Table of contents

The atomic structure of the (310) symmetric tilt grain boundary in Nb and of an interface between Mo and Re is calculated. The calculations are done within the tight binding (TB) approximation to quantum mechanics and are checked carefully against some accurate first-principles calculations in the local density approximation to density functional theory. A non-orthogonal spd electron TB model is tested, but is found to be no improvement on the much simpler orthogonal d-electron model; in particular there is no improvement in the volume dependence of the total energy. The structure of the Nb grain boundary is compared to that obtained by other authors using high resolution electron microscopy. The comparison enables some statements to be made about the nature of the interatomic interactions and especially about the opposing forces that are balanced at the equilibrium grain boundary expansion. The paper includes the first quantum mechanical calculation of a dissimilar metal interface with a view to obtaining the structure of a misfit dislocation and a value for the theoretical strength of the interface. It is concluded that the misfit dislocation in this case has a widely spread core and that the theoretical strength is considerably reduced relative to the bulk crystal.

The study of internal interfaces using spatially resolved electron energy loss near-edge structure (ELNES) appears to allow the determination of local atomic environments and valence states of interfacial atomic species via a simple fingerprint formulism. Using the results of multiple scattering theory, this formulism is investigated in depth for the case of diffusion bonded niobium/-alumina interfaces and conclusions are drawn in terms of the available information content. The prospects for employing ELNES as a probe of the medium-range order present at interfaces are also considered.

This paper presents examples of the chemical bond characterization taken from microanalytical investigations of fibre-reinforced borosilicate glasses. Chemical bonding is examined across the fibre/matrix regions at nanometre resolution by analysing energy loss near edge structures (ELNES), particularly the ELNES. In this context results are presented mainly concerning the chemical bonding of silicon with carbon and oxygen. To identify the bond state of silicon in the interfacial zone the ELNES measured of standard specimens (silicon carbide, dioxide and oxycarbide) was used as a fingerprint. Along a line crossing the interlayer the bonding state of silicon is determined by recording series of EEL spectra. In addition, experimental ELNES results are compared with local densities of unoccupied states calculated by molecular orbital (MO) methods, where the calculations reflect the dependence of fine-structure features on the oxidation state.

An external oxide film is formed on the surface of NiAl as a result of high-temperature oxidation in air. By conventional transmission electron microscopy and diffraction the oxide film was found to be . The relative orientation relationship between the oxide film and underlying substrate is: and . Facets formed along (011)NiAl. Both the facets along (011)NiAl and the natural (001)NiAl oxide interfaces were examined with electron energy loss spectroscopy (EELS). The electron energy loss near-edge structure (ELNES) of Ni L and O K edges were examined. From the changes observed, the terminating plane is determined for both interfacial geometries. For the (001)NiAl/(004) interfaces, the oxide planes consist of both Al and O atoms, whereas the metal could be either Ni or Al terminating. Both the O K and Ni L ELNES supported the theory that aluminium is the terminating plane in the metal. For the interfaces the metal planes consist of Ni and Al atoms, whereas the oxide planes could be Al or O terminating. Again, the O K and Ni L ELNES supported the theory that the terminating plane in the oxide is aluminium.

We report results of first-principles molecular orbital calculations using the discrete-variational method on a model cluster of -quartz . Self-consistent calculations of the cluster which include a half-filled core hole, i.e. at Slater's transition state, are made in order to evaluate the effect arising from the presence of a core hole associated with the electron energy-loss process. The presence of a half-filled Si-2p core hole does not change the unoccupied Si-3s/3d partial density of states (PDOS) significantly. On the other hand, a remarkable core hole effect appears on O-2p PDOS when a half-filled O-1s hole is introduced. The calculated PDOS at the transition states is in good agreement with the electron energy-loss near-edge structures (ELNES) at both the edge and O-K edge. Absolute transition energies at both edges are also reproduced to within an error of 3 eV when spin-polarization during the transition is taken into account. The photoabsorption cross sections (PACS) are calculated from first principles and are compared with the PDOS for the corresponding electric dipole transitions. The difference between the PACS and the PDOS is found to be small at both the ground state and the Slater's transition state in the present calculation.

Grain boundaries in copper doped with small amounts of bismuth have been examined by spatially resolved electron energy loss spectroscopy (EELS). The electron energy loss or x-ray absorption near edge structure (ELNES or XANES) yields information on the bonding state of the probed atoms. A white line was detected near the threshold energy of the bulk absorption edge when the electron probe is located within 1 nm of the grain boundaries. This spectroscopic feature provides direct evidence that the grain boundary influences the local electronic structure and may have implications on how Bi embrittles the grain boundaries in Cu. Effects are only observed in those boundaries where the presence of Bi was confirmed using energy dispersive x-ray EDX spectroscopy. Furthermore, no evidence was found to indicate, within detection sensitivity limits, any co-segregation of oxygen to these boundaries.

