Table of contents

Torsional and lateral vibrations of atomic force microscope (AFM) cantilevers can be used to measure elastic and frictional properties on a nanoscale. Recently a new dynamic operation mode called Torsional Resonance mode (TRmode) has been introduced. This paper describes the physical base of the TRmode and compares it to related dynamic AFM modes. In the theoretical part the torsional equation of motion of the cantilever beam is analysed. In the experimental part the contrast of images is interpreted based on the equation of motion. The route to quantitative measurements of contact stiffness, elastic moduli and friction is laid out.

The magnetometric (volume averaged) demagnetization factors for cylinders with elliptical cross section are computed using a Fourier-space approach and compared with similar results obtained with a different treatment. The demagnetization factors are given as a series expansion in the eccentricity of the elliptical cross section, where the terms up to order ¹⁰ are given explicitly as a function of the cylinder aspect ratio. Other simplified expressions, valid in restricted regimes, are also given. Two different series expansions, obtained previously and valid in particular combinations of shape parameters, are recalled and compared with the new results. After the computation of the magnetostatic and exchange-energy terms associated with a vortex closure-domain state in the elliptic cylinder, the single-domain limit, or the critical size below which the structure can support quasi-uniform magnetization, is derived and discussed.

Isothermal magnetization curves up to 23 T were measured in Gd₅(Si_xGe_1−x)₄ alloys for x ⩽ 0.1. We show that a field-induced transition occurs from the antiferromagnetic (AFM) phase to a state in which competing short-range AFM and ferromagnetic (FM) correlations are present. This is based on the abrupt change in the slope of the high-temperature magnetization isotherms at high fields (∼14–15 T). Results suggest that the transition is due to the breaking of the long-range AFM ordering by the magnetic field. This induces short-range FM correlations favouring the formation of coexisting FM and AFM clusters. A further increase of the magnetic field leads to the percolation of the former, giving rise to long-range FM order.

A stage has been constructed to supply a variable strength in situ magnetizing field for use in a focused ion beam system. Ion irradiation experiments were performed in the presence of the magnetic field in order to investigate its effect on the localized exchange bias field in thin CoFe/IrMn bilayers. Squares with dimensions 10 × 10 µm² were directly irradiated by Ga⁺ ions of energy 30 keV at doses between 1 × 10¹³ and 1 × 10¹⁵ ions cm⁻². TEM studies of the magnetization reversal behaviour of the squares showed that bias field reversal could be achieved with the maximum achievable bias field strength being > 50% of that along the original direction.

Iron oxide nanoparticles were prepared using the sol–gel process. In situ polymerization of a pyrrole monomer in the presence of oxygen in an iron oxide–ethanol suspension resulted in an iron oxide polypyrrole nanocomposite. The structure and magnetic properties of the nanocomposites with varying pyrrole concentrations are investigated. X-ray diffraction studies indicate the presence of the γ-Fe₂O₃ phase for the concentrations investigated. FTIR studies confirm the presence of polypyrrole. TEM studies show agglomeration in uncoated samples and in samples with a lower concentration of polypyrrole. Agglomeration is greatly reduced for samples coated with a higher concentration of polypyrrole. The ac susceptibility measurements performed in the temperature range 77–300 K show the presence of blocking, indicating the superparamagnetic phase. The blocking temperature is found to depend on the pyrrole concentration. Monte Carlo studies for an array of polydispersed single domain magnetic particles, based on an interacting random anisotropy model, were also carried out, and the blocking temperatures obtained from the simulation of the field cooled–zero field cooled magnetization compare favourably with experimental results.

