Effect of temperature on pulsed laser deposition of HgCdTe films

HgCdTe thin films have been deposited on Si(1 1 1) substrates at different substrate temperatures by pulsed laser deposition (PLD). An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as laser source. The influences of the substrate temperature on the crystalline quality, surface morphology and composition of HgCdTe thin films were characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). The results show that in our experimental conditions, the HgCdTe thin films deposited at 200 °C have the best quality. When the substrate temperature is over 250 °C, the HgCdTe film becomes thermodynamically unstable and the quality of the film is degraded.     

Carbon nitride films by RF plasma assisted PLD: Spectroscopic and electronic analysis

Carbon nitride (CNx) thin films have been grown on Si 〈1 0 0〉 by 193 nm ArF ns pulsed laser ablation of a pure graphite target in a low pressure atmosphere of a RF generated N₂ plasma and compared with samples grown by PLD in pure nitrogen atmosphere. Composition, structure and bonding of the deposited materials have been evaluated by X-ray photoelectron spectroscopy (XPS), and Raman scattering. Significant chemical and micro-structural changes have been registered, associated to different nitrogen incorporation in the two types of films analyzed. The intensity of the reactive activated species is, indeed, increased by the presence of the bias confined RF plasma, as compared to the bare nitrogen atmosphere, thus resulting in a different nitrogen uptake in the growing films. The process has been also investigated by some preliminary optical emission studies of the carbon plume expanding in the nitrogen atmosphere. Optical emission spectroscopy reveals the presence of many excited species like C⁺ ions, C atoms, C₂, N₂; and CN radicals, and N₂⁺ molecular ions, whose relative intensity appears to be increased in the presence of the RF plasma. The films were also characterised for electrical properties by the “four-probe-test method” determining sheet resistivity and correlating surface conductivity with chemical composition.     

Structural, optical and morphological studies on laser ablated nanostructured WO3 thin films

Thin films of tungsten trioxide (WO₃) are prepared by reactive pulsed laser deposition (PLD) technique on glass substrates at three different substrate temperatures (T_s). The structural, morphological and optical properties of the deposited films are systematically studied using X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), micro-Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-VIS spectrophotometry techniques. X-ray diffraction analysis reveals that crystalline WO₃ films can grow effectively even at 300 K at an oxygen pressure of 0.12 mbar. All the films deposited at various T_s exhibit mixed oxide phase consisting of orthorhombic and triclinic phase of tungsten oxide with a preferred orientation along (0 0 1) lattice plane reflection. Micro-Raman results are consistent with X-ray diffraction findings. The SEM analysis shows that deposited films are porous and crystalline grains are of nano-metric dimension. The effect of T_s on mean surface roughness studied by AFM analysis reveals that mean surface roughness decreases with increase in T_s. The optical response of WO₃ layers measured using UV-VIS spectrophotometry is used to extract the optical constants such as refractive index (n), extinction coefficient (k) and optical band gap (E_g), following the method of Swanepoel.     

Structural and optical properties of amorphous hydrogenated silicon carbonitride films produced by PECVD

Amorphous hydrogenated silicon carbonitride thin films (a-Si:C:N:H), deposited by plasma enhanced chemical vapour deposition (PECVD) using hexamethyldisilazane (HMDSN) as monomer and Ar as feed gas, have been investigated for their structural and optical properties as a function of the deposition RF plasma power, in the range of 100-300 W. The films have been analysed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis-NIR spectrophotometry and atomic force microscopy (AFM). From the analysis of the FT-IR spectra it results that the films become more amorphous and inorganic as RF plasma power increases. The incorporation of oxygen in the deposited layers, mainly due to the atmospheric attack, has been evaluated by XPS and FT-IR spectroscopy. Reflectance/transmittance spectra, acquired in the range of 200-2500 nm, allow to descrive the film absorption edge for interband transitions. A relationship between the optical energy band gap, deduced from the absorption coefficient curve, and the deposition RF plasma power has been investigated. The reduction of the optical energy gap from 3.85 to 3.69 eV and the broadening of the optical absorption tail with RF plasma power increasing from 100 to 300 W are ascribed to the growth of structural disorder, while the increase of the refractive index, evaluated at 630 nm, is attributed to a slight densification of the film. The AFM analysis confirms the amorphous character of the films and shows how the deposited layers become rougher when RF plasma power increases. The wettability of the film has been studied and related to the chemical composition and to the morphology of the deposited layers.     

