Epitaxial growth of atomically flat gadolinia-doped ceria thin films by pulsed laser deposition

Epitaxial growth of Ce_0.8Gd_0.2O₂(CGO) films on (001) TiO₂-terminated SrTiO₃ substrates by pulsed laser deposition was investigated using in situ reflective high energy electron diffraction. The initial film growth shows a Stransky–Krastanov growth mode. However, this three-dimensional island formation is replaced by a two-dimensional island nucleation during further deposition, which results in atomically smooth CGO films. The obtained high-quality CGO films may be attractive for the electrolyte of solid-oxide fuel cells operating at low temperature.     

Pulsed laser deposition of oxide thin films

The pulsed laser deposition (PLD) process was studied in detail during oxide thin film growth by constructing a sophisticated PLD chamber combined with an energy-stable excimer laser. It was revealed that the transmitting laser energy at the entrance view port decreased exponentially with deposition runs, roughly by A e^−0.02x%, where A is the original transmission and x is the run number, and transmission loss could become considerable (up to 90%) in 100 deposition runs. In addition, area of the focused spot on the target was found a function of charging high voltage, which is a parameter of excimer laser operation, even through a slit forming rectangular sharp-edge beam profile. Laser energy density is one of the most important parameter governing grown film properties, and therefore accurate laser energy and spot area calibration is vital for reproducible film growth. In course of this study, the importance of spot area as well as the energy density is discussed in the view of deposition rate.     

Pulsed laser deposition of BiCuOSe thin films

Undoped and 10% Ca-doped BiCuOSe thin films are prepared by pulsed laser deposition without ex-situ processing. The influence of the preparation conditions on structure and properties of Bi_0.9Ca_0.1CuOSe thin films on amorphous silica substrates is studied. The highest achieved concentration and mobility of free holes (3.9×10²⁰ cm⁻³ and 3.5 cm²/Vs) was close to that measured in strongly c-axis oriented samples on SrTiO₃ substrates (4.0×10²⁰ cm⁻³ and 7.5 cm²/Vs). The Bi_0.9Ca_0.1CuOSe films on SrTiO₃ show almost temperature-independent Seebeck coefficient and their resistivity increases with increasing temperature. The Seebeck coefficient of undoped BiCuOSe films on SrTiO₃ increases below 150°K, and the resistivity shows a flat plateau centered at this temperature. Optical measurements suggest that BiCuOSe has an indirect bandgap of 0.8 eV and a strong absorption edge at 1.45 eV. Ab-initio calculations of the electronic band structure, effective masses and optical properties of BiCuOSe are also presented.     

Pulsed laser deposition of doped skutterudite thin films

Ca_xCo₄Sb₁₂ skutterudite thin films have been prepared by pulsed laser deposition using a Nd:YAG laser working at 532 or 266 nm of wavelength. Characterization has been carried out by X-ray diffraction, atomic force microscopy and scanning electron microscopy. Emphasis has been put on the difficulty to obtain the skutterudite phase. Influence of the deposition temperature, the way of sticking the substrate, the laser fluence, the base pressure prior to deposition and the laser wavelength has been studied. All parameters revealed to have a drastic effect, and the skutterudite could only be achieved in a very narrow range of temperature and laser fluence, for a given wavelength, showing the importance on how these parameters are measured to ensure reproducible results.     

Pulsed laser deposition of photosensitive a-Si thin films

Si films have been fabricated by pulsed KrF excimer laser deposition (PLD) through the use of various Si targets and deposition conditions. The deposits consisted of droplets and homogeneous films, which were assigned to be crystalline and amorphous silicon, respectively, by the micro Raman scattering measurements. Not only the crystalline but also the amorphous Si part scarcely (<1 atomic %) contained hydrogen regardless of whether or not the films are prepared in the presence of H₂ gas. Conditions were explored to reduce the droplet formation and to produce photosensitive films. Amorphous Si films with photosensitivity (C_ph/C_d) exceeding 10³ were obtained, and they exhibited high stability against light soaking. Thus, PLD is a promising method to fabricate photosensitive and photostable a-Si films.     