Optical and electron-energy-loss spectroscopies are well established methods of probing the electronic structure of materials. Comparison of experimental spectroscopic results with theory is complicated by the fact that the experiments extract information about the interband transition strength of electrons, whereas theoretical calculations provide information about individual valence and conduction bands. Based on the observation that prominent features in the optical response arise from critical points in the joint density of states, critical point modelling was developed to gain an understanding of these spectral features in terms of specific critical points in the band structure. These models were usually applied to derivative spectra and restricted to the consideration of isolated critical points. The authors present a new approach to critical point modelling of the undifferentiated spectra and interpret the model in terms of balanced sets of critical points which describe the interband transition strength arising from individual pairings of valence and conduction bands. This approach is then applied to achieve a direct, quantitative comparison of theoretical and experimental data on aluminium nitride.

Valence electron energy-loss spectroscopy in a dedicated scanning transmission electron microscope has been used to obtain the interband transition strength of bulk . The interband electronic structure was obtained from critical point modelling. Comparison to established results from vacuum ultraviolet spectroscopy was used to improve the analysis of the energy-loss spectra and quantitative agreement between both methods was obtained. Spatially resolved measurements of a near- tilt grain boundary in were analysed with the same procedure. This revealed an increase in the electron occupancy of the O 2p valence band to conduction band transitions which can be associated with an increased ionic character of the bonding at the grain boundary with respect to the bulk material. This is consistent with the results of other studies which determined the atomic structure and then calculated the electronic band structure of the same near- tilt grain boundary. Quantitative analysis of valence electron energy-loss spectroscopy can be regarded as a new electronic structure tool for application to localized structures such as internal interfaces in our quest to better understand their micro- and macroscopic properties.

The electronic structure and the optical properties of a near- grain boundary in are studied by means of first-principles calculations based on a structural model constructed by Kenway. Results on the orbital-resolved partial density of states are presented for the grain boundary model and also for a perfect bulk supercell model containing the same number of atoms. An effective-charge calculation indicates an increased ionic character for atoms in the grain boundary region which is attributed to the distorted bonding pattern and a decrease in coordination number. The calculated optical properties show very similar results for the grain boundary model and the bulk supercell model. The electron energy-loss spectra are consistent with the recent experimental data on the near- grain boundary obtained by spatially resolved valence electron energy-loss spectroscopy.

The application of scanning transmission electron microscopy (STEM)-based techniques, atomic number (Z)-contrast imaging, electron energy-loss spectroscopy (EELS) and convergent beam electron diffraction (CBED) allows determination of chemical compositions at internal interfaces of semiconductor heterostructures as well as determination of local crystalline properties such as strain, relaxation effects or ordering with high lateral spatial resolution. Z-contrast images recorded at internal heterostructure interfaces exhibit atomic spatial resolution in combination with qualitative chemical information. EELS can be used to record the chemical composition quantitatively but with slightly decreased spatial resolution compared to Z-contrast imaging. However, EELS results can be used to calibrate the Z-contrast. Thus, the combination of both techniques can give quantitative information on the chemical composition at interfaces from monolayer to monolayer. The interpretation of Z-contrast imaging is further supported by Z-contrast simulations. Examples demonstrating the performance of Z-contrast imaging (and simulation) and EELS are given for technically relevant III - V heterostructure interfaces.

Additionally, we used CBED in order to investigate the crystalline properties of cross sectional specimens from ternary and quaternary heterostructures of on InP or GaAs substrates. Even when using subnanometer electron probes, the quality of the obtained CBED patterns is sufficient to perform local strain measurements with 1 nm spatial resolution and with a sensitivity of . This is proved by a CBED linescan across an alternately strained quaternary superlattice. CBED patterns recorded at interfaces directly exhibit symmetry violations, which are not yet understood satisfactorily. Therefore, further simulations are necessary for a detailed quantitative understanding of CBED patterns from internal interfaces.

The combination of Z-contrast imaging, EELS and CBED allows the extensive quantitative characterization of semiconductor heterostructures and interfaces with the necessary lateral spatial resolution down to the monolayer range. STEM-based techniques are therefore an important tool for heterostructure and device development.

