Heterodiffusion of aluminum in α-iron in a pulsed magnetic field

Using an X-ray diffraction technique, the coefficients of volume diffusion of Al in α-Fe at T = 730°C have been measured for the first time in a pulsed magnetic field with a pulse amplitude of 39.8–238.8 kA/m and a frequency of 1–8 Hz. It is established that both frequency and amplitude of magnetic field pulses significantly influence the diffusion process.     

Application of pulsed electric current in immiscible liquid and droplet processing

Electromagnetic, chemical and thermo-mechanical processing can be applied to the fabrication of polymeric materials which react to external fields such as stress, temperature, moisture, pH, electric or magnetic fields to optimise properties. In this article, the application of the pulsed electromagnetic field in an immiscible liquid phase is reviewed. The droplet behaviour of polymer emulsion's liquid phases is enriched with significant complex phenomena. In emulsion, droplet break-up, size evolution, coalescence, coarsening, flocculation and interfacial interaction among droplets are assessed as a function of processing.

This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Phase singularities and spectral switches of focused higher-order Bessel–Gauss pulsed beams

The phase singularities and spectral switches of focused higher-order Bessel–Gauss pulsed beams are studied. Numerical calculation results are given to illustrate the dependence of phase singularities and spectral switches of focused higher-order Bessel–Gauss pulsed beams on the truncation parameter, topological charge, spatial parameter and propagation distance. It is shown that there always exists an optical vortex at the center of focused higher-order Bessel–Gauss pulsed beams and the topological charge is conserved during the propagation. The spectral switch appears in the neighborhood of the zero- or minimum-intensity position. With increasing topological charge or spatial parameter, the size of the vortex core increases and the spectral transition height decreases.     

Concentration measurement of NO using self-absorption spectroscopy of the γ band system in a pulsed corona discharge

Nitric oxide (NO) concentrations were measured using the γ band system spectrum based on the strong self-absorption effect of NO in pulsed corona discharges. The radiative transitional intensities of the NO γ band were simulated based on the theory of molecular spectroscopy. The intensities of some bands, especially γ(0,0) and γ(1,0), are weakened by the self-absorption. The correlations between the spectral self-absorption intensities and NO concentration were validated using a modified Beer-Lambert law with a combined factor K relating the branching ratio and the NO concentration, and a nonlinear index α that is applicable to the broadband system. Optical emissive spectra in pulsed corona discharges in NO and N2/He mixtures were used to evaluate the two parameters for various conditions. Good agreement between the experimental and theoretical results verifies the self-absorption behavior seen in the UV spectra of the NO γ bands.     

The influence of process parameters on the structure and morphology of pulsed plasma‐polymerized octafluorotoluene films

Abstract

This work describes amorphous fluorinated polymer films deposited by pulsed plasma polymerizations of octafluorotoluene (PPP‐OFT) monomers on ITO glass as the hole‐injection layer of organic electroluminescent (EL) devices, in order to study the influence of sample position and duty cycle on PPP‐OFT film characteristics, and also to find a good process to yield a higher retention degree of monomers and lower roughness of PPP‐OFT fluorocarbon films. Experimental results revealed that PPP‐OFT films deposited at positions far away from the RF coil and close to the monomer inlet showed less roughness than films deposited near the high RF‐flux regions. In addition, the retention of the monomers in the PPP‐OFT layer will be high if the deposition is conducted near the monomer inlet but some distance away from the RF electrode. Moreover, amorphous fluorinated polymer films can be deposited with higher fluorine to carbon (F/C) ratios and CF₂ contents at proper substrate positions by means of different sticking coefficients of free radicals dissociated by octafluorotoluene monomers.     

Effect of beam interaction time on laser alloying with pulsed Nd–YAG laser

Abstract

Surface alloying of aluminium with nickel was carried out using a pulsed Nd–YAG laser. The effect of beam interaction time on laser alloying of aluminium with pulsed Nd–YAG laser has been studied. It was found that the beam interaction time of a pulsed laser has a significant effect on microstructure and properties of alloyed layers. The results indicated that with changes in the beam diameter, higher thickness of alloyed layer and higher microhardness are both obtained at a lower effective interaction time. When travel speed changes, the same conditions are obtained at a higher effective interaction time.     

