Amorphous Diamond-like Carbon Films Research Articles

Nanocomposite materials based on amorphous SiC-containing DLC structures modified with rhodium nanoparticles

From the 1980s to the present, interest in carbon has remained very high. The variety of polytypic forms of carbon is expected to have a large number of possible applications. The creation of electronic and optical devices based on them is a promising direction. One of the most interesting carbon materials could be amorphous diamond-like carbon (DLC) films. This work considers nanocomposite materials based on DLC with nanostructures of SiC components. Thin composite DLC:Si films modified with Rhodium nanoparticles (Rh NPs) were synthesized by magnetron sputtering. The structure of the films has been studied by transmission electron microscopy, Raman and X-ray photoelectron spectroscopy (XPS). It is shown that a diamond-like carbon matrix with inclusions of SiC nanostructures and Rh nanocrystals is formed. Significant influence of Rh NPs on the structures of the carbon matrix and SiC during the formation of the DLC: Si matrix is revealed. In addition, X-ray photoelectron spectroscopy shows a considerable effect of Rh NPs on the edge of the valence zone and the density of localized states. The significant effect of rhodium nanoparticles on the electronic component of the valence band of DLC:Si films can be used in the development of new optoelectronic devices.

Nanoscale friction of tetrahedral amorphous diamond-like carbon film after thermal annealing

Diamond-like carbon (DLC) coatings have demonstrated significant potential as solid lubricants for a wide range of applications. However, thermal-induced structural changes lead to alterations in its mechanical and frictional properties. In this study, we investigate the friction properties of DLC films after high-temperature annealing, by conducting reciprocating single asperity scanning experiments of self-mated hydrogen-free DLC tribopair under ultra-high vacuum (UHV) conditions. As the annealing temperature increases, the coefficients of friction (COFs) first increase owing to the desorption of water molecules; while, with the further increase of temperature, friction shows a decreasing trend because of the high-temperature-induced sp3-to-sp2 rehybridization which lowers the interfacial shear strength. The insights gained from this study provide a better understanding of the frictional properties of DLC films.

Highly Stable Electrochemical Supercapacitor Performance of Self-Assembled Ferromagnetic Q-Carbon.

Novel phase Q-carbon thin films exhibit some intriguing features and have been explored for various potential applications. Herein, we report the growth of different Q-carbon structures (i.e., filaments, clusters, and microdots) by varying the laser energy density from 0.5 to 1.0 J/cm2 during pulsed laser annealing of amorphous diamond-like carbon films with different sp3-sp2 carbon compositions. These unique nano- and microstructures of Q-carbon demonstrate exceptionally stable electrochemical performance by cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy for energy applications. The temperature-dependent magnetic studies (magnetization vs magnetic field and temperature) reveal the ferromagnetic nature of the Q-carbon microdots. The saturation magnetization and coercive field values decrease from 132 to 14 emu/cc and 155 to 92 Oe by increasing the temperature from 2 to 300 K, respectively. The electrochemical performances of Q-carbon filament, cluster, and microdot thin-film supercapacitors were investigated by two-electrode configurations, and the highest areal specific capacitance of ∼156 mF/cm2 was observed at a current density of 0.15 mA/cm2 in the Q-carbon microdot thin film. The Q-carbon microdot electrodes demonstrate an exceptional capacitance retention performance of ∼97.2% and Coulombic efficiency of ∼96.5% after 3000 cycles due to their expectational reversibility in the charging-discharging process. The kinetic feature of the ion diffusion associated with the charge storage property is also investigated, and small changes in equivalent series resistance of ∼9.5% and contact resistance of ∼9.1% confirm outstanding stability with active charge kinetics during the stability test. A high areal power density of ∼5.84 W/cm2 was obtained at an areal energy density of ∼0.058 W h/cm2 for the Q-carbon microdot structure. The theoretical quantum capacitance was obtained at ∼400 mF/cm2 by density functional theory calculation, which gives an idea about the overall capacitance value. The obtained areal specific capacitance, power density, and impressive long-term cyclic stability of Q-carbon thin-film microdot electrodes endorse substantial promise in high-performance supercapacitor applications.

Influence of Si atoms on the structure and electronic properties of amorphous DLC films

The paper considers the effect of silicon on the formation of the structure and properties of amorphous diamond-like carbon (DLC) films. Thin films of silicon-modified amorphous diamond-like carbon (DLC:Si) were synthesized by magnetron ion-plasma co-sputtering of a combined target. Studies of the structure and properties of amorphous DLC:Si films were carried out in the range of silicon concentrations up to 6.75 at.%. A change in the formation of the film structure is shown using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) revealed a significant change in the local structure of amorphous DLC:Si films. Which, in turn, leads to a change in the density of states of π-electrons in the band and, as a rule, to a change in the electronic properties.

