Pulsed laser deposition of silicon-substituted hydroxyapatite coatings

Thin films of Si-substituted hydroxyapatite (Si-HA) were deposited on Si and Ti substrates by pulsed laser deposition (PLD), in the presence of a water vapour atmosphere. The PLD ablation targets were made with different mixtures of commercial carbonated HA and Si powder, in order to produce the Si-HA thin films. The physicochemical properties of the coatings and the incorporation of the Si into the HA structure was studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Si atoms were successfully incorporated into the HA structure, and were found to be in the form of SiO₄⁴⁻ groups, principally displacing carbonate groups off the HA structure.     

Properties of pulsed laser deposited fluorinated hydroxyapatite films on titanium

Fluorinated hydroxyapatite coated titanium was investigated for application as implant coating for bone substitute materials in orthopaedics and dentistry. Pulsed laser deposition technique was used for films preparation. Fluorinated hydroxyapatite target composition, Ca₁₀(PO₄)₆F_1.37(OH)_0.63, was maintained at 2 J/cm² of laser fluence and 500-600 °C of the substrate temperature. Prepared films had a compact microstructure, composed of spherical micrometric-size aggregates. The average surface roughness resulted to be of 3 nm for the film grown at 500 °C and of 10 nm for that grown at 600 °C, showing that the temperature increase did not favour the growth of a more fine granulated surface. The films were polycrystalline with no preferential growth orientation. The films grown at 500-600 °C were about 8 μm thick and possessed a hardness of 12-13 GPa. Lower or higher substrate temperature provides the possibility to obtain coatings with different fine texture and roughness, thus tayloring them for various applications.     

Ellipsometric study of nanostructured carbon films deposited by pulsed laser deposition

When depositing carbon films by plasma processes the resulting structure and bonding nature strongly depends on the plasma energy and background gas pressure. To produce different energy plasma, glassy carbon targets were ablated by laser pulses of different excimer lasers: KrF (248 nm) and ArF (193 nm). To modify plume characteristics argon atmosphere was applied. The laser plume was directed onto Si substrates, where the films were grown. To evaluate ellipsometric measurements first a combination of the Tauc-Lorentz oscillator and the Sellmeier formula (TL/S) was applied. Effective Medium Approximation models were also used to investigate film properties. Applying argon pressures above 10 Pa the deposits became nanostructured as indicated by high resolution scanning electron microscopy. Above ~ 100 and ~ 20 Pa films could not be deposited by KrF and ArF laser, respectively. Our ellipsometric investigations showed, that with increasing pressure the maximal refractive index of both series decreased, while the optical band gap starts with a decrease, but shows a non monotonous course. Correlation between the size of the nanostructures, bonding structure, which was followed by Raman spectroscopy and optical properties were also investigated.     

ITO thin films deposited by advanced pulsed laser deposition

Indium tin oxide thin films were deposited by computer assisted advanced PLD method in order to obtain transparent, conductive and homogeneous films on a large area. The films were deposited on glass substrates. We studied the influence of the temperature (room temperature (RT)-180 °C), pressure (1-6 × 10^− 2 Torr), laser fluence (1-4 J/cm²) and wavelength (266-355 nm) on the film properties. The deposition rate, roughness, film structure, optical transmission, electrical conductivity measurements were done. We deposited uniform ITO thin films (thickness 100-600 nm, roughness 5-10 nm) between RT and 180 °C on a large area (5 × 5 cm²). The films have electrical resistivity of 8 × 10^− 4 Ω cm at RT, 5 × 10^− 4 Ω cm at 180 °C and an optical transmission in the visible range, around 89%.     

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%.     

Application of pulsed laser deposited zinc oxide films to thin film transistor device

Transparent zinc oxide (ZnO) thin films were deposited on various substrates using a pulsed laser deposition (PLD) technique. During the PLD, oxygen pressure and substrate temperature were varied in order to find an optimal preparation condition of ZnO for thin film transistor (TFT) application. Dependence of optical, electrical and crystalline properties on the deposition conditions was investigated. The ZnO thin films were then deposited on SiN/c-Si layer structures in order to fabricate a TFT device. The pulsed laser deposited ZnO films showed a remarkable TFT performance: field effect mobility (μ_FE) of 2.4-12.85 cm²/V s and ratio of on and off current (R_on/off) in 2-6 order range. Influence of ZnO preparation conditions on the resulting TFT performance was discussed.     

