Showing papers on "Evaporation (deposition) published in 1991"

Optical properties of vanadium dioxide and vanadium pentoxide thin films.

Abstract: Several oxides of vanadium undergo a transition from a semiconductor or insulating state to a metal phase at a critical temperature. Vanadium dioxide undergoes this transition near 68 degrees C, while V(2)O(5) undergoes a similar phase transition near 257 degrees C. During the transition a change in oxide crystal structure is accompanied by large changes in electrical and optical behavior. Thin films of vanadium oxides are capable of reversibly switching from the semiconductor to the metallic state at high speeds and with high spatial resolution. Therefore, these oxides have potential use, particularly in thin film form, for a wide variety of applications involving thermally activated electronic or optical switching devices. Such films are of considerable technical interest because of applications in chemical sensors, energy-conserving coatings, transparent conductors, and switching materials. The numerous potential electronic, optical, and optoelectronic device applications which have been suggested have stimulated work on the preparation of thin films by a variety of techniques, including chemical vapor deposition, solgel, evaporation, and sputter deposition. This paper reviews the optical properties of vanadium oxide coatings and stresses the dependence of film properties on sample preparation and resultant film microstructure.

Gold deposition from a scanning tunneling microscope tip

Abstract: We have demonstrated that a gold scanning tunneling microscope (STM) tip can be used as a miniature solid‐state emission source for directly depositing nanometer‐size gold structures. The process has been demonstrated in ultrahigh vacuum on gold substrates, and in air on gold and platinum substrates. Studies made in air suggest that the process is fast, repeatable, and field‐induced. The emission mechanism is believed to be field evaporation of tip atoms, which is enhanced by the close proximity of the substrate. The technique has been used to write several thousand features with no apparent degradation of the tip’s ability to write. Elevated and room temperature studies show the written structures to be stable over periods of weeks, in contrast to some previous STM measurements of gold self‐diffusion.

Microstructures of TiN films grown by various physical vapour deposition techniques

Abstract: A study has been made of TiN coatings deposited on steel substrates by five commercially available physical vapour deposition (PVD) methods; low voltage electron beam evaporation, triode high voltage electron beam evaporation, random-arc evaporation, steered-arc evaporation and magnetron sputtering. The microstructure and substrate-film interfacial microchemistry of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy-dispersive X-ray spectroscopy (EDX), cross-sectional transmission electron microscopy (XTEM) and scanning transmission electron microscopy (STEM) combined with EDX analyses of XTEM samples. The XRD analyses showed that all the films were in a state of compressive stress with interplanar distances as much as 1.7% higher than reference bulk values. SEM examination revealed only minor variations in surface roughness among the samples except for the arc-evaporated films which contained large droplets and craters resulting from the detachment of droplets. The number density and average sizes of droplets and craters were lower in the steered-arc sample than in the random-arc sample. XTEM analyses showed that all the films had columnar structures with clearly defined substrate-film interfacial layers. The films appeared dense except for the magnetron-sputtered sample which exhibited intercolumnar porosity. STEM-EDX analyses showed large variations in the microchemistry of the substrate-film interfacial regions which consisted, depending on the sample, of renucleated near-surface substrate grains, intentionally (or, in at least one case, unintentionally) introduced foreign material or gas-bubble-like inclusions. However, the microchemistry of these interfacial regions was, in most cases, understandable on the basis of the substrate pretreatment and/or choice of film growth parameters.

