Table of contents

Micro-electro-mechanical system, MEMS, is a rapidly growing interdisciplinary technology dealing with the design and manufacture of miniaturized machines with the major dimensions at the scale of tens, to perhaps hundreds, of micrometres. Because they depend on the cube of a representative dimension, component masses and inertias rapidly become small as size decreases whereas surface and tribological effects, which often depend on area, become increasingly important. Although our explanations of macroscopic tribological phenomena often involve individual events occurring at the micro-scale, when the overall component size is itself miniaturized it may be necessary to re-evaluate some conventional tribological solutions. While the absolute loads are small in such micro-devices, the tribological requirements, especially in terms of longevity—which may be limited by wear rather than friction—are particularly demanding and will require imaginative and novel solutions.

Magnetic and dielectric properties of a polycrystalline GaFeO₃ sample prepared by a solid-state reaction have been investigated. A ferrimagnetic phase transition T_N of the material was identified at a temperature of 225 K. An anomaly on the permittivity as a function of temperature has been observed near its magnetic transition point T_N, which could be induced by the magnetoelectric coupling between its electric and magnetic orders. At low temperature, T < T_N, the permittivity variation Δε depends on magnetization M and shows clearly a linear relationship between Δε and M², which indicates that a dielectric and magnetic correlation exists in the compound. Furthermore, its dielectric relaxation process is discussed in the temperature interval of 77–300 K.

A method of heat-assisted magnetic recording potentially suitable for probe-based storage systems is characterized. Field emission current from a scanning tunnelling microscope tip is used as the heating source. Pulse voltages of 5 V were applied to a granular CoNi/Pt multilayered film. Experimental results show that an average mark size of 90–120 nm was achieved with the minimum of 70 nm. A model of dynamic domain formation is built to quantitatively explain the experimental results. It agrees with experiments. Based on this model, we will be able to figure out the proposals to achieve small marks for ultra-high recording density.

Thermoluminescence (TL) studies have been carried out on CaSO₄ : Mn, CaSO₄ : Ag,Mn, CaSO₄ : Ag,Nd, CaSO₄ : Ag,Mn,Nd, CaSO₄ : Ag,Zr and CaSO₄ : Ag,Mn,Zr phosphors. It is found that TL at 360 °C in CaSO₄ : Ag,Mn,Nd is about 40 times that of CaSO₄ : Ag,Mn and about 170 times that of CaSO₄ : Ag,Nd. This shows that the presence of an efficient luminescent centre (Mn²⁺) as well as a trivalent impurity (such as Nd³⁺ or Y³⁺) is important for enhancement of TL at 360 °C in the CaSO₄ : Ag,Mn,Nd phosphor system. Electron spin resonance (ESR) studies show that the peak at 360 °C correlates with an Ag²⁺ centre formed due to γ-irradiation and observable only below −170 °C. The Ag²⁺ centre is characterized by an axial g-tensor with principal values g_|| = 2.38 and g_⊥ = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (−170 °C) appears to act as the recombination centre for the TL peak at 360 °C. The low temperature centre is characterized by the g-values g_|| = 2.0023 and g_⊥ = 2.0038 and is assigned to the radical.

Wire-like SnO₂ is fabricated by the wet chemical method. X-ray diffraction measurements show that the obtained samples have rutile-type structure. Electron transmission microscopy experiments illustrate that the wire-like SnO₂ ranged from 10 to 50 nm in width and several microns (µm) in length. The high-resolution TEM indicates that SnO₂ wires are single crystals. The possible growth mechanism is proposed, and it is found that polyethylene glycol plays an important role in obtaining the wire-like and nano-rods morphology of SnO₂. The band gap is determined to be 3.56 eV. Two photoluminescence peaks located at 389 and 470 nm are observed. Our fabrication method promises a simple way of synthesizing wire-like SnO₂ at a low temperature of 350°C.

