Table of contents

A range of physical properties can be achieved in micro-electro-mechanical systems (MEMS) through their encapsulation with solid-state, ultra-thin coatings. This paper reviews the application of single source chemical vapour deposition and atomic layer deposition (ALD) in the growth of submicron films on polycrystalline silicon microstructures for the improvement of microscale reliability and performance. In particular, microstructure encapsulation with silicon carbide, tungsten, alumina and alumina–zinc oxide alloy ultra-thin films is highlighted, and the mechanical, electrical, tribological and chemical impact of these overlayers is detailed. The potential use of solid-state, ultra-thin coatings in commercial microsystems is explored using radio frequency MEMS as a case study for the ALD alloy alumina–zinc oxide thin film.

We investigated the microstructures of Co₉₀Fe₁₀/Cu and Ni₇₀Co₃₀/Cu multilayers before and after annealing at 285 °C for 2 h, as well as the influence of microstructures on the thermal degradation of the GMR (giant magnetoresistance) effect, using innovative x-ray anomalous scattering techniques. It is found that there exists a significant asymmetry between the interfaces on both sides of the Cu layers during the deposition. The diffusion only occurs at the Cu/Ni₇₀Co₃₀ and Cu/Co₉₀Fe₁₀ interfaces while the Ni₇₀Co₃₀/Cu and Co₉₀Fe₁₀/Cu interfaces are sharp. After annealing at 285 °C, the Co₉₀Fe₁₀/Cu interface is still sharp, but the Ni₇₀Co₃₀/Cu interface forms a CuNi₂Co intermixing region. X-ray diffuse scattering profiles performed with x-ray energy close to the Fe, Co, Ni and Cu K edges show that the local lateral environments of Fe, Co, Ni and Cu at the interfaces are different for both the as-deposited multilayers. After annealing, the interfacial lateral correlation lengths and the fractal exponent of the Ni₇₀Co₃₀/Cu multilayer decrease significantly and the difference of the interfacial lateral correlation lengths of Co, Ni and Cu becomes smaller. However, those of the Co₉₀Fe₁₀/Cu multilayer do not change. This indicates that the main cause of thermal degradation of the GMR effect is the compositional intermixing at the multilayer interface, which has more influence on the GMR effect than the atom diffusion along the grain boundary.

Experimental and theoretical studies on the influence of ac magnetic field frequency on the axial diagonal (ζ_zz) and off-diagonal (ζ_ϕz) components of the magnetoimpedance (MI) tensor in (Co_0.94Fe_0.06)_72.5Si_12.5B₁₅ amorphous wires have been performed. The frequency (f) of an ac current flowing along the wire was varied from 1 to 20 MHz with the current amplitude less than 15 mA. In order to enhance the ζ_ϕz component, the amorphous wire was submitted to torsion annealing for developing and preserving a helical magnetic anisotropy in the surface of the wire. The experimental measurements show that the value of the impedance is proportional to the square-root of the ac current frequency, , in the vicinity of H_ex < H_K and this increase is due to the contribution of the resistance (real part of the impedance). The measurements also indicate that the peaks of the MI curve shift slightly towards higher field values with increasing f.

In a theoretical study the magnetoimpedance expressions ζ_zz and ζ_ϕz have been deduced using the Faraday law in combination with the solutions of the Maxwell and Landau–Lifshitz–Gilbert (LLG) equations. By analysing quantitatively the spectra of ζ_zz and ζ_ϕz, the phenomenon of the shift in the peaks of the MI curve with f has been considered as a characteristic of the helical anisotropy in the domain structure of the wire surface.

A model is presented for predicting the magnetic field, and the magnetic and fluidic forces on micro/nano-particles in a magnetophoretic microsystem. The microsystem consists of a linear array of soft-magnetic elements embedded beneath a microfluidic channel. The magnetic elements are magnetized using an external bias field, and produce a nonuniform field distribution that permeates the microchannel. This gives rise to a magnetic force on particles as they flow through the microsystem. Analytical expressions are derived for the field distribution within the microchannel, and the magnetic force on the particles. A linear magnetization model is used to predict the magnetic response of the particles, and the magnetic field and force expressions are verified using finite element analysis. The particles also experience a fluidic force, which is predicted using Stokes' law for the drag on a sphere in laminar flow. The model presented here includes magnetic and fluidic analysis, and enables rapid predictions of the field and force throughout the microsystem as a function of key variables including the particle size and properties, the properties and spacing of the magnetic elements, the bias field source, the dimensions of the microchannel, the fluid properties, and the flow rate. The model is well-suited for parametric analysis, and is demonstrated via practical calculations.