The electrical properties of the La_0.67(Ca_0.65Ba_0.35)_0.33MnO₃/Ag_x composite system are systematically investigated as a function of Ag-added content. Ag addition induces a decrease in resistivity (ρ) and an increase in temperature T_P where the ρ peak is located. This is due to the improvement of grain boundaries caused by the segregation of Ag on the grain surfaces. The T² dependence of the resistivity data in the low temperature region of T < T_P reflects that the conductive mechanism in the ferromagnetic (FM) metallic state mainly arises from electron–electron scattering. At high temperatures, above the Curie temperature T_C, the resistivity data for all samples follow the adiabatic spin polaron hopping model. Moreover, the ρ –T curves for x = 0.27 and 0.30 samples fit well to the phenomenological percolation model based on phase segregation. This result confirms the coexistence of FM clusters and paramagnetic regions near T_C, and indicates the prominent intrinsic behaviour of the La_0.67(Ca_0.65Ba_0.35)_0.33MnO₃ matrix. Note that a 27% molar ratio of added Ag induces a large room temperature magnetoresistance (MR) ratio of up to 41%. This value is attractive for the study of applications. The good agreement of experimental data with the Brillouin function indicates that the MR behaviour in this composite system accounts for the spin-dependent hopping of the electrons among the spin clusters.

The kinetics of the charge–carrier recombination in double-layer organic light-emitting diodes composed of indium–tin–oxide/N,N'-di(naphthalene-1-yl)-N,N' -diphenyl-benzidine/beryllium complexes/LiF/Al were studied by transient electroluminescence (EL). Two blue-emitting materials of bis[2-(2-hydroxyphenyl)-pyridine]beryllium (Bepp₂) and bis[2-(2-hydroxytoluenyl)-pyridine]beryllium (Betp₂) were used as the emissive layer. It was found that the EL efficiency of the Bepp₂-based devices was higher than that of the Betp₂-based devices. The improvement of the EL efficiency was well interpreted by the results that the Bepp₂ shows higher electron mobility and electron–hole recombination coefficients (γ) than Betp₂, which are determined from the onset of the transient EL after a rectangular voltage pulse is applied, and from the long-time component of the temporal decay of the EL intensity after the voltage pulse is turned off. The electron mobility and the recombination coefficients γ of the Bepp₂ reached 6 × 10⁻⁶ cm² V⁻¹ s⁻¹ and 7.3 × 10⁻¹² cm³ s⁻¹, respectively, which are approximately twice the magnitude of the Betp₂.

This paper presents a complete model for the complex underlying mechanisms of vectorial holography using orthogonal S- and P-polarized beams. This configuration is of great interest, being the only one allowing creation of purely-vectorial holographic gratings. We model both the interference process and the material's photoinduced vectorial anisotropy using simple matrix formalism. We demonstrate further that combined linear and circular vectorial anisotropy makes the grating polarization-selective in diffraction allowing non-destructive polarization-measurement on the incident beam. This strict material condition explains the very few experimental successes previously reported. Appropriate material selection might open the path to complete non-destructive polarimetric solutions, polarization-discrimination or routing applications. The presented model can be easily extended further to other polarization configurations.

The defect centres formed in the thermoluminescence (TL) phosphor CaSO₄ : Dy,Ag are studied using the technique of electron spin resonance (ESR). The Ag co-doped phosphor exhibits three glow peaks around 130°C, 220°C and 375°C, in contrast to the two glow peaks observed in the CaSO₄ : Dy phosphor at 130°C and 220°C, at gamma ray dose of 1 Gy when the TL measurements were carried out in the spectral region 300–650 nm. ESR studies show that the additional peak at 375°C correlates with a Ag²⁺ centre formed owing to γ-irradiation and observable 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 375°C; this radical is characterized by the g-values g_|| = 2.0023 and g_⊥ = 2.0038 and is assigned to the radical. It is observed that there is more incorporation of Ag in the CaSO₄ : Dy system as compared with that in the pure CaSO₄ system. The variation of Ag^{2 +} ESR intensity with Ag concentration as well as with dose in the range 0.3–120 kGy is studied. The Ag^{2 +} ESR signal and TL saturate at 2 × 10⁴ Gy, but the intensity of the radical continues to increase up to the studied dose of 1.2 × 10⁵ Gy. The intensity of the radical decreases with Ag concentration in CaSO₄ : Dy,Ag, in agreement with the TL model proposed in this work.

