Showing papers on "Pulsed laser deposition published in 1996"

A ferroelectric transparent thin‐film transistor

Abstract: Operation is demonstrated of a field‐effect transistor made of transparant oxidic thin films, showing an intrinsic memory function due to the usage of a ferroelectric insulator. The device consists of a high mobility Sb‐doped n‐type SnO2 semiconductor layer, PbZr0.2Ti0.8O3 as a ferroelectric insulator, and SrRuO3 as a gate electrode, each layer prepared by pulsed laser deposition. The hysteresis behavior of the channel conductance is studied. Using gate voltage pulses of 100 μs duration and a pulse height of ±3 V, a change of a factor of two in the remnant conductance is achieved. The dependence of the conductance on the polarity of the gate pulse proves that the memory effect is driven by the ferroelectric polarization. The influence of charge trapping is also observed and discussed.

Synthesis of Novel Thin-Film Materials by Pulsed Laser Deposition

Abstract: Pulsed laser deposition (PLD) is a conceptually and experimentally simple yet highly versatile tool for thin-film and multilayer research. Its advantages for the film growth of oxides and other chemically complex materials include stoichiometric transfer, growth from an energetic beam, reactive deposition, and inherent simplicity for the growth of multilayered structures. With the use of PLD, artificially layered materials and metastable phases have been created and their properties varied by control of the layer thicknesses. In situ monitoring techniques have provided information about the role of energetic species in the formation of ultrahard phases and in the doping of semiconductors. Cluster-assembled nanocrystalline and composite films offer opportunities to control and produce new combinations of properties with PLD.

Pulsed laser deposition of thin films of (

Abstract: Manganites of the series , with x = 0, 0.1, 0.3, 0.5, 0.7 and 1.0, have been characterized in ceramic form and thin films have been prepared by pulsed laser deposition. Characterization techniques included x-ray diffraction, conductivity and magnetoresistance, magnetization and susceptibility, optical spectroscopy and the Faraday effect. Both the films and ceramics exhibit a maximum low-temperature conductivity at which is coexistent with ferromagnetic order. The negative magnetoresistance effect is qualitatively different for the x = 0.3 and x = 0.5 compositions. For x = 0.3 the magnetoresistance peak occurs around the Curie point, whereas for x = 0.5 the onset of magnetoresistance is somewhat below and increases monotonically as . The applied field appears to modify the magnetic order (on the scale of the spin diffusion length) down to the lowest temperatures for x = 0.5, but for x = 0.3 the ferromagnetic order is essentially complete and collinear below the Curie point.

Preparation of amorphous diamond-like carbon by pulsed laser deposition: a critical review

Abstract: A critical review of the pulsed laser deposition (PLD) of amorphous diamond-like carbon (DLC) films is presented. A short review of the PLD process is followed by a review of various experimental configurations for DLC deposition and a discussion of the influence of process parameters on the composition and energy of ablated carbon plumes. Particular emphasis is given to the relationship between plume properties and film structure and mechanical characteristics. For the first time, a cumulative influence of the laser power density (fluence) and wavelength on the formation and properties of DLC films is shown. The influence of bias, additional auxiliary energy, substrate temperature, and the presence of hydrogen is also discussed. A fluence-wavelength region for DLC formation is proposed and correlated with the kinetic energy of ablated carbon species. It is shown that lower fluences are required to produce DLC films when shorter-wavelength lasers are used. The latest available results on applications of PLD DLC films as protective coatings for reducing friction and wear are also discussed. Methods are proposed to improve film adhesion to steel substrates, so that DLC films can be used in highly loaded friction contacts. Finally, process improvements that are necessary to permit scaling up PLD for growing DLC films are outlined.

The effect of annealing on the structure and dielectric properties of BaxSr1−xTiO3 ferroelectric thin films

Abstract: The effect of a postdeposition anneal on the structure and dielectric properties of epitaxial BaxSr1−xTiO3 (BST) thin films (x=0.35–0.65) have been measured. The films were grown by pulsed laser deposition on LaAlO3 (001) substrates. The films were single phase and (001) oriented with a lattice parameter larger than the bulk. The dielectric properties of the x=0.35 film exhibited a broad temperature dependence and a peak at 168 K, which is 36 K below the peak observed in bulk BST (x=0.35). Annealing films for 8 h in flowing oxygen at 900 °C caused the lattice parameter to decrease and dielectric properties to become more like the bulk. Annealing also resulted in an increased electric field dependent dielectric tuning without increased dielectric loss.

