Vacuum Deposition Techniques Research Articles

Electrochemical characterization of silver nanorod electrodes prepared by oblique angledeposition

Ag nanorod electrodes with different nanorod lengths are fabricated by asimple vacuum deposition technique, oblique angle deposition (OAD). Theas-grown Ag nanorods are aligned on the substrate and have a diameter of∼60–70 nm, a densityof ∼200–300 × 107 cm−2, and atilting angle of ∼70°–80° with respect to the surface normal. The electrochemical behaviours of the Ag nanorodelectrode are characterized by cyclic voltammetry at various scan rates with comparison toan Ag thin-film electrode. The capacitive current is found to be proportional to the actualsurface area, and the faradic redox current also increases monotonically with the surfacearea of the nanorod electrodes, but the increase is not as significant as that of thecapacitive current due to the diffusion layer overlapping for the highly compactednanorods. This indicates that the Ag nanorod electrode could improve the electrolyticsensor for amperometric response measurements, especially for the bimolecularmeasurements due to the biocompatibility of Ag. The high capacitance also suggests apromising usage of the developed nanostructures for battery and energy storageapplications.

Electrical properties of Schottky diodes based on Carbazole

Sandwich structures of Carbazole thin films have been prepared by using vacuum deposition technique. The plot of current density versus voltage (J–V characteristics) shows two distinct regions. In the lower voltage region ohmic conduction and in the higher voltage region space charge limited conduction (SCLC) is observed. Number of states in the valence band (Nv) is calculated from the temperature dependence of J in the ohmic region. From the temperature dependence of J in the SCLC region trap density (Nt) and activation energy are determined. The values of Nv and Nt are in the order 1023 m−3 and 1027 m−3 respectively. The value of activation energy is nearly equal to 0.1 eV and that of the effective mobility is 4.5 × 10−7 cm2 V−1 S−1. Schottky diodes are fabricated using Aluminium (Al) as Schottky contact. It is observed that gold (Au) is more suitable for ohmic contact compared to silver (Ag). From a semi logarithmic plot of J versus V, the barrier height (ϕb), diode ideality factor (n) and saturation current density (J0) are determined. The value of n increases and ϕb decreases on annealing.

Epitactic growth of a decagonal phase in an Al–Ni–Co alloy film deposited on a (0001) sapphire substrate

Thin films of Al–Ni–Co alloy with an average thickness of 15 nm were produced by means of conventional vacuum deposition technique on (0001) sapphire substrates heated at various test temperatures. The microstructures and textures of the films obtained were thoroughly investigated by atomic force microscopy, X-ray diffraction and transmission electron diffraction and imaging techniques. The diffraction measurements have evidenced that the vacuum deposition of Al72Ni15Co13 alloy on the substrates heated above 400°C allows a homogeneous poly-quasicrystalline film, consisting of the Ni-rich basic decagonal phase to grow. It has been further indicated by in-plane XRD analysis that the film deposited at 550°C contains a considerable amount of the decagonal grains epitaxially grown on the sapphire substrate. Possible epitaxial relations occurring between the deposit and the substrate will be detailed on the basis of results obtained from electron diffraction measurements.

Polyaniline thin films as a toxic gas sensors in SAW system*

Presented here are the preliminary results concerning an investigations of thin films ofpolyaniline (∼100 nm) as a toxic gas sensors in a Surface Acoustic Wave system. The investigations were performed with different concentrations of the following toxic gases: NO 2 , SO 2 , CO, H 2 S and hydrogen in synthetic dry air. These thin films were made by vacuum deposition technique and formed in one of the dual delay line systems on a LiNbO 3 Y-cut Z-propagation substrate, while the other serves as a reference, permitting an easy detection of the arising differential frequency Af. This frequency, depending on the operating frequency modes, is in the range of 50 kHz to 400 kHz, whereas the oscillator frequencies are in the range of 43,6 MHz. The wavelength is 80 μm.

THE INFLUENCE OF STRUCTURE IMPERFECTION ON THE GLASS-TRANSITION BEHAVIOR IN C60 FILMS

Two batches of C 60 films were grown at different growth rate, using a vacuum deposition technique. X-ray diffraction patterns indicate both films have preferential (111) orientation. We measured their dielectric constant and loss factor from 80K to room temperature, and observed distinct broad and asymmetric loss peaks, attributed to orientational glass transition. The apparent activation energy was determined as 344.4 and 304.8 meV for film A and B respectively, larger than the value 280 meV in bulk C 60. Ngai's correlated-state model is used to simulate relaxation spectrum, and the real activation energies were calculated, which agree with the reported activation value in bulk C 60 very well. We propose that the structure imperfection have contributed additional dipole correlation interactions, which make the relaxation behavior of our C 60 films deviate from that of bulk C 60.

