Table of contents

The magnetic properties of a carbon nanotube synthesized by chemical vapour deposition have been demonstrated in magnetic force microscopy using a metal current ring, which produces a well-defined magnetic field. The effective dipole and monopole moments of the metal particle at the end of the nanotubes are 1.8×10^-4 emu and 16 emu/cm, respectively. These values are very close to that of the conventional tip. This result suggests that the capped nanotube tip is useful for a magnetic force microscopy tip in spite of the minimal size of the particle.

We present the first results of the two-step growth of the quasi-bicrystal structures containing interblock boundaries in epitaxial zinc oxide layers on α-sapphire. Using the intermediate buffer layer technique we have successfully prepared highly oriented layers of (110)ZnO and (0001)ZnO with clearly pronounced boundaries between blocks on the same (102)Al₂O₃ substrate surface. The high quality of the quasi-bicrystal structures was confirmed by x-ray diffraction and reflected high-energy electron diffraction measurements.

The terms micro-thermal analysis and micro-spectroscopic analysis are used to include any form of localized characterization or analysis combined with microscopy that uses a near-field thermal probe to exploit the benefits of using thermal excitation. Individual regions of a solid sample are selected by means of surface or sub-surface imaging (atomic force microscopy and/or scanning thermal microscopy), so as to add spatial discrimination to four well-established methods of chemical fingerprinting, namely thermomechanometry, calorimetry, spectroscopy and analytical pyrolysis. We begin by describing the state of the art of scanning microscopy that uses resistive thermal probes, followed by an account of the various techniques of micro-thermal analysis.

Modern materials technology is increasingly concerned with the control of materials at the mesoscale. The ability to add an extra dimension of, say, chemical composition information to high-resolution microscopy, or microscopic information to spectroscopy, plays an increasingly useful part in applied research. Micro-thermal analysis is now being used commercially to visualize the spatial distribution of phases, components and contaminants in polymers, pharmaceuticals, foods, biological materials and electronic materials. This review outlines various applications that have been described in the literature to date, the topics ranging from multi-layer packaging materials and interphase regions in composites, to the use of the technique as a means of surface treatment.

A rigorous optical model of a multi-quantum-well nitride laser has been used to investigate the impact of its buffer layer located between the substrate and the laser structure on room-temperature laser operation. The above impact is usually neglected, whereas it has been demonstrated that the presence of this layer may stimulate essential mode modification or even mode transformation. Therefore a buffer layer may have a considerable influence on laser performance. In particular, it may enhance the generation of unwanted first-order modes. Therefore, to preserve fundamental-mode laser operation, a buffer layer should not be too thick and/or should not exhibit too high a refractive index. In addition, buffer layers may be intentionally designed to enhance mode selectivity.

This paper presents an advection-diffusion model that describes normal grain growth in `size-sides' space. Ordinary differential equations governing the self-similar distributions at the steady state of normal grain growth are derived. By solving numerically the continuity equations (time-dependent) and the corresponding ordinary differential equations (time-independent), we get the self-similar grain size distributions in time-dependent and time-independent form. The two sets of distributions have nearly the same shape, confirming the self-consistency of the model. Some comparisons with other models and simulations are given.

MBE growth of MgSe thin films on ZnSe/GaAs(001) substrates is studied. Insight into the formation mechanism of this type of surface, the interface, and the bulk has been provided by photoemission spectroscopy. Detailed lineshape analyses of Se, Mg, and Zn core levels have been performed, following their evolution as MgSe is deposited. Shifts for all core levels are very small during the deposition, indicating band bending is virtually negligible under the present growth conditions. After deposition of 1.7 nm of MgSe, emission from the substrate is fully attenuated. A value of 0.44 nm is obtained for the inelastic scattering mean free path for electrons with a kinetic energy of around 65.8 eV in the MgSe thin films. Annealing the sample at 500 °C for 30 min results in full desorption of the thick Se layer formed on the MgSe surface. The intensities of the MgSe core level emissions obviously decrease. In contrast, the ZnSe peak reappears. Emission from metallic Mg is also observed. Annealing at 500 °C for 30 min more results in the desorption of nearly all the MgSe layer, whereas the intensity of the bulk ZnSe emission remains almost unchanged.