Investigation of diamond-like carbon/silicon heterojunctions deposited by pulsed Nd:YAG laser

Diamond-like carbon (DLC) films were deposited on p-type silicon (Si-100) substrates by using a pulsed Nd:YAG laser for the ablation of a pyrolytic graphite target at a background pressure of 10⁻⁶ Torr. For a fixed distance of 3 cm between the target and substrate, samples of DLC/Si heterojunction were prepared for two different laser wavelengths of 355 nm and 1064 nm. All DLC films showed typical D and G bands in their Raman spectra. DLC films were also deposited on glass substrates for resistivity measurement by four-point probe. The electrical properties for DLC/Si heterojunctions were analyzed current-voltage measurement at room temperature in the dark and also under illumination. The dependencies of the electrical characteristics on the depositing parameters were discussed.     

Characterization of pulsed laser deposited hydrogenated amorphous silicon films by spectroscopic ellipsometry

The wide absorption band of hydrogenated amorphous silicon (a-Si:H) is being realized as a key component of solar cells on glass. In this study, a-Si:H films were prepared by reactive pulsed laser deposition onto silicon and glass substrates. Ellipsometry showed that the optical properties of the films are effectively independent on the choice of substrate. According to the optical properties, the character of the films changes from amorphous silicon to dielectric as the hydrogen background pressure increases from 0 to 25 Pa. This observation was attributed to oxygen incorporation indicated by Rutherford Backscattering Spectrometry. Furthermore, a refractive index gradient in depth was revealed, which was attributed to the oxygen concentration gradient.     

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.     

Wear resistant carbon coatings deposited at room temperature by pulsed laser deposition method on 7075 aluminum alloy

This paper presents the results of a study on the influence of the parameters (pressure and composition of the process atmosphere) of the deposition of carbon coatings on aluminum alloy 7075 by the PLD method on their selected mechanical properties. The study correlated the sp²/sp³ ratio and the relative fraction of CH₂/CH₃ groups formed during coating deposition with the hardness distribution, adhesion, friction and wear resistance of the analyzed systems. Carbon coatings with a titanium interlayer were found to be characterized by the highest adhesion (Lc = 6.9 mN). The introduction of nitrogen at the stage of the deposition of both the interlayer and/or the final carbon layer decreased the maximum adhesion of the coating, while, in this system, the highest value of adhesion Lc was obtained in the presence of nitrogen at the stage of the deposition of both the TiN interlayer and the a:CN carbon coating (Lc = 4.6 mN).     

The process of electrochemical deposited hydroxyapatite coatings on biomedical titanium at room temperature

Calcium phosphate (CaP) ceramics, especially hydroxyapatite (HA), have received much attention and have been clinically applied in orthopaedics and dentistry due to their excellent biocompatibility. Among several methods for preparing HA coating, electrochemical deposition is a relatively new and possible process. However, documented electrochemical processes were conducted at elevated temperature. In this study, uniform HA coatings have been directly deposited on titanium at room temperature. X-ray diffractometry (XRD) results demonstrated that dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) was the main component of the coating deposited at lower current densities (1 and 5 mA/cm²). HA structure was obtained at current density above 10 mA/cm² and remained stable after heat treatment at 100–600 °C for 1 h. Part of HA phase was transformed into β-TCP and became a biphasic calcium phosphate coating after annealing at 700 °C. Scratch tests showed that HA coating was not scraped off until a shear stress of 106.3 MPa. Coatings deposited at room temperature exhibited stronger adhesion than those at elevated temperature. HA coating revealed a dense inner layer and rough surface morphology which could fulfill the requisition of implant materials and be adequate to the attachment of bone tissue.     

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.     

Iridium thin films deposited via pulsed laser deposition for future applications as transition-edge sensors

The University of Miami has recently started developing and studying high-resolution microcalorimeters operating near 100 mK for X-ray and particle physics and astrophysics. These detectors will be based on Transition Edge Sensors technology fabricated using iridium thin films deposited via the Pulsed Laser Deposition technique. We report here the preliminary result of the room temperature characterization of the Ir thin films, and an overview of future plans to use the films as transition edge sensors.     

Synthesis and properties of close packed ZnO:Al submicro-rods deposited by pulsed laser ablation

Al-doped ZnO (AZO) semiconducting thin films consisting of perpendicularly aligned submicro-rods were deposited on silicon substrate by conventional pulsed laser ablation. No catalyst was used in this process. It was found that the rod structure can be grown at relatively high oxygen pressures (1-20 Torr) and relatively high substrate temperatures (550-700 °C). Low resistivity and high carrier concentration can be obtained in these Al-doped ZnO rods with relatively high Al concentrations. Increasing Al doping reduces the electric resistivity and increase carrier concentration. The photoluminescence property measurement indicates an increased UV emission with a small amount Al doping and reduced UV emission with further increase of Al concentration.     

