Study on the orientation of silver films by ion-beam assisted deposition

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar⁺ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar⁺ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar⁺ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed.     

Optimization of ZnSe film growth conditions for p-type doping

Wide bandgap semiconductors such as ZnSe and ZnO have attracted great interest due to their applications in solar cells, light emitting diodes, and lasers. However, these wide bandgap semiconductors are frequently difficult to be doped to heavy concentrations, greatly limiting their application. A substrate holder with a natural temperature gradient was developed for batch growth of films at different deposition temperatures, in order to investigate ZnSe film growth and doping challenges. Thin ZnSe films were grown by pulsed laser deposition and characterized using X-ray diffraction, optical transmission and reflection, Raman spectroscopy, and Energy Dispersive X-ray analysis. Deposition temperature and film stoichiometry (Zn:Se) are shown to be significant factors affecting ZnSe growth and doping. ZnSe films with improved crystallinity have been obtained by enriching with selenium and depositing at an optimized temperature. Heavily p-type ZnSe films with hole concentrations of ~2.7 × 10¹⁹ cm^?3 and resistivities of ~0.099 Ohm cm have been obtained (compared with previous reports of ~1 × 10¹⁸ cm^?3 and ~0.75 Ohm cm). The results, which are consistent with previous theoretical prediction of compensating defects in ZnSe films, can help to optimize ZnSe growth conditions and understand doping challenges in wide bandgap semiconductors.     

Effect of implantation regimes of silver ions on the structure and optical properties of zinc-oxide nanocrystalline films

Thin (about 270 nm) nanocrystalline films of zinc oxide (ZnO) are obtained on quartz substrates using ion sputtering and irradiated with Ag⁺ ions at an energy of 30 keV and relatively high fluences at ion current densities of 4, 8, and 12 µA/cm². The X-ray analysis, scanning electron microscopy, and optical spectroscopy are used to study the effect of irradiation dose and ion current density on the structural modification and optical properties of the ZnO films. Nontrivial dependences of the structural and optical parameters of the films on the ion irradiation regimes are due to radiation heating and film sputtering under the action of the ion beam, diffusion of impurity, formation of silver nanoparticles in the irradiated layer at high implantation fluences, and the diffusion of implanted impurity at relatively high ion current densities.     

Effects of γ rays irradiation on structure and property of TiO2 thin films

TiO₂ thin films were deposited on a glass substrate by the radio frequency magnetron sputtering method, and annealed for 2 h at temperatures of 550°C. Then, ⁶⁰Co γ rays with different doses were used to irradiate the resulting TiO₂ thin films. The surface features of films before and after irradiation were observed by scanning electron microscope (SEM). Simultaneously, the crystal structure and optical properties of films before and after irradiation were studied by X-ray diffraction (XRD), UV–VIS transmission spectrum and Photoluminescence (PL) spectrum, respectively. The SEM analysis shows that the film is smooth with tiny particles on the film surface, and non-crystallization trend was clear after irradiated with γ rays. The XRD results indicated that the structure of the film at the room temperature mainly exists in the form of amorphous and mixed crystal at a sputtering power of 200 W, and non-crystallinity was more obvious after irradiation. Obvious difference can be found for the transmissibility of the irradiated and pre irradiation TiO₂ films by the UV-VIS spectra. The color becomes light yellow, and the new absorption edge also appeared at about 430 nm. PL spectra and photocatalysis experiments indicate that the photocatalysis degradation rate of the TiO₂ films on methylthionine chloride solution irradiated with the maximum dose can be increased to 90%.     

Thickness dependent optical dispersion parameters and nonlinear optical properties of nanostructured Cr doped CdO thin films

Cr doped CdO thin films were deposited on glass substrates by reactive DC magnetron sputtering with varying film thickness from 250 to 400 nm. XRD studies reveal that the films exhibit cubic structure with preferred orientation along the (2 0 0) plane. The optical transmittance of the films decreases from 92 to 72%, whereas the optical energy band gap of the films decreased from 2.88 to 2.78 eV with increasing film thickness. The Wemple–DiDomenico single oscillator model has been used to evaluate the optical dispersion parameters such as dispersion energy (E_d), oscillator energy (E_o), static refractive index (n_o) and high frequency dielectric constant (ε_∞). The nonlinear optical parameters such as optical susceptibility (χ⁽¹⁾), third order nonlinear optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) of the films were also determined.     

