A comparative study of the wettability of ultrahard amorphous carbon (UAC), formed by sp3 bonds alone, and diamond (100) facets, has been performed experimentally using atomic force spectroscopy. The capillary forces for UAC and diamond are found to be similar within the 10 % measurement error. Based on a relationship between the capillary force and the contact angle for the substrates, it is concluded that the contact angles for hydrogenated diamond (81 degrees) and ultrahard amorphous sp3 carbon are close.

Synthesis of diamond layers with reduced dislocation density is vital for diamond application in electronics and photonics. The method of epitaxial lateral growth (ELO) based on blocking the dislocations propagation by a patterned mask on the substrate, is promising to control the dislocations. Here, we demonstrate the epitaxial diamond growth using a novel type of the mask for diamond ELO, consisting of a few monolayers thick self-assembled periodic lattice of submicron SiO2 spheres (opal structure). The method is simple, and does not require a lithography technique for the pattern definition. The porous opal mask with SiO2 spheres of approximate to 240 nm diameter was deposited on HPHT diamond substrates, then the epitaxial film was grown from bottom by microwave plasma CVD in a CH4-H-2-O-2 gas mixture. After penetration through the void system, a continuous smooth diamond film formed on the surface of the opal layer. High resolution transmission electron microscopy (HRTEM), electron diffraction and electron back scattering diffraction unambiguously indicated the single crystal structure of the formed diamond film, which were analyzed also with Raman and photoluminescence spectroscopy. The realized ELO version is promising for growth of low-defect single crystal diamond material, provided a further improvement of the opal mask colloidal templating.

We deposited self-assembled films of a few monolayers of silica spheres from the water-based colloid on vertically moving hydrophilic single crystal diamond substrates. The use of acoustic agitation of the water suspension with the SiO2 nanospheres significantly improved the long-range order of the films with opal structure. The study examines the evolution of the structure, specifically the size of single crystal domains, with the assistance of sound frequency (0-2500 Hz) and intensity (0-125 dB). Optimal (resonance) parameters are determined based on scanning electron microscopy and optical reflection spectroscopy of the films. The production of high-quality photonic crystals, including templates for diamond-based ordered composites and inverse opal structures, is a promising application of acoustic crystallization of opals on diamond substrates.

The kinetics of the synthesis of silica nanoparticles (<50 nm) has been studied under the conditions of heterogeneous hydrolysis of tetraethoxysilane (TEOS) using L-arginine as an alkaline catalyst. The rates of silica formation have been determined in a temperature range of 10–95°C at catalyst concentrations of 6–150 mM. It has been shown that the activation energy of the process depends on catalyst concentration and varies in a range of 21.5–13.9 kJ/mol, while decreasing linearly with increasing concentration of L-arginine in the system. The criterion of maintaining the monodispersity has been estimated for SiO2 particles being grown “onto seeds.” The density of submicron-sized silica particles has been experimentally determined as depending on the annealing temperature. Within a temperature range of 200–1000°C, the particle density varies from 2.04 to 2.20 g/cm3.

3D ordered hollow diamond spheres packed into opal structure have been synthesized by chemical vapor deposition using silicon inverse opal template which, in turn, was produced by molding of a bulk silica opal template. These 3D diamond opals demonstrate optical properties of photonic crystal with Bragg reflection peak in the visible range. Numerical modeling of the reflection spectra is performed using a scattering matrix calculation, and agrees well with the measured Bragg peak positions. The porous structure consisting of nanocrystalline diamond shells with thickness of the order of 10 nm composes the light-weight material with density of approximate to 0.50 g/cm3. The diamond opals showed bright photoluminescence at 738 nm wavelength due to siliconvacancy centers formation in course of the growth process. The diamond opals can be a new promising platform for versatile applications, primarily in photonics, due to wide transparency window, high chemical resistance and mechanical strength inherent to diamond.

It is recommended to use high-speed milling to maintain an effective material removal rate and the required cutting-edge geometry. However, on the other hand, high speed increases wear, so the surface of the cutters is modified by deposition functional coatings. The wear of end mills made of CTS12D and H10F tungsten carbides during the high-speed processing of aluminum A97075 (B95T1) was compared. To increase the durability of the tools, well-proven technologies for deposition diamond-like and polycrystalline diamond coatings in microwave plasma with different film structures, which were determined by the coating growth conditions, were used. The milling cutter corner was mostly worn out, but the nature of the wear had its characteristics. It was revealed that at a forced cutting mode of about 1000 m/min, cutters made of CTS12D alloy with a nanocrystalline diamond coating with a “cauliflower” structure and with a diamond-like film showed 10% higher resistance. The primary wear mechanism was adhesive. Images of worn cutting edges were obtained using a 3D optical digital image processing system.

