Table of contents

The characteristics of electromagnetic waves propagating along plasma filaments are studied for conditions of high-pressure discharges (when the collision frequency is much higher than the angular field frequency). Analytical expressions for the phase and attenuation coefficients are obtained. Their comparison is given with the results of numerical calculations.

The method of computerized glow curve deconvolution (CGCD) is a powerful tool in the study of thermoluminescence (TL). In a system where the plural trapping levels have the probability of retrapping, the electrons trapped at one level can transfer from this level to another through retrapping via the conduction band during reading TL. However, at present, the method of CGCD has no affect on the electron transition between the trapping levels; this is a fatal defect. It is shown by computer simulation that CGCD using general-order kinetics thus cannot yield the correct trap parameters.

The papers contained in this section are a selection of those presented at the conference `The Future of Technological Plasmas', which was a two day meeting within the IOP Annual Congress held in Brighton, UK, between 19-21 March 2001.

The term `technological plasmas' has been defined in several ways over the years, depending on how large the scope of the topic considered. For example, one definition stated that these are basically laboratory plasmas, which would include all pressure ranges, including atmospheric, and also different types of plasma such as arc or corona. To narrow this all encompassing definition, it is possible to restrict the scope to plasmas that are used for technological applications, rather than experimental characterisation of interesting phenomena. The term is now well established [1], even though the definition may not be so well defined! Our scope here was to address the future demands of technological plasmas, including plasmas used by the semiconductor industry, atmospheric plasmas, and plasmas for surface modification and we hoped to reflect the interaction of academia and industry. All issues related to technological plasmas were solicited, including equipment design, processes and process control, plasma measurement and diagnostic techniques, plasma and process modeling, feedback and interactive control strategies, material processing including thin film deposition and etching, plasma processing for applications such as nanofabrication, nanotechnology, biology, medicine, electronics and electrical engineering.

We hope that the readers of Journal of Physics D: Applied Physics will enjoy sampling the range and depth of topics covered by this issue. The timing of the meeting, and hence the publication of the cluster, reflects the various initiatives of the past ten years which have aimed to raise the profile of technological plasmas as an underpinning tool to many disciplines and industrial applications.

Acknowledgments

Thanks to Mahfuzer Rahman at Glasgow University, my conference co-organiser, who did much to cajole the invited speakers along and acted as co-guest editor for this cluster; The Institute's Surface Science and Technology Division; Marconi Caswell and also to the staff in the Conference Department of the Institute of Physics for undertaking the administrative tasks.

References

[1] See for example Graham B 2001 Physics World14 (3) 31-6

Dr A P Webb, Guest Editor

August 2001

Time-resolved measurements of the electron temperature T_e, plasma density n, floating V_f and plasma potentials V_p have been made at different positions along the centre line in a pulsed RF magnetron plasma (frequency 50 Hz, 50% duty cycle). In the afterglow, T_e and n were found to decay with two characteristic times. These are in the ranges τ_1t~25-50 µs, τ_2t~120-130 µs, and τ_1n~35-330 µs, τ_2n~100-485 µs for T_e and n, respectively. The density decay times increase with pressure over the chosen range (0.27-2.13 Pa), while the temperature decay times are generally insensitive to pressure. The rate of particle loss is found to increase at positions closer to the cathode. A simple one-dimensional diffusion model indicates that during the `off' times, the rate of density decay is governed by the ion flux across the floating sheath formed at the cathode. This sheath itself decays due to the falling electron temperature.

It is well known that the use of Langmuir probes in `high' pressure plasmas (atmospheric and above) is extremely difficult due to the high degree of collisionality. In addition, electric arcs used in industry are highly non-homogeneous. In particular the degree of ionization varies from zero at the arc edges to values close to full ionization near the axis. Existing probe theories are therefore inappropriate. The `traditional' use of the characteristic curve for arc temperature and particle density mapping is time consuming and also leads to errors due to the collisional nature of the discharge. Existing probe theories are examined with respect to the application at high pressure and in this, the first of a series of papers, an interpretation based on different assumptions is presented.

