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.     

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage (V_oc) of 168.8 mV and a short-circuit current density (J_sc) of 8.4 μA/cm² under light illumination (AM 1.5 100 mW/cm²). The energy conversion efficiency and fill factor were found to be 3.4 × 10^{− 4}% and 0.238 respectively.     

Optoelectronic properties of nitrogenated amorphous carbon films synthesized by microwave surface wave plasma chemical vapor deposition system

The n-type nitrogen doped amorphous carbon (a-C:N) thin films have been grown by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) system on silicon, quartz and ITO substrates at different nitrogen flow rates (1 to 4 sccm). The effects of nitrogen doping on chemical, optical, structural and electrical properties were studied through X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, Raman spectroscopy and solar simulator measurements. Argon, acetylene and nitrogen are used as plasma sources. Optical band gap decreased and nitrogen atomic concentration (%) increased with increasing nitrogen flow rate as a dopant. The a-C:N/p-Si based device exhibits photovoltaic behavior under illumination (AM 1.5, 100 mW/cm²), with a maximum open-circuit voltage (V_oc), short-circuit current (J_sc) and fill factor of 4.2 mV, 7.4 μA/cm² and 0.25 respectively.     

The role of pressure on thin amorphous carbon films deposited using microwave surface wave plasma CVD

We report the effects of gas composition pressure (GCP) on the optical, structural and electrical properties of thin amorphous carbon (a-C) films grown on p-type silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition (MW SWP CVD). The films, deposited at various GCPs ranging from 50 to 110 Pa, were studied by UV/VIS/NIR spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and current–voltage characteristics. The optical band gap of the a-C film was tailored to a relatively high range, 2.3–2.6 eV by manipulating GCPs from 50 to 110 Pa. Also, spin density strongly depended on the band gap of the a-C films. Raman spectra showed qualitative structured changes due to sp³/sp² carbon bonding network. The surfaces of the films are found to be very smooth and uniform (RMS roughness < 0.5 nm). The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm²) show that short-circuit current density, open-circuit voltage, fill factor and photo-conversion efficiency of the film deposited at 50 Pa were 6.4 μA/cm², 126 mV, 0.164 and 1.4 × 10^− 4% respectively.     

Effects of iodine doping on optoelectronic properties of diamond-like carbon thin films deposited by microwave surface wave plasma CVD

We report the effects of iodine (I) doping on the electrical and optical properties of diamond-like carbon (DLC) thin films grown on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition at low temperature (<100 °C). For film deposition, we used argon gas with methane or camphor dissolved with ethyl alcohol composition as plasma source. The optical gap and photoconductivity measurements of the samples were carried out before and after the iodine doping. The results show that optical gap dropped from 3.4 to 0.9 eV corresponding to nondoping to iodine-doping conditions, respectively. The photovoltaic measurements show that the open-circuit voltage (V_oc) and short-circuit current density (J_sc) of I-doped DLC film deposited on n-type silicon substrate under light illumination (AM1.5, 100 mW/cm²) were approximately 177 mV and 1.15 μA, respectively, and the fill factor was found to be 0.217.     

Nitrogen incorporated diamond-like carbon films by microwave surface wave plasma CVD

Nitrogen incorporated diamond like carbon films have been deposited by microwave surface wave plasma chemical vapor deposition (MW-SWP-CVD), using methane (CH₄) as the source of carbon and with different nitrogen flow rates (N₂ / CH₄ flow ratios between 0 and 3). The influence of the nitrogen incorporation on the optical, structural properties and surface morphology of the carbon films were investigated using different spectroscopic techniques. The nitrogen has been incorporated into DLC:N films which was confirmed by the X-ray photoelectron spectroscopy (XPS) measurement. Moreover, the nitrogen incorporation was accompanied by a variation in the optical gap, which was attributed to the removal or creation of band tail states.     

Study on metal-doped diamond-like carbon films synthesized by cathodic arc evaporation

In this study, we developed a novel method of synthesizing metal-doped diamond-like carbon films (DLC) using the cathodic arc evaporation (CAE) process. Intense Cr plasma energy activated the decomposition of hydrocarbon source gas C₂H₂ to form a metal-doped amorphous carbon film on steel substrates. We deposited a Cr interlayer to prevent interdiffusion between DLC and the steel substrates. When the C₂H₂ partial pressure is higher than 1.3 Pa, the deposition reaction switched from Cr₃C₂ to DLC formation. The result is a hydrogenated DLC thin film possessing excellent microhardness as high as 3824 Hv(25g), and for which the incorporation of a Cr interface and Cr doping in the DLC matrix ensure film ductility and sufficient film adhesion. We employed Raman spectroscopy to evaluate the influences of reactive gas flow and substrate bias on the DLC composition; we carried out the microstructure and mechanical property measurements by scanning electron microscopy (SEM), X-ray diffraction (XRD), glow discharge optical spectroscopy (GDS) and wear tests.     