Structure, properties and applications of diamond-like carbon coatings prepared by reactive magnetron sputtering

AbstractMetal containing and metal free amorphous diamond-like carbon films were prepared by reactive magnetron sputter deposition using targets from transition metals or graphite and acetylene as reactive gas. Both types of coating materials are well known for their low friction coefficients. However, metal containing films exhibit clearly lower wear resistances and lower hardness values than metal free films. To study the differences between both materials, tungsten containing and metal free coatings were compared. The deposition experiments were carried out in an industrial scale d.c. magnetron sputter machine. Transmission electron microscopy, secondary ion mass spectroscopy, and Raman spectroscopy as well as hardness measurements and wear tests were performed to characterize and to compare composition, structure, mechanical, and tribological properties of both coating materials.

Anomalous characteristics of nanostructured hydrogenated carbon thin films

Hydrogenated diamond-like carbon (DLC) films are sought for several technological applications including electronics, optics, mechanics, and tribology. However, conventional hydrogenated DLC films, that commonly deposit at low base pressure (~10−5 to 10−8 Torr), have many intrinsic limitations in terms of moderate hardness (15–25 GPa), low electrical conductivity (in insulating regime), and they display amorphous morphology. Here we develop high-performance hydrogenated carbon-based films using a cost-effective and fast deposition approach. We report the room temperature synthesis of nitrogen incorporated nanostructured hydrogenated carbon films (n-C:N:H) at a high base pressure of ~5 × 10−3 Torr, employing a non-conventional radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) system equipped with only a primary pump. The n-C:N:H films show appealing properties such as wide band gap (2.35–2.9 eV), high optical transparency, high hardness (up to ~ 40 GPa), ultrahigh elasticity (elastic recovery ~95%), reasonably good electrical conductivity, and diode-like behavior when examined in n-C:N:H/Si heterojunction device configuration. Interestingly, some of n-C:N:H films revealed the multifunctional activities with properties surpassing to those of many low base pressure grown traditional amorphous DLC films. This discovery solves many fundamental concerns of hydrogenated DLC films and opens new paths for their enhanced commercial applications.

Superlow friction of amorphous diamond-like carbon films in humid ambient enabled by hexagonal boron nitride nanosheet wrapped carbon nanoparticles

The friction and wear of amorphous diamond-like carbon (DLC) films will dramatically increase with the increment of ambient humidity. This drawback can lead to lubrication failure, which greatly impedes the practical applications of DLC films in humid environment. Herein, a simple method is proposed to improve the tribological performance of DLC films in humid environment by adding hexagonal boron nitride nanosheet wrapped carbon nanoparticles (CNP@h-BNNSs) as lubricants. The reciprocating friction tests demonstrate that DLC films with CNP@h-BNNSs as lubricants possess excellent antifriction and antiwear performance at the relative humidity (RH) of 7.5–55%. Especially, it can achieve a superlow friction and wear at the RH of 45–55% which decrease by respectively 13 and 25 times as compared to those obtained from DLC films without lubricants. The investigation on the steel ball surface after friction test shows that a protective tribo-layer containing carbon, boron and nitrogen elements is formed. The existence of this tribo-layer can effectively reduce the friction and protect the steel ball surface from excessive wear. Noteworthy, the h-BNNSs are exposed at the friction interface acting as lubricating layer while the carbon nanoparticles are adsorbed on steel ball surface playing as binding binder. Furthermore, the ball movement mode of CNP@h-BNNSs and the interaction between water molecules and CNP@h-BNNSs are also considered as key factors to reduce friction. All these results indicate that CNP@h-BNNSs which can be massively produced have the potential to reduce the friction and wear of DLC films in humid environment.

