Tetrahedral Amorphous Carbon Films Research Articles

Sp 3 content in ta-C films vs pulse bias width to the substrate: A correlative structural analysis

Tetrahedral amorphous carbon (ta-C) films were studied with and without applying fixed pulse bias and frequency at variable pulse widths in double bent Filtered Cathodic Vacuum Arc (FCVA) system. Both from Raman and X-ray photoelectron spectroscopy (XPS) analyses it has been observed that the ratio of sp 3/sp 2 is maximal at pulse width of 15 µs with fixed pulse bias 3 kV and frequency 200 Hz. Increasing or decreasing pulse width from this threshold value accompanies the decreasing sp 3 content in the film. It is also observed that with applying pulse bias width at said frequency and bias voltage G peak position was shifted to lower values and after reaching a minimum at 15 µs G peak position shifted to higher wave numbers. At the 15 µs pulse width, 3 kV bias voltage and 200 Hz frequency we have formed ta-C films with maximum sp 3 content. This study clearly suggests that it is possible to tune the ta-C film's most important properties such as percentage of sp 3 content, internal stress, and hardness by applying pulse width at particular frequency and bias voltage.

Effects and thermal stability of hydrogen microwave plasma treatment on tetrahedral amorphous carbon films by in situ ultraviolet photoelectron spectroscopy

This paper reports a comprehensive experimental study on the effects of hydrogen microwave plasma treatment on nonhydrogenated high sp3 content tetrahedral amorphous carbon (ta-C) film. In this study, a surface C–H dipole layer was first observed by high resolution electron energy loss spectroscopy, showing the presence of C–H bonding states. This resulted in the enhancement of electron field emission of the plasma treated films by largely lowering the turn-on field. Thermal stability tests using in situ ultraviolet photoelectron spectroscopy confirm that the C–H dipole layer not only reduces the work function of the films, it is extremely stable in both ambient and vacuum conditions and can sustain up to 600 °C annealing in vacuum. Atomic force microscopy studies also show minimal modifications to the surface morphology, leading to the conclusion that the C–H dipole layer is responsible for lowering the work function. This has improved the electron emission properties which can lead to potential applications such as electron emission displays.

Characterization of Boron- and Phosphorous-Incorporated Tetrahedral Amorphous Carbon Films Deposited by the Filtered Cathodic Vacuum Arc Process

This paper reports the X-ray photoelectron spectroscopy (XPS), X-ray-induced Auger electron spectroscopy (XAES), and Raman studies of boron- and phosphorous-incorporated tetrahedral amorphous carbon (ta-C) films deposited by the filtered cathodic vacuum arc process. A systematic study of the influence of varying boron (B) and phosphorous (P) content on the properties of the as-grown ta-C films deposited at high negative substrate bias (-300 V) is reported by analyzing the C 1s, B 1s, and P 1s core levels using photoelectron spectroscopy. The sp3 and sp2 contents in the films were determined by measuring the width of the X-ray-induced Auger peaks. B incorporation in ta-C films up to 2.0 at. % increases the sp2 content and decreases the sp3 content by 3.6%, whereas P incorporation up to 2.0 at. % results in an increase of sp2 content and decrease of sp3 content by ∼ 30%. The valence band spectra show changes in the Fermi level as B and P are incorporated into the ta-C films. The characteristic Raman spectra confirm the high sp3 content in the deposited films. Thus, the study demonstrates, in the case of high negative substrate bias films, that a pronounced decrease in sp3 fraction or the diamond-like nature of the ta-C films occurs upon P incorporation in comparison to that upon B incorporation.

Mechanical, Thermal, and Tribological Properties of Amorphous Carbon Films

In this paper, the correlation among the hardness, determined by the nanoindentation method, the thermal conductivity, by the 3ω method and friction coefficient, by the ball on disk (BOD) method; of tetrahedral amorphous carbon (ta-C) films deposited on Si substrates and WC/Co substrates by the filtered cathodic vacuum arc (FCVA) deposition method has been investigated. The films were also characterized by Raman spectroscopy and Rutherford backscattering/elastic recoil detection analysis (RBS/ERDA). The experimental results were discussed in terms of the microstructure of ta-C films depending on the kind of substrate. It was revealed that the hardness and the thermal conductivity of ta-C films on WC/Co substrates were higher than those on Si substrates and they increased with density. The increase in density was correlated with the decrease in ID/IG corresponding to the graphite cluster size La of the films. The density of a ta-C film on the wear track increased after BOD tests because of the mechanical stress during sliding.