Preparation of crystallized zinc oxide films on amorphous glass substrates by pulsed laser deposition

Abstract: Zinc oxide (ZnO) films with c‐axis orientation have been prepared on glass substrates by pulsed laser deposition with an ArF excimer laser. The fluctuations of c‐axis orientation of the ZnO films are evaluated by full width at half‐maximum (FWHM) of the rocking curve of the x‐ray diffraction. The ZnO films with a FWHM of 1.9° can be obtained on the optimum conditions (substrate temperature of 500–600 °C, O2 gas pressure of 2–6×10−4 Torr) even at a thickness of 200 nm. We have observed the crystallization of the ZnO during film formation by using in situ reflection high energy electron diffraction. It is confirmed that ZnO thin films with a thickness of up to about 50 nm have c‐axis orientation on the glass substrates.

CoFe2O4 thin films grown on (100) MgO substrates using pulsed laser deposition

Abstract: Thin films (≊04 μm) of cobalt ferrite (CoFe2O4) have been grown on single‐crystal (100) MgO substrates using pulsed laser deposition (PLD) The phase, orientation, and microstructure of the as‐deposited films were investigated as a function of substrate temperature (ie, 200–800 °C) at a constant oxygen deposition pressure of 30 mTorr The as‐deposited films were found to be single phase, well oriented, and approximately matching the stoichiometry of the target, but the cubic lattice constant of the films depended on the substrate temperature indicating that the films were strained The greatest effect of the substrate temperature was on the magnetic properties of the as‐deposited films At 800 °C, 4πMs was measured to be 5370 G which is approximately the accepted bulk value for cobalt ferrite In addition, PLD cobalt ferrite films grown at substrate temperatures of 600 and 800 °C exhibited a uniaxial magnetic anisotropy with an easy direction normal to the film plane Films grown at 200 and 400 °C also

Transparent Conducting Al-Doped ZnO Thin Films Prepared by Pulsed Laser Deposition

Abstract: Thin films of ZnO:Al have been deposited on glass substrates by a pulsed laser deposition technique employing an ArF laser ( λ=193 nm). For all experiments, a repetition rate of 10 Hz, an energy density of 1 J/cm2, and an irradiation time of 20–30 min (12000–18000 shots) were assumed. Optical transmittance of around 90% was observed in the visible region of the spectrum for the 150–200 nm thick film. Resistivities of 1.43×10-4 Ω·cm and 5.62×10-4 Ω·cm were obtained at substrate temperatures of 300°C and room temperature, respectively.

Ion beam process for deposition of highly wear-resistant optical coatings

Abstract: An ion beam deposition method is provided for manufacturing a coated substrate with improved wear-resistance, and improved lifetime. The substrate is first chemically cleaned to remove contaminants. Secondly, the substrate is inserted into a vacuum chamber onto a substrate holder, and the air therein is evacuated via pump. Then the substrate surface is bombarded with energetic ions from an ion beam source supplied from inert or reactive gas inlets to assist in removing residual hydrocarbons and surface oxides, and activating the surface. After sputter-etching the surface, a protective, wear-resistant coating is deposited by plasma ion beam deposition where a portion of the precursor gases are introduced into the ion beam downstream of the ion source, and hydrogen is introduced directly into the ion source plasma chamber. The plasma ion beam-deposited coating may contain one or more layers. Once the chosen coating thickness is achieved, deposition is terminated, vacuum chamber pressure is increased to atmospheric and the coated substrate products having wear-resistance greater than glass are removed from the chamber. These coated products may be ceramics, architectural glass, analytical instrument windows, automotive windshields, and laser bar code scanners for use in retail stores and supermarkets.

Computer controlled vapor deposition processes

Abstract: A method for computerized control of vapor deposition processes, including chemical vapor deposition and electron beam physical vapor deposition processes, uses optical imaging sensors and/or laser interferometers or infrared ellipsometers focused on the substrate being coated or on a nearby test blank to provide information which is computer analyzed to yield optimum control points for the coating process. A method is also disclosed for shaping or contouring one or more surfaces of an object(s) using the techniques disclosed here.

Method of making ferrolectric thin film composites

Abstract: A method of making ferroelectric thin film composites includes the step ofroviding a barium strontium titanate material with an additive magnesia-based and forming a thin film ferroelectric composite using pulsed laser deposition. The method forms a thin film composite having enhanced electronic properties.