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C₁₀H₁₆O) dissolved with ethyl alcohol (C₂H₅OH), methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10^{− 4} Ω^{− 1} cm^{− 1}) and under the light illumination (i.e. 9.9 × 10^{− 4} Ω^{− 1} cm^{− 1}). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10^{− 3} mA/cm². The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10^{− 4}% and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.     

Synthesis of cobalt/diamond-like carbon thin films by biased target ion beam deposition

Cobalt/diamond-like carbon (Co/DLC) composite thin films were synthesized on silicon wafers by biased target ion beam deposition (BTIBD) in which Co was deposited by sputtering a negatively biased Co target using an Ar ion beam and DLC was produced simultaneously by a second ion beam with CH₄ as carbon source. The surface morphology, chemical composition and binding states of the synthesised thin films were studied. The as-deposited Co/DLC films are continuous and smooth with a thickness of approximately 150 nm for an hour of deposition. The average roughness is 3.5 ± 0.3 Å and the root-mean squared roughness is 5.3 ± 1.1 Å. The films are low in contaminations and the mass concentration of Co is approximately 24%. Fourier transform infrared spectroscopy and Raman spectroscopy results indicate the Co did not react with C and barely changed the microstructure of DLC. X-ray photoelectron spectroscopy and synchrotron based near-edge X-ray absorption fine structure studies indicate that the Co is in metallic form in the as-deposited films. The preliminary results demonstrate the promise to synthesize high quality Co/DLC composite films by BTIBD.     

Effect of substrate bias voltage on the properties of diamond-like carbon thin films deposited by microwave surface wave plasma CVD

Diamond-like carbon (DLC) thin films were deposited on silicon and ITO substrates with applying different negative bias voltage by microwave surface wave plasma chemical vapor deposition (MW SWP-CVD) system. The influence of negative bias voltage on optical and structural properties of the DLC film were investigated using X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. Optical band gap of the films decreased from 2.4 to 1.7 with increasing negative bias voltage (0 to − 200 V). The absorption peaks of sp³ CH and sp² CH bonding structure were observed in FT-IR spectra, showing that the sp²/sp³ ration increases with increasing negative bias voltage. The analysis of Raman spectra corresponds that the films were DLC in nature.     

Effect of Ar:N2 flow rate on morphology,optical and electrical properties of CCTO thin films deposited by RF magnetron sputtering

Calcium copper titanate (CCTO) thin films were deposited on indium tin oxide (ITO) substrates using radio frequency (RF) magnetron sputtering, at selected Ar:N₂ flow rates (1:1, 1:2, 1:4, and 1:6 sccm) at ambient temperature. The effect of Ar:N₂ flow rate on the morphology, optical and electrical properties of the CCTO thin films were investigated using FESEM, XRD, AFM, Hall effect measurement, and UV–Vis spectroscopy. It was confirmed by XRD analysis that the thin films were produced is CCTO with cubic crystal structure. As the flow rate of Ar:N₂ increased up to 1:6 sccm, the thin film thickness reduced from 87 nm to 35 nm while the crystallite size of CCTO thin film decreased from 27 nm to 20 nm. Consequently, the surface roughness of thin film was halved from 8.74 nm to 4.02 nm. In addition, the CCTO thin films deposited at the highest Ar:N₂ flow rate studied, at 1:6 sccm; are having the highest sheet resistivity (13.27 Ω/sq) and the largest optical energy bandgap (3.68 eV). The results articulate that Ar:N₂ flow rate was one of the important process parameters in RF magnetron sputtering that could affect the morphology, electrical properties and optical properties of CCTO thin films.     

Influence of substrate temperature on formation of ultrananocrystalline diamond films deposited by HFCVD argon-rich gas mixture

The influence of the substrate temperature on the formation of ultrananocrystalline diamond (UNCD) thin films, prepared by an argon-based hot filament chemical vapor deposition (HFCVD), is discussed in this work. The gas mixture used for diamond growth was 1 vol.% methane, 9 vol.% hydrogen and 90 vol.% argon at a total flow rate of 200 sccm and at a total pressure of 30 Torr. The substrate temperature range was from 550 to 850 °C at deposition time of 8 h. Mass growth rate was determined at different deposition temperatures. The activation energy for UNCD growth, determined from the Arrhenius plot, was lower (5.7 kcal/mol) than the values found for standard diamond deposition (around 11 kcal/mol). In this work, we suggest that the activation energy was lower because the growth of these films occurs at conditions that there is a high growth competition between diamond phase and sp² phases. To support this hypothesis, systematic characterization studies based on Raman scattering spectroscopy, high-resolution X-ray diffractometry and high-resolution scanning electron microscopy were performed.     

