Table of contents

The subject of atmospheric pressure plasma actuators for aerodynamic flow control originated in the mid-1990s and is now flourishing, particularly in the aeronautical, aerospace, and fluid dynamics literature. The rapid growth of this field can be illustrated by the figure below, which tracks the results of Google searches on 'plasma actuator' from August 2003, at which time there were 19 'hits', to the present, at which time there are more than 600 'hits'. The activity in this field has been growing exponentially, as the figure illustrates.

This special Cluster within Journal of Physics D: Applied Physics begins with a broad survey of past and recent work done world-wide, proceeds with papers that look at the physics and phenomenology of several kinds of plasma actuators, and finally moves on to papers that look at the effects of the momentum addition by plasma actuators to subsonic and supersonic flows. This new technology is likely to have an important effect on military and commercial flight, and it is my hope that this Cluster will contribute to that end.

Active flow control is a topic in full expansion due to associated industrial applications of huge importance, particularly for aeronautics. Among all flow control methods, such as the use of mechanical flaps, wall synthetic jets or MEMS, plasma-based devices are very promising. The main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control at high frequency. This paper is a review of the worldwide works on this topic, from its origin to the present. It is divided into two main parts. The first one is dedicated to the recent knowledge concerning the electric wind induced by surface non-thermal plasma actuators, acting in air at atmospheric pressure. Typically, it can reach 8 m s⁻¹ at a distance of 0.5 mm from the wall. In the second part, works concerning active airflow control by these plasma actuators are presented. Very efficient results have been obtained for low-velocity subsonic airflows (typically U_∞ ⩽ 30 m s⁻¹ and Reynolds number of a few 10⁵), and promising results at higher velocities indicate that plasma actuators could be used in aeronautics.

This paper presents an experimental investigation of the characteristics of a plasma actuator design for flow control consisting of an annular electrode in quiescent and flat plate boundary layer flows. In quiescent flow, the circular plasma region produced on actuation was observed to generate a vertical zero-net mass flux (or synthetic) jet, hence the name plasma synthetic jet actuator, the characteristics of which were found to be affected by the actuator operation mode (steady or unsteady). Pulsed operation of the actuator results in the formation of a starting vortex ring that advects ahead of the jet and secondary vortex rings near the actuator surface due to the additional plasma-induced fluid entrainment in the boundary layer. By varying the actuator pulsing frequency, multiple vortex rings were created in the flowfield and the resulting vortex ring interactions were found to increase both the peak velocity and streamwise extent of the jet. The interaction of the actuator with a crossflow was observed to be similar to that seen in conventional or non zero-net mass flux jets with the plasma synthetic jet penetrating into the mean flow. As expected, the influence of the jet on the freestream was found to decrease with increasing mean velocity and the impact on displacement and momentum thickness values diminishes as well.

Surface dielectric barrier discharges (DBDs) have been proposed as actuators for flow control. In this paper we discuss the basic mechanisms responsible for the electrohydrodynamic (EHD) force exerted by the discharge on the gas molecules. A two-dimensional fluid model of the DBD is used to describe the plasma dynamics, to understand the basic physics associated with the EHD force and to give some quantitative estimation of the force under simplified conditions. The results show that for ramp or sinusoidal voltage waveforms, the discharge consists of large amplitude short current pulses during which a filamentary plasma spreads along the surface, separated in time by long duration, low current discharge phases of a Townsend or corona type. The contribution of the low current phases to the total force exerted by the discharge on the gas is dominant because their duration is much longer than that of the current pulses and because the force takes place in a much larger volume. A description of the different discharge regimes and a parametric study of the EHD force as a function of voltage rise time and dielectric thickness is presented.

The electrical characteristics of a plasma sheet device used for subsonic airflow control are studied in this paper. Experiments are undertaken with a two-wire asymmetrical (different diameters, opposite polarity) electrode configuration connected to dc high voltage sources in the presence of a dielectric plate and under different gases (dry air, nitrogen and oxygen). For large distances electrode-plates it has been found that the discharge current consists of a purely dc component. The proximity of the plate reduces notably this dc current component until a limit situation for which the electrodes practically lay on the plate and a current pulsed regime is superimposed on the dc (small) component, thus establishing a plasma sheet regime. This regime could be reached only when the small wire was positive. This work establishes that the pulsed regime may be associated with a succession of positive streamers (cathode directed) which formation is promoted by different parameters of the gas and surface characteristics (thresholds of photoionization and photoemission, charge deposition, ...). The dc component seems to be produced by a small number of electrons originated in the ionization region of the negative corona that are amplified in the ionization region of the positive corona. The charged particles produced during the streamer propagation could contribute appreciably to the ion momentum transfer to the gas. This transfer should be due very likely to the drift of the charged species present in the streamer channel during the streamer collapsing phase. The source of momentum transfer associated with the dc current would always persist with a magnitude that depends on the intensity of this current.

