Microstructure and mechanical properties of Mo/DLC nanocomposite films

Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH₄/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp² carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus.     

Surface modification of amorphous carbon thin films by 1,3-dipolar cycloaddition

Amorphous carbon thin film surfaces were successfully modified by 1,3-dipolar cycloaddition of nitrones, generated by the condensation of 4-(trifluoromethyl)benzaldehyde and N-methylhydroxylamine. Amorphous carbon thin films were deposited by electron cyclotron resonance sputtering and consisted of mainly sp²-hybridized carbon. The modification of amorphous carbon thin film surfaces with organic molecules was confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and atomic force microscopy (AFM). F 1s, N 1s, and C 1s electron spectra revealed the existence of organic molecules on the surface of modified amorphous carbon thin films. The surface coverage increased with reaction temperature, reactant concentration, and reaction time.     

Preparation and characterization of TiO2 thin films by PECVD on Si substrate

Titanium oxide thin films were prepared on p-Si(l00) substrate by plasma enhanced chemical vapor deposition using high purity titanium isopropoxide and oxygen. The deposition rate was little affected by oxygen flow rate, but significantly affected by RF power, substrate temperature, carrier gas flow rate, and chamber pressure. Morphology of the film became coarser with increasing deposition time and chamber pressure, and the film showed less uniformity at high deposition rates. It was also found that the overall deposition process is controlled by heterogeneous surface reaction below 200°C., but controlled by mass transfer of reactants at higher temperatures. TiO₂ films deposited at temperatures lower than 400°C was amorphous, but showed the anatase crystalline structure upon 400°C deposition. The dielectric constant was about 47 for the films post-treated by rapid-thermal annealing (RTA) at 800°C. The leakage current was about 2×10⁻⁵ A/cm² for the films deposited at 400°C and RTA-treated at 600°C. However, it was decreased to less than 3×10⁻⁷ A/cm² for the film RTA-treated at 800°C.     

Preparation and microstructure properties of tetrahedral amorphous carbon films by pulsed laser deposition using camphoric carbon target

The properties of tetrahedral amorphous carbon (ta-C) films grown by pulsed laser deposition (PLD) using camphoric carbon (CC) target and their respective effects of diamond percentages by weight in the target (Dwt.%) are discussed. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Visible-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the Dwt.% noticeably modified the sp³ bonds content and the morphology of the ta-C films. The optical gap (E_g) and electrical resistivity (ρ) increase with Dwt.% up to 1.6 eV and 5.63×10⁷ (Ω cm), respectively, for the ta-C films deposited using target with higher of 50 Dwt.%. We found that the Dwt.% has modified the surface morphological, structural, bonding and physical properties of the camphoric carbon films.     

Characteristics and surface energy of silicon-doped diamond-like carbon films fabricated by plasma immersion ion implantation and deposition

Diamond-like carbon (DLC) films doped with different silicon contents up to 11.48 at.% were fabricated by plasma immersion ion implantation and deposition (PIII-D) using a silicon cathodic arc plasma source. The surface chemical compositions and bonding configurations were determined by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results reveal that the sp³ configuration including Si–C bonds increases with higher silicon content, and oxygen incorporates more readily into the silicon and carbon interlinks on the surface of the more heavily silicon-doped DLC films. Contact angle measurements and calculations show that the Si-DLC films with higher silicon contents tend to be more hydrophilic and possess higher surface energy. The surface states obtained by silicon alloying and oxygen incorporation indicate increased silicon oxycarbide bonding states and sp³ bonding states on the surface, and it can be accounted for by the increased surface energy particularly the polar contribution.     

Deposition of amorphous carbon films from C60 fullerene sublimated in electron beam excited plasma

