Effect of oxygen plasma treatment on bonding states for columnar structured a-CNx thin films prepared by reactive sputtering

Amorphous carbon nitride (a-CN) thin films were deposited on silicon single crystal substrates by rf-reactive sputtering method using a graphite target and nitrogen gas. The substrate temperature was varied from room temperature (RT) to 853 K. After deposition, the effect of oxygen plasma treatment on bonding structures of the film surface has been studied by using an oxygen discharge at 16 Pa and rf power of 85 W. The chemical bonding states and film composition were analyzed by X-ray photoelectron spectroscopy (XPS), while film thickness was obtained from scanning electron microscopy (SEM) and ellipsometer. XPS study revealed that the films have NO₂ and NO₃ bonding structures when the films are deposited at temperatures higher than 673 K. After exposure to oxygen plasma, carbon in the film surface was etched selectively and this phenomenon was observed in all films. In contrast, the surface concentration of nitrogen was ket at constant values before and after oxygen plasma treatment. The NO₃ bonding state had dramatically increased after oxygen plasma treatment for films deposited at higher deposition temperatures. The film surfaces have been observed to change the function from hydrophobic to hydrophilic after oxygen plasma treatment.     

Formation of ZnO nanostructures in energy-controlled hollow-type magnetron RF plasma

In this study, we investigated how zinc, sputtered from a zinc target, reacts with oxygen on the substrate to form ZnO nanostructures when the discharge parameters, such as gas flow ratio and target bias voltage, are controlled in O₂/Ar plasma. The deposits were estimated by SEM and Raman spectroscopy. Under conditions of a Zn to Ar optical emission intensity ratio of 2/1, a target voltage of − 550 V, a total pressure of 40 Pa, a substrate temperature of 150 °C, an RF power of 50 W, and a deposition time of 30 min, many vertically aligned ZnO nanorods were observed to be deposited on the substrate. The diameter of the rods was typically 50 nm. It was found that the film morphology can be controlled by the sputtering rate of zinc varied by the target bias voltage and gas flow rate.     

Synthesis and characterization of W reinforced carbon coatings produced by Combined Magnetron Sputtering and Ion Implantation technique

W-containing carbon coatings were deposited on plain carbon steel and titanium substrates by Combined Magnetron Sputtering and Ion Implantation (CMSII) technique. A target made of fine grain graphite with cylindrical tungsten pins mounted in the area of maximum sputtering rate was used. High voltage pulses (− 30 kV, 20 μs, and 25 Hz) were superposed over the DC bias. By adjusting the processing parameters nanocomposite nc-WC_1 − x/a-C coatings with a W content from 20 to 45 at.%, with a hardness of 12-22 GPa and a friction coefficient in the range of 0.12-0.22 were produced. These coatings have a thickness of 10-13 μm, good wear resistance and a good thermal stability up to 673 K.     

Carbide formation in tungsten-containing amorphous carbon films by annealing

Tungsten-containing amorphous carbon films were produced by dual magnetron sputter deposition. The formation of carbide phases after heat treatment in inert gas at temperatures up to 2800 K was investigated by X-ray diffraction for tungsten concentrations below 25 at.%. After deposition, each film consists of an amorphous carbon matrix with atomically dispersed W inclusions. Annealing up to 2800 K leads to a formation of carbide phases and to nano clustering. Three tungsten carbide phases were observed (WC, W₂C, and WC_1 − x), mostly as mixtures of two phases. The phase combination depends on annealing temperature and W concentration. Additionally, nano diffraction was performed in a scanning transmission electron microscope, to determine the phase of single crystallites at scales, where X-ray diffraction fails.     

