Table of contents

The formation of Ge quantum dot arrays by deposition from a low-temperature plasma environment is investigated by kinetic Monte Carlo numerical simulation. It is demonstrated that balancing of the Ge influx from the plasma against surface diffusion provides an effective control of the surface processes and can result in the formation of very small densely packed quantum dots. In the supply-controlled mode, a continuous layer is formed which is then followed by the usual Stranski–Krastanow fragmentation with a nanocluster size of 10 nm. In the diffusion-controlled mode, with the oversupply relative to the surface diffusion rate, nanoclusters with a characteristic size of 3 nm are formed. Higher temperatures change the mode to supply controlled and thus encourage formation of the continuous layer that then fragments into an array of large size. The use of a high rate of deposition, easily accessible using plasma techniques, changes the mode to diffusion controlled and thus encourages formation of a dense array of small nanoislands.

Ar + NO microwave discharges are used for sterilization and the results are compared with additional experiments with Ar, O₂ and N₂–O₂ plasma mixtures. The NO^* species produced in the Ar–NO mixtures remain up to long distances from the source, thus improving the sterilization efficiency of the process. E. coli individuals exposed to the Ar + NO plasma undergo morphological damage and cell lysis. Combined effects of etching (by O^* and Ar^* species) and UV radiation (from deactivation of NO^* species) are responsible for the higher activity found for this plasma mixture.

In the separated microwave H and E fields, the heating behaviour of a SiO₂/Si substrate was first investigated. Subsequently, the heating behaviour was further compared with the samples deposited with Pt/Ti electrodes and PZT films, respectively. It was found that PZT thin films were much more efficiently heated and crystallized in the H field than in the E field; moreover, the heating of the samples was derived mainly from the contribution of Pt/Ti and Si, which is distinct from the previous assumption about microwave dielectric heating of the E field. This unexpected foundation indicates that susceptors or high power are not necessary for microwave annealing of thin films, and furthermore, this method provides a new path for annealing any kind of thin film deposited on semiconducting or conductive substrates.

Hydrogen-induced reduction of Young's modulus and hardness of BaTiO₃ single crystal have been investigated by nanoindentation experiments and first principles calculations. The experimental results showed that Young's modulus and hardness of the a and b domains are the same. However, Young's modulus of the c domains is much lower than that for a(b) domains. Young's modulus and hardness of three kinds of domains reduced after hydrogen charging and were restored after outgassing. The first principles calculations are well consistent with the experimental results.

Red-emitting phosphor powders of SrIn₂O₄ activated with Eu³⁺ ions were fabricated by high pressure assisted combustion synthesis. X-ray diffraction analysis of these oxide phosphors revealed the formation of single-phase orthorhombic SrIn₂O₄ for concentrations up to 4 at% Eu. A detailed photoluminescence (PL) and cathodoluminescence study showed bright red emission originated within the ⁵ D₀ → ⁷F_J intra-shell transitions of Eu³⁺. Furthermore, PL excitation spectroscopy revealed that an efficient energy transfer from the SrIn₂O₄ host lattice onto the Eu ions is accomplished in addition to the excitation band peaked at 396 nm that directly excites the Eu ions, making this material an excellent candidate for applications in solid state white lamps.

Bottom gate and top contact thin film transistors were fabricated using In₂O₃ thin films as active channel layers. Thin films of varying thicknesses in the range 5–20 nm were deposited on an SiO₂ gate dielectric by the thermal evaporation process in the presence of high purity oxygen. The results of atomic force microscopy show that all the films exhibit dense grain distribution with a root-mean-square roughness in the range 0.6–8.0 nm. Irrespective of the thickness of the channel layer, the on/off ratio of the device is 10⁴. The channel mobility and resistivity were found to be a strong function of the thickness of the active layer. The Levinson model was used to calculate the trap density and the grain boundary mobility. The low processing temperature shows the possibility of utilizing these devices on flexible substrates such as polymer substrates.

One hundred and one years after J J Thomson was awarded the Nobel Prize for the discovery of the electron, the 2007 Nobel Prize for Physics was awarded to Professors Peter Grünberg and Albert Fert for the discovery of giant magnetoresistance (GMR) in which the spin as well as the charge of the electron is manipulated and exploited in nanoscale magnetic materials. The journey to GMR started with Lord Kelvin who 150 years ago in 1857 made the first observations of anisotropic magnetoresistance and includes Sir Neville Mott who in 1936 realized that electric current in metals could be considered as two independent spin channels. Modern technology also has a significant role to play in the award of this Nobel Prize: GMR is only manifest in nanoscale materials, and the development of nanotechnology growth techniques was a necessary pre-requisite; further, the considerable demands of the magnetic data storage industry to drive up the data density stored on a hard disk fuelled an enormous international research effort following the initial discovery with the result that more than 5 billion GMR read heads have been manufactured since 1997, ubiquitous in hard disks today. This technology drive continues to inspire exploration of the spin current in the field now known as spintronics, generating new ideas and applications. This review explores the science underpinning GMR and spintronics, the different routes to its discovery taken by Professors Grünberg and Fert, the new science, materials and applications that the discovery has triggered and the considerable potential for the future.

This Cluster Issue of Journal of Physics D: Applied Physics highlights micro-pixellated gallium nitride light-emitting diodes or `micro-LEDs', an emerging technology offering considerable attractions for a broad range of scientific and instrumentation applications. It showcases the results of a Research Councils UK (RCUK) Basic Technology Research programme (http://bt-onethousand.photonics.ac.uk), running from 2004–2008, which has drawn together a multi-disciplinary and multi-institutional research partnership to develop these devices and explore their potential.

Examples of GaN micro-pixel LEDs in operation. Images supplied courtesy of the Guest Editors.

The partnership, of physicists, engineers and chemists drawn from the University of Strathclyde, Heriot-Watt University, the University of Sheffield and Imperial College London, has sought to move beyond the established mass-market uses of gallium nitride LEDs in illumination and lighting. Instead, it focuses on specialised solid-state micro-projection devices the size of a match-head, containing up to several thousand individually-addressable micro-pixel elements emitting light in the ultraviolet or visible regions of the spectrum. Such sources are pattern-programmable under computer control and can project into materials fixed or high-frame rate optical images or spatially-controllable patterns of nanosecond excitation pulses. These materials can be as diverse as biological cells and tissues, biopolymers, photoresists and organic semiconductors, leading to new developments in optical microscopy, bio-sensing and chemical sensing, mask-free lithography and direct writing, and organic electronics. Particular areas of interest are multi-modal microscopy, integrated forms of organic semiconductor lasers, lab-on-a-chip, GaN/Si optoelectronics and hybrid inorganic/organic semiconductor structures.

This Cluster Issue contains four invited papers and ten contributed papers. The invited papers serve to set the work in an international context. Fan et al, who introduced the original forms of these devices in 2000, give a historical perspective as well as illustrating some recent trends in their work. Xu et al, another of the main international groups in this area, concentrate on biological imaging and detection applications. One of the most exciting prospects for this technology is its compatibility with CMOS, and Charbon reviews recent results with single-photon detection arrays which facilitate integrated optical lab-on-chip devices in conjunction with the micro-LEDs. Belton et al, from within the project partnership, overview the hybrid inorganic/organic semiconductor structures achieved by combining gallium nitride optoelectronics with organic semiconductor materials. The contributed papers cover many other aspects related to the devices themselves, their integration with polymers and CMOS, and also cover several associated developments such as UV-emitting nitride materials, new polymers, and the broader use of LEDs in microscopy.

