V. Nelea

Pulsed laser deposition of hydroxyapatite thin films on Ti-5Al-2.5Fe substrates with and without buffer layers

We present a method for processing hydroxyapatite (HA) thin films on Ti-5Al-2.5Fe substrates. The films were grown by pulsed laser deposition (PLD) in vacuum at room temperature, using a KrF∗ excimer laser. The amorphous as-deposited HA films were recrystallized in ambient air by a thermal treatment at 550°C. The best results have been obtained when inserting a buffer layer of ceramic materials (TiN, ZrO2 or Al2O3). The films were characterized by complementary techniques: grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), cross-section transmission electron microscopy (XTEM), SAED, energy dispersive X-ray spectroscopy (EDS) and nanoindentation. The samples with buffer interlayer preserve the stoichiometry are completely recrystallized and present better mechanical characteristics as compared with that without buffer interlayer.

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10−2–10−1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca2P2O7, Ca2P2O9 and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.

Mechanical properties improvement of pulsed laser-deposited hydroxyapatite thin films by high energy ion-beam implantation

Major problems in the hydroxyapatite (HA), Ca 5 (PO 4 ) 3 OH, thin films processing still keep the poor mechanical properties and the lack in density. We present a study on the feasibility of high energy ion-beam implantation technique to densify HA bioceramic films. Crystalline HA films were grown by pulsed laser deposition (PLD) method using an excimer KrF + laser (λ = 248 nm, τ FWHM > 20 ns). The films were deposited on Ti-5Al-2.5Fe alloys substrates previously coated with a ceramic TiN buffer layer. After deposition the films were implanted with Ar + ions at high energy. Optical microscopy (OM), white light confocal microscopy (WLCM), grazing incidence X-ray diffraction (GIXRD) and Berkovich nanoindentation in normal and scratch options have been applied for the characterization of the obtained structures. We put into evidence an enhancement of the mechanical characteristics after implantation, while GIXRD measurements confirm that the crystalline structure of HA phase is preserved. The improvement in mechanical properties is an effect of a densification after ion treatment as a result of pores elimination and grains regrowth.

Sr-ferrite thin films grown on sapphire by pulsed laser deposition

High-quality epitaxial strontium-hexaferrite (SrFe12O19) thin films were grown by pulsed laser deposition (PLD) on c-cut sapphire using KrF∗ excimer laser at a fluency of 2 J/cm2 and substrate temperature of 800°C in 100 mTorr oxygen environment. The X-ray diffraction (XRD) and morphology analyzes showed films with excellent crystalline structure and flat surface. The thickness was found to influence considerably the surface morphology and magnetic properties of the as-deposited films. The highest orientation and the best morphology with smooth surface and fine grain structure was obtained for the film having a thickness of 750 nm. The highest coercive force of 1453 Oe was measured for this film in perpendicular to the plane direction.

Pulsed laser deposition of lithium niobate: a parametric study

We report the deposition of high optical quality LiNbO 3 thin films on Si(111) substrates by pulsed laser ablation using a KrF * excimer laser (λ = 248 nm, τ = 20 ns) source. Experiments have been conducted in oxygen at 5-20 Pa. Si(111) collectors were uniformly heated at 500-700°C. Some of the as-deposited collectors were submitted to an in-situ thermal treatment in oxygen (10 3 -10 4 Pa) at the same temperature. The deposited thin films were characterised by grazing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM) and spectroscopic ellipsometry (SE). Our LiNbO 3 thin films, achieved at relatively low temperature (550°C), are the first textured and high optical quality pulsed laser deposited films on Si.

Pulsed-laser deposition of hydroxyapatite thin layer on Ti alloy collectors with and without buffer interlayers