A crucial first step in understanding the effect that internal interfaces have on the properties of materials is the ability to determine the atomic structure at the interface. Because interfaces can contain atomic disorder, dislocations, segregated impurities and interphases, sensitivity to all of these features is essential for complete experimental characterization. By combining Z-contrast imaging and electron energy loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope (STEM), the ability to probe the structure, bonding and composition at interfaces with the necessary atomic resolution has been obtained. Experimental conditions can be controlled to provide, simultaneously, both incoherent imaging and spectroscopy. This enables interface structures observed in the image to be interpreted intuitively and the bonding in a specified atomic column to be probed directly by EELS. The bonding and structure information can then be correlated using bond-valence sum analysis to produce structural models. This technique is demonstrated for , and symmetric and and asymmetric [001] tilt grain boundaries in . The structures of both types of boundary were found to contain partially occupied columns in the boundary plane. From these experimental results, a series of structural units were identified which could be combined, using continuity of grain boundary structure principles, to construct all [001] tilt boundaries in . Using these models, the ability of this technique to address the issues of vacancies and dopant segregation at grain boundaries in electroceramics is discussed.

Grain boundary (GB) doped exhibits interesting electroceramic phenomena including varistor and barrier layer capacitor behaviour. We present here our investigation of GB acceptor-doped using analytical electron microscopy including electron holography. Mn was diffused into sintered polycrystalline to attain GBs which are rich in Mn. The presence and spatial extent of Mn at the GBs were analysed using x-ray emission spectroscopy (XES) and parallel electron energy loss spectroscopy (PEELS). The valence state of Mn was determined using PEELS to be predominantly +2. Finally, transmission high-energy electron holography was utilized to directly image and quantify the electrostatic potential and associated space-charge across the GBs directly. The holography results reveal a negatively charged GB with positive space-charge, indicating that Mn with a valence of +2 resides as an acceptor dopant on the Ti site at the GB core. The barrier height and local charge density distribution, including the Debye length, of the double Schottky barrier at the GB are derived from these holography results. This investigation demonstrates the usefulness of electron holography as a bulk-sensitive technique to probe the statics and dynamics of electrostatic field distribution and electrical charge across interfaces in technologically useful materials, and the need to employ diverse analytical techniques for such an investigation.

The aim of this paper is to show how old results obtained for the interpretation of transmission electron microscopy observations of reverse-biased p - n junctions can be updated and used for the case of electric fields arising at charged interfaces. In particular the effect of the external field on holographic and Fresnel images is investigated.

Optical second-harmonic and sum-frequency generation at surfaces and interfaces is discussed and recent work reviewed. Examples from well-characterized interfaces are emphasized and particular attention is paid to spectroscopic studies which have recently become simpler due to the availability of tuneable broad band laser sources. It is shown that the techniques are now well understood at the phenomenological level and, although theoretical calculations are proving to be difficult, interfaces not accessible to conventional surface techniques can now be studied with some confidence.

Surface and buried layers of ternary silicide were fabricated by implantation of iron and cobalt into (100) silicon wafers. For the surface layers two sets of samples with different iron to cobalt ratios were prepared. In the first set, cobalt was implanted first followed by iron and the implant order was reversed in the second set. In all cases the total implanted dose (Fe+Co) was kept constant. For the buried ternary silicides two samples were prepared with equal doses of iron and cobalt. In the first sample, cobalt was again implanted first with the implant order being reversed for the second sample. The physical properties of the synthesized layers were investigated by Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS) and cross sectional transmission electron microscopy (XTEM). The results indicate that the implantation order is critical to the subsequent development of the synthesized layer. The surface layers with iron implanted first were non-crystalline and showed no significant improvement of crystallinity with increasing anneal temperature. However, the surface layers with cobalt implanted first exhibited a large improvement of crystal quality with increasing anneal temperature. Segregation into separate iron- and cobalt-rich layers was also observed for surface layers where cobalt was implanted first for Co:Fe . The crystalline quality of the buried layers was also determined by the implant order, in a similar way to that for the surface layers.

Penetration depth is one of the most important factors critical to the quality of a laser weld. However, no on-line, non-destructive method exists by which to inspect this quantity. Indirect, model-based estimation schemes are feasible solutions for monitoring laser welding processes. In this paper, a model for estimating penetration depth based on a 2D heat conduction model and a conical keyhole assumption is developed. This model relates the penetration depth to the incident power and the Péclet number, which is a function of the welding speed, the keyhole radius and thermal diffusivity. The Péclet number is determined by measuring the weld width on the top surface. The model is validated by a number of laser welds made to join a low-carbon steel hub and plate assembly using a 5 kW laser with different combinations of power and speed. The results show that the proposed model is consistent with the experimental data and is computationally efficient. Therefore, this model is suitable as a basis for model-based, on-line depth estimation schemes.