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride coatings

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride (CN_x) coatings are investigated. CN_x coatings are fabricated by a hybrid coating process with the combination of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and DC magnetron sputtering at various substrate bias voltage and target sputtering power in the order of −400 V 200 W, −400 V 100 W, −800 V 200 W, and −800 V 100 W. The deposition rate, N/C atomic ratio, and hardness of CN_x coatings as well as friction coefficient of CN_x coating sliding against AISI 52100 pin in N₂ gas stream decrease, while the residual stress of CN_x coatings increases with the increase of substrate bias voltage and the decrease of target sputtering power. The highest hardness measured under single stiffness mode of 15.0 GPa and lowest residual stress of 3.7 GPa of CN_x coatings are obtained at −400 V 200 W, whereas the lowest friction coefficient of 0.12 of CN_x coatings is achieved at −800 V 100 W. Raman and XPS analysis suggest that sp³ carbon bonding decreases and sp² carbon bonding increases with the variations in substrate bias voltage and target sputtering power. Optical images and Raman characterization of worn surfaces confirm that the friction behavior of CN_x coatings is controlled by the directly sliding between CN_x coating and steel pin. Therefore, the reduction of friction coefficient is attributed to the decrease of sp³ carbon bonding in the CN_x coating. It is concluded that substrate bias voltage and target sputtering power are effective parameters for tailoring the structural and tribological properties of CN_x coatings.     

Effect of the radio-frequency power on the dielectric properties of hydrogen-containing boron carbon nitride films deposited by plasma-assisted chemical vapor deposition using tris(dimethylamino)boron gas

We investigated the properties of boron carbon nitride film containing hydrogen (BCNH film) deposited using tris(dimethylamino)boron as the source gas. The dielectric constant (k) of BCNH film decreases with decreasing radio-frequency plasma power used for deposition, and can be as low as 1.8 at 10 W. Thermal desorption spectroscopy analysis shows that the film contains a large amount of hydrogen. Fourier transform infrared spectroscopy shows an absorption band at 2960 cm−1, attributed to the asymmetrical stretching mode of C-H in the methyl group. It is thought that increasing the number of C-H bonds, which have a low polarizability, can achieve a lower k value.     

Preparation of inorganic solid state thin film for electrochromic application

All oxide solid state ITO (indium tin oxide)/Li_yWO_3−x/Li_1−zMn₂O₄/ITO stacked structure was deposited on a silica glass substrate by pulsed laser deposition for its electrochromic application. The Li doped amorphous tungsten trioxide Li_yWO_3−x thin film prepared at room temperature and in oxygen pressure of 7 Pa got the color of blue due to the mixture valence state of tungsten. We found that the amorphous Li_1−zMn₂O₄ thin film was suitable for the electrochromic application in spite of the low ion conductivity along in-plane direction. The ITO electrode thin film deposited at room temperature showed the relatively high transmittance and the usable conductivity. The transmittance at a wavelength of 750 nm for the ITO/Li_yWO_3−x/Li_1−zMn₂O₄/ITO stacked film changed from 50% to 80% by the applied voltage, while the transmittance at around 450 nm did not change. The blue-colored electrochromic property could be observed for the all oxide solid state film.     

Reflectance and photoluminescence spectra of as grown and hydrogen and nitrogen incorporated tetrahedral amorphous carbon films deposited using an S bend filtered cathodic vacuum arc process

The study of reflectance and photoluminescence (PL) spectra of as grown and also hydrogen and nitrogen incorporated tetrahedral amorphous carbon (ta-C) films, deposited using an S bend filtered cathodic vacuum arc process is reported here. First the effect of negative substrate bias on the properties of as grown ta-C films and next the effect of varying hydrogen and nitrogen partial pressure at a high substrate bias of − 300 V on the properties of hydrogen and nitrogen incorporated ta-C (ta-C:H and ta-C:N) films are reported for the first time. The values of the optical band gap (E_g) evaluated using the reflectance spectra were found to decrease with the increase of the substrate bias in the as grown ta-C films. Hydrogen incorporation up to 1.9 × 10^− 2 Pa partial pressure in as grown ta-C films increased the values of E_g and beyond which the values of E_g decreased while the nitrogen incorporation up to 3.0 × 10^− 1 Pa partial pressure has no effect on the E_g values. The PL spectra indicated a strong peak at ∼2.66 eV in as grown ta-C films deposited at − 20 V substrate bias. This main peak was found to shift to higher energy with the increase of the substrate bias up to − 200 V and thereafter the PL peak shifted towards the lower energy. Other peak at 3.135 eV starts appearing and this is found to start shifting to higher energy for films deposited at higher substrate bias. The intensity of the main PL peak was enhanced at low temperature and several other peaks started appearing in place of the broad peak at ∼3.16 eV. The peak width and area of both the main peak were found to decrease with the increase of substrate bias in as grown ta-C films and with the increase of the hydrogen and nitrogen partial pressure used in depositing ta-C:H and ta-C:N films. The current models on the source of luminescence in amorphous carbon have been discussed.     

