Graphite-like Amorphous Carbon Research Articles

Ballistic-aggregated Carbon Nanofoam in Target-side of Pulsed Laser Deposition for Energy Storage Applications.

In pulsed laser deposition, along the traditionally exploited deposition on the front-side of the plasma-plume, a coating forms on the surface of the target as well. For reproducibility, this residue is usually cleaned and discarded. Here we instead investigate the target-side coated materials and employ them as a binder-free supercapacitor electrode. The ballistic-aggregated, target-side nanofoam is compact and features a larger fraction of sp2-carbon, higher nitrogen content with higher graphitic-N and lower oxygen content with fewer COOH groups than that of diffusive-aggregated conventional nanofoams. They are highly hydrogenated graphite-like amorphous carbon and superhydrophilic. The resulting symmetric micro-supercapacitor delivers higher volumetric capacitance of 522 mF/cm3 at 100 mV/s and 104% retention after 10000 charge-discharge cycles over conventional nanofoam (215 mF/cm3 and 85% retention) with an areal capacitance of 134 μF/cm2 at 120 Hz and ultrafast frequency response. Utilizing the normally discarded target-side material can therefore enable high performing devices while reducing waste, cost and energy input per usable product. leading towards a greater sustainability on nanomaterials synthesis and deposition techniques.

Effect of carbon content on microstructure, mechanical properties and tribological behavior of HfZrC coating

The HfZrC coatings containing varying carbon contents were fabricated by magnetron sputtering method. The relationship between coating composition and mechanical properties as well as tribological behavior was studied. The coatings containing lower carbon are mainly composed of (Hf,Zr)C carbide, less metal and amorphous graphite-like carbon (GLC). The increasing carbon contents significantly favored the formation of (Hf,Zr)C carbide, leading to the enhanced hardness and elastic modulus. Excessive carbon increased the GLC content, thus degrading the two aforementioned performances. During the friction process, the low-carbon coating fractured in a short friction duration due to the remarkable shear stress. The abrasive wear dominated the following friction process, resulting in severe wear loss of TC4 substrate. Comparatively, the lubricant GLC in high-carbon coating alleviated the coating fracture. Hence, the wear rate of high-carbon coatings was decreased significantly by inhibiting the abrasive wear.

The Use of Sacrificial Graphite-like Coating to Improve Fusion Efficiency of Copper in Selective Laser Melting

Thin and ultrathin carbon films reduce the laser energy required for copper powder fusion in selective laser melting (SLM). The low absorption of infrared (IR) radiation and its excellent thermal conductivity leads to an intricate combination of processing parameters to obtain high-quality printed parts in SLM. Two carbon-based sacrificial thin films were deposited onto copper to facilitate light absorption into the copper substrates. Graphite-like (3.5 µm) and ultra-thin (25 nm) amorphous carbon films were deposited by aerosol spraying and direct current magnetron sputtering, respectively. The melting was analyzed for several IR (1.06 µm) laser powers in order to observe the coating influence on the energy absorption. Scanning electron microscopy showed the topography and cross-section of the thermally affected area, electron backscatter diffraction provided the surface chemical composition of the films, and glow-discharge optical emission spectroscopy (GDOES) allowed the tracking of the in-deep chemical composition of the 3D printed parts using carbon film-covered copper. Ultra-thin films of a few tens of nanometers could reduce fusion energy by about 40%, enhanced by interferences phenomena. Despite the lower energy required, the melting maintained good quality and high wettability when using top carbon coatings. A copper part was SLM printed and associated with 25 nm of carbon deposition between two copper layers. The chemical composition analysis demonstrated that the carbon was intrinsically removed during the fusion process, preserving the high purity of the copper part.