Memory properties of a Ge nanoring MOS device fabricated by pulsed laser deposition

The non-volatile charge-storage properties of memory devices with MOS structure based on Ge nanorings have been studied. The two-dimensional Ge nanorings were prepared on a p-Si(100) matrix by means of pulsed laser deposition (PLD) using the droplet technique combined with rapid annealing. Complete planar nanorings with well-defined sharp inner and outer edges were formed via an elastic self-transformation droplet process, which is probably driven by the lateral strain of the Ge/Si layers and the surface tension in the presence of Ar gas. The low leakage current was attributed to the small roughness and the few interface states in the planar Ge nanorings, and also to the effect of Coulomb blockade preventing injection. A significant threshold-voltage shift of 2.5?V was observed when an operating voltage of 8?V was implemented on the device.     

Structural and optical properties of γ-alumina thin films prepared by pulsed laser deposition

Preparation of γ-alumina thin films by pulsed laser deposition from a sintered α-alumina target is investigated. The films were deposited on (100) silicon substrates at 973 K with varying oxygen partial pressures in the range 2.0 × 10⁻⁵-3.5 × 10^− 1 mbar. X-ray diffraction results indicated that the films were polycrystalline γ-Al₂O₃ with cubic structure. The films prepared in the oxygen partial pressure range 2.0 × 10^− 5-3.5 × 10^− 2 mbar contained nanocrystals of sizes in the range 10-16 nm, and became amorphous at pressures > 3.5 × 10^− 1 mbar. Topography of the films was examined by atomic force microscopy using contact mode and it showed the formation of nanostructures. The root-mean square surface roughness of the film prepared at 2.0 × 10^− 5 mbar and 3.5 × 10^− 1 mbar were 1.4 nm and 3.5 nm, respectively. The thickness and optical properties were studied using ellipsometry in the energy range 1.5-5.5 eV for three different angles of incidence. The refractive index was found to decrease from 1.81 to 1.73 with the increase of oxygen partial pressures from 2.0 × 10^− 5 to 3.5 × 10^− 2 mbar. The variation in the refractive index has been found to be influenced by the microstructure of the films obtained as a function of oxygen partial pressure.     

Effect of low voltage pulsed magnetic field on microstructure and wear behaviour of eutectic Al–Si alloys

Abstract

Effect of discharging frequency of low voltage pulsed magnetic field (LVPMF) on the morphology and size of eutectic Si in eutectic Al–Si (Al–12Si) alloys has been investigated, and some characteristic parameters the characterised the microstructure of the eutectic Si phase were obtained. Dry sliding wear behaviour of eutectic Al–Si alloys without and with LVPMF treatment were also tested using a pin-on-disc wear testing machine, and scanning electron microscopy and energy dispersive spectroscopy X-ray of worn surfaces were carried out to determine the governing mechanisms in the eutectic Al–Si alloys without and with LVPMF treatment. The results show that the eutectic Si became smaller with the increase in discharging frequency. Fine short rod-like or rounded particle-like eutectic silicon with 2·3 μm in length, 0·6 μm in the width, and 3·8 in aspect ratio was formed in eutectic Al–Si alloy treated by 6 Hz LVPMF. The wear resistance of eutectic Al–Si alloys increased with the increase in discharging frequency. The adhesive wear was observed in eutectic Al–Si alloy without LVPMF treatment under normal load of 80 N. However, mainly abrasive was observed in eutectic Al–Si alloy with 6 Hz LVPMF treatment.     

