Fabrication of fluorine-terminated diamond-like carbon thin film using a hyperthermal atomic fluorine beam

Surface modification of diamond-like carbon (DLC) film was performed using a hyperthermal atomic fluorine beam on the purpose of production of hydrophobic surface by maintaining the high hardness of DLC film. By the irradiation of atomic fluorine beam of a 1.0 × 10²⁰ atoms/cm², the contact angle of a water drop against the DLC surface increased from 73° to 111°. The formation of CF₃, CF₂ and CF bonding on the modified DLC surface was confirmed from the measurements of X-ray photoelectron spectra and near-edge X-ray absorption fine structure spectra. Irradiation of hyperthermal atomic fluorine beam was concluded to produce insulator fluorine-terminated DLC film, which has high F content on the surface, by the taking of the use of neutral atomic beam as a fluorine source.     

Relationship between static friction and surface wettability of orthodontic brackets coated with diamond-like carbon (DLC), fluorine- or silicone-doped DLC coatings

In orthodontics, it is important to reduce the static friction between brackets and wires in order to enable easy tooth movement. The goal of the present study was to deposit diamond-like carbon (DLC), fluorine-doped DLC (F-DLC), and silicon-doped DLC (Si-DLC) coatings onto the slot surface in stainless steel orthodontic brackets using the plasma-enhanced chemical vapor deposition (PECVD) method and to characterize the frictional property between the coated bracket and wire under dry and wet conditions.In order to characterize DLC-, F-DLC- or Si-DLC-coated surface, XPS, the surface roughness and surface wettability of three deferent surfaces were measured. A nanoindentation test and a scratch test were performed in order to measure the hardness and adhesiveness, respectively, of DLC-, F-DLC- or Si-DLC coatings. The static friction between DLC-, F-DLC-, Si-DLC-coated brackets and 0.019 × 0.025-in stainless steel (SS) orthodontic wires was measured for several angulations under dry and wet conditions using a universal testing machine equipped with a custom-made friction-testing device.The F 1s or Si 2p and Si 2s peaks were observed for F-DLC (27.8 at.%:F) or Si-DLC (26.8 at.%:Si), respectively. There were no significant differences in the surface roughness of the slot surface of the bracket among the four types of specimens. The F-DLC was significantly hydrophobic and Si-DLC was significantly hydrophilic as compared to DLC. Doping the DLC with fluorine or silicon caused the surface hardness to decrease significantly.The results of the present study indicate that DLC, F-DLC and Si-DLC coatings provided a significant reduction in static friction. Among the coatings examined herein, F-DLC-coated bracket exhibited the significantly lowest static friction between the bracket and wire under the wet condition, which was lower than that under the dry condition. The F-DLC coating is highly promising as a means of promoting effective tooth movement and shortening treatment time for orthodontic treatments.     

Molecular structure of SiOx-incorporated diamond-like carbon films; evidence for phase segregation

Silicon-oxide incorporated amorphous hydrogenated diamond-like carbon films (SiO_x–DLC, 1 ≤ x ≤ 1.5) containing up to 24 at.% of Si (H is excluded from the atomic percentage calculations reported here) were prepared using pulsed direct current plasma-enhanced chemical vapour deposition (DC-PECVD). Molecular structure, optical properties and mechanical properties of these films were assessed as a function of Si concentration. The spectroscopic results indicated two structural regimes. First, for Si contents up to ~ 13 at.%, SiO_x–DLC is formed as a single phase with siloxane, O–Si–C₂, bonding networks. Second, for films with Si concentrations greater than 13 at.%, SiO_x–DLC with siloxane bonding and SiO_x deposit simultaneously as segregated phases. The variations in mechanical properties and optical properties as a function of Si content are consistent with the above changes in the film composition.     