This experimental work deals with active airflow control using non-thermal surface plasma actuators in the case of a rectangular cross section turbulent jet. A wide-angle diffuser composed of two adjustable hinged baseplates is linked at the jet exit. Two types of actuators are considered: the DC corona discharge and the dielectric barrier discharge (DBD). In both cases, an ionic wind with a velocity of several m s⁻¹ is generated tangentially to the wall surface. Thus, this induced aerodynamic effect is applied in order to create the separation along the lower hinged baseplate. The effects of both actuators on the flow separation are measured by means of particle image velocimetry for velocity up to 30 m s⁻¹. The main results show that the DBD seems more efficient than the DC corona discharge but the effect decreases with the jet velocity. However, in increasing the discharge frequency up to 1500 Hz, it is possible to separate a 30 m s⁻¹ jet. Finally, by reducing the actuators' length in the spanwise direction, results lead to a visualization of the three-dimensional effects on the separation along the lower hinged baseplate.

The paper discusses recent results on the development of localized arc filament plasma actuators and their use in controlling high-speed and high Reynolds number jet flows. Multiple plasma actuators (up to 8) are controlled using a custom-built 8-channel high-voltage pulsed plasma generator. The plasma generator independently controls pulse repetition rate (0–200 kHz), duty cycle and phase for each individual actuator. Current and voltage measurements demonstrated the power consumption of each actuator to be quite low (20 W at 20% duty cycle). Emission spectroscopy temperature measurements in the pulsed arc filament showed rapid temperature increase over the first 10–20 µs of arc operation, from below 1000 °C to up to about 2000 °C. At longer discharge pulse durations, 20–100 µs, the plasma temperature levels off at approximately 2000 °C.

Modelling calculations using an unsteady, quasi-one-dimensional arc filament model showed that rapid localized heating in the arc filament on a microsecond time scale generates strong compression waves. The results of the calculations also suggest that flow forcing is most efficient at low actuator duty cycles, with short heating periods and sufficiently long delays between the pulses to allow for convective cooling of high-temperature filaments. The model predictions are consistent with laser sheet scattering flow visualization results and particle imaging velocimetry measurements. These measurements show large-scale coherent structure formation and considerable mixing enhancement in an ideally expanded Mach 1.3 jet forced by eight repetitively pulsed plasma actuators. The effects of forcing are most significant near the jet preferred mode frequency (ν = 5 kHz). The results also show a substantial reduction in the jet potential core length and a significant increase in the jet Mach number decay rate beyond the end of potential core, especially at low actuator duty cycles.

Recent studies have shown atmospheric plasma discharges to be an effective means of air flow control. If in subsonic conditions the plasma's effect is explained by a transfer of momentum from the charged particles to the neutral ones, in supersonic conditions it seems that the effects are mainly of thermal origin but some authors think that this effect is not the only one to act. This paper presents experimental results of stagnation pressure, spectroscopic emission and drag performed in a rarefied Mach 2 flow over a flat plate model with a half-wedge leading edge. Changes caused by a negative dc discharge located on the upper surface of the flat plate are investigated in two cases. In the first case the negative potential is applied on the upstream electrode and in the second case it is applied downstream. The second electrode is grounded. The measurements carried out indicate two opposite effects depending on the localization of the negative potential.

In plasma processing, capacitive discharges have classically been operated in the electrostatic regime, for which the excitation wavelength λ is much greater than the electrode radius, and the plasma skin depth δ is much greater than the electrode spacing. However, contemporary reactors are larger and excited at higher frequencies which leads to strong electromagnetic effects. This paper gives a review of the work that has recently been carried out to carefully model and diagnose these effects, which cause major uniformity problems in plasma processing for microelectronics and flat panel displays industries.

A ferroelectric Bi_3.25Sm_0.75Ti_2.98V_0.02O₁₂ (BSVT) film and colossal magnetoresistive La_0.67Sr_0.33MnO₃ (LSMO) film heterostructure on Si with excellent performances of both ferroelectric and ferromagnetic properties at room temperature was fabricated by the pulsed laser deposition method. Saturated magnetization–magnetic field hysteresis loops and polarization–electric field loops proved the materials compatibilities in keeping their own intrinsic properties of LSMO and BSVT in the heterostructure. The remanent polarization (2P_r) of the BSVT is 56 µC cm⁻² at an applied electrical voltage of 11 V. Fatigue measurements show a 25% decrease in remanent polarization after 10⁶ read/write cycles but no further changes afterwards.

