Studies of physical and chemical properties of styrene-based plasma polymer films deposited by radiofrequency Ar/styrene glow discharge

Styrene-based plasma polymer (SPP) films having thickness in the range of 900–1800 nm are deposited from radiofrequency (RF) Ar/styrene glow discharge. Depositions of the SPP films are carried out at working pressure of 1.2 × 10^?1 mbar and in the RF power range of 40–130 W. The physical and chemical properties of the SPP films are investigated as a function of RF power. Optical emission spectroscopy (OES) studies on Ar/styrene glow discharge reveal that the relative concentrations of active plasma species are strongly dependent on the variation of RF power. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) are used to analyze the internal chemical structures of the films. It is revealed that the SPP film with highest carbon content exhibits enhanced scratch and corrosion resistance behavior along with stable thermal properties. The thermogravimetric (TGA) and gel permeation chromatography (GPC) results suggest the presence of both aliphatic and aromatic units in the SPP films. Attempts are made to correlate the results obtained from OES, FT-IR and XPS analyses with the deposited films properties. The possibility of using SPP films as protective coatings is also explored.     

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.     

Preparation,characterization and properties of Cr-incorporated DLC films on magnesium alloy

Cr-incorporated diamond-like carbon (Cr-DLC) films were deposited on AZ31 magnesium alloy as protective coatings by a hybrid beams deposition system, which consists of a DC magnetron sputtering of Cr target (99.99%) and a linear ion source (LIS) supplied with CH₄ precursor gas. The Cr concentration (from 2.34 to 31.5 at.%) in the films was controlled by varying the flow ratio of Ar/CH₄. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the microstructure and composition of Cr-DLC films systematically. An electrochemical system and a ball-on-disk tribotester were applied to test the corrosion and tribological properties of the film on the AZ31 substrate, respectively. At low Cr doping (2.34 at.%), the film mainly exhibited the feature of amorphous carbon, while at high doping (31.5 at.%), chromium carbide crystalline phase occurred in the amorphous carbon matrix of the film. In this study, all the prepared Cr-DLC films showed higher adhesion to AZ31 than the DLC film. Especially for the film with low Cr doping (2.34 at.%), it owned the lowest internal stress and the highest adhesion to substrate among all the films. Furthermore, this film could also improve the wear resistance of magnesium alloy effectively. But, none of the films could improve the corrosion resistance of the magnesium alloy in 3.5 wt.% NaCl solution due to the existence of through-thickness defects in the films.     

Zinc oxide thin films prepared by thermal evaporation deposition and its photocatalytic activity

Thin zinc oxide (ZnO) films have been grown on silicon substrates by thermal physical vapor deposition approach. X-ray diffraction (XRD) analyses reveal that the deposited films are polycrystalline ZnO phase. Atomic force microscopy images (AFM) show needle-like shape highly oriented ZnO crystals. Thin film thickness ranges from 10 to 80 nm. X-ray photoelectron spectroscopy (XPS) results declare that the films compose mainly of Zn and O. Nevertheless, Si is not detected in the films and consequently no possibility of any silicide formation as is confirmed by XRD analysis. Photocatalytic decomposition of azo-reactive dye on ZnO films is tested. The results show that the dye decomposition efficiency increases with decreasing pH. Maximum photodecomposition, 99.6% is obtained at pH 2 with 10 mg/l dye concentration.     

UV photodetection properties of pulsed laser deposited Cu-doped ZnO thin film

Nanocrystalline undoped and 2 at% copper (Cu) doped zinc oxide (ZnO) thin films were successfully grown onto SiO₂/n-Si substrates at 600 °C by using pulsed laser deposition (PLD) technique. The influence of Cu incorporation on structural, surface morphological, elemental composition and UV detection properties of ZnO film was investigated. X-ray diffraction studies of thin films show that they are polycrystalline and have a hexagonal wurtzite structure; however, Cu doping improves the preferential orientation along c-axis. The chemical state of constituent elements was analysed by X-ray photoelectron spectroscopy (XPS). It indicates the presence of Cu ions in the doped film that exist in a mixed univalent and bivalent state. FE-SEM observations support the crystallographic results. The effective incorporation of Cu ions into the lattice of the ZnO nanostructure without changing its wurtzite structure was confirmed by an energy dispersive X-ray spectroscopic analysis (EDX). The UV photodetection characteristics of both films were further studied in metal-semiconductor-metal (MSM) planar configurations at room temperature and are found to be greatly influenced by Cu doping. The incorporation of Cu into ZnO lattice increases the resistivity of thin film; which leads to lower dark current. As a result, the Cu-doped ZnO film based UV PD demonstrates improved UV sensitivity of about 66.92 upon 2 mW/cm² UV illumination at 365 nm peak wavelengths and 5 V applied bias. The reproducible UV detection performance of MSM devices was also ensured by periodically switching UV light on and off at fixed time intervals.     