Bragg gratings have been written within MCVD germanosilicate preform slices using CW laser light at 244 nm. Afterwards, scanning light interferometry was used to perform a 3D imaging analysis of the sample surface topography. The results show that the same process (namely densification) pointed out in a previous work in which we used UV pulsed exposure of preform slices is also active here. A simplified model which assumes that the UV-induced periodic corrugations result from both permanent and elastic strains, is presented. This model accounts not only for a large part of the measured refractive index change but also for the localization of the UV-induced birefringence along the grating wavevector. It also gives a satisfactory interpretation of the observations made by Fonjallaz et al, according to whom grating inscription within a germanosilicate fibre increased the axial tensile core stress.

This paper presents a theoretical study for modelling the thermoelastic excitation of transient Lamb waves propagating along the principal directions in an orthotropic plate. The normal mode expansion method is employed to express the transient displacement field by a summation of the antisymmetric and symmetric Rayleigh - Lamb wave modes in the surface stress-free orthotropic plate. This method is particularly suitable for waveform analyses of transient Lamb waves in thin sheet materials because one needs only to calculate contributions of the lowest few antisymmetric and symmetric modes. The dispersion characteristics and the transient Lamb waveforms excited by a pulsed laser in machine-made paper are analysed numerically and discussed in detail and attention is focused on the influence of the elastic stiffness constants. This work provides a quantitative analysis for noncontact and nondestructive detection of the elastic stiffness properties of the machine-made paper by the laser-generated Lamb wave technique.

The ionized cluster beam deposition of Ag-tetracyanoquinodimethane (TCNQ) and -TCNQ thin films is reported. These thin films were characterized by transmission electron microscopy and electron absorption spectroscopy. The microstructure of the thin films and the formation of a -TCNQ thin film were observed. Furthermore, the electrical properties of the thin films were measured and both films were able to exhibit electrical bistability. The conduction mechanism of the polymer thin films with Ag and is discussed.

The electrical properties of RF magnetron-sputtered aluminium-doped zinc oxide (AZO) films are studied. It is seen that the properties are closely related to their structural properties and doping incorporation. The highly conductive milky AZO films with a wedge-like surface consist of very small crystal grains. It is interesting to note that texturization is obtained in this case at a film thickness less than . At a substrate temperature of , texturization occurs and the resistivity obtained after hydrogen treatment is . This result is very significant and it may accelerate the application of inexpensive AZO films in hydrogenated amorphous silicon solar cells.

The adhesion of micronized Salmeterol Xinafoate to various surface materials has been investigated by the centrifuge technique. The adhesion of the drug to these materials used for manufacture and storage of interactive mixtures of the drug and milled lactose monohydrate depends on different properties of the surfaces. A longer contact with polyvinylchloride, polyethylene or aluminium surfaces, or a contact with these surfaces under mechanical pressure should be avoided because the adhesion force between the drug and these surfaces is much higher than between the drug and excipient particles. Hence detachment and a consequent loss of drug in the formulation could occur. Such a problem does not appear to exist for the contact with polyhydroxymethylene surfaces. Characteristics of the surface materials such as the surface free energy (acid - base concept), surface roughness and Young's modulus were determined and related to the experimental results. The work of adhesion appeared to have a very important influence on the adhesion forces measured. About 20% of the work of adhesion was due to acid - base interactions. The larger the work of adhesion, the stronger was the adhesion between the particles and the surfaces in contact. Surface roughness reduced the adhesion force, and stiffer materials (having a high Young's modulus) were found to have a lower adhesion force to the drug particles.

The important properties of thermal ovens for producing intense beams of F atoms by thermal dissociation of are analysed. After reviewing previous constructions a new source made of a single crystal of is described and characterized. This source has been tested for more than 3000 h at temperatures up to with a mixture of 10% in Ar at pressures up to 12 bar. A degree of dissociation of 50% and a F atom beam velocity spread of about 7% were achieved.

A study of numerical modelling and experiments of a soft rolling nip contact is described. A power law equation was found to be adequate in modelling the positive pressure zone in the nip, but was not capable of describing the film rupture pressure adequately. The index and exponent in the power law were noted to affect nip behaviour significantly and similarly. A shear rate cut-off model was used successfully to avoid singularity in the viscosity field at the mid-thickness and was found not to affect the behaviour in the nip significantly.