Microstructural, optical and spectroscopic studies of laser ablated nanostructured tantalum oxide thin films

Thin films of tantalum oxide (Ta₂O₅) have been prepared by pulsed laser deposition technique at different substrate temperatures (300-973 K) under vacuum and under oxygen background (pO₂ = 2 × 10⁻³ mbar) conditions. The films are annealed at a temperature of 1173 K. The as-deposited films are amorphous irrespective of the substrate temperature. XRD patterns show that on annealing, the films get crystallized in orthorhombic phase of tantalum pentoxide (β-Ta₂O₅). The annealed films deposited at substrate temperatures 300 K and 673 K have a preferred orientation along (0 0 1) plane, whereas the films deposited at substrate temperatures above 673 K show a preferred orientation along (2 0 0) crystal plane. The deposited films are characterized using techniques such as grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. FTIR and micro-Raman measurements confirm the presence of Ta-O, Ta-O-Ta and O-Ta-O bands in the films. Grain size calculations from X-ray diffraction and AFM show a decrease with increase in substrate temperature. The variation of transmittance and band gap with film growth parameters are also discussed.     

The characterization of fluorocarbon films on NiTi alloy by magnetron sputtering

Fluorocarbon films were deposited on nickel-titanium (NiTi) alloy substrate by radio-frequency (RF, 13.56 MHz) magnetron sputtering using a polytetrafluoroethylene (PTFE) target. The deposition parameters of fluorocarbon films including the RF power, the working gas pressure and Ar flow rate were systematically studied. The structure of the deposited films was studied by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The surface morphology of the deposited films was measured by atomic force microscopy (AFM). The mechanical properties of the deposited films were characterized by a nanoindenter. C-Fx and C-C units were found in the deposited fluorocarbon films, which corresponded to the results of XPS. The surface roughness of the fluorocarbon film was 7.418 nm (Ra).     

LiFePO4 thin films grown by pulsed laser deposition: Effect of the substrate on the film structure and morphology

Well crystallized and homogeneous LiFePO₄/C (LFPO) thin films have been grown by pulsed laser deposition (PLD). The targets were prepared by the sol-gel process at 600 °C. The structure of the polycrystalline powders was analyzed with X-ray powder diffraction (XRD) data. The XRD patterns were indexed having a single phase olivine structure (Pnma). LFPO thin films have been deposited on three different substrates: aluminum (Al), stainless steel (SS) and silicon (Si) by pulsed laser deposition (PLD). The structure of the films was analyzed by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). It is found that the crystallinity of the thin films depends on the substrate temperature which was set at 500 °C. When annealed treatments were used, secondary phases were found, so, one step depositions at 500 °C were made.Stainless steel is demonstrated to be the best choice to act as substrate for phosphate deposition. LiFePO₄ thin films grown on stainless steel plates exhibited the presence of carbon, inducing a slight conductivity enhancement that makes these films promising candidates as one step produced cathodes in Li-ion microbatteries.     

