Evgeny V. Zavedeev

Growth of single-crystal diamonds in microwave plasma

A microwave plasma (2.45 GHz) was used for depositing single crystal diamond layers at the deposition rate up to 40 μm/h in hydrogen-methane mixtures on the substrates from natural and synthetic diamond with the (100) deposition surface and with the size up to 5 × 5 mm. The structure and the defect-impurity composition of the fabricated single crystals with the thickness up to 600 μm have been investigated using Raman spectroscopy, photoluminescence spectroscopy, cathode luminescence spectroscopy, and electron and optical microscopy. A high quality and purity of the diamond layers deposited from a plasma was confirmed.

Scanning probe microscopy of laser-graphitized diamond-like carbon films

A complex technique of scanning probe microscopy/spectroscopy (SPM/SPS) based on the microscopy of lateral forces and registration of a local electrical conductivity in combination with measurements of the microrelief has been developed for studies of laser-graphitized carbon microstructures. The method includes multiple direct and reverse probe scanning with the subsequent correction of the map position, their pixel-by-pixel subtraction and averaging, and a statistical processing of resulting data arrays concerning the distribution of lateral forces (friction forces). In addition, based on the measurements of currentvoltage (I–V) characteristics, a distribution of the electrical conductivity is built in the probe-sample circuit. Carbon structures based on hydrogenated diamond-like films of a-C:H type, which were deposited onto Si substrates, are used as the objects for studies. A local graphitization of the surface has been carried out by the irradiation of the films with an excimer KrF laser according to a preset microscopic pattern. Based on the resulting data, it is found that the reaction of the lateral forces (friction forces) in the laser-graphitized region is reversed to the temperature variations: when the temperature increases (from room to ∼120°C), the distribution of the friction forces shifts towards higher values and returns practically to the initial values when the temperature decreases to the initial level, which proves the influence of a water adsorbate on the friction properties of laser-graphitized regions on the film surface. It is also found that the laser-graphitized region is structurally inhomogeneous, which is proven by a decrease in the electrical conductivity from the center to the periphery.

Fabrication of graphene nanostructures by probe nanoablation

We present the results of the study of graphene nanoablation under mechanical stress of an ultrasharp (the rounding radius is ∼2 nm) tip of a scanning probe microscope (SPM)). It was found that the SPM probe contact with graphene results in average removal of 7 · 10−3−5 · 10−2 nm of film per scan, i.e., only a few carbon atoms or clusters, in the impact area. The capability of this precision nanoablation process was shown in developing graphene nanoislands and nanoribbons ∼1 µm long and ∼10 nm wide.

New type of regular carbon nanostructures: Nanocones on the surfaces of carbon-silicon (a-C:H) composite films

The results of a study of a new type of regular carbon nanostructures, namely, nanocones on the film surfaces of carbon-silicon composites of the (a-C:H):Si type are given in this paper. Nanocones appear under the action of the electric field of the probe of an air-operated scanning probe microscope (SPM) in the case where the values of the voltage amplitude and the exposure times exceed the threshold ones. The produced nanoobjects preserve their shapes at thermal annealing up to 700°C. It is assumed that the process of nanocone formation is related to the local transformation of the carbon-silicon composite structure from the amorphous to the nanocrystalline state in the electric field of the SPM probe.

Deformation of a laser beam in the fabrication of graphite microstructures inside a volume of diamond

We report a theoretical and experimental study of the energy profile deformation along the laser beam axis during the fabrication of graphite microstructures inside a diamond crystal. The numerical simulation shows that the use of a focusing lens with a numerical aperture NA < 0.1 at a focusing depth of up to 2 mm makes it possible to avoid a noticeable change in the energy profile of the beam due to the spherical aberration that occurs in the case of refraction of the focused laser beam at the air – diamond interface. The calculation results are confirmed by experimental data on the distribution of the laser intensity along the beam axis in front of its focal plane, derived from observations of graphitisation wave propagation in diamond. The effect of radiation self-focusing on laser-induced graphitisation of diamond is analysed. It is shown that if the wavefront distortion due to self-focusing can be neglected at a minimum pulse energy required for the optical breakdown of diamond, then an increase in the beam distortion with increasing pulse energy has no effect on the graphitisation process.

Scanning Probe Lithography of Dendrite-Like Nanostructures in Ultrathin Diamond-Like Nanocomposite Films

Dendrite-like structure growth in ultrathin diamond-like nanocomposite a-C:H,Si:O films have been studied in the course of electrically induced scanning probe lithography in the presence of a water adsorbate. The threshold magnitude of the electrical action is about 2 V, which is close to the potential of water electrolysis—1.23 V. The environment humidity crucially influences the growth of dendrite-like structures. Therefore, at a relative humidity of ~20%, hill-like protrusions occur, whereas, at a relative humidity of ~40%, some radially directed protrusions (ridges) appear and, at a relative humidity of ~60%, some branches arise from the ridges. It is established that the surface of the dendrite-like nanostructures is characterized by a higher friction force in the nanoscale when compared with the initial material under AFM testing. The growth mechanism and friction properties of the dendrite-like nanostructures are discussed.

SPM probe-assisted surface nanostructuring of boron-doped diamond

Surface modification of conductive boron-doped diamond has been conducted using the electrical field of the probe of a scanning probe microscope (SPM) at varying relative humidity (RH) of the ambient environment. It has been found that, under the action of positive polarity pulses applied to the sample via a grounded SPM probe, the sample material undergoes modification. The modification pattern depends on atmospheric RH: low (up to 32%) and high humidity values (above 35%) lead to the formation of cavities and protrusions, respectively. It has been found that the resulting protrusions exhibit temporary instability; that is, a protrusion is partially transformed into an array of nanoobjects. The mechanism of modification of boron-doped diamond–local anodic oxidation–has been discussed.

Laser nanoablation of graphite in argon atmosphere

The results of comparative studies of laser ablation of highly oriented pyrolytic graphite in air and in an inert medium upon exposure to nanosecond pulsed laser irradiation with an energy density in the range E = 0.4 − 3 J/cm2 are presented. It is found that the nanoablation mode is established below the evaporative ablation threshold (E < Ea ≈ 1 J/cm2) in both cases (the average ablation rate is lower than 10−3 nm/pulse); in this case, the nanoablation rate in argon is lower than in air by a factor to 6. The experimental data count in favor of the oxidation mechanism of graphite nanoablation.

Regular nanocones on carbon-silicon composite surface

Presented in this paper is a new effect of nanostructuring, namely the formation of nano-cones under the action of local electric field induced in carbon-silicon composite films underneath the SPM probe

Formation of high-conducting nanostructures in low-conducting diamond-like carbon films using SPM-lithograph

Low-conducting hydrogenated diamond-like carbon (DLC) a-C:H films were examined for the purpose of nanometer-scaled modifications under the action of local electrical field. The capabilities of SPM technique for preparation of conducting nanostructures in the low-conducting a-C:H films have been demonstrated for the first time.