Effect of Cr Atom Plasma Emission Intensity on the Characteristics of Cr-DLC Films Deposited by Pulsed-DC Magnetron Sputtering

A pulsed-dc (direct current) magnetron sputtering with a plasma emission monitor (PEM) system was applied to synthesize Cr-containing hydrogenated amorphous diamond-like carbon (Cr-DLC) films using a large-size industrial Cr target. The plasma emission intensity of a Cr atom at 358 nm wavelength was characterized by optical emission spectrometer (OES). C2H2 gas flow rate was precisely adjusted to obtain a stable plasma emission intensity. The relationships between Cr atom plasma emission intensity and the element concentration, cross-sectional morphology, deposition rate, microstructure, mechanical properties, and tribological properties of Cr-DLC films were investigated. Scanning electron microscope and Raman spectra were employed to analyze the chemical composition and microstructure, respectively. The mechanical and tribological behaviors were characterized and analyzed by using the nano-indentation, scratch test instrument, and ball-on-disk reciprocating friction/wear tester. The results indicate that the PEM system was successfully used in magnetron sputtering for a more stable Cr-DLC deposition process.

Formation of Q-carbon by adjusting sp3 content in diamond-like carbon films and laser energy density of pulsed laser annealing

In this study, we prepared Q-carbon by adjusting the sp3 content in diamond-like carbon (DLC) films and the laser energy density of pulsed laser annealing (PLA). The amorphous DLC films were fabricated on sapphire Al2O3(0001) substrates using a pulsed laser deposition technique with a KrF excimer laser (λ = 248 nm). The sp3 content in the films varied between 20% and 42% by changing the laser energy density. Subsequently, PLA was performed on the DLC films by using the KrF excimer laser with energy densities between 0.5 and 1.2 J/cm2. The prepared films were characterized using scanning electron microscopy, Raman spectroscopy, and magnetization measurements. Consequently, for the combination of 20% sp3 content and laser density of 1.0 J/cm2, as well as 42% sp3 and 0.5 J/cm2, the films showed the characteristic features of Q-carbon: filamentary nanostructures, the presence of a T band in the Raman spectrum, room-temperature ferromagnetic behavior, and ∼80% sp3 content. The results indicate that Q-carbon can be obtained by using a proper combination of sp3 content in DLC films and an appropriate PLA energy density. This study provides important guidance for establishing a preparation method for Q-carbon.

The structure and properties of amorphous diamond-like carbon films deposited by helicon wave plasma chemical vapor deposition

The diamond-like carbon (DLC) films have been synthesized on silicon substrates by using chemical vapor deposition assisted with a high-density m=+1 mode helicon wave-excited plasma in Ar/CH4 gas mixtures. The structure and morphology of the DLC films are characterized by scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM). The surface energies of the DLC films are calculated by the the Owens–Wendt–Rabel–Kaelble (OWRK) method. SEM results show that the surfaces of DLC films are found to be very uniform and dense, and the deposition rate of the film can reach up to 45 μm/h. The Young's modulus of the DLC films reaches the maximum (11 GPa) value at 25 sccm CH4 flow rate. With the increase of CH4 flow rate from 5 sccm to 35 sccm, the surface energy and friction coefficient of the DLC films decrease from 73.5 to 37.6 mJ m − 2 and from 0.56 to 0.25, respectively. It indicates that the deposited DLC films have good friction properties.The Young's modulus value is obtained here using AFM [48]. The results show that the Young's modulus increases from 4.1 to 10. 77 GPa, as the CH4 flow rate increases from 5 to 25 sccm. However, with further increasing the CH4 flow rate, the Young's modulus decreases gradually. This is consistent with the trend of sp3 bond content in Raman results. According to literature [49], CC sp3 bond of DLC films has a certain influence on Young's modulus. The result shows that the CC sp3 content reaches its maximum when the CH4 flow rate reaches 25 sccm. Moreover, the RMS results of DLC films show that the smoother the film is, the higher the Young's modulus is, likewise the rougher the DLC film is, the lower the Young's modulus is. It can be inferred that when DLC film is rough, the accumulated carbon polymer sp3 content in DLC film is low.

OPTICAL PROPERTIES OF THE RAPID ANNEALED OXYGEN-DOPED DIAMOND-LIKE CARBON FILM

The amorphous oxygen-doped diamond-like carbon films were prepared by pulsed laser deposition. Compared with the pure diamond-like carbon film, there were much less graphite clusters on the surfaces of the oxygen-doped diamond-like carbon films, and the average transmission of the oxygen-doped diamond-like carbon films in the medium infrared band increased. However, some new absorption peaks in the infrared spectra of the oxygen-doped diamond-like carbon film were generated. Rapid annealing was experimented to remove the absorption peaks. XPS analysis showed that the fractions of the C–O and C=O bonds that generated the new absorption peaks were reduced more than the fractions of [Formula: see text] bonds by rapid annealing at 400[Formula: see text]C, and the absorption peaks in the medium infrared spectra decreased. It indicated that rapid annealing at right temperature during the right time could reduce greatly the absorption in the medium infrared band of oxygen-doped diamond-like carbon films.

