Direct Electron Beam Evaporation Research Articles

Improvement of Microcathode Arc Thruster Lifetime by Deposition of Boron-Containing Coating

Boron-containing coatings are actively used to improve the surface properties of mechanical parts of various devices and cutting tools. In this Paper, we demonstrate that deposition of boron-containing coatings by direct electron-beam evaporation of a boron target with a fore-vacuum plasma-cathode electron source can be used to substantially (by a factor of approximately 6–17) improve the lifetime of miniature (centimeter-sized), low-power (several watts), micronewton thrust level microcathode arc thrusters. Such improvement is a result of slowing down the interelectrode film degradation that occurs after numerous arc pulses. This improvement is observed after applying a hard (resistant to shock by plasma in a single pulse) sputter-resistant (able to maintain its protective properties for numerous pulses) boron coating on the interelectrode dielectric (alumina ceramic). This finding opens up a new way to improve the performance and lifetime of low-power vacuum-arc based propulsion devices for small satellites.

Fore-vacuum plasma-assisted deposition of dielectric coatings and process characterization

The paper aims at imparting electrical insulating properties to conductor surface via deposition of dielectric coatings. The originality of the method consists in the deposition of ceramic coatings as a result of direct electron-beam evaporation of solid dielectric (ceramic) target in the fore-vacuum pressure range (1-100 Pa). As the evaporating material we used alumina ceramics. The spatial distribution (geometrical shape of vapor clouds) of ceramics vapors was also studied using the system of the identical substrates placed at different angles and distances from the target. Raster microscopy have demonstrated that we achieved uniform alumina ceramic coatings with thickness up to 5 µm (measured by a non-contact profile meter), with deposition rate of ≈ 0.3 µm/min and surface resistance up to 140 MOhm (measured by thera ohmmeter).

Organic Electrodes Based on Grafted Oligothiophene Units in Ultrathin, Large-Area Molecular Junctions

Molecular junctions were fabricated with the combined use of electrochemistry and conventional CMOS tools. They consist of a 5-10 nm thick layer of oligo(1-(2-bisthienyl)benzene) between two gold electrodes. The layer was grafted onto the bottom electrode using diazonium electroreduction, which yields a stable and robust gold-oligomer interface. The top contact was obtained by direct electron-beam evaporation on the molecular layers through masks defined by electron-beam lithography. Transport mechanisms across such easily p-dopable layers were investigated by analysis of current density-voltage (J-V) curves. Application of a tunneling model led to a transport parameter (thickness of ~2.4 nm) that was not consistent with the molecular thickness measured using AFM (~7 nm). Furthermore, for these layers with thicknesses of 5-10 nm, asymmetric J-V curves were observed, with current flowing more easily when the grafted electrode was positively polarized. In addition, J-V experiments at two temperatures (4 and 300 K) showed that thermal activation occurs for such polarization but is not observed when the bias is reversed. These results indicate that simple tunneling cannot describe the charge transport in these junctions. Finally, analysis of the experimental results in term of "organic electrode" and redox chemistry in the material is discussed.

Evolution of chemical states within the HfO 2/Si(1 0 0) interface upon annealing, prepared by direct electron beam evaporation

We demonstrate the preparation of the system HfO 2/Si(1 0 0) by direct evaporation of hafnium dioxide from a specially prepared electron beam evaporator. Investigating the system by means of photoelectron spectroscopy in the soft X-ray regime, we show the system’s interface being free of silicon dioxide and hafnium silicide after evaporation. Upon annealing the formation of SiO 2 at the interface is investigated by using high resolution photoemission spectra. Their separation into different sub-oxides at the interface is presented. The structural order at the crystalline/amorphous interface is investigated by X-ray photoelectron diffraction. The system’s degradation is observed at above 700 °C.

