Showing papers on "Evaporation (deposition) published in 1988"

Epitaxial growth of YBa2Cu3O7−x thin films by a laser evaporation process

Abstract: Thin films of YBa2 Cu3 O7−x have been grown epitaxially in c‐axis orientation on 〈100〉 SrTiO3 by pulsed excimer laser evaporation from a stoichiometric 1‐2‐3 target. The substrate temperature was adjusted between 720 and 780 °C, and the oxygen partial pressure during the deposition was chosen in the range 0.1–0.3 mbar. Cooled to ambient temperature in situ for 1 h in flowing oxygen gas, the films showed complete diamagnetism and zero resistance at 90 K with a transition width of 2 K. Critical current densities of 2.2×106 A/cm2 in zero magnetic field and 1.5×105 A/cm2 at 2 T were measured at 77 K. The resistivity at 100 K was about 60 μΩ cm.

Observation of two distinct components during pulsed laser deposition of high Tc superconducting films

Abstract: Using Rutherford backscattering technique, we have measured the angular distribution of the composition and thickness of the Y‐Ba‐Cu oxide film deposited by firing excimer laser (30 ns, 248 nm) pulses at a stoichiometric Y1Ba2Cu3O7−x pellet. The angular distribution consisted of two distinct components: one a cos θ component, a result of evaporation, and the other a highly forward directed component, a result of a secondary ejection process. The evaporated component is nonstoichiometric, as one would expect, whereas the forward‐directed component has a composition close to that of the pellet. Further, the forward‐directed stoichiometric component increases with the laser energy density in comparison with the evaporated component. These observations are discussed in the context of current models of laser‐induced material ejection at surfaces.The laser energy dependence of the deposition is of critical importance in controlling the film stoichiometry.

Growth of thin films by laser-induced evaporation

Abstract: Among the various material growth techniques, physical vapor deposition of thin films encompasses many experimental forms. They can be categorized into equilibrium and none-quilibrium processes according to the ways in which the source materials are vaporized. Equilibrium process is typified by thermal evaporation including the conventional resistive heating, the more elaborate e-beam evaporation. as well as molecular beam epitaxy (MBE). Nonequilibrium processes include sputtering and many of its derivative forms such as ion beam deposition. In comparison with these techniques, thin-film deposition by laser evaporation is less well known and does not fall cleanly into either category. Depending on the laserconditions, the evaporation process can be either thermal, nonthermal, or a mixture of the two.

Production of high-quality amorphous silicon films by evaporative silane surface decomposition

Abstract: High‐quality hydrogenated amorphous silicon films (a‐Si:H) have been produced by decomposition of low‐pressure silane gas on a very hot surface with deposition on a nearby, typically 210 °C substrate. A high‐temperature tungsten filament provides the surface for heterogeneous thermal decomposition of the low‐pressure silane and subsequent evaporation of atomic silicon and hydrogen. These evaporated species (primarily) induce a‐Si:H growth on nearby substrates which are temperature controlled using a novel substrate holder. The light and dark conductivities, optical band gap, deposition rates, and light‐soaking effects of preliminary films are reported. The decomposition‐evaporation process has been examined using a mass spectrometer to directly detect the decomposition rate and the evaporated radical species. Based on this data and other information, a simplified model for the deposition process is suggested. The excellent film quality and the attributes of the deposition process make this technique, which was originally suggested by Wiessman, viable for the fast rate, large‐area deposition of a‐Si:H for solar cells and other applications.

Formation of polymer films by pulsed laser evaporation

Abstract: Films were produced by pulsed laser evaporation of various solid polymer targets in vacuum. Smooth films and relatively low deposition power thresholds (<107 W/cm2 peak) were observed for strongly absorbed ultraviolet wavelengths. Poorly absorbed wavelengths gave powdery deposits. For many polymers the evaporation process did not significantly alter the chemical structure, but the molecular weight was reduced.