High-rate reactive magnetron sputtering of zirconia films for laser optics applications

ZrO₂ exhibits low optical absorption in the near-UV range and is one of the highest laser-induced damage threshold (LIDT) materials; it is, therefore, very attractive for laser optics applications. This paper reports explorations of reactive sputtering technology for deposition of ZrO₂ films with low extinction coefficient k values in the UV spectrum region at low substrate temperature. A high deposition rate (64 % of the pure metal rate) process is obtained by employing active feedback reactive gas control which creates a stable and repeatable deposition processes in the transition region. Substrate heating at 200 °C was found to have no significant effect on the optical ZrO₂ film properties. The addition of nitrogen to a closed-loop controlled process was found to have mostly negative effects in terms of deposition rate and optical properties. Open-loop O₂ gas-regulated ZrO₂ film deposition is slow and requires elevated (200 °C) substrate temperature or post-deposition annealing to reduce absorption losses. Refractive indices of the films were distributed in the range n = 2.05–2.20 at 1,000 nm and extinction coefficients were in the range k = 0.6 × 10^?4 and 4.8 × 10^?3 at 350 nm. X-ray diffraction analysis showed crystalline ZrO₂ films consisted of monoclinic + tetragonal phases when produced in Ar/O₂ atmosphere and monoclinic + rhombohedral or a single rhombohedral phase when produced in Ar/O₂ + N₂. Optical and physical properties of the ZrO₂ layers produced in this study are suitable for high-power laser applications in the near-UV range.     

Plastic separators with improved properties for portable power device applications

We report a novel clay-intercalated polymer nanocomposites (PNC) having very high ionic conductivity (~10^?3 S cm^?1) and improved stability properties. The suitability of the PNC films for subsequent use as a separator component in energy storage devices has been explored in terms of desirable voltage (~4.3 V), thermal (~290 °C) and mechanical (~55 MPa) stability, and ion transport (t _ion, ~0.99) properties. Intercalation of (polyacrylonitrile (PAN)₈LiPF₆ complex into nanometric channels of organophilic clay has been confirmed by X-ray diffraction analysis. These observations agree well with transmission electron microscopy results. Impedance spectroscopy indicated bulk electrical conduction in the high-frequency region followed by electrode polarization effects at lower frequencies. The latter effect is clearly noticed in the admittance plots. Estimated value of ionic conductivity and stability is invariably higher in PNCs compared with clay-free polymer–salt complex film. The feasibility of ionic conduction in the PNC separators has been explained in terms of hopping mechanism. The optimized PNC film may be expected to serve the dual purpose of electrolyte as well as separator in portable energy storage/conversion devices.     

Influence of the annealing technique on the properties of Li ion-conductive Li1.3Al0.3Ti1.7(PO4)3 films

Li_1.3Al_0.3Ti_1.7(PO₄)₃ films were comparatively prepared by rapid thermal annealing (RTA) and conventional furnace annealing(CFA). The phase identification and surface morphology of the prepared films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical window, ionic conductivity, activation energy, and electronic conductivity were conducted by cyclic voltammetry, electrochemical impedance spectroscopy, and four-probe technique. The results show that the films prepared by RTA and CFA are homogenous and crack-free. The film prepared by RTA shows smaller grains and is denser than the one prepared by CFA. The electrochemical windows of the two films are beyond 2.4 V. The ionic conductivities of the films prepared by RTA and CFA are 2.7?×?10^?6 S cm^?1 and 1.4?×?10^?6 S cm^?1, respectively. The activation energy of the film prepared by RTA is 0.431 eV, which is slightly smaller than the one prepared by CFA. The electronic conductivity of the two films is about 10^?10 S cm^?1.     

