Mikhail Shupegin

Laser treatment of tribological DLC films

The friction and wear reduction in applications that allow only a minimal use of liquid lubricants is done with solid lubricant films or with protective coatings, such as diamond-like carbon (DLC). Further improvements are possible if the geometries of the contact surfaces are modified in a controlled way, as we have already demonstrated it for TiN and TiCN. In this work, the possibilities to generate patterned DLC coated low wear tribological surfaces by means of laser processing were investigated. In the first approach, a two step method was used: steel substrates were laser patterned and subsequently DLC films were deposited on them. The second considered approach was the laser processing of coated surfaces. DLC films were irradiated with laser pulses of different durations and energy densities (100 fs, 800 nm, <4 J/cm2; 150 ns, 1064 nm, <10 J/cm2) and the treated spots were examined using optical microscopy, SEM, AFM and Raman spectroscopy. The graphitisation of a-C:H films under both fs- and ns- regimes was shown as well as a film-peeling phenomenon during the ablation process. Microstructured and DLC coated surfaces obtained in the former approach were used for preliminary tribological tests (oscillation-friction-wear method). The results showed that the friction coefficient did not increase, as compared with the unstructured and DLC coated surfaces, and that the structure pores trapped the debris particles produced when the DLC film eventually broke.

Space-charge-limited current in hydrogenated amorphous carbon films containing silicon and oxygen

Abstract Evolution of the dark room-temperature current–voltage characteristics of hydrogenated amorphous carbon films containing silicon and oxygen with deposition energy growth was investigated at applied electric fields up to 6×10 5 V/cm. It was shown that the character of current voltage dependences is influenced by the deposition energy, which is determined by the value of the self-bias voltage, V sb , varied in the range from −100 to −1400 V, and is described in terms of the space-charge-limited current in the presence of bulk traps, presumably having an exponential energy distribution. In films deposited at moderate values of self-bias voltage (−400 to −800 V) the trap-filled limit mode of the Gaussian-distributed deep trap set in the electric fields 5×10 3 –10 5 V/cm was observed. At electric fields exceeding 3×10 5 V/cm, phonon-assisted tunneling through the reduced electric-field potential barrier of the trap enhances the space-charge-limited current. The absence of thermal activation of the carriers at the mobility threshold caused by the reduction in trap depth in the electric field suggests deviation of the trap potential from the Coulomb one.

Electron transport in W-containing amorphous carbon?silicon diamond-like nanocomposites

The electron transport in amorphous hydrogenated carbon?silicon diamond-like nanocomposite films containing tungsten over the concentration range 12?40?at.% was studied in the temperature range 80?400?K. The films were deposited onto polycrystalline substrates, placed on the RF-biased substrate holder, by the combination of two methods: PECVD of siloxane vapours in the stimulated dc discharge and dc magnetron sputtering of tungsten target. The experimental dependences of the conductivity on the temperature are well fitted by the power-law dependences over the entire temperature range. The results obtained are discussed in terms of the model of inelastic tunnelling of the electrons in amorphous dielectrics. The average number of localized states n in the conducting channels between metal clusters calculated in the framework of this model is characterized by the non-monotonic dependence on the tungsten concentration in the films. The qualitative explanation of the results on the basis of host carbon?silicon matrix structural modifications is proposed. The evolution of the carbon?silicon matrix microstructure by the increase in the tungsten concentration is confirmed by the Raman spectroscopy data.

Metal-Containing Diamond-Like Nanocomposite Thin Film for Advanced Temperature Sensors

The conductivity of metal-carbon-silicon nanocomposite films considered as potential candidates for the application as wide-range temperature sensors for severe environmental conditions is studied. The films combine unique properties of amorphous carbons with a new functionality imparted by the presence of metal nanoclusters in host matrix. The deposition of carbon-silicon phase was performed using PECVD of siloxane vapors. Metals (W, Nb, and Cr) with concentration in the range from 12 to 40 at. % were incorporated in the carbon-silicon host matrix by DC magnetron co-sputtering. The conductivity of the films decreases with temperature in the range 80-400 K, being well described by the power-law dependence. The conductivity mechanism found satisfactory explanation in the framework of the model of inelastic tunneling of electrons between metal nanoclusters dispersed in carbon-silicon matrix. The parallel study of the influence of metal concentration increase on carbon phase microstructure was carried out using Raman spectroscopy.

Electron Transport in Amorphous Carbon–Silicon Nanocomposites Containing Nb

The evolution of the electron transport in Nb-containing hydrogenated amorphous carbon–silicon nanocomposite films with an increase in niobium concentration in the range of 13–33 at.% was studied in the wide temperature range of 80–400 K. The films were deposited onto ceramics substrates by the combination of DC magnetron sputtering of a Nb target and decomposition of siloxane vapors in a stimulated DC discharge. The model of inelastic tunneling of electrons in amorphous dielectrics was applied to analysis of the experimental conductivity–temperature dependences. It was shown that the average number of localized states in the potential barriers between metal clusters is not greater than 2 and nonmonotonically depends on Nb concentration in the investigated films. This dependence can be explained in terms of the modifications both of metal and carbon phase structures by increasing metal concentration. The Raman spectroscopy data demonstrate that these structural transformations take place in the carbon phase of the host matrix as the Nb concentration exceeds 23–25 at.%. An increase in the average size of sp2 clusters from 0.7–0.9 up to 1.1–1.3 nm is observed.

Femtosecond-laser surface modification and micropatterning of diamond-like nanocomposite films to control friction on the micro and macroscale

Laser surface micropatterning (texturing) of hard materials and coatings is an effective technique to improve tribological systems. In the paper, we have investigated the laser-induced surface modifications and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H,Si:O) using IR and visible femtosecond (fs) lasers, focusing on the improvement of frictional properties of laser-patterned films on the micro and macroscale. The IR and visible fs-lasers, operating at λ = 1030 nm and λ = 515 nm wavelengths (pulse duration 320 fs and pulse repetition rate 101 kHz), are used to fabricate different patterns for subsequent friction tests. The IR fs-laser is applied to produce hill-like micropatterns under conditions of surface graphitization and incipient ablation, and the visible fs-laser is used for making microgroove patterns in DLN films under ablation conditions. Regimes of irradiation with low-energy IR laser pulses are chosen to produce graphitized micropatterns. For these regimes, results of nume...

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.

Superconducting property in tungsten containing amorphous carbon composite

Superconductivity in tungsten-containing carbon-oxide film was reported. The film with 500 nm thickness was deposited onto polycrystalline silicon-oxides using chemical vapor deposition and co-sputtering of tungsten metal target. The structure of the film was investigated by Raman spectroscopy and X-ray diffraction measurements and the results indicated that the structure of the film is amorphous. The temperature dependence on resistivity was measured in the temperature range of 2-300 K. At the temperature of around 4.2 K resistive superconducting transition was observed. In order that the tungsten oxide and tungsten carbide with which super-conductive transition temperature is different formed the finite cluster group, it can be understand by percolation theory that the superconducting phase of the total system appears. The diamagnetism was observed below 3.8 K, which is consistent with resistive superconducting transition.

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.