Emission patterns generated at the end of a multicore image fibre 600 μm in diameter, from article 094013 by H Xu et al of Brown University.

We would like to thank Paul French for suggesting this special issue, the staff of IOP Publishing for their help and support, Dr Caroline Vance for her administration of the programme, and EPSRC (particularly Dr Lindsey Weston) for organizational and financial support.

III-nitride micro-emitter array technology was developed in the authors' laboratory around 1999. Since its inception, much progress has been made by several groups and the technology has led to the invention of several novel devices. This paper provides an overview on recent progress in single-chip ac-micro-size light emitting diodes (μLEDs) that can be plugged directly into standard high ac voltage power outlets, self-emissive microdisplays and interconnected μLEDs for boosting light emitting diodes's wall-plug efficiency, all of which were evolved from III-nitride micro-emitter array technology. Finally, potential applications of III-nitride visible micro-emitter arrays as a light source for DNA microarrays and future prospects of III-nitride deep ultraviolet micro-emitter arrays for label-free protein analysis in microarray format by taking advantage of the direct excitation of intrinsic protein fluorescence are discussed.

Flip-chip InGaN micro-pixellated LED arrays with high pixel density and improved device performance are presented. The devices, with 64 × 64 elements, each of which have a 20 µm emission aperture on a 50 µm pitch, are fabricated with a matrix-addressable scheme at blue (470 nm) and UV (370 nm) wavelengths, respectively. These devices are then flip-chip bonded onto silicon mounts. Good emission uniformity across the LED array is demonstrated, which can be attributed to the introduced n-metal tracks adjacent to each n-GaN mesa and the p-contact lines running across parallel columns. More importantly, with a flip-chip configuration, the optical power output and the current-handling capability of these new devices are substantially enhanced, due to the improved heat dissipation capability and the increased light extraction efficiency. For instance, each pixel in the flip-chip blue (respectively UV) LED arrays can provide a maximum power density 43 W cm⁻² (respectively 6.5 W cm⁻²) at an extremely high current density up to 4000 A cm⁻² before breakdown. These flip-chip devices are then combined with a computer-programmable driver circuit interface to produce high-quality micro-scale displays. Other promising applications of these LEDs, such as colour conversion with quantum dots, are also demonstrated.

Previously, we reported that a thin GaN interlayer approach has been developed for growth of 340 nm ultraviolet light emitting diodes (UV-LEDs) with significantly improved performance. In this paper, more recent results on the further development of UV-LEDs with shorter wavelengths are reported, and the limitation of the wavelength of the UV-LEDs that can be pushed to, while retaining high device performance using the approach has been investigated. Transmission electron microscopy and device-performance data, including electrical and optical characteristics, indicated that the thin GaN interlayer approach can be effectively employed for growth of UV-LEDs to an emission wavelength approaching at least 300 nm. The approach should be taken into account in growth of UV-LEDs on sapphire substrates, as it provides a simple but effective growth method to achieve UV-LEDs with high performance. This paper also reports that a micro-LED array using the UV-LED wafer has been successfully fabricated, offering versatile micro-structured UV light sources for a wide range of applications.

Ultra-violet light emitting diodes with an increased efficiency have been produced. The increase in efficiency was brought about by the introduction of a thin GaN layer between the AlN buffer and the subsequent AlGaN layers. The GaN interlayer causes a reduction in the number of threading dislocations that propagate through the ultra-violet light emitting structure. Temperature dependent electroluminescence measurements show an improved performance at temperatures up to 400 K.

Tightly focused spots with small central lobes, high central intensity and low sidelobe intensity are desirable for many light-emitting diode based micro-projection system applications. Diffractive optical elements (DOEs) offer a potentially low cost and flexible choice for realizing this task. We have approached the design of suitable elements using two methods: various step size simulated quenching (VSSQ) and multiresolution various step size simulated quenching followed by direct binary search (M-VSSQ-DBS). M-VSSQ-DBS greatly increases the central intensity of the spots, and only slightly influences the sidelobe intensity, most often favourably reducing it. When the central lobe size is 0.8 times that of the geometrical-optics limit, the peak intensity can be as high as 97.73% that of the geometrical spot, and the relative maximum sidelobe intensity is 51.14% of the peak intensity. The designs are tolerant to variations in the actual width of the light source and to lateral misalignment. We verify the designed DOE using rigorous diffraction theory, i.e. the finite-difference time-domain method. The results obtained by scalar and rigorous diffraction theory are in excellent agreement with each other.

We present the highlights of a research programme on hybrid inorganic–organic light emitters. These devices combine recent developments in III–V nitride technology (including UV emitting micro-arrays and specifically tailored quantum wells) with conjugated polymers to access the entire visible spectrum. Two types of devices are studied, those based on down conversion of the quantum well emission by radiative transfer and those based on non-radiative resonant energy transfer. The spectral and operating characteristics of the devices are described in detail. Selectable colour micro-arrays and bar emitters are demonstrated. The nature of the non-radiative energy transfer process has also been studied and we find transfer efficiencies of up to 43% at 15 K, with a 1/R² dependence on the distance between quantum well and polymer layer, suggesting a plane–plane interaction. The relative importance of the non-radiative resonant energy transfer process increases with temperature to be up to 20 times more efficient, at 300 K, than the radiative transfer process.

We report for the first time a UV curable polymer with effective optical transmission below 300 nm. Through careful control of kinetics, various viscosities can be generated to optimize the film forming properties via spin coating. The transmission of the monomers and films is investigated over a spectral range which spans the 240–370 nm output of ultraviolet AlInGaN light-emitting diodes. The refractive index of the polymer has been measured by ellipsometry to give a value of 1.57 at 280 nm. Using standard lithography techniques with reactive ion etching, arrays of microlenses have been fabricated in this polymer with diameters of 30 µm and below and are characterized by atomic force microscopy and confocal microscopy.

We report the integration of micro-patterned polyfluorene conjugated polymers onto GaN-based ultraviolet (UV) micro-pixellated light-emitting diode arrays (micro-LEDs). The 64 × 64 element matrix-addressable AlInGaN devices have a pixel size of 20 µm diameter on a 50 µm pitch, emitting at 368 nm. Each array is covered with a 2.5 µm thick photo-curable deep-UV-transparent polymer and a 30 nm thick polyfluorene film. This polymer bi-layer is subsequently patterned into an array of 28 µm diameter discs aligned with the pixels of the micro-LED array. Polymer down-converted visible emission from these pattern-programmable organic/inorganic electroluminescent micro-arrays is achieved.

In this paper, we describe a series of improvements that have been made to our direct laser writing waveguide/microfluidic fabrication technology. We demonstrate significant increases in the writing speed (measured in micrometres of written structure per second) by both the use of customized photopolymers containing light emitting polymer and the inclusion of a diffractive optical element to enable the writing of multiple channels in a single pass.

Single-photon detection is useful in many domains requiring time-resolved imaging, high sensitivity and high dynamic range. In this paper the miniaturization and performance potential of solid-state single-photon detectors are discussed in the context of lab-on-chip applications where high accuracy and/or high levels of parallelism are suited. Technological and design trade-offs are discussed in view of recent advances in integrated LED matrix technology and the emergence of new multiplication based architectures.