Wettability of SiO2 and oxidized SiC by aluminium

Abstract: The silica layer grown naturally or artificially on the surface of SiC fibres or particles used in alumina-based matrix composites is supposed to have two functions: protection of the SiC from aluminium attack and improvement of the wettability of SiC by aluminium which would result from the reaction between aluminium and SiO 2 . The effective role of silica in the wetting of aluminium on SiC was studied using the sessile drop method and the immersion-emersion tensiometric technique. Aluminium contact angles were measured first on amorphous SiO 2 and then on thermally oxidized SiC monocrystals (silica layers of 10–50 nm), between 933 K and 1173 K, and under a dynamic vacuum of 10 −4 −10 −5 Pa. In the two systems it appeared that silica acts as an oxygen source which causes oxidation of liquid aluminium. As a result the wetting kinetics was slowed down and even blocked: the apparent contact angle at 973 K is very high (above 150°). At higher temperatures (above 1073 K) deoxidation of aluminium by evaporation of the alumina layer allowed a real interface to be established between the solid and the liquid. However, as the silica reduction reaction occurred before the wetting, the stationary contact angle of aluminium on SiO 2 was found to be that of aluminium on alumina, and the steady contact angle of aluminium on oxidized SiC was that on alumina (at temperatures less than 1073 K) or on SiC (at temperatures higher than 1173 K). The strong reactivity between aluminium and SiO 2 cannot be used to improve the wetting of this metal on SiC. Consequently, silica layers on SiC cannot help the incorporation of particles or the infiltration of fibres by aluminium.

Oxidation property of silicon small particles

Abstract: The oxidation rate of silicon small particles prepared by a gas‐evaporation method and with diameters ranging from about 20 to 500 nm is investigated by high‐resolution transmission electron microscopy. It is found that the oxidation rate of silicon small particles is less than the rate for wafers, and decreases with decreasing particle size. This phenomenon cannot be explained by the Deal–Grove model.

Electrochromic Behavior of Nickel Oxide Electrodes I . Identification of the Colored State Using Quartz Crystal Microbalance

Abstract: In the present paper the quartz crystal microbalance is used as a sensitive detector of mass changes taking place during an electrochromic process. Electrochemical and electrochromic characteristics of nickel oxide electrodes strongly depend on the preparation method of the samples. Three different types of materials are studied and their electrogravimetric responses compared: hydroxide film prepared by cathodic deposition from a Ni2+‐containing solution; porous and stoichiometric nickel oxide films formed by anodic oxdation of a nickel electrode in a concentrated solution; and nonstoichiometric films prepared by electron‐beam evaporation. A formula describing the colored film is proposed, taking into account the effect of hydrated alkaline cation (Li+; K+) incorporation.

Raman investigations of the surface modes of the crystallites in cds thin films grown by pulsed laser and thermal evaporation

Abstract: CdS films have been grown on Corning glass by pulsed laser evaporation (PLE) and thermal evaporation (TE) techniques at a substrate temperature between room temperature and 250 °C. The quality of these films is investigated by resonance Raman scattering, x‐ray diffraction and optical transmittance. Our results reveal that the Raman shifts of the surface phonon mode are observed with 300 and 297 cm−1 by PLE and TE techniques, respectively, and as many as four overtones are obtained by PLE method. The difference of Raman shift between these two techniques are caused by the discrepancy of crystallite sizes which is larger for PLE technique. The crystallite sizes are in the range of 200–500 A in diameter. Highly oriented films have been grown by both of the techniques even when the substrate is at room temperature.

Evaporation system and method for gas jet deposition of thin film materials

Abstract: A method and apparatus for depositing thin films of materials such as metals, oxides and nitrides at low temperature relies on a supersonic free jet of inert carrier gas to transport vapor species generated from an evaporation source to the surface of a substrate. Film deposition vapors are generated from solid film precursor materials, including those in the form of wires or powders. The vapor from these sources is carried downstream in a low pressure supersonic jet of inert gas to the surface of a substrate where the vapors deposit to form a thin film. A reactant gas can be introduced into the gas jet to form a reaction product with the evaporated material. The substrate can be moved from the gas jet past a gas jet containing a reactant gas in which a discharge has been generated, the speed of movement being sufficient to form a thin film which is chemically composed of the evaporated material and reactant gases.

Pulsed laser deposition of stoichiometric potassium-tantalate-niobate films from segmented evaporation targets

Abstract: The preparation of epitaxial potassium‐tantalate‐niobate (KTa0.7Nb0.3O3, KTN) films on strontium‐titanate substrates by means of pulsed excimer laser evaporation in vacuum is reported. In the most successful deposition experiments, a segmented evaporation target consisting of a semicircular KTN single crystal and a semicircular potassium nitrate pellet was utilized−to our knowledge for the first time; it was thus possible to overcome the otherwise observed partial loss of the volatile potassium and to avoid potassium deficiency in the KTN films. Rutherford backscattering spectrometry and x ray diffraction results indicate that the samples have the desired stoichiometric composition as well as the orientation prescribed by the substrate crystal.

