Table of contents

The effect of dispersal of ferroelectric ceramic materials Ba_0.70Sr_0.30TiO₃ (T_c ≈ 30°C) and Ba_0.88Sr_0.12TiO₃ (T_c ≈ 90°C) on the ionic conductivity of an ion conducting polymer electrolyte (PEO : NH₄I) is reported. The addition of 3 wt% of Ba_1−xSr_xTiO₃ (x = 0.30 and 0.12) results in an increase in the conductivity by one to two orders of magnitude. Further, a study on the temperature dependence of conductivity of these composites shows that the conductivity enhancement 'peaks' as we approach the dielectric phase transition of the dispersed ferroelectric material where the ε changes rapidly from ∼ 2400 to 7500 (for x = 0.30) and from 1100 to 5500 (for x = 0.12). This establishes the role of dielectric constant of the dispersoid in enhancing the ionic conductivity of the polymeric composites.

X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy are used to study Si nanocrystal formation in Si-implanted SiO₂ films as a function of thermal annealing. Analysis of the XPS Si 2p peaks shows the existence of five chemical structures corresponding to the Si oxidation states Siⁿ⁺ (n = 0, 1, 2, 3, and 4) in the SiO₂ films, and the concentration of each oxidation state is determined quantitatively. The XPS results show a clear picture of the evolution of the chemical structures and the formation of Si nanocrystals as functions of annealing temperature and annealing time. The evolution of the concentrations of the five oxidation states with annealing is explained in terms of the thermal decompositions of the suboxides corresponding to the three oxidation states Siⁿ⁺ (n = 1, 2, and 3) and the thermal oxidation of the implanted Si.

Combining ferromagnetic and semiconductor materials is a challenging route to create new options for electronic devices in which the spin of the electron is employed. The spin-valve transistor (SVT) is the first of such hybrid devices shown to work successfully. This review describes the basic science and technology of the SVT and derived devices, such as the magnetic tunnel transistor.

The FeCo/AlO_x/Co magnetic tunnel junction was fabricated using a two-step plasma oxidation technique. The tunnelling magneto-resistance ratio of the junction as-deposited was about 8.5%, and reached 14.0% after annealing at 200°C. Transmission electron microscopy, high-resolution electron microscopy and electron holography were used to study the microstructure of the junction. The enhancement of the magneto-resistance effect after annealing could be attributed to the uniformity of the barrier layer, the improvement of FM/I interfaces, and the deoxidization of the bottom ferromagnetic electrode.

A new approach to the understanding of biological activity caused by low-intensity laser radiation, in which coherence is a factor of paramount importance, has been developed. It is based on the dipole interaction of gradient laser fields with cells, organelles and membranes. The laser intensity gradients in an object arise due to the interference of the light scattered by the tissue with the incident light beam (speckle formation). Apart from speckles, different types of light spatial modulation can be created deliberately using different schemes for beam interference.

It is shown that gradient laser fields may cause spatial modulation of the concentration of particles and increase their 'partial temperature'. This paper presents the results of experimental observation of trapping of different types of particles, including human lymphocytes, in the interference fields of the He–Ne laser. The sweep-net effect on particles of different sizes on moving the laser field is demonstrated and crystal-like self-organization of particles in the laser gradient field is observed.

The influence of gradient laser fields on erythrocyte rouleaus, on the apoptosis of human lymphocytes as well as on their chromosome aberrations is demonstrated. It may be concluded from the experimental studies that the influence of an interference laser field with a rightly chosen period can stimulate the repair system of a cell, increasing its viability.

Non-doped-type white organic light-emitting devices based on the ultrathin yellow-emitting layer (0.1 nm) of 5,6,11,12-tetraphenylnaphthacene (rubrene) and the thick blue-emitting layer of 4,4'-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl (DPVBi) made from vacuum-deposited organic thin films are reported. The recombination zone of the devices can be adjusted by changing the thicknesses of DPVBi and the electron transport layers (tris-(8-hydroxyquinoline)aluminium, Alq₃). In the device with 30 nm DPVBi and 30 nm Alq₃, bright white light, over 10 000 cd m⁻², was successfully obtained at a low drive voltage of ∼10 V. The highest power efficiency is 3.18 lm W⁻¹ at 4 V, and stable 1931 Commision International de L'Eclairage coordinates are obtained for luminance ranging from 100 to 20 000 cd m⁻² (at ∼12 V).

Growth interruption and H-plasma exposure on stacking layers provide an intellectually challenging route for the deposition and control of Si nanostructures. Atomic H of the plasma not only acts as the terminator of the dangling bonds but also plays an important role in the chemical reactions during the propagation of the Si network, by offering either topological freedom or chemical potential to the growing surface. The use of time modulated gas flow in plasma enhanced chemical vapour deposition (PECVD) gives an additional degree of flexibility to the process of nucleation, growth, and control of grain size in the development of Si nanostructures. The density and the size of the nanocrystallites can be controlled by suppressing growth of nucleated Si particles within a critical dimension by optimization and repetition of deposition/plasma-exposure cycles. The degree of H-plasma treatment and the growth temperature both have individual influences on nanocrystallization. Nano-Si structures are obtainable with very narrow thicknesses and at a very low temperature, utilizing standard deposition techniques like PECVD, commonly used in silicon semiconductor technology, and thus hold great promise in device fabrication, extending a novel approach towards silicon nanotechnology.