A simple apparatus for the study of tungsten inert gas (TIG) welding arcs is described permitting data collection over short time periods (~0.1 s) for operating currents in the range 50-150 A. Difficulties encountered with probe applications are discussed highlighting the need for further theoretical developments.

The axial electric field is given by the derivative of the measured potential with respect to the axial position and shown to be in agreement with previous estimations. Results are discussed with reference to the sparse previous publications concerned with high pressure arc plasmas.

We describe radio frequency (rf) analysis of technological plasmas at the 13.56 MHz fundamental drive frequency and integer narrow-band harmonics up to n = 9. In particular, we demonstrate the use of harmonic amplitude information as a process end-point diagnostic. Using very high frequency (vhf) techniques, we construct non-invasive ex situ remote-coupled probes: a diplexer, an equal-ratio-arm bridge, and a dual directional coupler used as a single directional device. These probes bolt into the plasma-tool 50 Ω transmission-line between the rf generator and matching network, and hence do not require modification of the plasma tool. The 50 Ω probe environment produces repeatable measurements of the chamber capacitance and narrow-band harmonic amplitude with an end-point detection sensitivity corresponding to a 2 dB change in the harmonic amplitude with the removal of 1 cm² of photoresist.

The methodology and design of an instrument for the measurement of the plasma-tool frequency response, and the plasma harmonic amplitude and phase response are examined. The instrument allows the monitoring of the plasma phase delay, plasma-tool short- and long-term ageing, and process end-point prediction.

We have designed a low-cost and reliable 2.45 GHz waveguide-based applicator to generate a microwave plasma jet (MPJ) at atmospheric pressure. The MPJ system consists of a 1-6 kW magnetron power supply, a circulator, a water-cooled matched load and the applicator. The applicator includes a tuning section, which is required to reduce the reflected power, and the nozzle section. The plasma is formed by the interaction of the high electrical field, generated by the microwave power, between the waveguide aperture and the gas nozzle. A variety of gases have been used to produce the plasma including argon, helium and nitrogen. A 2 kW, 2.45 GHz MPJ, constructed using a rectangular waveguide WG9A (WR340), has been investigated. An MPJ has been used for material processing applications including cutting, welding, glass vitrification and quartz/ceramic processing. This paper discusses the design parameters and the potential of the MPJ for industrial applications and how the jet can be tailored to suit different tasks, by adjusting the various parameters such as the type of gas, the flow rate, the input power and the nozzle design.

A comprehensive model has been developed to study low-pressure, high-density plasma processing reactors. The model couples plasma generation and transport self-consistently to fluid flow and gas energy equations. The model and the simulation software have been used to analyse chlorine plasmas used in metal etching. The effect of the inductive coil frequency on the plasma characteristics has been examined and found to influence plasma uniformity only moderately. Model predictions for a CF₄ plasma have been found to agree well with experimental results.

Plasma etching of the widegap materials SiC and GaN is very important as there are only limited wet etches available. However, this is known to introduce defects into surface layers under typical etch conditions for widegap materials. Bulk defects are also present in these materials. We have conducted a series of experiments to compare the effects on electrical transport of surface and bulk damage. It is known that reactive ion etching a surface prior to Schottky metal deposition leads to degraded junction behaviour and our experiments confirm this. We have also irradiated these materials in a relativistic proton beam to induce additional bulk defects. For Schottky metal deposition after irradiation the usual effects of significant surface damage are observed. For deposition prior to irradiation the static I-V characteristics show only some degradation. Raman spectroscopy, which is usually sensitive to structural changes in the material subsurface region, shows, surprisingly, little change due to the high-energy proton bombardment. We conclude that even though there may be significant levels of bulk defects in widegap materials, transport is most sensitive to surface damage and it is very important to minimize the effects of any dry etch damage to obtain the best possible device performance.