Improved control of TiN coating properties using cathodic arc evaporation with a pulsed bias

Abstract: A combined d.c.-pulse bias voltage was used in combination with a cathodic arc evaporation process for the deposition of TiN on planar plates and drilling tools at substrate temperatures T between 330 and 500 °C. This new pulse technique appeared to be a powerful tool to achieve independent control of the substrate temperature, coating adhesion and uniformity of deposition. As a result, high coating adhesion can be obtained at low substrate temperatures. The adhesion uniformity across large-area samples is considerably improved. Unpolished rough substrate parts can be coated without cauliflower-like growth defects. Because of intensive ion bombardment in the pulse period, smoother TiN coatings with a reduced droplet size were obtained.

The Structural Changes of Indium-Tin Oxide and a-WO3 Films by Introducing Water to the Deposition Processes

Abstract: Indium-tin oxide (ITO) films and amorphous WO3 (a-WO3) films were deposited by DC magnetron sputtering and EB evaporation, respectively, under different water partial pressures (pH2O). The ITO films sputtered under higher pH2O showed higher resistivities because of the decrease in hall mobility and had rather different orientation distributions of the crystal axis of the grains. It was found from XPS analyses that the In-O-H bonds which were not found in the films existed at the interface between the glass substrates and the ITO films, and much more of these bonds existed for the higher pH2O films. This suggests that the structural change which increased the resistivity occurred at the first stages of the formation of the films. For the a-WO3 films deposited under high pH2O, the decreases of order parameters and increases of W=O bonds were observed by Raman spectroscopy, indicating a decrease in microcrystal sizes.

Method of manufacturing ultrafine particles and their application

Abstract: Ultrafine particles (9) are produced from a target 30) by laser beam evaporation. The laser beam (1) is directed to the target in such a manner that the removal of the target material takes place in the direction of movement of the laser beam. The ultrafine particles thus manufactured are preferably used for the manufacture of single or multi-component materials or moulded bodies from such materials; by coating substrates (15) with said ultrafine particles.

High-resolution electron microscopy study of NiMo nanocrystals prepared by high-energy mechanical alloying

Abstract: A growing interest has emerged in the past few years over a new class of materials called “nanocrystalline solids” (NS). These materials are made of extremely small crystals with dimensions ranging from 1 nm to 10 nm. Up to now, most of these solids were fabricated from the gas phase by an evaporation/ condensation process. Recently, however, high energy mechanical alloying (MA) has been shown to be an excellent tool to produce various types of metastable structures, including NS. Through high energy MA we have fabricated nanocrystalline nickel oversaturated with molybdenum which shows an extremely high electrocatalytic activity for the hydrogen evolution reaction in alkaline solutions. In order to fully understand the chemical properties of these new alloys, we have investigated, through high resolution electron microscopy, the microstructure and the size distribution of the crystalline throughout the milling process. A detailed study of the crystalline interfaces and grain boundaries is also presented.

Surface-enhanced Raman scattering study of polymer on metal. 2. Molecular chain orientation of polybenzimidazole and poly(L-histidine) and its transition

Abstract: Polybenzimidazole has been observed to show two orientations of its main chain on the surface of silver foil etched with nitric acid, resulting from different sample doping methods. By slow evaporation of the solvent from a dilute solution spread on Ag foil, the aromatic rings are deposited lying down flat on the surface, while dipping silver foil into a warm polymer solution resulted in a perpendicular orientation of the rings. Upon heating, the heteroaromatic rings stand up from the flat orientation to form and N-bonded geometry. Two orientations of side groups of poly(L-histidine) on Ag foil were also observed

Physical behaviour of CdO films prepared by activated reactive evaporation

Abstract: High transparent and conductive CdO films were prepared using the activated reactive evaporation technique on Corning 7059 glass substrates. The film resistivity and transmittance were found to be influenced by the glow power of the discharge. Electron mobilities of 4-28 cm2 V-1 s-1 and carrier density in the range 7.8*1018-6.97*1019 cm-3 were observed. The energy gap of the films calculated from the optical absorption measurements was 2.42 eV.