Nature of the pulsed laser process for the deposition of high Tc superconducting thin films

Abstract: The pulsed laser thin‐film deposition process can enable preparation of thin films of complex composition with good control over the film stoichiometry The film compositions are similar to that of the target pellet and as a consequence this technique appears to be an ideal method for preparing high Tc thin films on a variety of substratesThe factors which contribute to this beneficial phenomenon have been explored by a laser ionization mass spectrometry (LIMS) and a post ablation ionization (PAI) neutral velocity analysis technique in order to determine the mass and velocities of the laser ejected material In addition, x‐ray absorption measurements on films deposited onto substrates at room temperature were performed in order to identify the presence of short‐range crystalline order in the films Both of these studies rule out the ejection of stoichiometric clusters of material from the pellet during the laser ablation/deposition process Instead, binary and ternary suboxides are emitted from the targe

Diamond-like carbon films prepared by pulsed-laser evaporation

Abstract: Diamond-like carbon thin films were prepared by pulsed-laser evaporation In this method a carbon target was irradiated by a XeCl laser with a power density of 3×108 W/cm2 and carbon atoms, together with a small number of ions, were produced Deposition rates and film properties changed sensitively with substrate temperature The films deposited at 50°C were diamond-like, having reasonable hardness, high refractive index (21–22 at 633 nm), optical transparency in the infrared, electrical resistivity of 108 Ω cm and chemical inertness (no dissolution in a HF∶HNO3 solution) The band gap measured from optical absorption was 14 eV Raman spectrum and infrared absorption, whose features varied with the substrate temperature, were also measured The films were amorphous and no crystallinity was observed, as confirmed by x-ray diffraction, transmission electron diffraction and Raman spectroscopy Hydrogen atoms were incorporated in the films with a typical H/C ratio of 03 The application of a negative bias to the substrate modified the deposition due to the presence of ions

Stability and epitaxy of NiAl and related intermetallic films on III‐V compound semiconductors

Abstract: The cubic transition metal‐gallium and transition metal‐aluminum intermetallic compounds with the CsCl structure (e.g., NiGa and CoAl) have been identified as candidate materials for stable and epitaxical contacts to III‐V semiconductors. Fabrication of these stable and epitaxical contacts using only conventional vacuum deposition (e.g., electron gun evaporation) has been demonstrated for the NiAl/GaAs system. It is expected that this unique class of contact materials will find application in III‐V‐based field‐effect transistors as well as novel electronic and photonic devices based on multiple semiconductor/metal heterojunctions.

Laser evaporation deposition of superconducting and dielectric thin films

Abstract: We describe here the deposition of superconducting and dielectric thin films by the laser evaporation technique. The characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discussed.

Solid state light modulator incorporating metallized gel and method of metallization

Abstract: A solid state light modulator structure useful in a video display system includes a deformable silica containing gel layer on an array of charge storage elements, and an adherent, highly light reflective metal (e.g., Ag) electrode layer formed on the surface of the gel layer by evaporation, following treatment of the gel surface in an oxygen-containing plasma.

Y-Ba-Cu-O superconducting thin films by simultaneous or sequential evaporation

Abstract: Superconducting thin films of Y‐Ba‐Cu‐O near the 1:2:3 stoichiometry were produced by simultaneous (coevaporation) and sequential (multilayer) evaporation in the same evaporator. The best film obtained on yttria‐stabilized zirconia (YSZ) had a superconducting onset temperature of 104 K, a midpoint Tc of 92 K, and zero resistance at T≤74 K. Stoichiometry was deduced by inductively coupled plasma emission spectroscopy, and elemental depth profiles were obtained by x‐ray photoelectron spectroscopy. Film stoichiometry changes only near the film/substrate boundary for films on YSZ. Films on Si/SiO2 were not superconducting; depth profiling shows severe changes of film composition with depth. A major theme of this work is process reproducibility, which was found to be poor for coevaporation but improved considerably for sequential evaporation.

Preparation of oriented Bi‐Ca‐Sr‐Cu‐O thin films using pulsed laser deposition

Abstract: Oriented c‐axis thin films of Bi‐Ca‐Sr‐Cu‐O on [100] SrTiO3 substrates have been fabricated using the pulsed excimer laser evaporation technique. Deposition at room temperature in 1 mTorr oxygen followed by an 875 °C anneal in oxygen yields superconducting films with zero resistance at 80 K and a resistivity drop near 110 K, hinting at the presence of another superconducting phase. Transmission electron microscopy shows that the films are epitaxial with the substrate, with an abrupt and planar interface boundary. The observed crystal structure is consistent with diffraction results on bulk materials.

Preparation of superconducting Y-Ba-Cu-O films by a reactive plasma evaporation method

Abstract: Y‐Ba‐Cu‐O superconducting films were prepared by a reactive plasma evaporation method, in which mixed powders were coevaporated in a thermal radio‐frequency Ar+O2 plasma and the ternary composition controlled high‐temperature metallic vapors were codeposited onto a substrate. The deposition rate was much more than 10 μm/min, which is several orders of magnitude higher than those reported by the other methods previously. The structure of the prepared films was identified as an orthorhombic oxygen‐deficient perovskite phase and some films showed the preferred orientation of (001). The as‐deposited film without post‐annealing showed a superconducting transition temperature Tcm (midpoint) of 94 K.

