Table of contents

Films of silicon phthalocyanine dichloride deposited from solution onto a chemically prepared hydrogen-passivated Si(111) surface were manipulated with the scanning tunnelling microscope (STM) in air. We find that nanometre-scale square and trench patterns can be created in the film by the STM tip through repeated scans under normal imaging conditions ( V, I = 0.35 nA) or by a single scan using a high tunnelling current (10 nA). Spectroscopic measurements of the film show that the film is chemically unchanged by the machining process. The film cannot be machined after exposure to air for a period of days, suggesting that some form of hydrolysis of occurs.

The band structure theory of magnetism in 3d-4f compounds is reviewed. Among the open-shell electrons, a hierarchy of interactions is present which governs the intrinsic magnetic properties of these materials. Density functional theory (DFT) is an appropriate tool to describe and quantitatively investigate both ground state properties and model interaction parameters, which are necessary to calculate the temperature-dependent behaviour. The cornerstones of the DFT are explicitly sketched, as well as recent developments needed to cope with the treatment of localized 4f and itinerant 3d magnetism in one and the same framework. This includes the open-core scheme, self-interaction corrected DFT, relativistic DFT, and orbital polarization. On this basis, the exchange coupling among itinerant and localized states can be understood, together with the size of Curie temperature and ground state spin and orbital magnetic moments. Finally, the problem of magnetocrystalline anisotropy is addressed, concerning both the band and the 4f crystal field contribution.

The x-ray sensitivity of a-Se films as a function of combinational doping, i.e. chlorine ( to 40 ppm) and arsenic ( to 0.35%, by weight) has been studied using the potential decay technique. The films doped combinationally with chlorine and arsenic show the maximum sensitivity. This has been attributed to the optimum combinational and complementary roles played by the two dopants, i.e. the mobility enhancement role of chlorine and charge sustaining role of arsenic.

Monocrystalline was processed in a radio-frequency (27.12 MHz) discharge in hydrogen and subsequently in oxygen and the composition of the thus produced surface layers evaluated. The hydrogen plasma treatment caused a heavy blackening of the sample due to chemical reduction. At low pressures ( Torr) the niobate structure on the sample surface was completely destroyed; only niobium and its oxides remained on the surface. At higher pressures ( Torr) the niobate structure was preserved. Hydrogenation of the surface layer was found which persisted up to 500C. Subsequent treatment in an oxygen plasma under similar processing conditions brought about the restoration of the transparency of the sample. The following methods were used for the modified surface structure analysis: neutron depth profiling, Rutherford backscattering, x-ray photoelectron spectroscopy and VIS and IR spectrometry.

The ageing effect in silicon metal-semiconductor field effect transistors is studied by taking into account the reaction of the gate contact with the native layer on the silicon surface. Specifically, the effect of ageing on the threshold voltage and drain characteristics has been studied. It is shown that the change in the threshold voltage with time is quite significant until it becomes nearly constant after a considerably long time. The drain current-voltage characteristics of the device also show appreciable drift with time. It is also shown that, depending on the values of the interface parameters and doping, the device may make a transition from the normally on to a normally off state after prolong ageing. An expression for the critical time required to make such a transition in silicon devices is derived.

We present results of a computer simulation of protein crystal growth based on the Monte Carlo random process and surface kinetics of a growing crystal, which includes site-dependent detachment and migration, and site-independent attachment processes. The results indicate that, if only monomers are included in the attachment process, the simulation does not reproduce the experimentally observed rate of growth of lysozyme crystals at high supersaturation; however, using the same simulation parameters but allowing both monomers and aggregates to become attached to the crystal surface simulates the experimental results both at low and at high supersaturation. The results suggest possible influences of protein aggregates on the crystallization process.

The design, calibration and performance of the TOFLEA are described. The energy spectrum of charge-exchange neutral atoms emitted from the SINP tokamak plasma in the energy range 20-500 eV is measured by the TOFLEA. The flux of neutral particles is gated on a time scale by a slotted rotating chopper disc, placed in a suitably designed UHV compatibility vacuum chamber. The greater sensitivity of the detection of low-energy particles by the Cu-Be target is achieved through a specially designed conductance control arrangement in a different region of the vacuum chamber of the TOFLEA. An improvement in the uncertainty of the estimation of the differential flux emission function has been achieved in the present TOFLEA. The elegance of the TOFLEA is its capability of detecting higher momentum particles of low energy emitted from the plasmas.