Chemically disordered Ni3Al synthesized by high vacuum evaporation

Abstract: Films of chemically disordered fcc Ni3Al were synthesized by the vacuum evaporation of Ni3Al onto room temperature and liquid nitrogen temperature substrates. X-ray diffractometry and transmission electron microscopy showed the material to be single phase with an average grain size of about 4 nm. The formation of the equilibrium L12 ordered phase occurred simultaneously with grain growth at temperatures above 350°C. Differential scanning calorimetry provided ordering enthalpies of 7 kJ/mole and 9 kJ/mole for material evaporated onto room temperature and liquid nitrogen temperature substrates, respectively.

A comparison of the corrosion behaviour and hardness of steel samples (100Cr6) coated with titanium nitride and chromium nitride by different institutions using different deposition techniques

Abstract: Deposition of hard coatings may influence the mechanical properties of the bulk material and its corrosion resistance. In this work we study the hardness of the coated and the back side of 100Cr6 steel plates. Electrochemical corrosion tests were performed in O2-saturated acetate buffer of pH 5.6 at 25 °C. Chromium nitride and titanium nitride coatings prepared by different physical vapour deposition processes, such as arc, thermionic arc evaporation, magnetron sputtering and ion-beam-assisted deposition (IBAD) were compared. The results show that, for sufficient corrosion protection, chromium nitride layers have to be thicker than 500 nm. An increased nitrogen partial pressure in the evaporation chamber of the IBAD process improves the corrosion resistance significantly. The hardness of the substrates was reduced in the case of thermoionic arc evaporation only, indicating a deposition temperature of more than 250 °C. For this process, however, we obtained the best corrosion results.

TiAl)N advanced films prepared by arc process

Abstract: This paper reviews the influence of arc plasma parameters for deposition of (TiAl)N compound films. Various cathode designs and material compositions were used as evaporation sources for the deposition of (TiAl)N coatings. The experimental results showing the influence of the arc process parameters on composition, surface morphology, adhesion, microhardness and color values are discussed. The test results from cutting tools show that the arc technique is well suited to the industrial deposition of (TiAl)N coatings by evaporation of alloyed material in a reactive gas atmosphere. The observed dependence of the aluminum content on the bias voltage using the arc process offers an interesting possibility for varying the aluminum content of the growing film composition. Increasing aluminum content leads to an increase in surface coating roughness. To overcome this problem two modified arc process solutions under investigation are presented. It was found by using these solutions that the number of macroparticles can be considerably reduced.

Photostimulated evaporation of SiO2 and Si3N4 films by synchrotron radiation and its application for low‐temperature cleaning of Si surfaces

Abstract: SiO2 and Si3N4 films are shown to be removable by vacuum ultraviolet light irradiation with synchrotron radiation (SR) in an ultrahigh vacuum. The dependence of the photostimulated evaporation rate on substrate temperature shows that the reaction is induced by an electronic mechanism. Polycrystalline Si and crystal Si are unaffected by SR irradiation. By applying this reaction to the thin native oxide film grown during a wet pretreatment, Si surfaces can be cleaned at temperatures as low as 650 °C. Si(100)‐2×1 and Si(111)‐7×7 structures are observed by reflection high‐energy electron diffraction after a few hours irradiation. Two‐dimensional epitaxial growth by gas‐source molecular‐beam epitaxy with Si2H6 occurs selectively on the SR‐irradiated region of a Si(100) surface, indicating cleanliness and flatness of the irradiated area.

Thin films for gas sensors

Abstract: Thin tin dioxide films are used as sensitive elements for gas sensors. The physical properties of such materials and their electrical performance largely depend on their methods of production. This work presents two methods used to produce thin dioxide films, i.e., chemical vapour deposition and reactive evaporation. Optimization of the deposition parameters enables us to process highly sensitive materials and even materials able to discriminate between certain gases, such as alcohol, benzene or hydrogen sulphide.

