Showing papers on "Pulsed laser deposition published in 1992"

Fatigue and retention in ferroelectric Y‐Ba‐Cu‐O/Pb‐Zr‐Ti‐O/Y‐Ba‐Cu‐O heterostructures

Abstract: Fatigue and retention characteristics of ferroelectric lead zirconate titanate thin films grown with Y‐Ba‐Cu‐O(YBCO) thin‐film top and bottom electrodes are found to be far superior to those obtained with conventional Pt top electrodes. The heterostructures reported here have been grown in situ by pulsed laser deposition on yttria‐stabilized ZrO2 buffer [100] Si and on [001] LaAlO3. Both the a‐ and c‐axis orientations of the YBCO lattice have been used as electrodes. They were prepared using suitable changes in growth conditions.

Pulsed laser deposition of diamond‐like carbon films

Abstract: Carbon thin films have been prepared by 248 nm excimer laser vaporization of graphite targets. The effect of a variety of process parameters on the film properties is investigated. Deposition at or below room temperature yields diamond‐like films with low hydrogen content, high optical transmission, and high resistivity. Electron energy loss spectra indicate sp3 bond fractions of 70–85%. Detailed analyses of the pseudodielectric functions, measured using spectroscopic ellipsometry, show the films to have normal dispersion and an index of refraction of 2.5 in the visible wavelength region. The effects of a low pressure hydrogen background and the use of auxiliary pulsed and dc plasma enhancements are also examined.

Laser deposition of biaxially textured yttria‐stabilized zirconia buffer layers on polycrystalline metallic alloys for high critical current Y‐Ba‐Cu‐O thin films

Abstract: Pulsed laser deposition of yttria‐stabilized zirconia (YSZ) layers on polycrystalline metallic alloy substrates is used to produce an intermediate layer for YBa2Cu3O7−δ (YBCO) thin‐film growth. The desired (001) YSZ texture is obtained at 1.0 mTorr oxygen pressure and 70 °C. Significant improvement in (001) texturing is demonstrated by using an ion beam to assist growth. Argon‐ion‐assisted growth produces layers with alignment of the in‐plane crystal axes in addition to the (001)‐normal texture. Highly c‐axis‐oriented biaxially aligned YBCO thin films can be deposited on these layers, with Tc(R=0)=92 K and Jc (77 K, B=0 T)=6×105 A/cm2 and Jc (77 K, 0.4 T)=8×104 A/cm2. With further improvement of the YSZ texture, the YBCO current‐carrying capacity of films on polycrystalline metallic alloys may approach that of films on single‐crystal substrates.

Epitaxial growth of TiN films on (100) silicon substrates by laser physical vapor deposition

Abstract: We report epitaxial growth of TiN films having low resistivity on (100) silicon substrates using pulsed laser deposition method. The TiN films were characterized using x‐ray diffraction, Rutherford backscattering, four‐point‐probe ac resistivity, high resolution transmission electron microscopy and scanning electron microscopy techniques and epitaxial relationship was found to be 〈100〉 TiN ∥ 〈100〉 Si. TiN films showed 10%–20% channeling yield. In the plane, four unit cells of TiN match with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides a new mechanism of epitaxial growth in systems with large lattice misfits. Four‐point‐probe measurements show characteristic metallic behavior of these films as a function of temperature with a typical resistivity of about 15 μΩ cm at room temperature. Implications of low‐resistivity epitaxial TiN in silicon device fabrication are discussed.

Method and apparatus for low temperature, low pressure chemical vapor deposition of epitaxial silicon layers

Abstract: A method and apparatus for depositing single crystal, epitaxial films of silicon on a plurality of substrates in a hot wall, isothermal deposition system is described. The deposition temperatures are less than about 800° C., and the operating pressures during deposition are such that non-equilibrium growth kinetics determine the deposition of the silicon films. An isothermal bath gas of silicon is produced allowing uniform deposition of epitaxial silicon films simultaneously on multiple substrates. This is a flow system in which means are provided for establishing an ultrahigh vacuum in the range of about 10-9 Torr prior to epitaxial deposition. The epitaxial silicon layers can be doped in-situ to provide very abruptly defined regions of either n- or p-type conductivity.