Residual stress on nanocrystalline silicon thin films deposited under energetic ion bombardment by using internal ICP-CVD

Nano/microcrystalline silicon thin films were deposited using an internal-type, inductively coupled, plasma-chemical vapor deposition (ICP-CVD) at room temperature by varying the bias power to the substrate. The structural characteristics of the deposited thin film were investigated. The deposition rate was increased by the application of a small RF bias power of 30 W (12.56 MHz), but was then decreased as the bias power was increased above 30 W. In addition, the application of bias power generally increased the residual compressive stress, which was attributed to the increased defect formation in the thin film due to the formation of interstitial atoms. The crystalline volume fraction was also decreased with increasing bias power. However, in the low bias power range of 0-60 W, the compressive stress in the deposited thin film was in the range of − 34 to − 77 MPa, which was lower than the residual stress in the range of − 150 to − 1050 MPa that is observed for the nano/microcrystalline silicon thin films deposited by capacitively coupled plasma.     

Chemical vapor deposition of phase-rich WC thin films on silicon and carbon substrates

Chemical vapor deposition was used to deposit tungsten carbide from a mixture of WCl₆, H₂ and C₃H₈ at 750-1050 °C on silicon and carbon substrates. The phase composition of the films was correlated with substrate temperature, substrate position in the reactor, and total flow rates. X-ray diffraction and X-ray photoelectron spectroscopy were employed to investigate the surface and bulk properties of the thin films. Thick, adherent films of phase-rich hexagonal WC were deposited using 1.3 × 10³ Pa total pressure, 1050 °C substrate temperature, and reactant flow rates of H₂/C₃H₈/Ar/WCl₆ = 1.8 × 10^− 2/3.6 × 10^− 3/8.9 × 10^− 4/1.8 × 10^− 4 mol/min, where Ar is the carrier gas. The surface composition was oxygen and carbon rich as compared with the bulk.     

Properties of indium tin oxide thin films prepared on the oxygen plasma-treated polycarbonate substrate

We prepared the indium tin oxide thin (ITO) film on the polymer substrate by using facing target sputtering method. To obtain a smooth surface of the ITO thin film for application of OLEDs, before deposition of the ITO thin film, the polymer substrate was given plasma surface treatment. The electrical and surface properties were measured by a Hall Effect measurement and a contact angle measurement. The structural and optical properties were evaluated by an X-ray diffractometer, an atomic force microscope and a UV/VIS spectrometer, respectively. All ITO thin films deposited on plasma-treated polymer substrate showed an average transmittance over 85% in visible range, and the lowest resistivity was 4.17 × 10^− 4 Ω cm.     

Direct ion beam deposited carbon films and clusters

Carbon films and clusters have been formed by direct ion beam deposition. In all experiments crystalline n-Si 〈1 0 0〉 wafers with the 300 nm thermal SiO₂ film have been used as substrates. Effects of thermally microstructured Ni and substrate temperature were studied. Chemical structure of the carbon films was investigated using Raman spectroscopy. Surface morphology was studied by atomic force microscopy (AFM). Supplemental research on sheet resistance of the films has been performed. Rough diamond-like carbon film was grown onto the catalytic layer at 400 K temperature, and surface of the diamond-like carbon film deposited directly onto the SiO₂ layer at 400 K temperature was very smooth. At 750 K growth of the array of cylindrically shaped clusters was observed by AFM in the case of catalytically assisted deposition. Raman spectra of deposited films were typical for glassy carbon and/or carbon nanotubes with the carbonaceous deposits. Catalyticless deposition at 750 K temperature resulted in the formation of the conductive polymer-like carbon film with the graphite clusters in it.     