A scratch-resistant improvement of sol-gel derived nano-porous silica films by a base/acid two-step catalysis is reported. The silica films were prepared with the two-step catalytic sol-gel process and a dip-coating method, and then post annealed in air and a mixed gas atmosphere. The films were characterized with FE-SEM, AFM, TEM, XPS, FTIR, an ellipsometer, and an abrasion test. With the post annealing, the frequency shift of the FTIR absorption ω₄(TO₃) peak of the films to a lower wavenumber results from a decrease in the average Si-O-Si bridging angle. An increase in the full-width at half-maximum of the ω₄ peak is ascribed to a wide distribution of the bridging angle because of formation of strained Si-O-Si bonds caused by the post annealing. XPS analysis shows that the effect of the mixed gas annealing on the binding energy and full-width at half-maximum (FWHM) for Si (2p) and O (1s) peaks is attributed to the further condensation reaction of the films resulting from the disappearance of the OH groups. The abrasion and adhesion tests indicate that the two-step catalysis obviously improves the scratch resistance and adhesion of the films, and that the mixed gas treatment further strengthens the silica network. The increase in strength is attributed to more Si-O-Si bond cross-linkages between silica particles formed by the two-step catalysis and the mixed gas treatment.

The concentration inside a crystalline layer was explored theoretically and experimentally for solid layer melt crystallizations. The distribution of the purity in the crystalline layer is modelled by a mass balance equation coupled with an energy balance equation. The mass balance equation is established with the combination of the growth of the layer, the inclusion of the impurity and the migration of the impurity. The concentration profiles were obtained by considering both the migration of inclusions after the layer build-up and the entrapment of inclusion during the growth. The mathematical model established is solved by a numerical method. The predictions are discussed with respect to the interfacial distribution coefficient, the migration effect for removing the inclusion, the concentration and temperature at the solid-liquid interface, crystalline layer thickness, the concentration of the layer, the crystal growth rate and the migration rate. The purity distribution obtained by the model was appropriately verified with that obtained by the experiments.

A novel diagnostic technique is proposed for the in situ sensing of thin organic film deposition in gas discharge plasmas. The method is based on the evanescent wave spectroscopy using an infrared fibre, and allows one to analyse the molecular structure of a growing plasma polymer film in the process reactor. The styrene plasma polymerization on a fibre in the plasma bulk of a capacitively coupled rf discharge was studied. The infrared fibre sensor provides higher sensitivity than the crystals of comparable geometry usually employed in attenuated total reflection spectroscopy. Accumulated evanescent wave infrared absorption spectra give information not only on the molecular structure of the deposited films, but also on its time evolution during the deposition. It was also possible to make conclusions on the molecular orientation of plasma polymerized styrene films deposited under the various process conditions. The fibre was regenerated in an oxygen plasma. The etching process results in the destruction of phenyl rings and the ablation of the plasma polymer film from the surface of the fibre core.

Using the technique of differential phase contrast (DPC) Lorentz electron microscopy, the magnetic stray field distribution from magnetic force microscopy (MFM) tips can be calculated in a plane in front of the tip using tomographic reconstruction techniques. Electrostatic charging of the tip during DPC imaging can significantly distort these field reconstructions. Using a simple point charge model, this paper illustrates the effect of electrostatic charging of the sample on the accuracy of tomographic field reconstructions. A procedure for separating electrostatic and magnetic effects is described, and is demonstrated using experimental tomographic data obtained from a modified MFM tip.

