A Short-wave UV Nonlinear Optical Sulfate of High Thermal Stability

Compared with borates, carbonates, nitrates and phosphates, sulfates have been ignored as nonlinear optical(NLO) materials for a long time. Recently, researchers started to realize sulfates which have the potential as NLO materials, and synthesized some sulfate NLO materials by the water solution method and solvothermal method. However, all these sulfate NLO materials have the same problem of low thermal stability. Here, we synthesized a new Cs4 Mg6(SO4)8, which crystallizes in the orthorhombic space group P212121 with a = 9.102, b = 9.955, c = 16.127 ?, V = 1461.3 ?3, Z = 2, F(000) = 1352, μ = 5.777 mm-1, R = 0.0213 and wR = 0.0480. The single crystal structure can be described as a three-dimensional framework constructed by MgO6 octahedra and SO4 tetrahedra. Relevant optical measurements indicate that Cs4 Mg6(SO4)8 is short-wave ultraviolet transparent and has a moderate second harmonic generation response. Theoretical calculations by the CASTEP package reveal that S–O groups are NLO-active anionic groups. Significantly, Cs4 Mg6(SO4)8 has high thermal stability up to 781 ℃ based on thermal analyses. We believe that our work will provide a new strategy for researchers to develop new sulfate short-wave ultraviolet NLO materials of high thermal stability.     

Horizontal InAs nanowire transistors grown on patterned silicon-on-insulator substrate

High-density horizontal InAs nanowire transistors are fabricated on the interdigital silicon-on-insulator substrate. Hexagonal InAs nanowires are uniformly grown between face-to-face (111) vertical sidewalls of neighboring Si fingers by metal-organic chemical vapor deposition. The density of InAs nanowires is high up to 32 per group of silicon fingers, namely an average of 4 nanowires per micrometer. The electrical characteristics with a higher on/off current ratio of 2×10⁵ are obtained at room temperature. The silicon-based horizontal InAs nanowire transistors are very promising for future high-performance circuits.