Table of contents

The complex magnetic susceptibility of two magnetic fluids, with different degrees of colloidal stabilization, has been measured over the frequency range 100 MHz to 6 GHz. The colloidal stabilization of the magnetic fluids has been investigated using magneto-optical measurements. Based on complex magnetic susceptibility measurements, χ(ω) = χ'(ω)−iχ''(ω), the dependence of the maximum absorption frequency at resonance, f_max, and of line width, Δf, on an external magnetic polarizing field, H, over the range 0–1.45 kOe, has been examined for both magnetic fluids. The experimental results have been interpreted in terms of magnetic interparticle interactions and particle agglomeration.

This paper reports a suppressed ionic conductivity in a KTiOPO₄ (KTP) crystal grown from a potassium-rich K₄P₂O₇ flux. Potassium-rich KTP is shown to have an ionic conductivity, which is reduced by one order of magnitude relative to normal flux-grown KTP and is explained by an improved potassium–oxygen stoichiometry. However, it is found that the frequency dispersion of the conductivity is almost identical in form to that of conventional KTP, showing that the fundamental Debye-like origin of the conductivity is unchanged as the number of potassium vacancies is decreased. This behaviour is contrasted with that of Rb-doped KTP, in which the conductivity is reduced by a factor of more than 100 and the dispersion is drastically changed to resemble a disordered system rather than a Debye-like relaxor. Potassium-rich KTP is also found to have a reduced low-frequency dielectric constant, a contracted Cole–Cole plot and a lowered ferroelectric coercive electric field of only 3.0(±0.1) kV mm⁻¹ at room temperature. Successful periodic poling of a potassium-rich KTP crystal to produce a grating of 60 μm period is demonstrated at room temperature for the first time. X-ray topographs proving the existence of periodic domains throughout the bulk of potassium-rich KTP in both the usual [100] grating orientation and the unconventional [010] orientation are presented.

Nonlinear optical absorption in silver nanosol was investigated at selected wavelengths (456 nm, 477 nm and 532 nm) using open aperture Z-scan technique. It was observed that nature of nonlinear absorption is sensitively dependent on input fluence as well as on excitation wavelength. Besides, the present sample was found to exhibit reverse saturable absorption (RSA) and saturable absorption (SA) at these wavelengths depending on excitation fluence. RSA is attributed to enhanced absorption resulting from photochemical changes. SA observed for fluence values lower and higher than those corresponding to RSA are, respectively, attributed to plasmon bleach and saturation of RSA.

We fabricated a small molecule nondoped white organic light-emitting device whose structure included indium tin oxide glass substrate/50 nm N, N'-bis-(1-naphthyl)-N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine hole transporting layer/0.05 nm 4-(dicyano-methylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran/25 nm 4,4'-bis(2,2' diphenyl vinyl)-1,1'-biphenyl/15 nm tris(8-hydroxyquinoline) aluminium electron transporting layer/0.5 nm lithium fluoride/aluminium. It showed a maximum power efficiency of 1.74 lm W⁻¹ at 6 V (the brightness is 125 cd m⁻² and the CIE 1931 chromaticity coordinates are (0.34, 0.36)). Its brightness reaches 3750 cd m⁻² at 15 V. And the chromaticity coordinates, varying from (0.36, 0.38) to (0.30, 0.32) with increasing forward bias from 4 to 15 V, are well within the white region.

Experimental studies on vertical oscillations of few particle vertical structures are described. One and two particle strings were subjected to two types of vertically driven oscillations. The first was electrode driven, which excites the structure as a whole, while the second was laser driven, which excites one particle in the structure only. The latter experiments are highly original, enabling us to excite two vertical resonances in our two particle structures. From the close agreement between our experimental data and theoretical model, several important physical parameters have been estimated, including the charge ratio and the Debye length.

This paper introduces a thermodynamic model to determine composition, temperature and pressure of the plasma cloud induced by pulsed laser irradiation in the case where a relevant thermal sputtering mechanism is operating at the surface of a molten layer. The model concerns in particular pulse lengths of the order of several nanoseconds and completes the results of a previous paper concerning the physics of the evaporation and boiling driven thermal sputtering (Tosto S 2002 J. Phys. D: Appl. Phys.35); the recession rate and temperature at the molten surface are linked to the pulse fluence and plasma properties in the frame of a unique physical model. This paper shows that the plasma properties depend critically on the non-equilibrium character of the surface evaporation and boiling mechanisms. The extension of the model to the case of continuous laser irradiation is also discussed. Some examples of computer simulation aim to show the results available in the particular case of a metal target; the comparison between calculated and experimental data supports the validity of the model.

In this paper, a cutting plasma torch is studied. We show how experimental and theoretical approaches are complementary for a full characterization of the plasma due to its specific parameters: high temperature, shock wave, pumping of surrounding gas, high velocity. Classical measurement methods cannot be used and two original methods are proposed: the first in the shock wave, where the pressure is unknown, and the second 11.2 mm from the nozzle exit, where the plasma composition depends on the pumping of ambient air.