Pulsed laser deposition of fluoride glass thin films

The development of integrated waveguide lasers for different applications such as marking, illumination or medical technology has become highly desirable. Diode pumped planar waveguide lasers emitting in the green visible spectral range, e.g. thin films from praseodymium doped fluorozirconate glass matrix (called ZBLAN, owing to the main components ZrF₄, BaF₂, LaF₃, AlF₃ and NaF) as the active material pumped by a blue laser diode, have aroused great interest. In this work we have investigated the deposition of Pr:ZBLAN thin films using pulsed laser radiation of λ = 193 and λ = 248 nm. The deposition has been carried out on MgF₂ single crystal substrates in a vacuum chamber by varying both processing gas pressure and energy fluence. The existence of an absorption line at 210 nm in Pr:ZBLAN leads to absorption and radiative relaxation of the absorbed laser energy of λ = 193 nm preventing the evaporation of target material. The deposited thin films consist of solidified and molten droplets and irregular particulates only. Furthermore, X-ray radiation has been applied to fluoride glass targets to enhance the absorption in the UV spectral region and to investigate the deposition of X-ray treated targets applying laser radiation of λ = 248 nm. It has been shown that induced F-centres near the target surface are not thermally stable and can be easily ablated. Therefore, λ = 248 nm is not suitable for evaporation of Pr:ZBLAN.     

Pulsed laser deposition of molybdenum oxide thin films

Thin films of molybdenum oxide were deposited in vacuum by pulsed laser ablation using a xenon fluoride (351 nm) and a krypton fluoride (248 nm) excimer lasers. The films were deposited on unheated substrates and were post-annealed in air in the temperature range 300–500°C. The structural, morphological, chemical, and optical properties of the films were studied. As-deposited films were found to be dark. The transparency of the films was improved with annealing in air. The films were polycrystalline with diffraction peaks that belong to the orthorhombic phase of MoO₃. The surface morphology of the films showed a layered structure. Both the grain size and surface roughness increased with annealing temperature. The stoichiometry of the films improved upon annealing in air, with the best stoichiometry of MoO_2.95 obtained for films deposited by the XeF laser and annealed at 400°C. Similarly, the best transparency, with a transmittance exceeding 80%, was obtained with the films annealed in the temperature range 400–450°C.     

Pulsed laser deposition of silicate phosphor thin films

Three types of silicate phosphor thin films, emitting in the red-green-blue (RGB) primary colors, were fabricated by pulsed laser deposition, including manganese and lead doped calcium silicate (CaSiO₃:MnPb) for red color, manganese doped zinc silicate (Zn₂SiO₄:Mn) for green color and cerium doped yttrium silicate (Y₂SiO₅:Ce) for blue color. A correlation was observed between photoluminescence intensity with film crystallinity and surface morphology. RGB phosphor thin films with excellent color saturation were obtained. Luminescence mechanisms for these phosphor thin films are discussed.     

Pulsed laser deposition of NdNiO3 thin films

We report the structural and transport properties of NdNiO₃ thin films prepared via pulsed laser deposition over various substrates. The films were well textured and c-axis oriented with good crystalline properties. The electrical resistivity of the films undergoes a metal-insulator transition, depending on the deposition process. Well-defined first order metal-insulator phase transition (T_MI) was observed in the best quality films without high pressure processing. Various growth conditions such as substrate temperature, oxygen pressure and thickness were varied to see their influence on T_MI. Deposition temperature was found to have a great impact on the electrical and structural properties of these films. Further the films deposited on LaAlO₃ substrate were found to be highly oriented with uniform grain size as observed from X-ray diffraction and atomic force microscopy, whereas those on Si substrate were polycrystalline, dense and randomly oriented.     

