Electron Beam Gun Evaporation Research Articles

Multispectral antireflection coating simultaneously effective in visible, diode laser, Nd-YAG and eye safe laser wavelength

Multi-spectral antireflection coating effective in visible region for sighting system, Nd-YAG laser wavelength for designator/seeker system, both diode laser and eye safe laser wavelength for ranging purpose can use common objective/receiver optics highly useful for state of art laser instrumentation. In this paper, design and fabrication of antireflection coating simultaneously effective in visible region (500 to 650nm), diode laser at 904±25nm and Nd-YAG laser at 1064±25nm, and erbium-glass laser wavelength at 1540±25nm has been reported. Inhomogeneous refractive index profile as suggested by Southwell was used to design this coating. The inhomogeneous profile was then approximated with eleven steps from substrate to air medium in order to obtain desirable antireflection property in the visible and laser wavelengths. These steps were then converted into the available coating materials (titanium-di-oxide and magnesium fluoride) of twenty-two layer stack. The multilayer stack was fabricated by using electron beam gun evaporation system in Balzers BAK-600 vacuum coating unit. The result achieved were less than 2% average reflection (98% average transmission) from 500 to 650nm, 1.5% reflection (98.5% average transmission) at 904nm, 1064nm and 1540nm. The coated samples successfully passed the specifications of MIL-C-14806 tests.

Thickness dependence of optical parameters for ZnTe thin films deposited by electron beam gun evaporation technique

Zinc telluride thin films with different thicknesses have been deposited by electron beam gun evaporation system onto glass substrates at room temperature. X-ray and electron diffraction techniques have been employed to determine the crystal structure and the particle size of the deposited films. The stoichiometry of the deposited films was confirmed by means of energy-dispersive X-ray spectrometry. The optical transmission and reflection spectrum of the deposited films have been recorded in the wavelength optical range 450–2500 nm. The variation of the optical parameters, i.e. refractive index, n, extinction coefficient, k, with thickness of the deposited films has been investigated. The refractive index dispersion in the transmission and low absorption region is adequately described by the single-oscillator model, whereby the values of the oscillator strength, oscillator position, dispersion parameter as well as the high-frequency dielectric constant were calculated for different film thickness. Graphical representations of the surface and volume energy loss function were also presented.

Surface flatness of optical thin films evaluated by gray level co-occurrence matrix and entropy

The surface characteristics of titanium oxide films evaluated by gray level co-occurrence matrices (GLCMs) and entropy are demonstrated experimentally. A PC-based measurement system was set up to detect the interference fringe of optical coating surface as captured by a Fizeau interferometer. Titanium oxide films were prepared by an electron-beam gun evaporation method. The proposed measuring system was used to evaluate the surface flatness of titanium oxide films coated on glass substrates. The variation of entropy in titanium oxide films before and after film deposition was found to be related to the root-mean-square (rms) surface roughness. Surface characteristics of thin films were fast measured by our proposed method and the test results were verified by atomic force microscopy (AFM) and scanning electrical microscopy (SEM).

Optical properties of thermochromic Cu2HgI4 thin films

Cu2HgI4 powder has been prepared by precipitation from reactive chemical solutions. An electron beam gun evaporation system was used to deposit the prepared powder in a thin film form onto a Corning 7059 glass substrate. The x-ray diffraction study reveals that the as-deposited films are polycrystalline in nature and have a composition corresponding to the Cu2HgI4 single phase. The differential thermal analysis curve exhibits a strange endothermic peak located at a temperature of 355.5 K, corresponding to the phase change from the first-order phase to the fast ion-conducting phase. The phase change is accompanied by a colour change from bright-red (β-phase) to dark-brown (α-phase). The optical properties of as-deposited films have been calculated from the recorded transmission and reflection data in the spectral range 600–2500 nm. The refractive index of the as-deposited films was found to follow the two-term Cauchy dispersion relation and is adequately described by the effective-single-oscillator model. The refractive index–wavelength variation leads to the determination of the oscillator parameters Eo and Ed to be 3.113 and 9.883, respectively. The static refractive index, no(0), and static dielectric constant, εs, were also calculated as a result of the latter data and were found to be 2.043 and 4.175, respectively. The analysis of the optical absorption coefficient confirmed the presence of a direct optical transition with a band gap energy of 1.96 eV.