Off-axis laser deposition of YBa2Cu3O7-δ thin films

Abstract: We report on YBa2Cu3O7−δ thin‐film preparation by a new laser deposition geometry, the so‐called off‐axis laser deposition. Combined with radiation‐based substrate heating, this results in c‐axis oriented, epitaxial YBa2Cu3O7−δ thin films with critical current densities above 106 A/cm2 at 77 K and zero field and an exceptionally good surface quality, with complete absence of the otherwise observed laser droplets. As proved by atomic force microscopy, the surface roughness is <80 A over an area of at least 10×10 μm2. Using this off‐axis geometry it is possible to coat both sides of a substrate simultaneously, providing a one‐step process in double‐sided thin‐film deposition. Both YBa2Cu3O7−δ films on the substrate show identical superconducting properties.

Pulsed Laser Deposition

Abstract: Research on materials grown by pulsed laser deposition, or PLD, has experienced phenomenal growth since late 1987 when T. Venkatesan (one of the authors for this issue) and co-workers pointed out that extreme nonequilibrium conditions created by pulsed laser melting of YBaCuO allowed in-situ preparation of thin films of this high transition temperature (Tc) superconducting material. Since then, PLD has emerged as the primary means for high throughput deposition of high-quality superconducting thin films for research and devices. This probably came as no surprise to J.T. Cheung (another of this issue’s authors), who performed original research in this area and tirelessly labored during the 1980s to convince a skeptical audience of the advantages of PLD. Along with the success of PLD in the arena of high-temperature superconductivity, however, is the explosion of activity in the deposition of many other materials, made possible by the unique features of pulsed laser deposition, materials previously not amenable to in-situ thin film growth. Creative minds reasoned that since PLD can deposit a demanding, complex material such as the perovskite structure Y1Ba2Cu3O7-δ, why not other perovskites or multicomponent oxide materials? It also turns out that the range of properties of multicomponent oxides is virtually limitless. They can be metallic, insulating, semiconducting, biocompatable, superconducting, ferroelectric, piezoelectric, and so on. One is not limited to the properties of elements or binary compounds on which the electronics and microelectronics industries are based. Indeed, in a recent review of hybrid ferromagnetic- semiconductor structures, G. Prinz states, “… there has been little work devoted to incorporating magnetic materials into planar integrated electronic (or photonic) circuitry there are potential applications that have no analog in vacuum electronics but that remain unrealized, awaiting the development of appropriate materials and processing procedures.” In pulsed laser deposition, we may well have in hand the “appropriate processing procedure” to deposit sequential epitaxial layers of high quality materials that possess profoundly different properties.

Pulsed laser deposition of hydroxylapatite thin films on Ti-6Al-4V

Abstract: Pulsed laser deposition was used to deposit thin films of calcium hydroxylapatite (Ca10(PO4)6(OH)2), or HA, on polished substrates of Ti-6Al-4V. Thin films of pure, crystalline HA, uncontaminated by other calcium phosphate phases, were deposited over a range of temperatures between 400 and 800°C. The HA films were polycrystalline with a preferred (001) crystallographic orientation, as determined by transmission electron microscopy and x-ray diffraction. Adhesion of the HA films to the Ti-6Al-4V substrates was excellent when films were deposited at temperatures ≤600°C; in a scratch test, mean pressures of ca. 1010 Nm−2 produced conformational cracking in a film deposited at 600°C, but no decohesion from the substrates.

Epitaxial growth of MgO on GaAs(001) for growing epitaxial BaTiO3 thin films by pulsed laser deposition

Abstract: MgO buffer layers were deposited on GaAs by pulsed laser deposition for epitaxial growth of BaTiO3. MgO was grown epitaxially on GaAs for the first time; the orientation is (001) on GaAs(001). The best crystallographic quality was obtained at 350 °C in 5×10−6 Torr O2. BaTiO3 films with (001) orientation grew epitaxially on MgO/GaAs. The in‐plane epitaxial relationship was BaTiO3[100]∥ MgO[100]∥ GaAs[100] in spite of a large lattice mismatch (25.5%) between MgO and GaAs.