Nanocomposites of La_2/3Ca_1/3MnO₃(LCMO)/xCuMn₂O₄ (0 ⩽ x ⩽ 40%) have been prepared by a citrate gel route and characterized for microstructural and magnetotransport properties. Results show that fabrication with CuMn₂O₄ has an important effect on the electrical transport behaviour of the composites. With the increment of CuMn₂O₄ content x, the metal–insulator transition temperature T_MI for the composites shifts downwards and the resistivity increases. The susceptibility analysis indicates that the composites with x = 4, 20, 30 and 40% have a similar paramagnetic–ferromagnetic transition temperature T_C ∼ 240 K, which is lower than T_C of pure LCMO (∼262 K). The high temperature (T > T_MI) semi-conducting part of the resistivity (ρ) data follows a small polaron hopping conduction mechanism, and the metallic behaviour of the samples (T < T_MI) fits the model in terms of electron–magnon scattering of the carriers. Furthermore, a significant enhancement both in low-field magnetoresistance (LFMR) and in high-field magnetoresistance (MR) is observed for the composites at a wide temperature range below T_MI. The LFMR measured at 0.3 T reaches the maximum for the x = 40% sample when T = 10 K with the value of ∼23%, which is much larger than that of the pure LCMO (∼6.9%). We argue that such an enhancement in MR is attributed to the enhanced spin-polarized tunnelling, which is manipulated by the spin disorder at the LCMO surfaces caused by CuMn₂O₄ addition.

Atomic interdiffusion between FePt and Fe₃O₄ nanoparticles in annealed FePt-based nanocomposite magnets has been studied by means of structural and magnetic characterizations. The results show that the Fe₃Pt phase is formed during the annealing only when the mass ratio x of Fe₃O₄/FePt is larger than 1/20. When x ≤ 1/20, only FePt single phase is formed. It is interesting to find that the coercivity of the annealed samples increases with a small addition of Fe₃O₄ before the formation of the Fe₃Pt phase. This magnetic hardening behaviour indicates that the composition of the FePt phase can be further adjusted via the post annealing process. The characteristic of recoil loops and Henkel plots also give evidence for the transition from single-phase FePt magnets to nanocomposite magnets with the addition of Fe₃O₄.

It is well known that a coil shape generated by two overlapping ellipses produces the perfect dipole magnetic field. Similarly, a coil shape generated by two perpendicular and concentric intersecting ellipses produces the perfect quadrupole field. However, for a sextupole no such coil shape is available in the literature. We give here a coil shape for generating the perfect sextupolar magnetic field.

With a view to explaining the structural and electrical transport behaviour of some rare earth manganites, having the general formula Pr_0.67D_0.33MnO₃ (D = Ca, Sr, Pb and Ba), a systematic investigation of the electrical resistivity, thermopower and magnetic properties has been undertaken. These materials were prepared using the citrate–gel route by sintering at 900 °C. All the materials were characterized by x-ray diffraction, scanning electron microscopy, etc measurements. The x-ray data were analysed using the Rietveld method and the variation of various parameters involved in the process as explained. The average crystallite size of the materials has been estimated using the peak broadening method, while T_C and T_P values were determined from ac magnetic susceptibility and electrical resistivity measurements, respectively. Finally, the magnetoresistance (MR) measurements were also carried out over a magnetic field of 1–7 T and the data clearly exhibit the extrinsic MR in ferromagnetic metallic region.

The influence of average A-site cation radius ⟨r_A⟩ and cation mismatch parameter σ² on thermoelectric power (TEP), MR, electrical and magnetic transitions has been analysed. The TEP data at low temperatures (T < T_P) have been analysed by considering the magnon concepts, while the high temperature (T > T_P) data were explained by the Mott's small polaron conduction mechanism. The effects of ⟨r_A⟩ and σ² on polaron activation and hopping energies were also studied systematically.

We have studied the effects of electron–electron interactions on the far-infrared (FIR) spectrum of a two-electron vertical InAs quantum-dot molecule (QDM) by exact diagonalization. The interactions lead to the splitting of zero-field resonances and the resonance energies as functions of an axial magnetic field become less linear. The interactions reduce obviously the resonance energy for the spin S = 0, whereas for the spin S = 1 the resonance energy is not sensitive to the interactions. These effects are explained in terms of the single-electron and double-electron levels. The calculated results support the possibility of probing the effect of interactions by FIR spectroscopy in a vertical QDM.