Electrical properties of Al 2O 3–HfTiO laminate gate dielectric stacks with an equivalent oxide thickness below 0.8 nm

We report high quality nanolaminate films consisting of five Al 2O 3–HfTiO layers with a dielectric constant of about 29. The dielectric stack was deposited on unheated p-Si substrate from Al 2O 3 and 1HfO 2/1TiO 2 targets using an electron beam gun evaporation system without addition of oxygen. A dielectric constant for a thick HfTiO film of about 83 was also demonstrated. The electrical characteristics of as deposited structures and ones which were annealed for 5–10 min in an O 2 atmosphere at up to 950 °C were investigated. Two types of gate electrodes: Pt and Ti were compared. The dielectric stack which was annealed up to 500 °C exhibits a leakage current density as small as ∼ 1 × 10 − 4 A/cm 2 at an electric of field 1.5 MV/cm for a quantum mechanical corrected equivalent oxide thickness of ∼ 0.76 nm. These values change to ∼ 1 × 10 − 8 A/cm 2 and 1.82 nm respectively, after annealing at 950 °C for 5 min.

Thickness influence on optical and electrochemical properties of dititanium trioxide (Ti 2O 3) films deposited on glass substrates by electron beam gun evaporation

Dititanium trioxide (Ti 2O 3) films with thickness between 13 and 100 nm on glass substrates were prepared by electron beam gun evaporation at low temperature. They were characterized by transmittance absorbance and reflectance curves. The optical properties of film include band gap calculation, band to band transitions and electrochemical polarization in phosphate buffer solution were studied. The films produced have fairly high transmittance >62% between 330 and 400 nm wavelength region which was decreased by films thickness increasing. The films also showed poor transmittance below 330 nm but have good absorbance in the UV region. Furthermore, these films have good reflectance >67% between 400 and 800 nm wavelength region which was increased by films thicknesses increasing. By plotting the Taue plot ( ( α h υ ) n Versus h υ ) for Ti 2O 3 films, we also found that the band to band indirect transitions were most probable than the direct transitions by films thickness increasing. Band gaps of 4.08 eV for allowed direct transition and 3.81 eV for allowed indirect transition for the thinnest film were also obtained. Electrochemical polarization of Ti 2O 3 films in phosphate buffer solution (pH 7) results showed higher current for thinner films. Schottky barriers were produced for both films (13 and 30 nm in thickness) in contact with aqueous solution.

Influence of thermal annealing and ultraviolet light irradiation on LaF_3 thin films at 193 nm

Lanthanum fluoride (LaF3) thin films were prepared by resistive heating evaporation and electron-beam gun evaporation under the same deposition rate, deposition substrate temperature, and vacuum pressure. The coated LaF3 films were then treated by heat annealing and UV light irradiation. The optical properties, microstructures, stress, and laser-induced damage threshold (LIDT) at a wavelength of 193 nm were investigated. The surface roughness, optical loss, stress, and LIDT of the films were improved after the annealing. The films had better properties when irradiated by UV light as compared with heat annealing.

Characteristics of metal-insulator-semiconductor capacitors based on high-k HfAlO dielectric films obtained by low-temperature electron-beam gun evaporation

We describe the characteristics of thin HfAlO films deposited at low temperature by electron beam gun evaporation. As-deposited films thinner than 6 nm exhibit an effective dielectric constant (keff) of 9–11.5. The minimum quantum mechanical corrected effective oxide thickness is ∼1.45nm and the leakage currents are very low. Rapid thermal annealing in a N2 environment improves the leakage further and up to 750 °C does not affect keff. Higher annealing temperatures reduce keff, but even at 950 °C, it has a value of 6.5. These HfAlO films have the potential to serve as a substitute for SiO2 in small-scale metal-insulator-semiconductor structures.

Topical meeting on optical interference coatings (OIC'2001): manufacturing problem.

Measurements are presented of the experimental filters submitted to the first optical thin-film manufacturing problem posed in conjunction with the Topical Meeting on Optical Interference Coatings, in which the object was to produce multilayers with spectral transmittance and reflectance curves that were as close as possible to the target values that were specified in the 400- to 600-nm spectral region. No limit was set on the overall thickness of the solutions or the number of layers used in their construction. The participants were free to use the coating materials of their choice. Six different groups submitted a total of 11 different filters for evaluation. Three different physical vapor deposition processes were used for the manufacture of the coatings: magnetron sputtering, ion-beam sputtering, and plasma-ion-assisted, electron-beam gun evaporation. The solutions ranged in metric thickness from 758 to 4226 nm and consisted of between 8 and 27 layers. For all but two of the samples submitted, the average rms departure of the measured transmittances and reflectances from the target values in the spectral region of interest was between 0.98% and 1.55%.