Spatial spectral evolution in pulsed laser deposited lead-germanate thin films by micro-infrared spectroscopy

Lead-germanate thin films were developed on silicon substrates by pulsed laser deposition from bulk glassy targets of composition 0.4PbO-0.6GeO₂, and micro-infrared transmittance measurements were performed to assess the state of the grown films. Measurements across the radius of films revealed surprisingly large spectral changes, reminiscent of lead-oxide variations in corresponding bulk glasses. To search for the origin of this effect, the infrared spectra were simulated by employing the rigorous expression for the transmittance of a bilayer system to take into full account multiple internal reflections in both thin film and substrate. The results showed that the profiles of the experimental spectra can be accurately described by using as input the complex refractive index of the target glassy material and by considering film thickness variations from the center to the edges of the film. This work demonstrates the strong influence of optical effects on the infrared spectra of thin films, and manifests also the effectiveness of infrared spectroscopy when coupled with rigorous calculations to characterize the structure of thin films.     

A parametric study of AlN thin films grown by pulsed laser deposition

High quality AlN thin films were grown at 200–450°C on sapphire substrates by laser ablation of Al targets in nitrogen reactive atmosphere. The nitrogen pressure was varied between 10⁻³ and 10⁻¹ mbar. The reactive gas pressure during irradiation and the temperature of the substrate were found to essentially influence the quality of the layers. X-ray diffraction analysis evidenced the formation of highly orientated layers for a very restrictive set of parameters. Other analysis techniques, like X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, optical transmission spectroscopy have been used to evidence the good stoichiometry and purity of the films. The characteristics of these films were compared with those of AlN thin films deposited in similar experimental conditions, on Si (100) and Si (111) substrates.     

Structural properties of cobalt ferrite thin films deposited by pulsed laser deposition: Effect of the reactive atmosphere

Cobalt ferrite thin films have been elaborated by pulsed laser ablation of a CoFe₂ metallic target on Si (100) substrates. The films were deposited at low temperature (300 °C) in various pressures of two different reactive atmospheres (O₂/N₂, 20:80 and O₂). We present the influence of the nature of the reactive gas and of the deposition pressure on the crystallisation. It has been shown that a strong (111) preferential orientation is obtained for intermediate pressures of the O₂/N₂ reactive gas. The degree of orientation is higher for the O₂/N₂ mixture than for pure O₂. This behaviour is explained in terms of kinetic energy of the deposited species.     

Roughness evolution in Ga doped ZnO films deposited by pulsed laser deposition

We analyze the morphology evolution of the Ga doped ZnO(GZO) films deposited on quartz substrates by a laser deposition system. The surface morphologies of the film samples grown with different times are measured by the atomic force microscope, and they are analyzed quantitatively by using the image data. In the initial stage of the growth time shorter than 8 min, our analysis shows that the GZO surface morphologies are influenced by such factors as the random fluctuations, the smoothening effects in the deposition, the lateral strain and the substrate. The interface width uw(t) and the lateral correlation length ξ(t) at first decrease with deposition time t. For the growth time larger than 8 min, w(t) and ξ(t) increase with time and it indicates the roughening of the surface and the surface morphology exhibits the fractal characteristics. By fitting data of the roughness w(t) versus deposition time t larger than 4 min to the power-law function, we obtain the growth exponent β is 0.3; and by the height-height correlation functions of the samples to that of the self-affine fractal model, we obtain the value of roughness exponent α about 0.84 for all samples with different growth time t.     

AFM surface analysis of ZnO layers prepared by pulsed laser deposition at different oxygen pressures

Polycrystalline thin films of zinc oxide were deposited by pulsed laser deposition onto silicon substrates at different oxygen partial pressures in the range of 1-35 Pa. For ablation of the sintered zinc oxide target a pulsed Nd:YAG laser was used. Other processing parameters such as laser pulse energy, pulse repetition rate, substrate temperature and deposition pressure were identical. The effect of oxygen pressure on the structural properties of the films was systematically studied by using atomic force microscopy. The surface morphology, average roughness S_a, root mean square S_q, and mean size of grains on selected places with 2 × 2 μm² area of prepared samples were evaluated. Detailed structural analysis confirmed that partial oxygen pressure leads to the modification of surface morphology. Mean grain size in height and lateral direction decreases with raising oxygen pressure from 1 to 5 Pa while the further increase of oxygen pressure from 5 to 35 Pa results in grain size enlargement. The zinc oxide film formed at oxygen partial pressure 5 Pa shows smallest values of evaluated parameters (S_a = 0.6 nm, S_q = 0.7 nm and mean size of grains 50 nm).