Nanocomposites based on conducting polypyrrole (PPY) and inorganic SnO₂ have been synthesized by the soft chemical route. Absorption spectra of PPY–SnO₂ nanocomposites show peaks at wavelengths of 310–340 nm corresponding to nanosized SnO₂ and two broad bands present at around 450–475 nm and in the range 600–900 nm are due to polypyrrole. The absorption band at lower wavelength indicates a blue shift of about 30 nm with respect to bulk SnO₂. Direct current conductivity of nanocomposites as a function of temperature for different concentrations of polypyrrole have been interpreted by three-dimensional Mott's variable range hopping process. The observed diode like current–voltage characteristics are satisfactorily explained using the Schottky type barriers.

Room temperature pseudodielectric function spectra ε(ω) = ε₁ (ω) + iε₂(ω) of the ordered defects compounds Cu₂In₄Se₇, CuGa₃Se₅ and CuGa₅Se₈ have been measured by spectroscopic ellipsometry. The values of refractive index n and extinction coefficient k are given. The structures observed in ε(ω) spectra have been analysed using different methods, including fitting the numerically differentiated experimental spectrum (second derivative) to analytical line shapes. As a result, the energies corresponding to the fundamental gap (E₀) and higher critical points have been determined. A linear correlation of the fundamental gap values with Ga/Cu atomic ratio contents in CuGa_xSe_y samples is deduced.

Epitaxial tetragonal tungsten-bronze structure Sr_1.8Ca_0.2NaNb₅O₁₅ (SCNN) thin films of 650 nm thick have been grown on Si(0 0 1) substrates for the first time using pulsed laser deposition. The large lattice mismatch between SCNN films and Si substrates was overcome by making use of a MgO/TiN buffer layer. Excellent optical waveguiding properties of these SCNN films have been demonstrated using a prism-coupling technique. The ordinary and extraordinary refractive indices at 632.8 nm were calculated to be 2.2141 and 2.1727, respectively, implying a large birefringence of 0.0414. A propagation loss of 1.7 dB cm⁻¹ was measured in our waveguides. Our studies suggest that the SCNN/MgO/TiN/Si heterostructure is an ideal candidate for integrated optical waveguide applications.

This work numerically demonstrates a new anti-reflection coupler (ARC) with high coupling efficiency in a Si substrate solar cell. The ARC in which the grating is integrated on a glass encapsulation and a three-layer impedance match layer is proposed. A coupling efficiency of 90% is obtained at wavelengths between 350 and 1200 nm in the TE and TM modes when the incident angle is less than 30°. In comparison with a 1µm absorber layer, the integrated absorption of an a-Si thin-film solar cell without a new ARC is doubled, at long wavelengths (750 nm ⩽ λ ⩽ 1200 nm), as calculated by FDTD method.

K₃Na(SO₄)₂ : Eu nanocrystalline powder was synthesized by the chemical co-precipitation method. The x-ray diffraction pattern of the nanomaterials shows a hexagonal structure for its crystals having grain size of ∼28 nm. Transmission electron microscopy revealed that the K₃Na(SO₄)₂ : Eu nanoparticles are single crystals with almost a uniform shape and size. Thermoluminescence (TL) was taken after irradiating the samples at various exposures of γ-rays from a ⁶⁰Co source. A prominent TL glow peak is observed at 423 K along with three small peaks/shoulders at around 382, 460 and 509 K. The observed TL sensitivity of the prepared nanocrystalline powder is around 4 times more than that of LiF : Mg,Ti (TLD-100) phosphor. The 423 K peak of the nanomaterial phosphor eventually shows a near linear response with exposures increasing up to very high values (as high as 70 kGy), where all the other TLD phosphors saturate. This property along with its other desired properties such as high sensitivity, relatively simple glow curve structure and low fading makes the nanocrystalline phosphor a suitable dosimeter to estimate low as well as high exposures of γ-rays. TL analysis using the glow curve deconvolution technique was also done for determining different trapping parameters.

High-Al-content In_xAl_yGa_1−x−yN (x = 1–10%, y = 34–45%) quaternary alloys were grown on sapphire by radio-frequency plasma-excited molecular beam epitaxy. Rutherford back-scattering spectrometry, high resolution x-ray diffraction and cathodoluminescence were used to characterize the InAlGaN alloys. The experimental results show that InAlGaN with an appropriate Al/In ratio (near 4.7, which is a lattice-match to the GaN under-layer) has better crystal and optical quality than the InAlGaN alloys whose Al/In ratios are far from 4.7. Some cracks and V-defects occur in high-Al/In-ratio InAlGaN alloys. In the CL image, the cracks and V-defect regions are the emission-enhanced regions.