Pulsed laser deposited tetrahedral amorphous carbon with high sp3 fractions and low optical bandgaps

Amorphous carbon films with sp3 bonded carbon fractions over 70% are deposited by pulsed laser deposition. However, the optical bandgap obtained from optical transmittance and spectroscopic ellipsometry analysis shows the values to be below 1.0 eV. A wide range of measurements such as electron energy loss spectroscopy, visible Raman, spectroscopic ellipsometry, optical transmittance, and electrical characterization are performed to elucidate the bonding configurations that dictate microstructural, optical and electrical properties, and their linkage to band structure changes. It is found that stress-induced electronic localized states play an important role in the physical properties of the films deposited. The optical bandgap is shown not to be a good measure of the electrical bandgap, especially for high electric field conduction in these tetrahedral amorphous carbon films.

Tetrahedral amorphous carbon films as a frequency-increasing interlayer of surface acoustic wave devices with a ZnO/Si configuration

Tetrahedral amorphous carbon (ta-C) films deposited using filtered cathodic vacuum arc technology have been applied to the interlayer of surface acoustic wave devices with a ZnO/Si configuration. The phase velocity in the multilayered structure was analyzed in the first instance by theoretical calculations and was then measured by means of a network analyzer. It has been shown that the ta-C interlayer between piezoelectric film and Si substrate can strikingly increase the phase velocity of the surface acoustic wave. The greater the interlayer thickness is and the higher the content of the sp3 hybridization is, the faster surface acoustic wave propagates. However, the increment of phase velocity gradually decreases with increasing interlayer thickness. It was confirmed in this paper that the measured values of the phase velocity as a function of the interlayer thickness agree with the theoretical calculations.

Nanostructured carbide surfaces prepared by surfactant sputtering

Nanostructured surface layers of titanium carbide and tungsten carbide were prepared on tetrahedral amorphous carbon (ta-C) films using the surfactant sputtering technique. Surfactant sputtering is a novel ion beam erosion technique, which utilizes the steady state coverage of a substrate surface with foreign atoms simultaneously during sputter erosion by combined ion irradiation and atom deposition. These foreign atoms act as surfactants, which strongly modify the substrate sputtering yield on atomic to macroscopic length scales. The novel technique allows smoothing of surfaces, the generation of novel surface patterns and nanostructures, controlled shaping of surfaces on the nanometer scale and the formation of ultra-thin compound surface layers. We have sputter eroded ta-C films using 5keV Xe ions under continuous deposition of either tungsten or titanium surfactants. This leads to the steady state formation of a WxC or a TiC/a-C nanocomposite surface layer of few nm thickness. Depending on the ion angle of incidence the layer is either smooth or nanostructured with a ripple- or dot-like surface topography. We have analyzed the surface topography, the composition and microstructure of the metal-carbon nanocomposites, and compare coverage dependent sputtering yields with SRIM and TRIDYN simulations.

Structure and Haemocompatibility of Tetrahedral Amorphous Carbon Films Prepared by Pulsed Laser Ablation

Structure and Haemocompatibility of Tetrahedral Amorphous Carbon Films Prepared by Pulsed Laser Ablation

The role of a graphitic surface layer in electron-stimulated ordering in tetrahedral amorphous carbon films

The role of a graphitic surface layer in electron-stimulated ordering in tetrahedral amorphous carbon films

Corrosion protection of ultra-thin ta-C films for recording slider applications at varied substrate bias

Ultra-thin tetrahedral amorphous carbon (ta-C) films have been prepared by filtered catholic vacuum arc system for recording slider applications. In order to study the corrosion behavior of the slider coatings deposited at different substrate bias, the micro-structure and surface properties of the ta-C films were respectively investigated in terms of Raman spectroscopy, atomic force microscopy, water contact angle and corrosion measurements. Results showed that a very smooth ta-C film with lowest surface energy and highest sp 3 bonding content was obtained at the medium bias voltage of 100 V. However, as to the protection against corrosion, the optimum bias was found to be greater than that giving the maximum diamond-like properties.

