There is provided a self-supporting polycrystalline gallium nitride substrate having excellent characteristics such as high luminous efficiency and high conversion efficiency when used for devices, such as light emitting devices and solar cells. The self-supporting polycrystalline gallium nitride substrate is composed of gallium nitride-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate, and has a top surface and a bottom surface. The crystal orientations of individual gallium nitride-based single crystal grains as determined from inverse pole figure mapping by electron backscatter diffraction (EBSD) analysis on the top surface are distributed at various tilt angles from the specific crystal orientation, in which the average tilt angle thereof is 0.1 or more and less than 1 and the cross-sectional average diameter D.sub.T of the gallium nitride-based single crystal grains at the outermost surface exposed on the top surface is 10 m or more.

There is provided a self-supporting polycrystalline gallium nitride substrate having excellent characteristics such as high luminous efficiency and high conversion efficiency when used for devices, such as light emitting devices and solar cells. The self-supporting polycrystalline gallium nitride substrate is composed of gallium nitride-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate, and has a top surface and a bottom surface. The crystal orientations of individual gallium nitride-based single crystal grains as determined from inverse pole figure mapping by electron backscatter diffraction (EBSD) analysis on the top surface are distributed at various tilt angles from the specific crystal orientation, in which the average tilt angle thereof is 0.1 or more and less than 1 and the cross-sectional average diameter D.sub.T of the gallium nitride-based single crystal grains at the outermost surface exposed on the top surface is 10 m or more.

The seed substrate comprises a base substrate and a base layer comprising a Group III nitride semiconductor formed on the base substrate, which has a high dislocation density region and a low dislocation density region. The planar pattern of the high dislocation density region is a honeycomb pattern. A hollow exists between the base substrate and the low dislocation density region. The object layer is grown through a flux method using the seed substrate. The high dislocation density region is melted back at an initial stage of crystal growth, and thereafter, the object layer is grown on the top surface of the low dislocation density region. A cavity remains between the high dislocation density region and the object layer. The presence of the cavity and the hollow makes easy to peel the object layer from the seed substrate.

The seed substrate comprises a base substrate and a base layer comprising a Group III nitride semiconductor formed on the base substrate, which has a high dislocation density region and a low dislocation density region. The planar pattern of the high dislocation density region is a honeycomb pattern. A hollow exists between the base substrate and the low dislocation density region. The object layer is grown through a flux method using the seed substrate. The high dislocation density region is melted back at an initial stage of crystal growth, and thereafter, the object layer is grown on the top surface of the low dislocation density region. A cavity remains between the high dislocation density region and the object layer. The presence of the cavity and the hollow makes easy to peel the object layer from the seed substrate.

It is provided a layer of a crystal of a group 13 nitride having an upper surface and lower surface and composed of a crystal of the group 13 nitride selected from gallium nitride, aluminum nitride, indium nitride or the mixed crystals thereof. In the case that the upper surface of the layer of the crystal of the group 13 nitride is observed by cathode luminescence, the upper surface includes a linear high-luminance light-emitting part and a low-luminance light-emitting region adjacent to the high-luminance light-emitting part. A half value width of reflection at (0002) plane of an X-ray rocking curve on the upper surface is 3000 seconds or less and 20 seconds or more.

A layer of a crystal of a group 13 nitride selected from gallium nitride, aluminum nitride, indium nitride and the mixed crystals thereof has an upper surface and a bottom surface. The upper surface of a crystal layer of the group 13 nitride includes a linear high-luminance light-emitting part and a low-luminance light-emitting region adjacent to the high-luminance light-emitting part, observed by cathode luminescence. The high-luminance light-emitting part includes a portion extending along an m-plane of the crystal of the group 13 nitride.

A template-assisted method for the synthesis of 2D nanosheets comprises growing a 2D material on the surface of a nanoparticle substrate that acts as a template for nanosheet growth. The 2D nanosheets may then be released from the template surface, e.g. via chemical intercalation and exfoliation, purified, and the templates may be reused.

A template-assisted method for the synthesis of 2D nanosheets comprises growing a 2D material on the surface of a nanoparticle substrate that acts as a template for nanosheet growth. The 2D nanosheets may then be released from the template surface, e.g. via chemical intercalation and exfoliation, purified, and the templates may be reused.

An oxychloride infrared nonlinear optical crystal and the preparation method and use thereof, the optical crystal has a general chemical formula of Pb.sub.2+xOCl.sub.2+2x, therein 0<x<0.139 or 0.141<x<0.159 or 0.161<x0.6. The crystal is non-centrosymmetric, belongs to orthonormal system with space group of Fmm2, cell parameter is a=35.4963(14)0.05 , b=5.8320(2)0.05 , c=16.0912(6)0.05 . The crystal is prepared by high temperature melt method or flux method. The crystal has a strong second harmonic generation efficiency of 4 times that of KDP (KH.sub.2PO.sub.4) tested by Kurtz method, it is phase machable, transparent in the range of 0.34-7 m. The laser damage threshold is 10 times that of the current commercial infrared nonlinear optical crystal AgGaS.sub.2. No crystalline water exists in lead oxychloride, and it is stable in the air and has good thermal stability.

An oxychloride infrared nonlinear optical crystal and the preparation method and use thereof, the optical crystal has a general chemical formula of Pb.sub.2+xOCl.sub.2+2x, therein 0<x<0.139 or 0.141<x<0.159 or 0.161<x0.6. The crystal is non-centrosymmetric, belongs to orthonormal system with space group of Fmm2, cell parameter is a=35.4963(14)0.05 , b=5.8320(2)0.05 , c=16.0912(6)0.05 . The crystal is prepared by high temperature melt method or flux method. The crystal has a strong second harmonic generation efficiency of 4 times that of KDP (KH.sub.2PO.sub.4) tested by Kurtz method, it is phase machable, transparent in the range of 0.34-7 m. The laser damage threshold is 10 times that of the current commercial infrared nonlinear optical crystal AgGaS.sub.2. No crystalline water exists in lead oxychloride, and it is stable in the air and has good thermal stability.