Wear-corrosion behavior of ultra-thin diamond-like carbon nitride films on aluminum alloy

Diamond-like carbon films exhibit high hardness, high wear resistance and a low friction coefficient. They are extensively utilized in the mechanical, electronic and biomedical industries. This work evaluates the effect of the thickness of ultra-thin diamond-like carbon nitride films on their corrosion properties and their wear-corrosion resistance in a mixed 1 M NaCl + 1 M H₂SO₄ solution using electrochemical methods. The corrosion current density and weight loss of all films during and after wear-corrosion test are also recorded. This work employs ion beam-assisted deposition (IBAD) to deposit DLC nitride films of various thicknesses (1.5, 2.0, 2.5 and 3.0 nm), containing 60% nitrogen gas in the form of a gaseous mixture of C₂H₂ + 60%N₂. The thickness of the films was measured using a transmission electron microscope (TEM). The atomic bonding structures of these DLC nitride films are analyzed using a Raman spectrometer and by electron spectroscopy for chemical analysis (ESCA). A scanning electron microscope (SEM) was adopted to elucidate the surface morphologies of the specimens after corrosion and wear-corrosion. The results indicated that all of the nitrogen-containing DLC films excellently protected the 5088 Al–Mg alloy substrate with an electroless plated Ni–P interlayer against corrosion, and that the degree of protection increases with the thickness of the film. In the wear-corrosion tests various potentials were applied during wear in the particular corrosive solution. The results further demonstrated that the wear-corrosion resistance of all the nitrogen-containing DLC films was as effective as corrosion protection, and that the wear-corrosion loss decreased as the film thickness increased.     

Properties of DLC films deposited by an oxyacetylene flame

Diamond-like carbon (DLC) films were obtained by spinning a tungsten carbide substrate at a high speed using an oxyacetylene flame. The films deposited at a typical experimental condition of substrate temperature of 810°C, rotation of 600 rpm and 3 h deposition time, exhibited an uniform, very smooth, hard and glassy surface covering the entire exposed face of the substrate. These films were identified as DLC by their characteristic broad Raman spectra centered at 1554 cm⁻¹ and micro-Vicker's hardness >3400 kg mm⁻². For substrate temperatures <800°C the film started losing the uniform glassy surface and the hardness deteriorated. For temperatures >950°C the film was still hard and shiny, but black in color. DLC films were also obtained in a wide range of speeds of rotation (300–750 rpm), as long as the temperature remained close to 850°C.     

Influence of nitrogen plasma post-treatment on diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

DLC films were synthesized by RF plasma enhanced chemical vapor deposition and the effects of nitrogen plasma post-treatment at different pressures on the structure and properties of DLC films were investigated. Higher roughness was obtained after plasma post-treatment at higher pressures (0.3 and 0.9 torr) and plasma post-treatment at a lower pressure (0.15 torr) resulted in lower roughness than that of original films. The hardness of DLC films decreased with the decrease of post-treatment pressure, which is consistent with the Raman results of I_D/I_G ratio and G peak position. Compared to the original DLC film, the residual stress after plasma post-treatment decreased slightly due to the relatively thin region involved in the plasma post-treatment.     

Electrical and optical properties of diamond-like carbon films deposited by pulsed laser ablation

Pulsed laser ablation of a graphite target was carried out by ArF excimer laser deposition at a laser wavelength of 193 nm and fluences of 10 and 20 J/cm² to produce diamond-like carbon (DLC) films. DLC films were deposited on silicon and quartz substrates under 1 × 10^? 6 Torr pressure at different temperatures from room temperature to 250 °C. The effect of temperature on the electrical and optical properties of the DLC films was studied. Laser Raman Spectroscopy (LRS) showed that the DLC band showed a slight increase to higher frequency with increasing film deposition temperature. Spectroscopic ellipsometry (SE) and ultraviolet–visible absorption spectroscopy showed that the optical band gap of the DLC films was 0.8–2 eV and decreased with increasing substrate temperature. These results were consistent with the electrical resistivity results, which gave values for the films in the range 1.0 × 10⁴–2.8 × 10⁵ Ω cm and which also decreased with deposition temperature. We conclude that at higher substrate deposition temperatures, DLC films show increasing graphitic characteristics yielding lower electrical resistivity and a smaller optical band gap.     