We describe a single chip approach to time resolved fluorescence measurements based on time correlated single photon counting. Using a single complementary metal oxide silicon (CMOS) chip, bump bonded to a 4 × 16 array of AlInGaN UV micro-pixellated light-emitting diodes, a prototype integrated microsystem has been built that demonstrates fluorescence excitation and detection on a nanosecond time scale. Demonstrator on-chip measurements of lifetimes of fluorescence colloidal quantum dot samples are presented.

We demonstrate flexible use of low cost, high-power light emitting diodes as illumination sources for fluorescence lifetime imaging (FLIM). Both time-domain and frequency-domain techniques have been implemented at wavelengths spanning the range 450–640 nm. Additionally, we demonstrate optically sectioned fluorescence lifetime imaging by combining structured illumination with frequency-domain FLIM.

This paper reviews authors' laboratory's work on the development of nitride-based blue–green and ultraviolet microscale LED devices with particular classes of imaging and spectroscopic applications in cellular level biology. Starting from neuroscience, we illustrate the utility of blue–green micro-LEDs for voltage-sensitive dye imaging of individual neural cells, as well as their ultraviolet counterparts for photostimulation of neurons. Arrays of micro-LEDs are also shown to be useful in projecting spatiotemporal patterns of photoexcitation to study the visual system development in living animals. As another illustration of the utility of the emerging nitride microdevice technology, we demonstrate the application of UV micro-LED arrays in bio-sensing technology as the core of a real-time fluorescence spectroscopy biowarning system.

Stimulating neuron cells with light is an exciting new technology that is revolutionizing the neurosciences. To date, due to the optical complexity that is involved, photostimulation has only been achieved at a single site using high power light sources. Here we present a GaN based micro-light emitting diode (LED) array that can open the way to multi-site photostimulation of neuron cells. The device is a two-dimensional array of micrometre size LED emitters. Each emitter has the required wavelength, optical power and modulation bandwidth to trigger almost any photosensitizer and is individually addressable. We demonstrate micrometre resolution photoactivation of a caged fluorophore and photostimulation of sensitized living neuron cells. In addition, a complete system that combines the micro-LED array with multi-site electrophysiological recording based on microelectrode array technology and/or fluorescence imaging is presented.

FePt : Al₂O₃ nanocomposite thin films synthesized by magnetic trapping (MT) assisted pulsed laser deposition (PLD) were found to have lower transition temperature for L1₀ face-centred-tetragonal (fct) phase due to higher concentration of defects. The low phase transition temperature together with non-magnetic matrix materials helps to reduce grain growth and agglomeration during annealing. Small remanence ratio and coercive squareness for nanocomposite thin films annealed at 300 °C to fct phase confirm that the main intergranular interaction is magnetostatic interaction rather than exchange coupling. The MT assisted PLD can synthesize fct-FePt : Al₂O₃ nanocomposite thin films with reduced intergranular exchange coupling.

This paper presents an experimental investigation of two different magnetorheological (MR) fluids, namely, water-based and hydrocarbon-based MR fluids in compression mode under various applied currents. Finite element method magnetics was used to predict the magnetic field distribution inside the MR fluids generated by a coil. A test rig was constructed where the MR fluid was sandwiched between two flat surfaces. During the compression, the upper surface was moved towards the lower surface in a vertical direction. Stress–strain relationships were obtained for arrangements of equipment where each type of fluid was involved, using compression test equipment. The apparent compressive stress was found to be increased with the increase in magnetic field strength. In addition, the apparent compressive stress of the water-based MR fluid showed a response to the compressive strain of greater magnitude. However, during the compression process, the hydrocarbon-based MR fluid appeared to show a unique behaviour where an abrupt pressure drop was discovered in a region where the apparent compressive stress would be expected to increase steadily. The conclusion is drawn that the apparent compressive stress of MR fluids is influenced strongly by the nature of the carrier fluid and by the magnitude of the applied current.

Polycrystalline nickel layers, deposited on Si(1 1 0) wafers via electron beam evaporation to a thickness of 29 or 68–70 nm, were thermally annealed in vacuo at 493 or 530 K. The elemental interdiffusion across the Ni/Si interface was measured by means of Rutherford backscattering spectroscopy, and the relaxation of stress and grain growth by means of x-ray diffraction. At 530 K, a slight logarithmic increase in the interface variance with the annealing time, but no crystalline silicide formation was observed. The in-plane magneto-optical Kerr effect and magnetic force microscopy were used to investigate the changes in the magnetic properties. With increasing annealing time, the decrease in coercivity and gain in magnetic remanence were correlated with the relaxation of stress. Similarities with ion-irradiated Ni/Si couples will be discussed.

Dielectric properties of Ba_0.6Sr_0.4TiO₃ (BST) in a layered terfenol-D/BST/terfenol-D system were investigated. Dielectric properties of the BST layer can be adjusted by magnetostrictive strain of terfenol-D layers under applied magnetic fields. Our results show that the small-signal dielectric constant of BST can be tuned ranging from about 2300 to 4000 by a small magnetic field. By adjusting the relative layer thickness ratio, a more broad adjustable dielectric constant and tunability of BST layer can be designed, which may have potential applications in sensitive multifunctional devices and microwave devices.

We study the mechanism of domain wall depinning and propagation in Fe_77.5Si_7.5B₁₅ amorphous glass-covered microwires. These samples are ferromagnetic and spontaneously present the striking property of magnetic bistability, with the magnetization reversal process characterized by a single giant Barkhausen jump. This process allows one to easily measure the velocity of a domain wall propagating along the sample as a function of applied magnetic field and temperature and thus determine the wall mobility and the influence of different damping mechanisms on the domain wall dynamics. A discussion on the effects of thermal treatment on the wall mobility is presented. Domain wall velocities of the order of 850 m s⁻¹ are measured. The temperature dependence of the wall mobilities established at 300 and 77 K, for as-cast and annealed samples, clearly shows a damping mechanism arising from the structural relaxation mechanism and from domain wall/atomic defect interactions, the second one playing a major role in the dissipative dynamics of magnetization reversal through depinning and domain wall propagation in Fe_77.5Si_7.5B₁₅ microwires.

Hexagonal barium ferrite thick films (50–200 µm) have been deposited on Si and Al₂O₃/Si substrates using a screen printing technique. X-ray diffractometry, scanning electron microscopy and magnetometry were used to characterize and correlate the ferrite films' microstructure and magnetic properties. The experiments indicated that an Al₂O₃ underlayer was effective in preventing silicon diffusion into the barium ferrite films during a final sintering treatment at temperatures above 1100 °C. A two-stage sintering process allowed a reasonable tradeoff between mechanical and magnetic properties. This work reveals the feasibility of fabrication of thick ferrite films on large substrates (up to 25 mm in diameter) for future planar microwave devices compatible with semiconductor integrated circuits processing.

A giant magnetoresistance (GMR) is observed in the Mn_2−xZn_xSb (x < 0.3) system, with the largest MR ratio of −37.6% in a field of 5 T at 120 K for the Mn_1.9Zn_0.1Sb compound. Different from other Mn₂Sb-based compounds, the GMR in Mn_2−xZn_xSb is closely correlated with a field-induced transition from a weak ferrimagnetic (WFI) state to a ferrimagnetic (FI) state. It is understood that the influences of both super-zone gap and spin-dependent scattering are responsible for GMR in the present system. Magnetic hysteresis and phase coexistence of the WFI and the FI phases suggest that this WFI–FI transition is of first order. The different mechanisms responsible for butterfly loops of magnetization/resistivity curves in different magnetic states are discussed.

