Structural and optical properties of La-doped BaSnO3 thin films grown by PLD

In this study the structural and optical properties of lanthanum-doped BaSnO₃ powder samples and thin films deposited on fused silica were investigaed using laser ablation. Under an oxygen pressure of 5×10⁻⁴ mbar, phase pure BaSnO₃ films with a lattice constant of 0.417 nm and grain size of 21 nm were prepared at 630 °C. The band gap of BaSnO3 powder sample and thin films was calculated to be 3.36 eV and 3.67 eV, respectively. There was a progressive increase in conductivity for thin films of BaSnO₃ doped with 0~7 at% of La. The highest conductivity, 9 Scm⁻¹, was obtained for 7 at% La-doped BaSnO₃. Carrier concentration, obtained from Burstein-Moss (B-M) shift, nearly matches the measured values except for 3 at% and 10 at% La-doped BaSnO₃ thin films.     

Laser-induced changes in some of the optical properties of Ge20Bi10Se70 thin films

We have investigated photon-induced changes of optical parameters of amorphous Ge₂₀Bi₁₀Se₇₀ thin films due to illumination by laser irradiation. Absorption peaks were detected in the tailing area in the wavelength range between 300 and 600 nm. These peaks reduced to two peaks in the higher dose (9 J/cm²). The optical energy gap E _gd was found to have the well known direct-allowed transition mechanism. Values of E _gd show that all films exhibit a photo-induced photo-darkening effect indicated by a red shift of E _gd. The higher laser dose shows an increase in E _gd values. The effect of laser on other optical constants was also investigated. The refractive index (n), extinction coefficient (k) and dielectric constant of irradiated films were also calculated.     

Morphological and optical properties of silicon thin films by PLD

Silicon thin films have been prepared on sapphire substrates by pulsed laser deposition (PLD) technique. The films were deposited in vacuum from a silicon target at a base pressure of 10⁻⁶ mbar in the temperature range from 400 to 800 °C. A Q-switched Nd:YAG laser (1064 nm, 5 ns duration, 10 Hz) at a constant energy density of 2 J × cm⁻² has been used. The influence of the substrate temperature on the structural, morphological and optical properties of the Si thin films was investigated.Spectral ellipsometry and atomic force microscopy (AFM) were used to study the thickness and the surface roughness of the deposited films. Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased deposition temperature.     

Chemical composition of ZrC thin films grown by pulsed laser deposition

ZrC films were grown on (1 0 0) Si substrates by the pulsed laser deposition (PLD) technique using a KrF excimer laser working at 40 Hz. The nominal substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that films deposited under residual vacuum or under 2 × 10⁻³ Pa of CH₄ atmosphere were crystalline, exhibiting a (2 0 0)-axis texture, while those deposited under 2 × 10⁻² Pa of CH₄ atmosphere were found to be equiaxed and with smaller grain size. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed the usual high oxygen contamination of carbides. Once the topmost 2-4 nm region was removed, the oxygen concentration rapidly decreased, down to around 3-8% only in bulk. Simulations of the X-ray reflectivity (XRR) curves indicated a smooth surface morphology, with roughness values below 1 nm (rms) and films density values of around 6.30-6.45 g/cm³, very close to the bulk density. The growth rate, estimated from thickness measurements by XRR was around 8.25 nm/min. Nanoindentation results showed for the best quality ZrC films a hardness of 27.6 GPa and a reduced modulus of 228 GPa.     

Structural and optical properties of low temperature synthesized Nanostructured BiFeO3 thin films

Nanostructured bismuth ferrite (BiFeO₃) thin films were deposited on glass substrate by the sol-gel process. The as-fired film at 250 °C was found to be amorphous crystallizing to pure rhombohedral phase after annealing at 450 °C for 2 h in air. The XRD pattern shows that the sample is polycrystalline in nature. The average grain size of the film calculated from the XRD data was found to be 16 nm. The as-fired film show high transmittance that decreases after crystallization. The absorption edge of the films was found to be sharper and shifting towards the lower energy as the annealing temperature increases. The optical energy band gaps of the amorphous and crystalline films were found to be 2.63 and 2.31 eV, respectively. The refractive indices of the amorphous and crystalline films were 2.05 and 2.26, respectively.     

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.     