Pulsed laser deposition of polyhydroxybutyrate biodegradable polymer thin films using ArF excimer laser

We demonstrated the pulsed laser deposition (PLD) of high quality films of a biodegradable polymer, the polyhydroxybutyrate (PHB). Thin films of PHB were deposited on KBr substrates and fused silica plates using an ArF (λ = 193 nm, FWHM = 30 ns) excimer laser with fluences between 0.05 and 1.5 J cm⁻². FTIR spectroscopic measurements proved that at the appropriate fluence (0.05, 0.09 and 0.12 J cm⁻²), the films exhibited similar functional groups with no significant laser-produced modifications present. Optical microscopic images showed that the layers were contiguous with embedded micrometer-sized grains. Ellipsometric results determined the wavelength dependence (λ ∼ 245-1000 nm) of the refractive index and absorption coefficient which were new information about the material and were not published in the scientific literature. We believe that our deposited PHB thin films would have more possible applications. For example to our supposal the thin layers would be applicable in laser induced forward transfer (LIFT) of biological materials using them as absorbing thin films.     

Pulsed laser deposition of multiwalled carbon nanotubes thin films

The physical/chemical properties of multiwalled carbon nanotubes have attracted much interest for applications in different fields, from micro-electronic to coating technology due, in particular, to their peculiar conductivity properties, to their hardness and high resistance to thermal stress. The technology to produce carbon nanotubes thin films with the desired properties, however, is still under development. In this work, we report on multiwalled carbon nanotubes thin films deposited by pulsed laser deposition techniques ablating commercially polystyrene-nanotubes pellets on alumina substrates. MicroRaman spectroscopy and high resolution Transmission Electron Microscopy provide the experimental confirmation that carbon nanotubes-like structures are present on the alumina surface with both minimal morphological damage of the tubes and structural changes induced by laser beam.     

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.     

Pulsed laser deposition of NiMnGa thin films on silicon

Thin films of the magnetic shape-memory (MSM) material NiMnGa have been deposited on Si(100) substrates using pulsed laser deposition. The -–200 300nm-thick films were prepared at substrate temperatures ranging from 450 °C to 650 °C and at different background Ar pressures. Large saturation magnetizations, up to 60% of the bulk value, were measured for the films. Only the films deposited in vacuum or at Ar pressures below 10^-3 mbar and at temperatures between 500 °C and 600 °C were ferromagnetic. The films are mainly crystallized in the austenitic phase and they have a smooth surface with a low droplet density (0.01 m^-2). The magnetization and surface quality are sufficient that the films could be utilized in the realization of thin-film MSM devices. PACS 75.70.Ak     

Pulsed laser deposition process of PLZT thin films using an infrared Nd:YAG laser

Pulsed laser depositions of PLZT thin films were performed using an Nd:YAG (1064 nm) laser. The growths took place in vacuum or in an oxygen background. Room temperature and 500 °C were the used substrate temperatures. The X-ray diffraction analysis revealed a preferential crystallographic orientation in the films grown at room temperature in vacuum. Such result is discussed. The velocity distribution functions of the species in the plasma plume were obtained from a time of flight study using optical emission spectroscopy. The maximums of these distributions functions fall around 10⁶ cm/s, equivalent to an energy range of 18-344 eV. Ionic species of heavy elements (like lead) achieved higher velocities than other lighter species. This result is linked to the creation of an accelerating spatial charge and to the thermal nature of the target material extraction that allows some elements to be released first than others. Chemical state variations of the elements present in the films were analyzed. Under these different growing conditions, lead chemical states varied the most.     

Pulsed laser deposition of bioceramic thin films from human tooth

The possibility of pulsed laser deposition of thin films from human tooth targets was studied, since bioceramic thin film coatings on dental and orthopaedic implants may have their surface characteristics for biointegration improved. Pellets were pressed from tooth powder at different pressures and ablated with pulses of ArF (=193 nm) and KrF (=248 nm) excimer lasers with fluences up to 4.5 and 12 J/cm², respectively. Layers were deposited onto heated (250 °C) titanium, glass, and KBr substrates. The increase of the pellet pressing pressure from 150 to 450 MPa enhanced the roughness of the deposited films. IR spectroscopic measurements showed that the chemical composition of the films were close to that of original tooth material under appropriate fluence. The adherence of the layers to the substrates could be significantly improved by post annealing at 550 °C. PACS 81.15.Fg; 68.55.Jk; 87.68.+z     

