Properties of DLC films deposited by an oxyacetylene flame

Diamond-like carbon (DLC) films were obtained by spinning a tungsten carbide substrate at a high speed using an oxyacetylene flame. The films deposited at a typical experimental condition of substrate temperature of 810°C, rotation of 600 rpm and 3 h deposition time, exhibited an uniform, very smooth, hard and glassy surface covering the entire exposed face of the substrate. These films were identified as DLC by their characteristic broad Raman spectra centered at 1554 cm⁻¹ and micro-Vicker's hardness >3400 kg mm⁻². For substrate temperatures <800°C the film started losing the uniform glassy surface and the hardness deteriorated. For temperatures >950°C the film was still hard and shiny, but black in color. DLC films were also obtained in a wide range of speeds of rotation (300–750 rpm), as long as the temperature remained close to 850°C.     

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.     

Silicon carbide films from polycarbosilane and their usage as buffer layers for diamond deposition

Thin films of polycarbosilane (PCS) were coated on a Si (100) wafer and converted to silicon carbide (SiC) by pyrolyzing them between 800 and 1150 °C. Granular SiC films were derived between 900 and 1100 °C whereas smooth SiC films were developed at 800 and 1150 °C. Enhancement of diamond nucleation was exhibited on the Si (100) wafer with the smooth SiC layer generated at 1150 °C, and a nucleation density of 2 × 10¹¹ cm^− 2 was obtained. Nucleation density reduced to 3 × 10¹⁰ cm^− 2 when a bias voltage of − 100 V was applied on the SiC-coated Si substrate. A uniform diamond film with random orientations was deposited to the PCS-derived SiC layer. Selective growth of diamond film on top of the SiC buffer layer was demonstrated.     

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

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

Changes in chemical bonding of diamond-like carbon films by atomic-hydrogen exposure

We have deposited unhydrogenated diamond-like carbon (DLC) films on Si substrate by pulsed laser deposition using KrF excimer laser, and investigated the effects of atomic-hydrogen exposure on the structure and chemical bonding of the DLC films by photoelectron spectroscopy (PES) using synchrotron radiation and Raman spectroscopy. The fraction of sp³ bonds at the film surface, as evaluated from C1s spectra, increased at a substrate temperature of 400 °C by atomic-hydrogen exposure, whereas the sp³ fraction decreased at 700 °C with increasing exposure time. It was found that the sp³ fraction was higher at the surfaces than the subsurfaces of the films exposed to atomic hydrogen at both the temperatures. The Raman spectrum of the film exposed to atomic hydrogen at 400 °C showed that the clustering of sp² carbon atoms progressed inside the film near the surface even at such a low temperature as 400 °C.     

Structural and electrical properties of Sr2NaNb4O13 thin film grown by electrophoretic method using nanosheets synthesized from K(Sr2Na)Nb4O13 compound

Sr₂NaNb₄O₁₃⁻ (SNNO⁻) nanosheets were exfoliated from the K(Sr₂Na)Nb₄O₁₃ compound that was synthesized at 1200 °C. The SNNO⁻ nanosheets were deposited on a Pt/Ti/SiO₂/Si substrate at room temperature by the electrophoretic method. Annealing was conducted at various temperatures to remove organic defects in the SNNO film. A crystalline SNNO phase without organic defects was formed in the film annealed at 500 °C. However, a SrNb₂O₆ secondary phase was formed in the films annealed above 600 °C, probably due to the evaporation of Na₂O. The SNNO thin film annealed at 500 °C showed a dielectric constant of 74 at 1.0 MHz with a dielectric loss of 2.2%. This film also exhibited a low leakage current density of 9.0 × 10⁻⁸ A/cm² at 0.6 MV/cm with a high breakdown electric field of 0.72 MV/cm.     