Hydroxyapatite (HA), Ca10(PO4)6(OH)2, is the best substitute of the human bone. On the other hand, HA stands for more than 70% from the composition of the bone tissue. We note for HA is friable. Accordingly, it exhibits a very poor mechanical tenure and cannot be used as bulk ceramic for the manufacturing of prostheses. A solution was conceived to surpass this difficulty which resorts to the deposition of HA thin layers on prostheses or pivots of Ti and Ti alloys. The biological tissues enter under these conditions in contact with HA which is perfectly biocompatible. We previously performed Pulsed Laser Deposition (PLD) experiments on Ti, KCl and KBr substrates. We obtained the stoichiometric transfer of HA by PLD in vacuum or by RPLD in (1 - 50) Pa of oxygen, followed by a heat treatment in air. We use an excimer laser source ((lambda) equals 248 nm, (tau) FWHM >= 20 ns). The incident laser fluence was set an 0.8 Jcm-2. We report herewith the deposition of a more elaborate structure introducing a buffer interlayer between the Ti substrate and the HA coating in order to improve the quality of HA films and to prevent the diffusion of metal atoms into the deposited layer. The layer was obtained by RPLD from a Ti target in a slow flux of air having a dynamic pressure between the range (4 - 6) Pa. The deposited structures were characterized by electron microscopy (TEM, SAED), X-ray diffraction (XRD) and energy disversive X-ray spectroscopy (EDS) analyses.

Growth of polycrystalline hydroxyapatite thin films by pulsed laser deposition and subsequent heat treatment in air

Hydroxyapatite (HA), Ca10(PO4)6(OH)2, is the primary constituent of the human bone and one of the best biocompatible materials. In this work we developed a simple method for the deposition of polycrystalline HA thin films onto various collectors including substrates of medical interest (e.g. Ti). We proceeded by the pulsed laser deposition of HA targets onto parallel collectors placed at (2-5) cm in vacuum. After deposition the films were heated in air at 500 degree(s)C for 30 minutes. The heated film has a structure which appears in electron diffraction as identical to the structure of the base material. The obtained films are uniform and very adherent to the substrate. The P/Ca atomic ratio, determined by energy dispersive X-ray analysis, was found to be close to that characteristic to HA, for the post-depositing heated films.

High-optical-quality LiNbO3 thin films obtained by pulsed laser deposition

We report the successful growth of high optical quality LiNbO3 thin films (high birefringence and good transparency over the entire visible spectral range) by pulse laser deposition (PLD) on Si substrates. PLD of a LiNbO3 single-crystal target was carried out using a KrF* excimer laser ((lambda) equals 248 nm, E equals 80 mJ, (tau) equals 20 ns, v equals 2 Hz). The thin films have been deposited in oxygen and, for some of them, a thermal treatment has been applied in an oxygen atmosphere. The thin films have been characterized by grazing incidence X-ray diffraction, spectroscopic ellipsometry and Fourier transform infrared spectroscopy.

Hydroxyapatite thin films growth by pulsed laser deposition: effects of the Ti alloys substrate passivation on the film properties by the insertion of a TiN buffer layer

Hydroxyapatite (HA), Ca5(PO4)3OH, is now widely used in stomatology and orthopedic surgery. Due to a good biocompatibility combined favorable bioactivity make as HA to be considered as a challenge to successful bone repair. We grow HA thin films on Ti-5Al-2.5Fe alloy substrate by pulsed laser deposition (PLD) technique. The films were deposited in vacuum at room temperature using a KrF excimer laser ((lambda) equals 248 nm, (tau) FWHM >= 20 ns). After deposition the HA films were annealed at 550 degree(s)C in ambient air. The insertion of a bioinert TiN buffer layer at the HA film-metallic substrate interface was studied in terms of HA film microstructure and mechanical properties. SEM, TEM and SAED analysis structurally characterized films. The mechanical properties were evaluated by nanoindentation tests in static and scratch modes. Films with TiN interlayer contain uniquely crystalline HA phase and present better mechanical characteristics as compared with those deposited directly on Ti-alloy substrate.

Influence of substrate orientation on the characteristics of Sr-ferrite thin films obtained by pulsed laser deposition

We investigated the effect of substrate orientation and film thickness on the microstructure and magnetic properties of Sr- ferrite films grown on (0001) and 1102) sapphire substrates by pulsed laser deposition (PLD). The films grown on (1102) sapphire displayed a presence of various magnetic phases, including SrFe12O19 Fe2O3 and Fe3O4. The single hexaferrite phase was obtained in GIXRD at 1 degree and 5 degree for the thicker film. The structure measurements showed that all films on (0001) sapphire were single-phase c- axis oriented hexaferrites. The highest in-plane coercive force of 2.5 kOe was detected for the thicker film grown on (1102) sapphire. These films exhibit the highest in-plane squareness. The saturation magnetization of the films on (0001) sapphire rose when the film thickness was reduced.