Structural and morphological properties of thin ZnO films grown by pulsed laser deposition

The pulsed laser deposition technique was used to produce zinc oxide thin films onto silicon and Corning glass substrates. Homogeneous surfaces exhibiting quite small Root Mean Square (RMS) roughness, consisting of shaped grains were obtained, their grain diameters being 40-90 nm at room temperature and at 650 °C growth respectively. Films were polycrystalline, even for growth at room temperature, with preferential crystallite orientation the (0 0 2) basal plane of wurtzite ZnO. Temperature increase caused evolution from grain to grain agglomeration structures, improving crystallinity. Compressive to tensile stresses transition with temperature was found while the lattice constant decreased.     

Thickness effect on the structural and optical constants of stibnite thin films prepared by sulfidation annealing of antimony films

This paper deals with some physical properties of antimony sulphide Sb₂S₃ thin films obtained by an annealing process in sulphur vapors at 300 °C of Sb thermal evaporated thin films deposited on glass substrate. The crystal structure and surface morphology were investigated by both XRD and AFM techniques. This structural study shows that Sb₂S₃ thin films were well crystallized in orthorhombic structure and some parameters such as the lattice parameter, crystallite size, microstrain and degree of preferred orientation have been reported and correlated with the effect of crystallite size. On the other hand, the refractive index and the extinction coefficient were discussed in terms of the Forouhi–Bloomer model. The optical band gap was found to range from 1.75 to 2.23 eV. Finally, the analysis of the optical parameters extracted from the Urbach–Martienssen and Forouhi–Bloomer models lead to some explanations of the correlations between the structural properties in terms of the crystallite size and optical ones.     

Structural and optical properties of electrodeposited molybdenum oxide thin films

Electrosynthesis of Mo(IV) oxide thin films on F-doped SnO₂ conducting glass (10-20/Ω/□) substrates were carried from aqueous alkaline solution of ammonium molybdate at room temperature. The physical characterization of as-deposited films carried by thermogravimetric/differential thermogravimetric analysis (TGA/DTA), infrared spectroscopy and X-ray diffraction (XRD) showed the formation of hydrous and amorphous MoO₂. Scanning electron microscopy (SEM) revealed a smooth but cracked surface with multi-layered growth. Annealing of these films in dry argon at 450 °C for 1 h resulted into polycrystalline MoO₂ with crystallites aligned perpendicular to the substrate. Optical absorption study indicated a direct band gap of 2.83 eV. The band gap variation consistent with Moss rule and band gap narrowing upon crystallization was observed.Structure tailoring of as-deposited thin films by thermal oxidation in ambient air to obtain electrochromic Mo(VI) oxide thin films was exploited for the first time by this novel route. The results of this study will be reported elsewhere.     

Influence of glucose on the structural and optical properties of ZnO thin films prepared by sol-gel method

In this work, ZnO thin films were prepared by sol-gel method on glass substrates followed by calcinations at 500 °C for an hour. The effect of glucose on the structure and optical properties of the films was studied. The structural characteristics of the samples were analyzed by X-ray diffractometer (XRD) and atomic force microscope (AFM). The optical properties were studied by a UV-visible spectrophotometer. The results show that some of the prepared ZnO thin films have a high preferential oriented c-axis orientation with compact hexagonal wurtzite structure due to a proper amount of glucose introducing. After introducing the glucose additive in ZnO colloids, the intensity of (002) peak, the transmittance, and the optical band gap of the ZnO thin films increases because of the enhanced ZnO crystallization. On the contrary, the absorbance, the film thickness, and the surface root-mean-square (RMS) roughness of the ZnO thin films decreases. The glucose additive could not only improve the surface RMS roughness and microstructure of ZnO thin films, but also enhance the transmittance and the energy band gap more easily.     

Preparation and optical properties of barium titanate thin films

Barium titanate (BTO) films were prepared by sol-gel spin-coating technique. The crystal structure and optical properties of BTO films have been investigated. The results indicate that the BTO films are single perovskite phase having tetragonal symmetry. The band gap of the BTO films increases with the increasing of layer number and decreasing of solution concentration. The transmittance and band gap of the BTO films annealed at 900 °C is more than that of the BTO films annealed at 700 °C when wavelength is 200-1000 nm. When wavelength is 400-1000 nm, the absorption coefficient α obtained by experiment is higher than that obtained by calculation (close to zero).     