DLC–ceramic multilayers for automotive applications

The present work explores the deposition of hard, wear resistant multilayer coatings, by magnetron sputtering onto Aluminium (Al) alloy substrates that are used in the automotive industry. Multilayer coatings have been manufactured to increase surface hardness and wear resistance for a commercial powder metallurgy Al alloys (Al 2618). The multilayer coating consisted of 25 bi-layers of Titanium Diboride (TiB₂) and diamond-like carbon (DLC). These DLC/TiB₂ coatings were fabricated, maintaining a constant composition wavelength (sum of two layers [λ] = 200 nm) for an array of ceramic fractions ranging from 75% to 95% by volume. The effect of the DLC content on the structure and performance (hardness and adhesion) of the films was investigated. The bi-layer thickness influences the failure patterns resulting from the scratch testing. This study has found hardness values of 27.8 GPa, with a critical load of 20 N and a friction coefficient of 0.47. As a result of these findings the multilayer with 10% of DLC was found to be a better compromise between high hardness (23.8 GPa) and high adhesion (critical load higher than 20 N) and with no signs of cracking during friction testing, proving to be a solution to be employed in components located in the upper valve train area of high performance vehicles.     

Effect of nitrogen incorporation into diamond-like carbon films by ECR-CVD

Diamond-like carbon (DLC) and nitrogenated DLC (a-C:N) films were prepared on Si and glass substrates using an electron cyclotron resonance-assisted microwave plasma chemical vapour deposition (ECR-MPCVD) system with radio frequency substrate bias. The hardness and optical bandgap of the resulting films were investigated and correlated to the elemental and phase composition. The a-C:N films, deposited under conditions identical to those for the DLC films except for the introduction of a nitrogen flow, contain nitrogen which partly substitutes for hydrogen and forms carbon–nitrogen triple bonds. These bonds obstruct the formation of carbon–carbon cross-linking, resulting in softer films. These changes can be interpreted with reference to various changes of active vibronic states determined by Raman spectroscopy.     

Tribological properties of DLC films with different hydrogen contents in water environment

Diamond-like carbon (DLC) films were deposited on silicon wafers by thermal electron excited chemical vapor deposition (CVD). To change the hydrogen content in film, we used three types of carbon source gas (C₇H₈, CH₄, and a CH₄+H₂) and two substrate bias voltages. The hydrogen content in DLC films was analyzed using elastic recoil detection analysis (ERDA). Tribological tests were conducted using a ball-on-plate reciprocating friction tester. The friction surface morphology of DLC films and mating balls was observed using optical microscopy and laser Raman spectroscopy.Hydrogen content in DLC films ranged from 25 to 45 at.%. In a water environment, the friction coefficient and specific wear rate of DLC films were 0.07 and in the range of 10⁻⁸–10⁻⁹ mm³/Nm, respectively. The friction coefficient and specific wear rate of DLC film in water were hardly affected by hydrogen content. The specific wear rate of DLC film with higher hardness was lower than that of film with low hardness. Mating ball wear was negligible and the friction surface features on the mating ball differed clearly between water and air environments, i.e., the friction surface on mating balls in water was covered with more transferred material than that in air.     

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.     

Effects of experimental parameters on the physical properties of non-stoichiometric sputtered vanadium nitrides films

Polycrystalline vanadium nitrides thin films were deposited onto (1 0 0)-oriented silicon wafers by reactive dc planar magnetron sputtering. The influence of the nitrogen gas flow (from 0 to 15 sccm) was studied. Several substrate temperatures were investigated: 150, 400 and 650 °C. Analytical techniques including X-ray diffraction and reflectivity, atomic force microscopy and optical photospectrometry were used to characterize the structure, the morphology and the optical properties of the films. The measured thickness indicates that the deposition rate is decreased (from 3.5 Å for 0 sccm to 1.5 Å for 15 sccm) with increasing nitrogen gas flow. Obtained structures depend on the substrate temperature. The structure of pure vanadium (0 sccm) varies from amorphous phase at 150 and 400 °C to -V phase at 650 °C. The films crystallize dominantly in β-V₂N_1−x phase at low nitrogen gas flows and in δ-VN_1−x phase at high nitrogen gas flows. The as-deposited VN films were highly textured. The texture seems to depend on the nitrogen gas flow. The root mean square (rms) derived from atomic force microscopy (AFM) varies with the nitrogen gas flow. The optical reflectivity of VN films shows high values in the infrared region.     