Recent years have seen an increased interest in the physics of the generation of small liquid droplets from nozzles, largely motivated by the requirements of high-resolution inkjet printers and general microfluidic applications. Serious limitations on the desired downsizing are imposed by surface tension effects: the pressures encountered during droplet formation are inversely proportional to the length scale and tend to become unfeasibly large. With this in mind, and following upon the recent contribution of Chen and Brenner, we investigate the influence of the design of the micro-sized nozzle on the relationship between the encountered pressures and the volume of the attached droplet. Using numerical surface minimization techniques, we extend the previous work by showing that smaller droplets can be generated by employing nozzles with non-circular boundaries and that a further improvement is achieved by using nozzles with three-dimensional (3D) (i.e. non-planar) boundaries. For example, droplets formed from nozzles with a 3D curvilinear-triangular boundary can be 33% smaller than those formed from circular nozzles at the same maximum pressure.

a-axis fibres of lithium niobate produced by laser heated miniature pedestal growth can possess transverse and longitudinal birefringence variations due to faceted growth. When used for second harmonic generation, these characteristics cause conversion efficiencies to be two to three orders of magnitude smaller than predicted and the phasematchable lengths and apertures to be short. Second harmonic generation and associated birefringence mapping are shown to be sensitive indicators of their uniformity.

In this paper, we propose that two-dimensional photonic crystals can be employed in some kinds of polarization beam splitters due to their strong dielectric anisotropy. Numerical experiments with several examples have been carried out, and the results obtained support our opinion. We expect that two-dimensional photonic crystal polarization beam splitters will have important applications in some areas such as integrated optical circuits.

An inductively coupled SF₆/O₂ plasma is used to form a columnar microstructure (CMS) on silicon samples cooled at very low temperature (∼ −100 °C). The formation of this CMS is studied as a function of bias voltage, temperature, RF power and gas pressure. The characteristic mean diameter and mean height of the microstructure are evaluated by image processing tools from SEM micrographs. A crystallographic effect is also observed at very low temperature, which induces a needle-shaped structure. A physical mechanism is proposed to explain the formation of this CMS.

This paper describes theoretical and experimental investigations of the effect of an electrode coating on the onset voltage of a corona on negatively stressed electrodes. Dielectric-coated hemispherically-capped rod-to-plane gaps positioned in air are investigated. The onset voltage is calculated based on the self-recurring single electron avalanche developed in the investigated gap. Accurate calculation of the electric field in the vicinity of a coated rod and its correlation to the field values near a bare rod of the same radius are obtained using the charge simulation method. The calculated field values are utilized in evaluating the onset voltage of the corona. Also, laboratory measurements of the onset voltage on bare and coated electrodes are carried out. The effects of varying the field nonuniformity, the coating thickness and its permittivity on the onset voltage values are investigated. The results show that coating the electrodes with a dielectric material is effective in increasing the onset voltage of the corona on its surface. The calculated onset voltage values for coated and bare electrodes agree satisfactorily with those measured experimentally.

Recent work by Sternberg and Poggie (2004 IEEE Trans. Plasma Sci.32 2217), concerned with the structure of an active collisionless magnetized plasma-sheath, is extended to include the effect of collisions on the ion motion. In the collisionless case an expression for the eigenvalue of the problem analogous to that obtained by Franklin and Ockendon (1970 J. Plasma Phys.4 371) for an active unmagnetized plasma is obtained. As is to be expected with increasing collisionality, increased transport of ions across the magnetic field lines means that the effect of the magnetic field is diminished. Special attention is given to the case when the magnetic field is nearly parallel to the wall.

We report on the creation and propagation of ion-acoustic solitary waves in a high power pulsed magnetron sputtering discharge. A dense localized plasma is created by applying high energy pulses (4–12 J) of length ≈70 µs, at a repetition frequency of 50 pulses per second, to a planar magnetron sputtering source. The temporal behaviour of the electron density, measured by a Langmuir probe, shows solitary waves travelling away from the magnetron target. The velocity of the waves depends on the gas pressure but is roughly independent of the pulse energy.

A novel method to describe diffusive processes in plasmas in local thermodynamic equilibrium (LTE) was developed, based on the transport of elements instead of individual species. This method combines the elegance of the LTE description of a chemical composition with the flexibility of explicit transport for each element. A simple model of a metal halide lamp containing Hg dosed with NaI is used to illustrate the method.