Ion beam shaping of embedded metal nanoparticles by Si+ ion irradiation

Fine Co and Pt nanoparticles are nucleated when a silica sample is implanted with 400 keV Co⁺ and 1370 keV Pt⁺ ions. At the implanted range, Co and Pt react to form small Co _x Pt_(1?x) nanoparticles during Si⁺ ion irradiation at 300 °C. Thermal annealing of the pre-implanted silica substrate at 1000 °C results in the formation of spherical nanoparticles of various sizes. When irradiated with Si⁺ ions at 300 °C, particles in the size range of 5–17 nm undergo rod-like shape transformation with an elongation in the direction of the incident ion beam, while those particles in the size range of 17–26 nm turn into elliptical shape. Moreover, it is suspected that very big nanoparticles (size >26 nm) decrease in size, while small nanoparticles (size <5 nm) do not undergo any transformation. During Si⁺ ion irradiation, the crystalline nature of the nanoparticles is preserved. The results are discussed in the light of the thermal spike model.     

Photoluminescence of Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles applied in Bio-LED

In this work, transition elements, including Cu²⁺, Ag⁺, and Au³⁺, were used to dope in zinc sulfide (ZnS) by chemical solution synthesis to prepare Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles, respectively. Transition elements doping ZnS nanoparticles form the electronic energy level between the conduction band and valance band, which will result in the green light emission. There is a zinc sulfide emission shift from blue (~3.01 eV) to green light (~2.15 eV). We also found that Au:ZnS nanoparticles will emit a green light (~2.3 eV) and a blue light (~2.92 eV) at the same time because the mechanism of blue light emission was not broken after Au element had been doped. Furthermore, we used sodium chlorophyllin copper salt to simulate chlorophyll in biological light emission devices (Bio-LED). We combined copper chlorophyll with Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles by a self-assembly method. Then, we measured its photoluminescence spectroscopy and X-ray photoelectron spectroscopy to study its emission spectrum and bonding mode. We found that Au:ZnS nanoparticles are able to emit green and blue light to excite the red light emission of copper chlorophyll, which is a potential application of Bio-LED.     

Composition of the sputter deposited W-Ti thin films

Tungsten-titanium (W-Ti) thin film was deposited by dc Ar⁺ sputtering of W(70 at.%)-Ti(30 at.%) target. The thin film composition, determined by X-ray photoelectron spectroscopy (XPS) depth profiling, is W_(0.77±0.07)Ti_(0.08±0.03)O_(0.15±0.03). The presence of oxygen in the deposit is due to the rather poor vacuum conditions during the deposition, while significant deficiency of Ti, as compared to the sputtering target composition cannot be explained straightforwardly. Monte Carlo simulations of both, transport of sputtered particles from target to the substrate through the background gas (SRIM 2003 program) and thin film sputtering during the XPS depth profiling (program TRIDYN_FZR) are presented. The simulations show that the particle transport through the background gas is mainly responsible for the Ti depletion: the estimated composition of the thin film is W_0.61Ti_0.16O_0.23. Additional apparent Ti depletion occurs due to the preferential sputtering during the thin film composition analysis. The simulation of the sputtering process show that the surface concentration measured by XPS should be about W_0.74Ti_0.11O_0.15. The discrepancy between the estimated surface composition and the actual experimental result is in the range of the experimental error.     

AES analysis of nitridation of Si(100) by 2–10 keV N+2 ion beams

Ion beam nitridation of Si(100) as a function of N⁺₂ ion energy in the range of 2–10 keV has been investigated by in-situ Auger electron spectroscopy (AES) analysis and Ar⁺ depth profiling. The AES measurements show that the nitride films formed by 4–10 keV N⁺₂ ion bombardment are relatively uniform and have a composition of near stoichiometric silicon nitride (Si₃N₄), but that formed by 2 keV N⁺₂ ion bombardment is N-rich on the film surface. Formation of the surface N-rich film by 2 keV N⁺₂ ion bombardment can be attributed to radiation-enhanced diffusion of interstitial N atoms and a lower self-sputtering yield. AES depth profile measurements indicate that the thicknesses of nitride films appear to increase with ion energy in the range from 2 to 10 keV and the rate of increase of film thickness is most rapid in the 4–10 keV range. The nitridation reaction process which differs from that of low-energy (< 1 keV) N⁺₂ ion bombardment is explained in terms of ion implantation, physical sputtering, chemical reaction and radiation-enhanced diffusion of interstitial N atoms.     