Characterization of spray pyrolytically deposited high mobility praseodymium doped CdO thin films

Praseodymium (Pr) doped CdO thin films with high transparency and high mobility were deposited, using a homemade spray pyrolysis setup, on micro-slide glass substrates preheated at 300 °C. Polycrystalline nature and Cd-O bond vibration of deposited films were confirmed by X-ray diffraction, micro-Raman and Fourier transform infrared spectroscopy analyses. The oxidation state of Cd²⁺, O²⁻, and Pr³⁺ was confirmed by X-ray photoelectron spectroscopy analysis. The highest average particle size (92 nm-FESEM) and high RMS (13.48 nm-AFM) values are obtained for 0.50 wt% Pr doped CdO thin film. The optical band gap is varied between 2.38 eV and 2.52 eV, depending on the Pr doping concentration. Photoluminescence spectra revealed that Pr doped CdO thin film exhibits strong green emission at 582 nm. High mobility (82 cm²/V s), high charge carrier concentration (2.19×10²⁰ cm⁻³) and high transmittance (83%) were observed for 0.50 wt% Pr doped CdO film. A high figure of merit (9.79×10⁻³ Ω⁻¹) was obtained for 0.50 wt% Pr doped CdO thin films. The mechanism behind the above results is discussed in detail in this paper.     

The influence of ion beam assisted deposition parameters on the properties of boron nitride thin films

We studied ion beam assisted deposition of cubic boron nitride thin films on silicon (100) and high speed steel. The boron nitride films were grown by the electron beam evaporation of pure boron (99.4%) and the simultaneous ion bombardment of a mixture of nitrogen and argon ions from a Kaufman ion source. At a constant boron evaporation rate, the ion energy, ion current density, substrate temperature and process gas mixture was varied. The thickness of the films was kept between 200 and 300 nm. Boron nitride films with >80% of the cubic phase (determined by Fourier transform infrared spectroscopy) were obtained with nitrogen/argon mixtures of 50/50 at ion energies of 450 eV and substrate temperatures of 400°C. The current density amounted to 0.45 mA cm⁻² at a nominal boron rate of 200 pm s⁻¹. Cubic boron nitride films were deposited on high speed steel by introducing a titanium interlayer for adhesion improvement.     

Performance of spray deposited Gd-doped barium cerate thin films for proton conducting SOFCs

Doped barium cerate is a promising solid electrolyte for intermediate temperature fuel cells as a protonic conductor. In the present paper, the nanocrystalline Gd-doped barium cerate (BaCe_0.7Gd_0.1Y_0.2O_2.9) thin films have been successfully deposited on alumina substrate by spray pyrolysis technique. The films deposited from 0.1 M concentration and annealed at five different temperatures were characterized with different physio-chemical techniques. The BCGY is crystallized in orthorhombic perovskite structure with slight shift to the lower 2θ value compared with barium cerate (BC) and yttrium doped barium cerate (BCY). The grain growth and hence densification is also investigated by using SEM and AFM. The grain growth is almost complete at 1000 °C and the surface of the film appears to be smooth with typical roughness of 152 nm. Raman spectrum of BCGY film shows intense band at 463.8 cm⁻¹ compared to pure BC and BCY indicating the presence of more oxygen vacancies due to Gd doping. The proton conductivity of BCGY thin film in moist atmosphere is 1×10⁻³ Scm⁻¹.     

The effects of deposition temperature on structure and dielectric properties of Ba0.6Sr0.4TiO3 thin films produced by pulsed laser deposition

The effects of deposition temperature on orientation, surface morphology and dielectric properties of the thin films for Ba_0.6Sr_0.4TiO₃ thin films deposited on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition were investigated. X-ray diffraction patterns revealed a (2 1 0) preferred orientation for all the films. With rising substrate temperature from 650 °C to 700 °C, the crystallinity and crystal grain size of the films increase, the relative dielectric constant increases, but the dielectric losses have not obvious difference. The film deposited at 350 °C and annealed at 700 °C has strongly improved roughness and dielectric permittivity compared with the film only deposited directly at 700 °C. Three distinct relaxation processes within tan(δ) were found for the Ba_xSr_1?xTiO₃ film: a broadened process of the film relaxation, an intermediate peak which originates from Maxwell–Wagner–Sillars polarization, and an extremely slow process ascribed to leak current. The complex dielectric permittivity and loss can be fitted by an improved Cole–Cole model corresponding to a stretched relaxation function.     

