Table of contents

We use the magneto-optical Kerr measurement at room temperature to demonstrate an electric-field controlled switching of the local magnetization vector in a very simple multiferroic bilayer made up of an amorphous FeBSiC magnetic layer bonded on a Pb(Zr,Ti)O₃ slab. By applying an electric field on this simple bilayer structure, the magnetic hysteresis loops significantly change via magnetoelectric coupling between the two layers. An electric field larger than the ferroelectric coercive field of Pb(Zr,Ti)O₃ can rotate the magnetization direction away from the in-plane. These results would inspire further exploration of electric-field-controlled magnetization switching in heterogeneous multiferroic systems.

Cadmium selenide (CdSe) quantum dots (QDs) with different particle sizes have been used as an inorganic co-sensitizer in addition to organic dye for large band gap mesoporous TiO₂ dye sensitized solar cells. The QDs co-sensitized solar cells exhibited overall highest conversion efficiency of 3.65% at 1 sun irradiation for 3.3 nm particle size corresponding to a visible light absorption wavelength of 528 nm. The photovoltaic characteristics of CdSe QDs co-sensitized cells depend on the particle sizes rather than broad spectral light absorption as compared with CdSe QDs alone sensitized and standard dye-sensitized solar cells. Correlation between CdSe QDs adsorption on mesoporous TiO₂ surfaces and photoelectron injection into TiO₂ has been demonstrated.

In this contribution RF excited atmospheric pressure glow discharges are investigated in He–water mixtures in a parallel metal plate reactor by mass spectrometry. Positive and negative ion fluxes to the electrode are investigated as a function of varying water concentration and discharge power. The dominant positive ions are H₃O⁺ (and its clusters), OH⁺, O⁺, , , HeH⁺, and . Negative ions are detectable from a concentration of 900 ppm water in He onwards. Coinciding with the emergence of the negative ions, there is a drop in positive ion flux to the mass spectrometer and a significant increase in applied voltage indicating increasing electron loss by attachment and ion loss by mutual (three and two body) positive–negative ion recombination. The dominant negative ions are OH⁻ and its clusters. The negative ion flux increases with increasing water concentration. Positive and negative ion cluster formation increases with decreasing discharge power and increasing concentration of water vapour at constant power. It is shown that the size of the sampling orifice of the inlet of the mass spectrometer is important for sampling atmospheric pressure active plasmas due to the presence of the narrow sheath.

When the thickness of a metallic film is in the nanometre range, electrons in the film as well as those transmitting through the film can both manifest the quantum size effect (QSE). For the former, electrons are confined in the quantum well of a metal film to form quantum-well states. For the latter, electrons scattered by the quantum well in the film can bring about the phenomenon of transmission resonance. Scanning tunnelling microscopy (STM) combined with spectroscopy is a powerful tool to explore these two kinds of QSE. In this paper, we review our recent studies on the QSE of thin Pb and Ag films by using STM. We demonstrate that the formation of the quantum-well states in the Pb film can significantly affect the morphology, thickness, growth process and electronic structures of Pb films. On the other hand, the transmission resonance can be observed on the Ag film with Z–V spectroscopy in STM. The energy level of the transmission resonance varies with the film thickness and can be shifted by the electric field. Moreover, in the studies of transmission resonance, it is unavoidable to observe the standing-wave states, i.e. Gundlach oscillations, which are the QSE in the tunnelling gap. We have also discovered that the Gundlach oscillation can be exploited to measure the work function of thin metal films with very high precision.

Cu-doped ZnO (ZnCuO), Cu–Ga co-doped ZnO (Zn(Cu,Ga)O) and Cu–Na co-doped ZnO (Zn(Cu,Na)O) diluted magnetic semiconductor thin films have been deposited on (0 0 0 1) sapphire substrates by pulsed laser deposition. All the films have a hexagonal wurtzite ZnO structure with a high c-axis orientation. Hall-effect measurements showed that the ZnCuO film is n-type, in which the carrier concentration is greatly enhanced by the addition of Ga, while the introduction of Na resulted in p-type behaviour with a high resistivity. The magnetic hysteresis measurement indicated that the pure ZnCuO film is ferromagnetic at room temperature. Doping of Ga (n-type dopant) does not have a significant effect on the room temperature ferromagnetism. However, the room temperature ferromagnetic behaviour is destroyed by the addition of Na (p-type dopant). X-ray photoelectron spectroscopy analyses revealed that there exist more oxygen defects in the ZnCuO, Zn(Cu,Ga)O films than in the Zn(Cu,Na)O film. It was suggested that the interaction of Cu²⁺ with the oxygen defect in an n-type environment is responsible for the ferromagnetism observed in the ZnCuO system.

