Showing papers on "Evaporation (deposition) published in 1998"

Nanoscale silicon wires synthesized using simple physical evaporation

Abstract: We report the large-scale synthesis of silicon nanowires (SiNWs) using a simple but effective approach. High purity SiNWs of uniform diameters around 15 nm were obtained by sublimating a hot-pressed silicon powder target at 1200 °C in a flowing carrier gas environment. The SiNWs emit stable blue light which seems unrelated to quantum confinement, but related to an amorphous overcoating layer of silicon oxide. Our approach can be used, in principle, as a general method for synthesis of other one-dimensional semiconducting, or conducting nanowires.

Dilute hydrogen sulfide sensing properties of CuO–SnO2 thin film prepared by low-pressure evaporation method

Abstract: A low pressure evaporation method was adopted for preparing SnO2 and CuO–SnO2 thin films. Metallic tin and copper were evaporated on the alumina substrate under a low pressure (1 torr) of air atmosphere. As observed with AFM, these evaporated films had unique microstructure in which discrete clusters of SnO2 grains (30 nm) contacted to each other two-dimensionally with large mesopores penetrating between. The film added with a small amount of CuO exhibited very high sensitivity to H2S in air, being able to detect dilute H2S close to 0.02 ppm at 300 °C. The high sensitivity seems to result from the unique promoting effect of CuO coupled with the unique microstructure of the film.

(Cr:Al)N coatings deposited by the cathodic vacuum are evaporation

Abstract: (Cr:Al)N coatings were deposited using two cathodic vacuum arc evaporators fitted with chromium and aluminium cathodes. Both monolayer and multilayer coatings were deposited with different aluminium content. Selected mechanical and tribological properties of the coating were investigated as well as the oxidation behaviour. It is shown that the oxidation rate decreases with increasing aluminium content. The hardness of the (Cr:Al)N coating is higher than that of CrN coatings.

Comparison of fibre-optic SERS sensors with differently prepared tips

Abstract: Fibre-optic sensors using surface-enhanced Raman scattering (SERS) with a single fibre for both the excitation and the signal collection require the preparation of properly roughened metal films at the tip of the fibres. Suitable techniques are slow evaporation of metals forming island-films, vacuum deposition of metal films on alumina or diamond particles, and evaporation of metals on sandblast-roughened fibre tips. All of these preparations result in SERS-active sensor tips with similar enhancements of the Raman signal intensities. The newly proposed sandblast method may be superior in practical applications because it promises the highest durability and the easiest regeneration of the thus produced sensors.

Origins and evolution of stress development in sol-gel derived thin layers and multideposited coatings of lead titanate

Abstract: Stress development in thin layers of lead titanate prepared by sol-gel processing was monitored by in situ laser reflectance measurements. Layers were spin coated onto silicon substrates and thermally cycled to 500 °C. The shrinkage normal to the rigid substrate was determined by in situ ellipsometry. Changes that occurred on drying and firing, which related to densification and stress development, are reported. The observed changes were explained in terms of evaporation and solvent/polymeric network interactions at lower temperatures, and thermal expansion mismatch between the substrate and the coating after formation of the dense oxide. Crystallization into the perovskite structure occurred only in thicker or multideposited coatings, altering the state of stress from tensile, to progressively more compressive, on cooling. The importance of the choice of substrate material, deposition method and heat treatment conditions, in relation to stress development and dependent electrical properties, are discussed.

Pulsed laser deposition and characterization of high-Tc YBa2Cu3O7 − x superconducting thin films

Abstract: This article presents a systematic overview of the work carried out in the area of pulsed laser deposition (PLD), characterization and device application aspects of high temperature superconducting YBCO thin films. The theoretical and experimental aspects of the pulsed laser deposition process for the synthesis of YBCO thin films have been described in detail. The deposition technique has emerged as a very powerful method to make composition and microstructure controlled superconducting YBCO films. Some unique features of this process are due to the rapid heating and evaporation of the target and the interaction of the laser beam with the evaporated materials leading to the formation of a high temperature plasma. Major advantages of PLD process are congruent evaporation and crystallinity due to the presence of high energy evaporants and fast response time. It has the potential to encompass a wide scope of physical vapor-deposition techniques from thermal evaporation to sputtering and MBE. The electrical and structural studies performed on laser deposited YBCO films have shown that films produced by PLD are superior than films produced by other thin film growth techniques. The major technical obstacle of particulates emission, encountered initially with PLD, has now greatly been solved. Some new developments with PLD technology such as large-area and nonplanar substrates coatings and growth of novel superconductors as oriented films have been demonstrated.