Laser Ablation of Electronic Materials: Basic Mechanisms and Applications

Abstract: Historical Overview. First ages of the coherent electromagnetic waves generation applied to new materials transfer processes named laser ablation (J.-F. Eloy). I. Mechanisms, Spectroscopy and Diagnostics. Electron emission by laser irradiated surfaces (G. Petite et al.). Laser-ablation: Fundamentals and recent developments (D. Bauerle et al.). Laser ablation of solids: Basic principles and physical effects (M. von Allmen). Comparison of the ablation of dielectrics and metals at high and low laser powers (R.W. Dreyfus). Effects of ambient background gases on YBCO plume propagation under film growth conditions: Spectroscopic, ion probe, and fast photographic studies (D.B. Geohegan). Picosecond laser ablation of mono and multicomponent targets (W. Marine et al.). Laser ablation dynamics of superconductors: Photoacoustic and spectroscopic studies (P.E. Dyer et al.). Creation mechanism of a laser-plasma in front of a solid in an ambient gas (C. Boulmer-Leborgne et al.). Dynamics of laser ablation of high Tc superconductors and semiconductors and a new method for growth of films (K. Murakami). Plasma formation from laser-target interaction Basic phenomena and applications to superconducting thin film deposition (C. Champeaux et al.). Analytical tools using laser ablation (J.F. Muller et al.). II. Laser Ablation and Etching. Ultraviolet laser interactions with polymer surfaces in the microsecond regime: The photokinetic effect (R. Srinivasan). Surface modification of polymers with excimer lasers and its applications (A. Yabe, H. Niino). 248 nm laser ablation of chlorinated copper and CuCl surfaces (S. Kuper et al.). Surface modification of polymers and ceramics induced by excimer laser radiation (D.W. Thomas et al.). Polishing of diamond films by light (V.N. Tokarev et al.). Laser ablation and laser etching (J. Boulmer et al.). Excimer laser projector for materials processing applications (M.C. Gower, P.T. Rumsby). III. Thin Film Deposition and Materials Synthesis. Laser ablation synthesis and properties of epitaxial superconducting superlattices (D.H. Lowndes et al.). In-situ preparation of High thin films by pulsed laser deposition (H.-U. Habermeier). Laser ablation of BiSrCaCuO films (J. Perriere). Characterization of thin films of superconducting BiSrCaCuO and YBaCuO produced by laser ablation and spectroscopic analysis of intermediate species (A. Giardini Guidoni et al.). Growth of YBCO superconducting thin films (D. Chambonnet et al.). The unique applications of pulsed laser deposition to the epitaxial growth of semiconductor films (J.T. Cheung, H. Sankur). Laser ablation for the synthesis of oxides (F. Beech et al.). Influence of ambient gas and substrate temperature in preparation of silicon dioxide films by laser ablation (A. Slaoui et al.).

Preparation of thin films

Abstract: Vacuum Evaporation Sputtering Ion Beam and Ion-Assisted Deposition Reactive Deposition Techniques Ionized Cluster Beam Methods Chemical Methods of Film Deposition Epitaxial Film Deposition Techniques Other Methods of Film Deposition Summary

Pulsed laser deposition of epitaxial BaFe12O19 thin films

Abstract: Epitaxial thin films of barium hexaferrite (BaFe12O19) have been fabricated by the pulsed laser deposition technique on basal plane sapphire. Structural studies reveal the films to be predominantly single phase and crystalline, with the c axis oriented perpendicular to the film plane. The magnetic parameters deduced from vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are close to the parameters associated with bulk materials. Post annealing of the films reduced the FMR linewidth by more than a factor of 3 so that it compares reasonably well with single‐crystal films. The derivative FMR linewidth was measured to be 66 Oe at 58 GHz and 54 Oe at 86 GHz. Spin‐wave‐like modes have been observed for the first time in barium ferrite films. The deduced exchange stiffness constant of 0.5×10−6 ergs/cm is in reasonable agreement with recent calculations.