C₆₀ fullerene clusters are used as a carbon source for amorphous carbon films deposition in an electron beam excited plasma. C₆₀ clusters are sublimated by heating a ceramic crucible containing the C₆₀ powders up to 850 °C, which is located in a highly vacuumed process chamber. The sublimated fullerene powders are injected to the electron beam excited argon plasma and dissociated to be active species that are propelled toward the substrates. Consequently, the carbon species condense as a thin film onto the negatively biased substrates that are immersed in the plasma. Deposition rates of approximately 1.0 μm/h and the average surface roughness of 0.2 nm over an area of 400 μm² are achieved. Decomposition of the C₆₀ fullerene after injecting into the plasma is confirmed by optical emission spectroscopy that shows existence of small carbon species such as C₂ in the plasma. X-ray diffraction pattern reveals that the microstructure of the film is amorphous, while fullerene films deposited without the plasma show crystalline structure. Raman spectroscopic analysis shows that the films deposited in the plasma are one of the types of diamond-like carbon films. Different negative bias voltages have been applied to the substrate holder to examine the effect of the bias voltage to the properties of the films. The nano-indentation technique is used for hardness measurement of the films and results in hardness up to about 28 GPa. In addition, the films are droplet-free and show superior lubricity.     

Boron-doped hydrogenated amorphous carbon films grown by surface-wave mode microwave plasma chemical vapor deposition

We report the effects of boron (B) doping on optical and structural properties of the hydrogenated amorphous carbon thin films grown by surface-wave mode microwave plasma (SW-MWP) chemical vapor deposition (CVD) on n-type silicon and quartz substrates at room temperature. Argon and acetylene were used as a carrier and carbon source gases respectively. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy were employed to investigate the properties of the films. Low atomic concentration of B (0.08 at.%) was found in the doped film. The optical band gap of the undoped film was 2.6 eV and it decreased to 1.9 eV for the B-doped film. Structural property shows the crystalline structure of the film and it has changed after incorporating B as a dopant. The structural modifications of the films leading to being more graphite in nature were confirmed by the Raman and FT-IR characterization.     

Structural,optical and morphological evolution of Ga2O3/Al2O3 (0001) films grown at various temperatures by pulsed laser deposition

This study systematically investigated the structural, optical, and morphological evolution of Gallium oxide (Ga₂O₃) films deposited at different substrate temperatures on Al₂O₃(0001) using pulsed laser deposition (PLD). The thickness of the Ga₂O₃ films was standardized in order to eliminate its effect on the film properties. The effect of substrate temperature from room temperature to 600 °C on the film's transmittance, crystalline structure, chemical composition and surface morphology, was explored. The plasma species generated during the deposition of the PLD process were monitored and analyzed employing in situ optical emission spectroscopy. The deposition rate of the films decreased with increasing substrate temperature. X-ray photoelectron spectroscopy was used to detect both Ga³⁺ and Ga ⁺ oxidation states in all prepared films, which indicated substoichiometric Ga₂O₃ films deficient in oxygen. The percentage of non-lattice oxygen decreased with increasing substrate temperature. At optimal condition, mono-crystaline β-Ga₂O₃ was produced with a high visible and near-infrared transmittance, large grain size and smooth surface, which is suitable for the application in high-performance power electric devices and photoelectronic devices.     

Phase transformation of diamond-like carbon/silver composite films by sputtering deposition

This study fabricated hydrogenated diamond-like carbon/silver bioceramic films on glass substrates using radio frequency magnetron sputtering with a single silver target in an atmosphere of Ar/CH4 mixture. The effects of applied power on the composition and microstructure of bioceramic film were evaluated. A phase transformation, amorphous diamond-like carbon → nano-silver precipitation → nano-silver growth in the amorphous diamond-like carbon matrix was observed during sputtering. The film growth rate, surface roughness, silver content and size of silver nanoclusters in the films all increased with the silver target power due to the higher flux of sputtered silver species toward the substrate.     

Preparation of oxygen gas barrier polypropylene films by deposition of SiOx films plasma‐polymerized from mixture of tetramethoxysilane and oxygen

Silicon oxide (SiOx) film deposition on the surface of oriented poly(propylene) (OPP) films was done to form a new oxygen gas barrier material using plasma polymerization of the tetramethoxysilane (TMOS)/O₂ mixture. The SiOx film deposition on OPP films never improved oxygen gas barrier properties. The inefficacy of the SiOx deposition was due to poor adhesion at the interface between the deposited SiOx and OPP films and also to the formation of cracks in the deposited SiOx film. If prior to the SiOx film deposition surface modification of OPP films was done by a combination of the argon plasma treatment and TMOS coupling treatment, this contributed effectively to strong adhesion leading to success in the SiOx deposition on the OPP film surface, and then the oxygen gas barrier ability was improved. The oxygen permeation rate through the SiOx‐deposited OPP film was decreased from 2230 to 37–52 cm³/m²/day/atm, which was comparable to that of poly(vinylidene chloride), 55 cm³/m²/day/atm at a film thickness of 11 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2389–2397, 2000     