Chemical,optical, and electrical characterization of Ga2O3 thin films grown by plasma-enhanced atomic layer deposition

Thin Ga₂O₃ films were grown on Si (100) using trimethylgallium (TMG) and oxygen as the precursors through plasma-enhanced atomic layer deposition. The depositions were made over a temperature range of 80–250?°C with a growth per cycle of around 0.07 nm/cycle. Surface self-saturating growth was obtained with TMG pulse time ≥20?ms?at a temperature of 150?°C. The root mean square surface roughness of the obtained Ga₂O₃ films increased from 0.1?nm to 0.3?nm with increasing the growth temperature. Moreover, the x-ray photoelectron spectroscopy analysis indicated that the obtained film was Ga-rich with the chemical oxidation states Ga³⁺ and Ga¹⁺, and no carbon contamination was detected in the films after Ar⁺ sputtering. The electron density of films measured by x-ray reflectivity varied with the growth temperature, increasing from 4.72 to 5.80?g/cm³. The transmittance of Ga₂O₃ film deposited on a quartz substrate was obtained through ultraviolet visible (UV–Vis) spectroscopy. An obvious absorption in the deep UV region was demonstrated with a wide band gap of 4.6–4.8?eV. The spectroscopic ellipsometry analysis indicated that the average refractive index of the Ga₂O₃ film was 1.91?at 632.8?nm and increased with the growth temperature due to the dense structure of the films. Finally, the I-V and C-V characteristics proved that the Ga₂O₃ films prepared in this work had a low leakage current of 7.2?×?10^?11 A/cm² at 1.0?MV/cm and a high permittivity of 11.9, suitable to be gate dielectric.     

Microstructure and surface morphology of YSZ thin films deposited by e-beam technique

In present study yttrium-stabilized zirconia (YSZ) thin films were deposited on optical quartz (amorphous SiO₂), porous Ni-YSZ and crystalline Alloy 600 (Fe-Ni-Cr) substrates using e-beam deposition technique and controlling technological parameters: substrate temperature and electron gun power which influence thin-film deposition mechanism. X-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin-film structure and surface morphology depend on these parameters. It was found that the crystallite size, roughness and growth mechanism of YSZ thin films are influenced by electron gun power. To clarify the experimental results, YSZ thin-film formation as well evolution of surface roughness at its initial growing stages were analyzed. The evolution of surface roughness could be explained by the processes of surface mobility of adatoms and coalescence of islands. The analysis of these experimental results explain that surface roughness dependence on substrate temperature and electron gun power non-monotonous which could result from diffusivity of adatoms and the amount of atomic clusters in the gas stream of evaporated material.     

Structural, optical and electrical properties of Cd-doped SnO2 thin films grown by RF reactive magnetron co-sputtering

Transparent conducting SnO₂:Cd thin films were prepared by RF reactive magnetron co-sputtering on glass slides at a substrate temperature of 500 °C using CdO as cadmium source. The films were deposited under a mixed argon/oxygen atmosphere. The structural, optical and electrical properties were analyzed as a function of the Cd amount in the target. The X-ray diffraction shows that polycrystalline films were grown with both the tetragonal and orthorhombic phases of SnO₂. The obtained films have high transmittance and conductivity. The figure of merit of SnO₂:Cd films are in the order of 10⁻³ Ω⁻¹, which suggests that these films can be considered as candidates for transparent electrodes.     

Photoluminescence study of pure and Li-doped ZnO thin films grown by sol-gel technique

The effect of annealing atmosphere, temperature and aging on the photoluminescence of pure and Li-doped ZnO thin films has been investigated. Annealing the pure ZnO in N₂ and He above 800 °C results in green emission centered at ca. 500 nm; however annealing in air red-shifts the green emission to 527 nm. The visible emission of the Li-doped ZnO is found to be largely dependent on the annealing atmosphere. Warm-white photoluminescence with a broad emission band covering nearly the whole visible spectrum is obtained for the Li-doped ZnO films annealed in helium. The substitutional and interstitial extrinsic point defects created by lithium doping may mediate the relative concentration of the intrinsic defects and thereby tune the intrinsic-defect-related visible emission. The enhanced intensity ratio of near-band-edge ultraviolet emission to deep-level visible emission with aging time may be ascribed to both in-diffusion of oxygen from air and self-diffusion of oxygen interstitials to heal the oxygen vacancies during the aging process.     