We have used dc magnetization to measure the temperature dependences of the coercivity, squareness and maximum energy product for YCo₅(70 wt%)/Y₂Co₁₇(30 wt%) nanocomposite powders synthesized by mechanical milling and subsequent annealing. Our data show that all the above magnetic quantities have values that monotonically increase upon cooling within the 295–3 K temperature interval. On the other hand, hysteresis loops collected at low temperatures exhibit a 'knee' in the second quadrant of the demagnetization curve, which suggests that the inter-grain exchange coupling becomes less effective as the temperature is lowered. This cooling-induced weakening of exchange coupling, which is somewhat not expected to coexist with the magnetic property enhancement, is confirmed by the temperature dependence of the exchange-coupled volume ratio. Furthermore, the observed temperature behaviour of the coercive field yields evidence that the magnetostatic (dipolar) interactions are strengthened at low temperatures. We explain the low-temperature magnetic property enhancement by anisotropy modifications and the reduction of thermal fluctuations upon cooling, which compete with the weakening of exchange coupling and the enhancement of demagnetizing dipolar interactions.

Ultracompact 1 × N (N > 2) beam splitters based on coupling of multiple photonic crystal waveguides (PCWs) are numerically demonstrated. The operation of the devices is on the basis of the self-imaging phenomenon. Variation of the effective index of modified rods induces the transverse redistribution of the N-fold images with the same coupling length, and uniform or free splitting can be achieved. The devices with three and four output channels are discussed in details as examples. Results show that this kind of beam splitters are very short. At the operating wavelength of 1.55 µm, the splitting length of the devices is only 35 µm even if the output channel number reaches 20. It provides a new method and a compact model to export freely the beam to N channels in PCW devices and can find practical applications in future photonic integrated circuits.

Spectroscopic properties of Yb³⁺/Er³⁺ codoped tellurite glasses as a function of Er³⁺ and Yb³⁺ concentration have been investigated. Under 970 nm excitation three strong up-conversion emission bands centred at 525, 546 and 656 nm were observed, and the characteristic near infrared emission band was centred at 1.53 µm. With fluorescence and radiative lifetime the quantum efficiency (QE) of infrared (1.53 µm) and visible upconversion (546 and 660 nm) emissions was calculated. The maximum stimulated emission cross section for ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ is 9.7 × 10⁻²¹ cm² for 3/0.5 mol%. The energy transfer (ET) efficiency from Yb³⁺ to Er³⁺ (⁴F_5/2) + (⁴I_15/2) → (⁴ F_7/2) + (⁴I_13/2) was calculated, being the maximum ET of 69% for 0.5 mol% of Er³⁺ with 4.5 mol% of Yb³⁺. The results indicate that both ET and QE depend mostly on Er³⁺ rather than on Yb³⁺ concentration.

Eigenmode matching theory, which was developed originally for the band structure and the transmission property of the infinite phononic crystal (PC), is extended to deal with the PC thin plate. By this method, the transmission property of the one-dimensional PC thin plate with and without a uniform substrate is investigated. It is shown that in the PC thin plate without a substrate, the permitted band of the structure can be separated into two parts, which can be excited by the incident antisymmetric and symmetric Lamb modes, respectively. However, for the PC plate with a substrate, the energy conversion between the symmetric and antisymmetric modes can be found in the transmission spectrum. The physical origin of such an energy conversion is discussed.

ZnGa₂O₄ particles that are regular octahedra in shape and uniform in size were synthesized on Si substrates via catalyst-free chemical vapour deposition. The surfaces of the octahedra are bounded by {1 1 1} facets. A model based on surface energy dependent growth rate is proposed for interpreting the appearance of the octahedra. The field-emission (FE) properties of the octahedral particles were measured. The turn-on field required for producing an emission current density of 0.1 µA cm⁻² is 11 V µm⁻¹, and the field enhancement factor (β) is about 1256, which is high enough for various FE applications.

Paraelectric potassium–lithium–tantalate–niobate, or KLTN, crystals have been grown with two different Mn concentrations: 0.25 and 0.5 mol%. Detailed investigations have been made on the photorefractive (PR) properties of the as-grown crystals by the two-wave mixing technique. High diffraction efficiencies of 90% and 62.5% and PR sensitivities of 1.0 × 10⁻⁹E₀ cm² J⁻¹ and 3.0 × 10⁻⁹E₀ cm² J⁻¹ were achieved for 1.5 mm thick Mn_0.25 : KLTN and Mn_0.5 : KLTN, respectively. The measured two-wave mixing gains for 0.25 mol% and 0.5 mol% reached large values of 27 cm⁻¹ at the external field of E₀ = 3.4 kV cm⁻¹ and of 25 cm⁻¹ at E₀ = 3.9 kV cm⁻¹, respectively. The normalized PR response time under 1 W cm⁻² illumination is less than 1 s at 532 nm. It is shown that Mn can effectively enhance the PR properties of KLTN which is a very promising ideal material for electroholographic applications.

Theoretical analysis of a surface plasmon resonance based fibre optic sensor with a uniform semi-metal coated U-shaped probe is carried out using a bi-dimensional model. All the rays of the p-polarized light launched in the fibre and their electric vectors are assumed to be confined in the plane of bending of the U-shaped probe. The effect of the bending radius of the probe on the sensitivity of the sensor is studied. The study shows that as the bending radius of the probe decreases the sensitivity of the sensor increases. For the light launching conditions used, the maximum sensitivity achieved is several times more than that reported for a fibre optic tapered probe. In addition to high sensitivity, the most advantageous feature of a U-shaped probe is that it can be used as a point sensor.

Carrier transport mechanisms and a barrier height of Ni contacts to p-type GaN (p-GaN) with the structure of a transmission line model were investigated from current–voltage measurements in this study. We find that the method can be adopted for p-GaN, especially in the case where high-quality ohmic contacts are difficult to make. This provides a rational guideline for the development of processing methodologies to estimate the barrier-height value for Schottky diodes without ohmic contacts.

Amorphous As₂S₈ chalcogenide glass is shown to undergo changes in refractive index upon exposure to ultraviolet (UV) light. As₂S₈ film properties are studied, which were measured with testing techniques of prism coupler, x-ray diffraction spectrum and Raman spectra. It is found that the refractive index increases and the thickness decreases after UV light irradiation. The visible optical absorption spectra show that photo-darkening does not exist in the As₂S₈ film. Based on the study of these phenomena, the UV light irradiation technique is presented and employed for fabricating an As₂S₈ stripe waveguide, which is shown to be an effective guided mode device with a useful switching functionality based on the photo-optical effect, such as an all-optical attenuator.

Different techniques including admittance spectroscopy, noise spectroscopy and photocurrent measurements have been applied to Al_xGa_1−xN materials grown by metal–organic chemical vapour deposition to investigate their electrical properties. A continuous band of shallow donors with ionization energies ranging from 50 to 110 meV which contribute to the residual conductivity of Al_xGa_1−xN alloys is observed. We also identify a deep centre with optical ionization energy of 1.2 eV which controls the slow buildup of the photocurrent when the materials are illuminated with sub-bandgap photon energy. This centre also induces persistent photocurrent in the material. In the light of this finding we discuss DX-like defects, which may contribute to the slow relaxation phenomena in AlGaN related structures.

