Jinping Zhang

Growth Mechanism of Large-Size Rubrene Single Crystals Grown by a Solution Technique

Large-size and high-quality rubrene single crystals have been grown by a solution technique. The biggest crystal has 4 mm dimension. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy both indicate that the crystals obtained are pure rubrene and did not incorporate the solvent at the detection level. The morphology of surface and transect of the rubrene single crystals was observed by optical microscope, atomic force microscope (AFM), and scanning electron microscope (SEM). Three-dimensional nucleation was happened on the surface of single crystals. The array of small and large straight steps was observed on the surface of the rubrene single crystals. Layer-like structures were also observed on the cross-section of single crystals. All results indicate that each large step is most probably formed from the piling of small steps and the growth mechanism of rubrene crystals grown from solution is probably a three-dimensional nucleation–layer-by-layer periods growth.

Fabrication of crack-free AlN film on sapphire by hydride vapor phase epitaxy using an in situ etching method

Crack-free AlN films were grown on sapphire by hydride vapor phase epitaxy, with in situ etching applied during growth. Nanoscale voids were formed at a chosen growth stage by interrupting the growth and performing in situ etching in an H2 atmosphere at elevated temperature. Transmission electron microscopy showed the voids located at strongly distorted locations, and hence relaxing the strain and reducing the dislocation density. Raman spectra and X-ray diffraction measurements further demonstrated important role played by the nanoscale voids in releasing misfit strain and reducing dislocations. This work opens a promising perspective for fabricating thick, high-quality AlN.