The influence of substrate temperature and annealing on the properties of pulsed laser-deposited YIG films on fused quartz substrate

Yttrium iron garnet (YIG) thin films were deposited on fused quartz substrate at different substrate temperatures (T_s) varying from room temperature (RT) to 850 °C using pulsed laser deposition (PLD) technique. All the films in the as-deposited state were X-ray amorphous and non-magnetic at RT. The film deposited at RT after annealing at temperatures T_a?700 °C showed both X-ray peaks and the magnetic order. The films deposited at higher T_s (500–850 °C) and then annealed at 700 °C resulted in better-quality films with higher 4πM_s value. The highest value of magnetization was for the sample deposited at 850 °C and annealed at 700 °C, which is 68% of the bulk 4πM_s value.     

Optical properties of ITO/TiO2 single and double layer thin films deposited by RPLAD

Indium tin oxide (ITO) and titanium dioxide (TiO₂) single layer and double layer ITO/TiO₂ films were prepared using reactive pulsed laser ablation deposition (RPLAD) with an ArF excimer laser for applications in dye-sensitized solar cells (DSSCs). The films were deposited on SiO₂ substrates either at room temperatures (RT) or heated to 200-400 °C. Under optimized conditions, transmission of ITO films in the visible (vis) range was above 89% for films produced at RT and 93% for the ones deposited at higher temperatures. Increasing the substrate temperature from RT to 400 °C enhances the transmission of TiO₂ films in the vis-NIR from about 70% to 92%. High transmission (≈90%) was observed for the double layer ITO/TiO₂ with a transmission cut-off above 900 nm. From the transmission data, the energies gaps (E_g), as well as the refractive indexes (n) for the films were estimated. n ≈ 2.03 and 2.04, respectively for ITO films and TiO₂ film deposited at 400 °C in the visible region. Post-annealing of the TiO₂ films for 3 h at 300 and 500 °C was performed to enhance n. The refractive index of the TiO₂ films increases with the post-annealing temperature. The direct band gap is 3.6, 3.74 and 3.82 eV for ITO films deposited at RT, 200, and 400 °C, respectively. The TiO₂ films present a direct band gap of 3.51 and 3.37 eV for as deposited TiO₂ films and when annealed at 400 °C, respectively. There is a shift of about 0.1 eV between ITO and ITO/TiO₂ films deposited at 200 °C. The shift decreases by half when the TiO₂ film was deposited at 400 °C. Post-annealing was also performed on double layer ITO/TiO₂.     

Growth of oxide thin films for optical gas sensor applications

Tungsten trioxide and titanium dioxide thin films were synthesised by pulsed laser deposition. We used for irradiations of oxide targets an UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser source, at 2 J/cm² incident fluence value. The experiments were performed in low oxygen pressure. The (0 0 1) SiO₂ substrates were heated during the thin film deposition process at temperature values within the 300-500 °C range. The structure and crystalline status of the obtained oxide thin films were investigated by high resolution transmission electron microscopy. Our analyses show that the films are composed by nanoparticles with average diameters from a few to a few tens of nm. Moreover, the films deposited at substrate temperatures higher than 300 °C are crystalline. The tungsten trioxide films consist of a mixture of triclinic and monoclinic phases, while the titanium dioxide films structure corresponds to the tetragonal anatase phase. The oxide films average transmittance in the visible-infrared spectral range is higher than 80%, which makes them suitable for sensor applications.     

Crystallization and electrochemical performance of La0.6Sr0.4Co0.2Fe0.8O3 − δ-Ce0.8Gd0.2O1.9 thin film cathodes processed by single solution spray pyrolysis

La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ-Ce_0.8Gd_0.2O_1.9 (LSCF-CGO) thin films obtained by spray pyrolysis of a single precursor solution were investigated by XRD, TEM and impedance spectroscopy at annealing temperatures ranging from 500 to 900 °C. Films annealed at 600 °C contained a mixture of amorphous regions and crystalline regions composed of fine crystallites (< 5 nm). Annealing above 600 °C increased the ratio of crystalline to amorphous material, led to the segregation of the films into distinct LSCF and CGO phases, and promoted grain growth. The electrical behavior of the films depended on annealing temperature. At testing temperatures of 400 °C and below, the polarization resistance of films with lower annealing temperatures was larger than the polarization resistance of films with higher annealing temperatures. However, at testing temperatures of 500 °C and above the polarization resistance of films with lower annealing temperatures was equal to or lower than the polarization resistance of films with higher annealing temperatures. This was reflected by the activation energy that decreased with increasing annealing temperature. The varying electrical behavior may be related to microstructural changes that caused bulk diffusion to be the rate-limiting step in films with lower annealing temperatures and oxygen dissociation to be the rate-limiting step in films with higher annealing temperatures.     

Effects of deposition temperature on the structural and morphological properties of SnO2 films fabricated by pulsed laser deposition

Tin oxide (SnO₂) thin films were grown on Si (1 0 0) substrates using pulsed laser deposition (PLD) in O₂ gas ambient (10 Pa) and at different substrate temperatures (RT, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). XRD measurements showed that the almost amorphous microstructure transformed into a polycrystalline SnO₂ phase. The film deposited at 400 °C has the best crystalline properties, i.e. optimum growth conditions. However, the film grown at 300 °C has minimum average root mean square (RMS) roughness of 3.1 nm with average grain size of 6.958 nm. The thickness of the thin films determined by the ellipsometer data is also presented and discussed.     

Pulsed laser deposited Er,Yb:YVO4 waveguiding films on MgO/Si substrates

Erbium, and erbium and ytterbium co-doped YVO₄ waveguiding films were deposited on MgO/Si substrates by PLD. The samples were post-annealed at two different temperatures in air atmosphere. The influence on the crystalline structure and waveguiding properties of the films at these annealing temperatures for two dopant concentrations was investigated. Layers annealed up to 900 °C are polycrystalline. The dominant fraction of YVO₄ crystallites exhibited preferred orientation of the (0 0 1) zone axes parallel to the substrate surface. The polycrystalline samples show difference in the refractive indexes Δn (Δn = n_TE − n_TM) for TE and TM polarizations.     

Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide

SiC thin films were grown on Si (1 0 0) substrates by excimer laser ablation of a SiC target in vacuum. The effect of deposition temperature (up to 950 °C), post-deposition annealing and laser energy on the nanostructure, bonding and crystalline properties of the films was studied, in order to elucidate their transition from an amorphous to a crystalline phase. Infra-red spectroscopy shows that growth at temperatures greater than 600 °C produces layers with increasingly uniform environment of the Si-C bonds, while the appearance of large crystallites is detected, by X-ray diffraction, at 800 °C. Electron paramagnetic resonance confirms the presence of clustered paramagnetic centers within the sp² carbon domains. Increasing deposition temperature leads to a decrease of the spin density and to a temperature-dependent component of the EPR linewidth induced by spin hopping. For films grown below 650 °C, post-deposition annealing at 1100 °C reduces the spin density as a result of a more uniform Si-C nanostructure, though large scale crystallization is not observed. For greater deposition temperatures, annealing leads to little changes in the bonding properties, but suppresses the temperature dependent component of the EPR linewidth. These findings are explained by a relaxation of the stress in the layers, through the annealing of the bond angle disorder that inhibits spin hopping processes.     

Influence of temperature annealing on optical properties of SrTiO3/BaTiO3 multilayered films on indium tin oxide

We have prepared SrTiO₃/BaTiO₃ thin films with multilayered structures deposited on indium tin oxide (ITO) coated glass by a sol-gel deposition and heating at 300-650 °C. The optical properties were obtained by UV-vis spectroscopy. The films show a high transmittance (approximately 85%) in the visible region. The optical band gap of the films is tunable in the 3.64-4.19 eV range by varying the annealing temperature. An abrupt decrease towards the bulk band gap value is observed at annealing temperatures above 600 °C. The multilayered film annealed at 650 ° C exhibited the maximum refractive index of 2.09-1.91 in the 450-750 nm wavelength range. The XRD and AFM results indicate that the films annealed above 600 ° C are substantially more crystalline than the films prepared at lower temperatures which were used to change their optical band gap and complex refractive index to an extent that depended on the annealing temperature.     

Transmission electron microscopy studies of HfO2 thin films grown by chloride-based atomic layer deposition

Detailed transmission electron microscopy characterization of HfO₂ films deposited on Si(1 0 0) using atomic layer deposition has been carried out. The influence of deposition temperature has been investigated. At 226 °C, a predominantly quasi-amorphous film containing large grains of cubic HfO₂ (a₀ = 5.08 Å) was formed. Grain morphology enabled the nucleation sites to be determined. Hot stage microscopy showed that both the cubic phase and the quasi-amorphous phase were very resistant to thermal modification up to 500 °C. These observations suggest that nucleation sites for the growth of the crystalline cubic phase form at the growing surface of the film, rather homogeneously within the film. The films grown at higher temperatures (300-750 °C) are crystalline and monoclinic. The principal effects of deposition temperature were on: grain size, which coarsens at the highest temperature; roughness with increases at the higher temperatures due to the prismatic faceting, and texture, with texturing being strongest at intermediate temperatures. Detailed interfacial characterization shows that interfacial layers of SiO₂ form at low and high temperatures. However, at intermediate temperatures, interfaces devoid of SiO₂ were formed.     

Excimer laser processing of ZnO thin films prepared by the sol-gel process

ZnO thin films were prepared on soda-lime glass from a single spin-coating deposition of a sol-gel prepared with anhydrous zinc acetate [Zn(C₂H₃O₂)₂], monoethanolamine [H₂NC₂H₄OH] and isopropanol. The deposited films were dried at 50 and 300 °C. X-ray analysis showed that the films were amorphous. Laser annealing was performed using an excimer laser. The laser pulse repetition rate was 25 Hz with a pulse energy of 5.9 mJ, giving a fluence of 225 mJ cm⁻² on the ZnO film. Typically, five laser pulses per unit area of the film were used. After laser processing, the hexagonal wurtzite phase of zinc oxide was observed from X-ray diffraction pattern analysis. The thin films had a transparency of greater than 70% in the visible region. The optical band-gap energy was 3.454 eV. Scanning electron microscopy and profilometry analysis highlighted the change in morphology that occurred as a result of laser processing. This comparative study shows that our sol-gel processing route differs significantly from ZnO sol-gel films prepared by conventional furnace annealing which requires temperatures above 450 °C for the formation of crystalline ZnO.     

Structural and optical properties of YSZ thin films grown by PLD technique

We report on the structural and optical properties of yttria stabilized zirconia (YSZ) thin films grown by pulsed laser deposition (PLD) technique and in situ crystallized at different substrate temperatures (T_s = 400 °C, 500 °C and 600 °C). Yttria-stabilized zirconia target of ∼1 in. diameter (∼95% density) was fabricated by solid state reaction method for thin film deposition by PLD. The YSZ thin films were grown on an optically polished quartz substrates and the deposition time was 30 min for all the films. XRD analysis shows cubic crystalline phase of YSZ films with preferred orientation along 〈1 1 1〉. The surface roughness was determined by AFM for the films deposited at different substrate temperatures. The nano-sized surface roughness is found to increase with the increase of deposition temperatures. For the optical analysis, a UV-vis-NIR spectrophotometer was used and the optical band gap of ∼5.7 eV was calculated from transmittance curves.     

Improvement in micro-structural and mechanical properties of zinc film by surface treatment with low temperature argon plasma

Nanocrystalline zinc films were deposited on gold coated borosilicate glass substrates by thermal evaporation method using zinc powders as the source material and then treated with argon plasma at various temperatures. From X-ray diffraction study, the as-deposited films are found to be metallic Zn and polycrystalline in nature. The crystalline nature improves with the increase of temperature up to 200 °C and decreases with the further increase of temperature to 300 °C. The binding energy observed for Zn 2p_3/2, and the binding energy separation between Zn 2p_3/2 and Zn 2p_1/2 in the X-ray photoelectron spectrum indicate that the films are metallic zinc films. Transmission electron microscopic study shows hexagonal shaped grains having size ∼58 nm upon treatment with Ar plasma. It is clearly shown the grain growth and distinct grain boundary with the increase in temperature. The average Young's modulus (E) and hardness (H) are measured to be 84 GPa and 4.0 GPa for as-deposited film, whereas 98 GPa and 5.8 GPa for plasma treated film at 200 °C. The enhancement in mechanical properties is attributed to improvement in crystalline nature of the film and better interlinking between grains and boundaries.     

Doped thin metal oxide films for catalytic gas sensors

TiO₂ and Pt doped TiO₂ thin films were grown by pulsed laser deposition on 〈0 0 1〉 SiO₂ substrates. The doped films were compared with undoped ones deposited in similar experimental conditions. An UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser was used for the irradiation of the TiO₂ or Pt doped TiO₂ targets. The substrate temperatures were fixed during the growth of the thin films at values within the 300-500 °C range. The films’ surface morphology was investigated by atomic force microscopy and their crystalline quality by X-ray diffractometry. The corresponding transmission spectra were recorded with the aid of a double beam spectrophotometer in the spectral range of 400-1100 nm. No contaminants or Pt segregation were detected in the synthesized anatase phase TiO₂ thin films composition. Titania crystallites growth inhibition was observed with the increase of the dopant concentration. The average optical transmittance in the visible-infrared spectral range of the films is higher than 85%, which makes them suitable for sensor applications.     

Bioactive glass and hydroxyapatite thin films obtained by pulsed laser deposition

Bioactive glass (BG), calcium hydroxyapatite (HA), and ZrO₂ doped HA thin films were grown by pulsed laser deposition on Ti substrates. An UV KrF^* (λ = 248 nm, τ ≥ 7 ns) excimer laser was used for the multi-pulse irradiation of the targets. The substrates were kept at room temperature or heated during the film deposition at values within the (400-550 °C) range. The depositions were performed in oxygen and water vapor atmospheres, at pressure values in the range (5-40 Pa). The HA coatings were heat post-treated for 6 h in a flux of hot water vapors at the same temperature as applied during deposition. The surface morphology, chemical composition, and crystalline quality of the obtained thin films were studied by scanning electron microscopy, atomic force microscopy, and X-ray diffractometry. The films were seeded for in vitro tests with Hek293 (human embryonic kidney) cells that revealed a good adherence on the deposited layers. Biocompatibility tests showed that cell growth was better on HA than on BG thin films.     

High-throughput synthesis and characterization of Mg1−xCaxO films as a lattice and valence-matched gate dielectric for ZnO based field effect transistors

Using composition-spread technique, we have grown metastable Mg_1−xCa_xO solid solution films on ZnO layers by pulsed laser deposition. All the films exhibited (1 1 1) oriented cubic phase. Despite a large miscibility gap, no phase separation took place at growth temperatures up to 700 °C, whereas an optimal growth temperature was found at 400 °C in terms of the crystallinity. The composition-spread films were characterized by X-ray diffraction mapping technique. Both lattice parameters and diffraction intensity increased with increasing the CaO composition. The present isovalent heterointerfaces realized the perfect lattice-matching by properly adjusting the CaO composition, leading to particular interest for ZnO based field effect transistors.     

Investigation on upconversion photoluminescence of Bi3TiNbO9:Er:Yb thin films

Bi₃TiNbO₉:Er³⁺:Yb³⁺ (BTNEY) thin films were fabricated on fused silica by pulsed laser deposition. It was demonstrated that different laser fluence and substrate temperature during growth of BTNEY upconversion photoluminescence (UC-PL) samples control the film’s grain size and hence influences the UC-PL properties. The average grain size of BTNEY thin films deposited on fused silica substrates with laser fluence 4, 5, 6, and 7 J/cm² are 30.8, 35.9, 40.6, and 43.4 nm, respectively. The 525 nm emission intensities increase with the deposition laser fluence and the emission intensities of BTNEY thin film deposited under 700 and 600 °C are almost 24 and 4 times, respectively, as strong as those of samples under 500 °C. The grain size of BTNEY thin film increases with the increasing temperature. UC-PL of BTNEY films is enhanced by increasing grain size of the films.     

Surface characterization and luminescent properties of SrAl2O4:Eu,Dy nano thin films

SrAl₂O₄:Eu²⁺, Dy³⁺ thin films were grown on Si (1 0 0) substrates in different atmospheres using the pulsed laser deposition (PLD) technique. The effects of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological and photoluminescence (PL) properties of the films were investigated. The films were ablated using a 248 nm KrF excimer laser. Improved PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres compared to those prepared in vacuum. A stable green emission peak at 520 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions was obtained. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The diffusion of adventitious C into the nanostructured layers deposited in the Ar and O₂ atmospheres was most probably responsible for the quenching of the PL intensity after annealing.     

Structural and optoelectronic properties of antimony tin sulphide thin films deposited by thermal evaporation techniques

Thin films of SnSb₂S₄ have been prepared on glass substrate by using thermal evaporation techniques. The films were annealed in argon gas at low pressure in sealed glass ampoules at 85 °C, 150 °C, 275 °C and 325 °C. XRD of the films reveal that the low temperature annealed films are poly crystalline while the as deposited films and high annealed films are in amorphous states. There is no adequate variation in the photoconductivity response of the amorphous and crystalline phases. The transmittance of the films is low and having no transmittance below 740 nm. The band gap calculated by ellipsometry technique is in the range of 1.82–3.1 eV. The films have n-type conductivity but the film annealed at 325 °C show p-type conductivity.     

Enhanced ferroelectric properties of vanadium doped bismuth titanate (BTV) thin films grown by pulsed laser ablation technique

Bi_3.99Ti_2.97V_0.03O₁₂ (BTV) thin films were grown by pulsed laser deposition at substrate temperatures ranging between 650 and 750 °C. The structural phase, and orientation of the deposited films were investigated in order to understand the effect of the deposition parameters on the properties of the BTV films. As the substrate temperature was increased to 700 °C, the films started showing a tendency of assuming a c-axis preferred orientation, while at lower temperatures polycrystalline films were formed. The Au/BTV/Pt capacitor showed an interesting dependence of the remnant polarization (P_r) as well as dc leakage current values on the growth temperature. The film deposited at 675 °C showed a very large 2P_r of 42 μC cm⁻², which is the largest for BTV thin films among the values reported so far.     

Optical, structural and fluorescence properties of nanocrystalline cubic or monoclinic Eu:Lu2O3 films prepared by pulsed laser deposition

Eu³⁺-doped lutetium oxide (Eu:Lu₂O₃) nanocrystalline films were grown on fused-silica substrates by pulsed laser deposition. Depending on deposition conditions (oxygen pressure, temperature and laser energy), the structure of the films changed from amorphous to crystalline and the cubic or monoclinic phases were obtained with varying preferential orientation and crystallite size. The monoclinic phase could be prepared for the first time at temperatures as low as 240 °C and in a narrow range of parameters. Although this phase has been previously reported for powder samples, it occurs only for high pressures and high temperatures preparation conditions. The refractive indices were measured by m-lines spectroscopy for both crystalline phases and their dispersion curve fitted by the Sellmeier expression. The specific Eu³⁺ fluorescence properties of the different phases, monoclinic and cubic, were registered and show modifications due to the disorder induced by the nanometric size of the crystallites, emphasised in particular by quasi-selective excitation in the charge transfer band.