The room temperature nitriding of titanium is accomplished by utilizing nitrogen ion beams delivered by a 2.3 kJ plasma focus discharge. Titanium samples are exposed to ions at different axial positions (3, 5, 7 and 9 cm from the focus) in order to correlate their surface properties with ion beam parameters such as energy, number density, current density and energy flux (energy deliverance per unit time per unit volume). A BPX65 photodiode detector is employed to measure the ion beam parameters by using the time of flight technique. X-ray diffraction analysis as well as field emission scanning electron microscopy along with the energy dispersive x-ray spectroscopy is carried out to explore the structural, morphological and compositional profiles of the treated samples. The results demonstrate the formation of nanocrystalline TiN thin film with surface features strongly dependent on ion beam energy flux. A Vickers microindentation measurement reveals that the surface hardness is improved 4–5 times for typical nitrided samples.

In this work the impact of backscattered energetic atoms on film growth in reactive sputtering of CrN_x (x ⩽ 1) is manifested. We use film and plasma characterization techniques, as well as simulations in order to study the dynamics of the target–discharge–film interactions. The results show that the primary bombarding species of the growing film are plasma ions, which are neutralized and backscattered by the target in the form of atomic N. It is shown that the backscattered N atoms have energies which are significantly higher than those of other bombarding species, i.e. the backscattered Ar atoms, the sputtered atoms and the plasma ions. Moreover, it is found that CrN films exhibit compressive stresses of 2.6 GPa and a density close to the bulk value. We attribute these properties to the bombardment by backscattered energetic atoms, in particular N. Pure Cr films are also studied for reference.

Results of experiments with Ne, Ar and Xe as well as computer simulations are presented, aimed at testing an earlier proposed model of temporal dynamics of multichannel structure development in a pulsed high-current sliding gas discharge. The obtained and discussed experimental data include the values of an averaged channel radius, the pulsed near-surface breakdown voltage, the saturated spark resistance, the spatial structure of spark channels registered photographically under different discharge voltages and the oscilloscope traces of the discharge gap voltage. The experiments were performed at two values of gas pressure (30 and 100 kPa) with a setup in two modifications which differed from each other by an impedance (27 times) and a stored electric energy (250 times) of a pulsed power supply source. A comparison of the experimental channel structure and the discharge voltage time dependence with those calculated using the discussed model showed good agreement, and this approves an application of the model to quantitative estimations of the sliding discharge parameters. The relation revealed between the channel radii and the square root of mobility of electrons is explained by a drift of electrons in a transverse electric field. Attention is also paid to the problem of stability of a multichannel mode of the sliding discharge. Both experimental data and computer modelling demonstrate that the most stable mode of the discharge is a quasi-homogeneous one, in which the spark channels fill the interelectrode gap entirely. But a certain instability of plasma brightness seems to be an intrinsic feature of the multispark sliding discharge even in its quasi-homogeneous mode, which results from non-simultaneous initiation of the spark channels.

This paper focuses on the numerical investigation of low-voltage arc plasma behaviour with the contact opening process included. A flexible experimental setup with a rotating contact is designed to support this study. Based on the magnetohydrodynamic arc model, the elongation and the commutation behaviour of the arc plasma during the contact rotation progress are simulated. Under the given conditions of the external magnetic field and the contact rotating velocity, the arc motion is described in detail by the temperature distribution. The stagnation together with the following rapid jump of two arc roots is observed by both calculation and experiment. The rapid rise in the arc voltage is mainly caused by the increasing difference between the two arc roots displacement in the moving direction, and the jump instant of the arc root on the moving contact is according to the moment of the maximal voltage value.

Sterilization experiments using low-pressure air discharge plasma sustained by the 2.45 GHz surface-wave have been carried out. Geobacillus stearothermoplilus spores having a population of 3.0 × 10⁶ were sterilized for only 3 min using air-simulated N₂–O₂ mixture gas discharge plasma, faster than the cases of pure O₂ or pure N₂ discharge plasmas. From the SEM analysis of plasma-irradiated spores and optical emission spectroscopy measurements of the plasmas, it has been found that the possible sterilization mechanisms of air-simulated plasma are the chemical etching effect due to the oxygen radicals and UV emission from the N₂ molecules and NO radicals in the wavelength range 200–400 nm. Experiment suggested that UV emission in the wavelength range less than 200 nm might not be significant in the sterilization. The UV intensity at 237.0 nm originated from the NO γ system (A ²Σ⁺ → X ²Π) in N₂–O₂ plasma as a function of the O₂ percentage added to N₂–O₂ mixture gas has been investigated. It achieved its maximum value when the O₂ percentage was roughly 10–20%. This result suggests that air can be used as a discharge gas for sterilization, and indeed we have confirmed a rapid sterilization with the actual air discharge at a sample temperature of less than 65 °C.

