Crystalline Diamond Particles Research Articles

Tailoring structural, morphological and mechanical characteristics of mono-crystalline diamond-reinforced polyacrylonitrile based electrospun fibers

Composites of diamond-reinforced particles offer extraordinary thermal- and mechanical characteristics attributable to their manageable outer surface and huge available uppermost layer. Uniform distribution of diamond powder in polymeric matrix, and enhanced interactions between them are the two significant problems to attain robust polymer composites. In this work, the crystalline diamond particles as received and chemically modified ones were integrated in polyacrylonitrile (PAN) matrix uniformly by electrospinning method. This procedure avoided agglomeration of the reinforced diamonds through uniform distribution in the polymer matrix. The shapes of diamond-integrated PAN fibers were attuned by adapting diamond loading, polymer concentration, flow rate, and applied voltage to achieve beads free fibrous structures. PAN was chosen as a carrier polymeric-matrix to enhance the electrostatic forces between functionalized diamond-particles and PAN molecular chains. Tensile tests showed that the loading of 2 wt% modified diamond-particles improved Young’s modulus of fibers by 74.94% and tensile strength by 125%. Therefore, modification of the outer surface of the diamond particles improved the chemical interactions between the diamond surface and matrix, and stress was transferred to the diamond particles in composite fibers. Additionally, thermal stabilities of the diamond-based polymer composites were enhanced by the integration of diamond powder in composite fibers.

THERMAL STABILITY STUDY OF DIAMOND-LIKE CARBON FILMS CONTAINING CRYSTALLINE DIAMOND NANOPARTICLES

Nanocrystalline diamond (NCD) particles are incorporated into diamond-like carbon (DLC) films in order to prevent NCD-DLC electrochemical corrosion. In the current paper, the thermal stability of these films was investigated. The NCD-DLC films were deposited on 316L stainless steel substrates using plasma enhanced chemical vapor deposition. The grain size of the diamond crystallites and their concentration were varied in order to obtain different NCD-DLC films. The samples were annealed to 50°C for 1 h. The annealing temperature increased until the complete graphitization of the films (ramp of 50°C). Raman scattering spectroscopy was used to evaluate in detail the chemical structure of the DLC and NCD-DLC films. The atomic arrangements and graphitization level according to the increasing temperature are discussed. The influence of NCD particle sizes and concentration on NCD-DLC thermal stability are also discussed. The results showed that the presence of crystalline diamond particles increased the graphitization temperature, which permits the use of NCD-DLC films in high temperature environments.

Insulating diamond particles as substrate for Pd electrocatalysts

The suitability of insulating highly crystalline diamond particles as support for Pd based electrocatalysts is explored for the first time by evaluating the electrochemical stripping of CO and oxidation of formic acid in acid solutions.

Crystalline diamond particles into diamond-like carbon films: The influence of the particle sizes on the electrochemical corrosion resistance

Crystalline diamond (CD) particles are incorporated into diamond-like carbon (DLC) films in order to prevent CD–DLC electrochemical corrosion. In this paper, the influence of the diamond particle sizes on the electrochemical corrosion resistance of CD–DLC films was investigated. The films were grown over 304 stainless steel using plasma enhanced chemical vapor deposition. CD particles with 4 nm, 250 nm, 500 nm and 2–3 µm in diameter were incorporated into DLC during the deposition process. The investigation of CD–DLC electrochemical corrosion behavior was performed using potentiodynamic method. The results show that both protection efficiency and impedance increase with the decrease of I D / I G ratio. It means the increase of sp 3 bonds in DLC films reduces its electrochemical corrosion, improving the electrochemical protection efficiency and the impedance. Our results pointed out that CD–DLC films are promising corrosion protective coatings in aggressive solutions.

Controlled growth of filamentary crystals and fabrication of single-crystal whisker probes

The growth of filamentary crystals (whiskers) on a single-crystal substrate through the vapour-liquid-solid mechanism is described. The possibility of fabricating oriented systems of whiskers on the basis of this mechanism of crystal growth is noted. A phenomenon that is important for nanotechnology is noted: the existence of a critical diameter of whiskers, below which they are not formed. The phenomenon of radial periodic instability, which is characteristic of nanowhiskers, is described and the ways of its elimination are shown. The possibility of transforming whiskers into single-crystal tips and the growth of crystalline diamond particles at their apices are noted as important for practice. Possible applications of systems of whiskers and tips are described briefly. Particular attention is paid to the latest direction in whisker technology—fabrication of single-crystal whisker probes for atomic force microscopy.