Ti3C2Tx solid lubricant coatings in rolling bearings with remarkable performance beyond state-of-the-art materials

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, known as MXenes, are a growing class of 2D materials, which offer great solid lubrication ability for low friction applications due to their weakly bonded multi-layer structure and tribo-layer formation with self-lubricating characteristics. To date, most studies have assessed their tribological response in basic laboratory tests. However, these tests do not adequately reflect the complex geometries, kinematics, and stresses present in machine components. Here, we aim at bridging this gap through assessment of the friction and wear performance of multi-layer Ti3C2Tx MXene solid lubricant coatings used in rolling bearings. MXenes’ tribological response is compared with state-of-the art solid lubricant coatings, which include molybdenum disulfide (MoS2), tungsten-doped hydrogenated amorphous carbon (a-C:H:W), and hydrogen-free, more graphite-like amorphous carbon (a–C). Multi-layer Ti3C2Tx MXene coatings reduce wear on the bearing washers by up to 94%, which can be attributed to the transfer of the lubricious MXene nano-sheets to secondary tribo-contacts of the bearing. While the frictional torque of all solid lubricant coatings is similar during steady-operation, the MXene-coated bearings extend the service life by 30% and 55% compared to MoS2 and DLC, respectively. This contribution demonstrates the ability of MXene solid lubricant coatings to outperform state-of-the-art solid lubricants in dry-running machine components such as rolling bearings.

Voltammetric pH sensor based on electrochemically modified pseudo-graphite.

A nanocrystalline graphite-like amorphous carbon (graphite from the University of Idaho thermolyzed asphalt reaction, GUITAR) shares morphological features with classical graphites, including basal and edge planes (BP, EP). However, unlike graphites and other sp2-hybridized carbons, GUITAR has fast heterogenous electron transfer (HET) across its basal planes, and resistance to corrosion similar to sp3-C and boron-doped diamond electrodes. In this contribution, quinoid modified BP-GUITAR (q-GUITAR) is examined as a sensor for pH determination. This modification is performed by applying 2.0 V (vs. Ag/AgCl) for 150 seconds followed by 15 cyclic voltammetric scans from -0.7 to 1.0 V at 50 mV s-1 in 1.0 M H2SO4. The quinoid surface coverage of q-GUITAR is 1.35 × 10-9 mol cm-2, as measured by cyclic voltammetry. X-ray photoelectron spectroscopy analysis also confirms the high surface coverage. The quinoid surface concentration ranks highest in literature when compared with other basal plane graphitic materials. This yields a sensor that responds through a square wave voltammetric reduction peak shift of 63.3 mV per pH over a pH range from 0 to 11. The response on q-GUITAR is stable for >20 measurements and no surface re-activation is required between the measurements. The common interferents, Na+, K+ and dissolved oxygen, have no effect on the response of the q-GUITAR-based pH sensor.

Occurrence of Graphite-Like Carbon in Podiform Chromitites of Greece and Its Genetic Significance

The role of post-magmatic processes in the composition of chromitites hosted in ophiolite complexes, the origin of super-reduced phases, and factors controlling the carbon recycling in a supra-subduction zone environment are still unclear. The present contribution compiles the first scanning electron microscope/energy-dispersive (SEM/EDS) data on graphite-like amorphous carbon, with geochemical and mineral chemistry data, from chromitites of the Skyros, Othrys, Pindos, and Veria ophiolites (Greece). The aim of this study was the delineation of potential relationships between the modified composition of chromite and the role of redox conditions, during the long-term evolution of chromitites in a supra-subduction zone environment. Chromitites are characterized by a strong brittle (cataclastic) texture and the presence of phases indicative of super-reducing phases, such as Fe–Ni–Cr-alloys, awaruite (Ni3Fe), and heazlewoodite (Ni3S2). Carbon-bearing assemblages are better revealed on Au-coated unpolished sections. Graphite occurs in association with hydrous silicates (chlorite, serpentine) and Fe2+-chromite, as inclusions in chromite, filling cracks within chromite, or as nodule-like graphite aggregates. X-ray spectra of graphite–silicate aggregates showed the presence of C, Si, Mg, Al, O in variable proportions, and occasionally K and Ca. The extremely low fO2 during serpentinization facilitated the occurrence of methane in microfractures of chromitites, the precipitation of super-reducing phases (metal alloys, awaruite, heazlewoodite), and graphite. In addition, although the origin of Fe–Cu–Ni-sulfides in ultramafic parts of ophiolite complexes is still unclear, in the case of the Othrys chromitites, potential reduction-induced sulfide and/or carbon saturation may drive formation of sulfide ores and graphite-bearing chromitites. The presented data on chromitites covering a wide range in platinum-group element (PGE) content, from less than 100 ppb in the Othrys to 25 ppm ΣPGE in the Veria ores, showed similarity in the abundance of graphite-like carbon. The lack of any relationship between graphite (and probably methane) and the PGE content may be related to the occurrence of the (Ru–Os–Ir) minerals in chromitites, which occur mostly as oxides/hydroxides, and to lesser amounts of laurite, with pure Ru instead activating the stable CO2 molecule and reducing it to methane (experimental data from literature).