Optical and electrical properties of a fast (∼50 ns) discharge in pure Xe were studied experimentally and simulated numerically. Afterglow vacuum ultraviolet (VUV) emission was revealed lasting for a few microseconds. Its duration depended on the Xe gas pressure. The length of the discharge was 42 cm. Operation of the discharge was limited in gas pressure by the development of instability. The highest pressure of pure Xe for a stable discharge run was 0.9 bars. A detailed kinetic model of discharge plasma was developed, which calculated self-consistently the electron energy distribution function and excited states including dimer population dynamics. VUV emission dynamics observed experimentally can be explained theoretically only in a model with an essentially increased number of electronic states taken into account. Calculated discharge voltage history and VUV emission dynamics agree satisfactorily with measurements.

It is known that for 'tungsten inert gas' welding of stainless steel, the weld depth can be increased by a factor of two or more if a thin layer of flux powder is initially coated on the steel. Numerical predictions from a unified electrode-arc-weldpool model are made elucidating the possible role of three different mechanisms previously proposed to explain this effect, and we also examine a new fourth possible mechanism, namely the effect that the flux is an electrical insulator. (1) Calculations support the suggestion that if the dissolved flux in the weld pool changes the temperature dependence of the surface tension to increase rather than decrease with temperature, the direction of convective circulation within the weld pool can change from radially outwards to radially inwards, leading to an increased weld depth of the order of 2 mm. (2) The effect of electron attachment to flux vapour in the arc, if the vapour contains an attaching gas such as oxygen, is found to have a negligible effect in producing arc constriction and thus a higher current density to increase weld depth. (3) Our treatment assumes that the surface of the weld pool is undepressed by the arc, so that we have not examined the suggestion that increased weld depth is caused by the flux lowering surface tension and thus increasing depression of the weld pool surface. But experimental observations indicate that such depression is negligible for currents of less than 200 A. (4) If the flux produces an insulating layer on the metal surface, calculations indicate that there can be a marked increase in weld depth of the order of 5 mm or more due to the flux blocking the current in the outer regions of the arc thus producing a higher current density at the arc centre. Furthermore these calculations indicate that the flux causes an arc spot to form at the anode, in agreement with similar experimental observations of an anode spot in the presence of a flux.

The evolution of the OH radical density was measured in the afterglow of a pulsed homogeneous discharge using time-resolved laser induced fluorescence, and the acetaldehyde removal was quantified using chromatography for N₂/O₂/CH₃CHO mixtures at 460 mbar with 5% oxygen and an acetaldehyde concentration between 250 and 5000 ppm. It is shown that the radical density rapidly increases shortly after the discharge for all mixture compositions studied, although it does not contain water molecules. Afterwards this density decreases with a characteristic time much longer than the one estimated from the known reactivity of OH with CH₃CHO. This emphasizes that processes other than oxidation of acetaldehyde by O-atoms play a significant role in OH radical production.

In order to clarify whether a hollow cathode arc (HCA) can be used as a welding heat source in space, investigations into the fundamental characteristics of HCA were experimentally performed under low pressure conditions. The HCA method enables an arc discharge to ignite and maintain under low pressure conditions; in contrast, low pressure conditions make it extremely difficult for the conventional gas tungsten arc method to form an arc discharge. In an earlier paper, it was shown that the melting process by HCA is very sensitive to process parameters such as the gas flow rate and arc length, and a deep penetration forms when the arc length is long and the gas flow rate is low. In this paper, the distribution of the arc current on the anode surface and the plasma properties of the HCA under low pressure conditions have been made clear and the total heat energy to the anode has been discussed in order to understand the heat input properties of the HCA. The result shows that the HCA in the case of a low gas flow rate is a high and concentrated energy source, and the high energy input to the anode contributes to the deep penetration.

Temporal periodic variation and long-time decrease of optical emission intensity collected by a spectrometer in an inductively coupled CH₄/N₂ plasma, which deposits a film of growing thickness on the chamber wall, are measured. The periodic variation is interpreted as a result of the interference between the light reflected from the film surface and that which re-emerged from the surface after being reflected by the chamber wall. The re-emerged light is attenuated due to absorption by the film and thus leads to the long-time decrease of the intensity. The periodic variation of the line intensities, however, can be used for in situ film thickness monitoring.

