy peptide radical and complex of alkylperoxy peptide radical with HO₂are crucial in this O-base oxidation reaction.</p

Efficiency Improvement of Organic Solar Cells by Tuning Hole Transport Layer with Germanium Oxide

Improving optical property is critical for optimizing the power conversion efficiency of organic solar cells. In the present research, we show that modification of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layer with GeO2 leads to 15% improvement of power conversion efficiency in a polymer solar cells through enhancement of short circuit currents. Modified PEDOT:PSS layer with optimized concentration of GeO2 assists active layer absorbing much light by playing a role of optical spacer. Using AFM and grazing incidence X-ray diffraction (GIXD) data, we also present the evidence that an addition of GeO2 does not affect crystallinity of active layer

Orbital-selective confinement effect of Ru 4d orbitals in SrRuO3 ultrathin film

The electronic structure of SrRuO3 thin film with a thickness from 1 to 50 unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering (RIXS) technique at the O K edge to unravel the intriguing interplay of orbital and charge degrees of freedom. We found that the orbital-selective quantum confinement effect (QCE) induces the splitting of Ru 4d orbitals. At the same time, we observed a clear suppression of the electron-hole continuum across the metal-to-insulator transition occurring in the 4-u.c. sample. From these two clear observations we conclude that the QCE gives rise to a Mott insulating phase in ultrathin SrRuO3 films. Our interpretation of the RIXS spectra is supported by the configuration interaction calculations of RuO6 clusters. © 2019 American Physical Societ

Theoretical investigation of the photoinitiated folding of HP-36

A computational model was developed to examine the phototriggered folding of a caged protein, a protein modified with an organic photolabile cross-linker. Molecular dynamics simulations of the modified 36-residue fragment of subdomain B of chicken villin head piece with a photolabile linker were performed, starting from both the caged and the uncaged structures. Construction of a free-energy landscape, based on principal components as well as on radius of gyration versus root-mean-square deviation, and circular dichroism calculations were employed to characterize folding behavior and structures. The folded structures observed in the molecular dynamics trajectories were found to be similar to that of the wild-type protein, in agreement with the published experimental results. The free-energy landscapes of the modified and wild-type proteins have similar topology, suggesting common thermodynamic/kinetic behavior. The existence of small differences in the free-energy surface of the modified protein from that of the native protein, however, indicates subtle differences in the folding behavior