High-rate deposition of Ta-doped SnO2 films by reactive magnetron sputtering using a Sn-Ta metal-sintered target

Ta-doped SnO₂ films were deposited on glass substrate (either unheated or heated at 200 °C) by reactive magnetron sputtering with a Sn-Ta metal-sintered target using a plasma control unit (PCU) and mid-frequency (mf, 50 kHz) unipolar pulsing. The PCU feedback system precisely controlled the flow of the reactive and sputtering gases (O₂ and Ar, respectively) by monitoring either discharge impedance or the plasma emission of the atomic O* line at 777 nm. The planar target was connected to the switching unit, which was operated in unipolar pulse mode. Power density on the target was maintained at 4.4 W cm^− 2 during deposition. The lowest obtained resistivity for the films deposited on heated substrate was 6.4 × 10^− 3 Ωcm, where the deposition rate was 250 nm min^− 1.     

Effect of bias voltage on microstructure, mechanical and wear properties of Al-Si-N coatings deposited by cathodic arc evaporation

Al-Si-N coatings were deposited on tungsten carbide (WC-Co) and silicon wafer substrates using Cr and AlSi (12 at.% Si) alloy targets using a dual cathode source with short straight-duct filter in the cathode arc evaporation system. Al-Si-N coatings were synthesized under a constant flow of nitrogen, using various substrate bias voltages at a fixed AlSi cathode power. To enhance adhesive strength, the Cr/(Cr_xAl_ySi_z)N graduated layer between the top coating and the substrate was deposited as a buffer interlayer. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al-Si-N films were investigated. Experimental results reveal that the Al-Si-N coatings exhibited a nanocomposite structure of nano-crystalline h-AlN, amorphous Si₃N₄ and a small amount of free Si and oxides. It was also observed that the deposition rate of as-deposited films gradually decreased from about 25.1 to 18.8 nm/min when the substrate bias was changed from − 30 to − 150 V. The XRD results revealed that h-AlN preferred orientation changed from (002) to (100) as the bias voltage increased. The maximum hardness of approximately 35 GPa was obtained at the bias voltage of −90 V. Moreover, the grain size was inversely proportional to the hardness of the film. Wear test results reveal that the Al-Si-N film had a lower coefficient of friction, between 0.5 and 0.7, than that 0.7 of the AlN film.     

High-rate deposition of high-quality Sn-doped In2O3 films by reactive magnetron sputtering using alloy targets

Sn-doped In₂O₃ (ITO) films were deposited on heated (200 °C) fused silica glass substrates by reactive DC sputtering with mid-frequency pulsing (50 kHz) and a plasma control unit combined with a feedback system of the optical emission intensity for the atomic O* line at 777 nm. A planar In-Sn alloy target was connected to the switching unit, which was operated in the unipolar pulse mode. The power density on the target was maintained at 4.4 W cm^− 2 during deposition. The feedback system precisely controlled the oxidation of the target surface in “the transition region.” The ITO film with lowest resistivity (3.1 × 10^− 4 Ω cm) was obtained with a deposition rate of 310 nm min^− 1 and transmittance in the visible region of approximately 80%. The deposition rate was about 6 times higher than that of ITO films deposited by conventional sputtering using an oxide target.     

Nanostructured tungsten and tungsten trioxide films prepared by glancing angle deposition

Nanostructured tungsten (W) and tungsten trioxide (WO₃) films were prepared by glancing angle deposition using pulsed direct current magnetron sputtering at room temperature with continuous substrate rotation. The chemical compositions of the nanostructured films were characterized by X-ray photoelectron spectroscopy, and the film structures and morphologies were investigated using X-ray diffraction and high resolution scanning electron microscopy. Both as-deposited and air annealed tungsten trioxide films exhibit nanostructured morphologies with an extremely high surface area, which may potentially increase the sensitivity of chemiresistive WO₃ gas sensors. Metallic W nanorods formed by sputtering in a pure Ar plasma at room temperature crystallized into a predominantly simple cubic β-phase with <100> texture although evidence was found for other random grain orientations near the film/substrate interface. Subsequent annealing at 500 °C in air transformed the nanorods into polycrystalline triclinic/monoclinic WO₃ structure and the nanorod morphology was retained. Substoichiometric WO₃ films grown in an Ar/O₂ plasma at room temperature had an amorphous structure and also exhibited nanorod morphology. Post-deposition annealing at 500 °C in air induced crystallization to a polycrystalline triclinic/monoclinic WO₃ phase and also caused a morphological change from nanorods into a nanoporous network.     