A novel Eu²⁺ ion doped triple phosphate Ca₈MgGd(PO₄)₇ was synthesized by a general high-temperature solid-state reaction in a reductive atmosphere. X-ray powder diffraction analysis confirmed the formation of single phase Ca₈MgGd(PO₄)₇. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 1–2 µm. Photoluminescence excitation spectrum measurements show that the phosphor can be efficiently excited by UV–visible light from 250 to 480 nm to realize emission in the visible range. The emission spectrum showed a broad and asymmetric profile from 410 to 750 nm, which corresponds to the allowed f–d transition from three kinds of Eu²⁺ ions. The characteristics indicated that this phosphor is a candidate for application in the white light-emitting diodes. The luminescence mechanism and three site occupancies of Eu²⁺ ions in Ca₈MgGd(PO₄)₇ lattices are briefly discussed.

A photoacoustic (PA) imaging system based on an ultrasonic Fresnel zone plate (FZP) transducer is developed for the purpose of imaging biological tissue. This FZP transducer has a two-zone negative zone plate piezoelectric material pattern, and an optical fibre is integrated with the transducer on the symmetric axis of the zone plates to deliver laser pulses to the sample. The focal characteristic of the FZP transducer is analysed by theoretical prediction and experimental measurement, and the measured results are in good agreement with the predicted results. The limited-field back-projection deconvolution algorithm combined with the coherence-factor weighting technique is used to reconstruct the optical absorption distribution. The experiments were performed with phantoms and the blood vessels of chicken embryo chorioallantoic membrane. The results demonstrate that PA imaging using the FZP transducer has the ability to image biological tissue and has potential application in monitoring neovascularization in tumour angiogenesis.

Antimony sulfide thin films (thickness, 500 nm) were deposited on chemically deposited CdS thin films (100 nm) obtained on 3 mm glass substrates coated with a transparent conductive coating of SnO₂:F (TEC-15 with 15 Ω sheet resistance). Two different chemical formulations were used for depositing antimony sulfide films. These contained (i) antimony trichloride dissolved in acetone and sodium thiosulfate, and (ii) potassium antimony tartrate, triethanolamine, ammonia, thioacetamide and small concentrations of silicotungstic acid. The films were heated at 250 °C in nitrogen. The cell structure was completed by depositing a 200 nm p-type PbS thin film. Graphite paint applied on the PbS thin film and a subsequent layer of silver paint served as the p-side contact. The cell structure: SnO₂:F/CdS/Sb₂S₃ (i or ii)/PbS showed open circuit voltage (V_oc) of 640 mV and short circuit current density (J_sc) above 1 mA cm⁻² under 1 kW m⁻² tungsten–halogen radiation. Four cells, each of 1.7 cm² area, were series-connected to give V_oc of 1.6 V and a short circuit current of 4.1 mA under sunlight (1060 W m⁻²).

Surgical instruments are intended to come into direct contact with the patients' tissues and thus interact with their first immune defence system. Therefore they have to be cleaned, sterilized and decontaminated, in order to prevent any kind of infections and inflammations or to exclude the possibility of transmission of diseases. From this perspective, the removal of protein residues from their surfaces constitutes new challenges, since certain proteins exhibit high resistance to commonly used sterilization and decontamination techniques and hence are difficult to remove without inducing major damages to the object treated. Therefore new approaches must be developed for that purpose and the application of non-equilibrium plasma discharges represents an interesting option. The possibility to effectively remove model proteins (bovine serum albumin, lysozyme and ubiquitin) from surfaces of different materials (Si wafer, glass, polystyrene and gold) by means of inductively coupled plasma discharges sustained in different argon containing mixtures is demonstrated and discussed in this paper.

Research was performed to increase the efficiency of a plasma reactor for the H₂ yield. Ni as a transitional metal catalyst and TiO₂ as a photocatalyst were utilized for the generation of H₂ from an aqueous solution. The composition of aqueous solution, discharge properties and electrode geometry affected H₂ generation. It was found that the hollow type electrode configuration allowed discharge distribution along the perimeter of the electrode's tip, which increased the density of streamers and reduced plasma energy loadings, as the value of the inception voltage for the discharge propagation decreased. The maximum H₂ yield was observed at 2 kHz of discharge frequency and 12 kV of applied voltage, using distilled water, which was in compliance with a steep increase in electron density, n_e ≈ 10¹⁷ cm⁻³ and electron temperature, T_e ≈ 2 eV. Within this favourable discharge condition, the synergistic effect of a non-thermal plasma and TiO₂, Ni catalysts was investigated. The plasma state was studied by optical emission spectroscopy (OES), electrical and acoustical techniques. Emitted light, electric current and acoustical signals acquired from the discharge demonstrated systematical correlation. OES was used to estimate n_e and T_e by measuring the Stark broadening of the Balmer H_β line and emission of H_α and H_β lines ratio, respectively. The rotational and vibrational temperatures were deduced from OH(A ²Σ⁺–X ²Π, Δυ = 0) and N₂(C ³Π_u–B ³Π_g) bands.

The ion energy distribution function (IEDF) in high power impulse magnetron sputtering (HIPIMS) discharges was studied by plasma sampling energy-resolved mass spectroscopy. HIPIMS of chromium (Cr), titanium (Ti) and carbon (C) targets in argon (Ar) atmosphere was analysed. Singly and doubly charged ions of both the target and the gas were detected. Time-averaged IEDFs were measured for all detected ions at the substrate position at a distance of 150 mm from the target. The effects of target current and discharge pressure on the IEDF were investigated. Measurements were done at two pressures and for three peak discharge currents.

The IEDF of both the target and the gas ions was found to comprise two Maxwellian distributions. Quantitative analysis of target IEDFs at a low pressure showed that the main peak had a lower average energy with an approximate value of E_AV = 1 eV which is attributed to collisions with thermalized gas atoms and ions. The higher energy distribution has a tail extending up to 70 eV, which is assumed to originate from a Thompson distribution of sputtered metal atoms which, due to collisions, are thermalized and appear as a Maxwell distribution. The proportion of high energy IEDFs for metal ions increases monotonically as a function of I_d. The effective ion temperature k_BT, extracted from the main low energy peak, showed a weak dependence on peak current. The effective ion temperature extracted from the high energy tail showed a strong correlation with the change in I_d.

The IEDF at high pressure shows that a proportion of high energy IEDFs was very low and dominated by a low energy main peak. The gas IEDF at high pressure was completely thermalized. The metal-ion-to-gas-ion ratio was found to increase with I_d and with the sputtering yield of the target material.

We present a comparison of a finite element analysis of the atmospheric pressure RF-excited plasma needle interacting with different surfaces with corresponding experimental observations of light emission spatial profiles. The gas used is helium with 1 ppm nitrogen as an impurity. The needle has a point-to-plane geometry with a radius of 30 µm at the tip and an inter-electrode gap of 1 mm. We employ a fluid model in two-dimensional axisymmetric coordinates. Our simulation results indicate that the plasma structure strongly depends on the electrical properties of the treated surface as well as the discharge mode. In the lower power corona mode with a dielectric surface, the plasma is confined near the needle tip. As a result, particle fluxes to the dielectric surface are relatively low and follow a Gaussian-like radial profile. In the higher power glow mode with a dielectric surface, the particle fluxes to the surface are orders of magnitude higher and the spatial distribution of the particle fluxes becomes radially more uniform due to a uniform ionization layer just above the treated surface. When a conductive plate replaces the dielectric surface in the glow mode, a quite intense ionization spot appears near the surface closest to the needle tip. Consequently, the particle fluxes to the surface peak near the symmetry axis under these conditions. These simulation results are validated by experimental observation of light emission spatial profiles.