Surface morphology of thin lysozyme films produced by matrix-assisted pulsed laser evaporation (MAPLE)

Thin films of the protein, lysozyme, have been deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. Frozen targets of 0.3-1.0 wt.% lysozyme dissolved in ultrapure water were irradiated by laser light at 355 nm with a fluence of 2 J/cm². The surface quality of the thin lysozyme films of different thickness deposited on 7 mm × 7 mm Si-〈1 0 0〉-wafers was investigated with scanning electron microscopy and atomic force microscopy. Already at comparatively low thickness, ∼20 nm, the substrate is covered by intact lysozyme molecules and fragments. The concentration of lysozyme in the ice matrix apparently does not play any significant role for the morphology of the film. The morphology obtained with MAPLE has been compared with results for direct laser irradiation of a pressed lysozyme sample (i.e. pulsed laser deposition (PLD)).     

Structural investigations of TiO2:Tb thin films by X-ray diffraction and atomic force microscopy

In this work, structural investigations of TiO₂ thin films doped with Tb at the amount of 0.4, 2 and 2.6 at.% have been outlined. Thin films were deposited on Si and SiO₂ substrates by high energy reactive magnetron sputtering from mosaic Ti-Tb target. The influence of Tb dopant amount, post-annealing treatment and kind of applied substrate on microstructure has been discussed. Thin films were investigated by means of X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD analysis revealed the existence of crystalline TiO₂ in anatase and rutile forms, depending on Tb amount in examined samples. AFM images show that as-deposited samples with 0.4 at.% concentration of terbium (anatase structure) have bigger crystallites as compared to 2% and 2.6 at.% of Tb (rutile structure). The additional annealing at 1070 K results in a mixed anatase (77%) and rutile (23%) structure.     

Effect of deposition temperature on the microstructure and surface morphology of c-axis oriented AlN films deposited on sapphire substrate by RF reactive magnetron sputtering

In this paper, c-axis oriented AlN films were prepared on sapphire substrate by RF reactive magnetron sputtering at various deposition temperatures (30–700 °C). The influences of deposition temperature on the chemical composition, crystalline structure and surface morphology of the AlN films were systematically investigated. The as-deposited films were characterized by X-ray photoelectron spectroscopy (XPS), two-dimensional X-ray diffraction (2D-XRD) and atomic force microscopy (AFM). The experimental results show that it can be successfully grown for high-purity and near-stoichiometric (Al/N = 1.12:1) AlN films except for the segregation of a few oxygen impurities exist in the form of Al–O bonding. The chemical composition of as-deposited films is almost independent of substrate temperature in the range of 30–700 °C. However, the crystalline structure and surface morphology of the deposited AlN films are strongly influenced by the deposition temperature. The optimum deposition temperature is 300 °C, giving a good compromise between crystalline structure and surface morphology to grow AlN films.     

Deposition and characterization of low temperature silicon nitride films deposited by inductively coupled plasma CVD

Silicon nitride films have been deposited at a low temperature (70 °C) by inductively coupled plasma chemical vapor deposition (ICP-CVD) technique and their physical and chemical properties were studied. For a deposited SiN sample, β-phase was observed and refractive index of 2.1 at 13.18 nm/min deposition rate was obtained. The attained stress of 0.08 GPa is lower as compared to the reported value of 1.1 GPa for SiN thin films. To study the deposited film, characterization was performed using X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), micro Raman spectroscopy, Fourier transfer infrared spectroscopy (FTIR), cross-section scanning electron microscopy (SEM) and atomic force microscopy (AFM).     

Multilayered metal oxide thin film gas sensors obtained by conventional and RF plasma-assisted laser ablation

Multilayered thin films of In₂O₃ and SnO₂ have been deposited by conventional and RF plasma-assisted reactive pulsed laser ablation, with the aim to evaluate their behaviour as toxic gas sensors. The depositions have been carried out by a frequency doubled Nd-YAG laser (λ = 532 nm, τ = 7 ns) on Si(1 0 0) substrates, in O₂ atmosphere. The thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical resistance measurements. A comparison of the electrical response of the simple (indium oxide, tin oxide) and multilayered oxides to toxic gas (nitric oxide, NO) has been performed. The influence on the structural and electrical properties of the deposition parameters, such as substrate temperature and RF power is reported.     