Observations on the growth of Al–Ni–Co decagonal thin films by atomic force microscopy and transmission electron microscopy

Thin films of Al–Ni–Co alloy were produced by vacuum deposition technique using a substrate material of amorphous carbon thin-foil. Attempts were made to obtain a homogeneous decagonal quasicrystalline film, where the preparation technique was based on the direct evaporation of pre-alloyed ingot of Al 72Ni 15Co 13 onto the heated substrates. In order to explore early stages of the decagonal film growth, the Al–Ni–Co films with different thicknesses ranging from 2 nm to 30 nm were deposited on either substrates heated at 500 °C or non-heated substrates. The film samples so obtained were examined mainly by atomic force microscopy in combination with transmission electron diffraction and imaging techniques. On the basis of these observations, deposition conditions necessary for the growth of decagonal phase in the resulting films as well as the growth mechanism of the decagonal film will be discussed.

Rare-earth doped chalcogenide thin films fabricated by pulsed laser deposition

Erbium doped Ge–Ga–Se thin films were fabricated by the pulsed laser deposition (PLD) technique in vacuum using a KrF pulse laser with λ = 248 nm, and a pulse duration of 15 ns. The films were fabricated at room temperature onto glass substrates. The morphological, optical and thermal properties of the films showed good optical and thermal stability. The mechanical properties including film adhesion are relatively poor for thicker films and the microstructure reveals the presence of droplets. Annealing in vacuum improved the film adhesion and substantially enhanced the efficiency of photoluminescence.

Density of localized electronic states in a-Se from electron time-of-flight photocurrent measurements

Electron time-of-flight transient photocurrents have been investigated in stabilized a-Se as a function of electric field, annealing, aging (relaxation), and alloying with As and doping with Cl. The distribution of localized states (DOS) in stabilized a-Se has been investigated by comparing the measured and calculated transient photocurrents. The samples were prepared by conventional vacuum deposition techniques. The theoretical analysis of multiple-trapping transport has been done by the discretization of a continuous DOS and the use of Laplace transform formalism. The resulting DOS has distinct features: A first peak at ∼0.30eV below Ec with an amplitude ∼1017eV−1cm−3, a second small peak (or shoulder) at 0.45–0.50 eV below Ec with an amplitude 1014–1015eV−1cm−3, and deep states with an integral concentration 1011–1014cm−3 lying below 0.65 eV, whose exact distribution could not be resolved over the time scale of present experiments. The influence of doping, aging, annealing, and substrate temperature on the DOS distribution has been investigated. The doping with Cl does not affect the amplitudes of the first and second peaks while the concentration of deep states increases dramatically. The alloying with As reduces the density of deep states and seems to increase the amplitude of first and second peaks. The aging substantially reduces the deep states density and the amplitude of the second peak while the amplitude of the first one remains practically unchanged. The results have been interpreted primarily in terms of thermodynamic and intrinsic structural defects in the chalcogenide glass structure.

Fabrication of Core-shell Type FeCo-Au (Ag) High Moment Magnetic Nanoparticles

AbstractWe developed a physical vacuum deposition technique combining an on-line sputtering/evaporation process with an integrated nanocluster deposition process to prepare core-shell type nanoparticles. High magnetic moment (Fe60Co40)coreAushell and (Fe60Co40)coreAgshell superparamagnetic nanoparticles with controllable particle size of 10 – 20 nm and Au/Ag shell thickness of 1 – 3 nm were prepared successfully by using method. Au shell is not only functional for the potential biocompatibility but also the key to prevent oxidation of FeCo nanoparticles. Saturation magnetization of (Fe60Co40)coreAushell nanoparticles was found three times higher than that of iron oxide nanoparticles. This novel technique enables us to control independently the dimensions of core and shell and select individually materials for core and shell for other core-shell type nanoparticles.

Microwave characterization of magnetic thin films

An issue of current research is the integration of microwave ferrite devices with semiconductor technologies by using vacuum deposition techniques. Thin magnetic films may be used in commercial products and they can be more easily involved in the development of magnetic devices if we are able to extract their magnetic properties. One of the interesting points of this paper is to highlight the properties of a thin film, such as anisotropic behavior to release non reciprocal devices. A study of physicochemical and magnetic properties is tackled and experimental results are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of the effect of CdCl 2 processing on vacuum deposited CdS/CdTe thin film solar cells by DLTS

Thin film CdS/CdTe solar cells have been prepared by conventional vacuum deposition technique. Deep level transient spectroscopy (DLTS), temperature and frequency dependent capacitance–voltage ( C– V) measurements were utilised to investigate the performance limiting defect states in the CdTe layer subjected to the post deposition treatments such as CdCl 2-dipping and/or annealing in air. Five hole traps, all of which have been previously reported in the literature, were identified in as-grown CdTe at 0.19, 0.20, 0.22, 0.30 and 0.40 eV above the valence band. A single hole trap level has been evidenced at 0.45 eV after both post deposition heat and CdCl 2 treatments.