Boron doped amorphous carbon thin films grown by r.f. PECVD under different partial pressure

Boron doped hydrogenated amorphous carbon (a-C) thin films have been deposited by r.f.-plasma CVD with a frequency of 13.56 MHz at room temperature using pure methane as a precursor of carbon source mixed with hydrogen (H₂) as a carrier gas. The films were prepared by varying the r.f. power, different flow rates of CH₄, and partial pressure of mixed gas (CH₄/H₂) using solid boron as a target. The thickness, structural, bonding and optical properties of the as-deposited films were studied by Alpha step surface profiler, Raman, FT-IR, XPS and UV–visible spectroscopy. It was found that changing the deposition pressure in presence of solid boron dopant in the r.f. PECVD process has a profound effect on the properties of the deposited films, as evidenced from their Raman scattering and optical results. The grown p-C: B films were found very smooth and thickness in the range of 240 to 360 nm for 1 h deposition. Films deposited at lower pressure appear brownish color whereas those deposited at higher pressure appear pale yellowish. The as-deposited film is found to be dominated by sp² rather than sp³, which might be due to the formation of small crystallites. The optical band gap is found to be reduced from 2.601.58 eV as the partial pressure of CH₄/H₂ gas is reduced.     

Orientation of graphitic planes during annealing of “dip deposited” amorphous carbon film: A carbon K-edge X-ray absorption near-edge study

Annealing effect of amorphous carbon thin films on Si(1 0 0) substrates is studied by normal incidence and angle dependent carbon K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The angle dependence of the XANES signal shows that the graphitic basal planes are oriented perpendicular to the surface when the film is annealed at 1000 °C. Micro-Raman spectroscopy reveals two well-separated bands the D band at 1355 cm⁻¹ and G band at ∼1600 cm⁻¹, and their I_D/I_G intensity ratio indicates the formation of more graphitic film at higher annealing temperatures. X-ray diffraction pattern of 1000 °C temperature annealed film confirms the formation of graphite structure.     

Hydrogen plasma etching of diamond films deposited on graphite

Poly- and nanocrystalline diamond films have been deposited using microwave plasma enhanced CVD with gas mixtures of x%CH₄/15%H₂/Ar (x = 0.5, 1, 3, and 5). After deposition the resulting films were exposed to a hydrogen plasma etching for 30 min. The hydrogen plasma produced preferential etching of non-diamond carbon on the surface of the samples and the development of steps and pits. Raman spectroscopy and X-ray photoelectron spectroscopy analyses on the etched films showed increased sp³/sp² ratio and decreased surface oxygen. The etch mechanism proposed is regression of pre-existing steps and step flow.     

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.     

Effect of rapid thermal annealing on the properties of zinc tin oxide films prepared by plasma-enhanced atomic layer deposition

The effect of rapid thermal annealing treatments on the microstructure, surface morphology, and optical characteristics of zinc tin oxide (ZTO) films produced by plasma-enhanced atomic layer deposition was investigated. The ZTO films were annealed in oxygen atmosphere for 2 min at four selected temperatures from 500 to 800 °C. The X-ray diffraction showed that the annealing temperature has a great influence on the crystalline characteristics of ZTO films. The film shows complete amorphous structure for as-deposited ZTO film. Meanwhile, the spinel zinc stannate Zn₂SnO₄ was obtained for the samples annealed from 500 to 800 °C, which shows polycrystalline nature. The X-ray photoelectron spectroscopy proved that the annealing process in oxygen gas can effectively can reduce the oxygen vacancy defects in the films. In addition, the photoluminescence spectroscopy manifests an ultraviolet emission with a broad peak range from 345 to 385 nm. Moreover, the ultraviolet luminescence intensity increases continuously with the increase of annealing temperature. Spectroscopic ellipsometry analyses demonstrate that the refractive index of annealed films increases as the increase of annealing temperature, while the extinction coefficient decreases gradually with the increase of annealing temperature in the visible light range.     