Magnetization reversal in exchange biased Co/CoO dot arrays has been investigated systematically as a function of shape anisotropy, dot size, temperature, cooling field and training effect. Polycrystalline 24 nm Co films have been sputtered on a pre-patterned Si/SiO₂ substrate with the lateral dimensions of the dots varying from 200 to 900 nm at a fixed spacing of 800 nm. The Co dots have been oxidized using pure oxygen to create a Co/CoO bilayer. Below the Néel temperature, the hysteresis loop of this bilayer displays a normal unidirectional shift due to the exchange bias in the continuous film, while the patterned film displays an additional anomaly of the upper part of the hysteresis loop. This anomaly, which is shape dependent, increases with decreasing temperature and cooling field. On the other hand, it decreases for the trained loops with increasing aspect ratio (length/width) of the patterned dot. This anomaly is probably caused by incomplete biasing due to the competition between magnetostatic inter-dot interactions and exchange bias.

Complementary electron microscopy techniques that provide local information about structural, electronic and magnetic properties have been used to study thin films of Zn_0.85Co_0.15O grown on Si₃N₄ buffered (100) Si substrates at 673 K. No evidence of secondary phases at interfaces was found. For this growth temperature, Co is incorporated into the ZnO lattice by substituting for Zn, and its oxidation state is 2⁺. Off-axis electron holography reveals no measurable magnetic signal, either at domains or at interfaces, in agreement with macroscopic measurements that indicate a non-ferromagnetic behaviour.

Nanoparticles of a cobalt–platinum (CoPt) alloy near equiatomic composition, dispersed in a surfactant-polymer matrix, are synthesized using aqueous phase laser ablation. The magnetization dynamics of these particles is examined in the framework of the superparamagnetic blocking phenomenon based on a log-normal size distribution. Our analysis reveals, in accordance with electron microscopy results, two size distributions which peak at 1.3 and 5.9 nm. The magnetic anisotropy energy of these particles is 0.9 × 10⁶ J m⁻³ and 0.1 × 10⁶ J m⁻³, respectively.

The coercivity and grain size of equiatomic FePt alloy films annealed at 500 and 600 °C with different magnetic fields of 0–70 kOe have been investigated. It is found that applying a magnetic field with appropriate strength during postdeposition annealing not only enhances the coercivity but also reduces the grain size of the FePt films. Measurements of the microstructure and magnetic properties of the FePt films reveal that the coercivity is affected by both the ordered volume fraction and a microstructure factor that is related to the ordered volume fraction. The high coercivity in FePt films annealed with an appropriate strength of magnetic field is due to an increasing density of magnetic domain wall pinning sites concurrent with an increasing fraction of the ordered phase.

ZnS : Mn nanophosphor has been doped with quencher impurity Ni using the colloidal precipitation method with capping agent polyvinylpyrrolidone. The formation of ∼2.5 nm sized nanoparticles has been confirmed by x-ray diffraction and transmission electron microscope studies. Energy and time resolved photoluminescence spectra of the synthesized nanophosphors have been studied at room temperature. Photoluminescent spectra for ZnS : Mn, Ni show three peaks at 412 nm, 433 nm and 590 nm corresponding to Ni impurity, sulphide vacancies (Vs) and Mn impurity, respectively. The ZnS : Mn nanophosphor show typical nanosecond lifetimes for defect-related emission and millisecond lifetimes for Mn impurity-related emission. However, the ZnS : Mn, Ni samples showed lifetime shortening, with variation of dopant concentration for defect-related (420 nm) as well as impurity-related emission (590 nm), which is attributed to exchange interaction between Mn²⁺ and nearest neighbour Ni²⁺ impurities.

The spreading resistance of a round ohmic contact was calculated by solving the Laplace equation using analytical, numerical and finite element methods. From this, formulae were found to calculate accurate values (better than 0.1%) of the spreading resistance over the entire range of contact size to substrate thickness ratio.