The cyclic pressure - tension records as reported for the dynamic stressing of liquids by the `tube-arrest' and `bullet-piston' methods are explained in terms of the growth of cavitation bubbles. This explanation, which invokes a hydrodynamic argument based on incompressible theory, is shown to accord with experimental results and clarifies previous indications in the literature.

We report, we believe for the first time, experimental values of the rotational and vibrational temperatures of in an operative laser. The device under study is a DC-excited fast-axial-flow laser and can be viewed as a scaled down version of an industrial laser for cutting and welding. The gas inlet section is optimized for gain symmetry. The laser operates at a maximal electro-optic efficiency of 26%, reaching output from a 19 mm bore discharge at 24%. An infrared tuneable diode laser spectrometer was adapted to allow transverse probing of the discharge. The results show the significant cooling effect of the intra-cavity radiation intensity on the vibrational modes, and the observed gas temperature drop associated with the extraction of laser power is consistent with the mass flow through the discharge.

The ratio of the transverse diffusion coefficient to the mobility, , has been experimentally determined for ions drifting in Ne and Ar gases, in the presence of a uniform electric field. Results at 303 K are reported for electric field-to-neutral gas number density ratio E/N range 5 - 600 Td, with an overall accuracy of %. The results were effectively corrected for longitudinal end effects present in the drift tube. In addition, Monte Carlo simulation (MCS) calculations were performed for the mobility and for transverse and longitudinal diffusion coefficients using respectively the Koutselos, Mason and Viehland (KMV) interaction potential and a modified Tang - Toennies (MTT) interaction potential as input. The accuracy of the MCS calculations is estimated to be within 1% for K, 2% for and 3% for . Comparisons of the MCS results with available experimental data give an indication of the validity and accuracy of the respective assumed interaction potential at different interatomic distances. The calculated results did not reproduce the experimental data very well, suggesting that both potentials should be modified.

The different treatments of diffusion that have been used in published numerical models of plasmas in local chemical equilibrium (LCE) are examined. Four approximate formulations are identified. These are compared with the combined diffusion coefficient method, which is equivalent to the full multicomponent diffusion coefficient treatment when the assumption of LCE is made. Diffusion coefficients and diffusive mass fluxes are calculated using each formulation for a number of representive cases involving the diffusion of copper vapour and nitrogen in an argon plasma. The different formulations are further used in a two-dimensional numerical model of a free-burning arc in a gas mixture, and the predicted compositions and temperatures are compared with measured values. Serious deficiencies are identified in the approximate formulations, both in the calculation of the diffusion coefficients and, more importantly, in the equation used to derive the diffusive mass flux from the diffusion coefficients. Use of the combined diffusion coefficient method is found to give good agreement with the measurements.

A fast-rise-time capillary discharge was designed and investigated as a possible source of amplified spontaneous emission in the extreme ultraviolet spectral range. The capillaries were made of or with radii in the range 0.25 - 1 mm and lengths from 1 - 5 cm. Discharge currents of up to 15 kA and current rise-times down to 20 ns could be achieved. Spatially resolved spectra could be recorded with a time resolution of 5 ns. During the cooling phase an increase in the intensity of the H-like Li III 729 Å line could be found, accompanied by a decrease in spatial divergence. By a length variation of 3 - 5 cm of capillaries with 0.5 mm radius an indication of the gain of the Li-like O VI 520 Å line could be obtained.

The spark decomposition of and of mixtures was studied principally at a gas pressure of 200 kPa. The sparks were generated between a point and a plane either under 50 Hz ac voltage (0.09 J per spark) or by discharging a capacitor (3.59 J per spark). Our attention was only focused on the gaseous by-products: and which were assayed by gas chromatography. The last three compounds were principally observed under the higher energy sparks. Their yields were studied varying the cell preparation technique, the metal constituting the plane electrode (aluminium, copper, stainless steel) and the concentrations of two additives, (between 0 and 1%) and (between 0 and 0.2%). The cell preparation procedure had a strong effect on the formation of all products except ; the yield was for example multiplied by when the cell was carefully dried and outgassed and with an aluminium electrode. The aluminium led, whatever the procedure used, to the highest levels of products.