Fast magnetic measurements performed by means of a 20 T pulse-field magnet provide a good approach for directly monitoring the magnetocaloric effect of the MnFe(P,Ge) compounds. Based on the comparison of magnetization curves obtained either in an adiabatic or isothermal process, we propose that the method introduced by Levitin et al is applicable to determine the adiabatic temperature change for an equivalent field change in first-order magnetic transition materials. More strikingly, experimental results confirm that the first-order nature of the transition in MnFe(P,Ge) alloys is not a limiting factor to the operation frequency of a magnetic refrigerator.

The two-dimensional paramagnetic-impurity-embedded electron gas with Rashba spin–orbit interaction in a four-terminal Landauer setup is studied. The mean-field-assisted Landauer–Keldysh formalism is employed to investigate the electron and impurity magnetizations (spin polarizations). A mirror symmetry is identified to characterize both electron and impurity magnetizations when the impurities are symmetrically (with respect to this mirror) positioned and when pinning fields are absent. In the equilibrium Landauer setup where electrodes remain at the same chemical potentials, the adopted formalism is justified by recovering the conventional (without spin–orbit interactions) Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange by applying a pinning field to the impurity. In the same setup, when further the Rashba spin–orbit interaction is turned on, the exchange between two impurities with one of the spins being pinned is comprehended as a consequence of the interplay between spin precession and the exchange oscillation. We find that in such an equilibrium system, at most two components of the spins can show up. For biased (non-equilibrium) setup, on the other hand, three components of the impurity spins can all be non-vanishing, which is distinguishable from the equilibrium case.

This paper presents the design and development of a free-standing, magnetoelastic biosensor. The detection principle is presented and various resonance characteristics of the sensor are discussed. Experimental measurements of the sensor resonance frequencies agree with theoretical predictions. The influence of the external magnetic field on the resonance behaviour of the sensor was studied and the optimum dc magnetic fields for best sensitivity in air and in water solutions for 2000 × 400 × 15 µm (2 mm) sensors and 1000 × 200 × 15 µm (1 mm) size sensors were determined to be 75 Oe and 38 Oe, respectively. Both theoretical prediction and experimental results show that smaller sensors have greater mass sensitivity and can theoretically detect mass as small as one biological spore. The sensor platform was immobilized with JRB7 phages for specific, in vitro detection of B. anthracis spores. Real-time detection of spores suspended in water was demonstrated using a flowing system. The 1 mm and 2 mm sensors were found to have a detection limit of 10⁴ spores ml⁻¹ and 10⁵ spores ml⁻¹, respectively.

Consideration of temperature and anisotropy effects in hysteresis modelling allows for tailoring the operation point of magnetic circuits. The recently modified Jiles–Atherton model has been extended to describe the hysteresis loops in MnZn ferrites for two temperatures below the Curie point. Anisotropy is modelled by a proper choice of the value of the quantum number J in the Brillouin function.

Using spin-polarized density functional calculations, we have studied the magnetic states including collinear and noncollinear magnetic coupling in bimetallic Co_6−nMn_n clusters. The ground state of Co_6−nMn_n clusters displays collinear magnetic ordering for n ⩽ 3, whereas a magnetic transition to noncollinear ordering occurs at n = 4 and the noncollinear magnetic structure remains to be energetically favoured afterwards. Moreover, the total magnetic moment of Co_6−nMn_n increases with n by 2μ_B for n = 0–3 and decreases sharply from n = 3 to n = 4, while the decreasing trend becomes smooth for n = 4–6. The competition of ferromagnetic and antiferromagnetic interactions between the neighbouring magnetic moments induces the emergence of noncollinear magnetic coupling in the small bimetallic clusters.