The anodic vacuum arc. II: Experimental study of arc plasma

Abstract: The metal vapor plasma generated by an anodic vacuum arc was investigated experimentally in the current range between 20 and 45 A. Spectroscopic investigations of the interelectrodic plasma show that the discharge is totally sustained by evaporated anode material. The evaporating part of the anode is a source of a metalplasma with a high degree of ionization. The surfacetemperature at the anode is far above the melting point of the consumed material. With respect to coating application the expanding metal vapor plasma was investigated at distances of 0.12 and 0.24 m from the anode for the metals Al, Cr, and Ti; electron densities in the order of 101 6 m− 3 and electron temperatures between 0.2 and 1.0 eV were determined. Between 4% and 20% of the atoms arriving at the surface of a substrate are ionized. Deposition rates range from 1 to 50 nm/s.

Thin film magnetic head

Abstract: PURPOSE:To obtain a magnetic head which is suitable for high-frequency recording and reproducing for a VTR, etc and obviates the exfoliation of a thin magnetic film from a glass or ceramic substrate by forming a thin Cr film on the substrate then forming a thin metallic film for the magnetic head on the Cr film CONSTITUTION:The thin Cr film 2 is sputtered and deposited by evaporation on the glass or ceramic substrate 1, then the amorphous magnetic metallic film 3 consisting of a Co-Nb-Zr alloy or the like is sputtered and deposited by evaporation thereon The film is laminated to the thickness of the required track width The provision of an insulating layer 4 consisting of SiO2, etc on the film 3 and the provision of the magnetic metallic film 3 on the layer 4 is preferably repeated in order to improve the high-frequency characteristic An SiO2 layer 5 and further a low-temp adhesive glass layer 6 are provided on the final magnetic film a core part 7 for the thin film magnetic head is obtd in the above-mentioned manner A lining substrate 8 consisting of the same material as the material of the substrate 1 is superposed on the core part 7 and is united by melting the layer 6 Such block is cut to a rectangular strip 9 shape and winding grooves 10 are formed thereto to manufacture a core bar 11 The core bar is thereafter cut to individual chips 12

Deposition of tin oxide films by pulsed laser evaporation

Abstract: Thin films of SnO2−x (0

Structure and transport properties of amorphous Ge1−xCx:H thin films obtained by activated reactive evaporation

Abstract: Hydrpgenated amorphous germanium-carbon (a-Ge1−xCx:H) thin films have been prepared by an Activated Reactive Evaporation (ARE) technique. Germanium was evaporated from a resistively heated tungsten basket through an acetylene plasma. The films thus obtained were characterized for the compositional, structural, electrical and optical properties. The effects of substrate temperature, role of hydrogen and variation of optical energy gap with carbon content were also investigated. Typically, films deposited at 200 °C showed a sharp absorption edge corresponding to an optical gap of about 1.3 eV and thermally activated electrical conduction over a wide range of temperatures.

Stress measurements in sol-gel films

Abstract: Thin solid films of a wide variety of materials have received increased attention during the past decade. These films have been instrumental in the growth of numerous technologies. Until recently, “thin films” have primarily described layers of metallic or dielectric materials deposited onto substrates by evaporation, electron beam or ion beam techniques. Advances in sol-gel technology have extended film research to include “glassy” materials of either crystalline, or amorphous nature. Sol-gel films can be tailor-made to accommodate a diverse range of applications due primarily to flexibility in chemical make up which determines the respective film's structure. One important characteristic of such films is their inherent residual stress. This inherent stress, and the stress the film introduces to the substrate as it is deposited, can result in a complex stress profile. While “thin” in the case of sol-gel films generally means <1 μm in thickness, large (10–100s of nm of retardance) inherent stress per unit thickness can severely limit a film's performance and subsequent application. We describe our efforts to quantify the residual stress in silica-based sol-gel films as a function of several processing parameters.

Smectic Layer Structure of Thin Ferroelectric Liquid Crystal Cells Aligned by SiO Oblique Evaporation Technique

Abstract: Smectic layer structures were studied by high-resolution X-ray analysis for two kinds of cells aligned on SiO obliquely evaporated film; the glass plates were fabricated for the evaporation direction to be the same (parallel) or to be the opposite (antiparallel). For parallel cells, a chevron layer structure was formed. The temperature dependence was similar to that of a rubbing cell, although the chevron structure with a small layer tilt existed even in the SmA phase. For antiparallel cells, on the other hand, the smectic layer was uniformly tilted and the layer tilt angle showed weaker temperature dependence than that of the parallel cells.