This paper presents an optical diagnostic examination of dc planar magnetron discharge used for titanium deposition at 30 mTorr in argon bulk gas. The results were obtained by optical absorption (OAS) and emission (OES) spectroscopy for two distances from the target without substrate. The absolute density of titanium in the ground and metastable states at 4 cm from the target ranged, respectively, between 8 × 10¹⁰ cm⁻³ and 10¹² cm⁻³ and between 6 × 10¹⁰ cm⁻³ and 3 × 10¹¹ cm⁻³, in the range 0.2–1.0 A. OES results were used to prepare an assumed interpretation in terms of differences in loss mechanisms, mainly by either diffusion towards the walls for all particles at 8 cm from the target or collision losses for non-radiative species at 4 cm from the target, except for the titanium ground state. This was confirmed by our results of the argon metastable density measurement at 4 cm which was constant at around 7 × 10¹⁰ cm⁻³ with discharge current.

Titanium was laser nitrided by means of free electron laser (FEL) irradiation in pure nitrogen atmosphere. The variation of macropulse frequency and duration of the FEL micropulse trains resulted in the formation of δ-TiN_x coatings with different thicknesses and different micro- and macroscopic morphologies. The coatings revealed characteristic values for hardness, roughness and crystallographic texture, which originate from the growth mechanism, the solid–liquid interface energy and the strain. Further investigations showed that the dendritic growth begins at the surface and the alignment of the dendrites is normal to the surface. A correlation of the texture with the time structure of the laser pulses was found. Combined numerical simulations of temperature evolution and nitrogen diffusion were performed and the results were compared with the experimental findings. The simulations can explain the experimental results to a great extent.

A homogenized surface potential is desirable for the observation of a pre-irradiated insulating specimen using a scanning electron microscope because the residual surface potential may affect the imaging properties of the specimen. To homogenize the residual surface potential, the specimen should be subjected to the irradiation of an electron beam with the total electron yield greater than one. The expression of the equilibrium potential is derived based on the charge balance condition in the equilibrium state and the potential value is found to increase mainly with the secondary electron (SE) yield and the most probable emission energy of SEs. Further numerical calculations of SE trajectories show that affected by different surface potentials, SEs leave or return to the specimen surface to change the net charge flux into the specimen. This thereby increases the surface potential below the equilibrium potential and decreases that above the equilibrium potential, homogenizing the surface potential.

We report here that atomic force microscopy (AFM) in frictional force mode can be used to detect the onset of chain scission and crosslinking in polymeric and macromolecular samples upon irradiation. A systematic investigation to detect chain scission and crosslinking of two elastomers, (1) ethylene-propylene-diene monomer rubber and (2) fluorocarbon rubber, upon γ-ray irradiation has been carried out using frictional force microscopy (FFM). From the AFM results we observed that both the elastomers show a systematic smoothening of its surfaces, as the γ-ray dose rate increases. However, the frictional property studied using FFM of the sample surfaces show an initial increase and then a decrease as a function of dose rate. This behaviour of increase in its frictional property has been attributed to the onset of chain scission, and the subsequent decrease in friction has been attributed to the onset of crosslinking of the polymer chains. The evaluated qualitative and semi-quantitative changes observed in the overall frictional property as a function of the γ-ray dose rate for the two elastomers are presented in this paper.

Relaxor-based piezoelectric 0.955Pb(Zn_1/3Nb_2/3)O₃–0.045PbTiO₃ (PZN–4.5PT) single crystals were grown using the modified Bridgman method. The set of piezoelectric coefficients in the lateral mode has been measured. Samples with size of 10 × 2 × 1 mm³ were poled in the ⟨0 0 1⟩ and ⟨1 1 0⟩ crystallographic directions, with different vibration directions. Single crystals properties varied with the cut type. For the ⟨0 0 1⟩/⟨0 1 0⟩ poling/vibration direction (cut 1), PZN–4.5PT single crystals exhibited a piezoelectric constant d₃₃ of 2500 p C N⁻¹ and an electromechanical coupling factor k₃₁ of 50%. However, the most interesting properties in the lateral mode are obtained for ⟨1 1 0⟩/⟨0 1 0⟩ cut (cut 3). The influence of vibration direction on the electromechanical coupling was explained by a variation of the compliance, whereas polarization direction influences the characteristics via domain engineering effect. Finally, both thermal stability and stress dependence were studied in order to determine working conditions (temperature and stress) and the effect of phase transition on the single crystal properties.