Stimulated by recent intriguing experiments with a quantum dot in an Aharonov–Bohm (AB) ring, we investigate novel resonant phenomena by studying the total transmission probability of nanoscale AB rings with embedded double quantum dots in one arm and a magnetic flux passing through its centre. In this system, we show the overlapping and merging of both Breit-Wiger (BW) and Fano resonances as the interaction parameter between the dots changes. In the strong overlapping regime of Fano resonances, the transmission zeros leave the real-energy axis and move away in opposite directions in the complex-energy plane. The simultaneous swings (from Fano to BW and then back to Fano resonance) of a pair of Fano resonances in the overlapping regime are observed by modulating the magnetic flux threading the AB ring. The periodic tuning of the Fano resonance for a fixed interaction parameter is also discussed as the magnetic flux increases.

A first principles theory of electronic transport in quantum well infrared photodetectors (QWIPs) is presented. The model is based on the cascade scattering rate equations approach and uses the translation symmetry to reduce the computational cost of the problem. The model delivers a non-equilibrium electron distribution in both dark conditions and under illumination. The model was tested by simulating a non-conventional broadband InGaAs/AlGaAs QWIP and good agreement with experimental data available in the literature was achieved. The model can be applied to any QWIP structure and can be used for extending the range of materials employed.

A high-power He–Ne laser with a flat discharge tube has been realized. Its output power can be enhanced by increasing the transverse size of the discharge tube. This high-power flat He–Ne laser tube of 1.4 m discharge length can achieve above 180 mW of output power at a wavelength of 0.6328 µm. Its optimum discharge parameters and the gain characteristics are investigated experimentally. The experiments indicate that the optimum current increases with decreasing total gas pressure. But the increase in the optimum current is almost independent of the gas mixture ratio. The increase in the gain coefficient at the axis of the discharge tube with discharge current is not obvious. The boost in laser output power is mainly caused by the expansion of the lasing gain region. To achieve the higher output power, four of the laser tubes mentioned above are placed into one laser box. The laser beams are coupled into a quartz optic fibre and the output power from the end of the optic fibre can reach above 480 mW. This high-power He–Ne laser has been used in a clinical application, photodynamic therapy (PDT) of cancer, and its effective rate is above 90% in 183 clinical cases. The structure, characteristics and applications of this high-power flat He–Ne laser are introduced and discussed in this paper.

A highly sensitive thermoluminescence (TL) phosphor based on Ba_1−xCa_xSO₄ : Eu (0 ≤ x ≤ 1) has been prepared using the chemical co-precipitation technique. It has been found that the TL sensitivity of the material changes on varying the value of x with the maximum coming at x = 0.03. For this value of x the sensitivity is even more than that of the commercially available phosphor CaSO₄ : Dy (∼2.3 times more). Photoluminescence (PL) and XRD studies of the material show that the maximum TL sensitivity obtained at x = 0.03 is due to the conversion of Eu³⁺ to Eu²⁺ being highest in this case. Moreover, the phosphor Ba_0.97Ca_0.03SO₄ : Eu has a constant glow curve shape and a linear gamma-ray dose response over the range 0.1–50 Gy which makes it suitable for radiation dosimetry.

Amorphous films with compositions (As_0.33S_0.67)_100−xTe_x (x = 0, 1, 5 and 10 at.%) and Ge_xSb_40−xS₆₀ (x = 10, 20 and 30 at.%) have been prepared by thermal evaporation. The compositional dependences of their optical properties, with increasing Te and Ge content, respectively, are explained in terms of the modifications occurring in the film structure: Te joins the glassy network through the substitution of S atoms in the AsS₃ pyramidal units, to form new AsS₂Te mixed pyramidal units, on the one hand, and, on the other hand, there is a presence of GeS₄ and S₃Ge–GeS₃ structural units, when the Ge content is increased. The refractive-index dispersion has been analysed on the basis of the Wemple–DiDomenico single-oscillator approach. It has been found that the refractive index increases in the As–S–Te system, with increasing Te content, while it decreases instead, in the Ge–Sb–S system, with increasing Ge content. The behaviour of the Tauc gap, when the composition of the material is varied, shows, as expected, just the opposite trends.