Under the high-energy sparks an increase of the oxygen content of or of the mixture led to a decrease of the and formation rates and to an increase of that of the other compounds. An increase of the content had very little effect on production and led to increased production of and and to a lowering of the formation of other compounds. Under the low-energy sparks the addition of to or to the mixture led to a lowering of the and yields like under high-energy sparks and to an increase of (which became observable) and of . Addition of water resulted in an increase of the and yields, in a lowering of and had no effect on which remained unobservable. Finally it should be noted that the addition of 50% of to the had very little effect on the rates of formation of the gaseous by-products except under low-energy sparks where the mixture led to lower production rates for and .

It is shown that a laser beam (, ) of 17 ns pulse duration transversely directed on the axis of a parallel-plates device far below the breakdown threshold produces a current impulse in the external circuit. The analysis of the electrical signals, based on the Ramo - Shockley theorem, allows one to estimate the number of electrons moving in the gap and their velocity. It is shown that this velocity is characterized by two components: the drift velocity depending on the reduced electrostatic field and the other resulting from the spatial distribution of electrons. Even if is estimated, experiments show that, for pressures lying in the range 100 - 600 Torr, the physical processes responsible for the production of electrons when the laser beam crosses the gap are not only multiphoton transitions.

In the temperature range 1000 - 10 000 K, the composition and thermodynamic properties of ablated vapours of PMMA, PA6-6, PETP, POM and PE have been calculated with the Gibbs free energy minimization method. We indicate the formulae used in this method. We discuss the results and deduce the specific behaviour of POM vapours.

The two-dimensional expansion of a current carrying plasma jet in the interelectrode gap of a vacuum arc with an axial magnetic field is analysed by finding the steady state solution of the fully ionized plasma in the hydrodynamic approximation. Two models are presented: (1) expansion into a duct with known geometry and (2) free jet expansion. The first approach models the plasma jet expansion with a conical shape. In the second model the geometric position of the free boundary was determined by the free hydrodynamic jet expansion into vacuum without and with the influence of a magnetic field.

In the case of plasma expanding into a conical guide, it was found that the flow field in the near-axis region does not depend on the cone angle for cone angles . The radial velocity becomes comparable to the axial velocity due to the expansion, depending on the cone angle and the initial axial velocity.

A model of the free boundary plasma expansion was developed, based on the jet-like (i.e. axial velocity larger than the radial velocity) plasma flow in the vacuum arc near the cathode spot. The free jet boundary was calculated by solving the equations for the normal and tangential velocity components at the free boundary. It was found that the plasma jet had a conical shape, and for axial distances 3 - 4 times greater than the initial jet radius, the radial velocity becomes comparable with the axial velocity if no magnetic field is imposed. Imposition of a magnetic field reduces the radial component of the plasma velocity. The streamline angle is about for a 0.001 T magnetic field and about for a 0.01 T magnetic field. The plasma remains quasi-neutral in all regions except in the space charge boundary layer, where an outward directed electric field appears for low magnetic fields, and an inward directed field is present for strong magnetic fields.

Bead-like plasmas produced by a laser have guided and triggered electrical discharges in air gaps. The physical parameters (electron density, electron temperature, geometric structure) of the laser-produced plasmas have been measured using spectroscopy and laser interferometry. We compared the results of these measurements with the characteristics of laser-guided discharges, and found that the mechanisms of the guiding ability of the laser can be explained by the behaviour of the plasma as a conductor (metal ball model). We conducted model experiments of the laser-guided discharges using small metallic balls. The features of the discharge guided by metal balls were similar to those guided by laser-produced plasmas. We thus concluded that the behaviour of the plasma plays an important role in triggering and guiding the discharges.

The transient current technique has been used to examine current pulses in semi-insulating (SI) GaAs and comparisons have been made with calculated current pulse shapes obtained by analysing both theoretical and measured electric field shapes. This is the first time that this technique for examining such bulk behaviour has been used with SI GaAs. The results show that the form of the weighting field required to reproduce the experimental current pulse shapes in this case is not the expected 1/d, where d is the active region width, but rather is closer to , where E is the electric field across the detector due to the applied bias and is the bias necessary for the active region to extend fully across the detector.

Electrical switching behaviour of melt-quenched and glasses have been studied in the I - V mode, using a constant current source with incremental current steps. The samples are found to stay in the high-resistance OFF state up to a critical voltage (corresponding to a critical current ). Above , the sample switches to a low-resistance ON state with a stable negative resistance region, and lock-on to this state even if the current is reduced to zero. If the compliance voltage is turned off and switched on again, the switching transient introduced is found to reset the glasses back to the OFF state. The samples are found to switch again. The switching - resetting - switching cycle is repeated 50 times, with % variation in the switching voltages.