Infrared absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

Abstract: The Fourier transform infrared spectra of different compositions of evaporated V2O5/B2O3 thin films have been investigated. Most of the absorption bands corresponding to V2O5 and B2O3 films coincide with those reported by other authors. The short-range order in amorphous V2O5 films is found to be conserved. The absorption spectra indicate a boroxol ring structure for B2O3 films. In co-evaporated V2O5/B2O3 films the boron is observed to substitute in the V2O5 network such that the coordination number of vanadium ion remains unchanged. The presence of a number of bands corresponding to -OH groups indicates the hygroscopic character of the films.

Superconducting YBa2Cu3O7−δ thin films on Si (100) substrates with CoSi2 buffer layers by an in situ pulsed laser evaporation method

Abstract: We have prepared high‐quality c‐axis oriented superconducting YBa2Cu3O7−δ thin films on Si (100) substrates with CoSi2 buffer layers by in situ pulsed laser ablation processing. The films were characterized by x‐ray diffraction, four‐point ac electrical resistivity, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. YBa2Cu3O7−δ films were found to be textured with c axis perpendicular to the substrate. A plot of normalized resistance against temperature exhibited a metallic behavior followed by an onset superconducting transition at 91 K with zero resistance temperature (Tc0) of 83 K. Cross‐sectioned TEM results showed quite smooth interface between CoSi2 and Si with little interdiffusion; however, a reacted zone was observed between CoSi2 and YBa2Cu3O7−δ layers.

Properties and microstructure of tungsten films deposited by ion-assisted evaporation

Abstract: The modification of film properties in evaporated tungsten was studied as a function of deposition environment. Using concurrent argon ion bombardment of the growing film, the stress varied in the same manner at all ion energies and substrate temperatures. Initial increases in tensile stress are followed by a monotonic trend toward compressive stress, for all sets of films. On the other hand, the qualitative changes in film resistivity with concurrent bombardment were dependent on the ion energy and substrate temperature, showing increases at high temperature and energy and decreases at low temperature and energy. Changes in the microstructure and impurity content in deposited films were found to be strongly linked to stress and resistivity changes. The trend toward compressive stress induced by high levels of ion bombardment is primarily reflected in an increase in (110) orientation. Increased resistivity is related to decreased grain size, increased (110) texture, and increased levels of film argon and oxygen content. By choice of deposition conditions, both the resistivity and stress can be minimized.

Magneto-optical Kerr effect and perpendicular magnetic anisotropy of evaporated and sputtered Co/Pt multilayer structures

Abstract: Thin and ultrathin Co/Pt multilayered structures have been prepared on glass substrates by electron‐beam evaporation at room temperature and by sputtering at various substrate temperatures and sputtering pressures. Perpendicular magnetic anisotropy was found in samples with Co/Pt bilayer thicknesses near 3 A/10 A and total thicknesses of the layer stack of no greater than 300 A. X‐ray diffraction was performed on the samples to determine layer spacing and integrity, and possible crystallinity of films. Crystalline structures in the interface between the Co and Pt layers were found and identified. The effects of sputtering parameters, such as pressure and substrate temperature, on the magneto‐optical Kerr effect were studied. The two deposition methods, electron‐beam evaporation and sputtering, resulted in different magneto‐optical properties in samples with the same nominal layer structures. We have also investigated optical properties (reflectance, index of refraction, and extinction coefficient) of these materials using ellipsometry.

Manufacturing method for electrode

Abstract: A manufacturing method for an electrode in which ultra fine particles of active material formed in gas by an evaporation method are carried in a gas flow and blown onto a surface of a substrate, so that an electrode comprising a thin film of active material is formed on the surface of the substrate. A manufacturing method for an electrode-electrolyte composite in which ultra fine particles of active material formed in gas by the evaporation method are carried in a gas flow and blown onto a surface of a film comprising a solid electrolyte, so that an electrode comprising a thin film of active material is formed on the surface of the film. The above manufacturing method for an electrode can provide an anode or a cathode comprising an ultra thin film having an uniform thickness of under 10 microns inclusive, for example. The above manufacturing method for an electrode-electrolyte composite can provide, with good productivity, an electrode-electrolyte composite in which an adhesion of the electrode with the electrolyte is excellent and the electrode is of an ultra thin type having an uniform thickness.