The chemical vapor deposition synthesis of periodic structures in the form of single-crystal diamond–SiO2 nanosphere composites, which exhibit the properties of photonic crystals in the visible spectral range, are reported.

We report on synthesis of periodical structures by chemical vapor deposition in form of a composite “single crystal diamond – SiO2 nanospheres” which shows photon crystal properties in the visible.

Hydrogen plasma treatment of thin films and bulk silica is important process for surface cleaning, smoothing and patterning. We studied etching of SiO2 plates in H2 + O2 microwave plasma at moderate pressures at high temperatures in the range of 790-1300 degrees C. A low-coherent optical interferometer was used for simultaneous in situ measurement of etch rate (ER) and the SiO2 temperature. We show that even a small addition of O2 (<1%) in microwave H2 plasma can effectively reduce the SiO2 ER due to redox reaction. Using an optical profilometry and atomic force microscopy we observed not only a strong etching inhibition by O2 addition in gas, but a signifi-cantly smoother etched surface as well. The activation energies Ea = 128 +/- 8 kJ/mol and 276 +/- 23 kJ/mol are found for the etching in pure H2 and H2 + 0.4 %O2 plasmas, respectively. An exponential dependence of ER on O2 content in gas is established, particularly, the O2 concentration as small as 2.6 % is sufficient to reduce the ER by 100 times. The effect of oxygen induced etching slow-down is supported by thermodynamic consideration of the surface reactions involved. The experiments were complimented with the plasma diagnostics by optical emission plasma spectroscopy to detect volatile etching products, and other species such as OH, and correlate the Si emission intensity with the measured ER. Our results confirm the efficiency of oxygen to control in a wide range the etch rate and surface topography upon atomic hydrogen etching in a microwave plasma.

We report on a novel method for porous diamond fabrication, which is based on the synthesis of diamond-germanium composite films followed by etching of the Ge component. The composites were grown by microwave plasma assisted CVD in CH4-H-2-GeH4 mixtures on (100) silicon, and microcrystalline- and single-crystal diamond substrates. The structure and the phase composition of the films before and after etching were analyzed with scanning electron microscopy and Raman spectroscopy. The films revealed a bright emission of GeV color centers due to diamond doping with Ge, as evidenced by photoluminescence spectroscopy. The possible applications of the porous diamond films include thermal management, surfaces with superhydrophobic properties, chromatography, supercapacitors, etc.

In this study, we investigated the effect of the size of diamond seeds on the adhesion of multilayered poly-crystalline diamond (PCD) films, grown by microwave plasma-assisted chemical vapor deposition (MPCVD). For that, identical WC-Co substrates were separately seeded by a set of diamond powders with various average particle sizes from water-based suspensions using similar seeding procedures. This investigation included pow-ders with a difference in particle sizes of nearly 3 orders of magnitude: from 5 nm up to 2-4 mu m. Seeded substrates were used to grow 8-10 mu m thick multilayered PCD films using MPCVD with time-limited cycling injections of N2 gas. The Raman spectra and scanning electron microscopy (SEM) studies showed the similarity of microstructure and phase composition of all grown films, which confirmed that all films were grown in similar conditions. The performed scratch tests revealed sufficient differences in the adhesion of the films seeded with different diamond particles. The PCD film grown on 250-500 nm particles delaminated even before any mechanical investigations. The substrates seeded with 50 nm particles allowed the formation of the stable PCD film, but it started flaking under a load as small as 15 N. The 2-4 mu m powder allowed the formation of PCD film with decent adhesion, which had local flaking under scratch test, which can be explained by the inhomogeneity of seeds distribution. Detonation nanodiamond (DND) powders allowed the formation of continuous diamond films with decent adhesion, however, powders with positive zeta potential were superior due to a much lower agglomeration of separate particles.