We report here the room temperature ferromagnetic ordering in spray-pyrolized polycrystalline thin films of Ti_1−xCo_xO₂ (x = 0, 0.025, 0.05 and 0.10). The saturation magnetic moment in these films with x = 0.05 and 0.10 is estimated to be of 0.28 and 0.38μ_B/Co, respectively. The ambient air employed in the present case of the spray pyrolysis process resulted in ferromagnetic films possessing very high resistivity values (∼10⁷ Ω cm). This is in contrast to Ti_1−xCo_xO₂ films deposited by vacuum based techniques, which are relatively conducting. While pristine TiO₂ film exhibited the anatase phase, the rutile phase of TiO₂ also evolved with an increase in Co concentration in these films. X-ray diffractograms could not reveal segregation of Co atoms in the TiO₂ matrix; also, no formation of any oxide of cobalt was detected. X-ray photoelectron spectroscopic investigation established the Co cations to be bivalent, and suggests that Co⁺² is substituting Ti⁺⁴ in the TiO₂ matrix. Due to the highly resistive nature of these films, the observed room temperature ferromagnetism could be attributed either to the formation of bound magnetic polarons or to defect mediated ordering.

An integrated design of dye-sensitized solar cell with fluorescent layer is realized. A fluorescent layer is deposited on a fluorine-doped tin oxide (FTO) glass with a blank right above a N719 dye-sensitized TiO₂ coating which is printed on the central area of the conductive face of the FTO glass. Current density–voltage characteristic measurement indicates that our integrated system largely enhances photon harvesting by 44% compared with a cell without a fluorescent layer, which is attributed to the improvement of photon harvesting from the spectrum range and the space area.

In this work, Ge nanocrystals (nc-Ge) embedded in SiO₂ thin films have been synthesized by ion implantation. Both the higher and the lower implantation dose/energy samples exhibit significant memory effect as a result of charge trapping in the nc-Ge. Under a negative gate voltage, either electron trapping or hole trapping dominates, depending on the magnitude of gate voltage and charging time as well as the distribution of nc-Ge. However, under a positive gate voltage, only electron trapping is observed, and the flat-band voltage shift is also affected by the nc-Ge distribution. These results demonstrate that the unconventional memory effect can be modulated by the distribution of nc-Ge.

It is shown that BiB₃O₆ : Tm³⁺ glass nanoparticles incorporated into polymethylmethacrylate (PMMA) and polycarbonate (PC) polymer matrices show good second-order susceptibilities under bicolour coherent laser treatment. It is found that only during incorporation into highly polarized PC matrices could one observe an enhancement of the second-order susceptibilities with increasing laser treated power densities. The main increase is observed for all samples at power densities equal to about 0.4 GW cm⁻². After passing this value there is a saturation of the output susceptibilities and even an abrupt decrease. The most striking feature is the achievement of second-order susceptibilities equal to about 5 pm V⁻¹ for samples containing 4% nanoparticle (NP) content in the PC matrix. A further increase in the NP concentration to 6% leads to a decrease in susceptibility to 15%. In the case of PMMA matrices these changes do not exceed the background. The same situation is present for the pure BIBO and low-doped Tm materials. The effect is maximal for a low concentration of Tm—about 0.75%. In the case of bulk glasses the intensity dependences of the second-harmonic generation unambiguously show that the achieved maximal values of second-order susceptibilities do not exceed 3 pm V⁻¹ for 0.5% Tm concentration.

The photovoltaic effects of Nb-doped SrTiO₃ single crystals with different thicknesses were investigated under the illumination of ultraviolet pulsed lasers. The peak photovoltage increased and then decreased quickly with the decrease in crystal thickness, and a maximum photovoltage occurred for the 180 µm-thick crystal. The photovoltaic response time decreased monotonically with decreasing crystal thickness. The present results suggested the promising potential of reducing crystal thickness in high sensitivity detectors with fast response.