Low-temperature step-graded InAlAs metamorphic buffer layers on GaAs substrate grown by molecular beam epitaxy were investigated. The strain relaxation and the composition of the top InAlAs layer were determined by high-resolution triple-axis x-ray diffraction measurements, which show that the top InAlAs layer is nearly fully relaxed. Surface morphology was observed by reflection high-energy electron diffraction pattern and atomic force microscopy. Under a selected range of growth parameters, the root mean square surface roughness of the sample grown at 380 °C is 0.802 nm, which has the smallest value compared with those of other samples.Furthmore, The ω-2θ and ω scans of the triple-axis x-ray diffraction, and photoluminescence show the sample grown at 380 °C has better crystalline quality. With decreasing As overpressure at this growth temperature, crystalline quality became poor and could not maintain two dimensional growth with increasing overpressure. The carrier concentrations and Hall mobilities of the InAlAs/ InGaAs/GaAs MM-HEMT structure on low-temperature step-graded InAlAs metamorphic buffer layers grown in optimized conditions are high enough to make devices.

Three-dimensional full-wave electromagnetic analysis of a travelling-wave heterojunction phototransistor (HPT) is presented. Employing the finite-difference time-domain method and run on a fast, parallel processing machine the simulation herein allowed, for the first time to our knowledge, the simultaneous investigation of the optical and electrical characteristics of the travelling-wave structure. Snapshots of the field propagation inside the device provide valuable insight into its passive behaviour and conclusively demonstrate the velocity mismatch between the optical wave and the photogenerated electrical signal. Numerical results are presented for the device's output characteristic impedance, photocurrent and effective refractive indices of the optical and electrical signal that quantify the difference in the velocities of the two waves. Moreover, results obtained from the method's initial test in the simulation of an asymmetric planar optical waveguide, similar to the one integrated within the HPT's structure, compare very favourably with the theory.

The electronic structure and electron g factors of HgTe quantum dots are investigated, in the framework of the eight-band effective-mass approximation. It is found that the electron states of quantum spheres have aspheric properties due to the interaction between the conduction band and valence band. The highest hole states are S (l = 0) states, when the radius is smaller than 9.4 nm, the same as the lowest electron states. Thus strong luminescence from HgTe quantum dots with radius smaller than 9.4 nm has been observed (Rogach et al 2001 Phys. Status Solidi b 224 153). The bandgap of HgTe quantum spheres is calculated and compared with earlier experimental results (Harrison et al 2000 Pure Appl. Chem.72 295). Due to the quantum confinement effect, the bandgap of the small HgTe quantum spheres is positive. The electron g factors of HgTe quantum spheres decrease with increasing radius and are nearly 2 when the radius is very small. The electron g factors of HgTe quantum ellipsoids are also investigated. We found that as some of the three dimensions increase, the electron g factors decrease. The more the dimensions increase, the more the g factors decrease. The dimensions perpendicular to the direction of the magnetic field affect the g factors more than the other dimension.

The N₂ (C ³Π_u) and N₂ (B ³Π_g) triplet states are studied in the positive column of a nitrogen dc pulsed discharge by optical emission spectroscopy. Time variations of all vibrational levels are observed during a 700 µs pulse duration in a pressure range from 0.05 to 4 Torr. Even if the current remains constant during the pulse, the bands intensities emitted from the triplet states change during the pulse. According to the state and the vibrational level, we observe an increase or a decrease of line intensities as a function of pressure. It is pointed out that for N₂ (B ³Π_g) time variations are not similar for low and high vibrational levels. From the observation of individual vibrational levels, time evolution of vibrational distributions (VDs) are measured for N₂ (B ³Π_g) and N₂ (C ³Π_u). From these VDs a vibrational temperature is deduced. For a 4 Torr pressure, the deduced vibrational temperature increases from 5000 to 9000 K for N₂ (B ³Π_g) and from 3000 to 9000 K for N₂ (C ³Π_u). This vibrational temperature is representative of the temporal evolution of the plasma and, even after 700 µs, a steady state is not reached.