Atomic layer controlled deposition of silicon nitride with self‐limiting mechanism

Abstract: Thin (2–10 nm) silicon nitride films have been grown by repetitive plasma nitridation of Si using a NH3 remote plasma and deposition of Si by a SiH2Cl2 thermal reaction. The deposition rate is self‐limited at nearly half‐molecular layer (ML) per one deposition cycle. The process window for the half‐ML/cycle of growth has been investigated with respect to the NH3 plasma power, SiH2Cl2 exposure time, and substrate temperature. The thickness fluctuation of the film over a 2 in. wafer is within measurement accuracy of the ellipsometer (± 1.9%) for the atomic layer controlled film while it is ± 8.5% for all the remote‐plasma chemical vapor deposition film.

Electrical properties of (Zr,Sn)TiO4 dielectric thin film prepared by pulsed laser deposition

Abstract: We have been successful in obtaining temperature‐stable crystallized thin film of (Zr,Sn)TiO4. Preferential (111)‐oriented (Zr,Sn)TiO4 thin film was prepared by pulsed laser deposition. Effects of crystallization were elucidated based on a comparison of electric properties of crystallized and amorphous (Zr,Sn)TiO4 film. For crystallized film, the temperature coefficient of capacitance (TCC) was 20 ppm/°C at 3 MHz and the dielectric constant er=38 in the microwave range of 1–10 GHz. These values are superior to those for amorphous film (TCC=220 ppm/°C, er=27). The crystallization of this material was found quite effective for improving dielectrical properties. Atomic force microscope images showed the surface morphologies of crystallized and amorphous film of (Zr,Sn)TiO4 to differ.

Growth-related stress and surface morphology in homoepitaxial srtio3 films

Abstract: The lattice parameter and surface morphology of homoepitaxial SrTiO3 films were found to depend on the ambient oxygen pressure during growth. The homoepitaxial layers were grown by pulsed laser deposition with static ambient oxygen pressures of 100, 10, and 1 mTorr. The surface roughness of the films increased with increasing ambient growth pressure. In each case, the measured out‐of‐plane lattice parameter of the film was larger than that of the substrate. The mismatch between film and substrate increased with decreasing growth pressure. Compressive stresses of ∼0.28, 1.2, and 2.0 GPa were determined for homoepitaxial SrTiO3 layers deposited at 100, 10, and 1 mTorr, respectively.

Thermal stability of amorphous carbon films grown by pulsed laser deposition

Abstract: The thermal stability in vacuum of amorphous tetrahedrally coordinated carbon (a‐tC) films grown on Si has been assessed by in situ Raman spectroscopy. Films were grown in vacuum on room‐temperature substrates using laser fluences of 12, 22, and 45 J/cm2 and in a background gas of either hydrogen or nitrogen using a laser fluence of 45 J/cm2. The films grown in vacuum at high fluence (≳20J/cm2) show little change in the a‐tC Raman spectra with temperature up to 800 °C. Above this temperature the films convert to glassy carbon (nanocrystalline graphite). Samples grown in vacuum at lower fluence or in a background gas (H2 or N2) at high fluence are not nearly as stable. For all samples, the Raman signal from the Si substrate (observed through the a‐tC film) decreases in intensity with annealing temperature indicating that the transparency of the a‐tC films is decreasing with temperature. These changes in transparency begin at much lower temperatures (∼200 °C) than the changes in the a‐tC Raman band shape an...

X‐ray photoelectron spectroscopy of carbon nitride films deposited by graphite laser ablation in a nitrogen postdischarge

Abstract: Carbon nitride thin films have been deposited on silicon substrates, using a newly developed surface wave discharge/pulsed laser deposition system. Nitrogen incorporation in the films is examined by x‐ray photoelectron spectroscopy (XPS). It shows that interaction between the laser ablated carbon species and nitrogen atoms from the surface‐wave N2 plasma enhances the incorporation of N in the carbon nitride layers, for example, up to 19% at a deposition pressure of 2 mTorr. Increasing the deposition temperature decreases nitrogen incorporation and changes the local chemical environment of nitrogen atoms.

