Ion-beam densification of hydroxyapatite thin films

The goal of this study is to demonstrate the feasibility of using ion irradiation to densify a porous ceramic film. Ion irradiation is a room-temperature process, and thus may be preferable to the use of conventional high temperature sintering, which is typically performed at temperatures in excess of 1000°C. Thin films of the bio-ceramic hydroxyapatite (HA), Ca₁₀(PO₄)₆(OH)₂, were deposited on silicon substrates using a sol–gel technique. The films processed in this study were 600 nm thick and had a density of 36% of fully dense HA, after drying at 620°C for 3 min. The dried films were irradiated with 1 and 2 MeV Si⁺⁺ ions with fluences ranging from 10¹⁴ to 6 × 10¹⁵ ions/cm². Samples irradiated with the largest fluence reached densities of 83% of that of fully dense HA. Rutherford backscattering spectrometry was used to verify the HA stoichiometry of the films and to obtain the areal density. Scratch testing showed that implantation led to a substantial improvement in scratch resistance. Nano-indentation was also used to characterize the mechanical properties of the films. The hardness was increased by a factor of 15 by the irradiation. X-ray diffraction was used to characterize the crystalline phases present in the film. Ion irradiation caused some decrease in the already small degree of crystallinity of the film. The advantage of ion-implantation over high temperature sintering is shown as no secondary crystalline phases appear after densification.     

The structure of vacuum-evaporated UO2 thin films

A brief review of the methods used for obtaining thin polycrystalline and monocrystalline UO₂ films, by evaporation or sputtering in vacuum on alkali halide substrates, is presented. The presence of weak subsidiary reflections in the diffraction patterns of nearly epitaxial UO₂ thin films observed by us and by others, is attributed to crystallites grown in two (110) orientations, rotated 90° relative to each other. Some similarities in the growth behaviour of the thin UO₂ and CaF₂ films on the NaCl substrates are outlined. Finally the mean parameters are summarized which are necessary to ensure the epitaxial growth: the substrate temperature between 320 and 350°C, the existence of colloidal centres (Pb⁰, Ag⁰, Na⁰) in the NaCl substrate, the preheating treatment of the NaCl substrate at 400°C, and the deposition rate exceeding 5Å/s.     

Swift heavy ion induced structural modifications in indium oxide films

Sub-stoichiometric indium oxide (In_xO_y) films were fabricated by electron-beam evaporation method. One set of films was irradiated with 120 MeV Ag⁹⁺ ions of varying fluences. Another set was thermally annealed and subsequently irradiated. Irradiation of the as-deposited In_xO_y films leads to a phase separation resulting in In and In₂O₃ and the formation of nanometer crystalline In clusters. The In cluster size is in the range of 35-45 nm. Elastic recoil detection analysis indicates a decrease in the O/In ratio with an increase in ion fluence, suggesting oxygen loss during irradiation. On the other hand, thermal annealing of the as-deposited In_xO_y films leads to a complete conversion into stoichiometric In₂O₃. The structure of the stoichiometric films is further resistant to irradiation. Preliminary electrical investigations indicate a decrease in the resistivity of the as-deposited sub-stoichiometric In_xO_y films with irradiation, but a very large increase after irradiation of the stoichiometric thermally annealed films. Thus, structural and electrical modifications induced by swift heavy ions depend upon the stoichiometry of the film.     

Assessment of the models of urania fuel oxidation in steam-rich atmosphere

The urania fuel oxidation model for a steam-rich atmosphere developed by Cox et al. using the extensive experimental database has been subsequently used widely but with some inconsistencies in implementations. They are listed and evaluated in this work to help improve the existing models as well as for future model development. The comparison of the equilibrium stoichiometry deviation, calculated using various models, is also given. Small differences between the equilibrium constants used for steam dissociation are found. In one application, the original model for steam dissociation was rewritten in terms of component partial pressures for simplification. It is shown that the modified model differs from the original model by a multiplicative factor (1 ? p _O2 /P _tot). A more complex equation that preserves total pressure is derived. However, the effect on the calculated fuel oxidation is much smaller than the effect of the uncertainty of the equilibrium stoichiometry deviation. The discrepancies in stoichiometry deviations and the estimate of the surface area of a pellet may lead to a double underprediction of fuel oxidation rate.     

Properties of carbonization layers relevant to plasma-surface-interactions

Thin carbonaceous films have been prepared on samples of stainless steel, Inconel 600, Inconel 625 and silicon by carbonization from CH₄-H₂ mixtures. They were investigated by transmission electron microscopy, nuclear reaction and backscattering techniques and thermal desorption. The films are semi-transparent, amorphous and homogeneous down to ~10 Å. Their composition is H/C = 0.4 ± 0.1 and independent of the substrate. The density is 1.4 g cm⁻³, the average C-C atomic distance ~2.5 Å. The films release H₂ and about 3–10% CH₄ upon heating. The desorption of CH₄ occurs in a well defined peak around 500°C, whereas H₂ is relased up to 1100°C. The films turn black in colour after the CH₄ has been released, possibly due to a transformation from the initial amorphous into a graphitic structure.     