In this paper, we analyse, by the use of different plasma diagnostics, appearance potential mass spectrometry (APMS), optical emission spectroscopy (OES) and Langmuir probe measurements, a commercialized ICP source devoted to the etching of SiO₂ using a Si mask. First, the influence of the gas composition (C₂F₆ mixed with H₂ or CH₄) and the residence time (varying gas flow rate) on the etching rates and selectivity is studied to optimize the process. Second, in order to improve the understanding of the etching mechanisms, the plasma is characterized according to the previous discharge conditions. We point out the presence of plasma instability due to the electronegative character of the fluorocarbon gas used. To determine the ion flux (ϕ_i) which is an essential parameter for oxide etching, Langmuir probe measurements have been associated with a plot of the bias power versus bias voltage (P_bias(E_i)). Absolute concentrations of CF_x (x = 1–3), CH₃ and CHF₂ radicals have been determined by APMS and the atomic fluorine concentration has been sampled by OES using argon actinometry. The techniques employed for concentration determinations are largely discussed. Finally, we compare the evolutions of the etch rates and the evolutions of the different plasma species with experimental conditions.

The absolute populations of the vibrational levels ν = 0, 1, 3 and 6 of the state of molecular nitrogen produced in a low pressure inductively coupled plasma have been determined as a function of plasma operating conditions. The measurements were conducted using diode laser-based cavity enhanced absorption spectroscopy on a selection of vibrational bands within the strong first positive system, , and calibrated using cavity ring-down spectroscopy. At 25 mTorr and 200 W power applied to the discharge we find the populations of the ν = 0, 1, 3 and 6 levels to be (1.31 ± 0.16) × 10¹¹ cm⁻³, (8.44± 1.01) × 10¹⁰ cm⁻³, (2.83 ± 0.34) × 10¹⁰ cm⁻³ and (5.27 ± 0.63) × 10⁹ cm⁻³, respectively, corresponding to a vibrational temperature of 3600 ± 150 K. The vibrational temperature of the A-state was determined to lie in the range 2900–3700 K for the operating conditions employed. The translational and rotational temperatures of each vibrational state probed were considerably colder (in the range 300–500 K) and show the translational and rotational modes to be equilibrated. In addition, we present the observation of the ) molecular ion in its vibrational ground state using both cavity enhanced absorption spectroscopy and the same technique in combination with wavelength modulation spectroscopy. At 10 mTorr and 400 W we measure a translational temperature of (431 ± 80) K, which is the same as that for the A-state under the same conditions, and estimate the total population in ν = 0 to be (1.26 ± 0.15) × 10⁹ molecules cm⁻³. The combination of cavity enhanced and wavelength modulation methods is found to improve the sensitivity by approximately an order of magnitude in a plasma environment.

A statistical procedure for modelling the cumulative effect of multiple collisions in particle simulations is presented. The procedure approximates the probability density function (PDF) of the final scattering angle and that of the particle net displacement by parametric functions. Formulae for determining the moments of the exact PDFs as a function of the statistics of a single collision event are derived. Using these formulae, the parametric functions can be fitted to yield the same first moments as the real distributions. Therefore, in contrast to other approaches where after one iteration the error in the first moments depends on the number of collisions modelled, the present model provides always the right moments. Correlation between the scattering angle and the displacement of the particle is also considered and enforced by means of a Gaussian copula.

We report measurements of the breakdown curves of an rf capacitive discharge in low pressure nitrous oxide. The electron drift velocity was determined from the locations of the turning point and of the minimum in the breakdown curves in the range E/p = 87–840 V cm⁻¹ Torr⁻¹. We compare our results with values calculated from the published cross-sections in the range E/p = 1–5000 V cm⁻¹ Torr⁻¹ and find good agreement.

Based on an analysis of the wave propagation characteristics of an elliptic-groove waveguide, the use of this waveguide as a free electron laser (FEL) amplifier high frequency structure is proposed. A set of operating equations for this FEL amplifier is derived by using three-dimensional nonlinear theory. A numerical simulation code is developed, and the characteristics including the evolution of power, efficiency and bandwidth of the FEL amplifier are analysed numerically. The effects of electron energy spread and wiggler taper on the saturation efficiency are also considered.

ZnO–SnO₂ films were deposited onto glass substrates by filtered vacuum arc deposition. The source was equipped with a 70 at% Zn and 30 at% Sn cathode that was the source of Zn and Sn ion beam. Arc current was 200–300 A. The oxygen background pressure was 4–8 mTorr. The deposition time was 60 or 120 s, resulting in film thickness in the range 100–900 nm. The maximum deposition rate was 7.6 nm s⁻¹. All films were found to be amorphous. The transmission of the film in the VIS was 80%–90%, affected by interference. The refractive index and the extinction coefficient were determined from the measured optical transmission in the range 300–1100 nm by fitting a theoretically calculated film transmission to the measured one, using a single oscillator model. The values of n and k were determined from spectroscopic ellipsometry data and were in the ranges 2.38–1.97 and 0.24–0.013, respectively, depending on wavelengths and deposition parameters. The optical band gap (E_g) was determined by the dependence of the absorption coefficient on the photon energy at short wavelengths. Its values were in the range 3.5–3.62 eV, depending on the deposition conditions.