ELECTRICAL AND OPTICAL NONLINEARITY IN VACUUM-DEPOSITED THIN FILMS OF POLY[N-(4-BENZOYLPHENYL)-2-METHYLACRYLAMIDE

A new optically nonlinear material, poly[N-(4-benzoylphenyl)-2-methylacrylamide], for conversion of wavelength 1064 nm to 532 nm has been synthesized. The material possesses strong electrical and optical nonlinearity required for second harmonic generation (SHG). The thin films of poly[N-(4-benzoylphenyl)-2-methylacrylamide] were prepared by the vacuum-deposition technique. The optical UV-visible, IR, NMR studies, mass spectrometry, surface topography and nonlinear optical properties of the thin films were studied. The vacuum-deposited thin films of the polymer were subjected to optimized high potential multi-point corona poling at temperatures just below the glass transition temperature (Tg) to create directional orientation of the side chain groups. The optical UV-visible absorption indicates a complete transparency in the visible and IR regions with an absorption peak at ~350 nm. The energy band gap of the polymer was estimated to be ~2.9 eV, from the optical absorption spectra of the thin films. The electrical current–voltage (IV) and optical nonlinear characteristic indicate the strong potential of these polymeric thin films for nonlinear optical (NLO) applications.

Application of diamond-like carbon coatings on steel tools in the production of precision glass components

The application of highly wear-resistant diamond-like carbon (DLC) coatings with an extremely low friction coefficient and a low wettability with regard to glass melt has been performed on steel substrates. These coatings are of high interest for the glass industry to improve the performance of high precision glass forming tools for various products like high precision glass tubes for laboratory equipment or in the fabrication of wine glasses. Me-DLC coatings are a special type of DLC coating and consist of a metal-rich carbon phase near the metal substrate interface, which is graded into a carbon-rich diamond-like phase towards the interacting surface. The metal-rich phase optimises the adhesion to the ground substrate and the metal type can be varied (Ti, Cr, Si, etc.). The metal content influences the surface properties of the coating like its wettability. For the glass-producing industry there are mainly two advantages: environmentally hazardous release agents can be abandoned and the purity and surface quality of the produced glass products can be drastically improved. The presentation describes related vacuum deposition techniques and gives examples for industrial applications.

Effect of lithium impurity on the opto-electrical properties of zinc oxide films

Lithium-doped zinc oxide (ZnO) films were prepared on C-plane sapphire substrates by the e-beam deposition technique in vacuum. The dependences of the optical absorption edge characteristics, structural, and photoelectrical properties on Li content (from 0 to 10 at.%) were investigated. It is found that the variations of the energy bandgap Eg, the spread in the tail of the band edge (parameter E0), the electrical resistivity ρ, and the lattice constant c with impurity concentration do not have monotonic character. Abrupt jumps of the optical and electrical characteristics were observed as the impurity concentration changed near 0.8 at.% Li. The significant enhancement of photoconductivity response for 0.8 at.% Li-doped ZnO films also correlates with the enhanced electrical resistivity up to 2 × 106 Ω cm and the appearance of a photoinjection current. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Textured CeO/sub 2/ thin films on nickel tape by sol-gel process

Cerium oxide (CeO/sub 2/) is one of the preferred buffer layer for fabrication of coated conductors, especially when e-beam evaporation technique is used for YBCO processing. Therefore, processing of CeO/sub 2/ buffer layers has been extensively studied by several vacuum deposition techniques. However, a nonvacuum process is desired for fabrication of coated conductors to make coated conductors widely available in the market. In order to develop a nonvacuum process for fabrication of coated conductors, we fabricated textured cerium oxide (CeO/sub 2/) buffer layers on biaxially textured-Ni [100] substrates by sol-gel process. The solution was prepared from metal-organic precursor, Cerium 2,4-pentanedionate, and was deposited on the Ni substrates using a reel-to-reel sol-gel dip coating system. The textured films were annealed at 1150 /spl deg/C for 10 min under 4% H/sub 2/-Ar gas flow. Extensive texture analysis has been done to characterize the texture of CeO/sub 2/ buffer layers. X-ray diffraction (XRD) of the buffer layer showed strong out-of-plane orientation on Ni tape. The CeO/sub 2/ [111] pole figure indicated a single cube-on-cube textured structure. The omega and phi scans revealed good out-of-plane and in-plane alignments. The full-width-at-half-maximum (FWHM) values of omega and phi scans of CeO/sub 2/ films were 6.47/spl deg/ and 7.26/spl deg/, respectively. ESEM micrographs of the CeO/sub 2/ films revealed pinhole free, crack-free and dense microstructures.