Pulsed laser deposition of perovskite relaxor ferroelectric thin films

Structural, dielectric and ferroelectric properties of thin films of La-doped lead zirconate titanate (PLZT) and sodium bismuth titanate-barium titanate (NBT-BT) perovskite relaxor ferroelectric have been investigated. PLZT films were deposited on Pt/Si substrates in oxygen atmosphere by pulsed laser deposition (PLD) and radio frequency (RF) discharge-assisted PLD, using sintered targets with different La content and Zr/Ti ratio, near or at the boundary relaxor ferroelectric. The films are polycrystalline with perovskite cubic or slightly rhombohedral structure. A slim ferroelectric hysteresis loop, typical for relaxors, has been measured for all film sets. Dielectric characterization shows a large value of capacitance tunability and low dielectric loss. However, common problems related to lead diffusion into the metallic electrode layer do not allow one to obtain high capacitance values, due to the formation of an interface layer with low dielectric constant. Lead-free NBT-BT thin films have been deposited on single crystal (1 0 0)-MgO substrates starting from targets with composition at the morphotropic phase boundary between rhombohedral and tetragonal phase. Films deposited by PLD are polycrystalline perovskite with a slight (1 0 0) orientation. Capacitance measurements were performed using interdigital metallic electrodes deposited on the film's top surface and showed high relative dielectric constant, on the order of 1300.     

Investigations of the hydrophobic and scratch resistance behavior of polystyrene films deposited on bell metal using RF-PACVD process

Polystyrene films are deposited on bell metal substrates using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) process. The deposition of polystyrene film is carried out at working pressure of 1.6 × 10⁻¹ mbar and in the RF power range of 20-110 W. The hydrophobic and mechanical behaviors of the polystyrene films are studied as a function of RF power. The chemical compositions and surface chemistry of the polystyrene films are investigated using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It is revealed that enhanced cross-linked chemical structure and higher loss of oxygen by peroxy polystyryl radical with increasing RF power results in the formation of polystyrene films with more hydrophobic and scratch resistance behavior. However, extensive destruction of cross-linked chemical structure due to high energetic ion bombardment tends to decrease the hydrophobic and scratch resistance behavior of the polystyrene film deposited at RF power of 110 W. Atomic force microscopy (AFM) images show quite uniform and crack free surfaces of the polystyrene films having rms roughness in the range of 0.35-0.87 nm. Attempts are made to correlate the characterization results with the parameters that are used for thin film depositions.     

Pulsed-laser deposition of smooth thin films of Er, Pr and Nd doped glasses

Thin films of complex oxides have been obtained by pulsed-laser deposition (PLD) from glass targets belonging to the system Li₂O-Al₂O₃-P₂O₅-(RE)₂O₃, with RE = Nd, Pr, Er. The films were deposited on quartz, silicon and ITO/glass substrates using a F₂ laser (λ = 157 nm, ι ≈ 20 ns) for ablation in vacuum. The structural, morphological and optical properties of the oxide films were investigated through IR and UV-VIS spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Spectroscopic Ellipsometry. The laser wavelength was found to be the key parameter to obtain thin films with very smooth surface. In this way new possibilities are opened to grow multilayer structures for photonic applications.     

Effect of RF power and sputtering pressure on the structural and optical properties of TiO2 thin films prepared by RF magnetron sputtering

TiO₂ thin films were deposited onto quartz substrates by RF magnetron sputtering. The samples deposited at various RF powers and sputtering pressures and post annealed at 873 K, were characterized using X-ray diffraction (XRD), micro Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis spectroscopy and photoluminescence (PL) spectroscopy. XRD spectrum indicates that the films are amorphous-like in nature. But micro-Raman analysis shows the presence of anatase phase in all the samples. At low sputtering pressure, increase in RF power favors the formation of rutile phase. Presence of oxygen defects, which can contribute to PL emission is evident in the XPS studies. Surface morphology is much affected by changes in sputtering pressure which is evident in the SEM images. A decrease in optical band gap from 3.65 to 3.58 eV is observed with increase in RF power whereas increase in sputtering pressure results in an increase in optical band gap from 3.58 to 3.75 eV. The blue shift of absorption edge in all the samples compared to that of solid anatase is attributed to quantum size effect. The very low value of extinction coefficient in the range 0.0544-0.1049 indicates the excellent optical quality of the samples. PL spectra of the films showed emissions in the UV and visible regions.     

