Based on the idea that the hardness of covalent crystal is intrinsic and equivalent to the sum of the resistance to the indenter of each bond per unit area, a semiempirical method for the evaluation of hardness of multicomponent crystals is presented. Applied to β-BC2N crystal, the predicted value of hardness is in good agreement with the experimental value. It is found that bond density or electronic density, bond length, and degree of covalent bonding are three determinative factors for the hardness of a polar covalent crystal. Our method offers the advantage of applicability to a broad class of materials and initializes a link between macroscopic property and electronic structure from first principles calculation.

CNx/TiNy multilayers have been prepared by ion beam sputteringand analyzed by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray and X-ray photoemission spectroscopy. The structure analyses shows that the films may contain several different kinds of CaN crystals embedded in the amorphous matrix. These crystals have hexagonal and cubic crystalline structures. The TiNx layer in multilayers is primarily amorphous and contains only a few dispersed Ti2N crystals. The thickness of CNx and TiNy layers in the CNx/TiNy multilayers is about 20 and 30nm, respectively. The atomic ratios of [N]/([C]+[N]+[Ti]) in the multilayers vary from 20 to 41 at%. The bondingratios of CaN/C?N of the CNx layer in multilayers reach 0.447 or 0.585 as calculated from the C1s and N1s X-ray photoemission spectra, respectively.

B0.54C0.28N0.18 precursor powder with turbostratic structure was prepared by using melamine and boric acid. The precursor was transformed into orthorhombic B2CN under definite high pressure and temperature conditions. The composition of the orthorhombic B2CN powder is B0.47C0.23N0.30. Its lattice parameters are a=0.4776nm, b=0.4585nm and c=0.3629nm. A strong absorption band from 1088 to 1385cm-1 of orthorhombic B2CN was observed by infrared measurement. In the photoluminescence (PL) spectrum of orthorhombic B2CN powder measured at room temperature, a broad peak corresponding to its band-edge emission centers at 374nm.

CNx/TiNy bilayers have been prepared by ion beam sputtering. Transmission electron microscopy observation of the films shows that some crystals exhibiting a polyhedron-type shape contain cores. The crystal sizes range from 100 to 300 nm. The results obtained by selected area electron diffraction reveal that the crystals belong to the cubic-C3N4 phase and their core is the Ti2N phase. Two types of heteroepitaxial matching between cubic-C3N4 and Ti2N are found in the CNx/TiNy bilayers, namely (112) cubic-C3N4k(1113) Ti2N and [423] cubic-C3N4k [110] Ti2N. The heteroepitaxial lattice misfit of 5.78% is calculated by the Bramfitt's lattice misfit method.

Cubic-C3N4 nanoparticles were synthesized in CNx/TiNx multilayer films by a nitrogen ion beam sputtering in situ titanium and graphite targets alternatively. The CAN bonding states within the CNx layers, the morphologies and structure of compounds in the films have been investigated by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. Two types of bonding states, NAsp2C and NAsp3C, exist predominantly in the CNx layer, and crystalline particles with sizes of 10-60nm were observed in the CNx layer of the films. Their diffraction data can be assigned to the cubic-C3N4 structure.