Methodology and application of the nuclear resonance reaction 16O(α, α)16O for the profiling of titanium oxide

A method is presented for the application of the ¹⁶O(α,α)¹⁶O resonance at 3.045 MeV to the depth profiling of oxide films. The resonance yield is translated into oxygen to metal stoichiometry as a function of the depth probed. The method is applied to anodic titanium oxide films grown in the absence and presence of tungsten anions. The oxygen depth profile is then utilized to obtain the profile of the dopants (W) incorporated in the oxide. A depth resolution of 6 μg/cm is achieved. The incorporation of tungsten anions of the order of 2 at.%, evaluated from the RBS yields, precludes the establishment of a constant oxygen to metal stoichiometry in the doped film. The tungsten atomic fractions have an estimated error of 5%.     

Influence of Different CH4/N2 Ratios on Structural and Mechanical Properties of a-CNx:H Film Synthesized Using Plasma Focus

Carbon nitride films were synthesized by operating the dense plasma focus device with different CH₄/N₂ admixture gas ratios and fixed 20 focus shots. The pressure and axial distance from anode tip were kept constant at 3 mbar and 8 cm respectively. Raman and X-ray photoelectron spectroscopy (XPS) techniques were used to observe the effect of CH₄/N₂ ratio on carbon nitride bonding. The XPS analysis showed that the terminating group C≡N is more dominant for the films synthesized using higher concentration of nitrogen which gives softer films. Field emission scanning electron microscopy results showed that the deposited films consist of nanoparticles and their agglomerates. The size of agglomerates increases with decreasing concentration of nitrogen in CH₄/N₂ admixture gas. Nanoindentation results showed the increase in hardness and elastic modulus values of films with decreasing concentration of nitrogen in CH₄/N₂ admixture gas. The hardness and elastic modulus values were found to be dependent on sp³ content in the film as well as the C≡N. The hardness and elastic modulus values of 10.7 and 229.8 GPa respectively were achieved for the films deposited with fixed 20 focus deposition shots and using CH₄/N₂ admixture gas ratio of 7:3.     

MeV Si ion beam modification effects on the thermoelectric generator from Er0.1Fe1.9SbGe0.4 thin film

Effective thermoelectric materials and devices have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT. The purpose of this study is to improve the figure of merit of the single layer of Er_0.1Fe_1.9SbGe_0.4 thin film used as thermoelectric generators. We have deposited the monolayer of Er_0.1Fe_1.9SbGe_0.4 thin film on silicon and silica substrates with thickness of 302 nm using ion beam assisted deposition (IBAD). Rutherford backscattering spectrometry (RBS) was used to determine the total film thickness and stoichiometry. The MeV Si ion bombardments were performed on single layer of Er_0.1Fe_1.9SbGe_0.4 thin films at five different fluences between 5 × 10¹³?5 × 10¹⁵ ions/cm².The defect and disorder in the lattice caused by ion beam modification and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of annihilation of the phonon. The increase of the electron density of states in the miniband of the quantum dot structure formed by bombardment also increases the Seebeck coefficient and the electrical conductivity. We measured the thermoelectric efficiency of the fabricated device by measuring the cross plane thermal conductivity by the 3rd harmonic (3ω) method, the cross plane Seebeck coefficient, and the electrical conductivity using the Van Der Pauw method before and after the MeV ion bombardments.     

Compositional analysis of atom beam co-sputtered metal-silica nanocomposites by Rutherford backscattering spectrometry

Metal:SiO₂ (metal: Ni, Ag, Au) nanocomposite films of different compositions have been prepared by atom beam co-sputtering. The estimation of composition of films is done theoretically using sputtering yield and relative area of metal and SiO₂. The sputtering yields used for estimation of composition are calculated by three theoretical methods: Monte Carlo simulations (SRIM code), Sigmund’s theory and Sigmund’s theory modified by Anderson and Bay. Rutherford backscattering spectrometry (RBS) is also used to analyze the composition of the nanocomposite films. RUMP simulations of RBS data are performed. The errors in theoretical calculations and RBS results are estimated. It is found that SRIM is more appropriate for Ni:SiO₂ nanocomposite films, while modified Sigmund’s theory based method is better for Ag:SiO₂ and Au:SiO₂ nanocomposite films. The possible sources of errors in theoretical methods with respect to experimental (RBS) results are also discussed.     