The characteristics of axisymmetrical inductively-coupled argon plasmas with wafer biasing are examined using the particle-in-cell Monte Carlo method. The simulation is performed on the condition that gas pressure is fixed at 5 mTorr and power deposition is at 200 W. The effects of bias frequency and bias voltage on the distributions of flux and energy of the ions that are incident onto the wafer are investigated. The bias frequency and bias voltage are changed from 2 MHz to 13.56 MHz and 100 V to 300 V, respectively. The plasma structure is largely influenced by the wafer biasing. The ion energy distribution strongly depends on the bias frequency, bias voltage and sheath thickness. Decreasing the bias frequency results in the improvement of the uniformity of ion flux. These results are consistent with the previous theory.

Approximate solutions to the time-dependent radiative transfer equation, also called the phonon radiative transfer equation, for a plane-parallel system have been obtained by combining the flux-limited Chapman–Enskog approximation with the maximum entropy method. For problems involving heat transfer at small scales (short times and/or thin films), the results found by this combined approach are closer to the outcome of the more labour-intensive Laguerre–Galerkin technique (a moment method described recently by the authors) than the results obtained by using the diffusion equation (Fourier's law) or the telegraph equation (Cattaneo's law). The results for heat flux and temperature are presented in graphical form for x_L = 0.01, 0.1, 1 and 10, and at τ = 0.01, 0.1, 1.0 and 10, where x_L is the film thickness in mean free paths, and τ is the value of time in mean free times.

A new analytical theory for multiple scattering of cylindrical acoustic waves by an array of finite impedance semi-cylinders embedded in a smooth acoustically hard surface is derived by extending previous results for plane waves (Linton and Martin 2005 J. Acoust. Soc. Am.117 3413–23). Although the computational demands of the new theory increase as the number of the semi-cylinders in the arrays and/or the frequency increase, the theory offers an improvement on analytical boss theories since the latter (i) are restricted to non-deterministic (infinite) random distributions of semi-cylinders with spacing/radii small compared to the incident wavelength and (ii) are derived only for plane waves. The influence on prediction accuracy of truncation of the infinite system of equations introduced by the new theory is explored empirically. Laboratory measurements have been made over deterministic random arrays of identical varnished wooden semi-cylinders on a glass plate. The agreement between predictions and measured relative sound pressure level spectra is good both for single deterministic random distributions and for averages representing non-deterministic random distributions. The analytical theory is found to give identical results to those of a boundary element calculation but is much faster to compute.

Characteristics of electric parameters in the microarc oxidation (MAO) process of aluminium alloy at constant voltage were studied by a homemade data collecting system. The experimental results show that (1) the variations of the cathodic and anodic current amplitudes and the effective working current reflect obviously five different stages in the course of treatment and (2) variations of the dynamic forward resistance and electric resistivity of coatings have different stages too, while changes of the dynamic backward resistance and resistivity with treatment time are not evident. During the MAO process, the dynamic forward resistance is not equal to the backward resistance at any time, and the former is generally greater than the latter. Scanning electron microscopy analysis shows that these changes are attributed to variations of the coating porous structure during different treating times.

The temperature-dependent nonlinear current–voltage characteristics of polyacetylene nanofibres measured by Kaiser and Park (2002 Curr. Appl. Phys.2 33) are reinterpreted by the model based on quantum-mechanical phonon-assisted tunnelling theory. Assuming that the tunnelling of the charge carriers from dopant molecules to conducting states of polyacetylene dominates the current flow, experimental data are fitted to the temperature- and field-dependent tunnelling rate of charge carriers from localized states to conducting ones computed using multiphonon-assisted tunnelling theory. A good fit of experimental data with simulated results was found in a wide range of temperatures from 2 to 300 K. The same explanation is given for temperature- and field-dependent conductivity measured by Long et al (2004 Appl. Phys. Lett.84 2205) in polyaniline microspheres. From the fit of experimental data with theory, the density of traps taking part in current flow is derived.