Structural properties and electrical characteristics of electron-beam gun evaporated erbium oxide films

We report properties of Er2O3 films deposited on silicon using electron-beam gun evaporation. We describe the evolution with thickness and annealing temperature of the morphology, structure, and electrical characteristics. An effective relative dielectric constant in the range of 6–14, a minimum leakage current density of 1–2×10−8 A/cm2 at an electric field of 106 V/cm and breakdown electric field of 0.8–1.7×107 V/cm are demonstrated. Breakdown electric field and leakage current densities are correlated with the surface morphology. The obtained characteristics make the Er2O3 films a promising substitute for SiO2 as an ultrathin gate dielectric.

Optical and electrical characterization of the electron beam gun evaporated TiO 2 film

We report measured evolutions of the optical band gap, refractive index and relative dielectric constant of TiO 2 films obtained by electron beam gun evaporation and annealed in an oxygen environment. A negative shift of the flat band voltage with increasing annealing temperatures, for any film thickness, is observed. A dramatic reduction of the leakage current by about four orders of magnitude to 5×10 −6 A cm −2 (at 1 MV cm −1) after 700°C and 60 min annealing is found for films thinner than 15 nm. The basic carrier transport mechanisms at different ranges of applied voltage such as hopping, space charge limited current and Fowler–Nordheim is established. An equivalent SiO 2 thickness in order of 3.5 nm is demonstrated.

Effects of annealing conditions on optical and electrical characteristics of titanium dioxide films deposited by electron beam evaporation

We report measured evolutions of the optical band gap, refractive index, and relative dielectric constant of TiO2 film obtained by electron beam gun evaporation and annealed in an oxygen environment. A negative shift of the flat band voltage with increasing annealing temperatures, for any film thickness, is observed. A dramatic reduction of the leakage current by about four orders of magnitude to 5×10−6 A/cm2 (at 1 MV/cm) after 700 °C and 60 min annealing is found for films thinner than 15 nm. An equivalent SiO2 thickness of the order of 3–3.5 nm is demonstrated. An approach is presented to establish that at different ranges of applied voltage the hopping, space charge limited current, and Fowler–Nordheim are the basic mechanisms of carrier transport into the TiO2 film.

Making parabolic mirrors by electron-beam gun evaporation method with ion-assisted deposition

A spherical surface was modified to form a parabolic surface by the evaporation of Al 2O 3 films and an ion-assisted deposition process using a designed mask. The stress of the evaporated films was measured by a phase shifting Twyman–Green interferometer. Ion beam bombardment was proven to reduce the stress of Al 2O 3 films. The optimum ion beam voltage and ion beam current density for reducing the film stress were 300 V and 16 μA/cm 2 for Al 2O 3 films.

Mechanical properties of multilayer pvd Ti/TiB2 coatings

To obtain from a tribological perspective acceptable PVD coatings of covalently bonded materials, such as borides and oxides, it is essential to control and often reduce the very high compressive stresses which develop during coating growth, since such stresses not only reduce coating adhesion but also limit film thickness. A possible way to obtain lower stress levels could be to utilise multilayer coatings, that is to combine the stressed material with a more ductile material in a layered structure. In the present study a highly stressed PVD TiB2 material was layered with ductile Ti. The multilayer period, i.e. the combined thickness of one Ti lamella and one TiB2 lamella, and the lamellar thickness ratio of the two phases were varied in order to evaluate their influences on some important mechanical properties and on the abrasive wear resistance of the Ti/TiB2 coatings. The coatings were deposited using magnetron sputtering of TiB2 and electron beam gun evaporation of Ti. To evaluate the coating phase composition X-ray diffraction was used. Mechanical and tribological properties were examined by nanoindentation (hardness and modulus), beam deflection (residual stress), scratch testing (cohesion and adhesion), and dimple grinding (abrasive wear resistance). Hardness, Young’s modulus, compressive residual stress, and abrasive wear resistance were found to increase with the fraction of TiB2 in the coatings, and an inverse relation was found for the critical normal load obtained in scratch tests, i.e. cohesion/adhesion decreased with increasing TiB2 fraction. The investigation showed that a hybrid PVD technique combining electron beam evaporation of Ti and magnetron sputtering of TiB2 can be used to produce coatings with increased fracture toughness, decreased residual stress, and relatively high hardness as compared to homogeneous PVD TiB2 . It was also found that the yield/fracture strength of Ti was insufficient, i.e. it could not accommodate the level of stress generated in the TiB2 phase. Therefore, by choosing another material with higher yield/fracture strength than Ti it is believed that the properties of the multilayer coating could be improved even further.