Pulsed laser deposition conditions and superconductivity of FeSe thin films

We report the effects of growth conditions on the superconducting properties of FeSe films epitaxially grown on LaAlO₃ substrates by pulsed laser deposition (PLD). Customary materials characterization techniques [X-ray diffraction (XRD), in-situ X-ray photoelectron spectroscopy (XPS), in-situ ultra-violet photoelectron spectroscopy (UPS), and scanning electron microscopy (SEM)] revealed the films had a c-axis oriented tetragonal structure with lattice constants dependent on the growth temperature (varied from 100 to 600°C). The standard four-point probe method was used to measure the resistivity and superconducting transitions. Films grown at 400–550°C showed a clear superconducting onset but no zero resistance down to 2 K. The highest superconducting onset temperature (T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}}) of 8 K was observed in films grown at 500°C and the onset temperature was clearly correlated to the ratio of the lattice constants (c/a). As the thickness of the FeSe films increased from 27 nm to 480 nm, T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}} also increased as the strain in the system was relaxed.     

Pulsed laser deposition of lead-zirconate-titanate thin films and multilayered heterostructures

There is an increasing interest in lead-zirconate-titanate (PZT) based ferroelectric thin film and devices in recent years. Pulsed laser deposition (PLD) technique has been demonstrated to be a versatile and successful tool for the deposition of epitaxial multi-component metal oxide films and heterostructures. This review presents a reasonable understanding of the relationship between PLD processing and composition, crystal structure and orientation of PZT ferroelectric thin films, and heterostructures. Processing-related issues from PLD of PZT thin films and material-integration strategies developed to fabrication of highly oriented or epitaxial PZT thin film based capacitors with excellent ferroelectric properties are discussed in detail. PACS 81.15.Fg; 68.55.Jk; 77.22.Ej     

Pulsed laser deposition of PrFe4Sb12 thin films

Results from a growth and characterization study of PrFe₄Sb₁₂ thin films synthesized by pulsed laser deposition (PLD) are reported. Films were grown under a variety of conditions where substrate temperature, annealing schedule, and laser power were optimized to produce single phase material. Various substrates were used for film growth. X-ray diffraction data indicate that the films are primarily single phase with very small amounts of antimony inclusions. The high quality of the films is reflected in electrical resistivity vs temperature data which are consistent with previous results for bulk polycrystalline and single crystal specimens. PACS 71.27.+a; 73.50.-h; 81.15.Fg; 68.55.JK     

Pulsed laser deposition of Sr2FeMoO6 thin films

The effect of various deposition conditions and after-growth protocols on the magnetic and transport properties of Sr₂FeMoO₆ films has been explored. It is found that the saturation magnetization and the magnetoresistance (MR) are dominated by the degree of cationic order, and the strain effects are clearly evidenced in a lower T_C. The after-growth annealing of the films and the deposition of a buffer layer has been found to relax the film strains. This translates into a clear increase of the measured low-field magnetoresistance ratios.     

Pulsed laser deposition and characterization of multilayer metal-carbon thin films

Cobalt-DLC multilayer films were deposited with increasing content of cobalt, keeping carbon content constant by pulsed laser deposition technique. A cobalt free carbon film was also deposited for comparison. Excimer laser was employed to ablate the materials onto silicon substrate, kept at 250 °C, while post-deposition annealing at 400 °C was also performed in situ. The formation of cobalt grains within the carbon matrix in Co-DLC films can be seen through scanning electron and atomic force micrographs while no grains on the surface of the cobalt-free DLC film were observed. Raman spectra of all the films show D- and G-bands, which is a confirmation that the films are DLC in nature. According to Vibrating sample magnetometer (VSM) measurements, the DLC films with cobalt revealed ferromagnetic behaviour whereas the cobalt free DLC film exhibited diamagnetic behaviour. The pure DLC film also shows ferromagnetic nature when diamagnetic background is subtracted. Spectroscopic Ellipsometry (SE) analysis showed that the optical band gaps, refractive indices and extinction coefficients of Co-DLC films can be effectively tuned with increasing content of cobalt.