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The metallic films surrounding a synthetic diamond formed under high-pressure and high-temperature (HPHT) in the presence of Fe-based and Ni-based catalysts were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was showed that the carbide was the primary carbon source for the nucleation and growth of diamond. Based on the EET (empirical electron theory in solid and molecules) theory, the valence electron structure of interface between carbide (Fe3C, Ni3C, (Fe, Ni) 3C) and diamond was calculated using the bonding length difference (BLD) method. The boundary criterion of Thomas-Fermi-Dirac-Cheng (TFDC): " the electron density being equal on the contacting surfaces of atoms' was applied to analyze the valence structure of carbide-diamond interface. The result based on the calculation valance electron structure is in good accordance with the experimental result. This study is very helpful to reveal the catalytic mechanism of diamond...

The metallic film surrounding a diamond single crystal, which plays an important role in the diamond growth from an Fe-Ni-C system, has been successfully investigated by using transmission-electron microscopy (TEM), Raman spectroscopy and x-ray photo-electron spectroscopy (XPS). Diamond and graphite were not found in surface layer (near diamond) of the film by TEM and Raman spectroscopy, but a parallel relationship exists between the (1) plane of γ-(Fe,Ni) and the (100) plane of (Fe,Ni)3C in this region. Compared with that of solvent metal (catalyst) near diamond, the binding energy in the valence bands of iron, nickel and carbon atoms of the film has an increase of 0.9 eV. According to the microstructures on the film obtained by the TEM, Raman spectra, and XPS, the catalytic mechanism of the film may be assumed as follows. In the surface layer of the film, iron and nickel atoms in the γ-(Fe,Ni) lattice can absorb carbon atoms in the (Fe,Ni)3C lattice and make them transform to an sp3-like state. Then carbon atoms with the sp3-like structure are separated from the (Fe,Ni)3C and stack on the growing diamond crystal. This study provides a direct evidence for the diamond growth from a metallic catalyst-graphite system under high temperature and high pressure.

Diamond crystals, with dimensions of about 0.5-0.6 mm, were synthesized in the presence of Fe-Ni and Fe-Ni-Si catalyst solvents under high-pressure-high-temperature (HPHT) conditions. The as-known dendritic pattern was clearly seen on the (111) or (100) planes of diamond single crystals grown using Fe-Ni as a catalyst solvent. However, the conventional dendritic pattern was not observed in diamonds grown in the presence of Fe-Ni-Si alloy catalyst. Trigonal-type, pyramid-type, polygonal-type and rectangular-type growth hillocks were clearly observed on the (111) and (100) surfaces of diamonds grown from the Fe-Ni-Si-C system, and the density of the hillocks is very high at some positions. Clear successive growth layers can also be found on the (111) planes of the high-pressure diamond single crystals grown in the presence of Fe-Ni-Si alloy catalyst. The growth hillocks distributed on the (111) and (100) planes of the diamonds generally occur on or near growth steps, and some of the hillocks terminate at certain solid inclusions and voids. Growth hillocks on the (111) and (100) surfaces directly indicate the spiral growth mechanism under HPHT. A possible formation process for growth hillocks is proposed.

Cubic boron nitride (c-BN) crystals with dimensions of 0.3-0.4 mm, which have been synthesized using lithium nitride (Li3N) as a catalyst with a high-pressure high-temperature method, were examined by transmission electron microscopy (TEM). The TEM result shows that there are some nanostructrued areas containing several types of nanosized foreign particles within the as-grown c-BN crystals. We find that the nanometre inclusions are hexagonal BN with the lattice constants of a = 2.054 A and c = 6.66 A, tetragonal B25N with a = 8.79 A and c = 5.08 A, tetragonal B53N with a = 8.79 A and c = 5.08 A, and hexagonal Li3N with a = 3.648 A and c = 3.875 A.

γ-phase copper iodide (γ-CuI) is a wide bandgap p-type semiconductor with a band gap of 3.1 eV, which is suitable for optoelectronic devices like light-emitting diodes and solar cells. A simple and convenient method of iodination of copper film to prepare CuI film was reported. The effects of iodination time, reaction temperature, and copper/iodine ratio on the transparent and conductive properties of CuI film were explored. CuI films with high transmittance over 75% in the visible range and low resistivity of 4.4×10 Ω·cm were grown under the optimized iodination time (30 min) and iodination temperature (120°C). The CuI films were adopted as hole transporting layers for CuI/CH3NH3PbI3/PCBM inverted planar perovskite solar cell and a maximum photovoltaic efficiency of 8.35% was obtained. The influences of the transparent and conductive properties of CuI films on the solar cell photovoltaic efficiency were also discussed.

Twin diamond crystals grown at high temperature and high pressure (HPHT) in the presence of FeNi catalyst have been examined by transmission electron microscopy (TEM). Direct observation by TEM shows that there are a large amount of twins which lie on the {111} planes in the HPHT-grown diamonds. The twins in the diamond may be formed and may extend into the inner crystal from the twin nucleus formed in the nucleation process. The twins can be formed due to the carbon atoms falling mistakenly into positions where a twin crystal can form during diamond growth, or condensation of supersaturated vacancies on the {111} plane. Some hexagonal dislocation loops related to supersaturated vacancies are found on the twins. The Moire fringe image reveals that stacking faults terminate on the intersecting twin boundary. This suggests that, at the temperature that the HPHT diamond is grown, the bordering partial has propagated by gliding up to the twin interface, which can be described by the reaction of a Shockley partial dislocation with a twin on the {111} plane.

Diamond growth instability at high temperature and high pressure (HPHT) has been elucidated by observing the cellular interface in diamond crystals. The HPHT diamond crystals grow layer by layer from solution of carbon in the molten catalyst. In the growth of any other crystals from solution, the growth interface is not stable and should be of the greatest significance to understand further the diamond growth mechanism. During the diamond growth, the carbon atoms are delivered to the growing diamond crystal by diffusion through a diamond crystal-solution boundary layer. In front of the boundary layer, there is a narrow constitutional supercooling zone related to the solubility difference between diamond and graphite in the molten catalyst. The diamond growth stability is broken, and the flat or planar growth interface transforms into a cellular interface due to the light supercooling. The phenomenon of solute trails in the diamonds was observed, the formation of solute trails was closely associated with the cellular interface.