Control of the stoichiometry in the deposition of cobalt oxides on SiO2

Abstract: Both CoO and Co3O4 overlayers have been deposited on SiO2 by evaporation from metallic Co and subsequent oxidation with oxygen and a plasma of oxygen. The combined use of ion scattering spectroscopy and XPS shows that both oxides grow in the form of small particles on the surface of SiO2. Ion scattering spectroscopy also shows that the surface of cobalt oxide exposed to a plasma of oxygen is enriched in oxygen ions with respect to the surface of the cobalt oxide formed by exposure to oxygen. The Co 2p spectra corresponding to the deposits obtained by oxidation with O2 are characteristic of CoO, while those corresponding to the deposits obtained after oxidation with a plasma are typical of Co3O4. Moreover, the OCo/Co ratios determined by XPS and factor analysis indicate the formation of CoO stoichiometry in the former case and Co3O4 stoichiometry in the latter. It has also been observed that no shift in either binding energy or modified Auger parameter α′ appears as a function of coverage. This absence of shifts is interpreted as a consequence of the type of screening mechanism that dominates the relaxation of the photoholes in these oxides. © 1998 John Wiley & Sons, Ltd.

Physical investigations on electron-beam evaporated vanadium pentoxide films

Abstract: Thin films of vanadium pentoxide were prepared by the electron-beam evaporation technique onto Corning 7059 glass and silicon substrates maintained at Ts=553 K by varying the oxygen partial pressure in the range 01–20 mPa These films have been characterized by studying their chemical state, structure, optical and electrical properties V2O5 films of thickness 06 μm prepared at an oxygen partial pressure of 20 mPa exhibit an orthorhombic layered structure with an optical band gap of 23 eV The room temperature electrical conductivity of the films is 2×10−5 S cm−1 with an activation energy of 042 eV in the temperature range 303–523 K

Performance optimization of surface acoustic wave chemical sensors

Abstract: Acoustic wave devices coated with a thin layer of chemoselective material provide highly sensitive chemical sensors for the detection and monitoring of vapors and gases. In this work, a variety of coating materials and coating deposition techniques have been evaluated on surface acoustic wave (SAW) devices. A novel thin film deposition technique, matrix assisted pulsed laser evaporation (MAPLE), is utilized to coat high quality polymer films on SAW devices, and conventional pulsed laser deposition is used to deposit a passivation layer of diamond-like-carbon on a SAW device surface to prevent water adsorption. In addition, chemoselective coatings are formed by covalent attachment of functionalized species to the silica surface of SAW devices. The self-assembled monolayer or near monolayer structures are designed to populate the SAW device surface with the desirable hexafluoroisopropanol moeity. The rapid kinetic signals achievable with the various coated SAW sensors during vapor tests are examined as a function of the coating material and the quality of the thin films. In parallel to the thin film deposition, growth, and vapor testing, the electrical characteristics of the SAW sensor have been characterized. The quality factor and residual phase noise of polymer coated SAW devices are examined, and a prediction of the theoretical limit of the phase noise performance of the loop oscillator is made.

A study of some optical properties of hafnium dioxide (HfO2) thin films and their applications