Effects from 4% Fe or Ge for Mn in La_1-xCa_xMnO₃ (x = 0.15-0.6) are studied experimentally. All the compounds exhibit orthorhombic structure, unaffected by the introduction of Fe and Ge. The magnetic ordering temperature (T_c) and, accordingly, the metal-insulator transition decrease systematically due to the presence of secondary ions at the Mn lattice. The doping effects depend on dopant and Ca content, and the typical reduction in T_c, compared to the undoped counterparts, is ~60 K. Ge is more effective in suppressing the magnetic coupling for x⩽0.35, as indicated by the ~25 K lower Curie temperature in the Ge-doped compounds. When x exceeds 0.35, the Fe- and Ge-doping effects reverse. The other striking observation of the present study is the significant ferromagnetic enhancement below ~130 K, characterized by a sharp jump of the magnetization under a field of 5 T, and the re-entrance of the charge ordering state below ~50 K in the Ge-doped La_0.5Ca_0.5MnO₃. The different doping effects of Fe and Ge presumably originate from their different roles of charge carrier mobility. The magnetic coupling between Fe and host Mn seems unimportant.

The effect of γ-irradiation on some physical properties of rare earth ferrite of the general formula Li_{0.5 + z}Co_zYb_xFe_2.5-2z-xO₄, (z = 0.1, x = 0.00, 0.025, 0.050,...,0.200) was discussed. The temperature dependence of the polarization and resistance was studied in the range (300 K⩽T⩽700 K) at different frequencies (10 kHz⩽f⩽1 MHz). The relaxation time and the activation energy were calculated for γ doses of 1 and 3 Mrad. Also, a comparison was made between the ac resistance, before and after irradiation, for the samples with different Yb concentrations (0.0⩽x⩽0.2). The results after irradiation with a 1 Mrad dose of γ-rays showed that the resistance at the critical concentration decreases from 800 to 25 kΩ, at room temperature. Furthermore, with increasing temperature the resistance ranged from R≈130 kΩ at T≈310 K to R≈0.13 kΩ at T≈640 K. Thus, it is possible to improve the conductivity of this type of rare earth ferrite material to be used in technological applications at room temperature as well as at high temperatures.

The novel effect consisting of the spontaneous mechanical rotation when subjected to axial high-frequency ac magnetic field is reported for Fe_73.5Nb₃Cu₁Si_13.5B₉ amorphous as-cast wires and after devitrification. The rotation is observed at a spectrum of frequencies of the exciting applied field and as a consequence of the interaction of a generated magnetoelastic standing wave with an induced circular current. A correlation is found between complex spectra of rotational frequencies and the characteristics of the existing structural phases. Four characteristic frequencies and their harmonics are differentiated in the as-cast state. New rotational frequencies are observed at the very early stages of nanocrystallization, which can be ascribed to initial structural rearrangements. However, the spontaneous rotation vanishes in samples annealed at 550 °C and 570 °C where optimum ultra-soft magnetic behaviour is achieved and magnetostriction is drastically reduced. In this state, rotation is not observed as a consequence of the disappearance of the magnetoelastic wave because of the reduced magnetostriction. The rotation of the wire is observed again when annealed at 650 °C, due to a final increase of magnetostriction upon further crystallisation of the system. The direct correlation between magnetostriction and the field-induced rotation of the wire is thus shown.

The pulsed Townsend method has been used to measure the drift velocity v_e and the density-normalized effective ionization coefficient (α-η)/N, (α and η are the ionization and attachment coefficients, respectively) in c-C₄F₈ over the density-normalized electric field strength E/N, 12 Td⩽E/N⩽43 Td and 330 Td⩽E/N⩽600 Td (1 Td = 10^-17 V cm²), at pressures between 1 and 7.5 Torr (1 Torr = 133.3 Pa). For 12 Td⩽E/N⩽43 Td, the above parameters were found to be pressure independent, while for the range 330 Td⩽E/N⩽600 Td an inverse dependence of the above coefficients was found for gas pressures less than 2 Torr. Such dependence is believed to be due to the autodetachment of the originally formed, unstable parent negative ion c-C₄F₈^-*. At low E/N, no previous data for v_e or (α-η)/N were found for comparison with the present data. A critical field strength of E/N_crit = 439.5 Td, for which α = η, was found to be in good agreement with previous data.