Sol–gel derived, as-deposited amorphous tungsten oxide (WO₃) films become nanocrystalline with a pseudocubic triclinic structure upon annealing at 600 °C. The annealed films are constituted of nanorods along with interconnected nanoparticles and pores. While the high transmission modulation and colouration efficiency in the visible region and the fast bleaching kinetics as shown by the nanostructured film were typical of amorphous WO₃, the absorption coefficient spread in the 300–2000 nm wavelength range, the reflectance modulation and the colouration efficiency peak in the NIR region were reminiscent of crystalline WO₃. The larger magnitude of the indirect band gap shift to blue than the direct gap shift for the same level of lithium intercalation (18 mC cm⁻²) and the irreversibility of the direct gap shift upon bleaching are characteristic of the nanocrystalline structure of the film. The moderate decline in the anodic peak current maximum, the diffusion coefficient for lithium and the optical modulation at 632.8 nm upon repetitive switching between the coloured and bleached states ratified that nanostructured films sustain 1000 cycles without much deterioration.

In this paper, the properties of iron oxynitride films prepared by magnetron sputtering of an iron target in Ar–N₂–O₂ reactive mixtures using constant nitrogen and argon flow rates are presented. The oxygen flow rate varied from 0 to 2 sccm. The thickness of the films deposited on silicon substrates ranged from 0.2 to 2 µm. The structure and chemical composition of these films were determined by x-ray diffraction and Rutherford backscattering spectrometry, respectively. These studies revealed the formation of a new fcc intermediate phase of iron oxynitride FeN_xO_y films between iron nitride (ε-Fe₂N) and an oxide close to Fe₂O₃. In addition, optical and electrical properties measurements at room temperature were investigated during this work. Refractive index and extinction coefficient were determined from spectroscopic ellipsometry. The electrical behaviour of the films evolved from a metallic one to a semiconductor one which is consistent with other investigations. In order to determine the morphology of the films, scanning electron microscopy was used.

A numerical method for determining the elliptical adhesive contact in rectangular coordinates is proposed. Using a fast Fourier transform (FFT), the matrix multiplication can be performed. Then, using the preconditioned inexact Newton-bi-CGSTAG (bi-conjugate stabilized) method and the path-following method, the adhesive contact can be found. The elliptical adhesive contact can then be investigated by this method. It is found that the pull-off force depends on the Tabor parameter and the ratio between the principal relative radii of curvature. It is also found that the contact area is approximately elliptical.

The purpose of this study was to present a new underwater thermal insulation designed for flexibility and high thermal resistance. The insulation was a hybrid composite of two constituents: syntactic foam and an insulating aerogel blanket. Methods for treating and combining the constituents into a hybrid insulation of several designs are presented. A final configuration was selected based on high thermal resistance and was tested for thermal resistance and compressive strain to a pressure of 1.2 MPa (107 msw, meters of sea water) for five continuous pressure cycles. The thermal resistance and compressive strain results were compared to foam neoprene and underwater pipeline insulation. It was found that the hybrid insulation has a thermal resistance significantly higher than both foam neoprene and underwater pipeline insulation at atmospheric and elevated hydrostatic pressures (1.2 MPa). The total thermal resistance of the hybrid insulation decreased 32% at 1.2 MPa and returned to its initial value upon decompression. It was concluded that the hybrid insulation, with modifications, could be used for wetsuit construction, shallow underwater pipeline insulation, or any underwater application where high thermal resistance, flexibility, and resistance to compression are desired.