A model is presented to explain the effects of photoconductivity on the transport properties of grain boundary junctions recently measured. The model relies on the scaling behaviour of the nonlinear I - V curves near the transition temperature with its relevant critical exponents. The effects of increased disorder due to photoexcitations in the chain plane on the resistivity of an artificial grain boundary junction were examined. The results are in good agreement with recent reported measurements on thin films.

Longitudinal and shear velocities are measured for five polycrystalline Y - B - C - O samples presenting different porosities. The experimental data are compared with the velocity versus porosity curves calculated according to three different methods and a discussion is presented on the reliability of these methods in estimating the porosity effects, both at low and at high void concentrations. For the calculation several sets of the nine elastic constants of Y - B - C - O monocrystals are used. A remarkable good agreement between our data and those obtained from the single-crystal constants is observed, when the method of Sayers and Smith is used to take porosity into account.

In this paper, the contribution of leakage to the hysteresis curve in thin film ferroelectric capacitors is analysed quantitatively by applying a very simple circuit model and experiment. Based on our previous analysis of current - voltage characteristics in thin film ferroelectric capacitors, the deformed hysteresis loops due to leakage are calculated with respect to various barriers and frequencies, and are verified with our laser ablated thin film capacitors. Some interesting phenomena, such as gap in hysteresis curves, vertical drift of hysteresis loops, etc, are discussed.

The macroparticle content of titanium films deposited using a steered vacuum cathodic arc has been investigated. It has been found that the macroparticle number decreases with increasing steering magnetic field strength, and experimental results are found to be consistent with the model in which the number and mass of macroparticles arising from a cathode spot are proportional to the cathode spot volume.

Solidification characteristics of metastable and stable from melts were systematically investigated by x-ray diffraction, differential thermal analysis and thermogravimetry. The experimental results show that the solidification either of metastable or of stable directly from melts appears to be dependent both on the melt temperature and on the cooling rate. In general, high melt temperatures and high cooling rates tend to solidify metastable . Otherwise, low melt temperatures and low cooling rates tend to solidify stable . To produce stable single-crystal , the melt temperature should be controlled to be less than and the cooling rate near the solidifying temperature should be less than .

Recent holographic time-of-flight experiments in photorefractive polymers have shown the space charge field to depart from its expected behaviour. We show that this discrepancy arises due to the influence of disorder on the charge transport process.

It is shown that the rapid pinching of the cathodic plasma jet by its own magnetic field causes the ions to accelerate and to increase their kinetic energy from to if the current enhancement occurs before the plasma jet has reached the anode. This process is quite similar to that of fast jet formation from the collapse of a cylindrical metal liner driven by converging detonation waves. Energetic ions may be produced only in after the onset of breakdown of the vacuum, with being the velocity of the unpinched plasma jet and mm the distance from the cathode at which the magnetic pressure becomes similar to the kinetic pressure of the plasma.

Since poly (ethylene naphtalene-2,6- dicarboxylate) (PEN) gives high performance films with key properties superior to those of PET polyester films, it has been argued that it could be used as a substitute for the latter in a large number of applications. In this paper more information on the electrical properties of this material are given and compared to those of PET. These properties, i.e. complex permittivity and breakdown voltage, are investigated under controlled and uncontrolled environments and before and after thermal ageing at a temperature higher than the thermal rating of each material.

The direct longitudinal piezoelectric effect in lead zirconate titanate, barium titanate, bismuth titanate and strontium bismuth titanate ceramics was investigated with respect to the dependence on the amplitude of an alternating pressure. At low alternating pressure amplitudes, the behaviour of the piezoelectric charge and the piezoelectric coefficient may be explained in terms of the Rayleigh law originally discovered for magnetization and magnetic permeability in ferromagnetic materials. The charge versus pressure hysteresis loops measured for piezeoelectric ceramics may similarly be described as the Rayleigh loops. The results presented show that the Rayleigh law can be applied to irreversible displacement of several types of non- ferroelectric domain walls and imply universal validity of the Rayleigh law for displacement of ferromagnetic, ferroelastic and ferroelectric domain walls.

This issue of Journal of Physics D: Applied Physics sees the launch of a new section dedicated to the applied aspects of interface and surface science. The articles included in the section, in this, and in forthcoming issues reflect the growing practical importance of this field. The development of techniques for controlling growth and investigating characteristics of interfaces and surfaces has led to the creation of a wide range of devices whose performance may be highly dependent on interface and surface properties.

With the introduction of the Applied Interfaces and Surfaces section we hope to provide a forum tailored to the needs of scientists concerned with all aspects of this field, thus reflecting the interdisciplinary nature of the subject. The section is intended to complement the Surface and Interface Science section of Journal of Physics: Condensed Matter, which covers the fundamental aspects of this field.