Combined magnetron sputtering and pulsed laser deposition of carbides and diamond‐like carbon films

Abstract: A hybrid technique is reported, which combines magnetron sputtering and pulsed laser ablation to produce plasma fluxes intersected on a substrate surface to form metal, ceramic and diamond‐like materials Deposition of crystalline Ti, TixCy, TiCN, and amorphous diamond‐like carbon films at low temperatures by the new technique is discussed The variation of laser pulse frequency is found to be a simple way to control film chemical composition The technique can be used to prepare materials with transitional structure, as, for example, between metal carbides and diamond‐like carbon

Intense Ion-Beam Treatment of Materials

Abstract: Over the past decade, researchers in Japan, Russia, and the United States have been investigating the application of intense-pulsed-ion-beam (IPIB) technology (which has roots in inertial confinement fusion programs) to the surface treatment and coating of materials. The short range (0.1–10 μm) and high-energy density (1–50 J/cm2) of these short-pulsed (t ≥ 1 μs) beams (with ion currents I = 5–50 kA, and energies E = 100–1,000 keV) make them ideal flash-heat sources to rapidly vaporize or melt the near-surface layer of targets similar to the more familiar pulsed laser deposition (PLD) or laser surface treatment. The vaporized material can form coatings on substrates, and surface melting followed by rapid cooling (109 K/s) can form amorphous layers, dissolve precipitates, and form nonequilibrium microstructures.An advantage of this approach over laser processing is that these beams deliver 0.1–10 KJ per pulse to targets at expected overall electrical efficiencies (i.e., the ratio of extracted ion-beam energy to the total energy consumed in generating the beam) of 15–40% (compared to < 1% for the excimer lasers often used for similar applications). Consequently IPIB hardware can be compact and require relatively low capital investment. This opens the promise of environmentally conscious, low-cost, high-throughput manufacturing. Further, efficient beam transport to the target and excellent coupling of incident ion energy to targets are achieved, as opposed to lasers that may have limited coupling to reflective materials or produce reflecting plasmas at high incident fluence. The ion range is adjustable through selection of the ion species and kinetic energy, and the beam energy density can be tailored through control of the beam footprint at the target to melt (1–10 J/cm2) or to vaporize (10–50 J/cm2) the target surface. Beam pulse durations are short (≥ 1 μs) to minimize thermal conduction. Some disadvantages of IPIB processing over laser processing include the need to form and propagate the beams in vacuum, and the need for shielding of x-rays produced by relatively low-level electron current present in IPIB accelerators. Also these beams cannot be as tightly focused onto targets as lasers, making them unsuitable for applications requiring treatment on small spatial scales.

Large‐area double‐side pulsed laser deposition of YBa2Cu3O7−x thin films on 3‐in. sapphire wafers

Abstract: A pulsed laser deposition (PLD) technique for YBa2Cu3O7−x (YBCO) thin films with CeO2 buffer layers and gold contact films on both sides of 3‐in. diameter sapphire wafers, which are applied for microwave strip‐line filters, is described and some results of structural and compositional characterization are given. This large‐area multilayer PLD technique allows for a homogeneous and reproducible YBCO deposition on both wafer sides with inductively measured critical current densities of 3×106–5×106 A/cm2 at 77 K with a YBCO thickness of 350–500 nm. The results indicate that PLD seems to have unique capabilities for fast deposition of high‐quality large area oxide multilayers.

The growth and properties of epitaxial KNbO3 thin films and KNbO3/KTaO3 superlattices

Abstract: Potassium niobate (KNbO3) thin films and potassium niobate/tantalate (KNbO3/KTaO3) superlattices have been grown on KTaO3 (001) substrates by pulsed laser deposition. The thin‐film structures were analyzed by Rutherford backscattering/ion‐channeling techniques, x‐ray θ–2θ and Φ scans, and both conventional and Z‐contrast scanning transmission electron microscopy. Excellent film flatness and crystallinity are evidenced by these techniques. At room temperature, the KNbO3 films are characterized by an orthorhombic structure which differs from that of bulk KNbO3. The interfaces between the layers in the KNbO3/KTaO3 superlattice structures were found to be compositionally sharp on an atomic scale.