Structure and electronic properties of biomorphic carbon matrices and SiC ceramics prepared on their basis

Biomorphic carbon matrices (BCMs) were produced by pyrolysis from wood species of different forest and garden trees, after which the as-prepared BCMs were converted to SiC ceramics through their impregnation with liquid silicon and further heat-treatment. Both types of obtained samples were studied by scanning electron microscopy (SEM), Raman scattering (RS), and electron spin resonance (ESR) methods. The SEM data reveal that all BCM samples contain large (10–50 μm) and small (1–5 μm) micro-pores with surface densities ∼109 m−2 and 1011 m−2, respectively. Analysis of RS allowed to estimate carbon cluster sizes of about 5–11 nm depending on the sample type. The study of the electronic structure using ESR spectroscopy is carried out for BCM and SiC ceramics samples. Using theoretical analysis of the ESR spectra, it was found that spin resonance in BCMs is due to the contribution of three spin systems: free electron spins, “pseudo-free” electron spins from the tail of density states below the conduction band, and localized spins at dangling carbon bonds (DCBs). Their contributions depend on the ratio of different structural phases such as sp2-hybridized graphite-like carbon network and amorphous carbon phase. For most BCM samples, the large ESR line width is dramatically narrowed when samples are pumped out due to the exclusion of the broadening effect of molecular oxygen. The transformation of BCM into SiC by impregnation with liquid silicon can be clearly traced in the Raman spectra and in the ESR spectra. It is established that the electronic properties of synthesized SiC ceramics are due to the presence of residual graphite-like carbon nanoclusters.

An Alternative Scenario on the Origin of Ultra-High Pressure (UHP) and Super-Reduced (SuR) Minerals in Ophiolitic Chromitites: A Case Study from the Mercedita Deposit (Eastern Cuba)

The origin of the assemblage of ultra-high pressure (UHP), super-reduced (SuR) and several crustally derived phases in ophiolitic chromitites is still hotly debated. In this paper, we report, for the first time, this assemblage of phases in ophiolitic chromitites of the Caribbean. We studied the Mercedita chromitite deposit in the eastern Cuban ophiolitic complexes. The mineral phases were characterized using microRaman spectroscopy, energy-dispersive spectroscopy with a scanning electron microscope (SEM-EDS), X-ray microdiffraction and electron microprobe analyses. Mineral concentrates were prepared using hydroseparation techniques. We have identified oriented clinopyroxene lamellae in chromite, oriented rutile lamellae in chromite, moissanite hosted in the altered matrix of the chromitite, graphite-like amorphous carbon, corundum and SiO2 hosted in healed fractures in chromite grains, and native Cu and Fe–Mn alloy recovered in heavy-mineral concentrates obtained by hydroseparation. This assemblage may correspond to UHP-SuR conditions, implying recycling of chromitite in the mantle or formation of the chromite grains at deep mantle depths, followed by emplacement at a shallow level in the mantle. However, the chromitite bodies contain gabbro sills oriented parallel to the elongation of the chromitite lenses, and these show no evidence of HP/UHP metamorphism. Therefore, the identified “exotic” phases may not be indicative of UHP. They formed independently as oriented clinopyroxene lamellae in chromite during cooling (clinopyroxene and rutile), in super-reduced microenvironments during the serpentinization processes, and by transference of subducted crustal material to the mantle wedge via cold plumes.