Optical properties of magnesium fluoride thin films produced by argon ion-beam assisted deposition

Magnesium fluoride thin films were deposited on silica glass and single crystal silicon substrates by argon ion-beam assisted deposition (IBAD). The effects of argon ions impinging on the growing film on the optical and chemical properties of the single layers were investigated. Compared to MgF2 films produced by direct electron-beam evaporation, the films obtained by IBAD exhibited increased optical absorption and refractive indices, fluorine depletion and increased oxygen contamination. Optical data were analyzed and are discussed with regard to the chemical composition of the films.

Characterization of magnesium fluoride thin films deposited by direct electron beam evaporation

Magnesium fluoride films have been deposited on quartz and silicon substrates by direct electron beam evaporation. The structure, composition, and mass density of films were investigated as functions of the deposition temperature ranging from ambient temperature to 300 °C. The composition of films determined by infrared spectroscopy, and the residual stresses in films calculated from the change of the radius of curvature of Si substrates, were studied as functions of the aging time of films in room air and deposition temperature. The aging behavior is analyzed and discussed in connection with the microstructure and mass density of films.

Deposition and characterisation of TiAlBN coatings produced by direct electron-beam evaporation of Ti and Ti-Al-B-N material from a twin crucible source

TiAlBN coatings were synthesised by evaporating Ti and hot isostatically pressed TiAl 0.68B 3.67N 2.44 material from a twin crucible source in an Ar plasma at 450 °C. A combination of optical emission spectroscopy and partial pressure control was utilised to control the Ti and TiAl 0.68B 3.67N 2.44 evaporation rates and hence the Ti-Al-B-N composition in the coating. The goal of this investigation was to study the influence of composition on the structural and mechanical properties of these coatings. The influence of the Ti/B ratio (in the range of 0.34–2.31) in TiAlBN coatings containing approximately 12 at. % Al and 40 at. % N (calculated from glow discharge optical emission spectroscopy data) is described. All coatings, consisting of two hard phases TiB 2 and TiN, and a soft hexagonal BN phase, showed dense structures and a decrease in roughness values with increasing Ti/B ratios. The hardness and elastic modulus increased with increasing Ti/B ratios from 0.34 to 2.31 up to 37 GPa and 320 GPa, respectively. Coatings with Ti/B = 1.73–2.31 showed a twofold increase in wet cutting performance compared to commercially available TiN and TiAlN. However, due to the rather low amount of Al in the TiAlBN coatings no significant improvement in dry cutting compared to TiN was observed.

Structure, Composition and Residual Stresses of Magnesium Fluoride Thin Films Deposited by Direct Evaporation

Magnesium fluoride films have been deposited on quartz and silicon substrates by direct electron beam evaporation. The structure, composition and mass density of films were investigated as functions of the deposition temperature ranging from 20 °C to 300 °C. The composition of films determined by infrared spectroscopy, and the residual stresses in films calculated from the change of the radius of curvature of Si substrates, were studied as functions of the aging time of films in room air and deposition temperature. The aging behavior is analysed and discussed in connection with the microstructure and mass density of films.

Controlled growth of WO3 films

We have used reactive rf magnetron sputtering of a tungsten target in Ar/O2 mixtures and direct electron-beam evaporation of WO3 pellets with and without the presence of an electron cyclotron resonance (ECR) oxygen plasma to grow WO3 films on α-Al2O3(101̄2) single-crystal substrates (r-cut sapphire). The WO3 films exhibit a range of microstructures depending on deposition conditions. Using any of the deposition methods, the films are amorphous when grown at room temperature. Postdeposition annealing in O2 induces the formation of a random polycrystalline microstructure and an increased surface roughness. Growth of crystalline WO3 films can be achieved at deposition temperatures above 200 °C. During electron-beam evaporation of WO3 at 600 °C, reflection high-energy electron diffraction observations indicate that a tetragonal phase of WO3 grows epitaxially on r-cut sapphire with the (100) tetragonal plane coincident with the rectangular mesh of the r-cut sapphire substrate. Deposition of WO3 using plasma species generated by either a rf magnetron or ECR source promotes the formation of some nuclei of an orthorhombic and/or monoclinic phase coexisting with the tetragonal phase; the nearly identical lattice parameters make the orthorhombic and monoclinic phases difficult to distinguish. Compared to the polycrystalline films, the epitaxial films exhibit both a higher base-line conductivity and a larger conductivity change upon exposure to H2S gas.