Abstract: ), a series of films ranging in thickness from 50 to 10000 nm was prepared by using an electron beam gun inside an evacuated coating chamber of pressure 1×10-5 mbar. The films were obtained on optical glass substrate by using oxygen with a backfill pressure of 2.4×10-4 mbar during the deposition processes. The optical constants of the films were computed in the spectral wavelength region (350–2000 nm) from the transmission, reflection and thickness measurements. A computer program was created to determine two optical parameters n and k of the films, and this was achieved by entering the practical results into the computer program, which solved a series of equations for each wavelength. The effects created by changing various evaporation conditions (thickness, substrate temperature and evaporation rate) were studied in the spectral wavelength range, and the optimum values of the various conditions were obtained while achieving the best optical performance. According to the investigations of the HfO2 material, two applications of the anti-reflection (AR) multi-layer coatings were achieved in two different spectral wavelength ranges. The first application was measured in the visible and near infra-red (VIS/NIR) range from 500 nm to 850 nm deposited on the glass substrate. The second application was measured in the infrared (IR) range from 7500 nm to 11500 nm deposited on germanium substrate. Computer modelling for designing the optical multi-layer system has been presented. The theoretical formulation and experimental results with the same specification were achieved. The correlation between the theoretical and the experimental results reveals a close agreement that offers a convenient method for predicting and controlling the multi-layer coating. By continuous measurement of the optical and mechanical (durability) performances of the coating process, high-quality films were produced in the manufacture of various optical devices.

Flash evaporation of TiNi shape memory thin film for microactuators

Abstract: The flash evaporation, with which material for deposition is repeatedly evaporated in very small volumes, was investigated for formation of TiNi shape memory alloy thin film. Along with the flash method itself, the timing for opening the shutter proved a crucial factor in controlling thin film composition. Using our evaporation system, a thin film with a composition of around 50 at.% Ti-50 at.% Ni was obtained with an interval of about 5 s between the beginning of material evaporation and opening of the shutter. The deposited thin film had a lamella structure, corresponding to repeated deposition cycles, and showed small fluctuations in alloy composition in each deposition cycle. However, these effects on its shape memory properties could be considered tolerable. The deposited thin film showed martensitic (monoclinic structure) and reverse martensitic (B2 parent structure) transformation during cooling and heating cycles, respectively. In particular, thin film with a composition of 45–50 at.% Ni showed martensitic transformation at near room temperature and reverse martensitic transformation at about 70°C. This means that such thin film could be used as material for microactuators driven at room temperature without requiring any special cooling device.

Growth and characterization of 10-nm-thick c-axis oriented epitaxial pbzr0.25ti0.75o3 thin films on (100)si substrate

Abstract: A 10-nm-thick PbZr025Ti075O3 thin film is epitaxially grown on a SrRuO3/BaTiO3/ZrO2/Si heterostructure substrate by reactive evaporation Structural and electrical properties of the film are investigated It is concluded that the film is ferroelectric and retains a native uniform upward polarization Artificial downward polarization domains, whose average diameter is 24 nm, can be formed in the film

Method of deposition of thin films of amorphous and crystalline microstructures based on ultrafast pulsed laser deposition

Abstract: Powerful nanosecond-range lasers using low repetition rate pulsed laser deposition produce numerous macroscopic size particles and droplets, which embed in thin film coatings. This problem has been addressed by lowering the pulse energy, keeping the laser intensity optional for evaporation, so that significant numbers of the macroscopic particles and droplets are no longer present in the evaporated plume. The result is deposition of evaporated plume on a substrate to form thin film of very high surface quality. Preferably, the laser pulses have a repetition rate to produce a continuous flow of evaporated material at the substrate. Pulse-range is typically picosecond and femtosecond and repetition rate kilohertz to hundreds of megahertz. The process may be carried out in the presence of a buffer gas, which may be inert or reactive, and the increased vapour density and therefore the collision frequency between evaporated atoms leads to the formation of nanostructured materials of increasing interest, because of their peculiar structural, electronic and mechanical properties. One of these is carbon nanotubes, which is a new form of carbon belonging to the fullerene (C60) family. Carbon nanotubes are seamless, single or multishell co-axial cylindrical tubules with or without dome caps at the extremities. Typically diameters range from 1 nm to 50 nm with a length >1 μm. The electronic structure may be either metallic or semiconducting without any change in the chemical bonding or adding of dopant. In addition, the materials have application to a wide range of established thin film applications.

