Table of contents

The geometric optics model of light scattering from droplets is based on the interference of the reflected and refracted light. Although the relationships are regularly quoted, we have found that the assumptions in the underlying derivations are incorrect. In this rapid communication, we derive the correct optical path difference between reflected and refracted beams scattered from a droplet. Furthermore, we show that the standard form used for the scattering factor relating the fringe separation to the droplet diameter is wrong - we derive the correct analytical result, which leads to a correction in droplet-size calculations based on optical measurements.

Hydrogenated Si cluster ions have been grown from silane gas under electron irradiation in an ion trap with five different gases, , He, Ne, Ar and Xe, as ambient. The mass spectra of always had three peaks corresponding to x = 1, 7 and 13, but their peak heights varied depending on the ionization energy of the ambient gas except that produced an exceptionally large amount of . This dependence was attributed to the ability of the ambient gas to dissociate to form reactant, which is essential to the growth of .

Results for the angular dependence of the backscattering coefficient for 3.0 and 5.0 keV electrons incident on a tungsten target are presented. The values of measured at extreme angles of incidence , namely, at and , are found to be 0.389 and 0.468 for 3.0 keV and 0.429 and 0.524 for 5.0 keV respectively. Experimental data are compared with the available theoretical and experimental results. The agreement between experiment and theory is found to be satisfactory for the low angles of incidence but deviations are observed for higher values. Possible reasons for these discrepancies are pointed out and discussed.

A memory-type colour reflective display device is proposed. Introducing smectic liquid crystal to holographic polymer dispersed liquid crystal (HPDLC) successfully produced a memory function while keeping the advantages of HPDLC. This device is electrically writable and thermally erasable. It was able to maintain the memory state for more than 4 months. The mechanism of the memory function was analysed by comparing three HPDLC devices which were made with three different cyano-biphenyl compounds. The compounds had similar molecular structures but different phase transition temperatures. Small passive matrix devices for three primary colour devices were successfully demonstrated and colour mixing was confirmed to occur on stacking.

Two types of atomically resolved scanning tunnelling microscopy (STM) images from a - surface are observed. Depending on the chemical identity of the tip apex, the five-fold coordinated surface cations can appear either as protrusions or as depressions. The interaction between the tip apex atom and the surface is examined and discussed in relation to image formation.

We report new results concerning the composition and the structure of the particulates covering the surface of the thin films deposited by reactive pulsed laser deposition (RPLD) from a Ti target in low-pressure methane. We show that the small particulates having diameters smaller than 0.5 m have a composition and a morphology identical to that of the deposited films which consist of pure, stoichiometric, cubic TiC with a lattice parameter of 0.436 nm. In contrast, the larger particulates with diameters up to 3 m are a mixture of TiC and prevalent unreacted Ti. All particulates seem to have a spherical geometrical shape at the moment of their impact onto the collector. We consider that this feature is congruent with the formation of particulates by expulsion in a liquid phase from the melted layer existing inside the crater forming on the target's surface under the action of the pulsed laser irradiation.

Nanoscale Al/AlN multilayers have been fabricated by ion beam assisted deposition at various nitrogen ion energies, fluxes and ion-to-atom arrival rate ratios. Computer simulations are performed to describe the deposition process and for comparison with the experimental results. At lower ion energies, fluxes and ion-to-atom ratios, the calculated results are in good agreement with the experimental data. Under this condition film formation is dominated by ballistic processes. For higher ion energies, fluxes and ion-to-atom ratios, comparison of the simulations with experiments reveals that, in addition to ballistic processes, diffusional and chemical processes may play a significant role in film formation.

In this paper, the photorefractive properties of a low-glass-transition-temperature polymeric composite based on poly(N-vinylcarbazole) doped with an azo dye system with various lengths of alkoxy chain as an electro-optical (EO) chromophore and 2,4,7-trinitro-9-fluorenone as photosensitizer were studied by using two-beam coupling and four-wave-mixing experiments. The results showed that the alkoxy chain attached to azo dye can perform plasticization. An optimal length of alkoxy chain was selected.

The experimental validation of a mathematical model that predicts the shading coefficient (SC) and the solar rejection factor (SRF) of various types of solar control coatings is presented. The model allows us to input the solar absorptance and predict the temperature of the solar control glazing as a function of the thermal emittance and exterior temperature for typically AM2-solar radiation. With the additional knowledge of the solar reflectance, the SC and SRF are calculated. The model is tested using a chemically ZnS- solar control coating deposited on a 6 mm clear glass and the results are compared with those for commercial glasses.