An atmospheric pressure non-equilibrium plasma (APNEP) developed in the UK by EA Technology Ltd is currently being investigated in collaboration with the University of Surrey. Of the many applications of surface modification that can be induced using plasmas, adhesion enhancement is one of the most commercially important. In this paper, we illustrate the use of an atmospheric plasma to enhance the adhesion characteristics of low-density polyethylene (LDPE) and poly(ethylene terephthalate) (PET). The polymers were treated in the remote afterglow region of an atmospheric pressure plasma to avoid the thermal effects that can cause degradation for thermally sensitive materials when placed in direct contact with the plasma. Reactive (oxygen containing) and inert (oxygen free) atmospheric plasmas rapidly impart adhesion enhancement by a factor of two to ten as measured by 180° peel tests. However, extended exposure to the atmospheric plasma does not impart additional adhesion enhancement as the surface is ablated revealing the underlying polymer with poor adhesive characteristics. In contrast, vacuum plasma treated LDPE and PET show increased adhesion with extended plasma treatment. An adhesion enhancement in excess of two to three orders of magnitude was found to be achievable for vacuum plasma treatment times greater than 10 min.

An atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in collaboration with the University of Surrey. The main focus is the use of atmospheric pressure plasmas to modify the surfaces of commercially important polymers including polyolefins, poly(ethylene terephthalate) and poly(methyl methacrylate). These surface modifications include surface cleaning and degreasing, oxidation, reduction, grafting, cross-linking (carbonization), etching and deposition. When trying to achieve targeted surface engineering, it is vital to gain an understanding of the mechanisms that cause these effects, for example, surface functionalization, adhesion promotion or multi-layer deposition. Hence comparisons between vacuum plasma treated surfaces have also been sought with a view to using the extensive vacuum plasma literature to gain further insight. In this paper, we will introduce the APNEP and compare the key characteristics of the plasma with those of traditional vacuum plasma systems before highlighting some of the surface modifications that can be achieved by using atmospheric plasma. Data from the analysis of treated polymers (by spectroscopy, microscopy and surface energy studies) and from direct measurements of the plasma and afterglow will be presented. Finally, our current understanding of the processes involved will be given, particularly those that are important in downstream surface treatments which take place remote from the plasma source.

Dry etching of Si is critical in satisfying the demands of the micromachining industry. The micro-electro-mechanical systems (MEMS) community requires etches capable of high aspect ratios, vertical profiles, good feature size control and etch uniformity along with high throughput to satisfy production requirements. Surface technology systems' (STS's) high-density inductively coupled plasma (ICP) etch tool enables a wide range of applications to be realized whilst optimizing the above parameters.

Components manufactured from Si using an STS ICP include accelerometers and gyroscopes for military, automotive and domestic applications. STS's advanced silicon etch (ASE^TM) has also allowed the first generation of MEMS-based optical switches and attenuators to reach the marketplace. In addition, a specialized application for fabricating the next generation photolithography exposure masks has been optimized for 200 mm diameter wafers, to depths of ~750 µm.

Where the profile is not critical, etch rates of greater than 8 µm min^-1 have been realized to replace previous methods such as wet etching. This is also the case for printer applications. Specialized applications that require etching down to pyrex or oxide often result in the loss of feature size control at the interface; this is an industry wide problem. STS have developed a technique to address this.

The rapid progression of the industry has led to development of the STS ICP etch tool, as well as the process.

Low-pressure mercury lamps are commonly used for germicidal applications. The germicidal effect is due to the emission of light at 254 nm, which leads to the destruction of the most waterborne bacteria and viruses. The microwave plasma ultraviolet (UV) lamp (MPUVL) is a new technology for generating a high-intensity UV light and that can be also controlled to operate at 185 nm; irradiation is in air at this wavelength produces ozone. The microwave power is injected into a resonant cavity and the surface wave excitation takes place within the cavity through that part of the discharge tube (fused silica) protruding inside it. The MPUVL has many advantages over conventional lamps, which are limited to an output power in the region of 30 W m^-1, while MPUVL can deliver any amount of power per unit length and the tube can be of any shape, length or diameter. This paper describes the design of the MPUVL and compares its efficiency with that of conventional lamps through spectral analysis. Other results, which include the effects of temperature and different power inputs, are also discussed.