Structure of As‐Deposited LPCVD Silicon Films at Low Deposition Temperatures and Pressures

Abstract: In this work we studied the effect of the deposition temperature, total pressure, source gas dilution, and deposition rate on the structure of the as‐deposited silicon films. Depositions were performed by low pressure chemical vapor deposition (LPCVD) in the temperature range of 530 to 600°C and in the pressure range of 2 to 300 mTorr. For a fixed deposition temperature a phase transition from polycrystalline to amorphous silicon was shown to occur when the deposition rate exceeded a critical value. The critical value for the deposition rate was found to depend only upon the deposition temperature and to decrease as the temperature was decreased. By controlling the rate, as‐deposited polycrystalline silicon was obtained by conventional LPCVD at temperatues as low as 530°C. A relationship between the deposition rate and the partial pressure of the source gas was established via a kinetic model for the decomposition of silane and used to provide a simple model for the dependence of the structure of the as‐deposited silicon films upon the deposition parameters. This model was subsequently used to provide guidelines for both the expected structure of the as‐deposited films and the grain size of the as‐deposited polycrystalline silicon films over an extensive range of deposition conditions.

Correlation between target‐substrate distance and oxygen pressure in pulsed laser deposition of YBa2Cu3O7

Abstract: It is shown that in pulsed laser deposition, there exists an optimal target‐substrate distance for each deposition O2 pressure necessary for the growth of high quality superconducting films. This result indicates that plasma dynamics plays an important role in forming the superconducting films. A scaling law of PD2=constant is obtained for the optimized conditions.

Microwave plasma assisted supersonic gas jet deposition of thin film materials

Abstract: An apparatus for fabricating thin film materials utilizing high speed gas dynamics relies on supersonic free jets of carrier gas to transport depositing vapor species generated in a microwave discharge to the surface of a prepared substrate where the vapor deposits to form a thin film. The present invention generates high rates of deposition and thin films of unforeseen high quality at low temperatures.

Pulsed Laser Deposition History and Laser-Target Interactions

Abstract: The laser, as a source of “pure” energy in the form of monochromatic and coherent photons, is enjoying ever increasing popularity in diverse and broad applications from drilling micron-sized holes on semiconductor devices to guidance systems used in drilling a mammoth tunnel under the English Channel. In many areas such as metallurgy, medical technology, and the electronics industry, it has become an irreplaceable tool. Like many other discoveries, the various applications of the laser were not initially defined but were consequences of natural evolution led by theoretical studies. Shortly after the demonstration of the first laser, the most intensely studied theoretical topics dealt with laser beam-solid interactions. Experiments were undertaken to verify different theoretical models for this process. Later, these experiments became the pillars of many applications. Figure 1 illustrates the history of laser development from its initial discovery to practical applications. In this tree of evolution, Pulsed Laser Deposition (PLD) is only a small branch. It remained relatively obscure for a long time. Only in the last few years has his branch started to blossom and bear fruits in thin film deposition. Conceptually and experimentally, PLD is extremely simple, probably the simplest among all thin film growth techniques. Figure 2 shows a schematic diagram of this technique. It uses pulsed laser radiation to vaporize materials and to deposit thin films in a vacuum chamber. However, the beam-solid interaction that leads to evaporation/ablation is a very complex physical phenomenon. The theoretical description of the mechanism is multidisciplinary and combines equilibrium and nonequilibrium processes. The impact of a laser beam on the surface of a solid material, electromagnetic energy is converted first into electronic excitation and then into thermal, chemical, and even mechanical energy to cause evaporation, ablation, excitation, and plasma formation.