Highly-ordered TiO₂ nanotube arrays are made by potentiostatic anodization of a titanium film in a fluoride containing electrolyte. Here we describe the application of this unique material architecture in both front-side and back-side illuminated dye-sensitized solar cells (DSSCs). The back-side illuminated solar cells are based on the use of 6.2 µm long (110 nm pore diameter, 20 nm wall thickness) highly-ordered nanotube-array films made by anodization of a 250 µm thick Ti foil in a KF electrolyte. Front-side illuminated solar cells use a negative electrode composed of optically transparent nanotube arrays, approximately 3600 nm in length (46 nm pore diameter, 17 nm wall thickness), grown on a fluorine doped tin oxide coated glass substrate by anodic oxidation of a previously deposited RF-sputtered titanium thin film in a HF electrolyte. After crystallization by oxygen annealling the nanotube-arrays are treated with TiCl₄ to enhance photocurrent amplitudes. The arrays are then sensitized by a self-assembled monolayer of bis(tetrabutylammonium)-cis-(dithiocyanato)-N, N'- bis(4-carboxylato-4'-carboxylic acid-2, 2'-bipyridine)ruthenium(II) (commonly called 'N719'). Superior photoresponse is obtained using acetonitrile as the dye solvent. Voltage decay measurements indicate that the highly-ordered TiO₂ nanotube-arrays, in comparison with nanoparticulate systems, provide excellent pathways for electron percolation with superior electron lifetimes. The front-side illuminated DSSCs, show a typical AM 1.5 photocurrent of 10.3 mA cm⁻², open circuit voltage of 0.84 V, 0.54 fill factor, and 4.7% efficiency although the transparent nanotube-array negative electrode is only 360 nm thick. The back-side illuminated DSSCs show an AM 1.5 short-circuit current density of 10.6 mA cm⁻², 0.82 V open circuit potential and a 0.51 fill factor yielding a solar conversion efficiency of 4.4%.

Photosensitive materials offer great potential for passive and active optical devices in communication, data manipulation and storage. We prepared photosensitive germanosilicate (20GeO₂ : 80SiO₂) inorganic thin films by the sol–gel method. These films were annealed at various temperatures in the range of 700–900 °C. The films annealed at 900 °C were found to be fully densified and were porous when annealed below 900 °C. The UV KrF laser (248 nm) has been used to induce refractive index change (Δn). We have studied the Fourier transform infra-red (FTIR) spectroscopy and the refractive index changes of the hydrogen-loaded and as-deposited samples before and after UV illumination. For the porous samples, the −OH absorption band around 3400 cm⁻¹ increases with hydrogen-loading and decreases with UV radiation. The hydrogen-loading has induced absorption around 500–600 cm⁻¹ for all our samples (both porous and dense samples) and that indicates the formation of Si–H bonds. The Si–H absorption bands disappeared after UV illumination. We observed the high Δn of about 0.0094 for the as-deposited dense film annealed at 900 °C and value enhanced to 0.0096 after H₂-loading. For our samples, the large induced refractive index change is explained in terms of the formation of the oxygen related defects upon UV exposure. This is related to the induced absorption band around 620–740 cm⁻¹ in the FTIR spectra.

The values and wavelength dependence of the electronic and ionic contributions, r^e and rⁱ, to the clamped electro-optic (EO) coefficients r₂₂ and r_c in a LiTaO₃ crystal have been determined and are given over a wavelength range from 0.514 up to 1.321 µm. This work has been realized on the basis of measurements of the clamped EO coefficients, using a series of laser sources, combined with recorded data on the second-harmonic generation coefficients. The above results are discussed and compared with those obtained for a LiNbO₃ crystal.

The electronic band structures of GaN_xAs_1−x alloys were investigated versus the nitrogen mole fraction x and the nitrogen atomic configuration. The computational method is based on the sp³s^* tight-binding technique. Two main nitrogen atomic distributions were considered: (i) the nitrogen atoms grouped in one region to form like a GaN dot inside the GaAs so as to have a maximally N-clustered (MNC) configuration; and (ii) the nitrogen atoms homogeneously distributed over the alloy and, of course, the minimal N-clustered distribution as the maximally As-clustered (MAsC) configuration. The former is found to always have the lowest band gaps. More interestingly, the results show that in the latter distribution the nitrogen atoms introduce resonant states above the conduction-band edge by about 230 meV, which is consistent with the literature, whereas they introduce a deep gap state above the valence-band edge at about 150 meV in the former distribution. As a suitable model for experimental samples, the MAsC configuration, was used to model some available photoluminescence data in the dilute regime.

