V. G. Ral’chenko

Bolometric detector embedded in a polycrystalline diamond grown by chemical vapor deposition

A fast bolometric detector embedded in a plate of chemical-vapor-deposited polycrystalline diamond was developed and fabricated. The working element of the bolometer is a buried graphitized layer (with temperature-sensitive resistance) fabricated in the bulk of a diamond by C+ ion implantation followed by annealing. The kinetics of the response of the structure to irradiation with light from an LGI-21 pulsed nitrogen laser (λ = 337 nm, τP ∼ 8 ns) were studied. The room-temperature response width at half-maximum is ∼ 20 ns. Using the space-time distribution of responses of the structure, thermal (bolometric) signals were resolved from signals of different nature (photoconductivity or photovoltage).

Losses in diamond in the millimeter range

A theoretical and experimental investigation is made of the magnitude and nature of the dielectric losses in weakly absorbing synthetic diamonds in the wavelength range 1.75–6.8 mm at temperatures T=20–500 °C. Some samples exhibited extremely low losses (tan δ <10−5) which makes plasma-chemically deposited diamond wafers suitable for fabricating windows for megawatt continuous gyrotrons. It is shown that in principle, a further substantial reduction in losses can be achieved.

Novel hybrid ultrahard material

A novel hybrid ultrahard polycrystalline composite material has been produced by the reinforcement of the polycrystalline diamond composite thermostable material with a CVD grown polycrystalline diamond. It has been found that a thermal treatment of a polycrystalline diamond grown at high pressure ensures an increase of the CVD diamond hardness from 77 to 140 GPa. Tests of drilling tools have shown that in turning granite of the XI drillability index the wear intensity of rock destruction elements of the hybrid ultrahard material is lower than that of rock destruction elements of polycrystalline diamond composite thermostable material by a factor of 14.

Thermal conductivity of polycrystalline CVD diamond: Experiment and theory

The temperature dependences of thermal conductivity κ of polycrystalline CVD diamond are measured in the temperature range from 5 to 410 K. The diamond sample is annealed at temperatures sequentially increasing from 1550 to 1690°C to modify the properties of the intercrystallite contacts in it. As a result of annealing, the thermal conductivity decreases strongly at temperatures below 45 K, and its temperature dependence changes from approximately quadratic to cubic. At T > 45 K, the thermal conductivity remains almost unchanged upon annealing at temperatures up to 1650°C and decreases substantially at higher annealing temperatures. The experimental data are analyzed in terms of the Callaway theory of thermal conductivity [9], which takes into account the specific role of normal phonon-phonon scattering processes. The thermal conductivity is calculated with allowance for three-phonon scattering processes, the diffuse scattering by sample boundaries, the scattering by point and extended defects, the specular scattering by crystallite boundaries, and the scattering by intercrystallite contacts. A model that reproduces the main specific features of the thermal conductivity of CVD diamond is proposed. The phonon scattering by intercrystallite contacts plays a key role in this model.

Thermal parameters of layers and interfaces in silicon-on-diamond structures

The heat propagation at room temperature was studied in a heterostructure consisting of a polycrystalline diamond film deposited from a hydrocarbon plasma on an oriented silicon substrate. The dynamics of cooling of a thin-film indium thermometer evaporated atop the diamond film was measured following its heating by nanosecond nitrogen laser pulses. The experimental data were compared with the values calculated in the framework of the theory of thermal conductivity for multilayer systems. This analysis permitted the determination of both the thermal conductivity of the diamond film and the thermal resistance of the diamond/Si and In/diamond interfaces.

Hydrophobic diamond films

The peculiarities of wettability of diamond that was obtained in a nanostructured form as ultrananocrystalline diamond (UNCD) films by deposition from a gas phase are considered. Surface hydrogenation leads to hydrophobicity: advancing contact angle θ for UNCD films reaches 106 ± 1° (for diamond single crystals θ = 93°). Even higher values of θ equal to 124 ± 3° were detected for nanoporous samples of UNCD, in which a graphite-like component was removed by etching. High hydrophobicity is achieved owing to the specific surface morphology of the nanostructured diamond (anisotropic, with high content of nanopores) and chemical modification, which on the whole provides for very low values of free surface energy of the films. It was shown that laser-drilled microholes in polycrystalline diamond also can enhance the hydrophobicity. The wetting behavior of the nanostructured surfaces agrees well with the Cassie-Baxter equation for heterophase porous surfaces. The oxidation and hydrogenation of UNCD films allows controlling of θ in considerably wider ranges compared to single crystal diamond.

Percolation model of an insulator-conductor transition in ultrananocrystalline diamond films

A percolation model has been proposed to explain an insulator-conductor transition in ultrananocrystalline diamond films upon addition of nitrogen to a gas mixture used to synthesize films. An observed jump of the conductivity by 10–12 orders of magnitude is a result of the rearrangement of the structure of films leading to the formation of diamond nanorods in a graphite shell. A nitriding-induced increase in the volume fraction of these nanorods (up to 0.22) has been determined from small-angle X-ray scattering data. Conduction occurs through graphite shells and the percolation threshold corresponds to the volume fraction of conducting nanorods of 0.06.

Nanocomposite electrodes “Titanium nanophase in a silicon-carbon matrix”

The electrode behavior of nanocomposite films deposited onto a sitall substrate is studied, the films containing a titanium-based conducting phase in a dielectric silicon-carbon matrix. With the films’ resistance decreasing, their electrochemical behavior changes from that of “poor conductors” to a nearly “metal-like” one. The electrode’s differential capacitance increases, and the electron transfer in the [Fe(CN)6]3-/4- redox system accelerates. This is explained by an increased number of conducting metal-containing clusters at the film/electrolyte interface.

Electrochemical intercalation of lithium into diamond-pyrocarbon nanocomposites

The electrochemical behavior of composite materials based on nanodiamond and carbal is investigated in the course of cathodic intercalation of lithium from an LiPF6 solution in a mixture of propylene carbonate and diethyl carbonate. The amount of lithium intercalated into the composite increases monotonically with an increase in the content of nondiamond carbon. It is concluded that, in the studied composites, the electrochemically active phase is graphite-like carbon distributed over the nano-(micro-)diamond skeleton. The intercalation capacity of carbal is approximately equal to 33 mA-h per gram of graphite-like carbon.

Stimulated Raman scattering-active isotopically pure 12С and 13С diamond crystals: A milestone in the development of diamond photonics

Isotopically pure 12С and 13С diamonds are synthesized by chemical vapor deposition and impulsive stimulated Raman scattering in these crystals is investigated. The thermal conductivity of 12С isotopically pure damond and natC diamond with natural isotopic composition is measured. Phonon-nondegenerate Stokes lasing based on the χ(3) nonlinearity in the 12С, 13С, and natC diamond “triad” is attained, which opens a new stage in the development of diamond photonics.