Comparison of candidate secondary electron emission materials

Secondary electron emission (SEE) yields obtained with empirical models deviate significantly from experiment. Therefore they cannot be used to predict the SEE data for various materials. The angular dependencies of SEE in empirical models are also drastically different and inconvenient for comparison. SEE coefficients were calculated by a theoretical method that uses Monte Carlo simulation, empirical theories, and close comparison to experiment, in order to parameterize the SEE yields of highly emissive materials. We have successfully applied this method to bulk Al₂O₃, a highly emissive material for micro-channel plates, as well as to thinly deposited films of Al₂O₃. The simulation results will be used in the selection of an emissive material, and if the emission yield of the material is small, as a resistive material for the deposition and characterization experiments that will be conducted by a large-area fast detector project at Argonne National Laboratory.     

Comparative study of structural and morphological properties of CuIn3S5 and CuIn7S11 materials

CuIn₃S₅ and CuIn₇S₁₁ powders were prepared by solid-state reaction method using high-purity elemental copper, indium and sulphur. The films prepared from CuIn₃S₅ and CuIn₇S₁₁ powders were grown by thermal evaporation under vacuum (10^?6 Torr) on glass substrates at different substrate temperature Ts varying from room temperature to 200 °C. The powders and thin films were characterized for their structural properties by using X-ray diffraction (XRD) and energy dispersive X-ray (EDX). Both powders were polycrystalline with chalcopyrite and spinel structure, respectively. From the XRD data, we calculated the lattice parameters of the structure for the compounds. For CuIn₃S₅ powder, we also calculated the cation–anion bond lengths. The effect of substrate temperature Ts on the structural properties of the films, such as crystal phase, preferred orientation and crystallinity was investigated. Indeed, X-ray diffraction analysis revealed that the films deposited at a room temperature (30 °C) are amorphous in nature while those deposited on heated were polycrystalline with a preferred orientation along (1 1 2) of the chalcopyrite phase and (3 1 1) of the spinel phase for CuIn₃S₅ and CuIn₇S₁₁ films prepared from powders, respectively. The morphology of the films was determined by atomic force microscopy AFM. The surface roughness and the grain size of the films increase on increasing the substrate temperature.     

Pressure Balanced Type Membrane Covered Polarographic Oxygen Detectors for Use in High Temperature-High Pressure Water, (II)

Performance tests of a pressure balanced type membrane covered polarographic oxygen, detector were carried out in water at 285°C (BWR operating conditions) to determine the effects of environmental factors. Dependencies of detector current on pressure and sample water flow velocity were ascertained and response time of the detector was determined. Effects of H₂ present in the water were also examined. The following conclusions were obtained:

1. The detector current increased in proportion to the 0.67th power of the flow velocity, but was independent of the pressure.

2. Response time was about 7 s.

3. Hydrogen caused a decrease in the current at cathode potentials more positive than ?0.75 V against the Ag/AgCl electrode. However, at more negative potentials, the current was independent of H₂ concentration and in proportion to O₂ concentration.

Oxygen concentrations in water containing H₂ at 285°C could be determined by the detector under the measurement conditions of constant flow velocity and cathode potentials more negative than ?0.75 V.     

Effects of MeV Si ions bombardment on the thermoelectric generator from SiO2/SiO2 + Cu and SiO2/SiO2 + Au nanolayered multilayer films

The defects and disorder in the thin films caused by MeV ions bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We prepared the thermoelectric generator devices from 100 alternating layers of SiO₂/SiO₂ + Cu multi-nano layered superlattice films at the total thickness of 382 nm and 50 alternating layers of SiO₂/SiO₂ + Au multi-nano layered superlattice films at the total thickness of 147 nm using the physical vapor deposition (PVD). Rutherford Backscattering Spectrometry (RBS) and RUMP simulation have been used to determine the stoichiometry of the elements of SiO₂, Cu and Au in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardments have been performed using the AAMU-Center for Irradiation of Materials (CIM) Pelletron ion beam accelerator to make quantum (nano) dots and/or quantum (quantum) clusters in the multilayered superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we have measured Seebeck coefficient, cross-plane electrical conductivity, and thermal conductivity in the cross-plane geometry for different fluences.     

Deposition of Alumina Films on Si (1 0 0) Substrate Using a Low Energy Dense Plasma Focus Device

A 1.5 kJ pulsed low energy Mather type plasma focus (PF) is used to deposit thin films of alumina (α-Al₂O₃) on Si (1 0 0) substrates. The PF device with its anode made of aluminum was operated with argon-oxygen mixture as the filling gas. The Al₂O₃ thin film samples were prepared using 10, 20 and 30 successive shots with substrates placed at 60 mm from the top of the anode at approximately zero angular position with respect to the anode axis. The crystallography of the as-deposited and annealed samples was studied by X-ray diffractometry (XRD). Raman Spectroscopy studies verified the formation of α-Al₂O₃ phase in the annealed films. Scanning electron micrographs (SEM) of the annealed films present many different sized particulates (50–300 nm) distributed upon the film surface. The cross-sectional SEM micrographs show that the thickness of deposited alumina film is linear with a typical rate of 45 nm/shot at focus storage energy of 850 J.     