Singlet delta oxygen (SDO) yield, small signal gain, and output power have been measured in a scaled electric discharge excited oxygen–iodine laser. Two different types of discharges have been used for SDO generation in O₂–He–NO flows at pressures up to 90 Torr, crossed nanosecond pulser/dc sustainer discharge and capacitively coupled transverse RF discharge. The total flow rate through the laser cavity with a 10 cm gain path is approximately 0.5 mole s⁻¹, with steady-state run time at a near-design Mach number of M = 2.9 of up to 5 s. The results demonstrate that SDO yields and flow temperatures obtained using the pulser-sustainer and the RF discharges are close. Gain and static temperature in the supersonic cavity remain nearly constant, γ = 0.10–0.12% cm⁻¹ and T = 125–140 K, over the axial distance of approximately 10 cm. The highest gain measured is 0.122% cm⁻¹ at T = 140 K. Positive gain measured in the supersonic inviscid core extends over approximately one half to one third of the cavity height, with absorption measured in the boundary layers near top and bottom walls of the cavity. Laser power has been measured using (i) two 99.9% mirrors on both sides of the resonator, 2.5 W, and (ii) 99.9% mirror on one side and 99% mirror on the other side, 3.1 W. Gain downstream of the resonator is moderately reduced during lasing (by up to 20–30%) and remains nearly independent of the axial distance, by up to 10 cm. This suggests that only a small fraction of power available for lasing is coupled out, and that additional power may be coupled in a second resonator. Preliminary laser power measurements using two transverse resonators operating at the same time (both using 99.9–99% mirror combinations) demonstrated lasing at both axial locations, with the total power of 3.8 W.

A new method for experimentally determining the electron density (n_e) and the electron temperature (T_e) in the negative glow of a nitrogen pulsed discharge is presented. It is based on optical emission spectroscopy (OES) and consists of a variation and refinement of relatively similar schemes previously reported for different working conditions by other authors. The bottom line is the measurement of the emission intensities of the (0,0) bands of the first negative system at 391.44 nm and of the (0,2) bands of the second positive system at 380.49 nm.

The suggested procedure allows the establishment of the absolute values of n_e and T_e, as long as one calibration point is provided, such as the electron density at one specific discharge condition. If this calibration point is unavailable, the method nonetheless yields a qualitative dependence of T_e and n_e. Langmuir probe measurements confirm and validate the OES results for n_e, thereby legitimizing the diagnostic technique developed. The interpretation of the results for T_e is slightly more complex, and in some circumstances an accurate determination of T_e may require further analysis.

The application of a high frequency (∼2.5 MHz) burst (amplitude-modulated sinusoidal) excitation voltage waveform is investigated for driving a fluorescent dielectric barrier discharge (DBD) light source. The excitation waveform presents a novel method for generating spatially stable homogeneous Xe DBD possessing a high conversion efficiency from electrical energy to VUV excimer radiation (∼172 nm), even at a significantly higher electrical energy deposition than realized by pulsed excitation. Simulation and experimental results predict discharge efficiencies around 60%. Lamp efficacy above 74 lm W⁻¹ has been achieved. VUV emission and loss mechanisms are investigated extensively and the performance of burst and pulsed waveforms is compared both theoretically and experimentally.

A simple collisional–radiative model for the Paschen 1s and 2p levels is proposed for low-temperature argon discharges. This model can predict the population distribution of 1s and 2p levels over a wide discharge pressure range 1–10⁵ Pa and ionization ratio range 10⁻⁶–10⁻³. The modelling results are found to be in good agreement with observed optical emissions from several different types of argon discharges at 1, 100 and 10⁵ Pa. By using the model, the dominant kinetic processes of 1s and 2p levels are investigated for an electron beam plasma, an inductively coupled plasma, a capacitively coupled plasma and a microwave microplasma. A kinetic diagram is given, which can be used to identify the kinetic state of 1s and 2p levels in many low-temperature argon discharges reported in the literature. This model is also useful for obtaining discharge parameters from optical emissions in low-temperature argon discharges.

Wear is a major obstacle limiting the useful life of implanted ultra-high molecular weight polyethylene (UHMWPE) components in total joint arthroplasty. It has been a continuous effort in the implant industry to reduce the frictional wear problem of UHMWPE by improving the structure, morphology and mechanical properties of the polymer. In this paper, a new paradigm that utilizes nanoimprint lithography (NIL) in producing textures on the surface of UHMWPE is proposed to efficiently improve the tribological properties of the polymer. Friction and wear experiments were conducted on patterned and controlled (non-patterned) UHMWPE surfaces using a commercial tribometer, mounted with a silicon nitride ball, under a dry-sliding condition with normal loads ranging from 60 to 200 mN. It has been shown that the patterned UHMWPE surface showed a reduction in the coefficient of friction between 8% and 35% as compared with the controlled (non-patterned) surface, depending on the magnitude of the normal load. Reciprocating wear experiments also showed that the presence of surface textures on the polymer resulted in lower wear depth and width, with minimal material transfer to the sliding surface.

Films of amorphous aluminium nitride (AlN) were prepared by conventional radio frequency sputtering of an Al + Cr target in a plasma of pure nitrogen. The Cr-to-Al relative area determines the Cr content, which remained in the ∼0–3.5 at% concentration range in this study. Film deposition was followed by thermal annealing of the samples up to 1050 °C in an atmosphere of oxygen and by spectroscopic characterization through energy dispersive x-ray spectrometry, photoluminescence and optical transmission measurements. According to the experimental results, the optical–electronic properties of the Cr-containing AlN films are highly influenced by both the Cr concentration and the temperature of the thermal treatments. In fact, thermal annealing at 1050 °C induces the development of structures that, because of their typical size and distinctive spectral characteristics, were designated by ruby microstructures (RbMSs). These RbMSs are surrounded by a N-rich environment in which Cr³⁺ ions exhibit luminescent features not present in other Cr³⁺-containing systems such as ruby, emerald or alexandrite. The light emissions shown by the RbMSs and surroundings were investigated according to the Cr concentration and temperature of measurement, allowing the identification of several Cr³⁺-related luminescent lines. The main characteristics of these luminescent lines and corresponding excitation–recombination processes are presented and discussed in view of a detailed spectroscopic analysis.

Self-assembled monolayers of octadecylphosphonic acid and 16-phosphonohexadecanoic acid (PHDA) were formed on the semiconductor substrates gallium nitride (GaN) and aluminium gallium nitride (AlGaN). The presence of the molecular layers was verified through x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Structural information was acquired with infrared spectroscopy which verified the bonding orientation of the carboxyl-containing PHDA. The impact of the molecular layers on the channel conductivity and the surface electronic structure of an AlGaN/GaN heterostructure was measured. Our results indicate that pinning of the surface Fermi level prohibits modification of the channel conductivity by the layer. However, a surface dipole of ∼0.8 eV is present and associated with both phosphonic acid layers. These results are of direct relevance to field-effect-based biochemical sensors and metal–semiconductor contact formation for this system and provide a fundamental basis for further applications of GaN and AlGaN technology in the fields of biosensing and microelectronics.

Polymer-dispersed liquid crystals (PDLCs) are composite materials that consist of micrometre-sized liquid-crystal (LC) droplets embedded in a polymer matrix. From ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and a nematic LC, PDLC films containing 10 and 60 wt% LC were prepared, and their electro-optical and piezo-optical behaviour was investigated. The electric field that is generated by the application of mechanical stress leads to changes in the transmittance of the PDLC film through a combination of piezoelectric and electro-optical effects. Such a piezo-optical PDLC material may be useful, e.g., in sensing and visualization applications.

The photoelectric effects of LiTaO₃ (LTO) single crystals are experimentally studied with two kinds of LTO wafers, 10° tilted and untilted, at room temperature. A transient open-circuit photoelectrical response of 143 ps rise time is observed in the 10° tilted LTO when a 266 nm pulsed laser with a duration of 25 ps is irradiated directly onto the LTO surface. The untilted LTO with interdigitated electrodes of 10 µm finger width and 10 µm interspacing exhibits a linear dependence on the applied bias and power density of incident light, a response peak at about 235 nm and a sharp cutoff at about 270 nm. The noise current is only 61 pA at 20 V bias under the illumination of sunlight outdoors at midday. The experimental results suggest the promising application of the LTO single crystal in UV detection, in particular, as a solar-blind fast-response photodetector.