By using a back and forth approach between the theory and experiment, all the plasma characteristics can be estimated. The shock wave location is well predicted and temperatures around 18 kK are obtained in the shock wave and around 14 kK near the anode.

We present an experimental and numerical modelling study of dielectric barrier discharges in pure, flowing helium at atmospheric pressure, in a 3.0 mm length needle-plane gap. Ultra-high speed imaging and synchronous, real-time dual detection (optical–electrical) diagnostics have been carried out. The high-voltage electrode was a hyperboloidal steel needle with a sharp point of 40 μm radius, while the grounded electrode was covered with 1.6 mm of Al₂O₃. The surface of the latter was either bare (case 1) or coated with ∼20 nm of semiconducting graphite (case 2) or metallic aluminium (case 3), all at floating potential. Axial [z(t)] and radial [r(t)] time-evolutions (⩽2 μs) of discharge propagation across the gap were found to depend very strongly upon surface charging or conduction (cases 1–3). A two-dimensional model of the needle-plane discharge, based on coupled solution of the continuity equations for electrons, ions and excited neutral particles and of Poisson's equation, was found to agree very well with the observed [r,z](t) behaviour.

This paper describes the utilization of a 3 kW continuous wave CO₂ laser to modify the wettability characteristics of the magnesia partially stabilized zirconia (MgO-PSZ) bioceramic and analyses the changes in the physical characteristics of the MgO-PSZ surface following the CO₂ laser interaction. The measurement with a set of test liquids revealed that CO₂ laser surface treatment of the MgO-PSZ brought about a reduction in the contact angles, θ, indicating that the wettability characteristics of the MgO-PSZ had been enhanced. It was subsequently deduced that the factors active in causing the observed modification in the wettability characteristics of the MgO-PSZ were the increase in the surface O₂ content and the increase in the polar component of the surface energy, γ_sv^p. Furthermore, it was noted that the considerable decrease in contact angle was disproportional to the increase in surface roughness, showing surface roughness plays a minor role in inducing changes of the wettability characteristics of the MgO-PSZ. The value of this paper is that establishes the CO₂ laser as a controllable and flexible process for improving the surface properties of the MgO-PSZ bioceramic.

Raman microscopy has been used to investigate phase transitions within Vickers diamond residual indentations, made at room temperature and at 77 K, in single crystal Si(100) and 0.3 μm thick amorphous silicon film deposited on a sapphire single crystal. It has been found that for room temperature residual indentations in the single crystal silicon (Si-I) and amorphous silicon film phase transition to the Si-III phase occurs, as indicated by the existence of Raman peaks corresponding to this phase. On the other hand, in the case of the indentations made at 77 K, only the Si-I crystalline phase and amorphous silicon were found within the residual indentations. It has been suggested that when Vickers diamond indentations are made at 77 K, there is no phase transition to the Si-II (i.e. the β-Sn phase) during indenter loading, which would give rise to the Si-III phase on the removal of indenter load. Moreover, the existence of a very strong peak due to the Si-I phase gives further support to the suggestion that during Vickers indentations in single crystal silicon and in amorphous silicon at 77 K there is no structural phase transition. It has also been suggested that during room temperature indentations there is a substantial temperature rise, which may help to cause structural phase transitions.

The ferroelectric behaviour of KNO₃ : PVDF composite films was studied. The ferroelectric polarization versus voltage (P–V) and polarization current density versus voltage (J–V) characteristics were simultaneously investigated in 20% KNO₃ composite film. The remanent polarization and coercive voltage have been obtained. The frequency dependence of coercive voltage (V_c) shows V_c∝f^1/n, where n≈6.6. The polarization fatigue effect investigations on the composite films gave P_r to be approximately constant up to 4×10⁵ cycles. The switching response was studied using square wave signal and Ishibashi and Takagi theory was applied to the switching current transient. The needle like domain growth is believed to be involved in the switching process of the composite films. The effective of voltage and doping per cent of KNO₃ (by weight) on switching transients has been also investigated. The effective dimensionality has been found to decrease with doping percentage of KNO₃. The switched charges do not show monotonic increase with voltage for the composite films below 50% KNO₃ doping level.