Structural, electrical and optical properties of AgInS2 thin films grown by thermal evaporation method

Structural electrical and optical properties of AgInS₂ (AIS) thin films grown by the single-source thermal evaporation method were studied. The X-ray diffraction spectra indicated that the AIS single phase was successful grown by annealing above 400 °C in air. The AIS grain sizes became large with increasing the annealing temperatures. All polycrystalline AIS thin films were sulfur-poor from the electron probe microanalysis and indicated n-type conduction by the Van der Pauw technique. It was deduced that the sulfur vacancies were dominant in the films and enhanced n-type conduction.     

Structural and optical properties of nanocrystalline ZnO thin films synthesized by the citrate precursor route

Nanocrystalline zinc oxide (ZnO) thin films have been deposited by spin-coating polymeric precursors synthesized by the citrate precursor route using ethylene glycol and citric acid as chelating agents. The ZnO thin films were annealed in air at different temperatures for 10 min. The films were characterized by different structural and optical techniques, including X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectroscopy, and photoluminescence (PL). The thermal decomposition of polymeric precursor was studied by thermogravimetric analysis (TGA). XRD analysis with grazing incidence and rocking curves indicate that the ZnO films are polycrystalline with preferential orientation along the c-axis direction with a full-width at half-maximum (FWHM) of 0.31° for 600 °C-annealed samples. On annealing, the texturing in films increased along with a decrease in FWHM. AFM micrographs illustrate that the ZnO films are crack-free with well-dispersed homogeneous and uniformly distributed spherical morphology. The synthesized ZnO thin films have transparency >85% in the visible region exhibiting band edge at 375 nm, which becomes sharper with anneal. Room temperature PL spectra of these films show strong ultraviolet (UV) emission around 392 nm with an increase in intensity with annealing temperature, attributed to grain growth. Deconvolution of the PL spectra reveals that there is coupling of free excitons with higher orders of longitudinal optical (LO) phonon replicas leading to a broad asymmetric near-band-edge peak.     

Study by AES of the titanium nitruration in the growing of TiN thin films by PLD technique

A series of different TiN_x thin films were grown by PLD. The purpose for this work was to study through the AES interpretation, how the different conditions of the partial pressure of N inside the chamber during the growing of these thin films, affects the stoichiometry of the TiN_x deposited. The results obtained were that the different thin films change each one through TiN_x (x = 0.88-1.33). The results were supported with XPS and EELS spectroscopy doing also an analysis of elemental ratio to show the stoichiometry and sub-stoichiometry obtained. This work concludes the adequate conditions for this experiment to obtain TiN as thin film by PLD at room temperature, supported with the results in the present work and the interpretation of the AES spectra even when Ti and N peaks overlap.     

Structural characterization and optical properties of UO2 thin films by magnetron sputtering

Uranium dioxide films were deposited on Si (1 1 1) substrates by dc magnetron sputtering method at different sputtering parameters. The structure, morphology and chemical state of the films were studied by field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and atomic force microscopy. Influences of film thickness on the microstructure and optical properties were investigated. Experimental results show that the film crystallites are preferentially oriented with the (1 1 1) planes. The average grain size increases with increasing film thickness. AFM images show that the root mean square roughness of the films is between 1.2 nm and 2.1 nm. Optical constants (refractive index, extinction coefficient) of the films in the wavelength range of 350-1000 nm are obtained by ellipsometric spectroscopy. The result shows that the refractive index decreases with the increasing film thickness, while extinction coefficient increases with the film thickness.     

Control of wettability of hydrogenated amorphous carbon thin films by laser-assisted micro- and nanostructuring

A flexible and rapid surface functionalization of amorphous carbon films shows a great potential for various application fields such as biological surfaces and tribological systems. For this purpose, the combination of thin film deposition and subsequent laser material processing was investigated. Amorphous carbon layers doped with hydrogen were deposited on silicon wafers by reactive direct-current magnetron sputtering. Films with three different hydrogen contents were synthesized. Subsequent to the thin film deposition process, UV laser material processing at wavelengths of 193 nm or 248 nm was performed with respect to chemical surface modification and surface structuring on micro- and nanometer scale. Depending on structure size and laser-induced chemical surface modification the adjustment of the surface energy and wetting behaviour in a broad range from hydrophobic to hydrophilic was possible. The chemical modification and the ablation mechanisms near the ablation threshold were strongly influenced by the hydrogen content in amorphous carbon thin films.Structural and chemical information of the as-deposited and modified films was obtained by Raman spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements.