Physical properties of CuCrO2 films prepared by pulsed laser deposition

High-quality CuCrO₂ films were prepared by pulsed laser deposition (PLD). The film deposited with the pulse energy density (PED) of 2 mJ/cm² is highly c-axis oriented. The refractive index of the CuCrO₂ films is about 1.29 obtained by transmission spectra of the films, which implies that the CuCrO₂ film will be a potential antireflection coating in visible light. The films prepared with different PEDs show different conduction mechanism, which suggested the different band structure between these CuCrO₂ films.     

Electrical characterization of Ta2O5 films deposited by laser reactive ablation of metallic Ta

Tantalum oxide films have been deposited by 355 nm pulsed laser ablation of metallic Ta target in O₃/O₂ ambient. The structure and the composition of as-deposited and annealed films were examined by X-ray diffraction and Fourier transform infrared spectroscopy. The measurements of the current–voltage and capacitance–voltage characteristics of the Al/Ta₂O₅/Si capacitors were performed to reveal the electrical properties of the Ta₂O₅ films. The effects of annealing temperature on the characteristics of thin films have been studied. The results suggest that the films annealed above 700°C have the structure of orthorhombic β-Ta₂O₅, thc annealing treatment at high temperature decreases the bulk trap charge, the border trap, and the interface trap densities of as-deposited films, and improves significantly the dielectric and electrical properties of Ta₂O₅ film.     

Composition controlling of KNbO3 thin films prepared by pulsed laser deposition

The composition of KNbO₃ thin films prepared by pulsed laser deposition is crucially influenced by the deposition configuration. In the present study, the composition of KNbO₃ thin films grown on Si (100) substrates by pulsed laser ablation was tried to be controlled by adjusting the target-substrate distance and the oblique angle of substrate from the plume axial direction. It was found that the K deficiency in the films can be effectively avoided by setting the substrate at an appropriate oblique angle from the plume axial direction. The stoichiometric KNbO₃ thin films with a K/Nb molar ratio of 0.98 were successfully obtained, where the substrates were set at an oblique angle of 3-12° from the plume axis while the target-substrate distance was kept at 40 mm.     

Luminescence of Cr-doped ZnGa2O4 thin films deposited by pulsed laser ablation

Chromium-doped zinc gallate powder is synthesized via a solid-state reaction and subsequently deposited as a thin film on quartz substrates by using a pulsed laser deposition technique under two different deposition conditions. The films are characterized with X-ray diffraction, scanning electron microscopy, UV-vis spectrophotometry and luminescent measurements. As the oxygen pressure is changed from 0 to 1 Pa, we find that the grain size gets smaller, the crystallinity improves, the band-gap energy increases, the excitation peaks of the charge transfer band exhibit a remarkable blue-shift from 263 to 247 nm and the intensity of the red emission (694 nm) is enhanced. The results suggest that the structural and luminescent properties of ZnGa₂O₄:Cr^3 + thin film phosphors are improved by deposition at an oxygen pressure of 1 Pa.     

Composition, structural and electrical properties of thin films prepared by laser ablation of neodymium-doped potassium gadolinium tungstate

Thin films were grown on (001) SiO₂, SiO₂/(100) Si or (100) MgO substrates by laser ablation of neodymium-doped potassium gadolinium tungstate (Nd:KGW) single crystal target. The films were deposited at temperatures between room temperature and 750 °C and pressures between 1 × 10^− 4 Pa and 50 Pa of oxygen ambient. The influence of the deposition conditions on the composition, structure, morphology and electrical properties of the films was investigated. Special attention was paid to the films deposited in vacuum (1 × 10^− 4 Pa) or at very low oxygen pressures. Under such conditions, the potassium (K), gadolinium (Gd) and oxygen (O) content decreased strongly as the temperature was increased. At room temperature, the films were K and O stoichiometric, in contrast with Gd, which showed a concentration twice higher. The films were polycrystalline, with the exception of those deposited at temperatures below 500 °C, which were amorphous. However, all were smooth and dense. The films grown in vacuum and at temperatures between 500 and 700 °C consist mainly of “â-tungsten” - tungsten oxide (W₃O) phase. The films grown on SiO₂/Si possessed the best surface quality with nano-size relief. The resistivity measurements as a function of the temperature showed that the films produced in vacuum and at temperatures below 500 °C were highly insulating, whereas at 600 °C they exhibited semiconducting behavior or a metallic one at 700 °C. This behavior can be attributed to the existence of various valence states for tungsten below W⁶⁺ in the films and to their crystal structure.     

Needle-like LiFePO4 thin films prepared by an off-axis pulsed laser deposition technique

Lithium iron phosphate (LiFePO₄) thin films were prepared by pulsed laser deposition with an off-axis geometry. Amorphous, needle-like and crystallized granular thin films were prepared on Si and titanium substrates. The preferred orientation of these crystallized LiFePO₄ thin films is (120). Microstructures of the deposited films are dependant on the substrate temperature (room temperature, 500 °C and 700 °C) and Ar pressure (5 Pa and 30 Pa) in the chamber. The needle-like film grows following a self-shadowing mechanism. LiFePO₄ thin film with high crystallinity shows a voltage plateau which is a typical feature of the phase transition reaction for bulk material, while the sloped profiles are observed clearly in the charging and discharging curves of LiFePO₄ thin films with low cystallinity.     

ZnO thin films prepared by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by pulsed laser deposition (PLD) in an oxygen-reactive atmosphere. The structural, optical, and electrical properties of the as-prepared thin films were studied in dependence of substrate temperature and oxygen pressure. High quality polycrystalline ZnO films with hexagonal wurtzite structure were deposited at substrate temperatures of 100 and 300 °C. The RMS roughness of the deposited oxide films was found to be in the range 2-9 nm and was only slightly dependent on substrate temperature and oxygen pressure. Electrical measurements indicated a decrease of film resistivity with the increase of substrate temperature and the decrease of oxygen pressure. The ZnO films exhibited high transmittance of 90% and their energy band gap and thickness were in the range 3.26-3.30 eV and 256-627 nm, respectively.     

Structural and optical properties of Ti oxide cluster-assembled films prepared by plasma-gas-condensation

Ti and Ti oxide cluster-assembled films have been prepared using a plasma-gas-condensation apparatus. Transmission electron microscopy and electron diffraction measurement indicates that their structures vary from a face-centered-cubic (fcc) Ti phase, via an NaCl-type TiO_x phase, to an amorphous and rutile-type TiO₂ mixture phase with increasing the O₂ flow rate in the Ar/He gas mixture. Cluster shapes are spherical for the fcc phase, cubic for the NaCl-type, and spherical for the amorphous and rutile-type mixture, while the cluster size monotonically decreases with increasing O₂ flow rate. The Ti and Ti oxide cluster-assembled films have a sooty appearance, showing a very porous morphology in the scanning electron microscopy images. The electrical resistivity dramatically increases between R_O2 = 0.065 and 0.075 sccm, while the optical transmittance spectra in the visible wavelength range rapidly increases between R_O2 = 0.1 and 0.12 sccm, well reflecting the structure variations in these Ti and Ti oxide cluster-assembled films.     

Structural and textural characterization of LiFePO4 thin films prepared by pulsed laser deposition on Si substrates

LiFePO₄ thin films were grown on silicon (100) substrates by pulsed laser deposition using Traditional Geometry (TG) and Off-Axis Geometry (OAG) deposition chambers. We examined and compared the structure and composition of the so formed thin films. The nails observed on the OAG-film present an amorphous “body” and a crystallized “head”. The Fe/P ratio determined using energy dispersive spectrometry combined with high angle annular dark field images reveals a metallic iron heart surrounded by LiFePO₄ shell. On the other hand, the protuberances on TG-film are pure iron. The focused ion beam prepared cross-section of the film suggests the presence of iron particles and iron dendritic like filaments inside the LiFePO₄ layer.     

Optical properties of translucent CaGa2S4:Ce films prepared by pulsed laser deposition

Translucent CaGa₂S₄:Ce thin films were prepared by pulsed laser deposition. Optical absorption associated with the 4f₁ (²F_5/2) to 5d₂ second-highest excited state transition of the Ce³⁺ ion was clearly observed at 3.60 eV as well as the 4f₁ (²F_5/2) to 5d₁ lowest excited state transition at 2.93 eV. Energy splitting of the 5d state by the crystal field is discussed in terms of a model of a square antiprism structure with D_4d symmetry.     

Study on TiO2 thin films grown by advanced pulsed laser deposition on ITO

TiO₂ films were grown by an advanced pulsed laser deposition method (PLD) on ITO substrates to be used as functional electrodes in the manufacturing of solar cells. A pure titanium target (99.99%) was irradiated by a Nd:YAG laser (355 and 532 nm, 5 ns, 35 mJ, 3 J/cm²) in an oxygen atmosphere at different pressures (20-160 mTorr) and at room temperature. After deposition, the films were subjected to an annealing process at 350 °C. The film structure, surface morphology, thickness, roughness, and optical transmission were investigated. Regardless of the wavelength used, the films deposited at room temperature presented only Ti₂O and TiO peaks. After thermal treatment, the TiO₂ films became strongly crystalline, with a tetragonal structure and in the anatase phase; the threshold temperature value was 250 °C. The deposition rate was in the range of 0.035-0.250 nm/pulse, and the roughness was 135-305 nm. Optical transmission of the films in the visible range was between 40% and 60%.     

GaN thin films deposited by pulsed laser ablation in nitrogen and ammonia reactive atmospheres

Well-oriented, crystalline GaN films were grown on (11

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0) sapphire substrates in reactive atmospheres of N₂ and NH₃ by pulsed laser deposition. GaN targets were ablated at 2.8 J cm⁻² and the substrate temperature was varied from 500 to 700°C. The background gas pressure was varied from 0.04 to 0.3 mbar. All the films had a wurtzite structure. The crystal quality and preferential orientation depended on the substrate temperature, laser fluence and the presence of the nitriding atmosphere. For both N₂ and NH₃, the most resistive films were preferentially orientated in the [000l] direction. For 700°C the film resistivity was found to increase from 10⁻³ Ω cm when deposited in NH₃ to 10² Ω cm when deposited in N₂. The band-gap, obtained from optical transmission measurements shifted from 3.1 to 3.4 eV. Violet photoluminescence was found in all samples and was centered at 3.2 eV with a full width at half maximum of 0.2 eV. A broad peak in the yellow, centered at 2.1 eV, was detected for films grown in vacuum and ammonia.     

Transparent conducting F-doped SnO2 thin films grown by pulsed laser deposition

Transparent conducting fluorine-doped tin oxide (SnO₂:F) films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of the SnO₂:F films have been investigated as a function of F-doping level and substrate deposition temperature. The optimum target composition for high conductivity was found to be 10 wt.% SnF₂ + 90 wt.% SnO₂. Under optimized deposition conditions (T_s = 300 °C, and 7.33 Pa of O₂), electrical resistivity of 5 × 10^− 4 Ω-cm, sheet resistance of 12.5 Ω/□, average optical transmittance of 87% in the visible range, and optical band-gap of 4.25 eV were obtained for 400 nm thick SnO₂:F films. Atomic force microscopy measurements for these SnO₂:F films indicated that their root-mean-square surface roughness ( 6 Å) was superior to that of commercially available chemical vapor deposited SnO₂:F films ( 85 Å).     

Nanoporous films obtained by sacrificial layer pulsed laser deposition

Integration of solid state gas sensors and solid oxide fuel cells into third generation microelectronic products requires the development of unique fabrication methods. Highly porous electrodes, critical to the performance of many gas dependent devices, typically require harsh production methods and high sintering temperatures that are incompatible with a variety of platforms including those based on silicon or glass. In this study, an alternative procedure for overcoming these problems has been developed. It is based on the synthesis of nano-porous films at reduced fabrication temperatures by means of the Sacrificial Layer Pulsed Laser Deposition (SL-PLD). SL-PLD utilizes simultaneous oxide and carbon deposition to deposit thin dense films. These amorphous films are then transformed into nano-porous perovskite films by thermal annealing in ambient air at 600 ºC. In this paper, an alternative process for the development of nano-porous thin films at reduced fabrication temperatures is presented. It takes advantage of the low temperatures needed for both carbon burn-off and the structural transformation of many perovskite oxides. This alternative method for thin film fabrication opens the possibility for low temperature fabrication of porous ceramic materials.     

Transparent p-AgCoO2/n-ZnO diode heterojunction fabricated by pulsed laser deposition

Transparent diode heterojunction on ITO coated glass substrates was fabricated using p-type AgCoO₂ and n-type ZnO films by pulsed laser deposition (PLD). The PLD of AgCoO₂ thin films was carried out using the pelletized sintered target of AgCoO₂ powder, which was synthesized in-house by the hydrothermal process. The band gap of these thin films was found to be ∼ 3.89 eV and they had transmission of ∼ 55% in the visible spectral region. Although Hall measurements could only indicate mixed carrier type conduction but thermoelectric power measurements of Seebeck coefficient confirmed the p-type conductivity of the grown AgCoO₂ films. The PLD grown ZnO films showed a band gap of ∼ 3.28 eV, an average optical transmission of ∼ 85% and n-type carrier density of ∼ 4.6 × 10¹⁹ cm^− 3. The junction between p-AgCoO₂ and n-ZnO was found to be rectifying. The ratio of forward current to the reverse current was about 7 at 1.5 V. The diode ideality factor was much greater than 2.     

Reversible wettability of ZnO nanostructured thin films prepared by pulsed laser deposition

This work reports on the photoinduced wettability changes of high quality nanostructured ZnO films grown on Si by pulsed laser deposition (PLD) under different growth parameters. The wetting behavior of the resulting films can be reversibly switched from hydrophobic to hydrophilic, through alternation of UV illumination and dark storage. The kinetics of this wetting transition are studied by monitoring the time evolution of the corresponding contact angles. Finally, the influence of the film properties over the observed wetting response is discussed.     

Piezoelectric coefficient of InN films prepared by radio-frequency sputtering

An interferometric method has been used to measure the piezoelectric coefficient d₃₃ in indium nitride films deposited by radio-frequency sputtering on borosilicate glass coated with gold. This low temperature growth technique has the advantage of being able to produce samples for piezoelectric measurements where the InN film is grown directly on an Au metal back contact, allowing the accurate measurement of the piezoelectric coefficient of the InN layer without any parasitic series resistance. The InN growth conditions are described, and both crystal and optical characterizations of the film are presented. The measured value of the coefficient was found to be 4.0 ± 0.1 pm V^− 1.     

Metal-semiconductor transition in Nb-doped ZnO thin films prepared by pulsed laser deposition

The structural, electrical and optical properties of Nb-doped ZnO films were investigated with different Nb contents (0, 0.15, 0.31, 0.46, 0.62, and 0.94 at.%) in this article. The film with 0.46 at.% Nb content showed the lowest resistivity of 8.95 × 10^− 4 Ω cm and high transmittance about 80% with high c-axis orientation. The undoped ZnO film showed a semiconducting behavior. And Nb-doped ZnO films showed a metal-semiconductor transition (MST), which was connected with localization of degenerate electrons. The films showed metallic conductivity at temperatures closer to the ambient temperature and semiconducting behavior at lower temperatures. It was noted that the NZO films with much lower Nb concentration of 0.15 at.% presented MST compared with other transparent conducting oxides films.     

Effects of ambient oxygen pressures and substrate temperatures in pulsed laser deposited Zn0.85Li0.15O thin films

Li doped zinc oxide Zn_1−xLi_xO (x = 0.15) thin films were grown by using the pulsed laser deposition method. The depositions were done onto Pt(111)/Ti/SiO₂/Si(100) substrate set at temperatures ranging from 300 °C to 700 °C, with varying the ambient O₂ pressure range of 3-20 mTorr. The effects of substrate temperatures and ambient O₂ pressures on the surface morphology and structural properties of the Zn_0.85Li_0.15O thin films were investigated by using the scanning probe microscopy and X-ray diffraction spectra, respectively. Also the chemical structures of the films were investigated by observing the X-ray photoelectron spectra of the core and shallower levels. We observed the deep blue PL emissions centered at about 390 nm (3.20 eV) from the Zn_0.85Li_0.15O thin films. It was investigated with respect to the ambient O₂ pressures during the deposition. It is considered that the deep blue PL emission in the Zn_0.85Li_0.15O thin film may be related to the incorporation of oxygen vacancies.     

Improved dielectric and ferroelectric properties in Ti-doped BiFeO3-PbTiO3 thin films prepared by pulsed laser deposition

Ti-modified thin films of multiferroic 0.72Bi(Fe_1 − xTi_x)O₃-0.28PbTiO₃ (BFPT, x = 0 and 0.02) solid solution were prepared by pulsed laser deposition. The BFPT (x = 0 and 0.02) films possess a tetragonal structure with highly preferential (001) orientation. The effects of the ionic substitution on the properties of BFPT (x = 0 and 0.02) films have been investigated. The leakage current of the BFPT (x = 0.02) thin film is significantly reduced, and the dielectric and ferroelectric properties greatly improved by the aliovalent ionic substitution of Ti⁴⁺ for Fe³⁺. The BFPT (x = 0.02) thin film exhibits a reasonably high remnant polarization P_r with 2P_r up to 90 μC/cm² at 312 kV/cm and a switchable polarization up to 92 μC/cm² at 417 kV/cm.