Synthesis and mechanical properties of carbon nanotube/diamond-like carbon composite films

Diamond-like carbon (DLC) coatings were successfully deposited on carbon nanotube (CNT) films with CNT densities of 1 × 10⁹/cm², 3 × 10⁹/cm², and 7 × 10⁹/cm² by a radio frequency plasma-enhanced chemical vapor deposition (CVD). The new composite films consisting of CNT/DLC were synthesized to improve the mechanical properties of DLC coatings especially for toughness. To compare those of the CNT/DLC composite films, the deposition of a DLC coating on a silicon oxide substrate was also carried out. A dynamic ultra micro hardness tester and a ball-on-disk type friction tester were used to investigate the mechanical properties of the CNT/DLC composite films. A scanning electron microscopic (SEM) image of the indentation region of the CNT/DLC composite film showed a triangle shape of the indenter, however, chippings of the DLC coating were observed in the indentation region. This result suggests the improvement of the toughness of the CNT/DLC composite films. The elastic modulus and dynamic hardness of the CNT/DLC composite films decreased linearly with the increase of their CNT density. Friction coefficients of all the CNT/DLC composite films were close to that of the DLC coating.     

Mechanical properties and thermal stability of SiBCN films prepared by ion beam assisted sputter deposition

The high hardness, exceptional high temperature stability, and oxidation resistance of bulk Si–B–C–N ceramics have led to the expectation that these materials will be good candidates for superior coating materials in high-temperature applications. In this study, SiBCN films were prepared using ion beam assisted sputter (IBAS) deposition, and the mechanical properties and thermal stabilities of the films at 600, 700, and 800 °C in air were investigated. In particular, the effects of the ion beam assist on the properties of the SiBCN films were examined. The SiBCN films were deposited on Si plates by sputtering a target composed of Si + BN + C using a 2-keV Ar⁺ ion beam. A low-energy N₂⁺ and Ar⁺ mixed ion beam irradiated the samples during the sputter deposition. The Si content in the SiBCN films was controlled by changing the Si/(BN + C) ratio of the target. BCN films were also deposited for comparison. The composition and chemical bonding structure of the prepared films were investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. We found that c-BN bonds were formed in the ion-assisted BCN film. The oxide layer thickness on the SiBCN films after thermal annealing decreased due to the IBAS deposition and an increase in the Si content. Ion-assisted SiBCN films annealed at 800 °C showed the highest hardness of 20 GPa.     

Low temperature processed SnO2 films using aqueous precursor solutions

We present a comparison study of the microstructure developments during aqueous solution deposition of SnO₂, particularly, through chemical bath deposition (CBD) and liquid phase deposition (LPD) at very low temperatures (40–75 °C). The effects of solution chemistry on the microstructural details and electrical properties of SnO₂ thin films are presented and discussed. Smooth, nanoparticulate SnO₂ films were obtained from supersaturated precursor solutions with lower precursor concentrations while more aggregated SnO₂ films were generated from higher precursor concentrations. Loosely-packed and porous structures were obtained from low supersaturation solutions with very low pHs. The deposition rates were also evaluated under various deposition conditions. XRD result shows that annealing process helps improve the degree of crystallinity of the as-deposited films that are composed of 3–10 nm nanocrystalline particles. One advantage of LPD of SnO₂ films is in-situ fluorine doping during deposition. The resulting electrical resistivity of F-doped SnO₂ films was about 18.7 Ω cm after the films were annealed at 450 °C.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

Growth and properties of hydrogen-free DLC films deposited by surface-wave-sustained plasma

Hydrogen-free diamond-like carbon (DLC) films were deposited by a new surface-wave-sustained plasma physical vapor deposition (SWP-PVD) system in various conditions. Electron density was measured by a Langmuir probe; the film thickness and hardness were characterized using a surface profilometer and a nanoindenter, respectively. Surface morphology was investigated using an atomic force microscope (AFM). It is found that the electron density and deposition rate increase following the increase in microwave power, target voltage, or gas pressure. The typical electron density and deposition rate are about 1.87 × 10¹¹–2.04 × 10¹² cm^− 3 and 1.61–14.32 nm/min respectively. AFM images indicate that the grain sizes of the films change as the experimental parameters vary. The optical constants, refractive index n and extinction coefficient k, were obtained using an optical ellipsometry. With the increase in microwave power from 150 to 270 W, the extinction coefficient of DLC films increases from 0.05 to 0.27 while the refractive index decreases from 2.31 to 2.11.     