The technique of electron cyclotron resonance (ECR) plasma enhanced chemical vapour deposition (PECVD) is increasingly being used in electronic and photonic device applications. ECR offers a number of advantages including improved control of the deposition process, less damage to the growing film and the possibility of high deposition rates. ECR occurs in a plasma under appropriate magnetic and electric field conditions. In most cases, as in our system, this is achieved with a combination of 2.45  GHz microwave radiation and a 0.0875 T magnetic field, due to the use of standardized microwave supplies. We have studied the effects on silicon film growth of changing the magnetic field configuration to produce one or more planes of ECR within the system, and of changing the positions of the plane(s) relative to the deposition substrate. The films were grown in silane-hydrogen discharges. The magnetic field in our system was provided by two electromagnets. It was measured experimentally for a number of operating current values and then a detailed profile achieved by modelling using a proprietary software package. A process condition discharge under identical magnetic field configurations to growth was analysed by the use of a Langmuir probe and the results correlated with film properties determined by Raman spectroscopy and Dektak profilometry.

Dry etch damage is a potential worry when etching III-V semiconductors. Even though very low levels of damage are possible in modern dry etch processes, it is nevertheless of interest to be able to detect any residual damage and understand its origins. We have used measurements of photoluminescence intensity from GaAs and InGaAs quantum well heterostructures to probe the damage in a non-invasive way. At low damage levels, two factors influencing possible damage penetration have been found: the ratio of atomic to molecular ions in the discharge and the effect of ambient light. Samples were etched using SiCl₄ reactive ion etching and also a more complex multi-component discharge. Comparative studies were made on samples bombarded by the separate constituent ions of a SiCl₄ discharge using a mass-resolving ion implanter fitted with a deceleration lens. The experiments show that molecular ions contribute less to deep damage than do atomic ions. This is relevant, for example, if using high pump powers to sustain the discharge, such as in ICP or ECR. Further studies of laser illumination on the sample during etching show that a form of radiation enhanced diffusion can modify the damage distribution. This is relevant, for example, if laser interferometry is used for end-point detection. Thus for low damage in low damage etch processes, etch parameters that minimize atomic ion content in the discharge should be used and ambient illumination should be avoided if possible.

Steam reforming with oxygen (SRO) is a combination of non-catalytic partial oxidation and steam reforming of methane, industrially used for syngas production. There are several models of the chemical reactors used for this purpose but in the last decade a new direction has developed - plasma devices. The aim of the present paper is to make a comparative analysis between the autothermal reformers, including their improved variants, and the plasma reactors. The study is conceived in terms of advantages and disadvantages coming from the exploitation parameters, methane conversion, selectivity, energy efficiency and investment costs. Although SRO by means of chemical reactors may be the most efficient, plasma reactors represent an incisive approach by their simplicity, compactness and low price.

The production of high-density, large-area microelectrode arrays for neurophysiology studies requires a combination of electron beam lithography and photolithography, together with dry etch pattern transfer. The retina is one of the few parts of the animal nervous system to which the input (image) and output (ganglion) signals are accessible. To read out the signals from the ganglion cells, we have made microelectrode arrays in the transparent conductor indium tin oxide (ITO) by CH₄/H₂ reactive ion etching (RIE) using a novel masking technique that avoids the usual problem of resist cross-linking. An electron beam lithography process has also been developed exploiting multiple plasma steps. The ITO layer lies on a glass substrate to allow the retinal cells and the electrode positions to be photographed using a CCD camera. SF₆ RIE of vias through a thick protective silicon nitride coating deposited by plasma onto the ITO/glass permits the platinization of the electrodes. Both CH₄/H₂ and SF₆ RIE require low electrical damage to the ITO, which we verify.