Effect of temperature on pulsed laser deposition of ZnO films

ZnO thin films have been deposited on Si(1 1 1) substrates at different substrate temperature by pulsed laser deposition (PLD) of ZnO target in oxygen atmosphere. An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as laser source. The influences of the deposition temperature on the thickness, crystallinity, surface morphology and optical properties of ZnO films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), photoluminescence (PL) spectrum and infrared spectrum. The results show that in our experimental conditions, the ZnO thin films deposited at 400 °C have the best surface morphology and crystalline quality. And the PL spectrum with the strongest ultraviolet (UV) peak and blue peak is observed in this condition.     

Deposition of Ni, Ag, and Pt-based Al-doped ZnO double films for the transparent conductive electrodes by RF magnetron sputtering

Ni, Ag, and Pt-based Al-doped ZnO (AZO) films have been deposited as transparent conductivity layers on quartz by RF magnetron sputtering and characterized by X-ray diffraction, Hall measurement, optical transmission spectroscopy, scanning electron microscopy (SEM). The deposition of thicker metal layer in double layers resulted in lowering the effective electrical resistivity with a slight reduction of their optical transmittance. A film consisting of AZO (250 nm)/Ni (2 nm) double structure, exhibits a sheet resistance of 21.0 Ω/sq, a high transmittance of 76.5%, and characterize good adhesion to substrate. These results make the satisfactory for GaN-based light-emitting diodes (LEDs) and solar cells with metal-based AZO double films as current spread layers.     

Epitaxial ZrC thin films grown by pulsed laser deposition

ZrC thin films were grown on (0 0 1)Si, (1 1 1)Si and (0 0 0 1)sapphire substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction, X-ray reflectivity and Auger electron spectroscopy investigations were used to characterize the structure and composition of the deposited films. It has been found that films grown at temperatures higher than 700 °C under very low water vapor pressures were highly textured. Films deposited on (0 0 1)Si grew with the (0 0 1) axis perpendicular to the substrate, while those deposited on (1 1 1)Si and (0 0 0 1)sapphire grew with the (1 1 1) axis perpendicular to the substrate. Pole figures investigations showed that films were epitaxial, with in-plane axis aligned to those of the substrate.     

Effect of annealing on properties of electrochemically deposited CdTe thin films

Thin films of CdTe have been deposited onto stainless steel and fluorine-doped tin oxide (FTO)-coated glass substrates from aqueous acidic bath using electrodeposition technique. The different preparative parameters, such as deposition time, bath temperature and pH of the bath have been optimized by photoelectrochemical (PEC) technique to get good quality photosensitive material. The deposited films are annealed at different temperature in presence of air. Annealing temperature is also optimized by PEC technique. The film annealed at 200 °C showed maximum photosensitivity. Different techniques have been used to characterize as deposited and also as annealed (at 200 °C) CdTe thin film. The X-ray diffraction (XRD) analysis showed the polycrystalline nature, and a significant increase in the XRD peak intensities is observed for the CdTe films after annealing. Optical absorption shows the presence of direct transition with band gap energy 1.64 eV and after annealing it decreases to 1.50 eV. Energy dispersive analysis by X-ray (EDAX) study for the as-deposited and annealed films showed nearly stoichiometric compound formation. Scanning electron microscopy (SEM) reveals that spherically shaped grains are more uniformly distributed over the surface of the substrate for the CdTe film.