Structural state of diamond-like amorphous carbon films, obtained by laser evaporation of carbon target

A homogeneous diamond-like film was obtained on an area of 75 × 25 mm2. Study of the film structure, using transmission electron microscopy and Raman spectroscopy, showed a mixture of carbon atoms with sp2- and sp3-bonds. Structure of carbon film is determined by the presence of randomly oriented carbon clusters bound by diamond sp3-bonds (tetrahedral amorphous carbon, ta-C). Electron diffraction patterns demonstrate strongly distorted interfacial distances. Raman spectra show that there are carbon atoms with graphite sp2-bonds in the film, but a signal of graphite crystal lattice is absent in electron diffraction: This implies that hexagonal units are not shaped into a graphite crystal lattice. Broad D-band in Raman spectra shows strongly distorted carbon bonds in graphite. If diamond phase dominates, the space between diamond clusters is filled with carbon atoms with sp2-bonds (turbostratic structure). Thus, diamond areas are bound into a single discontinuous aggregate of carbon diamond-like film.

The correlation between optical and mechanical properties of amorphous diamond-like carbon films prepared by pulsed filtered cathodic vacuum arc deposition

Diamond-like carbon (DLC) films were deposited by pulsed filtered cathodic vacuum arc (FCVA) deposition. The microstructure, mechanical and optical properties of DLC films have been investigated as functions of the variation in the substrate negative direct current bias voltage (Vbias) from 0.0 to 1.5 kV. Raman and X-ray photoelectron spectroscopy results show a correlation between the ID/IG ratio and the microstructure in terms of the sp3/sp2 ratio to Vbias. This fact shows that a significant change in the sp3 content, which is attributed to the transformation from graphite-like to diamond-like, is accompanied by a decreasing ID/IG ratio. The relatively high mass density of the films in the range of 2.51 to 2.79 g/cm3 can be obtained with biasing. The mechanical properties, i.e., the hardness and elastic modulus, were 13–25 and 114–145 GPa, respectively. The improvement of the mechanical properties is due to the formation of the compressive residual stress and the local density depending on Vbias. The relationship between the refractive index and the ID/IG ratio agree well with the microstructure and mechanical properties of DLC films. All of these results indicate a vital role of Vbias in determining the DLC properties.

MoDTC-induced wear acceleration mechanism of a hydrogenated amorphous carbon diamond-like carbon film

MoDTC-induced wear acceleration mechanism of a hydrogenated amorphous carbon diamond-like carbon film

Preparation and characteristics study of diamond like carbon/silicon heterojunction photodetector by pulsed laser deposition

In this paper, amorphous undoped diamond-like carbon films were deposited on glass and silicon substrates by pulsed laser ablation of graphite target; using nanoseconds frequency doubled Nd: YAG laser pulses. The effect of laser fluence (9.5–14.3 J/cm2) on optical, structural, morphological, and electrical properties of diamond like carbon films was studied by X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, photoluminescence, and UV–Vis transmittance. UV–Vis results revealed a decreased indirect optical band gap from 2.2 to 1.92 eV with increasing laser fluence from 9.5 to 14.3 J/cm2 leads. The ID/IG ratio and sp2 bonded percentage of DLC films increased with laser fluence increase. Films prepared at a higher laser fluence yield lower electrical resistivity. The dark and illuminated current–voltage characteristics at room temperature of diamond like carbon/Silicon heterojunction under the effect of laser flunce were examined and analyzed. Our results demonstrated an optimum photodetectors’ responsivity of 450 m AW−1 at 10 V bias.

Understanding heterogeneity in Genesis diamond-like carbon film using SIMS analysis of implants

An amorphous diamond-like carbon film deposited on silicon made at Sandia National Laboratory by pulsed laser deposition was one of several solar wind (SW) collectors used by the Genesis Mission (NASA Discovery Class Mission #5). The film was ~1 μm thick, amorphous, anhydrous, and had a high ratio of sp3–sp2 bonds (>50%). For 27 months of exposure to space at the first Lagrange point, the collectors were passively irradiated with SW (H fluence ~2 × 1016 ions cm−2; He fluence ~8 × 1014 ions cm−2). The radiation damage caused by the implanted H ions peaked at 12–14 nm below the surface of the film and that of He about 20–23 nm. To enable quantitative measurement of the SW fluences by secondary ion mass spectroscopy, minor isotopes of Mg (25Mg and 26Mg) were commercially implanted into flight-spare collectors at 75 keV and a fluence of 1 × 1014 ions cm−2. The shapes of analytical depth profiles, the rate at which the profiles were sputtered by a given beam current, and the intensity of ion yields are used to characterize the structure of the material in small areas (~200 × 200 ± 50 μm). Data were consistent with the hypothesis that minor structural changes in the film were induced by SW exposure.