Preparation of diamond like carbon thin films above room temperature and their properties

Diamond like carbon (DLC) thin films were deposited on p-type silicon (p-Si), quartz and ITO substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at different substrate temperatures (RT ∼ 300 °C). Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C₂H₂: 20 sccm) and nitrogen (N: 5 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), FT-IR and UV–visible spectroscopy were employed to investigate the structural and optical properties of the DLC thin films respectively. FT-IR spectra show the structural modification of the DLC thin films with substrate temperatures showing the distinct peak around 3350 cm^− 1 wave number; which may corresponds to the sp² C–H bond. Tauc optical gap and film thickness both decreased with increasing substrate temperature. The peaks of XPS core level C 1 s spectra of the DLC thin films shifted towards lower binding energy with substrate temperature. We also got the small photoconductivity action of the film deposited at 300 °C on ITO substrate.     

Structure and mechanical properties of oxygen doped diamond-like carbon thin films

In this study, structure and mechanical properties of doped diamond-like carbon (DLC) films with oxygen were investigated. A mixture of methane (CH₄), argon (Ar) and oxygen (O₂) was used as feeding gas, and the RF-PECVD technique was used as a deposition method. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by Stoney equation. The XPS and ERDA-RBS results indicated that by increasing the oxygen in the feeding gas up to 5.6 vol.%, the incorporation of oxygen into the films' structure was increased. The ratio of sp² to sp³ sites was changed by the variation of oxygen content in the film structure. The sp²/sp³ ratios are 0.43 and 1.04 for un-doped and doped DLC films with 5.6 vol.% oxygen in the feeding gas, respectively. The Raman spectroscopy (RS) results showed that by increasing the oxygen content in doped DLC films, the amount of sp² CC aromatic bonds was raised and the hydrogen content reduced in the structure. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the decrease of hydrogen content and the increase the ratio of CC aromatic to olefinic bonds. Hardness and residual stress of the films were raised by increasing the oxygen content within the films' structure. The maximum hardness (19.6 GPa) and residual stress (0.29 GPa) were obtained for doped DLC films, which had the maximum content of oxygen in structure, while the minimum hardness (7.1 GPa) and residual stress (0.16 GPa) were obtained for un-doped DLC films. The increase of sp³ CC bonds between clusters and the decrease of the hydrogen content, with a simultaneous increase of oxygen in the films' structure is the reason for increase of hardness and residual stress.     

Influence of bias voltage on diamond like carbon (DLC) film deposited on polyethylene terephthalate (PET) film surfaces using PECVD and its blood compatibility

In this paper, diamond like carbon (DLC) films were coated on polyethylene terephthalate (PET) film substrate as a function of biasing voltage using plasma enhanced chemical vapour deposition. The surface morphology of the DLC films was analyzed by scanning electron microscopy and atomic force microscopy. The chemical state and structure of the films were analyzed by X-ray photoelectrons spectroscopy and Raman spectroscopy. The micro hardness of the DLC films was also studied. The surface energy of interfacial tension between the DLC and blood protein was investigated using contact angle measurements. In addition, the blood compatibility of the films was examined by in vitro tests. For a higher fraction of sp³ content, maximum hardness and surface smoothness of the DLC films were obtained at an optimized biasing potential of ? 300 V. The in vitro results showed that the blood compatibility of the DLC coated PET film surfaces got enhanced significantly.     

Electron field emission from filtered arc deposited diamond-like carbon films using Au and Ti layers

In this work, tetrahedral diamond-like carbon (DLC) films are deposited on Si, Ti/Si and Au/Si substrates by a new plasma deposition technique — filtered arc deposition (FAD). Their electron field emission characteristics and fluorescent displays of the films are tested using a diode structure. It is shown that the substrate can markedly influence the emission behavior of DLC films. An emission current of 0.1 μA is detected at electric field E_DLC/Si=5.6 V/μm, E_DLC/Au/Si=14.3 V/μm, and E_DLC/Ti/Si=5.2 V/μm, respectively. At 14.3 V/μm, an emission current density J_DLC/Si=15.2 μA/cm², J_DLC/Au/Si=0.4 μA/cm², and J_DLC/Ti/Si=175 μA/cm² is achieved, respectively. It is believed that a thin TiC transition layer exists in the interface between the DLC film and Ti/Si substrate.     