Chemical vapor deposition of tungsten oxide

Abstract: Crystalline and amorphous thin films of tungsten(VI) oxide can be prepared by chemical vapor deposition using a variety of volatile precursors below 500 °C Deposition parameters for preparation of WO3 films from tungsten hexacarbonyl [W(CO)6], tungsten hexafluoride (WF6), tungsten ethoxides [W(OEt)x, x = 5, 6] and tetra(allyl)tungsten [W(η3-C3H5)4] are summarized The electrochromic behavior of these films is comparable with that observed for WO3 films prepared by evaporation, sputtering and electrodeposition © 1998 John Wiley & Sons, Ltd

MgO buffer layers on rolled nickel or copper as superconductor substrates

Abstract: Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

Deposition of Heteroepitaxial In2O3 Thin Films by Molecular Beam Epitaxy

Abstract: Highly oriented thin film In2O3 was heteroepitaxially grown on an optically polished (001) plane of single crystalline yttria stabilized zirconia (YSZ) substrate using molecular beam epitaxy (MBE). The full-width at half maximum (FWHM) of the X-ray rocking curve was 0.08° for 200-nm-thick In2O3 layers indicating excellent uniformity of the crystallographic orientation compared with the heteroepitaxially-grown In2O3 deposited by a conventional method such as electron-beam (e-beam) evaporation. The minimum yield (χmin ) of the MBE grown In2O3 film obtained from Rutherford backscattering (RBS) spectra was also extremely small with a value of 3.1% implying high crystallinity with very low lattice defect density.

The hollow cathode: a high-performance tool for plasma-activated deposition

Abstract: The hollow cathode will be presented as a plasma source for reactive evaporation processes. The hollow cathode generates an arc discharge plasma. This contains a high portion of directed electrons with an enhanced mean energy, the so called low-voltage electron beam (LVEB). The mean energy of the LVEB, in the range of 11 eV, results in a very effective ionization of the gas and vapor particles. Consequently, very high plasma densities can be achieved, which corresponds to high particle densities in high-rate deposition processes. Furthermore, a high self bias potential of about 16 V is obtained on insulating substrates. For the coating of heat-sensitive substrates with high deposition rates a process with a low ratio between thermal load and deposition rate is necessary. The heat flux on plastic substrates has been measured at the reactive Al evaporation process. The overall thermal load of about 4 W/cm2 related to a deposition rate of 100 nm/s is low in comparison to other processes. This makes the hollow cathode a favorable tool for the plasma-activated high-rate deposition. The oxide layers deposited by this process show dense and glassy structures even at comparatively low condensation temperatures. This is caused by the high ion current densities in the order of 30 mA/cm2. The low ion energy determined by the self bias potential results in relatively low compressive stress below 100 MPa. The low thermal load and the moderate intrinsic stress of the layers makes the hollow cathode plasma-activated deposition (HAD) process the method of choice for the deposition of oxides as abrasion resistant layers on plastic films and sheets.

Electrochemical fabrication of n-si/au schottky junctions

Abstract: We report on the electrochemical deposition of gold films onto n-type silicon. Gold deposition occurs through progressive nucleation and diffusion limited growth. A high density of gold nuclei was obtained by using a short potential pulse to −1.6 V(Ag/AgCl), and subsequent growth was performed at about −1.1 V(Ag/AgCl) where the growth rate is kinetically limited. Transmission electron microscopy showed that high quality, continuous gold films were formed with an average grain size on the order of 50–70 nm. The electrical properties of the electrochemically deposited Si/Au Schottky junctions are comparable to junctions prepared by evaporation or sputtering techniques.

In situ growth of evaporated TiO2 thin films using oxygen radicals: Effect of deposition temperature

Abstract: The growth and characterization of TiO2 thin films deposited by electron-beam evaporation of TiO2 have been studied. The growing film was exposed to a flux of atomic oxygen supplied from an oxygen radical beam source at a total deposition pressure of 1×10−5 mbar. The properties of as-deposited 1000 A thick films on silicon substrates have been studied in the growth temperature interval 100–680 °C. X-ray diffractometry demonstrated a phase evolution as a function of growth temperature, from amorphous (100 °C) to anatase (300 °C) and eventually rutile (680 °C). While the amorphous film surface had a smooth film surface as evidenced by atomic force microscopy, the anatase and rutile specimens exhibited a grain-like morphology. No apparent difference in surface roughness was observed between the anatase and rutile phase. Secondary ion mass spectrometry indicated that silicon diffused into the rutile film grown at the highest temperature. Ellipsometry measurements revealed that the crystallized films exhibited...