The study of adaptable amorphous carbon films deposited on As40Se60 glass

The adaptable amorphous carbon films were deposited on As40Se60 glass by radio frequency magnetron sputtering method (rf MS). The effect of CH4 flow rate (0 sccm to 20 sccm) on the structural, optical and mechanical properties of films was investigated by Raman Spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscope (SEM), UV–vis spectrophotometer, Fourier Transformed Spectroscopy and Continuous Stiffness Measurement. The results reveal that the radical ions and neutrals decomposed from CH4 precursor transform fused aromatic rings clusters of amorphous carbon films to olefinic chains clusters, promote the CH sp3 structure and transforms the amorphous carbon films from diamond-like carbon (DLC) structure to highly hydrogenated graphite-like amorphous carbon (GLCHH) structure. GLCHH films show high visible transmittance, wide optical gap (Eg = 3.30 eV, 20 sccm), well infrared antireflection ability, relative high nanohardness (3.61 GPa, 5 sccm), high ERP (72.5%, 5 sccm), high H/E (0.15, 5 sccm), low residual stress (0.20 GPa, 20 sccm) and well adhesion on As40Se60 glass. Meanwhile, the deposition temperature of GLCHH films (≤115 °C) is much lower than the transition temperature (185 ± 5 °C) of As40Se60 glass, which can minimize the thermal deformation of optical lens made from As40Se60 glass.

Preparation, biocompatibility, and biotribological properties of TiN-incorporated graphite-like amorphous carbon bio-ceramic composite films

In this work, TiN-incorporated graphite-like amorphous carbon (a-GLC) bioceramic films were successfully fabricated on Ti alloy (Ti6Al4V) using the magnetron sputtering technique. The biocompatibility and biotribological properties of the TiN/a-GLC-coated Ti alloy were evaluated. Based on the clinical application, the microstructure, biocompatibility, histomorphological observation, and mechanical properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nanoindentation test, and in vitro and in vivo tests including MTT, cell adhesion test, and slice observation of hard tissues. These techniques confirmed that there was strong bonding between the Ti alloy and the TiN/a-GLC film. In addition, face-centered cubic TiN and hexagonal close-packed Ti were clearly detected in the TiN/a-GLC films. A partial nanocomposite structure, comprised of homogeneous nanoclusters and crystalline particles, was detected in the amorphous matrix. Cell adhesion and MTT test results indicated that the TiN/a-GLC film could promote cell attachment and proliferation. Phase composition and the film morphology were determined to be the crucial factors that contributed to the improved biocompatibility. The biotribological property test showed that the TiN/a-GLC film with a Ti content of 7.8at% had the lowest coefficient of friction (COF) of 0.076 and the lowest wear rate of 1.76 × 10–6mm3(Nm)–1. The low COF was attributed to the superior mechanical properties of the TiN/a-GLC composite film. The TiN/a-GLC-coated Ti alloy implants were placed subcutaneously into rabbits for different time periods, and the tissue response decreased significantly as compared to that of the pure a-GLC film. The excellent biocompatibility and function reliability of the TiN/a-GLC bioceramic films showed that they are potential candidates for bone tissue implants.

The Effect of Stress in the Density of States of Amorphous Carbon Films Determined by X-Ray Excited Auger Electron Spectroscopy

Amorphous carbon films can be prepared with a large variety of structure and have been used in a number of technological applications. Many of their properties have been determined, but very little is known concerning the effect of pressure on their properties. In this work we investigate the influence of pressure of graphite-like amorphous carbon films on the density of states (DOS) using X-ray Excited Auger Electron Spectroscopy (XAES) and the second derivate method of the XAES. The films were deposited by ion beam deposition and simultaneously bombarded with argon, which is responsible for the variation of the film stress, reaching extremely high values (4.5 GPa). Marked variations of the density of states of the pπ, pσ, sp, and s components were observed with increasing stress.

Comparison of the scuffing behaviour and wear resistance of candidate engineered coatings for automotive piston rings

Continuous optimization of advanced coatings is required to achieve technology advances and strict emission standards in automotive systems. Integration of conventional ceramic coatings and hard amorphous graphite-like carbon (GLC) with low friction is an economically feasible way of achieving superior efficiency of oil and durability as well as scuffing resistance. This work evaluates the scuffing resistant capacity and durability of engineered coating materials. The presence of GLC not only combats the scuffing damage and running instability effectively for conventional chromium-based coatings, and also improves the reliability and robustness of the piston rings. The scuffing mechanism of the engineered rings with and without GLC surface will be discussed by the observation of the damaged characteristics and the chemistry of the rubbing parts. This will potentially benefit to optimize the coating material in the piston assembly of engine.

Computational Evaluation of Amorphous Carbon Coating for Durable Silicon Anodes for Lithium-Ion Batteries.