A powerful method for the study of time-dependent electron kinetics in spatially one-dimensional plasmas is presented. The method is based on the solution of the space- and time-dependent kinetic equation for the electron velocity distribution function in two-term approximation. The resulting three-dimensional partial differential equation for the isotropic part of the velocity distribution function is numerically solved as an initial-boundary value problem over the space of the spatial coordinate and the total energy proceeding in time. As an application, the spatiotemporal relaxation of electrons in the column-anode plasma of a glow discharge in krypton, acted upon by a space-independent electric field and initiated by a constant electron influx at the cathode side of the plasma, is studied. The electron relaxation process is traced up to the establishment into a spatially structured, time-independent state. A detailed analysis of the spatiotemporal behaviour of the velocity distribution function and relevant macroscopic quantities of the electrons is given for different electric field strengths and boundary conditions. In particular, a significant increase in the relaxation time of the spatiotemporal electron relaxation compared with the relaxation time to approach steady state in spatially homogeneous plasmas has been found.

We consider the process of excitation of a strong axisymmetrical plasma wave by a relativistic electron bunch. It is well known that in one-dimensional geometry the excited wave becomes essentially nonlinear when the beam density approaches half the plasma density, and wavebreaking occurs at beam densities higher than that. Such a simple relation, however, does not hold in three dimensions. We find that the total beam current, not only the current density, should exceed a certain threshold for nonlinearity to become visible. Just recently, new developments in accelerator technology have made it possible to produce relativistic electron beams powerful enough to enter this nonlinear regime. We show that a realistic electron bunch from an advanced accelerator can generate in its wake accelerating fields well above 10 GeV m^-1.

Experiments are described in which spark discharges in long non-uniform gaps are studied in Ar with a small addition (1-5%) of O₂ under standard conditions. The results obtained show that even the addition of 1% O₂ drastically reduces the conductivity of the streamer channel and increases the average electric field required to bridge the discharge gap by a streamer. Breakdown, producing short circuiting, is developed through leader propagation in Ar:O₂ mixtures, in contrast to a non-thermal streamer mechanism of breakdown that was previously observed in pure Ar. A 1.5-dimensional simulation was carried out which supports the general observed properties of streamers in long gaps in Ar:O₂. An analysis of the simulation results shows that the effect of small O₂ additions on the streamer properties in Ar is explained by the quenching of excited Ar atoms by O₂ molecules, which leads to the deceleration of two-step ionization in the streamer channel.

This work, based on the numerical solution of the Boltzmann equation, analyses the influence of ionization processes on the shape of the electron energy distribution function (EEDF) in a mixture of molecular nitrogen, heavy inert gases and resonant excited lithium vapour. The convergent close-coupling method is used to estimate the singly differential cross sections for the ionization of Li(2S) and Li(2P) atoms by electron impact. The composition of the three-component mixture, when the negative electron mobility (NEM) can be observed, is determined. The mixture's ionization degree range and the relative density of the resonant excited lithium atoms favourable for the maximal NEM are found. It is shown that under optimal conditions the ionization rate is determined by electron-impact ionization of the Li(2P) states. In this case the characteristic time of EEDF formation proved to be shorter than the ionization time. Based on this fact, it is suggested how to realize NEM in a quasi-stationary regime under conditions of increasing electron density caused by the resonant radiation.

Electrical treeing in an epoxy resin under an ac voltage for a point-to-plane gap configuration has been investigated using a phase-resolved partial discharge measurement system and shadow survey and light emission registration techniques. A self-consistent model based on the concepts of energy and electric field has been developed and used for quantitative description the temporal-spatial and electric characteristics of electrical treeing obtained in experiment. The electrical treeing is considered to be a phenomenon of self-organized criticality.

The polarimetric probability distribution functions (PDFs) of laser speckle for incident linear and circular polarization states have been determined from the measured Stokes parameters for a limited range of targets that may be encountered in remote sensing applications: two rough surface samples, and two samples which exhibit both surface and volume scattering. The resultant speckle patterns of the total intensity are found to be partially polarized with variations in the contrast and degree of polarization between samples and with incident polarization state. The intensity PDFs are compared to published theory expressed in terms of the sum of completely polarized and unpolarized speckle patterns. This theory is modified to incorporate speckle averaging caused by an imperfectly aligned rotating optical component. The measured ellipticity and azimuth PDFs were shown to be reasonably well predicted by a model based on the degree of polarization of the speckle pattern and the incident polarization state. The PDFs are shown to be useful in highlighting experimental problems that would have been less obvious by other methods. In addition, it is noted that the global polarimetric parameters provide valuable insight into speckle statistics, which is less apparent than using only the intensity information.

