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.     

Deposition and characterization of diamond-like carbon films by microwave resonator microplasma at one atmosphere

Diamond-like carbon (DLC) films have been deposited at atmospheric pressure by microwave-induced microplasma for the first time. Typical precursor gas mixtures are 250 ppm of C₂H₂ in atmospheric pressure He. Chemically resistant DLC films result if the Si (100) or glass substrate is in close contact with the microplasma, typically at a standoff distance of 0.26 mm. The films deposited under this condition have been characterized by various spectroscopic techniques. The presence of sp³ CH bonds and ‘D’ and ‘G’ bands were observed from FTIR and Raman spectroscopy, respectively. The surface morphology has been derived from SEM and AFM and shows columnar growth with column diameters of approximately 100 nm. Likely due to the low energy of ions striking the surface, the hardness and Young's modulus for the films were found to be 1.5 ± 0.3 GPa and 60 ± 15 GPa respectively with a film thickness of 2 μm. The hypothesis that a high flux of low energy ions can replace energetic ion bombardment is examined by probing the plasma. Rapid deposition rates of 4–7 μm per minute suggest that the method may be scalable to continuous coating systems.     

Thin-film nanocomposites of diamond-like carbon and titanium oxide; Osteoblast adhesion and surface properties

Thin films of a novel, nanocomposite material consisting of diamond-like carbon and polycrystalline/amorphous TiO_x (DLC-TiO_x, x ≤ 2) were prepared using pulsed direct-current plasma enhanced chemical vapour deposition (PECVD). Results from Raman spectroscopy indicate that the DLC and TiO_x deposit primarily as segregated phases. Amorphous TiO₂ is found to be present on the surface region of the film and there is evidence for the presence of crystalline TiO in the bulk of the film. The hydrophilicity of the DLC-TiO_x films increased with increasing titanium content. Culture studies with human osteoblasts revealed that the differences in three-day cell adhesion properties (count, morphology and area) between DLC and DLC-TiO_x films containing up to 13 at.% Ti were not statistically significant. However, the cell count was significantly greater for the films containing 3 at.% of Ti in comparison to those containing 13 at.% of Ti. A post-plasma treatment with Ar/O₂ was used to reduce the water contact angle, θ, by nearly 40° on the DLC-TiO_x films containing 3 at.% of Ti. A cell culture study found that the osteoblast count and morphology after three days on these more hydrophilic films did not differ significantly from those of the original DLC-TiO_x films. We compare these results with those for SiO_x-incorporated DLC films and evaluate the long-term osteoblast-like cell viability and proliferation on modified DLC surfaces with water contact angles ranging from 22° to 95°.     

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.     

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.     

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.     

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.     

Termination of diamond surfaces with hydrogen,oxygen and fluorine using a small,simple plasma gun

We have formed and characterized polycrystalline diamond films with surfaces having hydrogen terminations, oxygen terminations, or fluorine terminations, using a small, simple and novel plasma gun to bombard the diamond surface, formed by plasma assisted CVD in a prior step, with ions of the wanted terminating species. The potential differences between surface regions with different terminations were measured by Kelvin Force Microscopy (KFM). The highest potential occurred for oxygen termination regions and the lowest for fluorine. The potential difference between regions with oxygen terminations and hydrogen terminations was about 80 mV, and between regions with hydrogen terminations and fluorine terminations about 150 mV. Regions with different terminations were identified and imaged using the secondary electron signal provided by scanning electron microscopy (SEM), since this signal presents contrast for surfaces with different electrical properties. The wettability of the surfaces with different terminations was evaluated, measuring contact angles. The sample with oxygen termination was the most hydrophilic, with a contact angle of 75°; hydrogen-terminated regions with 83°, and fluorine regions 93°, the most hydrophobic sample.     

Microstructural evolution of YSZ electrolyte aerosol-deposited on porous NiO-YSZ

Dense, crack-free, ～7.5 μm thick, 8 mol% yttria stabilized zirconia (YSZ) film was aerosol deposited on porous NiO-YSZ anode substrates at room temperature without additional high-temperature sintering. The films’ microstructures and gas permeability were observed after annealing at various temperatures. The dense, gas-tight film that was observed up to 1000 °C became porous at higher temperatures probably due to structural instability related to oxygen non-stoichiometry. A cell using such film as electrolyte showed an open cell voltage of 1.10 V and a maximum power density of 0.51 W/cm² at 750 °C.     