Sputtering yield and morphological changes of TiB 2 coatings induced by different incident beams

The properties of TiB 2 coatings deposited by direct electron-beam evaporation and by plasma spray deposition as well as their behavior during the interaction with the energetic beam are discussed. These coatings are considered as a plasma facing material for some parts of the next step tokamak. Sputtering yields were determined for: Ar + ion bombardment in the energy region 3–12 keV and laser beam bombardment in the range up to 10 9 W/m 2. It was found that whatever the mechanism of sputtering is, a similarity between sputtering yield and energy dependence for used combinations of incident beams and target does exist.

Production of protective coatings by electron beam evaporation

In this paper we briefly describe the principles and technological feasibilities of three methods of electron beam evaporation of materials: direct electron beam evaporation, activated reactive electron beam evaporation and electron ion evaporation. The advantages and drawbacks of electron beam vapour phase technology are discussed with respect to the deposition of corrosion-resistant, heat-resistant and wear-resistant coatings. Examples of electron beam equipment for deposition of these coatings in continuous and batch operation are given. It is emphasized that the electron beam evaporation of metallic and non-metallic materials should be considered as the most physicochemically precise set of methods for designing composite coatings of dispersed or laminar type, which cannot be deposited by other methods. The effect of structural parameters and interphase interactions on the strengthening and plasticity of coatings of the dispersion-strengthened type is studied. Further progress in the creation of protective coatings using electron beam evaporation should be based on the development of composite materials with special properties and on the simultaneous improvement of electron beam equipment and reduction in its cost.

Radio frequency dielectric dissipation measurements on yttrium oxide thin films

The dielectric dissipation factor (tan δ) of evaporated thin film Al-Y 2-O 3-Au capacitors has been measured in the frequency range 1 kHz-40 MHz. The yttrium oxide films (≈ 5000 Å) were fabricated by the direct electron-beam evaporation of 99.9% Y 2O 3 powder. The geometry of these capacitors (≈ 40 pF) deposited on alumina substrates provided large contact pads for direct attachment to the measuring bridges. Lead inductance was minimal while lead and contact resistance was less than 0.2 ω. Tan δ measurements were made at 20°C with a capacitance bridge, a Wayne Kerr bridge and a Q-meter at appropriate frequencies. At 1 kHz, tan δ values of various specimens varied from 0.004–0.009. These values decreased rapidly with increasingly frequency, however, to a resistance-corrected constant value tan δ≦0.004 over the range 100 kHz-40 MHz.

Some dielectric properties of electron-beam evaporated yttrium oxide thin films

Thin films of yttrium oxide have been fabricated by the direct electron-beam evaporation, in an oxygen atmosphere, of 99.9% yttrium oxide powder. Such films, ranging in thickness from about 2000 Å to 15,000 Å, have been observed to be quite stable and free of pinholes over areas as large as 0.5 in. × 0.5 in. At 1000 Hz and 25 °C the lowest value of dielectric dissipation factor (tan δ) obtained was 0.00255, decreasing to a value of 0.0024 at 100 kHz. Bridge measurements on such films forming capacitors of the type AlY 2O 3Au further yielded an average dielectric permittivity value ε′ = 13.5 ± 1.5 and a temperature coefficient of capacitance of + 320 p.p.m./°C. Typical breakdown field strengths were in the order of 2.8 × 10 6 volt/cm for such capacitors as large as 0.065 μF, whilst the measured resistivity of the dielectric was estimated to be > 2 × 10 14 Ω cm .