Preparation of tetrahedral amorphous carbon films by filtered cathodic vacuum arc deposition

Tetrahedrally bonded amorphous carbon (ta-C) and nitrogen doped (ta-C:N) films were obtained at room temperature in a filtered cathodic vacuum arc (FCVA) system incorporating an off-plane double bend (S-bend) magnetic filter. The influence of the negative bias voltage applied to substrates (from −20 to −350 V) and the nitrogen background pressure (up to 10⁻³ Torr) on film properties was studied by scanning electron microscopy (SEM), electron energy loss spectroscopy (EELS), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray reflectivity (XRR). The ta-C films showed sp³ fractions between 84% and 88%, and mass densities around 3.2 g/cm³ in the wide range of bias voltage studied. In contrast, the compressive stress showed a maximum value of 11 GPa for bias voltages around −90 V, whereas for lower and higher bias voltages the stress decreased to 6 GPa. As for the ta-C:N films grown at bias voltages below −200 V and with N contents up to 7%, it has been found that the N atoms were preferentially sp³ bonded to the carbon network with a reduction in stress below 8 GPa. Further increase in bias voltage or N content increased the sp² fraction, leading to a reduction in film density to 2.7 g/cm³.     

Photoelectrochemical properties of Ni-doped Fe2O3 thin films prepared by electrodeposition

Ni-doped Fe₂O₃ thin films which were active photoanodes for water splitting were prepared by electrodeposition. By adjusting Ni molar ratios (Ni/(Ni + Fe)) in the electrolyte, Fe₂O₃ thin films with various compositions of Ni could be tuned. The films were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic absorption spectrophotometer, and UV–vis spectroscopy. The highest photo-response obtained from Fe₂O₃ doped with 2.08 mol.% Ni is 1.5 mA/cm² at 0.65 V vs. Ag/AgCl in 1.0 M NaOH solution. The high performance is attributed to the improvement of charge transport properties and retardation of the charge recombination resulting from the dopants in the lattice. The optical absorption spectra of the films reveal that the bandgaps of the Ni-doped Fe₂O₃ films are approximately 1.9–2.2 eV for all samples regardless of their doping level. XPS shows that the concentration of Ni is much higher on the surface than that in bulk.     

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.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

Three-dimensional MnO/reduced graphite oxide composite films as anode materials for high performance lithium-ion batteries

MnO/reduced graphite oxide (MnO/RGO) composite films with three dimensionally porous structures have been synthesized by an improved electrostatic spray deposition setup and their microstructure and electrochemical properties have been characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric, Raman spectrometry and galvanostatic cell cycling. The results show that the structure and electrochemical performance of the electrode film are influenced significantly by the RGO content. The three dimensionally porous structure collapse does not occur in the MnO/RGO thin films for a RGO content lower than 16.58 wt%, the 16.58 wt% reduced graphite oxide content being optimal. Such an improvement in the cycling performance (772 mAh g⁻¹ after 100 cycles at 1 C) and rate capability (425 mAh g⁻¹ at 6 C) might be attributed to the excellent microstructure and electrical conductivity of MnO/reduced graphite oxide composite film electrodes.     

Preparation and oxidation of composite TiN–AlN films from alkoxide solutions by plasma-enhanced CVD

Composite and compositionally graded (CGed) TiN–AlN films were deposited on Si wafers at 600 °C from Ti- and Al-alkoxide solutions by N₂ plasma-enhanced chemical vapor deposition (CVD). The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Vickers micro-hardness. In the composite TiN–AlN films, the Ti and Al contents varied linearly and complementarily with solution composition, the N content ranging from 35 to 40 at.%. In the CGed films, the Al component decreased complementarily with increasing Ti toward the substrate. Cross-sectional SEM observation showed both films to be about 1 μm thick with a columnar structure. Oxidation of the composite and CGed films was performed at 500, 700, and 900 °C in air for 1 h. The improvement of oxidation resistance in both composite and CGed films is discussed on the basis of the XRD and SEM observations, and the XPS analysis of the oxidized films.     