Effect of O2 in O2/Ar Gas Mixture on Morphological and Optical Properties of TiO2 Thin Films Deposited by DC Cylindrical Magnetron Sputtering

TiO₂ films have been deposited on BK7 substrates by DC cylindrical magnetron sputtering setup in ambient temperature. The samples were fabricated at various O₂/Ar reactive gas mixtures. The effects of changing O₂ amount in O₂/Ar reactive gas mixture on structural, morphological and optical properties of films were studied. The thickness of films was measured by surface profile meter. Thickness of films decreases with increasing the O₂ amount in gas mixture. XRD studies shows that the films are amorphous. Atomic Force Microscopy was used to evaluate and compare the surface roughness and morphologies. The optical properties (transmission and reflection) of the samples were measured by UV–Vis–NIR spectrophotometer. Results show that increasing the O₂ amount in O₂/Ar mixture changes the surface morphologies and optical properties of films. All films exhibit a transmittance higher than 65 % in the visible region. The band gap of films was calculated from the optical measurements. The band gap of TiO₂ thin films increases from 3.471 to 3.526 for different O₂/Ar amounts.     

Effect of H+ and O+ implantation on electrical properties of SrBi2Ta2O9 ferroelectric thin films

The effect on the crystalline structure and ferroelectric properties of ion implantation in SrBi₂Ta₂O₉(SBT) ferroelectric thin films has been investigated. 25 keV H⁺, 140 keV O⁺ with doses from 1 × 10¹⁴/cm² to 3 × 10¹⁵/cm² were implanted into the Sol–Gel prepared SBT ferroelectric thin films. The X-ray diffraction patterns of SBT films show that no difference appears in the crystalline structure of as-H⁺-implanted SBT films compared with as-grown films, H⁺ and O⁺ co-implanted SBT films show an obvious degradation of crystalline structure. Ferroelectric properties measurements indicate that both remnant polarization and coercive electric field of H⁺ implanted SBT films decrease with increasing the implantation dose. The disappearance of ferroelectricity was found in the H⁺, O⁺ co-implanted SBT films at room temperature. The great recovery of hydrogen-induced degradation in SBT films was obtained with O⁺ implantation using a heat-target-implantation technique.     

ERD analysis and modification of TiO2 thin films with heavy ions

Titanium dioxide (TiO₂) films have been deposited on Si substrates using reactive magnetron sputtering. The resulting films, having a polycrystalline anatase phase with a dense columnar structure, were analysed by time-of-flight elastic recoil detection analysis (ToF-ERDA) using 40 MeV I⁹⁺ ions. A clear decrease in the areal atomic density (atoms/cm²) of Ti and O was observed during measurement, but the stoichiometry remained essentially constant up to a fluence of 4 × 10¹³ ions/cm².To investigate this effect in more detail, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were applied in order to characterize the films prior to and after ion irradiation with fluences in the range of 10¹⁰–10¹³ ions/cm². Distinct morphological and structural changes of the polycrystalline film were observed. XRD revealed that the crystallinity of the film was gradually destroyed, and the film became amorphous at a fluence above 5 × 10¹² ions/cm². SEM and AFM measurements revealed topographical changes in the form of surface recession and smoothing compared to the pristine polycrystalline surface. The observed change in areal atomic density during ERD measurement is believed to be due to the combined effects of electronic sputtering, amorphization and ion hammering.     

Visible light active TiO2 films prepared by electron beam deposition of noble metals

TiO₂ films prepared by sol-gel method were modified by electron beam deposition of noble metals (Pt, Pd, and Ag). Effects of noble metals on the chemical and surface characteristics of the films were studied using XPS, TEM and UV-Vis spectroscopy techniques. Photocatalytic activity of modified TiO₂ films was evaluated by studying the degradation of methyl orange dye solution under visible light UV irradiation. The result of TEM reveals that most of the surface area of TiO₂ is covered by tiny particles of noble metals with diameter less than 1 nm. Broad red shift of UV-Visible absorption band of modified photocatalysts was observed. The catalytic degradation of methyl orange in aqueous solutions under visible light illumination demonstrates a significant enhancement of photocatalytic activity of these films compared with the un-loaded films. The photocatalytic efficiency of modified TiO₂ films by this method is affected by the concentration of impregnating solution.