This paper describes the concentration dependences of piezoelectric coefficients, squared figures of merit and electromechanical coupling factors which have been calculated for 1–3 and 1–0–3 piezo-active composites based on single crystals of relaxor-ferroelectric solid solutions of (1 − x)Pb(A_1/3Nb_2/3)O₃–xPbTiO₃ where A = Mg, Zn. The role of the single-crystal component, its electromechanical properties and the polymer matrix (monolithic or porous) in forming these concentration dependences is analysed to demonstrate the ranges in which effective composite parameters are most sensitive to material properties and composite architecture, with particular emphasis on where their maximum values are attained. The basic variables in this study are the chemical composition (x and A), volume concentrations of the single-crystal component, the presence of pores in the polymer matrix and the aspect ratio of the spheroidal pores. It has been shown that particularly high values of piezoelectric coefficient and hydrostatic piezoelectric coefficients and are expected in the 1–0–3 0.67Pb(Mg_1/3Nb_2/3)O₃– 0.33PbTiO₃ single crystal/porous araldite composite with spheroidal pores in the matrix.

A practical problem in the reflection method for measuring permittivity of thin materials is the difficulty in ensuring the sample is placed exactly at the waveguide flange. A small position offset of the dielectric slab will give rise to significant errors in calculating the permittivity. To circumvent this problem, a measurement method using a waveguide partially filled with a thin material slab has been developed. The material sample can be easily prepared and inserted into the guide through a longitudinal slot on the broad wall of the waveguide. Multiple material slabs can be measured rapidly because one does not have to disconnect the waveguide system for sample placement. The method is verified with measurement of Teflon, glass and FR4 fibreglass. The measured permittivity show good agreement with published data. Subsequently, the permittivity of a vegetation leaf was measured. The method presented in this paper is particularly useful in measuring the permittivity of a thin and narrow slab of natural materials such as a paddy leaf.

The electrical properties of crosslinked polyethylene (XLPE), employed in mid-voltage cable insulation are studied using thermally stimulated depolarization currents (TSDC), differential scanning calorimetry (DSC) and x-ray diffraction. A complex heteropolar peak appears by TSDC between 50 and 110 °C, with a maximum at 105 °C. These measurements reveal that there is an optimal polarization temperature (T_po) around 90 °C. For this polarization temperature, the measured discharge peak area is maximum. Although the presence of a T_po is common in the study of relaxations by TSDC, in this case one would expect a monotonic decrease in the TSDC response with increasing polarization temperatures due to the decrease in the total crystalline fraction. In this paper, TSDC curves obtained under several conditions are interpreted in terms of recrystallization processes in XLPE during the polarization stage, if the sample is polarized in the melting temperature range. In this case, the recrystallization of a fraction of the material molten at this temperature promotes the formation of more stable and defect-free crystals. The presence of recrystallization processes is detected by DSC and confirmed by x-ray diffractometry. TSDC measurements have been performed with samples polarized at several temperatures (T_p) cooling from the melt or heating from room temperature. Also, TSDC results are obtained with previous annealing or with several cooling rates. These results allow us to infer that crystalline material grown from recrystallization processes that take place in the polarization stage attains a particularly stable polarization. Possible microscopical causes of this effect are discussed.

Nanocrystalline δ-Bi₂O₃ thin films have been deposited onto Si (100) and quartz substrates by reactive sputtering. The structural characteristics and thermal stability of the thin films have been investigated by x-ray diffraction and Raman spectra. It was found that the δ-Bi₂O₃ thin films could exist stably below 200 °C and undergo a phase transition sequence δ → β → α with increasing annealing temperature beyond 200 °C. These phase transitions were further confirmed by optical constant and optical band gap studies.

Electron spin resonance (ESR) of electrochemically doped polypyrrole with various concentrations (c) of calf-thymus DNA is reported here. The concentration and thermal dependence of the ESR linewidth (ΔH) clearly depicted a quasi-metallic to metallic transition at a critical doping concentration (c₀) of DNA. The thermal and concentration dependences of various ESR parameters are interpreted by considering the possible spin dynamics of carriers and the conformational change in the polypyrrole structure induced by DNA chains.

Molecular dynamics simulations have been performed to investigate the role of H- and C-fluxes on the structure and growth of thin a-C : H films. A first series of simulations was carried out using experimentally observed hydrocarbon radicals and additional H-fluxes to grow the films. The selected conditions correspond to the experimental deposition using remote plasma sources without substrate bias. A second series of simulations was performed to investigate the influence of a fixed additional C particle flux towards the substrate. It is found that H-incorporation into the film considerably changes its microstructure. The mass density of the films increases as the H-flux towards the film surface increases. A maximum in the mass density is found at H-flux of 20%. A decrease in mass density is found when using higher H-fluxes. The additional C-flux further increases the mass density. The results are explained in terms of the role of the H-atoms in the film and the deposition behaviour of the hydrocarbon radicals. These results provide information regarding the deposition and structure of thin a-C : H films grown from low-kinetic energy hydrocarbons, suggesting that densification and hence hardening of the films is possible, even without additional ion bombardment, by applying an additional H-flux and/or C-flux towards the substrate.