We investigate the structural, mechanical, and electronic properties of graphite-like amorphous carbon coating on bulky silicon to examine whether it can improve the durability of the silicon anodes of lithium-ion batteries using molecular dynamics simulations and ab-initio electronic structure calculations. Structural models of carbon coating are constructed using molecular dynamics simulations of atomic carbon deposition with low incident energies (1–16 eV). As the incident energy decreases, the ratio of sp2 carbons increases, that of sp3 decreases, and the carbon films become more porous. The films prepared with very low incident energy contain lithium-ion conducting channels. Also, those films are electrically conductive to supplement the poor conductivity of silicon and can restore their structure after large deformation to accommodate the volume change during the operations. As a result of this study, we suggest that graphite-like porous carbon coating on silicon will extend the lifetime of the silicon anodes of lithium-ion batteries.

Sol–gel based simonkolleite nanopetals with SnO2 nanoparticles in graphite-like amorphous carbon as an efficient and reusable photocatalyst

Sol–gel based simonkolleite nanopetals/SnO2 nanoparticles embedded in graphite-like amorphous carbon is described as a photocatalyst towards degradation of rhodamine 6G dye under UV illumination.

Tribological Properties of Si-Doped Graphite-Like Amorphous Carbon Film of PEEK Rubbing with Different Counterparts in SBF Medium

The present investigation has been conducted in order to evaluate the friction and wear behaviors of polyaryl-ether-ether-ketone coated with a Si/GLC film sliding against 100Cr6 steel, Al2O3 and Si3N4 balls in a biological medium of simulated body fluid, using the ball-on-disk tribological tests. The test results show that the wear volume loss of the rubbing pairs is two orders of magnitude greater than that determined for the tribo-pairs in SBF lubrication, coefficient of friction decreases by 50 % at least, as compared to that in dry conditions. The friction coefficient showed the same varied trend with Hertzian contact radius. The wear rate showed the inverse varied trend with the contact pressure. The interfacial tribochemically reacted with moisture available in SBF medium plays an effect role of the difference in the wear-resistant and lubricating behavior. Furthermore, some indexes including hardness ratio of pair and film were employed to predict the wear behavior of GLC composite films sliding against different counterparts. The Si/GLC nanocomposite films would be a new kind of promising materials applied to artificial heart valves and stents.

Raman and thermal desorption spectroscopy analyses of amorphous graphite-like carbon films with incorporated xenon

Structural and thermodynamic properties of xenon incorporated in amorphous carbon films deposited by means of a sputtering system free of vacuum pumping during the deposition were investigated by visible Raman (Vis–Raman) scattering and thermal desorption spectroscopy (TDS), respectively. Vis–Raman measurements, carried out before and after the xenon desorption, revealed a polycrystalline material rich in C-sp2 sites that form randomly dispersed nanosized graphite clusters (nanocrystals) of approximately 1 nm. After xenon desorption, a compensating mechanism, activated by the thermal heating, promotes a more ordered C-sp2 network as revealed by the linewidths of both D and G bands, as well as by the ID/IG ratio evolution. The TDS thermograms show that the xenon onset effusing temperature is approximately 120 °C. Besides, they also revealed two different regimes, at low and at high temperatures, associated with desorption of xenon atoms trapped either in an interconnecting void network or within the graphite nanocrystals. From the latter regime, the xenon diffusion free energy (activation energy) was determined to be 1.2 eV (115.7 kJ/mol) on the basis of the diffusion-limited desorption standard model.

Pressure-enhanced decomposition of Ag3[Co(CN)6

The structural stability of silver hexacyanocobaltate, Ag3[Co(CN)6], was investigated at high pressure and moderate temperature using X-ray diffraction, Raman spectroscopy, and Fourier Transform Infrared spectroscopy. Pressure induced amorphization (PIA) or pressure enhanced decomposition were observed depending of the processing conditions. In situ X-ray diffraction analysis unequivocally confirmed the PIA at room temperature for pressures higher than 13GPa. The usual decomposition temperature at ambient pressure, 227°C, decreased to 180°C at 7.7GPa, and to 150°C at 14GPa. The decomposition products after moderate heating at high pressure are at least two phases: crystalline elemental silver and an amorphous phase containing the remaining elements (Co, C and N), which presents a Raman spectrum similar to that observed for amorphous graphite-like carbon nitride (CNx). Our findings confirm the previously reported pressure induced amorphization of Ag3[Co(CN)6] at room temperature, and indicate that this amorphization is the result of a kinetically hampered decomposition.