Direct preparation of silver nanoparticles and thin films in CO2-expanded hexane

Small, uniform and suspended silver nanoparticles were directly prepared in CO₂-expanded hexane by reducing a synthesized metal precursor, silver isostearate, with hydrogen but without introducing additional capping agents. By increasing CO₂ pressure, the suspended silver nanoparticles could be further deposited on a solid substrate to form silver thin film via gas antisolvent and the subsequent supercritical drying processes. The silver thin films prepared by the aforementioned method possessed a uniform thickness of about 150 nm without surface cracking and low electrical resistivity (5.64 × 10⁻⁶ Ω cm) after applying an annealing process. Due to the deposition of nano-sized silver particles, the annealing temperature could be as low as 175 °C that is lower than the softening points of many transparent polymeric substrates used for fabrication of flexible conductive films.     

Schottky barrier effect of ZnO modified methyl glycol thin films for detection of hydrogen sulfide gas

Highly nanocrystalline ZnO modified methyl glycol thin films have been deposited on a p-type silicon substrate via the sol–gel spin coating manner. The morphology of the as-deposited film was scrutinized using scanning electron microscopy. I–V characteristics of the as-prepared ZnO film under vacuum and in open air were monitored. The results showed that the ZnO films have a barrier height of 0.38 eV under vacuum and 0.62 eV in open air. The Schottky barrier height between ZnO grains was determined for different reducing gases. The ZnO film showed high sensitivity to H₂S gas compared with other reducing gases due to the reduction of barrier height between ZnO grains. The as-prepared ZnO film was annealed at four different temperatures. X-ray diffraction manifested that the wurtzite hexagonal structure of ZnO deviated from ideality at annealing temperature greater than 650 °C. The barrier height of ZnO film decreased due to the increase of annealing temperature up to 650 °C and then decreased. The results also confirmed that the change of barrier height strongly affected the sensitivity of ZnO film.     

Electrical and optical properties of diamond-like carbon films deposited by pulsed laser ablation

Pulsed laser ablation of a graphite target was carried out by ArF excimer laser deposition at a laser wavelength of 193 nm and fluences of 10 and 20 J/cm² to produce diamond-like carbon (DLC) films. DLC films were deposited on silicon and quartz substrates under 1 × 10^? 6 Torr pressure at different temperatures from room temperature to 250 °C. The effect of temperature on the electrical and optical properties of the DLC films was studied. Laser Raman Spectroscopy (LRS) showed that the DLC band showed a slight increase to higher frequency with increasing film deposition temperature. Spectroscopic ellipsometry (SE) and ultraviolet–visible absorption spectroscopy showed that the optical band gap of the DLC films was 0.8–2 eV and decreased with increasing substrate temperature. These results were consistent with the electrical resistivity results, which gave values for the films in the range 1.0 × 10⁴–2.8 × 10⁵ Ω cm and which also decreased with deposition temperature. We conclude that at higher substrate deposition temperatures, DLC films show increasing graphitic characteristics yielding lower electrical resistivity and a smaller optical band gap.     

Electrical properties of a-C: Mo films produced by dual-cathode filtered cathodic arc plasma deposition

Molybdenum-containing amorphous carbon (a-C:Mo) thin films were prepared using a dual-cathode filtered cathodic arc plasma source with a molybdenum and a carbon (graphite) cathode. The Mo content in the films was controlled by varying the deposition pulse ratio of Mo and C. Film sheet resistance was measured in situ at process temperature, which was close to room temperature, as well as ex situ as a function of temperature (300–515 K) in ambient air. Film resistivity and electrical activation energy were derived for different Mo and C ratios and substrate bias. Film thickness was in the range 8–28 nm. Film resistivity varied from 3.55 × 10^− 4 Ω m to 2.27 × 10^− 6 Ω m when the Mo/C pulse ratio was increased from 0.05 to 0.4, with no substrate bias applied. With carbon-selective bias, the film resistivity was in the range of 4.59 × 10^− 2 and 4.05 Ω m at a Mo/C pulse ratio of 0.05. The electrical activation energy decreased from 3.80 × 10^− 2 to 3.36 × 10^− 4 eV when the Mo/C pulse ratio was increased in the absence of bias, and from 0.19 to 0.14 eV for carbon-selective bias conditions. The resistivity of the film shifts systematically with the amounts of Mo and upon application of substrate bias voltage. The intensity ratio of the Raman D-peak and G-peak (I_D/I_G) correlated with the pre-exponential factor (σ₀) which included charge carrier density and density of states.     