Nucleation and growth of crystalline diamond particles on silicon tips

The data on the deposition, structure, and electric properties of crystalline diamond particles at silicon tips grown on single-crystal silicon substrates obtained over the last decade, mainly at the Institute of Crystallography of the Russian Academy of Sciences, have been reviewed. It is shown that silicon emitters coated with crystalline diamond are highly electrically stable. They are used to prepare long-life cathodoluminescence light sources.

Formation of crystalline diamond by ion beam deposition

Direct ion beam deposition was used to study the effect of ion bombardment on the formation of carbon films. Amorphous carbon films were deposited on mirror-polished (0 0 1) silicon substrates by means of a low-energy ion beam of Ar/H 2/CH 4. High-resolution transmission electron microscopy, field emission scanning electron microscopy and micro-Raman microscopy were used to determine some of the properties of the samples. We found that the amorphous carbon film condensed to form clusters and the surface roughness of the film increased with increasing the ion dose. At ion doses ∼10 19/cm 2, crystalline diamond particles with sizes of 15–30 nm were formed in the matrix of amorphous carbon films. The formation of crystalline diamond particles may be due to the ion bombardment induced stress and energy fluctuation.

Cold emission from the single-crystalline microparticle of diamond on a Si tip

Single crystalline diamond particles were grown on the ends of sharp silicon tips. The typical form of the particles was cubooctahedron with a (111) plane on the top. Field emission experiments of Si emitters with single crystalline diamond coating demonstrated hysteresis and normal emission modes. In the hysteresis mode, emission saturated at about 2 μA. Fowler–Nordheim plots for data points below the saturation limit were nonlinear. Transformation from hysteresis to normal behavior occurred with increasing voltage. A modified model of emission through dielectric layers was proposed for explanation of emission properties of diamond.

Diamond synthesis form the gas phase

This paper reviews structural features and some properties of diamond prepared from the gas phase. Single crystalline diamond films are grown on (100), (110) and (111) faces of diamond, and analyzed using secondary ion mass spectrometer. The results indicate that the contamination from a reaction vessel cannot be neglected, and that other impurities with concentration higher than that in natural diamond were not detected. The studies of texture of polycrystalline films deposited on Si by etching in oxidative plasma have revealed that the texture depends on the synthetic conditions. Single crystalline diamond particles and polycrystalline films have been characterized using optical techniques. The results indicate that single crystals prepared under optimum conditions have good crystalline quality similar to type IIa diamond, which is a high purity form in natural diamond. In contrast, the polycrystalline films grown under the same conditions have appreciable amounts of double-bond structures and strain.

An auger electron spectroscopy study of the surface of Ni-Mo cemented Ti(CN) substrates used for deposition of crystalline diamond particles

The surface composition of Ni-Mo cemented Ti(CN) tool inserts was studied by Auger electron spectroscopy under various conditions associated with diamond particle deposition in a microwave plasma using CH 4−H 2 mixtures as the feedstock. The presence of a nickel-rich phase at the surface did not appear to prohibit diamond particle growth, but rather reduced the growth rate relative to a pure TiC surface. Surfaces deliberately enriched in the nickel binder phase did, however, appear to show poor adherence for continuous diamond films grown on them.

マイクロ波プラズマＣＶＤ法によるダイヤモンド種結晶の成長

Crystal growth in a microwave plasma CVD was studied using as seeds crystalline diamond particles produced by an HP-HT technique. Reaction pressure and hydrogen gas flow rate were fixed at 3.3kPa and 2.8cm3/s, respectively, while the methane concentration and reaction duration were variable. A microwave power of 220W was used for most of the runs. Results were evaluated in terms of increase in linear grain dimension. The growth rate reached a maximum at a microwave power of around 220W (1170K estimated) and a methane concentration of about 5.4%. There was a tendency for growth rate to be high in the early stage and to decrease as the process went on, with larger seeds growing more slowly. It was also observed that the growth rate was significantly affected by the surface condition in the early stage.Based on observation of deposited particles and analysis by X-ray diffraction and Raman spectroscopy, methane concentrations not exceeding 1.0% are necessary for producing idiomorphic diamond crystals. Specifically, at concentrations higher than 1.8%, the product was round, with amorphous carbon co-deposited.