This paper presents a study of the development of a surface dielectric barrier discharge in air under conditions similar to those of plasma actuators for flow control. The study is based on results from a 2D fluid model of the discharge in air that provides the space and time evolution of the charged particle densities, electric field and surface charges. The electrohydrodynamic (EHD) force associated with the momentum transfer from charged particles to neutral molecules in the volume above the dielectric layer is also deduced from the model. Results show that the EHD force is important not only during the positive part of the sinusoidal voltage cycle (i.e. when the electrode on top of the dielectric layer plays the role of the anode) but also during the negative part of the cycle (cathode on top of the dielectric layer). During the positive part of the cycle, the EHD force is due to the formation of a positive ion cloud that is periodically interrupted by high current breakdown. The EHD force during the negative part of the cycle is due to the development of a negative ion cloud that continuously grows during the successive high frequency current pulses that form in this regime.

Plasma gas temperatures were measured via in situ optical emission spectroscopy in a microwave CH₄–H₂ plasma under carbon nanotube (CNT) growth conditions. Gas temperature is an important parameter in controlling and optimizing CNT growth. The temperature has a significant impact on chemical kinetic rates, species concentrations and CNT growth rates on the substrate. H₂ rotational temperatures were determined from the Q-branch spectrum of the (0) transition. N₂ rotational and vibrational temperatures were measured by fitting rovibrational bands from the N₂ emission spectrum of the C ³Π_u → B ³Π_g transition. The N₂ rotational temperature, which is assumed to be approximately equal to the translational gas temperature, increases with an increase in input microwave plasma power and substrate temperature. The measured H₂ rotational temperatures were not in agreement with the measured N₂ rotational temperatures under the CNT growth conditions in this study. The measured N₂ rotational temperatures compared with the H₂ rotational temperatures suggest the partial equilibration of upper excited state due to higher, 10 Torr, operating pressure. Methane addition in the hydrogen plasma increases the gas temperature slightly for methane concentrations higher than 10% in the feed gas.

Interactions between protein molecules and inorganic substrates were studied both experimentally and numerically to obtain fundamental insight into the assembly of biomacromolecules for engineering applications. We experimentally traced individual fluorescent-labelled lysozyme (F-lysozyme) molecules, diffusing in the vicinity of interfaces between a protein solution and oxidized Si(1 0 0) and glass plates. The results indicate that diffusion coefficients of F-lysozyme molecules on both substrates are more than three orders of magnitude smaller than those in a bulk solution. The molecular dynamics simulations reveal a drastically diminished diffusion coefficient of lysozyme on the substrates of pure Si(1 1 1) and oxidized Si(1 0 0) with a hydroxy-terminated surface compared with that in bulk solution due to molecular adsorption behaviour on the substrate, which is in good agreement with experimental results. Furthermore, full atomistic description of the behaviour provides detailed information of deformation due to the adsorption process. Lysozyme on pure Si(1 1 1) undergoes substantial deformation whereas that on oxidized Si(1 0 0) does not, which indicates the importance of substrate surface condition to preserve the structure, i.e. functionality of adsorbed biomolecules.

PbTiO₃/BiFeO₃ (PB film), BiFeO₃/PbTiO₃ (BP film) multilayer structural films and pure BiFeO₃ film (BFO film) have been deposited on LaNiO₃/SiO₂/Si substrates by the sol–gel process annealed at 600 °C. XRD results indicate that the films are well crystallized and no impure phases are observed. The results of ferroelectricity show that the PB film and BP film have larger polarization than the BFO film under the same applied electric field. The double remanent polarizations of the PB film, the BP film and the BFO film are 82.2 µC cm⁻², 85.6 µC cm⁻² and 3.5 µC cm⁻² under 500 kV cm⁻¹, respectively. The dielectric property study shows that the multilayer structural films have a larger dielectric constant and dielectric loss than the BFO film. Leakage current is found to be reduced in the multilayer structural films.

ZnO films co-doped with H and Al (HAZO) were prepared by sputtering ZnO targets containing 1 wt% Al₂O₃ on Corning glass at a substrate temperature of 150 °C with Ar and H₂/Ar gas mixtures. The effects of hydrogen addition to Al-doped ZnO (AZO) films with low Al content on the electrical, the optical and the structural properties of the as-grown films as well as the vacuum- and air-annealed films were examined. Secondary ion mass spectroscopy analysis showed that the hydrogen concentration increased with increasing H₂ in sputter gas. For the as-deposited films, the free carrier number increased with increasing H₂. The Hall mobility increased at low hydrogen content, reaching a maximum before decreasing with a further increase of H₂ content in sputter gas. Annealing at 300 °C resulted in the removal of hydrogen, causing a decrease in the carrier concentration. It was shown that hydrogen might exist as single isolated interstitial hydrogen bound with oxygen, thereby acting like an anionic dopant. Also, it was shown that the addition of hydrogen to ZnO films doped with low metallic dopant concentration could yield transparent conducting films with very low absorption loss as well as with proper electrical properties, which is suitable for thin film solar cell applications.

This work reports the formation of conducting carbon nanopatterns (nano-wires) in a semi-inorganic polymer by irradiation with energetic ions. The conducting nano-patterns/wires are evidenced by conducting atomic force microscopy. The typical diameter of the conducting wires is observed to be about ∼50–200 nm. The density (spacing), growth direction and length of these carbon nanowires can be changed simply by ion fluence, angle of irradiation and the film thickness, respectively. The formation of conducting nanopatterns in an insulating matrix (polymers/gels) is correlated with the structural transformation of films, investigated by means of Raman spectroscopy.

This paper presents an experimental study of friction characteristics of electroless Ni–P (EN) coatings sliding against steel and optimization of coating process parameters based on the Taguchi method. Experiments are carried out by utilizing the combination of process parameters based on the L₂₇ Taguchi orthogonal design with four process parameters, namely, bath temperature, concentration of nickel source solution, concentration of reducing agent and annealing temperature. It is observed that concentration of nickel source solution has the most significant influence in controlling friction characteristics of EN coating. The optimum combination of process parameters for minimum friction coefficient is obtained from the analysis. The surface morphology and composition of coatings are also studied with the help of scanning electron microscopy, energy dispersed x-ray analysis and x-ray diffraction analysis.

The phase transition process from the Si(1 1 1)-(7 × 7) surface to the Cu/Si(1 1 1)-(5 × 5) surface structure has been studied by scanning tunnelling microscopy and synchrotron radiation photoemission spectroscopy. The nucleation and growth of Cu/Si(1 1 1)-(5 × 5) on the Si(1 1 1)-(7 × 7) surface progress gradually with the increase in Cu coverage. Cu deposition on the Si(1 1 1)-(7 × 7) surface at room temperature may only involve the saturation of the surface dangling bonds, whereas a new surface phase of Cu/Si(1 1 1)-(5 × 5) is formed upon annealing, which saturates at a Cu coverage of 0.9 ML. Our experiments clearly show the surface phase transition process of the (5 × 5) structure as a function of the Cu coverage and provide useful insight into the Cu/Si(1 1 1)-(5 × 5) structure.