Effects of nitrogen addition on morphology and mechanical property of DC arc plasma jet CVD diamond films

Nitrogen-doped diamond films have been synthesized by 100 KW DC arc plasma jet chemical vapor deposition using a CH₄/Ar/H₂ gas mixture. The effect of nitrogen addition into the feed gases on the growth and surface morphology and mechanical property of diamond film was investigated. The reactant gas composition was determined by the gas flow rates. At a constant flow rate of hydrogen (5000 sccm) and methane (100 sccm), the nitrogen to carbon ratio (N/C) were varied from 0.06 to 0.68. The films were grown under a constant pressure (4 KPa) and a constant substrate temperature (1073 K). The deposited films were characterized by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The fracture strength of diamond films was tested by three point bending method. The results have shown that nitrogen addition to CH₄/H₂/Ar mixtures had led to a significant change of film morphology, growth rate, crystalline orientation, nucleation density and fracture strength for free-standing diamond films prepared by DC arc plasma jet.     

Piezo-ferroelectric response of bismuth ferrite based thin films and their related photo/piezocatalytic performance

Bismuth ferrite based thin films were grown by RF magnetron sputtering under different experimental conditions. The effects of substrate temperature, Ar:O₂ mass flow ratio and gas mixture pressure on the films’ microstructure, phase evolution, optic, ferroelectric and magnetic properties were systematically investigated. The structural analysis results revealed an amorphous phase for the films deposited at a substrate temperature below 500 °C, while for the thin films deposited at 700 °C, a ε-Fe₂O₃ secondary phase was detected. The diffraction lines of the samples deposited at 600 °C were associated with Bi₂Fe₄O₉ and Bi₂₅FeO₄₀ phases. The increase in the mixture gas pressure up to 1 Pa showed an improved crystallinity of the deposited films, while, at higher working gas pressures, the films were found to be amorphous. The use of low O₂ to Ar mass flow ratio during the deposition led to a phase transformation process. EDX and RBS measurements exposed a uniform distribution of the main elements, revealing some stoichiometry changes induced by the pressure variation. The optical band gap values were influenced by the substrate temperature and pressure of the Ar:O₂ gas. The magnetic properties were correlated with the structural features, the highest magnetic response being observed for the sample deposited at 600 °C, 1 Pa and 3:1 Ar:O₂ gas pressure. According to the PFM results, the film deposited at 700 °C, Ar:O₂ ratio 3:1 and total gas pressure 1 Pa clearly outperformed the others due to their excellent ferroelectric properties and outstanding piezo-response. The sample deposited at 700 °C showed both visible light-driven degradation and piezodegradation activities. The piezocatalytic and photocatalytic activities were ascribed to the high piezoresponse and to a more efficient separation of electrons and holes induced by a built-in electric field that is caused by the larger remnant polarization of Bi₂Fe₄O₉ and Bi₂Fe₄O₉/ε-Fe₂O₃ hetero-junction.     

Electrochemical properties of N-doped hydrogenated amorphous carbon films fabricated by plasma-enhanced chemical vapor deposition methods

Nitrogen-doped hydrogenated amorphous carbon thin films (a-C:N:H, N-doped DLC) were synthesized with microwave-assisted plasma-enhanced chemical vapor deposition widely used for DLC coating such as the inner surface of PET bottles. The electrochemical properties of N-doped DLC surfaces that can be useful in the application as an electrochemical sensor were investigated. N-doped DLC was easily fabricated using the vapor of nitrogen contained hydrocarbon as carbon and nitrogen source. A N/C ratio of resulting N-doped DLC films was 0.08 and atomic ratio of sp³/sp²-bonded carbons was 25/75. The electrical resistivity and optical gap were 0.695 Ω cm and 0.38 eV, respectively. N-doped DLC thin film was found to be an ideal polarizable electrode material with physical stability and chemical inertness. The film has a wide working potential range over 3 V, low double-layer capacitance, and high resistance to electrochemically induced corrosion in strong acid media, which were the same level as those for boron-doped diamond (BDD). The charge transfer rates for the inorganic redox species, Fe^2+/3+ and Fe(CN)₆^4−/3− at N-doped DLC were sufficiently high. The redox reaction of Ce^2+/3+ with standard potential higher than H₂O/O₂ were observed due to the wider potential window. At N-doped DLC, the change of the kinetics of Fe(CN)₆^3−/4− by surface oxidation is different from that at BDD. The rate of Fe(CN)₆^3−/4− was not varied before and after oxidative treatment on N-doped DLC includes sp² carbons, which indicates high durability of the electrochemical activity against surface oxidation.