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Ovonic threshold switching (OTS) selectors can effectively improve the storage density and suppress the leakage current of advanced phase-change memory devices. As a prototypical OTS material, amorphous GeSe is widely investigated. But the attention paid to amorphous Se (i.e., the functional constituent in amorphous GeSe) has been very limited up to now. Here we have explored the structure, bonding and electronic characteristics of amorphous Se using ab initio molecular dynamics simulations. The results reveal that the Se atoms in amorphous Se tend to form 2-coordinated configurations, and they connect with each other to form long chains. The fraction of the vibrational density of state located in the high frequency range is relatively large, and the formation energy of the Se–Se bond is as large as 4.44 eV, hinting that the Se–Se bonds in chains possess high stability. In addition, the mid-gap state related to the OTS behavior is also found in amorphous Se despite the small proportion. Our findings enrich the knowledge of amorphous Se, which aids the applications of Se-based OTS selectors. [ABSTRACT FROM AUTHOR]

Improving the luminescence efficiency of InGaN-based long wavelength LEDs for use in micro-LED full-colour displays remains a huge challenge. The strain-induced piezoelectric effect is an effective measure for modulating the carrier redistribution at the InGaN/GaN heterointerfaces. Our theoretical results reveal that the hole injection is significantly improved by the diminution of the valence band offset (VBO) of the InGaN/GaN heterointerfaces along the [0001] direction, and inversely, the VBO increases along the [0001] direction. The energy band structures showed that the tensile strain of the GaN film grown on a silicon (Si) substrate could weaken the internal electric field of the InGaN well layer leading to a flattening of the energy band, which increases the overlap of electron and hole wave functions. In addition, the strain-induced piezoelectric polarisation of the InGaN layer on the Si substrate generates opposite sheet-bound charges at the heterointerfaces, which causes a reduction in the depletion region of the InGaN/GaN quantum wells (QWs). A systematic analysis illustrates that the control of the piezoelectric polarisation of the InGaN QW layer is available improve the internal quantum efficiency of the InGaN-based LEDs. [ABSTRACT FROM AUTHOR]

For effective overall water splitting (OWS) in alkaline media, a novel Ru-doped bimetal oxide (Ru-NiCo2O4) catalyst deposited onto a conductive nickel foam (NF) is fabricated by a multi-step hydrothermal reaction, ion exchange, and subsequent annealing process. The distinctive 3D nanoneedle-like arrays not only provide an even distribution of Ru decorated NiCo2O4, but also expose additional active sites, facilitating electron transport and improving reaction kinetics. Besides, density functional theory (DFT) studies elucidate the electronic structure regulation in Ru-NiCo2O4 and the modification of the d-band center optimizes H* adsorption energy, which considerably increased the hydrogen production efficiency. Considering the aforementioned advantages, the as-prepared Ru-NiCo2O4 electrocatalyst exhibits greatly improved catalytic activity, requiring only 25 mV and 249 mV at 10 mA cm−2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, as well as robust stability. Amazingly, the Ru-NiCo2O4 electrode in a two-electrode alkaline electrolyzer only needs 1.55 V to produce 10 mA cm−2, making it more efficient than the commercial RuO2‖‖Pt/C electrode (1.62 V). More importantly, 0.33 M urea only needs a low voltage of 1.427 V to drive the urine-mediated electrolysis, which is about 123 mV less than the urea-free electrolysis cell. This work presents an effective electronic structure engineering approach based on heteroatom doping that may be extended to design and fabricate novel high-performance OWS catalysts. [ABSTRACT FROM AUTHOR]

Two-dimensional 1T-ZrO2 material is investigated via first-principles calculations based on density functional theory (DFT) method. The band gap of cubic, tetragonal and monoclinic ZrO2 is 6.095 eV, 5.784 eV and 5.835 eV respectively obtained in the paper also. GGA + U d + U p method is determined to adopt to study two-dimensional 1T-ZrO2 in the paper. The results show that the band gap of 1T-ZrO2 material is 7.513 eV and it is an indirect wide band gap semiconductor structure. At the same time, it can be seen from the density of states (DOS) that the valence band of the 1T-ZrO2 material is mainly due to the contribution of 2p electron of O atom. 4p, 4d and 5s electron of Zr atom also contributes a little to the valence band. 4p, 4d, 5s electron of Zr atom and 2s, 2p electron of O atom contribute to the conduction band, but main contribution has come from 4d of Zr atom. These results are in good agreement with the electron orbitals diagram. 1T-ZrO2 material has maximum reflectivity of 11.61% and refractive index of 1.62. It has high absorption coefficient and energy loss in this region. The peak of dielectric function may be mainly caused by the inter-band transition from electron-occupied state to non-occupied state. The real part of the photoconductivity tends to zero in the visible region with low energy and the maximum conductivity of 2.087 corresponds to the peak of other photoelectric properties of 1T-ZrO2 material. [ABSTRACT FROM AUTHOR]

Two-dimensional 1T-ZrO2 material is investigated via first-principles calculations based on density functional theory (DFT) method. The band gap of cubic, tetragonal and monoclinic ZrO2 is 6.095 eV, 5.784 eV and 5.835 eV respectively obtained in the paper also. GGA + U d + U p method is determined to adopt to study two-dimensional 1T-ZrO2 in the paper. The results show that the band gap of 1T-ZrO2 material is 7.513 eV and it is an indirect wide band gap semiconductor structure. At the same time, it can be seen from the density of states (DOS) that the valence band of the 1T-ZrO2 material is mainly due to the contribution of 2p electron of O atom. 4p, 4d and 5s electron of Zr atom also contributes a little to the valence band. 4p, 4d, 5s electron of Zr atom and 2s, 2p electron of O atom contribute to the conduction band, but main contribution has come from 4d of Zr atom. These results are in good agreement with the electron orbitals diagram. 1T-ZrO2 material has maximum reflectivity of 11.61% and refractive index of 1.62. It has high absorption coefficient and energy loss in this region. The peak of dielectric function may be mainly caused by the inter-band transition from electron-occupied state to non-occupied state. The real part of the photoconductivity tends to zero in the visible region with low energy and the maximum conductivity of 2.087 corresponds to the peak of other photoelectric properties of 1T-ZrO2 material. [ABSTRACT FROM AUTHOR]