Structure and magnetoresistance of a Ni79.7Fe14.0Co2.8Zr2.0Cu1.5 thin film

The structure and magnetoresistance R of thin films based on Ni₈₀Fe₂₀ permalloy doped with Co, Zr, and Cu have been examined by X-ray diffraction analysis and resistance measurement. The films have been obtained by ion plasma sputtering on oxidized silicon, fused quartz, and glass ceramic cold substrates. It has been shown that the structure of a film in the initial state is a mixture of solid solutions based on two phases: Ni(fcc) particles with a size of L ≈ 8 nm and (Zr_0.67Ni_0.22O_0.11)γ particles with a size of L ≈ 12 nm. The R(H) dependences on the strength and direction of the magnetic field H have been obtained at room temperature for film samples in the initial state and after isothermal annealing at 653 K for 1 h. According to R(H) dependences and X-ray diffraction analysis, films in the initial state are assumingly in a superparamagnetic state, whereas they exhibit ferromagnetic properties after isothermal annealing.     

RF-sputtered LiCoO2 thick films: microstructure and electrochemical performance as cathodes in aqueous and nonaqueous microbatteries

Films of LiCoO₂ are prepared on metallized silicon substrates using RF-magnetron sputtering technique. The microstructural properties of the films are investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The films deposited at a substrate temperature of 250 °C with subsequent annealing at 650 °C exhibited hexagonal layered structure with R $ \overline 3 $ m symmetry. The kinetics of lithium ions in LiCoO₂ film cathode host matrix and its cycleability are studied in aqueous Pt//LiCoO₂ and nonaqueous Li//LiCoO₂ cell. Both the electrochemical cells at same current density of 50 μA cm^?2 delivered the same initial discharge capacity of about 60 μA h?cm^?2 μm^?1 with a chemical diffusion coefficient of ca. 10^?11 cm² s^?1 for Li⁺ ions. The capacity fade rates for the Pt//LiCoO₂ and Li//LiCoO₂ cells, in average are 3.0 and 0.15 % per cycle, respectively, for the first 20 cycles. The Pt//LiCoO₂ cell is found to be advantageous for small number of cycles and is cost effective than the Li//LiCoO₂ cell.     

Die ZerstÄubung von Kupfer durch Edelgas-Ionen im Energiebereich von 100 keV bis 1 MeV als Funktion des Einfallswinkels

Using a 1.3MeV Van de Graaff-accelerator the sputtering ratioS of polycristalline copper bombarded by Ne⁺-, Ar⁺-, Kr⁺- and Xe⁺-ions was measured as a function of the angle of incidence in the range from 0? to 45?. The ion-energy was varied from 100 keV to 1 MeV. The sputtering ratio was found to increase with bombarding angle asS=S(0?)· (2- cos α)/cos α for Ne⁺-, Ar⁺- and Kr⁺-ions and asS=S(0?)/cos^3/2 α for Xe⁺-ions. The increase of the sputtering ratio was found to be independent of the ion-energy.     

Cobalt redistribution over the surface of inhomogeneous cobalt-copper alloy films

The surfaces of electrodeposited 1-μm-thick Co_xCu_100−x (x=8, 11, and 20 at. %) films and also of 0.2-μm-thick films obtained by sputtering targets made of the electrodeposited films with an argon ion beam are analyzed by atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). XPS data indicate that cobalt is absent on the surface of the electrodeposited films but is present in the bulk and on the surface of the sputtered films. The difference in the XPS spectra of copper in the electrodeposited and sputtered films of the same composition is less significant. The data obtained are explained within the framework of a qualitative model according to which subgrains of the basic (copper) component coalesce into large clusters, which subsequently take on a regular oval shape on the free surface. This process favors cobalt atom migration from the free surface to near-surface voids. High-energy particles existing in the flux of the target sputtering products bombard the growth front of the ion-sputtered films, causing the fastest sputtered cobalt atoms to penetrate into the copper matrix as point defects.     