The Applied Interfaces and Surfaces section particularly invites papers on the topics listed below. Emphasis will be given to research relating to practical techniques for the growth, analysis and characterization of surfaces and interfaces, and on the effects of surface and interface properties on devices and applications.

• Practical aspects of the growth of interfaces, surfaces and thin films

• Nanoscale mechanical properties of interfaces and residual stresses

• Thermal treatment of surfaces

• Techniques for the preparation of surfaces

• Techniques for the analysis and characterization of surfaces and interfaces, such as AES, SIMS, STM, TEM, AFM, etc

• Surface modification using plasmas and other techniques

Given its aims and scope, I am particularly pleased to launch this new section with a collection of papers from the recent International Symposium on Atomic Bonding at Internal Interfaces: Modelling and Spectroscopy. This meeting was held at the conference site of the Max-Planck-Gesellschaft and the conference organizers have kindly provided an introduction to the resulting papers that can be found on the next page. This collection of papers demonstrates that the combination of modern experimental techniques with sophisticated theoretical modelling is providing the understanding of internal interfaces which is a prerequisite for obtaining control of their properties.

In addition to a number of regular research articles, also appearing in this first issue is an Invited Article by John McGilp, the scientist who coined the generic term, EPIOPTICS, for the family of optical probe techniques that have considerable potential for the study of interfaces and surfaces. I trust that you will enjoy this first appearance of the Applied Interfaces and Surfaces section. I believe that this is a field of great importance and I am sure that the new section will bring together more high quality research in the forthcoming issues of the journal.

Peter Weightman Editor, Applied Interfaces and Surfaces

The International Symposium on Atomic Bonding at Internal Interfaces: Modelling and Spectroscopy was held from 24 - 28 April 1995 at Schloss Ringberg, near Tegernsee, south of Munich, Germany. As the conference site of the Max-Planck-Gesellschaft, Schloss Ringberg provided an ideal location for this symposium which involved forty leading scientists from all over the world. In a pleasant, but somewhat secluded environment, the participants could entirely concentrate on the exchange and discussion of scientific ideas.

The oral presentations were attended by all participants and intensive discussions were held after presentations, during coffee breaks, meal times and in the evenings. The meeting brought together experimentalists and theorists who have made significant contributions to our understanding of internal interfaces. Among the subjects discussed were a variety of experimental methods, in particular spectroscopy, used to gain information on localized electronic structure. On the theoretical side, several researchers explained how the modelling of complicated interface structures has now become possible. Furthermore, some key presentations addressed issues relating to surface science, reflecting our more developed understanding of this field.

Both experimental investigations and theoretical calculations provide new opportunities to aid our understanding of bonding at internal interfaces from a spatially resolved perspective at (near) atomic dimensions. With the help of these tools and analytical approaches it is now possible to couple quantitative information about electronic structure with real space images at previously unapproached resolutions. These methods can be improved by the detailed analysis of the discrepancies between experiment and calculation.

The most actively pursued areas of research into atomic bonding at internal interfaces are well represented in this special issue of Journal of Physics D: Applied Physics. The experimental work of Bruley uses energy-loss near-edge structure (ELNES) to study the atomic coordination and bonding at interfaces; Brydson has worked on the quantitative modelling of these results. Another major area concerns the use of valence electron energy-loss spectroscopy (VEELS) and the experimental work of Müllejans uses this to uncover information on interband transitions and interface band structure. The theorists have also been making advances, such as the work of Mo to calculate interband transitions from first principles. Z-contrast imaging, such as that done by Browning, is another important area covered where individual atom column imaging and spectroscopy exposes a new level of understanding of the atomic and electronic structure of interfaces. The conference focused on progress made in these areas, and we look forward to witnessing even greater progress from these new techniques in forthcoming years.

By bringing together experts from such a variety of different fields many new contacts were made and we are sure these will be exploited in future research. The participants who presented new, original research were encouraged to submit manuscripts of their work to this journal. All of the papers were subjected to the usual refereeing procedures and in all, the conference yielded thirteen articles which appear at the beginning of this issue.

The International Symposium on Atomic Bonding at Internal Interfaces: Modelling and Spectroscopy was jointly funded by the Deutsche Forschungsgemeinschaft and the Max-Planck-Gesellschaft.

Manfred Rühle, Harald Müllejans, Joachim Mayer, RogerH French and Rishi Raj

Conference Organizers