X-ray reflectivity analysis on initial stage of diamond-like carbon film deposition on Si substrate by RF plasma CVD and on removal of the sub-surface layer by oxygen plasma etching

The multi-layered structure of thin diamond-like carbon (DLC) films was investigated by X-ray reflectivity (XRR) analysis. Thin DLC films were deposited on Si substrate by RF plasma chemical vapor deposition (CVD) from acetylene source gas with short duration of plasma operation from 0.08 to 4.99 s. It was confirmed from XRR analysis that the thin DLC film on Si substrate had 3 layers consisting of a subsurface layer on the grown surface, a mixing layer at the interface to Si substrate, and a bulk-DLC layer sandwiched between the 2 layers. The 3 layers had been formed in 0.08 s at beginning of deposition with distinctive bulk-DLC layer of 1.7 nm thick already appeared due to extremely higher deposition rate only at the initial stage of CVD. The thickness of bulk-DLC layer increased with increasing CVD duration while both the mixing layer of higher density and the sub-surface layer of extremely low density continuously existed. By oxygen plasma etching, it was confirmed by XRR analysis that the sub-surface layer was clearly removed and another layer of lower density than the bulk DLC appeared.     

Structural and mechanical properties of DLC films prepared by bipolar PBII&D

In the present study, diamond-like carbon (DLC) films were prepared by bipolar plasma based ion implantation and deposition (PBII&D), and the structural and mechanical properties of the DLC films deposited on Si substrates were evaluated by Raman spectroscopy. In the PBII&D processing, the positive and negative pulse voltages were varied from 1 to 3 kV and from ? 1 to ? 15 kV, respectively. With an increase in the pulse voltages, the Raman G-peak position and I(D) / I(G) ratio increased, and the G-peak full width at half maximum (FWHM(G)) decreased, indicating graphitization of the DLC films. In the low wavenumber regime, the FWHM(G) increases when the G-peak shifts to higher wavenumbers, reaching a maximum value at around 1540 cm^? 1, and then decreases. This behavior was due to the structural changes occurring in the DLC films with an increase in the wavenumber. DLC to polymer-like carbon (PLC) transition occurred in the low wavenumber regime, and DLC to graphite-like carbon (GLC) transition occurred in the high wavenumber regime. Further, two different trends were observed in the relationship between the mechanical properties (hardness, elastic modulus, and internal stress) of the DLC films and the FWHM(G), originating from the structural change from DLC to GLC and PLC.     

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.     

Atmospheric plasma deposition of diamond-like carbon coatings

The atmospheric pressure plasma-enhanced chemical vapor deposition of diamond-like carbon (DLC) has been investigated. The DLC coatings were grown with a mixture of acetylene, hydrogen and helium that was fed through a linear plasma source. The plasma was driven with radio frequency power at 27.12 MHz. Deposition rates exceeded 0.10 µm/min at substrate temperatures between 155 and 200 °C. Solid-state carbon-13 nuclear magnetic resonance revealed that the coatings contained approximately 43% sp²-bonded carbon and 57% sp³-bonded carbon. Coefficient of friction values for the coatings were found to be 0.24 ± 0.02, which is within the range observed for vacuum deposited DLC.     

A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2×10⁻⁴ Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl), N) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (≥20 μm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1–3 μm) were investigated using a ‘Fischerscope’, and Young's module of thin films (20–70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS), X-ray excited Auger electron spectroscopy (XAES), and X-ray photoelectron spectroscopy (XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coefficient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43–3.65 g/cm³. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.     

Localized DLC etching by a non-thermal atmospheric-pressure helium plasma jet in ambient air

Using a versatile atmospheric-pressure helium plasma jet, diamond-like carbon (DLC) films were etched in ambient air. We observed that the DLC films are etched at a nominal rate of around 60 nm/min in the treated area (230 μm in diameter) during a 20-min exposure. The etching rate increased after the initial 10-min exposure. During this period, the flat DLC surface was structurally modified to produce carbon nanostructures with a density of ~ 2.4 × 10¹¹ cm^− 2. With this increase in surface area, the etching rate increased. After 20 min, the DLC film had a circular pattern etched into it down to the substrate where silicon nanostructures were observed with sizes varying from 10 nm to 1 μm. The initial carbon nanostructure formation is believed to involve selective removal of the sp²-bonded carbon domains. The carbon etching results from the formation of reactive oxygen species in the plasma.     