Investigation of substrate bias effects on the reactively sputtered ZrN diffusion barrier films

ZrN diffusion barrier films were prepared by DC reactive magnetron sputtering under different negative substrate bias. The composition, microstructure, resistivity and diffusion barrier properties of ZrN films, with respect to substrate bias, were studied by means of X-ray diffraction, electron probe microanalyzer, Auger electron spectroscopy, and four point probe method. Results showed that the deposition rate and impurity oxygen content of ZrN films were substantially influenced by the resputtering effects due to the ion bombardment on the film surface. The competition between surface energy and strain energy made the preferred orientation of ZrN films change from (1 1 1) to (2 0 0) and then back to highly (1 1 1) preferred orientation as a function of substrate bias. The application of negative substrate bias could effectively decrease the electrical resistivity due to the decrease of impurity oxygen content and the densification of films, resulting from the moderate-energy ion irradiation. The biased ZrN films could successfully be used as a diffusion barrier layer, between Cu and SiO₂, even up to the high temperature of 800 °C for 30 min.     

Hydrogen incorporation,bonding and stability in nanocrystalline diamond films

The hydrogen concentration in hot filament and microwave plasma CVD nanocrystalline diamond films is analysed by secondary ion mass spectrometry and compared to the film grain size. The surface and bulk film carbon bonds are analysed respectively by X-ray photoelectron spectroscopy (XPS) and ultra-violet Raman spectroscopy. XPS results show the presence of the hydrogenated p-type surface conductive layer. The respective intensities of the 1332 cm^− 1 diamond peak, of the G and D bands related to sp² phases, and of the 3000 cm^− 1 CH_x stretching mode band, are compared on Raman spectra. The samples are submitted to thermal annealing under ultra-high vacuum in order to get hydrogen out-diffusion. XPS analysis shows the surface desorption of hydrogen. Thermal annealing modifies the sp² phase structure as hydrogen out diffuses.     

The role of nitrogen in the deposition of polycrystalline diamond films

The role of nitrogen in the formation of polycrystalline diamond films prepared using a microwave plasma CVD system has been studied using micro-Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Although the nitrogen concentration in the films was too low to be detected by XPS, the Raman spectrum was found to be significantly affected by the nitrogen flow ratio. The intensity of the Raman peak at 1480 cm⁻¹ significantly decreases, whereas that of 1190 cm⁻¹ peak remains almost unchanged in comparison with the 1350 and 1550 cm⁻¹ peaks with increasing nitrogen flow ratio. In contrast, the preferentially (111)-orientated growth and the growth rate were little influenced by the nitrogen flow ratio. These results indicate that nitrogen plays a special role in the formation and structure of the polycrystalline diamond films studied in this report.     

Low-temperature fabrication of sol–gel NiO film for optoelectronic devices based on the ‘fuel’ of urea

In this work, NiO coating is fabricated by a low temperature ‘combustion process’ driven by ‘chemical oven’ on quartz and indium tin oxide (ITO) substrates followed by an annealing process in air at 225 °C for 2 h. The NiO coating is analyzed by means of thermalgravimetric differential thermal analysis (TG-DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electric microscopy (SEM), atomic force microscope (AFM), and UV–visible spectrometer. A prelimilary photovoltaic performance measurement of the fabricated device (ITO/NiO/poly-TPD/PC₇₁BM/Al) shows a short circuit current density (J_sc) of 5.28 mA cm⁻² and power conversion efficiency (PCE) of 1.56% under an illumination of 100 mW cm⁻². The PCE of device with combustion NiO HTLs is almost 10-fold higher than those of the devices based on common NiO HTLs. The combustion fabricated NiO coating may provide an effective approach to fabricate other NiO-based optoelectrical devices at relative low temperature.     