One-fluid MHD equations are numerically solved for an axisymmetric flow of thermal water plasma inside and outside a discharge chamber of a plasma torch with water vortex stabilization of electric arc. Comparisons with experimental data and previous calculations are given. For arc currents of 300–600 A, the respective temperatures and velocities in the range 16 700–26 400 K and 2300–6900 m s⁻¹ are obtained at the centre of the nozzle exit. The flow velocity on axis increases by 1–2 km s⁻¹ in the 5 mm long nozzle. Ohmic heating and radiative losses are two competitive processes influencing most the plasma temperature and velocity. The radiative losses represent 39% to 46% of the torch power of 69–174 kW when optical thickness of 3 mm is assumed for the plasma column. In front of the cathode, inside the discharge chamber, a recirculation zone is predicted and discussed. Effects of the temperature dependence of the plasma viscosity and sound velocity and of the optical thickness are examined. It is shown that the results such as waviness of the Mach number isolines are direct consequences of these dependences. Different lengths of 55 and 60 mm of the water vortex stabilized part of the electric arc do not substantially influence the plasma temperature and velocity at the nozzle exit.

In a capillary electrolyte cathode atmospheric glow discharge (ELCAD) plasma, the current density and the length of the cathode dark space (LCDS) were measured and the gas temperature (T_g) in the cathode surface-dark space boundary layer was estimated. Using a CCD camera, the current density (the diameter of the cathode spot) and the LCDS were determined from the light intensity distribution provided by the FITSVIEW image processing software. The current density was significantly higher compared with that measured in a normal ELCAD glow and increased with increasing current. The LCDS was also estimated by means of the similarity law relating to the ELCAD plasma. The estimated and measured values of the LCDS are in good agreement and smaller than that observed in a normal ELCAD. In the boundary layer a higher T_g was estimated because of the increased current density.

A particle's surface is not heated uniformly during plasma arc spraying: the side of the surface that faces the torch is hotter than the opposite side. If the particle temperature is high enough for substantial evaporation to occur, the imbalance of the vapour pressure gives rise to a net recoil force accelerating the particle toward the substrate. Estimations show that if particle loss of mass due to evaporation , the suggested effect is as important for particle dynamics as aerodynamic drag. (M is the particle mass, U_d is the particle speed and is the speed of the evaporating atom, m is its mass, and T is the particle surface temperature.)

The time development of the electron distribution function and electron macroscopic parameters was studied by solving the time-dependent Boltzmann equation for low temperature plasma. A new technique for solving the time-dependent Boltzmann equation was developed. This technique is based on a multi-term approximation of the electron distribution function expansion in Legendre polynomials. The results for electron relaxation in Reid's ramp model and argon plasma are presented. The effect of negative mobility was studied and is discussed for argon plasma. Finally, the time-dependent Boltzmann equation was solved for pulsed microwave discharge in nitrogen. The accuracy of all results was confirmed by the Monte Carlo simulation.

A numerical model is constructed using the PLASIMO toolkit to simulate a microwave configuration which is similar to that which is in use for optical glass fibre production. The simulations offer the flow patterns and the electromagnetic (EM) energy incoupling of a two-temperature argon plasma. The Yee algorithm was used for the EM module, whereas the Semi implicit method for pressure linked equations algorithm was used to calculate the pressure and velocity field. It is found that at 400 W coupling of 2.46 GHz EM radiation in 1000 Pa argon results in a plasma that is not in local thermodynamic equilibrium, in the sense that T_e/T_h ≥ 4 and the ionization degree is smaller than that predicted by the Saha equations. The model results are subjected to various sanity checks.