Characteristics of titanium nitride films grown by pulsed laser deposition

Abstract: Laser physical vapor deposition (LPVD) has been used to grow titanium nitride films on hydrogen-terminated silicon(100) substrates at deposition temperatures ranging from room temperature to 600 °C. A pulsed KrF excimer laser (λ = 248 nm, τ = 25 ns) was used with the deposition chamber maintained at a base pressure of 10−7 Torr prior to deposition. Different properties of the films were investigated by x-ray diffraction, Auger electron spectroscopy, Raman spectroscopy, optical, scanning, and high resolution transmission electron microscopy, and measurement of electrical resistivity. When the substrate temperature was low (at and below 500 °C), oxygen atoms from the residual gases were incorporated in the films. The microstructures and resistivities of TiN films were found to be strongly dependent on the temperature of the silicon substrates. The TiN films deposited at 600 °C were oxygen-free, as observed from Auger analysis, and the room temperature resistivity was found to be 14–15 μΩ-cm. Raman spectroscopy of the films showed that the nitrogen-related optical phonon peak increased with deposition temperature in comparison with the titanium-related acoustic peak. Transmission electron microscopy and x-ray diffraction analyses showed that the films were polycrystalline at low temperature with grain size ranging from 300–600 A, depending on the temperature of the substrate. At 600 °C, the films were found to be single crystals with occasional presence of dislocation loops. The spacing of Moire fringes in TiN/Si samples deposited at 600 °C established the nearly periodic elastic strain field extending into the TiN and Si at the interface. Although there exists a large misfit between TiN and Si (24.6%), the epitaxial growth of TiN films on Si(100) substrates was explained by means of domain-matched epitaxy with a 4-to-3 match in unit cells for TiN/Si structure, giving rise to a residual lattice misfit of only 4%.

Near‐edge x‐ray absorption fine structure study of bonding modifications in BN thin films by ion implantation

Abstract: Near‐edge x‐ray absorption fine structure (NEXAFS) has been used to study the defect content and the bonding modifications induced in BN thin films by ion implantation. The initial films were hexagonal‐like BN grown on Si(100) by pulsed laser deposition. Subsequent ion implantation with N2+ at 180 keV induces the formation of a significant proportion of sp3 bonding (cubic‐like), and the formation of nitrogen void defects in the remaining sp2 BN. These modifications in the bonding of a film lacking long range order can only be distinguished with a local order technique like NEXAFS.

Growth mechanism of YMnO3 film as a new candidate for nonvolatile memory devices

Abstract: We have proposed ReMnO3 (Re: rare earth) thin films for nonvolatile memory devices. We examine the growth mechanism of YMnO3 films on (0001)ZnO:Al/(0001) sapphire substrate using rf magnetron sputtering and pulsed laser deposition methods with oxide compound target. We have succeeded in obtaining (0001) epitaxial YMnO3 films on (111) MgO and (0001)ZnO:Al/(0001) sapphire substrate, and polycrystalline films on (111)Pt/(111)MgO. For an optimal structure, the film needed much less oxygen from the gas phase compared to other oxide films. The composition (Y/Mn ratio) of the YMnO3 films changed drastically by varying the partial oxygen pressure in the sputtering gas. In addition the Y/Mn ratio slinfled with sputter time due to target surface modification, probably caused by Y segregation. An extremely small amount of oxygen is required to form the YMnO3 crystal. This was confirmed by pulsed laser deposition experiments.

Growth of c‐axis oriented gallium nitride thin films on an amorphous substrate by the liquid‐target pulsed laser deposition technique

Abstract: Gallium nitride (GaN) thin films with a wurtzite structure were grown on fused silica (FS) substrates by pulsed laser ablation of a liquid gallium target in the presence of ammonia gas X‐ray diffraction measurement shows a single c‐axis orientation for the GaN film grown with a thin (<1000 A) zinc oxide (ZnO) film as an alignment layer There is a great improvement in the surface morphology as well as optical transmission for the GaN film grown on the ZnO buffered FS substrate The energy band gap obtained from the absorption spectrum is about 345 eV

Electron field emission from amorphous tetrahedrally bonded carbon films

Abstract: Electron field emission from two amorphous, tetrahedrally bonded diamondlike carbon films, one with (a‐tC:N), and a second without nitrogen doping (a‐tC), prepared by pulsed laser deposition has been investigated using a scanning probe apparatus with micrometer spatial resolution Electric fields of 100 V/μm (180 V/μm) were required to initiate emission from our a‐tC:N (a‐tC) films; however, once emission was established at a particular location, electrons could be drawn at average fields as low as 10 V/μm (60 V/μm) from the same region The initiation of emission was concomitant with electrical discharges which were observed by video techniques These discharges left craters with micrometer dimensions on the surfaces of otherwise smooth films

Laser operation of an Nd:Gd3Ga5O12 thin‐film optical waveguide fabricated by pulsed laser deposition

Abstract: We report the laser operation of a thin-film waveguide structure grown by the pulsed laser deposition technique. A 2.7-µm-thick crystalline film of neodymium doped Gd3Ga5O12 (Nd:GGG) lases at a wavelength centered at 1.06µm when pumped by a Ti:sapphire laser at 808 nm.