Epitaxial YBa2Cu3O7−δ on GaAs(001) using buffer layers

Abstract: Epitaxy of YBa2Cu3O7−δ (YBCO) on GaAs substrates has been demonstrated using epitaxial buffer layers. Recently developed methods for growing epitaxial YBCO thin films on Si have been adapted to achieve similar results on GaAs. MgO thin films were grown epitaxially on GaAs at below 400 °C. This layer provides a suitable template for the growth of YBCO or YBCO on BaTiO3. All materials are deposited in situ by pulsed laser deposition in a single growth process. The in‐plane crystallography of MgO on GaAs is [100] parallel to [100], accommodating a lattice mismatch of −25.5%. Zero resistance at temperatures as high as 87 K and transition widths as narrow as 1.5 K are reported. Critical current densities as high as 9×106 A/cm2 at 4.2 K and 1.5×105 A/cm2 at 77 K have been measured.

Effects of homoepitaxial surfaces and interface compounds on the in-plane epitaxy of YBCO films on yttria-stabilized zirconia

Abstract: Control of the in-plane epitaxial alignment of c-axis YBa2Cu3O7−δ (YBCO) films on yttria-stabilized zirconia (YSZ) substrates is necessary for achieving optimal transport properties. We have used pulsed laser deposition to grow homoepitaxial YSZ and heteroepitaxial CeO2 on YSZ single crystal substrates. This procedure dramatically improves the epitaxy of YBCO and reduces the number of low and high angle grain boundaries. We have also studied the effects of preparing the YSZ growth surface with approximately monolayer amounts of CuO, Y2O3, BaO, and BaZrO3 to determine the effects these compositional variations have on the subsequent YBCO epitaxy. CuO, Y2O3, and BaZrO3 induce an in-plane crystallography of YBCO distinct from that initiated with BaO. Both homoepitaxy and monolayer depositions may be carried out in situ and are simple and effective for controlling the epitaxy and electrical properties of YBCO on YSZ. The effects of substrate temperature, oxygen pressure, and yttria content have also been studied.

Preparation of SrTiO3 thin films on Si(100) substrates by laser ablation: Application as buffer layer for YBa2Cu3O7 films

Abstract: SrTiO3 thin films have been deposited on Si(100) by pulsed laser ablation. The films were characterized by x‐ray diffractometry, field emission scanning electron microscopy, and secondary ion mass spectrometry. The films show the (h00) or (hh0) preferential orientations depending on the substrate temperature and oxygen partial pressure during the deposition. Depth profiles indicate that films grow without an important reaction with the substrate. Superconducting YBa2Cu3O7−x thin films were successfully deposited by laser ablation on Si(100) substrates coated with SrTiO3 buffer layer. This indicates that SrTiO3 is a good material as a buffer layer for deposition of YBa2Cu3O7−x on silicon.

Growth of epitaxial Pb(Zr,Ti)O3 films by pulsed laser deposition

Abstract: Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary have been grown on MgO (100) and Y1Ba2Cu3Ox (YBCO) coated MgO substrates. Substrate temperature and oxygen pressure were varied to achieve ferroelectric films with a perovskite structure. Films grown on MgO had the perovskite structure with an epitaxial relationship with the MgO substrate. On the other hand, films grown on the YBCO/MgO substrate had an oriented structure to the surface normal with a misorientation in the plane parallel to the surface. The measured dielectric constant and loss tangent at 1 kHz were 670 and 0.05, respectively. The remnant polarization and coercive field were 42 μC/cm2 and 53 kV/cm. A large internal bias field (12 kV/cm) was observed in the as‐deposited state of the undoped PZT films.

Pulsed laser deposition of stoichiometric LiNbO3 thin films by using O2 and Ar gas mixtures as ambients

Abstract: Stoichiometric thin films of LiNbO3 have been deposited on (100) silicon by a pulsed excimer laser deposition technique. By studying several cases of depositions in vacuum, oxygen, and argon, as well as oxygen‐argon mixture as ambients, it is brought out that the desired stoichiometry in the film can be attained only by having an appropriate oxygen‐argon mixture during deposition. The films have been characterized by x‐ray diffraction, infrared transmission, and spectroscopic ellipsometry techniques.