A new model for a class of irreversible absorption heat transformers is presented, in which not only the irreversibilities of heat conduction but also the irreversibilities resulting from the internal working fluid dissipation are considered. An ecological optimization criterion is proposed for the best mode of operation of such a class of heat transformers. It consists of maximizing a function representing the best compromise between the rate of heat pumping and the loss rate of heat pumping. It is shown that the model adopted here may be treated as a combined cycle of an irreversible Carnot heat engine and a reversible Carnot heat pump, and by using the combined cycle method, many problems of the heat transformer can be solved simply and conveniently. The ecological optimal performance of the heat transformer is investigated by using such a method and the significance of the ecological optimization criterion is discussed. The results obtained here are of importance in the optimal design and reasonable use of the energy of heat transformers.

A study of viscoelastic shear wave dispersion in a simulated gelation process involving mechanically self-similar nodal networks is reported. The network formed at the gel point (the infinite network cluster, or `critical gel') shares a common structural feature of smaller network clusters and the onset of a recognizably `gel-like' feature is shown to occur when the characteristic wavelength of the network cluster becomes twice that of an individual node. It is shown that, during gelation, the dispersion of shear waves can be exploited to assess the proximity of a system to an equivalent `critical gel' state at any single frequency, thereby identifying the smallest length scale at which gel-like characteristics are established prior to the gel point. In this way, and for the first time, a rheometrical basis is established for examining the gel-like, self-similar characteristics of pre-gel point viscoelastic liquid systems, in terms of the gel equation but in the absence of a frequency-independent loss tangent. Experiments are reported for a critical gel in which the high-frequency wave dispersion is in good agreement with theory.

An approximate formulation of the column calibration factor (CCF), , at any given temperature is derived for thermal diffusion columns (TDC) from the Navier-Stokes equation in cylindrical coordinates. The values of are then used to estimate the experimental thermal diffusion factor of a neon gas mixture with its natural isotopic abundances from measured in four columns of different column geometries. The molecular force parameters of the molecule are estimated from the intercepts and slopes of the linear variations of and the collision integral against and respectively. The excellent agreement of the estimated force parameters with the available literature values and the comparison of the temperature variation of by the CCF method with the existing experimental and theoretical ones establish the fact that the derived relationship of with the column geometries is more than adequate.

The streamer-to-spark transition is an important sub-process of the flashover of high-voltage apparatus. In this paper an investigation of this transition in an electrode gap of the order of 1 cm in dry air with a non-uniform field distribution is presented. Parameters such as the gap distance, polarity of applied voltage and pressure were varied, but the study was concentrated upon the influence of a large series resistance (0-6 M) in the discharge circuit ( inhibited discharges). Mainly, the positive discharge was studied, but some results for negative applied voltages are also included. The main finding was that the presence of a large series resistance in the discharge circuit substantially prolonged the duration of the streamer-to-spark transition. The effect of the inhibiting series resistance seems to be that the disruptive discharge is delayed, but not prevented.

For plasma immersion ion implantation (PIII) the ion flux onto the target is determined by the expansion of the plasma sheath during the voltage pulses. Spatially resolved probe measurements of the electron density during the pulses in the plasma sheath and presheath are presented. An empirical model is used to describe the delayed reaction of the original presheath to the moving sheath edge and the formation of a new presheath. An increased electron density far away from the target, probably caused by electrons displaced by the sheath or secondary electrons, is also detected. Additionally, the refill of the depleted sheath after the pulses is observed and described.

A high-voltage nanosecond breakdown in the form of a fast ionization wave (FIW) has been obtained and investigated in a large discharge volume (of 40 l). For various regimes in the air pressure range -4 Torr the velocity of breakdown front propagation and energy absorption by the plasma were measured. A high level of spatial uniformity and reproducibility of the discharge was demonstrated. The possibility of propagation of FIWs in electrodeless systems was shown. It is demonstrated that the FIW propagates quasi-spherically in a free-boundary space until the reduced electric field in the wavefront is close to or exceeds the electron run-away threshold, otherwise the FIW loses its homogeneity and becomes transformed into a streamer corona discharge.

The piezoresistive response of constantan strain gauges to shock loading has been investigated by bonding them between tiles of a number of materials. The gauged samples have been shock loaded under conditions of one-dimensional strain by the technique of plate impact. Strain gauges have also been placed in mild steel samples to investigate the effect of the phase transition on their response. Results indicate that the strain gauges are affected by this structural phenomenon.