Diamond-like carbon films synthesized under atmospheric pressure synthesized on PET substrates

Diamond-like carbon films were synthesized under atmospheric pressure (AP-DLC) and their gas barrier properties and hardness were measured. The AP-DLC films were uniformly obtained by RF-plasma CVD method at room temperature with a size of 450 mm². The growth rate increased as a function of C₂H₂ concentration and the average growth rate was around 12 μm/min. The maximum deposition rate was ~ 1 μm/s, which is approximately 2000 times larger than that by low-pressure plasma CVD of 1–2 μm/h. The gas barrier properties of AP-DLC films, ~ 1 μm thick, were 5–10 times larger than those of uncoated PET substrates. The microhardness of AP-DLC films was around 3 GPa, measured by the nano-indentation method. The issue lies in the removal of macro-particles of the films to improve the microhardness and the surface roughness.In this paper, we report the physical properties of DLC films synthesized under atmospheric pressure by the radio-frequency CVD method. We also summarize a brief history of PET bottle coating by vacuum-DLC films, as well as that of the development of atmospheric pressure technology and related DLC films, focused on gas barrier properties and micro-hardness.     

Improvement of DLC electrochemical corrosion resistance by addiction of fluorine

The combination of chemical and mechanical properties of diamond-like carbon (DLC) films opens the possibilities for its use in electrochemical applications. DLC electrochemical corrosion behavior is heavily dependent on deposition techniques and precursor gas. Fluorinated-DLC combines the superlative properties of diamond and teflon and becomes one of the most suitable coating for tribological applications. F-DLC was grown over 316L stainless steel using plasma enhanced chemical vapor deposition by varying the ratio of carbon tetrafluoride and methane. The influence of fluorine content on deposition rate, composition, bonding structure, surface energy, hardness, stress, and surface roughness was investigated. Emphasis was placed on the investigation of F-DLC electrochemical corrosion behavior, which was tested by potentiodynamic method. As F content increased, F-DLC films presented lower stress, hardness values and surface free energy. In addition, Raman G-band peak position shifted to higher frequency. The corrosion potential becomes more negative and the anodic and cathodic current densities decreased with the increase of F content, as compared to the pure DLC and the substrates. These results were confirmed by Nyquist plot, which shows a stronger ohmic behavior for F-DLC and Bode plots with different corrosion behaviors. The electrochemical analysis indicated F-DLC films present superior impedance, polarization resistance and breakdown potential as compared to the pure DLC, which indicate they are promising corrosion protective coating in aggressive solutions.     

Changes in chemical bonding of diamond-like carbon films by atomic-hydrogen exposure

We have deposited unhydrogenated diamond-like carbon (DLC) films on Si substrate by pulsed laser deposition using KrF excimer laser, and investigated the effects of atomic-hydrogen exposure on the structure and chemical bonding of the DLC films by photoelectron spectroscopy (PES) using synchrotron radiation and Raman spectroscopy. The fraction of sp³ bonds at the film surface, as evaluated from C1s spectra, increased at a substrate temperature of 400 °C by atomic-hydrogen exposure, whereas the sp³ fraction decreased at 700 °C with increasing exposure time. It was found that the sp³ fraction was higher at the surfaces than the subsurfaces of the films exposed to atomic hydrogen at both the temperatures. The Raman spectrum of the film exposed to atomic hydrogen at 400 °C showed that the clustering of sp² carbon atoms progressed inside the film near the surface even at such a low temperature as 400 °C.     

Microstructure and optical band gap control of DLC film deposited by pulsed discharge plasma CVD

DLC films were deposited on silicon and quartz glass substrates by pulsed discharge plasma chemical vapor deposition (CVD), where the plasma was generated by pulsed DC discharge in H₂–CH₄ gas mixture at about 90 Torr in pressure, and the substrates were located near the plasma. The repetition frequency and duty ratio of the pulse were 800 Hz and 20%, respectively. When CH₄ / (CH₄ + H₂) ratio, i.e. methane concentration (Cm), increased from 3 to 40%, C₂ species in the plasma was increased, and corresponding to the increase of C₂, deposition rate of the film was increased from about 0.2 to 2.4 μm/h. The absorption peaks of sp³C–H and sp²C–H structures were observed in the FT-IR spectra, and the peak of sp²C–H structure was increased with increasing Cm, showing that sp² to sp³ bonding ratio was increased when Cm was increased. Corresponding to these structural changes due to the increase of Cm, optical band gap (Eg) was decreased from 3 to 0.5 eV continuously when Cm was increased from 3 to 40%.