M.B. Guseva

Oriented carbyne layers

Abstract The paper reports on the study of oriented carbyne layers prepared using three different techniques: 1. (a) chemical carbonization of a poly(vinylidene fluoride) film, 2. (b) ion sputtering of graphite, and 3. (c) condensation of carbon vapor produced by an electrical arc. The crystalline structure of both oriented carbyne films and single crystal microinclusions were studied by electron diffraction. The electronic structure of the carbyne was studied by Auger electron spectroscopy. The one-dimensional cumulene nature of carbyne has been confirmed. On the basis of the electron diffraction data, a Patterson function was calculated. From that, a picture of the crystal potential as well as a model of the location of the atoms in the crystal unit cell have been developed. It could be shown that carbyne exhibits a layered structure.

A new carbon modification: ‘n-diamond’ or face-centred cubic carbon?

A new carbon modification having a face-centred cubic (fcc) structure has been obtained as a result of the transformation of a diamond surface during treatment in hydrogen plasma. The calculated density of electronic states of the fcc carbon phase provides evidence that it is a metallic form of carbon. The experimentally obtained crystal lattice parameter of the fcc carbon phase is found to be 0.3563 nm, which is close to that computed by the linear combination of atomic orbitals (LCAO) method. The fcc carbon phase has a characteristic edge offset in the electron energy loss spectrum distinguishing it from diamond, amorphous carbon and graphite. Here we show for the first time clear evidence for the existence of a carbon phase with the fcc crystal structure.

Carbyne — the third allotropic form of carbon

The history of the discovery of carbyne, the chemical and physical methods used to obtain it, the analysis of its structure, and some of its properties are briefly considered. The prospects for its practical applications are discussed

High quality diamond films on WC-Co surfaces

Abstract Diamond coatings chemically vapor deposited onto WC-Co cemented carbides by use of specially developed barrier underlayers are described. Preliminary seeding the barrier underlayers with nano-grain diamond particles by laser ablation allows obtaining fine-grained and uniform diamond coatings. The diamond coatings obtained in this way have high adhesion to the cemented carbide substrate due to enhanced interaction between the underlayer, nano-grained diamond nuclei and gas phase employed in their plasma-assisted chemical vapor deposition.

Electronic structure of carbynes studied by Auger and electron energy loss spectroscopy

Abstract The experimental carbon Auger lineshape for two samples of carbyne has been obtained. The electronic structure of carbynes has been calculated by the self-deconvolution of experimental Auger spectra. Results are discussed in terms of the electronic properties of linear molecules with 2–6 carbon atoms. It is shown that both carbyne samples have a linear structure with cumulene-type bonds but with different numbers of atoms in the chain. The influence of annealing at T

Thin films comparable with WC-Co cemented carbides as underlayers for hard and superhard coatings : the state of the art

Abstract A new method for deposition of barrier underlayers, which completely prevent Co penetration to the substrate surface and are highly compatible with WC-Co cemented carbides, has been developed. It allows deposition of thin hard continuous, highly adherent and defect-free TiCN-based films by the use of high energy titanium ions. The method ensures deposition without any damage of the cemented-carbide substrate or its decarburization, leading to formation of the η phase near the surface layer. As a result, CVD TiC, TiCN, TiN etc. coatings can be deposited onto cemented carbides preliminarily plated with barrier underlayers almost without a decrease in transverse rupture strength. Special additional interlayers are applied for enhancement of the adhesion between the underlayers and plasma CVD diamond coatings, resulting in excellent resistance of the near-surface layer of the cemented-carbide substrate with these coatings to high static loading when subjected to indentation.

DEPOSITION OF THIN HIGHLY DISPERSIVE DIAMOND FILMS BY LASER-ABLATION

Abstract A new method for diamond film preparation by laser ablation of a highly dispersive diamond target is proposed. Transmission and scanning electron microscopy, Raman and Auger spectroscopy data prove that the deposited film consists of cubic diamond. The density of diamond crystallites is 1011–1012cm−2. They were used as nucleation centres for subsequent CVD growth of thick diamond film.

COMPARATIVE-STUDY OF MICROCRYSTALLINE DIAMOND

Abstract Raman spectra of diamond powders and polycrystalline CVD diamond films with diamond crystalline size from 4 μm to 5 nm have been measured as a function of the crystallite size. The Raman diamond line at 1332 cm −1 was found for the powder to become more asymmetric with decreasing particle size to 5 nm. A strong influence of substrate temperature and methane-hydrogen gas mixture pressure during diamond films growth by the d.c. glow discharge method on linewidths and peak position have been found. The observed results are explained by “phonon confinement” and by strain effects. CVD and laser-evaporated nanophase diamond films were produced and have shown a Raman line at 1140 cm −1 .

The influence of excited hydrogen species on the surface state of sp2-hybridized boron nitride

Abstract The surface of sp2-hybridized boron nitride, namely well-crystallized hexagonal and poorly-crystallized turbostatic boron nitride, after its treatment in a hydrogen plasma was studied with the aid of high-resolution Auger spectroscopy. The surface state of both modifications of boron nitride is found to change due to interaction with excited hydrogen species. This interaction is thought to lead to termination of π (dangling) bonds of sp2-hybridized boron nitride by hydrogen atoms, which results in transformation of the sp2-hybridized state into the sp3-hybridized state on the surface of boron nitride.

Diamond films deposited on WC-Co substrates by use of barrier interlayers and nano-grained diamond seeds

Abstract Results on the structure, composition and properties of diamond films deposited onto WC-Co cemented carbides via special multilayer barrier interlayers preliminary seeded by nano-grained diamond particles are presented. The barrier interlayers comprise a layer adjacent to the substrate, which completely prevents substrate decarburization and Co diffusion from the substrate, and a diamond-bonding layer needed to obtain an enhanced adhesion of the PACVD diamond coating. Preliminary seeding the barrier interlayers with nano-grain diamond particles by use of a laser ablation technique allows a fine-grained, uniform and highly adherent diamond coating of high quality to be deposited by use of a conventional PACVD technique. Results on the nature of the interaction between the diamond nano-grained seeds and barrier interlayer are also presented.