Cyclic Voltammetric Behavior of Nitrogen‐Doped Tetrahedral Amorphous Carbon Films Deposited by Filtered Cathodic Vacuum Arc

AbstractNitrogen‐doped tetrahedral amorphous carbon (ta‐C : N) films were deposited by filtered cathodic vacuum arc (FCVA) technique using nitrogen as a background gas. The structure of the ta‐C : N films was studied with X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy in terms of nitrogen flow rate used during the film deposition. Potential windows of the films measured in deaerated and unstirred solutions, such as 0.5 M HCl, 0.1 M KCl, 0.1 M NaCl, 0.1 M KOH, and 0.1 M NaOH, were about 2.4, 2.32, 3.2, 3.1, and 3.25 V, respectively. This study showed that the potential windows of the ta‐C : N films were also affected by nitrogen flow rate. The ta‐C : N films used in this study had the desired voltammetric characteristics suitable for electrochemical analysis.

Thermal stability of UBM sputtered DLC coatings with various hydrogen contents

Thermal stability of tetrahedral amorphous carbon ( ta-C) films is higher than that of hydrogenated amorphous carbon. This study investigates hydrogen content effects on thermal stability of diamond-like carbon (DLC) coatings using materials with two different hydrogen contents (H: 10.8 and 25.3 at.%) annealed in vacuum at up to 600 °C. Indentation measurements of the films showed decreased hardness of the films annealed at temperatures greater than 400 °C. Raman spectroscopy revealed D-band and G-band splitting at those temperatures for films with 25.3 at.% hydrogen content. Structural change with hydrogen effusion occurred ca. 440 °C in both hydrogen content films. Structural changes in 25.3 at.% hydrogenated films affected tribological properties, but 10.8 at.% of hydrogen content films showed only slight changes.

Thermal Stability of Tetrahedral Amorphous Carbon Films Fabricated by Filtered Cathodic Arc Technique

In order to investigate the thermal stability of the tetrahedral amorphous carbon(ta-C) films fabricated by filtered cathodic arc deposition technique,ta-C films were annealed in ambient air for 3h. The annealing temperature was 200℃,400℃and 500℃,respectively.XPS and Raman spectroscope were employed to characterize the changes of the microstructure of the films.The results show that the XPS Cls peaks and the Raman peaks of the samples annealed at 400℃or below change little.When the annealing temperature is 500℃,the shape of the XPS Cls peak doesn't change too;the Raman I_D/I_G increases,the G-peak position doesn't change and the shape of Raman peak becomes more symmetry. This reveals that the sizes of the graphite clusters in the films increase and no obvious graphitization occurs during annealing process.All these indicate that the ta-C film fabricated by filtered cathodic vacuum arc technique has excellent thermal stability due to its hydrogen free and dense structure. Besides,parts of the films along the edge of the samples is evaporated by oxidation when the annealing temperature is up to 500℃.

Thermal conductivity of ultrathin tetrahedral amorphous carbon films

We investigate the thermal conductivity of ultrathin tetrahedral amorphous carbon (ta-C) films on silicon, down to subnanometer thickness. For films with an initial sp3 content of 60%, the thermal conductivity reduces from 1.42to0.09W∕mK near room temperature as the thickness decreases from 18.5to∼1nm. The variation in ta-C film thickness is accompanied by changes in Young’s modulus, density, and sp3 content. The thermal resistance of the finite-thickness interface layer, which forms between ta-C and silicon, is ∼10−8m2K∕W near room temperature, thus producing a noticeable effect on thermal transport in ultrathin ta-C films.

Spectroscopic Characterization of Boron Doped Tetrahedral Amorphous Carbon

A set of boron doped tetrahedral amorphous carbon (ta-C:B) films were prepared in a filtered cathodic vacuum are system using boron mixed graphite as targets with weight percentage ranging from 0 to 15%.The chemical bonding states of ta-C:B were studied by X-ray photoelectron spectroscope.The result shows that B is mainly threefold coordinated and the fraction of sp~3 hybridized carbon decreases in magnitude with increasing boron content.Raman analysis also shows that the introduction of B in the ta-C:B films facilitates the clustering of sp~2 carbon sites which reduces the bonding distortion and intrinsic stress of the films.