The heterostructure of Pt/Ba_0.5Sr_0.5TiO₃/La_0.67Sr_0.33MnO₃ (Pt/BST/LSMO) with the BST thickness ranging from 120 to 550 nm was fabricated by pulsed laser deposition. The dielectric constant (ε) of the heterostructure was measured under different electrical fields (E) and frequency (f). A strong thickness dependence of the value of ε, the ε–E dependence and the ε–f dependence were observed, which can be well explained by the series-capacitor model, based on the assumption that the heterostructure electrically consists of a 'bulk' layer and an interfacial layer between the Pt and BST layers. The dielectric properties of the 'bulk' layer and the interface layer were obtained. At room temperature, the dielectric constant of the 'bulk' layer was 1204 (at 100 kHz) and had a power law dependence on frequency. The ratio of thickness over the dielectric constant (d_i/ε_i) of the interface layer, which was used to characterize the property of the Pt/BST interface, was found to be around 0.08 nm at room temperature and to be independent of frequency.

The interrelation between energy gap and high frequency refractive index in semiconductors and dielectrics is manifested by an inverse law which is popularly known as the Moss rule. This semi-empirical relationship is based on the fundamental principle that in a dielectric medium all energy levels are scaled down by a factor of the square of the dielectric constant. Such a rule is obeyed by most pure semiconductors and dielectrics with a few rare violations in composite materials which display several interesting parametric and microstructural evolutions. The present results are based on some specific oxide composite thin films involving Gd₂O₃/SiO₂ and ZrO₂/SiO₂ codeposited systems that have displayed a superior refractive index and energy gaps violating the semi-empirical Moss rule. Also, morphological supremacy is also distinctly noticed in these composites. The novel microstructural and polarizability properties of such composite systems were probed through multi-mode atomic force microscopy and phase modulated spectroscopic ellipsometry using refractive index modelling, autocorrelation and height–height correlation functional analyses. These binary composite thin films have shown their potential as well as the possibility of meeting expectations in satisfying the challenging optical coating requirements of the deep ultraviolet spectral region.

Multi-walled carbon nanotubes (MWNT) and polyaniline are coated on an electro-active paper (EAPap) to improve the performance of the bending actuator, and its performance is tested. EAPap actuators made with cellulose paper have merits in terms of large bending displacement, ultra-lightweight, dryness, low actuation voltage and power consumption, low cost and biodegradability. However, the force output of actuators is small and the actuation frequency is low. Thus, MWNT and emeraldine salt polyaniline (PANI) are coated on the EAPap material to improve the force and the actuation frequency. The MWNT and PANI solution is made by sonication, and the sonication time and the weight per cents of the MWNT and PANI are optimized to improve the hybrid actuator performance. The optimum condition is associated with conversion of the partial conductive state PANI into the emeraldine formed PANI by the chemical bonding between the MWNT and PANI. The performance improvement of the EAPap actuator coated with MWNT/PANI is investigated in terms of displacement, blocking force and efficiency. In the presence of an electric field (0.35 V µm⁻¹) on the hybrid EAPap actuator, 250% of the output force, 160% of the resonance frequency and 50% of efficiency are improved.

Lead zirconate titanate (PZT) film is prepared on Pt/Ti/SiO₂/Si substrate by proposed processes based on the sol–gel method and rapid thermal anneal (RTA). The ratio of Zr/Ti in the PZT film is 40/60. The PZT film has a mixture of perovskite orientations in which the (110) orientation is dominant. The Pt/PZT/Pt capacitor has remanent polarization of approximately 28.8 µC cm⁻² and coercive voltage of approximately 0.76 V at 3 V voltage amplitude. The Pt/PZT/Pt capacitor has excellent fatigue properties. Switch polarizations decrease to 93.1% after 6 × 10¹² switch cycles. The excellent fatigue properties result from the ameliorations of PZT/Pt interface conditions, restraining Pb volatilization and the directions of crystal domains in the RTA process. Some electric properties of the PZT capacitor proposed are contrasted with those of PZT capacitors with a different anneal process in the preparation.