Surface characterization and orientation interaction between diamond- like carbon layer structure and dimeric liquid crystals

Diamond-like carbon (DLC) and amorphous carbon films are very promising type of semiconductor materials. Depending on the hybridization sp2/sp3 ratio, the material’s band gap varies between 0.8 and 3 eV. Moreover carbon films possess different interesting for practice properties: comparable to the Silicon, Diamond like structure has 22-time better thermal conductivity etc. Here we present one type of implementation of such type nanostructure. That is one attempt for orientation of dimeric LC by using of pre-deposited DLC layer with different ratio of sp2/sp3 hybridized carbon content. It could be expected a pronounced π1-π2interaction between s and p orbital levels on the surface and the dimeric ring of LC. We present comparison of surface anchoring strengths of both orientation inter-surfaces DLC/dimeric LC and single wall carbon nanotubes (SWCNT)/dimeric LC. The mechanism of interaction of dimeric LC and activated surfaces with DLC or SWCNT will be discussed. In both cases we have π-π interaction, which in combination with hydrogen bonding, typical for the dimeric LCs, influence the LC alignment. The Raman spectroscopy data evidenced the presence of charge transfer between contacting hexagonal rings of DLC and the C = O groups of the LC molecules.

Образование графита в алмазоподобных тонких углеродных пленках

In the present work, particularities of the formation and structure of a graphite phase appearing in a thin amorphous diamond-like carbon (ta-C) film were studied using the method of high resolution electron microscopy. In order to obtain a thin carbon film, a neodymium laser NTS300 with a wavelength of 1064 nm was used. The film was deposited on a glass substrate in the process of a direct evaporation of a graphite target. Study of the graphite phase formation in the film was carried out using the high resolution transmission electron microscopy that allowed for a direct observation of the thin film atomic structure. Electron diffraction analysis shows that in local areas of a thin film a phase transition from amorphous diamond-like ta-C state to graphite occurs. Single crystals of graphite are oriented so that their basic hexagonal planes are parallel to the film surface. This is due to the fact that sp3 bonds are metastable and can be unstable, particularly on the film surface. Therefore, the transition of sp3 bonds to sp2 ones with the formation of planar complexes with a ring structure initially occurs on the film surface. The growth of a graphite crystal nucleus in the ta-C matrix increases the stress and stabilizes the diamond state. Due to this, the graphite phases form dominantly on the film edges. Analysis of electron diffraction patterns has shown that the interplanar spacings depend on the orientation of the planes relative to the film edge. Measurements of interplanar spacings reveals a complicated character of the stress state of the graphite lattice in the thin film. Along with tension-compression stresses, shear stresses are present and they result in a change of the angles between carbon interatomic bonds.

Amorphous carbon buffer layers for separating free gallium nitride films

The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al2O3) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the “GaN film–Al2O3” substrate interface decreases, which facilitates separation of the GaN layers.

Influence of Cr content on the micro-structural and tribological properties of PLD grown nanocomposite DLC-Cr thin films

Improved adhesion and low friction coefficient of diamond-like carbon (DLC) films has been a major challenge which otherwise would have opened door to many engineering applications. Amorphous DLC films doped with different concentrations of Chromium (Cr) (5, 10, 15 & 20 at%) were deposited on to stainless steel (AISI SS304) substrate using Nd-YAG pulsed laser deposition technique (PLD). Raman spectroscopy was used to calculate the internal stress of the films. DLC with lower Cr concentration (5 at%) showed significant internal stress reduction (3 GPa) compared to DLC with higher Cr concentration. Formation of Cr3C2 nanoclusters in the DLC matrix was confirmed by XPS and TEM analysis which enhanced the adhesion strength of the film. DLC films with lower Cr concentration exhibited ultra-low friction coefficient (0.04–0.09) and the value increased significantly in higher Cr concentration. An optimum metal concentration in DLC film leads to improved adhesion and friction behaviour that houses many engineering applications.