Structural investigations of Ge nanoparticles embedded in an amorphous SiO2 matrix

Transmission electron microscopy and X-ray photoelectron spectroscopy analyses are performed to investigate Ge nanoparticles embedded in an amorphous SiO₂ matrix. GeSiO thin films are prepared by two methods, sol?Cgel and radio frequency magnetron sputtering. After the deposition, the sol?Cgel films are annealed in either N₂ (at 1 atm and 800 °C) or H₂ (at 2 atm and 500 °C), and the sputtered films in H₂ (at 2 atm and 500 °C), to allow Ge segregation. Amorphous Ge-rich nanoparticles (3?C7 nm size) are observed in sol?Cgel films. Crystalline Ge nanoparticles in the high pressure tetragonal phase (10?C50 nm size) are identified in the sputtered films. The size of the nanoparticles increases with Ge concentration in the volume of the film. At the film surface, the Ge concentration is much larger that in the volume for both sol?Cgel and sputtered films. At the same time, at the film surface, only oxidized Ge is observed.     

On the response of semitransparent nanoparticulated films of LuPO<Subscript>4</Subscript>:Eu in poly-energetic X-ray imaging applications

In the present work, we demonstrate the fabrication technique of highly translucent layers of nanoparticulated (~50 nm) LuPO₄:Eu phosphor, present their basic luminescent properties and give results of their performance in a planar imaging system coupled to a CMOS photodetector. For comparison, the imaging performance of an opaque Gd₂O₂S:Eu phosphor screen prepared by sedimentation is also shown. The X-ray detection parameters as well as the luminescence efficiency of the investigated films were discussed. Results show that the in-line transmittance at ~600–700 nm, in the range of the phosphor luminescence, varies with respect to the thickness of the films from 40 to 50 % for a film of 67 μm thick to 4–12 % when the thickness increases to 460 μm. Yet, X-ray detection parameters get enhanced as the thickness of the films increases. Those results affect the luminescence efficiency curves of the films under poly-energetic X-ray radiation of various tube energies. The normalized noise power spectrum values were found similar for LuPO₄:Eu films and a phosphor screen made using commercial Gd₂O₂S:Eu powder. The detective quantum efficiency of our films is clearly lower compared to the Gd₂O₂S:Eu screen from 2 to 10 cycles mm^?1 frequency range while the modulation transfer function is lower from 0 to 5.5 cycles mm^?1 frequency range. The acquired data allow to predict that high-temperature sintering of our films under pressure may help to improve their imaging quality, since such a processing should increase the luminescence efficiency without significant growth of the grains and thus without sacrificing their translucent character.     

Optimization of magnetron deposition process for formation of high-quality oriented ZnO films

The thickness distribution and structure of ZnO films deposited by DC-magnetron sputtering of a zinc target in argon-oxygen gaseous medium at substrate temperature of 27°C and gas pressure in the chamber within 5×10^?3 ? 5×10^?2 mm Hg was investigated. It was revealed that the use of a target with a certain depression in the sputtering zone allows depositing high quality c-oriented films at lower gas pressure than with a flat target. The dependence of film quality on geometric factors is interpreted on the basis of theoretical computations with the assumption that the film structure is improved when the flux of deposited Zn particles decreases while their energy increases.     

Effect of Ag underlayer thickness on the microstructure and magnetic properties of L10-FePt films

FePt/Ag films were deposited on thermally oxidized Si(100) substrates by magnetron sputtering at room temperature and then the as-deposited films were annealed at 500 ^°C. The microstructure and magnetic properties of the films have been investigated by X-ray diffraction and vibrating sample magnetometry. The results indicate that introduction of the Ag underlayer promotes an ordering transformation of the FePt phase due to thermal tensile stress between the Ag underlayer and the FePt film. The in-plane tensile stress induced by the Ag underlayer should stretch the horizontal lattice parameter of FePt; thus, it is helpful for the ordering transformation. With increasing Ag underlayer thickness, the ordering parameter and coercivity first increase and then decrease. When the Ag underlayer thickness is 12 nm, the ordering parameter and coercivity of the film reach the maximum values, respectively. The Ag underlayer thickness also affects the magnetization reversal mechanism.