Commercially available neutron image plates (NIPs) consist of a mixture of a powdered x-ray storage phosphor and a neutron converter, both embedded in an organic binder supported on a polymer sheet. The initiation of the storage mechanism in the phosphor is caused by conversion electrons generated in the neutron converter due to neutron absorption and activation and its subsequent decay. The organic binder phase just provides mechanical stability to the NIP but reduces its efficiency through two effects: first by the absorption of low energy electrons and second by introducing an inactive volume fraction to the layer. Avoiding the organic fraction, for example by preparing a ceramic NIP without binder, could increase the efficiency and spatial resolution without a loss in mechanical stability. In the following, two processes for preparation of ceramic NIPs are reported, both delivering ceramic NIPs consisting solely of GdF₃, as the neutron converter and BaFBr : Eu²⁺, as the storage phosphor. The correlation between the sintering parameters and volume fraction of the neutron converter is investigated with respect to high efficiency and high spatial resolution. The generally observed antidromic behaviour between these two quantities was observed in this study also.

Pulsed laser ablation (PLA) in an inert background gas is a promising technique for preparing Si nanoparticles. Although an inert gas is appropriate for preparing pure material, a reactive background gas can be used to prepare compound nanoparticles. We performed PLA in hydrogen gas to prepare hydrogenated silicon nanoparticles. The mean diameter of the primary particles measured using transmission electron microscopy was approximately 5 nm. The hydrogen content in the deposits was very high and estimated to be about 20%. The infrared absorption corresponding to Si–H_n (n = 1, 2, 3) bonds on the surface were observed at around 2100 cm⁻¹. The Raman scattering peak corresponding to crystalline Si was observed, and that corresponding to amorphous Si was negligibly small. These results indicate that the Si nanoparticles were not an alloy of Si and hydrogen but Si nanocrystallite (nc-Si) covered by hydrogen or hydrogenated amorphous silicon. This means that PLA in reactive H₂ gas is a promising technique for preparing surface passivated nc-Si. The deposition mechanism and optical properties of the surface passivated silicon nanocrystallites are discussed.

Friction and wear characteristics of monomolecular layers of self-assembled monolayers (SAMs) with and without perfluoropolyether (PFPE) overcoat were studied using ball-on-disk experiments. Ultra-thin layer of PFPE was dip-coated onto two different SAMs, one with non-reactive terminal group (octadecyltrichlorosilane (OTS)) and the other with reactive terminal group (3-aminopropyltrimethoxysilane (APTMS)), which were formed on Si substrate by self-assembly. The effects of PFPE overcoating on physical and chemical properties were evaluated using contact angle measurement and x-ray photoelectron spectroscopy. For a comparison, PFPE was also coated onto the Si surface and their properties were evaluated. All PFPE modified surfaces were baked at 150°C for 2 h, to investigate the effect of thermal treatment on tribological properties. PFPE coating has shown higher water contact angles irrespective of the SAM surface. Coating of PFPE on both SAM surfaces has lowered their coefficients of friction. PFPE overcoating has shown remarkable increase in the wear resistance when it was coated on reactive APTMS SAM and little increase on OTS SAM. Thermal treatment after PFPE coating onto SAMs further reduced the coefficient of friction to a smaller extent. Moreover, thermal treatment has shown an additional increase in wear-life by approximately 30% in the case of PFPE coated APTMS SAM surface and a decrease in the wear-life in the case of PFPE coated OTS SAM. The reasons for these observed phenomena are explained in terms of the amounts of PFPE bonded or mobile, surface energies of SAMs, uniformity and molecular packing of SAM surfaces.

A previously developed field matching technique for the analysis of a metal disc-loaded circular waveguide, excited in a non-azimuthally varying transverse electric (TE) mode, was used to explore the advantage of the presence of a dielectric in controlling its dispersion characteristics for widening the bandwidth of a gyro-travelling-wave tube (gyro-TWT). The modelled structure, consisting of an axial dielectric insert and dielectric discs alternately placed between metal discs, was analysed considering the propagating and stationary waves in the disc-free and disc-occupied regions, respectively. While the axial dielectric insert gave no specific advantage with respect to dispersion control, the dielectric disc axial thickness, permittivity and periodicity and disc-hole radius quite effectively shaped the structure dispersion. In controlling the structure dispersion, the disc-hole radius, which was not as effective as the disc-periodicity in a conventional metal disc-loaded waveguide, became more effective, though the disc periodicity did not enjoy any additional advantage. The thickness or permittivity of dielectric discs controlled the passband frequencies and hence helped attain operating frequencies of a gyro-TWT. The passband of the lower and higher order modes remaining unchanged by a suitable choice of the structure parameters, a higher order mode, for instance the TE₀₂ mode, gave a better wideband potential than the TE₀₁ mode.