Fully solution-processed metal oxide thin-film transistors via a low-temperature aqueous route

We report a facile and low-temperature aqueous route for the fabrication of various oxide thin films (Al₂O₃, In₂O₃ and InZnO). A detail study is carried out to reveal the formation and properties of these sol-gel-derived thin films. The results show that the water-based oxide thin films undergo the decomposition of nitrate group as well as conversion of metal hydroxides to form metal oxide framework. High quality oxide thin film could be achieved at low temperature by this aqueous route. Furthermore, these oxide thin films are integrated to form thin-film transistors (TFTs) and the electrical performance is systematically studied. In particular, we successfully demonstrate In₂O₃/Al₂O₃ TFTs with high mobility of 30.88 cm² V⁻¹ s⁻¹ and low operation voltage of 4 V at a maximum processing temperature of 250 °C.     

Effect of excess Bi2O3 on structures and dielectric properties of Bi1.5Zn1.0Nb1.5O7 thin films deposited at room temperature by RF magnetron sputtering

To compensate for bismuth loss that occurred during the film deposition process, Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were deposited at room temperature from the ceramic targets containing various excess amounts of bismuth (0–20 mol%) on Pt/TiO₂/SiO₂/Si substrates by using RF magnetron sputtering technique. The effect of bismuth excess content on the microstructure and electrical properties of BZN thin films was studied. The microstructure and chemical states of the thin films were studied by SEM and XPS. EPMA was employed to assess the film stoichiometry. The X-ray diffraction analysis reveals that the BZN thin films exhibit the amorphous structure in nature. An appropriate amount of excess bismuth improves the dielectric and electrical properties of BZN thin films, while too much excess bismuth leads to deterioration of the properties. BZN thin film with 5 mol% excess bismuth exhibits a dielectric constant of 61 with a loss of 0.4% at 10 kHz and leakage current of 7.26×10^?7 A/cm² at an electric field of 200 kV/cm.     

Effect of substrate temperature on microstructure and optical properties of nanocrystalline alumina thin films

Aluminum oxide (Al₂O₃) thin films were deposited on silicon (100) and quartz substrates by pulsed laser deposition (PLD) at an optimized oxygen partial pressure of 3.0×10^?3 mbar in the substrate temperatures range 300–973 K. The films were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy, spectroscopic ellipsometry, UV–visible spectroscopy and nanoindentation. The X-ray diffraction studies showed that the films deposited at low substrate temperatures (300–673 K) were amorphous Al₂O₃, whereas those deposited at higher temperatures (≥773 K) were polycrystalline cubic γ-Al₂O₃. The transmission electron microscopy studies of the film prepared at 673 K, showed diffuse ring pattern indicating the amorphous nature of Al₂O₃. The surface morphology of the films was examined by atomic force microscopy showing dense and uniform nanostructures with increased surface roughness from 0.3 to 2.3 nm with increasing substrate temperature. The optical studies were carried out by ellipsometry in the energy range 1.5–5.5 eV and revealed that the refractive index increased from 1.69 to 1.75 (λ=632.8 nm) with increasing substrate temperature. The UV–visible spectroscopy analysis indicated higher transmittance (>80%) for all the films. Nanoindentation studies revealed the hardness values of 20.8 and 24.7 GPa for the films prepared at 300 K and 973 K respectively.     

Low-cost preparation of a conductive and catalytic graphene film from chemical reduction with AlI3

AlI₃ synthesized by I₂ and Al in ethanol was used as reductive agent to directly obtain flexible reductive graphene oxide (RGO) films with high conductivity of 5320 S/m from graphene oxide (GO) films at a low temperature of 80 °C. This reductive method has provided a low-cost and effective route for large-scale production of graphene with high catalytic activity. Structural evolution during the reduction of GO was studied by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The RGO films served as counter electrode exhibited high electrochemical activity.     

Electrochromic Nb-doped WO3 films: Effects of post annealing

The Nb-doped WO₃ films were deposited by e-beam co-evaporation method using ceramic WO₃ targets and metal Nb slugs. The films were analyzed by glancing incident angle X-ray diffraction (GIAXRD), UV/visible spectrophotometer, electrochemical cyclic voltammetry, X-ray photoelectron spectroscopy (XPS). The as-prepared film is brown and amorphous in structure. The film has low transmission in optical visible region. The XPS results indicate that the as-deposited film is non-stoichiometric. By applying a negative potential, the as-deposited film does not show obvious electrochromic effect. However, the electrochromic properties of Nb-doped WO₃ films are improved by post annealing treatment at 350, 400, and 450 °C in oxygen atmosphere. The Nb-doped WO₃ films transform into crystalline structure and become transparent after post annealing treatment. The energy band gap, optical modulation, and color efficiency increase with annealing temperature.