By using an ab initio local-density approach and considering the defect locations of substitutional sites and midplane sites in hexagonal boron nitride (h-BN) graphite structure, the defect formation energies of N, O, C ions in h-BN ceramic and then the ionic conductivities are calculated. On comparing with the experimental results, it is indicated that the main contribution of ionic conductivity is due to the oxygen ionic defects. At high temperatures, no loss peak is observed in the measured dielectric loss spectrum, because the large conduction loss may obscure the loss peaks, which reflect the intrinsic dielectric relaxation. By eliminating the conduction loss in the measured dielectric loss, the loss peaks can be recovered. This research is helpful for the application of h-BN at high temperatures by understanding the ionic conduction and high temperature relaxation processes.

A novel method of preparation of organic films is described, which employs an alternating magnetic field applied to the film cast from a solution and results in an improved film morphology. The changed film morphology is explained by a magnetomechanical effect due to the interaction of the applied field and the induced magnetic moment in an organic molecule. The effect is demonstrated for a range of materials, such as polymers and low-weight organic dyes, which have different tendencies to form aggregates or crystallites in the condensed state. It is proposed that the method can be used as a reasonable alternative to the spin-coating technique for preparation of cast films with a high-quality morphology.

Using a torsion pendulum, the peculiarities of low-frequency shear elastic and anelastic properties of the improper ferroelastic crystal K₂Ba(NO₂)₄ have been investigated for various crystallographic oriented samples at a temperature range in the vicinity of the phase transition point (T_C = 420 K). The work gives insights into the nature of the internal friction and spontaneous torque arising in the samples at the Curie point.

Phase evolution, microstructure and dielectric behaviour of Li and Ta codoped NiO (LTNO) ceramics were studied. The content of Ta₂O₅ was mainly dispersed into the grain boundaries and exists as the NiTa₂O₆ phase. The concentration of Ta has a remarkable effect on the dielectric properties of the LTNO ceramics. The sample with Ta = 5% has the highest dielectric constant of the three LTNO samples. The activation energy for the LTNO (Ta = 5%) sample was 0.126 eV and relaxation time was 3.51 × 10⁻¹⁰ s. These correspond to the dielectric relaxation processes. The high dielectric constant response of the LTNO ceramics is due to the formation of a barrier layer between the grain boundaries. Orientational and space charge polarization contribute to the dielectric behaviour observed.

Simultaneous measurements of the thermal conductivity, thermal diffusivity and heat capacity per unit volume of monocrystalline silver bromide (AgBr), using the Gustafsson probe, in the temperature range 77–350 K are reported. Both thermal conductivity and thermal diffusivity follow Eucken's law in the temperature region studied. The heat capacity at constant pressure (C_P), determined from the volumetric heat capacity, agrees with the calculated value at room temperature. The ratio of the thermal conductivity (λ) of AgBr and AgCl calculated from the Leibfried–Schlömann formula is in excellent agreement with the ratio λ_(AgBr)/λ_(AgCl) measured experimentally. The dielectric constant and loss factor of crystalline AgBr are also reported as a function of frequency in the range 100 Hz–1 MHz at room temperature.

There is currently great interest in combining focused ion beam (FIB) and scanning electron microscopy technologies for advanced studies of polymeric materials and biological microstructures, as well as for sophisticated nanoscale fabrication and prototyping. Irradiation of electrically insulating materials with a positive ion beam in high vacuum can lead to the accumulation of charge, causing deflection of the ion beam. The resultant image drift has significant consequences upon the accuracy and quality of FIB milling, imaging and chemical vapour deposition. A method is described for suppressing ion beam drift using a defocused, low-energy primary electron beam, leading to the derivation of a mathematical expression to correlate the ion and electron beam energies and currents with other parameters required for electrically stabilizing these challenging materials.

The n-type doping of (Al)GaAs grown on GaAs using silicon (Si) was studied in metal-organic vapour-phase epitaxy using reflectance anisotropy spectroscopy. The reflectance anisotropy (RA) of GaAs was measured on undoped layers and on layers with increasing Si n-type doping concentrations up to 1 × 10²⁰ cm⁻³. It was found that the RA still changes even though the carrier concentration stays constant and only the Si concentration in the crystal lattice is increasing at values above 5 × 10¹⁸ cm⁻³. The doping dependence of the RA of Al_xGa_1−xAs layers up to aluminium concentrations of x = 0.7 is similar to the GaAs case with an increasing amplitude while for highly doped AlAs it is slightly different. While the broad peak in the RA spectra around 3.9 eV of Si-doped GaAs and Al_xGa_1−xAs up to x = 0.7 shows a steady decrease with increasing doping concentration the RA of AlAs in this spectral region shows a shift of the peak towards lower photon energies and an increase in amplitude for doping concentrations above 2 × 10¹⁸ cm⁻³. Finally, the temperature dependence was studied for Al_0.5Ga_0.5As showing that the influence of the doping on the RA spectra is decreasing with increasing temperature.