Single crystal titanium nitride epitaxial on silicon

Abstract: Epitaxial growth of films on single crystal substrates having a lattice mismatch of at least 10% through domain matching is achieved by maintaining na1 within 5% of ma2, wherein a1 is the lattice constant of the substrate, a2 is the lattice constant of the epitaxial layer and n and m are integers. The epitaxial layer can be TiN and the substrate can be Si or GaAs. For instance, epitaxial TiN films having low resistivity can be provided on (100) silicon and (100) GaAs substrates using a pulsed laser deposition method. The TiN films were characterized using X-ray diffraction (XRD), Rutherford back scattering (RBS), four-point-probe ac resistivity, high resolution transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. Epitaxial relationship was found to be TiN aligned with Si. TiN films showed 10-20% channeling yield. In the plane, four unit cells of TiN match with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides a new mechanism of epitaxial growth in systems with large lattice misfits. Four-point probe measurements show characteristic metallic behavior of these TiN films as a function of temperature with a typical resistivity of about 15 μΩ-cm at room temperature.

Composition variations in pulsed-laser-deposited Y-Ba-Cu-O thin films as a function of deposition parameters

Abstract: The composition of pulsed-ultraviolet-laser-deposited Y-Ba-Cu-O films was examined as a function of position across the substrate, laser fluence, laser spot size, substrate temperature, target conditioning, oxygen pressure and target-substrate distance. Laser fluence, laser spot size, and substrate temperature were found to have little effect on composition within the range investigated. Ablation from a fresh target surface results in films enriched in copper and barium, both of which decrease in concentration until a steady state condition is achieved. Oxygen pressure and target-substrate distance have a significant effect on film composition. In vacuum, copper and barium are slightly concentrated at the center of deposition. With the introduction of an oxygen background pressure, scattering results in copper and barium depletion in the deposition center, an effect which increases with increasing target-substrate distance. A balancing of these two effects results in stoichiometric deposition.

Layer‐by‐layer deposition of La1.85Sr0.15CuOx films by pulsed laser ablation

Abstract: Reflection high‐energy electron diffraction (RHEED) has been used to monitor the growth of La1.85Sr0.15CuOx (LSCO) thin films on (100) SrTiO3 substrates by pulsed laser deposition. The films are grown using a combination of pulsed molecular oxygen and a continuous source of atomic oxygen, with the average background pressure maintained as low as 1 mTorr. The RHEED pattern is sharp and streaky, and the intensity of the specular beam oscillates during the deposition, indicating a two‐dimensional layer‐by‐layer epitaxial growth. The film thickness measured by x‐ray small‐angle interference is consistent with the thickness determined by the RHEED oscillation period with a growth unit of half a unit cell. Thin films of YBa2Cu3O7−δ (YBCO) with good RHEED oscillations have also been grown under similar oxygenation conditions. The low‐pressure‐grown LSCO and YBCO films are superconducting, with zero‐resistance temperatures of 15 and 80 K, respectively.

High quality YBCO films grown over large areas by pulsed laser deposition

Abstract: High quality films of YBCO have been grown in situ by pulsed laser deposition (PLD) on small samples as well as both 5 cm (2 in.) and 7.6 cm (3 in.) diam (100) LaAlO3 and 5 cm (100) NdGaO3 substrates. Films grown on small LaAlO3 and NdGaO3 substrates display critical temperatures Tc in excess of 89 K while critical current densities Jc of 5 MA/cm2 at 77 K have been obtained. Films grown on 5 cm diam substrates display Tc’s in excess of 89 K, and Jc’s in excess of 2 MA/cm2 at 77 K. Also, a patterned three‐piece strip line resonator (1.56 GHz fundamental frequency) fabricated using samples cut from a 5 cm diam LaAlO3 substrate yielded a microwave surface resistance Rs of 700 μΩ at 77 K when scaled to a frequency of 10 GHz. Substrates were radiatively heated without the use of absorbing layers such as nickel or thermally conductive layers such as silver paint or indium, thus making backside film deposition a clean and simple process. YBCO films grown on the backside of small LaAlO3 substrates (previously coa...