Growth and characterization of chromium carbide films deposited by high rate reactive magnetron sputtering for electrical contact applications

Chromium carbide films with different phase contents were deposited at 126±26°C by industrial high rate reactive magnetron sputtering, using both direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS). Film structure and properties were studied by SEM, XRD, TEM, XPS, NRA, Raman spectroscopy, nanoindentation, unlubricated reciprocating sliding experiments, and a laboratory setup to measure electrical contact resistance. The films consisted of amorphous a-CrCy, a nanocrystalline minority phase of metastable cubic nc-CrCx, and a hydrogenated graphite-like amorphous carbon matrix (a-C:H). The DCMS and HiPIMS processes yielded films with similar phase contents and microstructures, as well as similar functional properties. Low elastic modulus, down to 66GPa, indicated good wear properties via a hardness/elastic modulus (H/E) ratio of 0.087. Unlubricated steady-state friction coefficients down to 0.13 were obtained for films with 69 at.% carbon, while the electrical contact resistance could be reduced by two orders of magnitude by addition of a-C:H phase to purely carbidic films. The present films are promising candidates for sliding electrical contact applications.

Diamond formation by carbon saturation in C–O–H fluids during cold subduction of oceanic lithosphere

Microdiamonds in garnet of graphite-free ultrahigh pressure metamorphic (UHPM) rocks from Lago di Cignana (western Alps, Italy) represent the first occurrence of diamond in a low-temperature subduction complex of oceanic origin (T=∼600°C; P⩾3.2GPa). The presence of diamonds in fluid inclusions provides evidence for carbon transport and precipitation in an oxidized H2O-rich C–O–H crustal fluid buffered by mineral equilibria at sub-arc mantle depths. The structural state of carbon in fluid-precipitated diamonds was analyzed with 514nm excitation source confocal Raman microspectroscopy. The first order peak of sp3-bonded carbon in crystalline diamonds lies at 1331 (±2)cm−1, similar to diamonds in other UHPM terranes. The analysis of the spectra shows additional Raman features due to sp2 carbon phases indicating the presence of both hydrogenated carbon (assigned to trans-polyacetylene segments) in grain boundaries, and graphite-like amorphous carbon in the bulk, i.e. showing a structural disorder much greater than that found in graphite of other UHPM rocks. In one rock sample, disordered microdiamonds are recognized inside fluid inclusions by the presence of a weaker and broader Raman band, downshifted from 1332 to 1328cm−1. The association of sp3- with sp2-bonded carbon indicates variable kinetics during diamond precipitation. We suggest that precipitation of disordered sp2 carbon acted as a precursor for diamond formation outside the thermodynamic stability field of crystalline graphite. Diamond formation started when the H2O-rich fluid reached the excess concentration of C required for the spontaneous nucleation of diamond. The interplay of rock buffered fO2 and the prograde P–T path at high pressures controlled carbon saturation. Thermodynamic modeling confirms that the C–O–H fluids from which diamond precipitated must have been water rich (0.992<XH2O<0.997), assuming that fO2 is fixed by the EMOD equilibrium.

Graphite-like carbon films by high power impulse magnetron sputtering

High-power impulse magnetron sputtering (HiPIMS), coupled with a direct-current magnetron sputtering (dcMS) in parallel, was employed to fabricate graphite-like amorphous carbon (GLC) films. Different impulse voltages were applied in HiPIMS during the film deposition. The structure and mechanical properties of the GLC films deposited by the HiPIMS were investigated. The bonding structure of the films was analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Atomic force microscopy (AFM) and Nano-indentation were used to characterize the surface quality and micro-hardness, respectively. Internal stress of the films was calculated based on the curvature measured by a laser tester. Tribological behavior of the GLC films is studied by a ball-on-disk tribometer in ambient condition. The effects of impulse voltage on deposition rate, internal stress, mechanical and tribological properties of the GLC films were investigated. The results are analyzed and discussed.