Intumescent coatings are designed to react when they are heated, by building up a swollen multi-layered insulating structure. The substrate onto which they are applied is then actively protected. In a military framework, it is crucial to provide efficient protection to a wide range of devices and vehicles, which must be able to sustain intense thermal conditions such as fires or explosions. For this purpose, the behaviour of intumescent paints under exposure to high thermal fluxes is investigated. In order to develop and validate a model describing heat transfers in materials protected by intumescent coatings, experimental simulations of different types of radiative aggressions were carried out. A 45 kW solar furnace was used as a heat source, which allowed simulating fires and explosions. Temperature ranges and kinetics calculated by the model are similar to those observed and measured during the experiments. The mathematical model, initially developed for fire simulations, also proves efficient in the case of thermal fluxes induced by brief, violent explosions. However, the results show that a better identification of each layer's thermal properties is needed to improve the accuracy of the model. For this purpose, an experimental identification campaign using the solar furnace has to be developed.

Electrons trapped in a certain unidentified defect in feldspars can escape it by tunnelling to a nearby site. We show that, for plagioclase feldspars with up to 5% Ca cation (peristerites), the tunnelling rate is directly related to the Ca content. Any explanation must take into account the two-phase nature of such crystals, and three different models that can account for the correlation are discussed. We also show that the light emission that occurs in conjunction with tunnelling is from Mn²⁺ ions and that this tunnelling may be from a different defect. That plagioclases with low Ca contents have no detectable fading due to tunnelling leads to prospects for optical dating to a million years or more.

The behaviour concerning classical heat diffusion on fixed thermal surfaces, studied by observations, still holds surprises. As soon as convective and radiative processes are negligible within the medium, this is considered to be free from energy sources and sinks. Then, the heat diffusion equation is conveniently solved using standard Fourier methods. Some considerations about the contrast effect suggest that the surface boundary would rather be observed to follow specific area decay dynamics than remaining fixed and static. Here it is shown that the apparent boundary lies on a specific isothermal spatiotemporal curve, which depends on the observing device. This is characterized by a slight, though determinative, difference between its radiance and that of the ambient background. Thereafter, the heat diffusion yields apparent boundary shrinkage with the passing of time. This phenomenon is particularly notable for two reasons: its lifetime and final decay rate depend only on the medium thermal properties, while being independent of the apparent boundary spatiotemporal curve. Thus, the former provides a suitable method for measuring the medium thermal properties via the observational data. The latter strongly reveal a kind of universality of some characteristic properties of the phenomenon, common to all observers.

The induction of transmembrane potentials (Δϕ) by an external field is the basis of numerous applications in biotechnology, cell-technology and medicine. We have developed new, simplified analytical equations that avoid the complicated description by the depolarizing factors. The equations apply to the Δϕ induced in cells resembling ellipsoids of rotation, i.e. spheroids by homogeneous dc or ac fields. They will be especially useful for experimental scientists. The equations describe the dependence of the Δϕ on the electric media properties, the field frequency and the axis ratio for oblate and prolate spheroids for which the symmetry semiaxis (c) is shorter and longer than the other two semiaxes (a and b, with a = b), respectively. According to the Schwan equation, an electric field E may induce a maximum Δϕ of 1.5aE at the poles of a spherical cell. For the poles of spheroidal cells, the maxima can be easily described by Δϕ = (a + 2c)E/2 and Δϕ = a(a + 2c)E/(a + c) for fields oriented along and perpendicular to the symmetry axis, respectively. For practically important shapes the error in the magnitude of Δϕ is smaller than 5% except along the c-axis for axis ratios larger than 2. Nevertheless, the errors vanish for the three limiting shapes of infinitely thin disc, sphere and cylinder.

An analytical, two-dimensional, stationary model of heat distribution in a broad-area laser is discussed. In the model the laser is treated as a stack of layers of different thicknesses and thermal conductivities. We show how to adjust the geometry of such a stack to take into account a non-ideal heat sink (made of material of finite thermal conductivity) and thus obtain reliable values of the device temperature. The calculated and measured thermal resistances of an exemplary laser series are compared. Our experiment is based on the analysis of a spectral shift of the laser radiation, which provides information about the mean temperature of the active region. A discussion of different types of bonding imperfections and their influence on the obtained results is provided.