Characterization of Cu–Ni alloy electrodeposition and synthesis of nanoparticles by pulsed sonoelectrochemistry

Binary alloy Cu–Ni nanoparticles were synthesized by sonoelectrochemical technique from aqueous bath in presence of Na-citrate as complexing agent, to allow co-deposition of Cu and Ni. Alloy Pulsed Electro-Deposition (PED) was carried out to study nucleation kinetic and the effects of pH and surfactant on the final product physical and chemical properties, with the aim to determine optimized parameters for subsequent sonoelectrosyntheses of nanoparticles. Role of pH and Na-citrate in the synthesis process was investigated and it was found that i) pH is the main parameter affecting the stability of synthesis solutions, ii) Na-citrate content influences the sonoelectrochemical process efficiency but at the same time iii) the complexing agent is necessary to obtain Cu and Ni co-deposition; iv) produced nanoparticles are made of CuNi alloy with a fcc crystalline structure and v) pH is weakly responsible of increase in mean grain size of produced nanoparticles.     

Transport properties of thin SnO2〈Sb〉 films grown by pulsed laser deposition

Thin SnO₂<Sb> films grown by pulsed laser deposition have been characterized by X-ray diffraction, optical spectroscopy, and scanning electron microscopy. The carrier mobility and concentration in the films have been determined as functions of target composition (0–8 at % Sb) using Hall effect measurements, and the resistivity of the films has been measured by a four-probe technique. The lowest resistivity (ρ = 2 × 10^?3 Ω cm) and the highest transmission (? 85%) of the films in the spectral range 400-800 nm have been obtained at a target composition Sb/(Sn + Sb) = 2 at %. The observed variation in the resistivity of the films is determined by changes in carrier concentration to a greater extent than by changes in carrier mobility. X-ray photoelectron spectroscopy results demonstrate that the predominant charge state of the antimony in the films is Sb⁵⁺.     

In vivo evaluation of titanium implants coated with bioactive glass by pulsed laser deposition

During the past years, different techniques, like chemical treatment, plasma spraying, sputtering, enamelling or sol–gel; and materials, like metals, hydroxylapatite, calcium phosphates, among others, have been applied in different combinations to improve the performance of prostheses. Among the techniques, Pulsed Laser Deposition (PLD) is very promising to produce coatings of bioactive glass on any metal alloy used as implant. In this work the biocompatibility of PLD coatings deposited on titanium substrates was examined by implantation in vivo. Different coating compositions were checked to find the most bioactive that was then applied on titanium and implanted into paravertebral muscle of rabbit.     

Characterization of β-Ga2O3 films deposited under different growth temperature by pulsed laser deposition

Journal of Materials Science: Materials in Electronics - A series of β-Ga2O3 films were prepared on polished Al2O3 substrates by pulsed laser deposition at temperatures between 580 and 780...     

Development of a compact and reliable repetitively pulsed Xe Cl (308 nm) excimer laser

Development and operation characteristics of a repetitively pulsed UV spark pre-ionized XeCl (Xenon Chloride) excimer laser is described. The laser uses discharge pumped C–C charge transfer excitation. A compact gas circulation loop was adopted to achieve high repetition rate operation. The laser generates optical pulses of energy 150 mJ at 150 Hz reliably. The electrical to optical conversion efficiency obtained is 1%. The laser pulse duration is ~8 nS (FWHM). The single fill gas lifetime have been found to be 2 × 10⁶ shots for 20% reduction of energy without any halogen injection. The system is compact and reliable.     

Formation of hydroxyapatite coating on titanium at 200°C through pulsed laser deposition followed by hydrothermal treatment

Pulsed laser deposition (PLD) has emerged as an acceptable technique to coat hydroxyapatite on titanium-based permanent implants for the use in orthopedics and dentistry. It requires substrate temperature higher than 400°C to form coatings of good adhesion and crystallinity. As this range of temperatures is likely to affect the bulk mechanical properties of the implant, lowering the substrate temperature during the coating process is crucial for the long-term performance of the implant. In the present study, hydroxyapatite target was ablated using a pulsed Nd:YAG laser (355 nm) onto commercially pure titanium substrates kept at 200°C. The coating thus obtained has been subjected to hydrothermal treatment at 200°C in an alkaline medium. The coatings were analysed using microscratch test, optical profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and infrared spectroscopy (FTIR). XRD, EDS and FTIR showed that the as-deposited coating contained amorphous calcium phosphate and the hydrothermal treatment converted it into crystalline hydroxyapatite. The micro-morphology was granular, with an average size of 1 micron. In the micro-scratch test, a remarkable increase in adhesion with the substrate was seen as a result of the treatment. The plasma plume during the deposition has been analysed using optical emission spectroscopy, which revealed atomic and ionic species of calcium, phosphorous and oxygen. The outcomes demonstrate the possibility of obtaining adherent and crystalline hydroxyapatite on titanium substrate at 200°C through pulsed laser deposition and subsequent hydrothermal treatment.     