Barrier open discharge at atmospheric pressure

A barrier open discharge operating under extremely hindered conditions is proposed, in which the working gas (helium) pressure admitting the electron beam formation can be increased up to 0.8 atm (more than ten times as compared to the usual open discharge) without any loss in stability. The anode grid (with 0.17 mm holes) was made separately and then placed on a dielectric substrate (e ≈ 1000), but it can also be formed using vacuum deposition or photolithographic techniques. It is suggested that, by decreasing the diameter of holes in the anode grid, it is possible to provide for a stable discharge operation under still higher gas pressures.

Investigation of the Effect of Uv-Assisted Oxidation and Nitridation of Hafnium Metal Films

AbstractHf metal thin films were deposited on Si substrates using a pulsed laser deposition technique in vacuum and in ammonia ambients. The films were then oxidized at 400 °C in 300 Torr of O2. Half the samples were oxidized in the presence of ultraviolet (UV) radiation from a Hg lamp array. X-ray photoelectron spectroscopy, atomic force microscopy, and grazing angle X-ray diffraction were used to compare the crystallinity, roughness, and composition of the films. It has been found that UV radiation causes roughening of the films and also promotes crystallization at lower temperatures.Furthermore, increased silicon oxidation at the interface was noted with the UVirradiated samples and was shown to be in the form of a mixed layer using angle-resolved X-ray photoelectron spectroscopy. Incorporation of nitrogen into the film reduces the oxidation of the silicon interface.

High-purity Magnesium Coating on Magnesium Alloys by Vapor Deposition Technique for Improving Corrosion Resistance

Microstructures in coated magnesium alloy with high purity magnesium fabricated by applying a vacuum deposition technique were investigated. Moreover, relationships between microstructures in coated and un-coated magnesium alloys and corrosion behaviors were interpreted by in-situ laser microscopic observations during salt immersion tests. Magnesium with 3N-grade and AZ31 magnesium alloy were used for an evaporation source and a substrate for deposition. Temperature of the substrates was changed resulting in change in temperature profile in a furnace in order to optimize deposition coating conditions for obtaining homogeneous microstructures and thickness in deposited layer. The coated specimen revealed superior corrosion resistance to those on 3N–Mg, AZ31 and AZ91E alloys, and comparable to that on 6N– Mg in salt immersion tests using 3% NaCl solution at 300 K for 587 ks. In-situ observations showed that inhomogeneity in microstructures, such as second phases and grain boundary segregations, deteriorate corrosion resistance in magnesium alloys. Therefore, pure magnesium coated layer without inhomogeneity in metallographic and electrochemical meanings can improve the corrosion resistance on magnesium alloys.

Influence of thickness and substrate temperature on electrical and photoelectrical properties of vacuum-deposited CdSe thin films

Polycrystalline cadmium selenide thin films are prepared in different thicknesses and substrate temperatures by vacuum deposition technique. The XRD patterns recorded for the CdSe thin films show that these films are polycrystalline in nature and crystallise in the hexagonal form. The crystallinity increases with increase in substrate temperature. The optical measurements reveal that the CdSe thin films possess direct band gap and the band gap energy decreases with the increase of thickness and substrate temperatures. The electrical conductivity measurements show that they possess three different activation energies in the temperature range 298 to 118K. The steady-state photoconductivity measurements reveal that the photocurrent varies linearly with the applied voltage and the photocurrent obeys a power law of the form, Iph∝Fγ, where γ is a constant. The transient photoconductivity measurements show that the decay process is very rapid in the beginning followed by a slow process.

An alkylated europium(III) complex for photoelectric devices

A novel long alkyl chain-containing Eu(III) complex, tris(α-thenoyltrifluoroacetonato)(1-octadecyl-2-(2-pyridyl)benzimidazole)europium(III), Eu(TTA) 3(L18), was designed for electroluminescent (EL) devices. The complex exhibited a low melting point and a large temperature difference between the melting point and onset decomposition compared to a shorter alkyl chain (ethyl) analogue. By vacuum deposition technique, a two-layer ITO/TPD/Eu(TTA) 3(L18)/Al and a three-layer ITO/TPD/Eu(TTA) 3(L18)/AlQ/Al EL device were fabricated and EL properties of the devices were studied. The two devices gave dominant red light emission from the europium complex with maximum luminance efficiency comparable to the two-layer device made of the short alkyl chain congener.