ZnO thin films deposited by chemical bath deposition (CBD) have been studied using x-ray diffraction, scanning electron microscopy, electron microprobe analysis and electrical measurements. The optimum CBD conditions for achieving structured, but adherent, ZnO films are as follows. Zinc acetate (0.0188 mol l⁻¹) and ethylenediamine (0.03 mol l⁻¹) are mixed. The pH of the bath is raised by addition of a base (0.5 mol l⁻¹, NaOH). The solution is maintained at a temperature between 60 °C and 65 ° C, while the bath is continuously stirred. We proceeded to anneal in room air for 30 min at 300 °C and under vacuum for 2 h at 300 °C. All the films obtained are nearly stoichiometric ZnO films crystallized in the usual hexagonal structure. As expected the films are rough and porous. The main difference between the two ZnO film families is their conductivity. The conductivity of the films annealed under vacuum is five orders of magnitude higher than that of those annealed in room air.

Carbon powder from catalysed carbon black (CPCCB) was prepared after a pyrogenation of carbon black (CB) with nanosized iron catalyst at atmospheric pressure and a temperature of 1100 °C. The complex relative permittivity and permeability of the CPCCB were measured by a reflection/transmission technique in the X and Ku bands. The reflection loss of CPCCB/paraffin wax composite was recorded. A wider absorption frequency range in the X band and Ku band could be obtained by adding 3 vol.% and 6 vol.% CPCCB in paraffin wax, respectively. Our results indicate that CPCCB could be a promising microwave absorption material.

A new comprehensive model has been developed for the pyroelectric activity of 0-3 ferroelectric composites which includes additional contributions from the electrical conductivity of the constituents and the frequency of measurement when the secondary pyroelectric effect resulting from the coupled thermoelectroelastic behaviour is considered. The boundary conditions are obtained in terms of the Laplace equation and Maxwell's equations. The analytical expressions have been derived for primary and secondary pyroelectric coefficients. The effects of the electrical conductivity of the matrix σ_m and the measuring frequency f on the pyroelectric property have been investigated in detail. Possible methods for improving the pyroelectric effect are also discussed. Our model can reflect comprehensively the pyroelectric property of the material and shows reasonably good agreement with experimental data.

This paper describes the electrification characteristics of water droplets on a hydrophobic surface and their influence on the induced discharge in an ac electric field. Tests were conducted by placing water droplets with different conductivities and volumes on an electrically stressed silicone rubber (SR) sheet, and their electrohydrodynamic behaviours were observed using a high-speed video camera. It is demonstrated that a locally high electric field at the tip of a droplet can trigger corona discharges, and droplets are always charged negatively during a corona discharge process. The deposited droplets are deformed and synchronized with the ac field. Once the deformation becomes noticeable, it increases rapidly until the droplet becomes mechanically unstable and ejects water filaments from its vertices. This can bridge the electrode gap and result in a flashover. In addition, the volume and conductivity of the water droplets have a marked effect on the mode of corona discharge and flashover development.

Radiative transfer in a one-dimensional absorbing and isotropically scattering plane-parallel grey medium with a collimated short-pulse Gaussian irradiation on one of its boundaries is studied. The medium is non-emitting and the boundaries are non-reflecting and non-refracting. The Galerkin method is extended for the solution of the transient radiative transfer problem. The transient transmittance and reflectance of the medium are evaluated for various optical thicknesses, scattering albedos and pulse durations.

Previous work on ultra-thin P(VDF-TrFE) Langmuir–Blodgett films has indicated a transition from extrinsic to intrinsic ferroelectric switching. The lack of several key features of intrinsic switching in the experimental work reported by Kliem et al argues against intrinsic switching. In this Comment we discuss two published papers and new experimental results that support a lack of intrinsic switching and point to the conclusion that the thickness dependence of the Langmuir–Blodgett films is due to the influence of the electrode interfaces.