Ru-doped nanostructured carbon films

Pure and Ru-doped carbon films are deposited on Si (100) substrates by electron cyclotron resonance chemical vapor deposition. The films are characterized by transmission electron microscopy, electron energy loss spectroscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. In both the pure and Ru-doped samples, diamond nanocrystallites are formed in amorphous carbon matrices. The Ru-doped film contains much smaller diamond nanocrystallites (approx. 3 nm) than the pure samples (approx. 11 nm). Lower surface roughnesses are observed in both pure and Ru-doped samples as compared to other reported nanocrystalline diamond films. The conductivity of the Ru-doped film is significantly higher than that of the pure film. The results show that Ru-doped nanocrystalline diamond films have unique structures and properties as compared to pure nanocrystalline diamond films or metal doped diamond-like carbon films, which may offer advantages for electrochemical, optical-window, field emission or tribological applications.     

Preparation and blood compatibility of carbon/TiO2 nanocomposite

A carbon/TiO₂ nanocomposite, which consists of carbon film with various sp³C content and TiO₂ nanowire arrays, has been synthesized, in which the top surface of TiO₂ nanowire arrays prepared using hydrothermal method on fluorine-doped tin oxide glass were coated with carbon thin films. The carbon thin films with a higher, medium and lower sp³C content were deposited by pulsed magnetic filtered cathodic vacuum arc deposition, plasma-enhanced chemical vapor deposition and magnetron sputtering deposition, respectively. The surface morphology and structure of TiO₂ nanowire arrays were investigated by scanning electron microscopy, transmission electron microscope and X-ray diffraction. The sp³C content in carbon films was characterized using Raman spectroscopy. The blood compatibility of the samples including the TiO₂ nanowire arrays, carbon films and carbon/TiO₂ nanocomposite was assessed by tests of platelet adhesion in vitro. Results showed that the carbon/TiO₂ composite can effectively improve the anticoagulant function compared to the single materials. It is believed that the excellent blood compatibility of the carbon/TiO₂ nanocomposite is attributed to a joint function of surface properties adjusted by nanowire arrays and electronic structure of carbon thin films.     

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.     

Enhancement of fluorine doped amorphous carbon thin films from microwave surface wave plasma activated above room temperature

Fluorinated amorphous carbon (a-C:F) thin films were synthesized above room temperature by microwave surface wave plasma chemical vapour deposition (MW SWP CVD). The effect of deposition temperature on optical, electrical, chemical and bonding properties of the a-C:F films were studied by ultraviolet–visible spectroscopy (UV–VIS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrometry (XPS), Raman spectrometry and TEM measurements. The film exhibits high transparency and decrease in optical band gap with increasing deposition temperature. FTIR study shows the increase in CC and decrease in C–Fx bonds of the films with increasing deposition temperature. Raman study shows some important structural changes in the films due to fluorine incorporation. XPS result shows the shift of carbon peak to higher binding energy due to carbon fluorine link to the films. TEM shows the increasing graphitic layer in the films with increasing deposition temperature.     

Electro-optical performances of nanostructured SrTiOx films: The effect of plasma power,Ar/O2 ratio and annealing

The present work evaluates the effects of plasma power and oxygen mixing ratios (OMRs) on structural, morphological, optical, and electrical properties of strontium titanate SrTiO_x (STO) thin films. STO thin films were grown by magnetron sputtering, and later thermal annealing at 700°C for 1 h was applied to improve film properties. X-ray diffraction analysis indicated that as-deposited films have amorphous microstructure independent of deposition conditions. The films deposited at higher OMR values and later annealed also showed amorphous structure while the films deposited at lower OMR value and annealed have nanocrystallinity. In addition, all as-deposited films were highly transparent (~80%–85%) in the visible spectrum and exhibited well-defined main absorption edge, while the annealing improved transparency (90%) within the same spectrum. The calculated direct and indirect optical band gaps for films were in the range of 3.60-4.30 eV as a function of deposition conditions. The refractive index of the films increased with OMRs and the postdeposition annealing. The frequency dependent capacitance measurements at 100 kHz were performed to obtain film dielectric constant values. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 μC/cm² charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). The leakage current density was relatively low (3 × 10⁻⁸Acm⁻² at +0.8 V) indicating that STO films are promising for future dynamic random access memory applications.