In this paper, we report the development of TiO₂ films by reactive electron beam evaporation, using a recently introduced Ti₃O₅ material as the starting material. During experiments, considerable effort was undertaken to optimize the deposition conditions for preparation of high quality TiO₂ films. The processing window for preparation of high quality stoichiometric TiO₂ was found to be quite narrow. The refractive index at 550 nm was approximately 2.41 for the samples. Combinations of spectroscopic ellipsometry and transmittance or reflectance spectrophotometry were used to measure and characterize the optical properties of the films. The surface morphology and microstructure were investigated by using atomic force microscopy and field emission scanning electron microscopy, respectively. The hardness and Young's modulus were calculated to be approximately 12 and 138 GPa by the nanoindentation measurements.

This paper presents a detailed investigation of the influence of rare earth (RE) oxide (La₂O₃) addition on densification and microstructure of direct laser sintered submicrometre WC–Co_p/Cu metal matrix composites (MMCs) possessing 50.0 wt% reinforcement (WC–Co). It was found that with increasing La₂O₃ addition to a suitable amount (1.0 wt%), the particulate dispersion was homogenized and the particulate/matrix interfacial bonding was improved. However, with an excessive addition of La₂O₃ (1.5 wt%), a heterogeneous microstructure consisting of highly accumulated particulates was present. The exact metallurgical roles of RE element in direct laser sintering of particulate reinforced MMCs were addressed. It showed that a proper addition of RE element (i) decreased surface tension of the melt and enhanced solid–liquid wettability; (ii) dragged and/or pinned grain/phase boundaries and resisted grain coarsening and particulate aggregating. However, the balling phenomenon occurred and the activity of RE atoms decreased at an even higher La₂O₃ content, thereby producing detrimental effects on laser forming ability.

The basic mechanical equilibrium equation is employed to model the cantilever system which consists of two giant magnetostrictive films (GMSFs), one with positive and the other with negative magnetostriction, and a non-magnetic substrate (NMS) for actuators. The bending and loading characteristics of the cantilever system are discussed systematically, and the optimal condition for actuator application is presented. The results show that a thicker substrate is favourable for larger force exerted by the cantilever when one of its sublayer thickness is kept constant. But a thinner substrate is required when the total thickness of the cantilever needs to be kept constant so that a proper balance is needed in choosing the sublayer and substrate thicknesses. It is also found that, to obtain the maximum exerted force, the thickness configuration of GMSFs should be fixed at the optimal value. The GMSF/NMS/ GMSF cantilever is generally superior in loading characteristics to the GMSF/NMS and GMSF/GMSF cantilevers. Our discussion may be helpful to the designing and fabricating of the giant magnetostrictive cantilever actuators with more realistic and optimal geometry.

For the immiscible Zr–Nb system characterized by a positive heat of formation (+6 kJ mol⁻¹), thermodynamic calculation showed that the Gibbs free energy of the properly designed Zr–Nb multilayered films could be elevated to a higher level than that of the corresponding amorphous phase as well as the supersaturated solid solutions. Accordingly, nano-sized Zr–Nb multilayered films were prepared and then irradiated by 200 keV xenon ions. It was found that amorphous phases could be obtained within a composition range 12–92 at% of Nb. Also, two metastable crystalline phases of fcc structures with different lattice parameters were also obtained. Molecular dynamic simulation was carried out, based on a proven realistic Zr–Nb potential, to reveal the atomistic mechanism of the solid-state crystal-to-amorphous transition. A brief discussion on the formation of the two metastable crystalline phases is presented.

Using Monte Carlo and finite element simulations, we analyse the critical exponents s and t governing the behaviour of the real, ε', and imaginary, ε'', parts of the effective permittivity of two-phase random heterostructures near the percolation threshold ϕ_2c. Specifically, we report on a systematic study of the critical behaviour of statistically isotropic distributions of penetrable discs of radius R (or random arrays of parallel, infinitely long, identical, partially penetrable circular cylinders) randomly placed in a unit square subject to periodic boundary conditions. Interestingly, we find that the radial distribution function shows great sensitivity to the degree of impenetrability λ of the discs. The present data set indicates that s > t for a given value of λ and that 1.34 ≤ s ≤ 1.54 and 0.70 ≤ t ≤ 1.11, in contrast to the universal values (s = t = 1.3) for two-dimensional continuum percolation systems. One might speculate that this value of t is a signature of finite-size effects. However, a finite-size analysis carried out by considering systems of increasing size, i.e. 0.03 ≤ R ≤ 0.1, at each λ, indicates that there is no appreciable change in t over the range of R explored. As the distance to ϕ_2c is decreased, ε' and ε'' display a smooth transition from a power-law dependence, which is well fitted by the standard percolation expression, to a plateau regime. We associate the plateau with finite-size effects and the short-range multipolar interactions localized in disc clusters.

An Al-rich In_xAl_1−xN ternary alloy was grown on a GaN template by metal–organic chemical vapour deposition (MOCVD). The GaN template was fabricated on a c-plane sapphire with a low temperature GaN nucleation layer. The growth of the 300 nm thick In_xAl_1−xN layer was carried out under various growth temperatures and pressures. The surface morphology and the InN molar fraction of the In_xAl_1−xN layer were assessed by using atomic force microscopy (AFM) and high resolution x-ray diffraction, respectively. The AFM surface images of the In_xAl_1−xN ternary alloy exhibited quantum dot-like grains caused by the 3D island growth mode. The grains, however, disappeared rapidly by increasing diffusion length and mobility of the Al adatoms with increasing growth temperature and the full width at half maximum value of ternary peaks in HR-XRD decreased with decreasing growth pressure. The MOCVD growth condition with the increased growth temperature and decreased growth pressure would be effective to grow the In_xAl_1−xN ternary alloy with a smooth surface and improved quality. The optical band edge of In_xAl_1−xN ternary alloys was estimated by optical absorbance and, based on the results of HR-XRD and optical absorbance measurements, we obtained the bowing parameter of the In_xAl_1−xN ternary alloy at b = 5.3 eV, which was slightly larger than that of previous reports.

Sn–0.7Cu is a low cost lead-free solder alloy that is targeted to replace the eutectic Sn–Pb solder. The main limitation of this alloy is its poor strength characteristics. Accordingly, this study aims at improving the mechanical properties of Sn–0.7Cu using Al₂O₃ particulates in the nanolength scale. The development of nanocomposite solders was accomplished using the powder metallurgy technique incorporating microwave sintering. Results of characterization studies conducted on the extruded samples revealed the presence of equiaxed grains, Cu₆Sn₅ phase and pores. The mechanical properties (microhardness, 0.2%YS and UTS) increase with the increasing presence of reinforcement with the best tensile strength realized for the composite containing 1.5% alumina that far exceeds the strength of the eutectic Sn–Pb solder.

Full-potential linearized augmented plane wave and local orbital method calculations were performed for Fe₂TiSn in order to investigate the optical properties and to show the origin of the different optical transitions. It is found that the band gap is indirect for Fe₂TiSn. Then our calculated reflectivity spectra are in good agreement with the experimental results. On the other hand, the contributions of various transition peaks are analysed from the imaginary part of the dielectric function. Furthermore, the different optical properties have been investigated.