Electrical characteristics of Ta2O5 thin films deposited by electron beam gun evaporation

We report electrical characteristics of Ta2O5 films deposited by a simple electron beam gun evaporator. We describe thickness-dependent characteristics for films with thicknesses of 7–130 nm. An equivalent SiO2 thickness of 3.5–4.5 nm for films whose leakage current density at an electric field of 106 V/cm is lower than 10−7 A/cm2 is demonstrated.

Transparent indium tin oxide films prepared by ion-assisted deposition with a single-layer overcoat

Transparent indium tin oxide (ITO) films have many applications as electrodes in Liquid Crystal displays and EMI/RFI shielding. We have compared two processes for obtaining ITO thin films with low resistivity (below 15B/sq) and high transmittance (above 90%) in the visible region. The first process was deposition using electron beam gun evaporation. The second process was using Ion Assisted Deposition (lAD) of low energy oxygen ions from an end-Hall ion source. In both cases the conductive layer was overcoated with 50-250 nm thickness of a MgF2 layer to enhance the transmittance. When ITO produced by IAD was overcoated with a MgF2 layer, the surface was found to be conductive. The surface was analyzed using the Auger Electron and Second Ion Mass Spectroscopy methods. Traces of indium were found on the MgF2 layer. We speculate that indium that diffused through the overcoat layer gives assistance to the conductivity and enables the measurement of the resistivity from the top surface of the coating. This effect occurred only when the ITO was deposited using IAD. This is an advantage in manufacturing of optical conductive windows. Otherwise there is a need to leave exposed areas of ITO for conductive contacts. The diffusion process was not observed with oxide layers. Atomic Force Microscopy scans show that the IAD process decreased the average roughness of the surface.

Properties of TiO 2 films prepared by ion-assisted deposition using a gridless end-Hall ion source

TiO 2 thin films were deposited using electron-beam gun evaporation with ion-assisted deposition (IAD) of low energy oxygen ions from an end-Hall ion source. The index of refraction and stress were measured as a function of the ion source voltage and current and were compared with results without IAD. The index of refraction increased with the increase of the ion gun voltage. The stress changed from compressive to tensile with the voltage increase, resulting in a better performance than conventional thermal evaporation. Atomic force microscopy was used to study the microstructure of the films. Quantitative roughness measurements of the surface showed that the roughness of the IAD films was smaller than that of layers without IAD.

The production of molybdenum targets for heavy-ion experiments by electron beam evaporation

Self-supporting targets of 92,98Mo, with thicknesses of 100 and 200 μg/cm 2, were prepared by electron beam gun evaporation. Substrate heating proved crucial for the production of these foils. The numerous parting agents explored will be discussed. Targets of 92,98Mo were also prepared on carbon backings of various thicknesses. Problems encountered in the production of 100–200 μg/cm 2 thick self-supporting and carbon-backed Mo targets for reactions with heavy ions are discussed.

Dielectric properties of vanadium pentoxide thin films in the audiofrequency range

Amorphous thin films of vanadium pentoxide (V 2O 5) were fabricated by the electron beam gun evaporation method. The variation of dielectric constant, ϵ, and loss factor, tan δ, with frequency and temperature were studied in the range 0.5 to 20 KHz and 300 to 423 K, respectively. Both ϵ and tan δ were found to depend on frequency and temperature. The activation energy calculated (0.41 ± 0.02 eV) for the dielectric relaxation process was found to have good agreement with the activation energy calculated from the temperature dependence of DC conductivity (0.43 ± 0.015 eV). The DC conductivity of these films was remarkably low in comparison with DC conductivities of the films reported earlier, by other methods. The conduction was ascribed to small polaron motion. The application of a higher measuring voltage level at lower frequencies was found to give a negative capacitance and this is associated with a memory switching effect.

Investigation of the evaporation process conditions on the optical constants of zirconia films

Deposition parameters required for producing zirconia films for use in optical multilayer systems by electronbeam gun evaporation of zirconia and zirconium starting materials were investigated. The optical constants were determined as a function of distance, partial pressure of oxygen, and angle of incidence. The direct and reactive evaporation processes yielded ZrO(2) films with refractive indices of 2.08 and 2.14, respectively, for vapor incident on the substrate at normal incidence.