Preparation and characterization of La0.9Sr0.1Ga0.8Mg0.2O3−δ thin film electrolyte deposited by RF magnetron sputtering on the porous anode support for IT-SOFC

Thin films of solid electrolyte La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) were deposited by RF magnetron sputtering onto porous La_0.7Sr_0.3Cr_0.5Mn_0.5O_3−δ (LSCM) anode substrates. The effects of substrate temperature, sputtering power density and sputtering Ar gas pressure on the LSGM thin film density, flatness and morphology were systematically investigated. RF sputtering power density of 7.8 W cm⁻², substrate temperature of 300 °C and sputtering Ar gas pressure of 5 Pa are identified as the best technical parameters. In addition, a three-electrode half cell configuration was selected to investigate the electrochemical performance of the thin film. The LSGM film deposited at optimum conditions exhibited a lower area specific ohmic resistance of 0.68 Ω cm⁻² at 800 °C, showing that the practicability of RF magnetron sputtering method to fabricate LSGM electrolyte thin film on porous LSCM anode substrates.     

Tungsten-doped ZnO transparent conducting films deposited by direct current magnetron sputtering

Highly conducting and transparent thin films of tungsten-doped ZnO (ZnO:W) were prepared on glass substrates by direct current (DC) magnetron sputtering at low temperature. The effect of film thickness on the structural, electrical and optical properties of ZnO:W films was investigated. All the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity first decreases with film thickness, and then increases with further increase in film thickness. The lowest resistivity achieved was 6.97 × 10⁻⁴ Ω cm for a thickness of 332 nm with a Hall mobility of 6.7 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.35 × 10²¹ cm⁻³. However, the average transmittance of the films does not change much with an increase in film thickness, and all the deposited films show a high transmittance of approximately 90% in the visible range.     

Nanocrystalline diamond film as cathode for gas discharge sensors

Nanocrystalline diamond (NCD) film was deposited on a silicon substrate utilizing microwave plasma-enhanced chemical vapor deposition in a mixed flow of methane, hydrogen and argon. The deposited film had a cauliflower-like morphology, and was composed of NCD, carbon clusters and mixed sp²- and sp³-bonded carbon. Electron field emission (EFE) in vacuum and electrical discharges in Ar, N₂ and O₂ using the NCD film as the cathode were characterized. The turn-on field for EFE and the geometric enhancement factor for the NCD film were 8.5 V/μm and 668, respectively. The breakdown voltages for Ar, N₂ and O₂ increased with pressures from 1.33 × 10⁴ Pa to 1.01 × 10⁵ Pa, following the right side of the normal Paschen curve.     

Ion beam deposition of α-Ta films by nitrogen addition and improvement of diffusion barrier property

Ta thin films were deposited on Si (100) substrates by an ion beam deposition method at various substrate bias voltages under Ar + N₂ atmosphere with different pressure ratios of Ar and N₂. The effects of nitrogen pressure in the plasma gas and the substrate bias voltage on the surface morphology, crystalline microstructure, electrical resistivity and diffusion barrier property were investigated. It was found that the fraction of a metastable β-phase in the Ta film deposited at the substrate bias voltage of − 50 V films decreased by adding nitrogen gas, while the α-Ta phase became dominant. As a result, the Ta films deposited at the substrate bias voltage of − 50 V under Ar (9 Pa) + N₂ (3 Pa) atmosphere showed a dominant α-phase with good surface morphology, low resistivity, and superior thermal stability as a diffusion barrier.