A variety of schemes are presented, suitable for the temporally and spatially controlled generation of ultrasound pulses with a centre frequency near 1 GHz. Direct excitation of acoustic waves in water, serving as the coupling and transport medium, relies on the resonant absorption of short erbium laser pulses in water: at the interface with an adjoining solid material or at a free water surface. Ultrasonic amplitudes, leading to nonlinear acoustic effects, have been demonstrated. The photoacoustic excitation methods presented here are suitable for scanning acoustic microscopy, for example for the real-time study of biological cells in vivo.

The paper addresses minimization of the dissipation in systems maintaining constant temperature or other constant intensive variables (potentiostatted systems). The entropy production and energy consumption of such systems are reduced from those of the traditional scheme if additional chambers are interposed between the system and its surroundings, in which intermediate values of thermodynamic potentials are maintained. The analysis is applied to a cryogenic system but it can be extended to high-temperature systems and to the systems in which insulation from mass transfer (constant chemical potential) or electrical conductivity (constant electrical potential) is maintained.

In an effort to establish the optimum conditions for depositing high-quality diamond films at high deposition rates using a plasma torch, modelling work has been focused on developing a realistic model for determining temperature, velocity and particle density distributions in the plasma jet. To enhance molecular decomposition, which favourably improves diamond synthesis, high-speed gas is passed through a supersonic anode nozzle. In the subsequent low-pressure chamber, the chemical reactions cannot follow the fast macroscopic translation, resulting in distributions of dissociated precursors that are far from chemical equilibrium. To simulate the finite rate chemistry, a generalized implicit multi-component algorithm is introduced and examined in the context of a two-dimensional computational model of a chemically reacting Ar- supersonic plasma jet. The scheme can be adapted to other plasma flows in which chemical non-equilibrium is encountered.

The dynamic potential formation of a radio-frequency (rf) sheath near the substrate was experimentally studied over a wide range of the frequency under a fixed plasma density produced by an Ar dc discharge plasma. Potential structures of the rf sheath obtained by detecting spatial profiles of the crest and trough potentials in the rf oscillation provided a strong frequency dependence. The sheath thickness of the trough potential expanded in the high-frequency region unlike the rf electrode in the conventional capacitively coupled rf discharge plasma. The potential well with a depth of an electron temperature formed in front of the substrate on the crest profile in the low-frequency region. Similar experiments in a dc discharge plasma producing negative ions were also performed. The virtual anode formed in the crest profile and its potential height grew with increasing applied frequency.

Laser-induced plasmas are needed as sources capable of delivering intense radiation in the VUV, XUV and soft x-ray spectral range through amplified spontaneous emission (ASE). As an example transition emission on the He II line at nm is studied and investigated with respect to ASE.

A laser-induced plasma (optical discharge) is produced by a focused beam of a Q-switched laser at high pulse repetition rates from 4 to 87 kHz and a pulse width of 35 ns and 200 ns respectively. The laser intensity required to ignite a laser-induced plasma is considerably reduced compared with single-shot experiments, because the electron density between two laser pulses remains on a relatively high level. Thus up to about 70% of the incoming photons are absorbed with helium and carbon dioxide as the working gas and heat the plasma. The absorption effectiveness is definitely lower in oxygen and nitrogen.

The temporal and spatial distribution of electron temperature and density have been measured. In the centre of the helium plasma the electron temperature and density reach K and respectively. Strong quasi-steady transient line emission of He II lines has been observed but ASE was not found.

The spatial profiles of charged particles in multipolar magnetically confined Ar- plasmas produced by dc discharges are investigated by varying the total pressure from 2 to 10 mTorr, the discharge current from 10 to 90 mA and the oxygen content from 4 to 20%. The measured spatial negative ion and electron density profiles, which are approximated as a parabolic distribution and a uniform one except in the vicinity of the chamber wall, respectively, allow us to divide the entire discharge into three regions: (i) an electronegative region, (ii) an electropositive region and (iii) the sheath. The ratio of the negative ion density to the electron density measured at the centre increases with increasing oxygen content and pressure, but decreases with increasing discharge current. Oxygen content- and discharge current-dependences of the electronegative region's length are similar to those of the ratio, although the length does not strongly depend on the pressure. A global model, in which the flux balance equations for charged particles and a power balance equation for electrons are taken into account, to estimate plasma parameters such as the individual charged particle density and electron temperature is proposed, and then compared with the experimental results.