Samples of selenium rich Se₈₅Cd_15−xZn_x (x = 0, 3, 7, 11 and 15) system in bulk form have been prepared using a technique of slow cooling of the melt. Measurements of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of Se₈₅Cd_15−xZn_x pellets, prepared at constant load of 10 tons, have been carried out from room temperature to 200 °C using the transient plane source technique. The variation in λ_e and χ_e of Se₈₅Cd_15−xZn_x with the concentration of zinc and temperature is explained on the basis of structure modifications of the samples and the mean free path of the phonons due to scattering from defects and voids.

A polypyrrole (PPy) film electrochemically grown in a thin slab vessel consisting of poly(tetrafluoroethylene) walls exhibits a notable anisotropy along the thickness direction. This anisotropy allows the film to bend in a regular direction upon electrochemical undoping and revert upon doping. In this study, the size effect, i.e. the length dependence of reduction current, of the actuator has been studied. The length was changed by trimming the tip of the actuator, 12 mm of which was initially soaked in an electrolyte. It has been clarified that current saturates when the actuator exceeds a certain length. This may reflect the reduction in the conductivity of PPy upon undoping, which makes the tip of the actuator almost insulated from the power source. It is also found that the width of the actuator and the electrolyte do not influence the size effect.

This study reports on calorimetric measurements of the glass transition at various heating rates stretching over three orders of magnitude for Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ metallic glass powders synthesized by gas-atomization and subjected to varying thermal treatments. A Vogel–Fulcher–Tammann-type relation was fitted to the data recorded for the heating rate dependent shift of the glass transition. The fragility of the alloy is evaluated in terms of the fragility parameter. Its value is 44 for the as-prepared Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ metallic glass powder and decreases with increasing annealing treatment temperature. The decrease in the fragility parameter is due to partial crystallization, which shifts the composition of the remaining supercooled liquid to that of a strong glass-forming alloy.

This paper presents an optical method to measure independently the effect of swelling on the optical properties of strongly scattering porous media. The method was tested by measuring the swelling behaviour of cellulose fibre tissue using optical coherence tomography. The experimental results proved that the effect of swelling on optical and physical properties of paper can be measured.

This paper presents a mathematical model of laser powder deposition (LPD) to predict temperature field, melt pool depth and dilution. The model validated by experiments is developed using the moving heat source method. In this method, the temperature distribution inside the clad and the substrate is obtained using the superposition principle and the solution of the heat diffusion due to a point heat source. The model, which can be used in real-time applications, predicts the melt pool depth and dilution as a function of clad height and clad width, which in practice can be measured by a vision system. Numerical and experimental analyses show a non-linear behaviour of the melt pool depth as a function of process speed. This indicates that the melt pool depth has a maximum at a certain process speed. The comparisons between the numerical and experimental results show that this model is capable of predicting the characteristics of the LPD process accurately. Using the model, some general curves that show the behaviours of the melt pool depth and dilution as a function of clad height, scanning speed and laser power are illustrated.

A fundamental study on the Q-switched diode-pumped solid-state laser interaction with silicon was performed both experimentally and numerically. Single pulse drilling experiments were conducted on N-type silicon wafers by varying the laser intensity from 10⁸–10⁹ W cm⁻² to investigate how the mass removal mechanism changes depending on the laser intensity. Hole width and depth were measured and surface morphology was studied using scanning electron microscopy. For the numerical model study, Ki et al's self-consistent continuous-wave laser drilling model (2001 J. Phys. D: Appl. Phys.34 364–72) was modified to treat the solidification phenomenon between successive laser pulses. The model has the capabilities of simulating major interaction physics, such as melt flow, heat transfer, evaporation, homogeneous boiling, multiple reflections and surface evolution. This study presents some interesting results on how the mass removal mode changes as the laser intensity increases.

It is argued that the experimental results presented by Paris et al in J. Phys. D: Appl. Phys. (2005) 38 3894 are correct. It is shown that there is no evidence of filamentation or local electric field reinforcement in discharge. It is discussed that reaction scheme and rate constants for deactivation of excited nitrogen ion proposed by Pancheshnyi in his Comment must be specified for conditions corresponding to the experiment carried out by Paris et al.