The paper deals with the dynamics of a bubble initiated in the vicinity of a sharp electrode in a liquid dielectric gap submitted to an electric field, and to the conditions leading to the generation of a streamer at the bubble-liquid interface. By taking into account the different stresses acting at any point of the surface of the bubble, we establish a mathematical expression describing the shape of the bubble and allowing us to analyse its deformation and instability. The frequency of the disturbances at the interface is studied and the zone at which the local electric field is the highest is determined. It is shown that depending on this frequency and therefore on the value of the local electric field, different streamer patterns can be generated. Some examples of the topology of the disturbed interface are given and discussed.

The ceramics of PbTiO₃ and its powders have been prepared by a sol-gel process. The constitution of its phase and structure was examined by x-ray diffraction and Fourier transform infrared spectroscopy. Characterization studies were performed to determine the effects of particle size and degree of tetragonality. The dielectric properties of ceramics and powders of PbTiO₃, composited with paraffin, were measured from 1 MHz to 18 GHz. All samples exhibited evidence of relaxation phenomena in their dielectric spectra. The relaxation frequencies increased with decreasing particle size.

Thermal expansion measurements have been carried out using dilatometry on the (RE)BaCuO system in the temperature range 300-1100 K. The peak in the thermal expansion coefficient (α) at 890 K presages the high-temperature orthorhombic-to-tetragonal phase transition in YBa₂Cu₃O_7-δ. The thermal expansion behaviours of YBa₂Cu₃O_7-δ, Y₂BaCuO₅, NdBa₂Cu₃O_7-δ and Nd₄Ba₂Cu₂O₁₀, which are the constituent phases of melt-processed high-J_c superconducting ceramics, are compared. The relevance of dilatometric studies at high temperature to such multiphase ceramic bodies is discussed.

We present a stochastic model which simulates electromigration damage in metallic interconnects by biased percolation of a random resistor network in the presence of degradation and recovery processes. The main features of experiments including Black's law, times to failure distribution, current threshold for the onset of electromigration, etc are properly reproduced. Compositional effects showing up in early resistance changes measured on Al-0.5%Cu and Al-1%Si lines are also studied.

It is shown that large and well faceted hexagonal crystallites can grow on Si and Ti substrates under higher nitrogen gas flow in the gaseous mixture of CH₄ and H₂ in the normal process of diamond deposition using microwave plasma chemical vapour deposition (MP-CVD). Grazing incidence x-ray diffraction (GIXRD), energy dispersive x-ray spectrometry (EDX), wavelength dispersive x-ray spectroscopy (WDX) and Raman analysis revealed that these crystals are silicon carbonitride rather than carbonitride as we expected and usually regarded. This indicates that the hypothetical covalent carbonitride is not as easily formed as the crystallite with Si substitution. Comparing films deposited on Ti alloy substrates, with and without Si chips present during the deposition, we found that the Si chips activated by the plasma sputtering provides Si sources for crystallite SiCN formation on Ti substrate. The hexagonal SiCN structure and its lower hardness are attributed to the C_3v-symmetric quasi-tetrahedral nitride with a nonbonding lone pair. The involvement of the less electronegative Si specimen may make the SiCN form easier than the covalent carbonitride.

On page 467, the W_i just after equation (8) is corrected to over bar W_i

In table 5, column 8, X₂ is corrected to X₃ and upsilon₂ is corrected to upsilon₃.

On page 469, line 8, `gamma° (0) using equation' is corrected to `gamma_{| |}(0) using equation (5)'.

On the same page, C₁₂₃ is added alongside C₁₁₂ at the end of the first paragraph on the right-hand side.