A partial discharge model has been developed to simulate experimental partial discharge activity within electrical tree structures grown in polymeric based insulation. A pin plane electrode arrangement and tree were defined on a grid representing an area 2 mm by 2.1 mm. A sinusoidal 50 Hz voltage was applied to the pin tip and 3600 time steps per cycle were used to give a phase resolution of . Partial discharges were simulated at each time step by adding one or more dipoles of charge onto the tree structure to reduce the potential difference between adjacent points in the tree from to . Each dipole of charge represents a local electron avalanche occurring over a distance equal to the grid spacing. The model parameters, and , represent the discharge properties of the decomposition gas. Partial discharge current pulses in the external circuit and the induced image charge were calculated as a function of time. The spatial distribution of the emitted light in the tree structure over one cycle of the applied voltage was also calculated. The close agreement between the calculated and experimental data suggests that the underlying assumptions used in the construction of the partial discharge model are appropriate for the case of electrical trees grown in the flexible epoxy resin.

The UV exposure of Fe:PVA thin films induces modifications of both the refractive index and the absorption coefficient. M-line spectroscopy showed the variation of the refractive index while Mössbauer measurements present the ratio versus the exposure energy. The diffraction efficiency experimental data were satisfactorily explained in correlation with the ratio.

A new acoustoelectric method is developed in order to study solid state layered structures. The method is based on the transient transverse acoustoelectric voltage (TAV) measurements. The decay of the TAV signal is read when a surface acoustic wave (SAW) producing the signal is switched off. The shape of the transient voltage and its spectral dependence on the wavelength of a light irradiation are studied. A theoretical model is presented to explain the transient TAV data. The results demonstrate that the transient acoustoelectric technique is an effective means of characterizing trapping centres in the bulk and at surfaces or interfaces of epitaxial semiconductor structures.

On illumination, selenium deposited on nanoporous n- transfers photogenerated electrons into . When p-CuCNS is coated on top of the selenium deposited on nanoporous n-, holes are directed into the p-CuCNS. A photovoltaic cell of nanoporous n-/selenium/p-CuCNS based on the above charge transfer process generates a photocurrent of and a photovoltage of mV at simulated sunlight. The efficiency of the cell seems to be limited by surface recombination and the presence of voids in the film. Photoelectrochemical experiments also indicate that when selenium is deposited on nanoporous n- photogenerated electrons in selenium are efficiently transferred to .

Two different types of Nd:YAG laser oscillators are used simultaneously in order to increase the weld penetration depth. A rectangularly modulated CW beam emitted from a CW-pumped laser oscillator together with a pulse beam emitted from a pulse-pumped oscillator is irradiated onto stainless steel (304). This paper investigates the contribution of a pulsed beam to welding characteristics in two-laser-beam welding. A pulsed beam with high peak power is effectively combined with a modulated CW beam for adjusting the power density in order to obtain deep penetration. The plume is extinct during modulated CW beam irradiation after the emission of a pulsed beam under deep penetration conditions. On the basis of this phenomenon, keyhole behaviour could be considered and it is recognized that a pulsed beam with high peak power would play a significant role in enlarging the keyhole. A strong correlation between the penetration depth and the plume extinction time is apparent. Therefore, the keyhole might be temporarily but sufficiently enlarged and penetration might be consequently deepened by a pulsed beam with high peak power.

Ac electrokinetics is concerned with the study of the movement and behaviour of particles in suspension when they are subjected to ac electrical fields. The development of new microfabricated electrode structures has meant that particles down to the size of macromolecules have been manipulated, but on this scale forces other than electrokinetic affect particles behaviour. The high electrical fields, which are required to produce sufficient force to move a particle, result in heat dissipation in the medium. This in turn produces thermal gradients, which may give rise to fluid motion through buoyancy, and electrothermal forces. In this paper, the frequency dependency and magnitude of electrothermally induced fluid flow are discussed. A new type of fluid flow is identified for low frequencies (up to 500 kHz). Our preliminary observations indicate that it has its origin in the action of a tangential electrical field on the diffuse double layer of the microfabricated electrodes. The effects of Brownian motion, diffusion and the buoyancy force are discussed in the context of the controlled manipulation of sub-micrometre particles. The orders of magnitude of the various forces experienced by a sub-micrometre latex particle in a model electrode structure are calculated. The results are compared with experiment and the relative influence of each type of force on the overall behaviour of particles is described.