S p 3 -rich deposition conditions and growth mechanism of tetrahedral amorphous carbon films deposited using filtered arc

Tetrahedral amorphous carbon (ta-C) films with many superior properties approaching those of diamond crystal were prepared using filtered cathodic vacuum arc technology. To ascertain the sp3-rich deposition condition, the dependence of the film microstructure on the deposition energy was investigated by means of visible Raman spectroscopy, x-ray photoelectron spectroscopy, electron energy loss spectroscopy, x-ray reflectivity, and nanoindentation. The maximum hardness and Young’s modulus are achieved at a bias of −80V, at which the maximum sp3 fraction of about 82% is obtained. Under this condition, the most symmetric Raman line shape, the highest x-ray photoemission C 1s core level position and a π* transition peak with the smallest integral area in the K-edge spectra are simultaneously achieved. The structural properties are found to be strongly correlated with the mass density of the films. At the optimal substrate bias of −80V, the film mass density reaches its maximum value. The cross section of the films is characterized with a layered distribution in mass density. A surface layer with low density is an intrinsic feature and experimental evidence of the subplantation growth of the films.

Platelet adhesion on phosphorus-incorporated tetrahedral amorphous carbon films

The haemocompatibility of phosphorus-incorporated tetrahedral amorphous carbon (ta-C:P) films, synthesized by filtered cathodic vacuum arc technique with PH 3 as the dopant source, was assessed by in vitro platelet adhesion tests. Results based on scanning electron microscopy and contact angle measurements reveal that phosphorus incorporation improves the wettability and blood compatibility of ta-C film. Our studies may provide a novel approach for the design and synthesis of doped ta-C films to repel platelet adhesion and reduce thrombosis risk.

Stress, mechanical and adhesion properties of multilayer tetrahedral amorphous carbon films

To reduce the stress of tetrahedral amorphous carbon (ta-C) films and improve the adhesion, a graded multilayer film was deposited using a filter cathodic vacuum arc (FCVA) deposition system. Nanoindentation measurement revealed the high hardness and Young's modulus of the multilayer films. Nanoscratch test was used to estimate the scratching resistance of the multilayer films on Si substrate. The high critical scratch load implied the good cohesive and adhesive strengths of the graded multilayer films.

Structural Analysis for the Stress Variation of ta-C film with Deposition Energy: A Molecular Dynamics Simulation

Molecular dynamics simulations are performed on the atomic origin of the evolution of residual stress in tetrahedral amorphous carbon (ta-C) film using the empirical Tersoff potential. The densities of and residual stresses in the amorphous films generated by molecular dynamics simulations were found to be in good agreement with the corresponding experimental results. A radial distribution function analysis shows that the peak at approximately 2.1 A found in high-stress configurations, which is referred to as a satellite peak, is closely linked with the variation of the residual stress in ta-C film.

Evolution of compressive stress and electrical conductivity of tetrahedral amorphous carbon films with phosphorus incorporation

Successful modification of stress and conductivity for tetrahedral amorphous carbon (ta-C) films is realized by phosphorus incorporation via filtered cathodic vacuum arc technique with PH 3 as the impurity source. By establishing the structure as a function of phosphorus content, it is found that phosphorus fraction in phosphorus incorporated ta-C (ta-C:P) films increases with varying levels of PH 3 from 3 to 30 sccm, and that all samples retain their amorphous structures without remarkable changes, just exhibiting the clustering of sp 2 sites and the evolution of structural ordering. Furthermore, the addition of phosphorus causes the compressive stress relaxation in terms of the rearrangement in atomic bonding structures. The increased number of localized electronic π and π⁎ states as hopping sites after phosphorus incorporation results in several orders of magnitude increase in the conductivity, and the films represent the hopping conduction in band tail states in the temperature range of 293–463 K. However, more H induced by excessive PH 3 may saturate some defects and compensate the hopping sites, leading to a slight drop in the conductivity. The nature of ta-C:P films as n-type semiconductors is proved from the features of rectifying current–voltage cures.