For approximately the past ten years, atmospheric pressure non-thermal plasmas have been increasingly promoted as a technology for a number of applications in the area of pollution abatement. In such plasmas, the electrons have a significantly higher temperature compared to the ions, atoms and molecules. This paper provides an overview of both the technologies involved and the diverse potential application areas. A general description of these atmospheric plasmas and the basic principles involved in the destruction or removal of gaseous phase pollutants, based on the nature of the processes taking place within these plasmas, are given. A number of examples of the different plasma technologies are described. The technologies described are pulsed corona, microwave and dielectric barrier plasmas. Their suitability and use in various application areas are also discussed including incinerator off gas treatment, industrial process off gas treatment and diesel exhaust aftertreatment. The use of modelling of the physical and chemical processes involved to predict system performance and as a tool for sizing systems to meet customer requirements is also discussed.

Thermally stimulated discharge (TSD) current behaviour of amorphous selenium (a-Se) films (~100 µm thick) has been studied as a function of polyvinyl fluoride (PVF) interface barrier layer thickness in the range of 2000-8000 Å (temperature range of 295-385 K). TSD spectra of these films show that charge storage in a-Se reduces considerably on incorporation of a PVF interface barrier layer. These effects have been attributed to the blocking and field enhanced mobility role of the PVF interface layer.

The pre-exponential factor of an Arrhenius-type temperature dependence of the relaxation time of the interfacial polarization processes is sensitive to the size distribution and the orientation of (conductive) inclusions. An alternative narrow-window thermal sampling thermally stimulated depolarization currents (TSDC) procedure was applied in order to decompose two different overlapping mechanisms of interfacial polarization in a calcite matrix accommodating a random distribution of quartz and dolomite inclusions, which are more conductive than the host. The distribution of the activation energy and the pre-exponential factors were obtained from the analyses of the TSDC constituents. The orders of magnitude of the relaxation times agree with those predicted theoretically. The distributions in the values of the activation energy and the pre-exponential factor are discussed with respect to predictions of the theory for conductive ellipsoids dispersed in an insulating matrix.

The intent of this paper is to cross-correlate the information obtained by space charge distribution analysis and electroluminescence (EL) detection in cross-linked polyethylene samples submitted to dc fields, with the objective to make a link between space charge phenomena and energy release as revealed by the detection of visible photons. Space charge measurements carried out at different field levels by the pulsed electro-acoustic method show the presence of a low-field threshold, close to 15-20 kV mm^-1, above which considerable space charge begins to accumulate in the insulation. Charges are seen to cross the insulation thickness through a packet-like behaviour at higher fields, starting at about 60-70 kV mm^-1. EL measurements show the existence of two distinct thresholds, one related to the continuous excitation of EL under voltage, the other being transient EL detected upon specimen short circuit. The former occurs at values of field corresponding to charge packet formation and the latter to the onset of space charge accumulation. The correspondence between pertinent values of the electric field obtained through space charge and EL analyses provides support for the existence of degradation thresholds in insulating materials. Special emphasis is given to the relationship between charge packet formation and propagation, and EL. Although the two phenomena are observed in the same field range, it is found that the onset of continuous EL follows the formation at the electrodes of positive and negative space charge regions that extend into the bulk prior to the propagation of charge packets. Charge recombination appears to be the excitation process of EL since oppositely charged domains meet in the material bulk. To gain an insight into specific light-excitation processes associated with charge packet propagation, EL has been recorded for several hours under fields at which charge packet dynamics were evidenced. It is shown that current and luminescence oscillations are detected during charge packet propagation, and that they are in phase. The mechanisms underlying EL and charge packets are further considered on the basis of these results.

The approach to the saturation magnetization of a nanocrystalline Fe₉₀Zr₇B₃ alloy has been studied by means of differential magnetic susceptometry. The influence of the microstructure of the alloy on the approach to saturation magnetization has been studied. It has been found that for the optimum heat-treated sample (heated at 923 K for 0.25 h), which had an average grain size of 12 nm and a coercivity, H_c = 6.4 A m^-1, the approach to saturation magnetization can be expressed using the law of approach to saturation magnetization, χ = aM_sH^-2 + 2bM_sH^-3 + c/2(H^-1/2) (where χ is the differential magnetic susceptibility, M_s is the saturation magnetization, H is the magnetic field, and a, b and c are constants), without the H^-3 term, while for the sample heated at 923 K for 240 h, which had an average grain size of 82 nm and a coercivity, H_c = 950 A m^-1, the approach to saturation magnetization cannot be expressed in the same form. For both samples, the magnetic-anisotropy-related H^-3 term cannot be found. As a result, the magnetic anisotropy in this nanocrystalline alloy cannot be determined by using the law of approach to saturation magnetization. The measurement with the differential susceptometer has been compared with the measurement made on the SQUID magnetometer. The result has shown that the measurement of differential susceptibility using a long ribbon sample on the differential susceptometer is more reliable than that using a small sample on the SQUID.