Very hard ZrC thin films grown by pulsed laser deposition

Thin ZrC films were grown on (1 0 0) Si substrates at temperatures from 30 to 500 °C by the pulsed laser deposition technique. Auger electron spectroscopy investigations found that films contained oxygen concentration below 2.0 at%, while X-ray photoelectron spectroscopy investigations showed that oxygen is bonded in an oxy-carbide type of compound. The films’ mass densities, estimated from X-ray reflectivity curve simulations, and crystallinity improved with the increase of the substrate temperature. Williamson–Hall plots and residual-stress measurements using the modified sin² ψ method for grazing incidence X-ray diffraction showed that the deposited films are nanostructured, with crystallite sizes from 6 to 20 nm, under high micro-stress and compressive residual stress. Nanoindentation investigations found hardness values above 40 GPa for the ZrC films deposited at substrate temperatures higher than 300 °C. The high density of the deposited films and the nm-size crystallites are the key factors for achieving such high hardness values.     

Effect of the type of plasma on the polydimethylsiloxane/collagen composites adhesive properties

Polydimethylsiloxane (PDMS) films were treated with either oxygen (O₂), nitrogen (N₂) or argon (Ar) plasma between 40 W and 120 W for 5–15 min and their surface properties studied by contact angle measurements, infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Lower contact angles and increases in surface roughness, assessed by SEM and AFM, were observed for all used gases when plasma power and time increased, with argon treatment being the one that showed the most significant change in roughness.PDMS/collagen type I composites obtained after treating PDMS with oxygen at 80 W for 13 min or nitrogen and argon at 80 W for 14 min showed a peel strength of 0.1N/mm (oxygen plasma), 0.08 N/mm (nitrogen plasma) and 0.09 N/mm (argon plasma). In all cases, peel strength was higher than that measured for the untreated bilayer composite. An increase in adhesion strength, after oxygen and nitrogen plasma, was mostly attributed to chemical interaction between functional groups introduced on the PDMS surface and the functional groups on collagen as detected by FTIR. In contrast, the high peel strength observed on PDMS treated with argon plasma was attributed to its increased roughness which in turn increased mechanical interlocking. The properties of these composites render them suitable for adhesive free skin substitutes.     

Structure and dielectric properties of barium titanate thin films for capacitor applications

BaTiO₃ is a typical ferroelectric material with high relative permittivity and has been used for various applications, such as multilayer ceramic capacitors (MLCCs). With the tendency of miniaturization of MLCCs, the thin films of BaTiO₃ have been required. In this work, BaTiO₃ thin films have been deposited on Pt-coated Si substrates by RF magnetron sputtering under different deposition conditions. The films deposited at the substrate temperature from 550 °C–750 °C show a pure tetragonal perovskite structure. The films deposited at 550 °C–625  °C exhibit (111) preferential orientation, and change to (110) preferential orientation when deposited above 650 °C. The film morphologies vary with working pressure and substrate temperature. The film deposited at 625 °C and 4.5 Pa has the relative permittivity of 630 and the loss tangent of 2% at 10 kHz.     

Aqueous chemical route deposition of nanocrystalline ZnO thin films as acetone sensor: Effect of molarity

Nanocrystalline ZnO thin films were deposited onto glass substrate using a simple and inexpensive aqueous chemical method at low temperature (90 °C). The concentration of precursor solution was varied in order to study its effect on structural, morphological, and gas response properties. Field-emission scanning electron microscopy (FESEM) images indicate the growth of ZnO with hexagonal shaped nanostructure. Further these films were used to explore gas response properties towards acetone, propanol and ethanol vapors. The sensor response was found to be decreased with increase in precursor concentration. The highest sensor response of 92% was observed towards acetone for the film deposited at 0.05 M at an operating temperature of 350 °C. The higher vapor response towards acetone is attributed to size and surface morphology of the film deposited at 0.05 M.     

Synthesis,spray granulation and plasma spray coating of lanthanum phosphate nanorods for thermal insulation coatings

Nanorods of lanthanum phosphate obtained by a wet chemical precipitation route were granulated to obtain sizes in the range of 10–15 µm by spray drying from aqueous slurry of 35 wt% solid loading and 2 wt% of PVA binder. The powders thus obtained displayed enhanced flowability and were plasma sprayed on to stainless steel substrates resulting in the formation of adherent coatings of 150–180 µm thickness. These coatings were characterized using electron microscopy, X-ray diffraction analysis and Raman spectroscopy. X-ray analysis indicated phase instability of LaPO₄ during plasma spraying resulting in the formation of oxy and polyphosphates of lanthanum (La₂P₄O₁₃ and La₃PO₇). However, post deposition heat treatment of coated samples at 1100 °C for 2 h resulted in the reversible formation of stoichiometric lanthanum orthophosphate (LaPO₄). Raman spectral analysis was used to confirm the phase structure of the coatings deposited at various plasma input powers. The coatings obtained were found to effectively lower the thermal conductivity of the substrates from ~24 W/mK to less than 19 W/mK (~10%) even at 200 °C.