The irradiation effect of a Nd–YAG pulsed laser on the CeO2 target in the liquid

The irradiation of an Nd–YAG pulsed laser on the CeO₂ target in water was investigated. The reaction products depend mainly on the energy density of the Nd–YAG laser. The CeO₂ nanoparticles with sizes of 20–80 nm were formed in water, while the energy density was larger than 32 kJ/cm². The nanocrystalline films with grain sizes of 50–150 nm were formed on the target with the energy density of 20–25 kJ/cm². Finally, the amorphous films were formed with the energy density of 6–15 kJ/cm². The formation mechanisms of the nanoparticles and the films were discussed according to the triple-point phase diagram of CeO₂.     

Growth and properties of HfxZn1−xO thin films on flexible PET substrate using pulsed laser deposition

Hf-doped ZnO thin films with different Hf contents of target (Hf_xZn_1?xO 0 ≤ x ≤ 10 at.%) were deposited on flexible PET substrates under different oxygen pressure using pulsed laser deposition. Microstructures, optical and electrical properties of the films were studied. The results show that the as-deposited Hf_xZn_1?xO (0 ≤ x ≤ 5 at.%) films crystallized in ZnO hexagonal wurtzite structure with a highly preferred c-axis orientation. The films exhibited a transmission of higher than 80 % in the visible region. With increasing Hf content, the lattice constants increased; the morphology of the films deteriorated. The sheet resistance reached a minimum value of 16 Ω/□ when the doping level was about 0.5 at.%.     

Can the use of pulsed direct current induce oscillation in the applied pressure during spark plasma sintering?

Abstract

The spark plasma sintering (SPS) process is known for its rapid densification of metals and ceramics. The mechanism behind this rapid densification has been discussed during the last few decades and is yet uncertain. During our SPS experiments we noticed oscillations in the applied pressure, related to a change in electric current. In this study, we investigated the effect of pulsed electrical current on the applied mechanical pressure and related changes in temperature. We eliminated the effect of sample shrinkage in the SPS setup and used a transparent quartz die allowing direct observation of the sample. We found that the use of pulsed direct electric current in our apparatus induces pressure oscillations with the amplitude depending on the current density. While sintering Ti samples we observed temperature oscillations resulting from pressure oscillations, which we attribute to magnetic forces generated within the SPS apparatus. The described current–pressure–temperature relations might increase understanding of the SPS process.     

Determination of (40)ca(+) in the presence of (40)ar(+): an illustration of the utility of time-gated detection in pulsed glow discharge mass spectrometry

The glow discharge ionization source operated in the pulsed, or modulated, power mode affords a number of distinct advantages over its steady-state counterpart. It is well-known that pulsed plasma operation permits the application of higher instantaneous powers by allowing time for the sample to cool. This minimizes sample overheating while effecting higher sputtering yields and lower limits of detection. The presence of discrete time regimes affords the added advantage of temporal selectivity. Such selectivity allows the observation of analyte ions during a time regime in which their signal is at a maximum while that of electron ionized background species is declining. Significantly, time regimes are found when no background argon ion signals are observable but analyte ion signals remain. This means that discrimination against isobaric interferences arising from the discharge gas is possible. A prime example of the utility of this advantage arises in the determination of calcium with an argon glow discharge. Both the major argon and calcium isotopes are found at a nominal m/z of 40. Time-gated mass spectrometeric detection during the afterpeak time regime enables the ready determination of (40)Ca(+) in samples at the ppm level. A linear calibration curve is obtained that also demonstrates the elimination of the (40)Ar(+) signal from mass spectra obtained with either a dc or rf glow discharge ion source.