In inductively coupled low-pressure oxygen plasmas, planar Langmuir probes were used to determine the variation of the plasma parameters (positive and negative ion densities, electron density, electron temperature) with applied pressure (1-40 mTorr) and power (1-800 W). Simultaneous optical emission spectra were obtained. The relative abundance of the species was estimated from the intensities of the two spectral lines from excited oxygen atoms and molecular oxygen ions. In conjunction with the Langmuir probe data, the scaling behaviours of the charged and neutral species were investigated. A change of scaling behaviour in charged and neutral species densities which was due to the transition from the ion-flux-loss-dominated region to the recombination-loss-dominated region was observed by Langmuir probe measurement and optical emission spectroscopy.

Mathematical modelling and optical emission spectroscopy are applied to study the effect of the chamber pressure on the structure and properties of supersonic plasma jets formed by a direct current arc. In this installation the plasma is created inside the nozzle where the flow is accelerated. As a result some deviation from thermal and ionization equilibrium can be found, even at the working chamber inlet. In this paper, by means of a two-temperature model, we study the argon jet flow using the data of the emission spectroscopy measurements to make realistic assumptions about the inlet boundary conditions. The results show that, when the chamber pressure is low, a strongly underexpanded jet with a Mach disc is formed. For the higher ambient pressure values, the core region of the jet changes to a mildly underexpanded structure with alternating oblique expansion and compression zones. The predicted shock zone positions are in a very good agreement with measurement. The general analysis shows that the deviation from local thermodynamic equilibrium in the jet is inversely related to the chamber pressure. Along the jet core the deviation from thermal equilibrium is less in the shock regions than in the expansion zones, where the electrons are heated by three-particle recombination. Downstream of the jet core the velocity drops, but the ionization and thermal equilibria are not attained because of the correlation between the characteristic recombination and the hydrodynamic times. Both the modelling and the emission spectroscopy show that the axial electron number density is much closer to its frozen value than to equilibrium value. The results obtained are helpful for different applications such as plasma processing, rocket propulsion systems and the simulation of re-entry conditions.

In negative corona discharges in ambient air different discharge modes can be observed. In this paper the discharge current regions corresponding to these modes are determined. The influence of anode geometry, anode resistivity, inter-electrode distance and gas flow on the threshold currents that mark the corona-to-glow and glow-to-spark transitions is investigated. The experimental data are backed up by an analytical treatment of ionization instability development within a local current spot on metallic and resistive anodes.

This paper describes a novel method for generating electrical transients. A small charged metal sphere coming into contact with the centre conductor of a coaxial transmission line is used to produce pulses with a risetime below 60 ps and amplitude of 500 V or more. The phenomenon is investigated experimentally to determine whether the gaseous medium in which the discharge takes place affects the pulse shape. Measurements in sulphur hexafluoride, argon and rough vacuum indicate that the breakdown mechanism is not a gas discharge, but the gas does affect the amplitude range, shape and variability of the current pulses. Results are interpreted in the light of previous investigations into arcs between electrodes separated by gaps of less than 100 µm, in which field emission of electrons from the cathode was recognized as the principal source of charge carriers. Potential applications for the contact discharge pulse generator are proposed and aspects of its operation that could be refined to reduce pulse shape variability are identified.