We demonstrate submillimetre-wave Fourier transform spectroscopy as a novel technique for biological molecule characterization. Transmission measurements are reported at frequencies 10–25 cm⁻¹ for single- and double-stranded RNA molecules of known base-pair sequences: homopolymers poly[A], poly[U], poly[C] and poly[G], and double-stranded homopolymers poly[A]–poly[U] and poly[C]–poly[G]. Multiple resonances are observed (i.e. in the microwave through terahertz frequency regime). We also present a computational method to predict the low-frequency absorption spectra of short artificial DNA and RNA. Theoretical conformational analysis of molecules was utilized to derive the low-frequency vibrational modes. Oscillator strengths were calculated for all the vibrational modes in order to evaluate their weight in the absorption spectrum of a molecule. Normal modes and absorption spectra of the double-stranded RNA chain poly[C]–poly[G] were calculated. The absorption spectra extracted from the experiment were directly compared with the results of computer modelling thereby, confirming the fact that observed spectral features result from electromagnetic wave interactions with the DNA and RNA macromolecules. Correlation between experimental spectrum and modelling results demonstrates the ability of normal mode analysis to reproduce RNA vibrational spectra.

Positively charged ²⁰⁸Tl ions are transported through liquid xenon using electric fields in the range of 4–10 kV cm⁻¹ and for drift distances up to 50 mm. From these measurements we deduce upper limits on the attenuation length for Tl ions in liquid xenon, resulting in a lifetime >5.5 s. In addition to these results, the field independent mobility of Tl bearing species in liquid xenon was measured to be 1.33±0.04×10⁻⁴ cm² V⁻¹ s⁻¹. This result, when coupled with those for other species by previous workers, suggests that positive ion mobility in liquid xenon is proportional to the hard-core radius. Applications to Ba ion collection in a double beta decay experiment are also discussed.

The structural and magnetic order changes induced by mechanically assisted nitridation of Zr_1−xFe_x alloys and compounds as a function of composition, initial structure and processing time have been studied. It was observed that at the applied conditions, as N is incorporated, phase transformations occur following the schematic sequence: Zr_1−xFe_x→a-(Zr_1−xFe_xN_y)→δ-Zr_1−xFe_xN→δ-ZrN+Fe (a = amorphous). In this way, regardless of the initial composition and structure, the final product after prolonged milling was a mixture of nanocrystalline δ-ZrN and almost pure iron and/or Fe–Zr complexes, evidencing the strong tendency of Zr to combine with N and that of transition metals to segregate. The formation of δ-Zr_1−xFe_xN proceeds through the growth of δ-ZrN structure in the amorphous matrix keeping Fe inside, replacing some Zr. For Zr-poor samples the amorphization stage is practically unobservable, obscured by the dominating Fe segregation. This contrasts with the results of milling in Ar, where the steady state is an amorphous phase for Zr_1−xFe_x compounds or mixtures in a wide compositional range. These findings are discussed in terms of possible basic mechanisms for the mechanically activated reaction and keeping in mind its application to the formation of nanoprecipitates of δ-ZrN in various Zr alloys.

We re-analyse earlier measurements of resistance R and piezoresistance K in RuO₂-based thick-film resistors (TFRs). The percolating nature of transport in these systems is well accounted by values of the transport exponent t larger than its universal value t≃2.0. Furthermore, we show that the RuO₂ volume fraction dependence of the piezoresistance data fit well with a logarithmically divergence at the percolation threshold. We argue that the universality breakdown and diverging piezoresistive response could be understood in the framework of a tunnelling–percolating model proposed a few years ago to apply in carbon-black–polymer composites. We propose a new tunnelling–percolating theory based on the segregated microstructure common to many TFRs, and show that this model can in principle describe the observed universality breakdown and the diverging piezoresistance.

Experimental and theoretical studies were carried out to understand an ultrasonic micro dry powder feeding mechanism. The ultrasonic micro feeding system was used to deliver ultra-fine dry powders through capillary tubes with an inner diameter of 125 μm and 50 μm, respectively. The powder flow rates were measured and various powders were discharged continuously at a flow rate as low as 10 μg s⁻¹. The powder packing inside the capillary tube was densified by the ultrasonic waves since the powder density at the feeding tip was much higher than that in the hopper. Acoustic streaming and friction driving might be the driving forces for the powder feeding through the micro capillary tubes. Further theoretical study will be needed to fully understand the behaviour of this feeding mechanism. It was also found that thermal effects in the lead zirconate titanate plate influenced the performance of powder feeding significantly. With this system, micro dry powder patterns can be deposited directly and precisely on substrates.

Tantalum (Ta) diffusion barrier films were deposited on un-patterned and patterned silicon substrates at ambient temperature and without substrate bias by filtered cathodic vacuum arc (FCVA). The films were characterized by atomic force microscopy, scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, four-point resistivity probe and surface profilometer. It was found that the Ta film was 750 Å thick and free of C and O except for surface contamination. The film morphology was smooth and uniform with root-mean-square roughness of ∼0.82 Å. The Ta film was polycrystalline β phase with a mean grain size of ∼3 nm and possessed a dense microstructure, which are ascribed to the high energy of the condensing species in FCVA. It was shown that the Ta filling of the trenches (0.33 μm wide, 1 : 1 aspect ratio) was very conformal and quite uniform. Also, it was preliminarily found that at the Ta film was effective against diffusion of Cu into Si at 600°C.