RESUMEN
Deuterium (D) labeling is of great value in organic synthesis, pharmaceutical industry, and materials science. However, the state-of-the-art deuteration methods generally require noble metal catalysts, expensive deuterium sources, or harsh reaction conditions. Herein, noble metal-free and ultrathin ZnIn2 S4 (ZIS) is reported as an effective photocatalyst for visible light-driven reductive deuteration of carbonyls to produce deuterated alcohols using heavy water (D2 O) as the sole deuterium source. Defective two-dimensional ZIS nanosheets (D-ZIS) are prepared in a surfactant assisted bottom-up route exhibited much enhanced performance than the pristine ZIS counterpart. A systematic study is carried out to elucidate the contributing factors and it is found that the in situ surfactant modification enabled D-ZIS to expose more defect sites for charge carrier separation and active D-species generation, as well as high specific surface area, all of which are beneficial for the desirable deuteration reaction. This work highlights the great potential in developing low-cost semiconductor-based photocatalysts for organic deuteration in D2 O, circumventing expensive deuterium reagents and harsh conditions.
RESUMEN
Highlighted by the discovery of high-temperature superconductivity, strongly correlated oxides with highly distorted perovskite structures serve as intriguing model systems for pursuing emerging materials physics and testing technological concepts. While 3d correlated oxides with a distorted perovskite structure are not uncommon, their 4d counterparts are unfortunately rare. In this work, we report the tuning of the electrical and optical properties of a quasi-2D perovskite niobate CsBiNb2O7 via hydrogenation. It is observed that hydrogenation induces drastic changes of lattice dynamics, optical transmission, and conductance. It is suggested that changing the orbital occupancy of Nb d orbitals could trigger the on-site Coulomb interaction in the NbO6 octahedron. The observed hydrogen doping-induced electrical plasticity is implemented for simulating neural synaptic activity. Our finding sheds light on the role of hydrogen in 4d transition metal oxides and suggests a new avenue for the design and development of novel electronic phases.
RESUMEN
Atomically thin materials, leveraging their low-dimensional geometries and superior mechanical properties, are amenable to exquisite strain manipulation with a broad tunability inaccessible to bulk or thin-film materials. Such capability offers unexplored possibilities for probing intriguing physics and materials science in the 2D limit as well as enabling unprecedented device applications. Here, the strain-engineered anisotropic optical and electrical properties in solution-grown, sub-millimeter-size 2D Te are systematically investigated through designing and introducing a controlled buckled geometry in its intriguing chiral-chain lattice. The observed Raman spectra reveal anisotropic lattice vibrations under the corresponding straining conditions. The feasibility of using buckled 2D Te for ultrastretchable strain sensors with a high gauge factor (≈380) is further explored. 2D Te is an emerging material boasting attractive characteristics for electronics, sensors, quantum devices, and optoelectronics. The results suggest the potential of 2D Te as a promising candidate for designing and implementing flexible and stretchable devices with strain-engineered functionalities.
RESUMEN
The low-dimensional, highly anisotropic geometries, and superior mechanical properties of one-dimensional (1D) nanomaterials allow the exquisite strain engineering with a broad tunability inaccessible to bulk or thin-film materials. Such capability enables unprecedented possibilities for probing intriguing physics and materials science in the 1D limit. Among the techniques for introducing controlled strains in 1D materials, nanoimprinting with embossed substrates attracts increased attention due to its capability to parallelly form nanomaterials into wrinkled structures with controlled periodicities, amplitudes, orientations at large scale with nanoscale resolutions. Here, we systematically investigated the strain-engineered anisotropic optical properties in Te nanowires through introducing a controlled strain field using a resist-free thermally assisted nanoimprinting process. The magnitude of induced strains can be tuned by adjusting the imprinting pressure, the nanowire diameter, and the patterns on the substrates. The observed Raman spectra from the chiral-chain lattice of 1D Te reveal the strong lattice vibration response under the strain. Our results suggest the potential of 1D Te as a promising candidate for flexible electronics, deformable optoelectronics, and wearable sensors. The experimental platform can also enable the exquisite mechanical control in other nanomaterials using substrate-induced, on-demand, and controlled strains.
RESUMEN
The metal-to-insulator transition (MIT) in rare earth perovskite oxides has drawn significant research interest for decades to unveil the underlying physics and develop novel electronic materials. Recently, chemical doping induced MIT in SmNiO3 has been observed experimentally, with its resistivity changed by eight orders of magnitude. The mechanism of switching from one singly occupied Ni eg orbital to two singly occupied eg orbitals upon doping has been proposed by experimentalists and verified by computation. Here, we tested if this mechanism can be generally applied to other perovskite oxides with non-Ni B site elements. We applied first principles density functional theory (DFT) to study a series of perovskite oxides, CaFeO3, SrFeO3, BaFeO3 and SmMnO3. We investigated the geometry and electronic structures of pure and hydrogen doped oxides. We found that pure CaFeO3, SrFeO3 and BaFeO3 are metallic while pure SmMnO3 has a small band gap of 0.69 eV. Upon hydrogen doping, band gap opening was predicted for all four oxides: HSE06 predicted band gap values of 1.58 eV, 1.40 eV, 1.20 eV and 2.55 eV for H-doped CaFeO3, SrFeO3, BaFeO3 and SmMnO3, respectively. This finding opens up research opportunities for exploring a broader range of materials for MIT to be used in optical and electronic devices.
RESUMEN
A typical vibrational spectrum in the ice phase has four separate bands: Translation, libration, bending, and stretching. Ice X, the final ice phase under high pressure, shows an exotic vibrational spectrum. Based on harmonic approximation, an ideal crystal of ice X has one peak, at 998 cm-1, for Raman scattering and two peaks, at 450 cm-1 and 1507 cm-1, for infrared absorption in this work. These three characteristic peaks are indicators of the phase transition between ice VII and VIII and ice X. Despite many experimental and theoretical works on ice X, only this study has clearly indicated these characteristic peaks in the region of the IR band. The phonon density of states shows quite different features than ice VIII, which could be verified by inelastic neutron scattering in the future. The dynamic processes of 15 vibrational normal modes are discussed and the typical hydrogen bonds are missing.