Conformal multilayer micro-nanocrystalline diamond coatings were grown on substrates of a hard alloy with 9% Co with a high aspect number in microwave plasma from gas mixtures CH4/H2 and CH4/H2/N2. The substrates were of a cylindrical axial tool model with a size ratio: d = 12 mm to l = 75 mm. An original tool holder made of molybdenum, in the form of a sector of the excessive ring with the axis of the hole parallel to the central conductive platform, protects part of the substrate from heating due to the edge effect of plasma. The uniformity of heating of the growth part, which is located inside the excessive ring, is calculated using mathematical modeling and is provided by rotation at a speed of at least 12 rpm, which ensures the uniformity of the coating. The average grain size of the nanocrystalline film measured along the cylinder forming was 41 nm.

We report on synthesis of periodical structures by chemical vapor deposition in form of a composite “single crystal diamond – SiO2 nanospheres” which shows photon crystal properties in the visible.

Laser milling of silicon by IR picosecond pulses (lambda = 1030 nm) has been investigated with a special emphasis on influence of laser fluence, spot size and spot overlapping on the surface roughening and ablation productivity. The detailed recipe for optimization of the silicon milling process has been formulated: reduction of the maximum laser fluence down to about ~1 J/cm(2) by means of corresponding laser spot enlargement, while the ratio of the laser spot displacement to the spot radius is maintained below the level of 0.3. Fulfillment of these conditions provides minimal possible surface roughness at moderate reduction of the ablation productivity. The silicon ablation process under multi-spot irradiation was numerically simulated to specify which of two factors plays a decisive role in the surface roughening at different processing conditions: spatial non-uniformity of laser exposure or ablation-induced surface instabilities.

The production of carbide tools with polycrystalline diamond coatings, which are used for processing modern carbon composite materials, includes a number of technological techniques that ensure reliable adhesion of the coating to the substrate. This review examines these features of substrate-surface pretreatment to improve adhesion, which includes chemical etching, mechanical hardening, modification by ion beams, plasma treatment and application of buffer layers between the substrate and the coating. This review also discusses the advantages and disadvantages of the most common methods for obtaining polycrystalline diamond coatings using hot filament and deposition of coatings from microwave plasma.

Radio transparency of polycrystalline CVD-diamond disks with diameter up to 75 mm in millimeter-wave range was measured by free-space method. The structure of the disks was characterized by Raman spectroscopy and scanning electron microscopy. Dielectric loss tangent of the samples in the frequency range of 50-67 GHz was found to be in the range of 7.5· 10-3-8· 10-2, increasing with frequency. The transmission loss due to the radiation absorption is about 1%. Keywords: millimeter-waves, polycrystalline diamond, radio transparency.

We produced microcrystalline diamond coatings with nanocrystalline top diamond layer on WC-Co cutting inserts in a microwave plasma (2.45 GHz) chemical vapor deposition reactor. The coatings have a high uniformity of the substrate surface owing to elimination of the plasma edge effect by application of a moveable quartz ring above the substrate holder. Computer modeling showed how the positioning of the ring changes the electromagnetic field around the substrates. A new approach was used to stabilize the temperature of the cutting inserts during the coating process, which is based on in situ control of the quartz ring position by proportional-integral-differential (PID) regulation. The coatings have been characterized with microRaman spectroscopy in a mapping mode in cross section of the samples. Depth profiles of diamond Raman peak position and width are demonstrated and the stress in the films is estimated, the minimum stress being determined for the cutting insert apex. (C) 2020 Elsevier Ltd. All rights reserved.

An increase in the radiation power of terahertz (THz) sources requires the development of new optics working with it. The laser-assisted replication technique is proposed to fabricate the diamond cylindrical diffractive lens with a continuous profile for the THz range. The procedure involves the inverted structuring of a silicon substrate by laser ablation for its further replication to the diamond surface utilizing the chemical vapor deposition process. Testing of the fabricated lens performed with a free-electron laser at the wavelength of 141 µm has demonstrated high diffraction efficiency ( 95 ± 5 % ) and a good agreement between the measured and expected intensity distribution in the focal plane.

Radio transparency of polycrystalline CVD-diamond disks with diameter up to 75 mm in millimeter-wave range was measured by free-space method. The structure of the disks was characterized by Raman spectroscopy and scanning electron microscopy. Dielectric loss tangent tan δ of the samples in the frequency range of 50 – 67 GHz was found to be in the range of 7.5·10−3 − 2.8·10−2, increasing with frequency. The transmission loss due to the radiation absorption is about 1%.