Effect of annealing temperature on structural and optoelectronic properties of γ-CuI thin films prepared by the thermal evaporation method

High quality transparent conducting CuI thin films were deposited at room temperature via thermal evaporation technique followed by post deposition annealing at different temperatures. The samples were characterised by X-ray diffraction (XRD), UV–Vis spectrophotometry, Scanning electron microscopy and I-V measurements. The structural, morphological and optical properties were studied as a function of the annealing temperature from room temperature (RT) to 200 °C. XRD results revealed that the films were polycrystalline with zinc blende structure of cubic phase. Increasing the annealing temperature increased the crystallite size from 33 to 49 nm whilst the dislocation density and lattice strain shifted to lower values. High transmittance of about 70–80% was exhibited by all films in the entire visible spectral range. The as deposited film possesed the lowest resistivity of 3.0×10⁻³ Ω cm.     

Effect of substrate temperature on structural and electrical properties of BaZr0.2Ti0.8O3 lead-free thin films by pulsed laser deposition

Barium zirconate titanate (BaZr_0.2Ti_0.8O₃, BZT) 250 nm thick thin films were fabricated by pulsed laser deposition and the influence of the substrate temperature on their preferred orientation, microstructure, morphology and dielectric properties was investigated. Dielectric measurements indicated the (1 1 0)-oriented BZT thin films deposited at 750 °C to show good dielectric properties with high dielectric constant (~500 at 100 kHz), low loss tangent (<0.01 at 100 kHz), and superior tunability (>70% at 400 kV/cm), while the largest figure of merit was 78.8. The possible microstructural background responsible for the high dielectric constant and tenability is discussed. In addition, thin films deposited at 750 °C with device quality factor of 8738 and dielectric nonlinearity coefficient of 1.66×10⁻¹⁰ J/C⁴m⁵ were demonstrated.     

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

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

Fabrication of apatite-type lanthanum silicate films and anode supported solid oxide fuel cells using nano-sized printable paste

Apatite-type lanthanum silicate based films have attracted significant interests to use as an electrolyte of solid oxide fuel cells (SOFCs) working at intermediate temperature. We have prepared Mg doped lanthanum silicate (MDLS) films on NiO–MDLS cermet substrates by spin coating and sintering of nano-sized printable paste made by beads milling. Changes in crystal structure and microstructure of the paste films with the sintering temperature have been investigated to show that porous network structure with a grain growth evolves up to 1300 °C, whereas densification occurred above 1400 °C. Anode supported SOFCs using the pasted MDLS films were successfully fabricated: an open circuit voltage of 0.91 V and a maximum power density of 150 mW cm⁻² measured at 800 °C were obtained with the electrolyte film sintered at 1500 °C.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

Anode-supported SOFCs based on Sm0.2Ce0.8O2−δ electrolyte thin-films fabricated by co-pressing using microwave combustion synthesized powders

Decreasing the electrolyte thickness is an effective approach to improve solid oxide fuel cells (SOFCs) performance for intermediate-temperature applications. Sm_0.2Ce_0.8O_2−δ (SDC) powders with low apparent density of 32±0.3 mg cm⁻³ are synthesized by microwave combustion method, and SDC electrolyte films as thin as ~10 μm are fabricated by co-pressing the powders onto a porous NiO–SDC anode substrate. Dense SDC electrolyte thin films with grain size of 300–800 nm are achieved at a low co-firing temperature of 1200 °C. Single cells based on SDC thin films show peak power densities of 0.86 W cm⁻² at 650 °C using 3 vol% humidified H₂ as fuel and ambient air as oxidant. Both the thin thickness of electrolyte films and ultra-fine grained anode structure make contributions to the improved cell performance.