The purpose of this work is to understand keyhole formation observed during pulse Nd:YAG laser welding. An analysis of the evolution of the keyhole geometry during a laser pulse was carried out by radiography x-ray flash, for tantalum and a titanium alloy target. From the images obtained by x-ray radiography, we determined the evolution of the geometry of the keyhole (depth and width) during the laser pulse. The keyhole appears after a delay, and increases linearly. We compare the measured creation delay with a value obtained by an analytical thermal model. We present a calculation of the energy deposit law by Fresnel absorption; the aim is to calculate the ray trajectory in the keyhole to deduce the local absorption. The absorption increases strongly during the formation of the keyhole, and tends towards a limit value. Further, we compare the mean absorption during a pulse with a measurement using a differential microcalorimeter.

The mechanisms of charge injection, transport and trapping in low-density, high-density and cross-linked polyethylene (LDPE, HDPE and XLPE) are investigated in this paper through charging-discharging current measurements and space-charge observations. The conductivity of LDPE is much larger than that of XLPE and HDPE. The threshold for space-charge accumulation and that for a space-charge-limited current mechanism, coinciding for the same material, are almost identical for LDPE and HDPE, while the threshold of XLPE is higher. However, HDPE accumulates more charge than the other two materials. The depolarization space-charge curves and the conduction current versus field characteristics indicate that the mobility of LDPE is larger than that of XLPE and HDPE, which supports the significant difference in conductivity. The lower mobility, as well as the nature, depth and density of trap sites, can explain the difference in space-charge accumulation and thresholds.

A recently developed experimental-analytical x-ray diffraction method for the direct, comprehensive, non-destructive characterization of crystalline materials is applied to analyse x-ray scattering data from amorphous materials. High-resolution refraction/small-angle scattering intensity profiles from a homogeneous, non-crystalline sample were collected at the 1 km long beamline, SPring-8, Japan. A logarithmic dispersion relation is used to determine the x-ray phase. A priori knowledge of the sample structure is utilised to reconstruct the physical characteristics of the sample with a resolution of 0.25 µm. These studies have demonstrated the viability of the technique as a new characterization method for amorphous materials.

An analytical model for laser drilling is proposed which includes three-dimensional heat conduction in a simplified manner. For that purpose, the heating of the curved surface is locally described by that of a spherical cavity with comparable curvature within an infinite medium. Additionally, the absorption of laser radiation on the inclined side wall is taken into account. Using these components, it is possible to calculate the evolution of the hole shape from pulse-to-pulse in an iterative way. Therefore, this model is suitable to study the main aspects of deep drilling such as ablation rates and hole shapes without the disadvantage of long computational times. As a drilled hole deepens and the walls become steeper, its surface area grows and, thereby, in principle the absorbed intensity drops. This can lead to a considerable reduction of ablation rate. At the same time, extremely curved surface areas will heat much faster or slower than plane ones which, again, results in local changes of drilling velocity. It is shown that the former is particularly of interest for the description of the resulting hole shape while the latter has a considerable influence on the ablation velocity at the tip of the hole. To verify the analytical model, its results are compared with those of three-dimensional numerical simulations. It is shown that the simplified assumptions introduced here are, up to some extent, suitable to explain the final surface shapes for blind holes as well as the experimentally observed dependence of ablation rate on hole depth.

The equivalent plate conduction model is employed to simulate the structure evolution in Poiseuille flow of electrorheological (ER) fluids subjected to the short-range interaction of multi-particles. It is found that the time taken to form the plug zone is greatly shortened from 18.5 for a dipole model to 7.8 for a conduction model. The velocity peak value of the breathing transition zone increases markedly compared with the simulation results using the dipole model, which is attributed to (1) the strong interaction between contact zone particles and adjacent particles and (2) there is no slip between particles of the contact zone and the electrodes. Moreover, we obtain the three-dimensional evolving graphs of the velocity profile of particles in the ER fluid, and the structure of the particles evolves from a plug zone to a transition zone, finally becoming a wider plug zone.

A paper by Gmelin et al examines the thermal contact resistance between copper surfaces above 1 K. It was concluded that dielectric and metallic interposers significantly increase the conductance of demountable joints. I argue that an extrapolation of electrical resistance measurements, and of thermal measurements at lower temperatures, implies that it is possible to construct considerably better joints without interposers. Moreover, dielectric interposers would reduce the conductance of such joints.