The shock response of a Li₂O–SiO₂ glass ceramic has been studied by the technique of plate impact. The Hugoniot in terms of impact stress and particle velocity has been measured using embedded stress gauges, showing an increasing complexity of behaviour as impact stress increases. Back surface measurements have revealed the presence of a reload signal, indicating the presence of a moving damage front behind the main shock—the so-called failure wave. This has been confirmed by stress gauges mounted so as to be sensitive to the lateral component of stress. Results show that the shear strength ahead of the failure wave is near elastic in its response. Behind the failure wave, shear strength drops, but is still higher than the equivalent results in silicate glasses, suggesting that this material has superior ballistic resistance.

Metallic tin having a dendritic structure was grown within a silica-based gel by an electrodeposition technique. The dendrites were shown to consist of nanoparticles with a median diameter of 31 nm. By giving a controlled oxidation treatment to the composite, a tin core–tin oxide shell nanostructure was induced. The shell thicknesses varied from 1.5 to 4.0 nm depending on the duration of oxidation. The electrical conductivity of the composite structure was shown to be controlled by a small polaron hopping conduction. The nanoshell comprised SnO and SnO₂ phases, respectively, and electrical conduction is believed to arise due to the hopping of electrons between Sn²⁺ and Sn⁴⁺ ions at the interfaces of these two regions. The composite films exhibited a three order of magnitude decrease in resistivity as the relative humidity was varied from 35% to 95%. Electrons from hydroxyl groups of adsorbed water molecules are believed to form localized states at the tin ion sites which cause an increase in electrical conductivity. The nanocomposites also exhibit substantial resistivity changes when exposed to CO, C₂H₅OH and NO₂ gases, respectively. The effect is believed to result from reduction or oxidation of the tin ions by the gas molecules concerned.

We have examined the spectral photoresponse and photoelectrochemical properties of novel highly-ordered TiO₂ nanotube-array photoelectrodes, made by anodization of a titanium foil, as a function of nanotube-array aspect-ratio and propane flame annealing. One geometry consisted of high aspect ratio (∼50) nanotube-arrays 4.4 µm in length, while the other geometry comprised shorter nanotube-arrays, approximately 0.2 µm in length, having a smaller aspect ratio (∼10). The propane flame annealing significantly enhances the visible spectrum absorption of the short nanotubes (NTs), as well as their solar-spectrum induced photocurrents, while not significantly affecting the absorption spectrum of the longer NTs. X-ray photoelectron spectroscopy shows that flame annealing increases the carbon content in the NTs of both geometries. For visible spectrum illumination incident photon to charge carrier efficiencies up to 5% were recorded for the flame annealed samples, while a maximum photocurrent density of 1.5 mA cm⁻² was obtained under simulated solar spectrum AM 1.5 illumination at high anodic polarization in 1 M KOH. Comparative results of the I–V characteristics, photon conversion efficiencies, composition and the surface morphology of these arrays are discussed.

Electron ionization of quadricyclane (C₇H₈) has been examined by Fourier transform mass spectrometry. The ionization produces the parent ion and 21 fragment ions with cross sections greater than 10⁻¹⁷ cm² at 50 eV. The total ionization cross section reaches 2.3 × 10⁻¹⁵ cm² at ∼60 eV. Relaxation of the fragment ion composition by ion–parent molecule reactions mainly proceeds through 14 ion–molecule reactions.

The scaling in the polarization axes of Figures 10(a), (b), (c) should be corrected to read as:

Figure 10(a): 0 to 20 μC cm^-2 instead of 0 to 10 μC cm^-2.

Figure 10(b): 0 to 16 μC cm^-2 instead of 0 to 8 μC cm^-2.

Figure 10(c): 0 to 20 μC cm^-2 instead of 0 to 10 μC cm^-2.

All other conclusions and further results are not influenced by this correction.