The High Pressure Synthesis And Application Research Of CBN And BCN Compounds

Cubic boron nitride (cBN) is man-made superhard material only next to diamond in hardness, and natural cBN is not discovered up to now. Cubic BN doesn`t react with ferrous metals, and has higher anti-oxidized temperature and good electricity insulation than diamond. Therefore, it is an excellent material for machining ferrous metals and alloy in the field of industry. Besides, cBN is the typicalⅢ-Ⅴcompound semiconductor material. It has the energy gap about 6.4eV, and can be made easily into both P- and N-type with suitable impurity additions. As a result, cBN has an obvious superiority in making the high-power semiconductor and optoelectronic devices with the excellent properties.However, cBN crystal is usually synthesized by high pressure and high temperature (HPHT), and the crystal growth is extra difficult. Hitherto, the maximal size of cBN single crystal is only 3mm synthesized by HPHT under the laboratory condition. Especially, the irregular shapes block seriously the application in devices and so on. Therefore, it takes on a crucial application value in production how to prepare the special shape of cBN monocrystal basis on the actual needs, and the choice of catalyst is the key to the problem. Under HPHT conditions, cBN particles synthesized are small in size and irregular in shape, and its application has been greatly restricted. Hence, people cast their sight to cBN films prepared by vapour deposition. In order to prepare excellent performance cBN films, the researchers use Si, diamond and different metals as the substrate materials. However, the substrate structures used in the film deposition processes are always mismatched to that of cBN, which results in the lattice parameter mismatch at the interface of substrates and new films. So, large stress is induced, which affects seriously the quality at the interface and hinders the application of cBN films in high-performance optoelectronic devices. Obviously, the choice of apropos substrate is the key to solve the problem. In all substrate materials, the structure of single crystal material cBN is perfectly matched, as the most suitable for the growth of cBN film. Nevertheless, usually cBN monocrystal is small in size and especially irregualar in shape, which isn`t suitable as the substrate of thin film. Therefore, the preparation of flaky cBN monocrystal suitable for the deposition of cBN film will possess an obvious application potential, and play a certain role in the development of cBN film.In addition, ternary boron carbon nitride (BCN) compound possess cubic and hexagonal structure like BN. The similarity of the crystalline structures and the contrast of electrical property of graphite and hBN suggest the possibility of obtaining hexagonal BCN (hBCN), which possesses adjustable semi-conducting properties by modifying the ratio of C:BN. In recent years, various techniques have been employed to synthesize the new BCN phase. However, the structures of the synthesized products are generally layer chaos graphite structure or amorphous. Neither enough excellent cubic or hexagonal BCN monocrystal nor credible XRD pattern is obtained. The study of electrical, optical as well as mechanical properties is not much advanded yet. Thus, it is an important topic to explore the synthesis and characterization of BCN compound.In this thesis, we mainly researched the synthesis of cBN and BCN compound by HPHT method, and the deposition of BN thin film on the surface of cBN substrate which was especial shape prepared under HPHT conditions. Specific results are as follows:Firstly, under HPHT conditions, we used hBN as raw materials, Li3N,Li3N+LiH,LiH,LiH+LiNH2,Li3N+LiNH2 as catalyst, and successfully prepared thick plate, spherical, octahedron or hex-octahedron, flat cone and flaky hexagon morphology.1. Various catalyst/additives have their own private natures in HPHT conditions. Catalyst Li3N possesses the function of cBN crystal synthesized taking on thick plate morphology, catalyst LiH prefers cBN crytal synthesized to integrity octahedral morphology, and a little additive LiNH2 allows one side grown of cBN crystal synthesized. So, the morphology of cBN crystal can be controlled by selecting or adjusting the proportion of the different catalysts/additives2. By analyzing various crystal face, we obtained that flaky cBN monocrystal was actually a distorted crystal of cBN crystal.3. During the growth of flaky cBN crystal process, the color change of various regional communities can be attributed to the selective entrance of impurity atoms in {100} or {110} facet. The growth cone morphology of flaky cBN crystal was observed by microscope.Secondly, by RF magnetron sputtering method, cBN thin films were deposited on the substrate of flaky cBN {111} facet.1. By a large mount of deposition experiments, we obtained the most suitable deposition condition of cBN films in current system: 150W of the RF power, 1:20 of the ratio of partial pressure N2:Ar, 1.3Pa of the total pressure, 450℃of the substrate temperature and -200V of the substrate dc bias.2. Observed by SEM, the deposition films are the high crystallization electron transparent cBN films even if the films interior nuclei profile can be seen clearly. But some cracks appear on the films due to the intrinsic compressive stress.3. A large amount of hemispherical cBN nuclei, the size of which is very uniform and the diameter is about 3μm, were clearly observed on the overlapped smooth substrate surface.4. Due to the homogeneity of substrate and thin film materials, the deposition impact from lattice mismatch is eliminated, and cBN nucleation become more easily. This process seems to be very promising for the understanding of c-BN nucleation and growth mechanism.Thirdly, we used B powder and CNH by pyrolyzing melamine as starting materials, and prepared hexagonal phase BCN compound by HPHT chemical reaction.1. The product synthesized by HPHT has composition of B0.18C0.64N0.16, and nearly BC4N compound.2. The testing results of XPS, FTIR and so on suggest that the product is atomic-level hybrid composed of B, C and N atoms, and contains B-N, C-N, B-C and B-N-C bonds.3. SEM was used to observe the morphology of hBCN compound. The results show that h-BCN compound is almost flakes, the size is relatively uniform, and the width is about 1μm, thickness 200 nm.