Arrival time measurements of films formed by pulsed laser evaporation of polycarbonate and selenium

Abstract: By measuring the rapid change in reflectivity of a substrate during film growth induced by pulsed laser evaporation, the time‐of‐arrival profiles of material emanating from polycarbonate and selenium targets were determined. Results for both targets are reasonably well described by Maxwell–Boltzmann velocity distributions. Selenium evaporation appears to be atomic while for polycarbonate a range of masses are involved. The high velocity of the material leaving polycarbonate strongly suggests that small polymers are not transported directly. The mechanism for polymer film formation must involve repolymerization on the substrate of species not weighing more than a few hundred amu. For both polycarbonate and selenium the time‐of‐arrival profiles were affected very little by changing the excitation wavelength from 248 to 1064 nm.

Production of magnetic recording medium

Abstract: PURPOSE:To improve coercive force and to improve the corrosion resistance and wear resistance characteristics of a magnetic recording medium by depositing a ferromagnetic metal by evaporation on a nonmagnetic substrate while blowing gaseous oxygen thereto and forming a vapor deposited film with high efficiency while preventing the disorder in the crystal growth of the metal CONSTITUTION:After a PET film 4 is mounted to a tape transfer device 10, the inside of a vacuum vessel 1 is maintained at a high vacuum by an evacuation device 2 and the gaseous oxygen is supplied from a 1st supply device 41 into the vacuum vessel 1 The flow of the gaseous oxygen is simultaneously acted on the surface of the PET film to be deposited with the evaporating metal by a 2nd supply device 45 A partially oxidized Co-Ni alloy is uniformly and efficiently deposited by evaporation on the PET tape in the thickness direction thereof if the Co-Ni alloy is heated and operated by operating an electron beam heater 22 and the tape is run simultaneously by the device 10 Since the oxygen of a uniform pressure is thereby acted on the deposited film, the high coercive force is assured and the vapor deposition efficiency is improved while the same squareness ratio is maintained There is no disturbance in the gaseous flow of the oxygen and the distribution control of the oxidation degree in the thickness direction of the vapor deposited film is permitted; therefore, the corrosion resistance and wear resistance of the vapor deposited film are improved

Method of in situ photo induced evaporation enhancement of compound thin films during or after epitaxial growth

Abstract: In situ evaporation of selected surface regions or layers of compound semiconductors is accomplished without breaking the growth system environment employing photo induced evaporation enhancement in chemical vapor deposition epitaxy. Intense radiation from an energy source desorbs or causes evaporation of consecutive monolayers of atoms or combined atoms from the surface crystal by thermal evaporation. The desorbed atoms from the growth surface are removed atomic layer by atomic layer in a fairly uniform and systematic manner and may be characterized as "monolayer peeling" resulting in a morphology that is sculpturally smooth and molecularly continuous. In this sense, the method of this invention is analogous to erasing or the etching of crystal material and is the antithesis to laser deposition patterning wherein erasure after growth or reduced rate of growth during growth provide "negative growth patterning". In principal, then, this patternable negative growth process is coupled with a positive growth process for providing selective thinning regions of semiconductor layers in three dimensional crystal structures limited only by the functional capabilities of the growth reactor. Selective monotonic increasing and decreasing film thickness in situ can be accomplished while beam illumination remains stationary for a predetermined period of time with exposure of the growth surface accomplished through a patterned mask or, alternatively, while the beam spot or multiple beam spots are modulated and scanned across the growth surface of the film.

Mechanical properties of LaNi5 thin films prepared by sputtering and vapor deposition methods and determination of the hydrogen content in these films

Abstract: Amorphous LaNi5 films were prepared using a sputtering method Mechanical properties and hydrogenation characteristics of the films were investigated and the results were compared with those of the deposited films The density of the sputtered LaNi5 film was about 6 g/cm3, which was larger than that of the evaporation deposited film but smaller than that of crystalline LaNi5 Thermal conductivities of amorphous films were larger than those of bulk samples Mechanical strength of the sputtered films deposited on various substrates was measured after 100 cycles of hyrogen absorption–desorption process The result was in the following order for the substrates used: Ni foil>Ni>Al foil>Cu foil>Cu>Al>glass The hydrogen content in a sputtered film with a thickness of 13 μm was found to be 24 H/LaNi5 The hydrogen concentration in the film increased monotonically with increasing the hydrogen pressure in both cases between 333 and 363 K