Epitaxial Na_xCoO₂ thin films were deposited on (0 0 1) sapphire by the pulsed laser deposition method. Epitaxial Na_0.5CoO₂ thin film with a high crystallinity was achieved resulting from Na deintercalation of epitaxial Na_0.7CoO₂ with the solution of iodine-dissolved acetonitrile. Based on the x-ray diffraction data along the out-of-plane and the in-plane, there was only elongation of the c-lattice constant of Na_0.5CoO₂ after sodium deintercalation. The Na_0.7CoO₂ and Na_0.5CoO₂ thin films show layer-by-layer growth closely following an ideal step flow growth mode. The metallic behaviour of the Na_0.7CoO₂ thin film and the charge-ordered insulator property of the Na_0.5CoO₂ thin film were confirmed.

The feasibility of using complex gratings for mid-infrared wavelength-selective absorbers is investigated. Nano/microscale surface features are employed for tailoring thermal radiative properties, which are much different from those of plain surfaces. High absorptance from heavily doped (>10²⁰ cm⁻³) silicon for the transverse magnetic wave incidence can be achieved with one-dimensional periodic gratings by exciting surface plasmon polaritons. For simple binary gratings, the associated absorptance peak is narrowband and direction sensitive. These drawbacks can be remedied by using complex gratings, whose features are a superposition of multiple simple surface-relief gratings. The spectral absorptance displays a peak whose full-width-at-half-maximum exceeds 1.5 µm and is less sensitive to the angle of incidence. Moreover, the peak wavelength can be adjusted by varying the doping concentration and the grating geometry. This study demonstrates that the use of complex gratings may significantly enhance the performance of infrared detectors.

We report the results of spectral, structural and electrical investigations on plasticized polyaniline/polymethylmethacrylate blend films (PAni/PMMA), obtained by the co-dissolution method using three different molecular weights of the PMMA matrix. The use of dibuthylphtalate as a plasticizer allowed us to obtain free standing thin films. The system showed percolation behaviour with an extremely low percolation threshold, independently of the PMMA molecular weight. The ac conductivity is well described by the universal Jonscher's law. By using the dielectric modulus, we have observed a dielectric relaxation assigned to the hopping of charge carriers (polarons and bipolarons) between localized states. The characteristic frequency of this relaxation follows an Arrhenius law and the activation energy depends on the PMMA molecular weight. This relaxation is well described by a simple Debye process for the lowest PMMA molecular weight and deviates from this model when the molecular weight of the PMMA increases.

Ferroelectric SrBi₂Ta₂O₉ (SBT) thin films have been deposited by the radio-frequency magnetron sputtering technique on bare p-Si as well as on HfO₂ insulating buffer p-Si. XRD patterns revealed the formation of a well-crystallized SBT perovskite thin film on the HfO₂ buffer layer. The electrical properties of the metal–ferroelectric–insulator–semiconductor (MFIS) structure were characterized by varying thicknesses of the HfO₂ layer. The MFIS structure exhibits a maximum clockwise C–V memory window of 1.60 V when the thickness of the HfO₂ layer was 12 nm with a lower leakage current density of 6.20 × 10⁻⁷ A cm⁻² at a positive applied voltage of 7 V. However, the memory window reaches a maximum value of 0.7 V at a bias voltage of ±5 and then decreases due to charge injection in the case of the insulating buffer layer thickness of 3 nm. The density of oxide trapped charges at/near the buffer layer–ferroelectric interface is studied by the voltage stress method. Capacitance–voltage (C–V) and leakage current density (J–V) characteristics of the Al/SBT/HfO₂/Si(1 0 0) capacitor indicate that the introduction of the HfO₂ buffer layer prevents interfacial diffusion between the SBT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Al/SBT/HfO₂/Si structures exhibit excellent retention characteristics, the high and low capacitance values clearly distinguishable for over 1 h and 30 min. This shows that the proposed Al/SrBi₂Ta₂O₉/HfO₂/Si structure is ideally suitable for high performance ferroelectric memories.

We report on a novel and facile thermal chemical vapour deposition method for fabricating dense and vertically well-aligned bamboo-like carbon nanotube (CNT) arrays on a copper substrate from ethanol and acetone for the first time. The effect of growth time, temperature and catalysts has been systematically studied. Using ethanol as the carbon source, well-aligned CNTs were produced at 800 °C, and random, long and large carbon fibres/tubes were formed at 900 °C. When acetone was used, mushroom-like carbon nanostructures were formed at 800 °C, and well-aligned CNTs were produced at 850 °C. In contrast, large amounts of random carbon micro-fibres were formed at 800 °C using ethanol as the carbon source when Fe or Ni was employed as the substrate. The electrochemical properties of the novel mushroom-like carbon nanostructures are presented; the growth mechanisms for the formation of the bamboo-like CNTs and the mushroom-like carbon nanostructures are discussed.

Structural, electronic and elastic properties for NiAl with 4d alloying elements M (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd) have been studied using the first-principles pseudopotential density functional method within a generalized gradient approximation. From the elastic constants, C₁₁, C₁₂, C₄₄, bulk modulus B₀, Young's modulus E, the shear modulus G, the ratios of shear modulus to bulk modulus G/B₀, negative Cauchy pressure parameter (C₁₂ − C₄₄) and Poisson's ratio ν calculated after structural full relaxation, M (Tc, Ru, Rh, Pd) alloying addition in NiAl has been shown to increase the stiffness of NiAl and improve its ductility. The density of states and charge density contour involving alloying additions of Ru were further investigated to clarify the electronic causes of the alloying additions.

Using the method of multiple scale we have studied the nonlinear stability of a travelling wave solution of an evolution equation for the viscoelastic fluid flowing down a vertical plane. Bifurcation analysis of first and second order Benney equations (BEs) for the viscoelastic fluid shows that the first order BE gives both subcritical unstable and supercritical stable zones depending on the Reynolds number greater or smaller than its critical value and the supercritical stable/subcritical unstable region decreases/increases as the viscoelastic parameter increases. However, the second order BE exhibits only supercritical bifurcation and this stable region increases with the increase in either the Reynolds number or the viscoelastic parameter. The spatially uniform solution of the complex Ginzburg–Landau equation for sideband disturbances is also investigated.

This paper derives the exact solution of the model #3 proposed by Zhang et al for the rectangular cantilever beam. The model is solved by a reduced differential equation and the designated exact solution is formally presented in the integration form in terms of the Airy functions, Ai(X) and Bi(X). Both the deflection and curvature are presented as containing the constituents contributed by Ai(X) and Bi(X) and an additional portion attributed to the interaction between the Airy functions. The results show that the curvature at the fixed end is primarily determined by the contribution of Bi(X), while the dominant constituent for the deflection at the free end is dependent on the magnitude of the loading scenario. The relations for the directions of the constituent deflections and curvatures are deduced from the derived exact solution and by the properties of the Airy functions, which reveal that the contribution of Ai(X) results in forward deflection, and the curvature and the deflection are of the same sign. However, the curvature contributed by Bi(X) induces retrograde deflection, which means that the curvature and the deflection are of opposite sign. The results also suggest that the hardening effect of the present model can be represented by the contribution of Bi(X), with which the beam resists being deflected as if it were stiffened by Bi(X) under all loading scenarios. Nonetheless, there is no simple relation for the curvature and deflection attributed to the interaction of the Airy functions, which should be evaluated by direct integration and differentiation of the derived exact solution.