Xinyuan Zhang

Large-scale GaN nanobelts and nanowires grown from milled Ga2O3 powders

Abstract Large-scale hexagonal GaN nanobelts and nanowires were synthesized by direct reaction of milled Ga 2 O 3 powders with flowing ammonia at 1000 °C. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray were used to characterize the structures, morphologies and compositions of the samples. The results show that those GaN nanobelts and nanowires are single crystals with hexagonal structure. The simple method presented here demonstrates that GaN nanobelts and nanowires can be grown on a large scale without using templates or catalysts.

Widely tunable and monochromatic terahertz difference frequency generation with organic crystal 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile

We report an experimental study on widely tunable terahertz (THz) wave difference frequency generation (DFG) with hydrogen-bonded crystals 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1). The organic crystals were pumped by a ∼1.3u2009μm double-pass KTiOPO4 optical parametric oscillator. A tuning range of 0.02–20 THz was achieved. OH1 crystals offer a long effective interaction length (also high output) for the generation below 3 THz, owing to the low absorption and favorable phase-matching. The highest energy of 507 nJ/pulse was generated at 1.92 THz with a 1.89-mm-thick crystal. Comprehensive explanations were provided, on the basis of theoretical calculations. Cascading phenomenon during the DFG process was demonstrated. The photon conversion efficiency could reach 2.9%.

Synthesis, crystal growth, and second-order nonlinear optical properties of new configurationally locked polyene derivatives

Five new crystals based on configurationally locked polyene (CLP) structure are synthesized. This series of crystals all consists of a π-conjugated hexatriene bridge between the dicyanomethylidene electron acceptor and the electron donors with strong hyperpolarization. In particular, the acentric 2-(3-(4-phenylstyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (PSDCM) exhibits a large powder second-harmonic generation intensity about 0.3 times that of OH1 (a commonly used CLP nonlinear optical crystal), and the mechanism is elucidated by first-principle studies. Single-crystal X-ray diffraction and diffuse reflectance spectroscopy are performed and the thermal properties in PSDCM are characterized.

Isoxazolone-based single crystals with large second harmonic generation effect

Two nonlinear optical (NLO) crystals based on the 3-phenyl-5-isoxazolone moiety, (Z)-4-(4-(dimethylamino)benzylidene)-3-phenylisoxazol-5(4H)-one (C18H16N2O2, DLS) and (Z)-4-(4-methoxybenzylidene)-3-phenylisoxazol-5(4H)-one (C17H13NO3, MLS), have been successfully grown by a slow evaporation method. The powder second-harmonic generation intensities of DLS and MLS are strong, about 2.8 and 1.5 times that of OH1, respectively. Such a large SHG effect is further elucidated by structure analyses and theoretical calculations. The optical and thermal properties of DLS and MLS have been characterized by UV-vis absorption spectroscopy, IR spectroscopy, thermal gravimetric analysis and differential scanning calorimetry.

Molecular design on isoxazolone-based derivatives with large second-order harmonic generation effect and terahertz wave generation

A series of 3-phenyl-5-isoxazolone and 3-methyl-5-isoxazolone-based compounds with different electron donors were synthesized. Fourteen single crystals in this family were obtained by slow evaporation. Single crystal X-ray studies showed that four new 3-phenyl-5-isoxazolone-based crystals, C20H18N2O2 (PDI), C15H11NO2S (PTI), C23H15NO2 (PFI), and C17H13NO2S (PMI-(I)), belong to the noncentrosymmertric space group. The inclinations to achieve noncentrosymmetric space groups in the 3-phenyl-5-isoxazolone-based crystals have been confirmed by first-principles calculations. Powder second harmonic generation (SHG) tests revealed that the abovementioned four acentric crystals exhibited very large SHG intensities that were about 1 to 3 times that of OH1 (a commonly used nonlinear optical crystal) under 2.09 μm light. Their UV-vis absorption, diffuse reflectance spectroscopy, and thermal properties were also characterized. Moreover, widely tunable and monochromatic terahertz difference frequency generation in the 3-phenyl-5-isoxazolone-based crystal C17H13NO3 (MLS) was realized for the first time.

Trisodium scandium bis(orthoborate)

Single crystals of trisodium scandium bis(orthoborate), Na3Sc(BO3)2, have been obtained by spontaneous crystallization from an Na2O–Sc2O3–B2O3 melt. The crystal structure features a three-dimensional framework composed of planar [BO3]3− groups and distorted ScO6 octahedra with Na atoms in the cavities. The Sc atom occupies a special position (Wyckoff position 2b, site symmetry -1) and of the two Na atoms, one occupies a special position (Wyckoff position 2c, site symmetry -1).