The desired morphology, narrowed band gap and good photoelectric properties are the key factors for achieving the wide application of hybrid perovskite materials. During the preparation of novel hybrid perovskite materials, preserving the morphology of highly crystalline materials and narrowing their band gap will be desirable for designing photoelectric devices with outstanding performance. Here, with broad band gap 1D/2D hybrid perovskite single crystals as a template, we design a universal conversion process from single crystal to single crystal for a variety of large-sized hybrid perovskite materials induced by CH₃NH₂ (MA) gas under an ambient atmosphere. Most significantly, the hybrid perovskite single crystals keep their original morphology, narrow their optical band gap, and enhance their carrier mobility and photo-response dramatically after induced conversion by MA gas molecules, especially for DMAPbI₃ (NH₂(CH₃)₂PbI₃). The optical band gap of DMAPbI₃ was lowered from 2.58 eV to 1.53 eV and its photo-response performance was enhanced greatly by even a small amount of replacement of DMA⁺ by MA⁺, which provides a new idea for designing novel hybrid perovskite single crystals with a desired morphology and their optoelectronic devices with good performance.

We have studied the threading dislocations of 4H-SiC substrates with different conductivity types by means of molten KOH defect selective etching.

The high-quality single crystal diamond (SCD) grown in the Microwave Plasma Chemical Vapor Deposition (MPCVD) system was studied. The CVD deposition reaction occurred in a 300 torr high pressure environment on a (100) plane High Pressure High Temperature (HPHT) diamond type II a substrate. The relationships among the chamber pressure, substrate surface temperature, and system microwave power were investigated. The surface morphology evolution with a series of different concentrations of the gas mixture was observed. It was found that a single lateral crystal growth occurred on the substrate edge and a systemic step flow rotation from the [100] to the [110] orientation was exhibited on the surface. The Raman spectroscopy and High Resolution X-Ray Diffractometry (HRXRD) prove that the homoepitaxy part from the original HPHT substrate shows a higher quality than the lateral growth region. A crystal lattice visual structural analysis was applied to describe the step flow rotation that originated from the temperature driven concentration difference of the C₂H₂ ion charged particles on the SCD center and edge.

The diamond mosaic grown on the single-crystal diamond substrates by the microwave plasma chemical vapor deposition (MPCVD) method has been studied. The average growth rate was about 16–17 μm/h during 48 hours’ growth. The surface morphologies of the as-grown diamond layer were observed. It was found that the step flow was able to move across the substrates and cover the junction interface. Raman spectroscopic mapping in the central area of the junction revealed the high stress region movement across the junction interface from one substrate to the other for about 200–400 μm. High-resolution X-ray diffractometry (HRXRD) results proved that the surface step flow movement direction had nothing to do with the off-axis directions of the original substrates. It was found that the surface height difference of substrate was the main driving force for the step flow movement, junction combination and surface morphology changing. The mechanism of the mosaic interface junction combination and step flow transformation on the mosaic surface was proposed.

Characterization of residual stress in bulk crystals is of vital importance since it can provide abundant information on the crystal growth and process techniques. In this paper, the residual stress in 4H-SiC bulk crystals was investigated by neutron diffraction. Detailed strain and stress calculations were performed using the Bragg equation and Hooke's law. The (0004), (11−20) and (1−100) plane diffraction profiles were measured. The strain and stress in three directions were found to be on the order of 10⁻⁴–10⁻³ and 100–1000 MPa, respectively. Moreover, the stress distributions in different directions were anisotropic. Amongst the stresses in these three directions, the stresses in the direction were tensile and the maximum value was up to 2953 MPa, which indicated that there was a high risk of the grown crystals cracking in this direction.