P-type Zn-doped Zn_xIn_1−xSb(0 ⩽ x ⩽ 0.10) compounds with different Zn content are synthesized by slow growth from melt. The effects of Zn content on the structure and thermoelectric properties are investigated. The results show that all the specimens exhibit p-type conduction characteristics. The solubility limit of Zn doping in Zn_xIn_1−xSb is found to be close to 0.05. The room-temperature carrier concentration N_p of the samples increases obviously with increasing Zn content for the Zn-doped Zn_xIn_1−xSb compounds, while the room-temperature carrier mobility and the thermal conductivity decrease with increasing Zn content for the Zn-doped Zn_xIn_1−xSb compounds. The Zn-doped Zn_xIn_1−xSb compounds possess a high power factor. The maximum power factor of 2.44×10⁻³ W m⁻¹ K⁻² is obtained at 460 K for Zn_0.0075In_0.9925Sb compound. The maximum ZT value of 0.27 is obtained at 700 K for Zn_0.01In_0.99Sb due to the lower thermal conductivity and higher power factor.

A novel hydrogenated carbon film containing fullerene-like nanostructure was prepared by pulse bias-assisted plasma enhanced chemical vapour deposition, and the fullerene-like arrangement in the film was characterized by high resolution transmission electron microscopy. The as-prepared hydrogenated carbon film exhibited super-low friction and wear in both dry N₂ and humid ambient atmospheres, and was superior to the conventional hydrogenated carbon films. These excellent tribological properties could be attributed to the unique fullerene-like nanostructure, which endows the film with some special chemical and physical features, such as high chemical inertness, hardness and elastic recovery owing to the closed, curved and caged graphite planes, and hence, improves the tribological properties of the hydrogenated carbon film.

The phase transition behaviour and its effect on the electromechanical properties of 0.65Pb_1−xSr_x(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ ceramics with 0 ⩽ x ⩽ 0.08 were investigated. A morphotropic phase boundary between tetragonal and rhombohedral phases was revealed by XRD results in compositions with 0.02 ⩽ x ⩽ 0.06. An electric field induced monoclinic–tetragonal phase transition was determined by dielectric constant and elastic constant measurements. Enhanced electromechanical properties were obtained by shifting the electrical field induced phase transition to room temperature. An optimal performance corresponding to d₃₃ = 706 pC N⁻¹ and k_p = 0.587 was obtained for the composition with x = 0.02.

Single-crystalline porous hematite nanorods and spindle-like nanostructures were successfully synthesized by a low temperature reflux condensation method. Two different iron sources, namely, FeCl₃·6H₂O and Fe(NO₃)₃·9H₂O, were hydrolyzed in the presence of urea to selectively prepare nanorods and spindle-like nanostructures. Initially, the akagenite phase was obtained by refluxing the precursor for 12 h and then the as-prepared akagenite nanostructures were transformed to porous hematite nanostructures upon calcination at 300 °C for 1 h. The shape and the aspect ratio of the 12 h refluxed sample was retained even after calcination and this shows the topotactic transformation of the nanostructure. TEM and HRTEM investigations have shown the porous nature of the prepared sample. Brunauer–Emmett–Teller and Barret–Joyner–Halenda measurements have shown a large surface area and distribution of mesopores in the nanorods sample. The photocatalytic activity of the prepared nanostructures towards RhB has reflected this variation in the pore size distribution and specific surface area, by showing a higher activity for the nanorods sample. Magnetic studies by VSM have shown a weak ferromagnetic behaviour in both the samples due to shape anisotropy.

Multi-track laser cladding is now applied commercially in a range of industries such as automotive, mining and aerospace due to its diversified potential for material processing. The knowledge of temperature, velocity and composition distribution history is essential for a better understanding of the process and subsequent microstructure evolution and properties. Numerical simulation not only helps to understand the complex physical phenomena and underlying principles involved in this process, but it can also be used in the process prediction and system control. The double-track coaxial laser cladding with H13 tool steel powder injection is simulated using a comprehensive three-dimensional model, based on the mass, momentum, energy conservation and solute transport equation. Some important physical phenomena, such as heat transfer, phase changes, mass addition and fluid flow, are taken into account in the calculation. The physical properties for a mixture of solid and liquid phase are defined by treating it as a continuum media. The velocity of the laser beam during the transition between two tracks is considered. The evolution of temperature and composition of different monitoring locations is simulated.