The structure of PtSi/p⁺/p-Si fabricated by chemical vapour doping has been investigated for reduction of the Schottky barrier height. The interface structure and photoelectric properties of PtSi/p⁺/p-Si thin film structure have been studied. The results from AES profile analysis show that doped boron moves with the PtSi/Si interface during silicide growth. Concomitantly, the boron at the PtSi/Si interface out-diffuses to the Pt–PtSi interface. Finally, the boron piles up at the surface. It has been considered that the redistribution of the dopant boron is due to the solubility of the dopant in the silicide. The Schottky barrier height of PtSi/p⁺/p-Si is 0.13 eV (for cutoff wavelength 9.5 µm). That is lower than the 0.19 eV value of PtSi/p-Si (for cutoff wavelength 6.5 µm). Since the Schottky barrier height is lowered, the cutoff wavelength can be extended. Due to the Fowler dependence, the detector's quantum efficiency can be improved.

An analytical expression for calculating the modulation transfer function (MTF) due to distributed carrier trapping in the bulk of the photoconductor of a direct conversion pixellated x-ray image detector is derived using the trapped charge distribution across the photoconductor. The analytical expressions of trapped charge distributions are also derived by solving the continuity equation for both types of carriers (electrons and holes). The MTF of photoconductive x-ray detectors is analysed in terms of normalized parameters, namely (a) the normalized x-ray absorption depth (absorption depth/photoconductor thickness) and (b) normalized carrier schubwegs (schubweg/thickness). Trapping of the carriers that move towards the pixel electrodes degrades the MTF performance, whereas trapping of the carriers that move away from the pixels improves the sharpness of the x-ray image. The MTF model is applied to polycrystalline CdZnTe detectors and is fitted to recently published experimental results. The theoretical model shows very good agreement with reported experimental data.

Inspired by the Talbot effect, a grating projection system was designed. Periodic patterns were produced from a projection of a diffraction grating illuminated by a spherical wave of monochromatic coherent light. The diffracted light was collimated by a lens, the focal distance of which was at the centre of the incident spherical wave. Experiments demonstrated that the diffracted orders were also spherical waves centred on the same transverse plane as the incident light. The periodic illumination observed at different locations along the optic axis was proven to be the result of interference between the diffracted orders. It was demonstrated that this system could be used to measure velocities up to 20 m s⁻¹ of particles crossing the fringes at distances up to 3 m.

The cross-sectional structure of the two lowest ion-acoustic instability modes in the positive column of a cylindrical, high-current discharge, traditionally used as an active medium in CW ion gas lasers, has been investigated. The diameter and length of the discharge column in our experiments were 16 mm and 1 m, respectively, and the discharge current was 250–350 A. Under these conditions, the observed mode frequencies were ν₁ = 190 kHz and ν ₂ = 390 kHz. To obtain the spatial structure of these modes, time-resolved integral projections of spontaneous argon-plasma emission were measured in planes normal to the discharge axis. From the power spectra of the measured projections, the structures of the modes ν₁ and ν ₂ were reconstructed using computerized tomography algorithms. Based on available theoretical models of the instability, the modes have been identified as the (1, 1) and, tentatively, the (1, 2) modes of oscillation.

A study of the K_α radiation emitted from Ti foils irradiated with intense, ∼0.2 J, 67 fs, 800 nm laser pulses, scanning a range of intensities (∼10¹⁵–10¹⁸ W cm⁻²), is reported. The brightness of single-shot K_α line emission from the front of the targets is recorded. The yield from bare titanium (Ti) is compared to that from plastic (parylene-E) coated Ti. It is demonstrated that, for a defocused beam, a thin layer of plastic increases the yield.

CuO–SnO₂ thin film elements were prepared by sequential evaporation of Sn and Cu metals in high vacuum conditions by an electron beam evaporation technique and subsequent oxidation of the metallic bilayer under flowing oxygen conditions. The electrical properties of the thin film element were studied by a two probe method in the temperature range 110–220°C. On exposing the CuO–SnO₂ thin films to a H₂S–air mixture, it is observed that the resistance decreases by several thousand times. The H₂S sensitivity of the thin film element was measured at three sensor operating temperatures. While the sensitivity decreased with an increase in temperature, both the response and recovery times improved with increasing temperature. The sensor element was selective to H₂S gas and did not show any sensitivity to hydrogen and ethanol. The extraordinarily high sensitivity to H₂S gas is attributed to the outstanding promoter action of CuO along with the unique porous structure of the thin film element as revealed by scanning electron microscopy studies.

The reversible transformations between the metastable paraelectric phase induced in irradiation and polar ferroelectric phase (FEP) during both applied external field and thermal cycling process, were observed experimentally. The transition induced by thermal is interpreted by the ferroelectric theory of first-order transition, and the other one induced by electric field is explained by Landau–Devonshire phase transition theory. It is useful to elucidate the microscopic mechanism involved, and this might also be the most possible microscopic interpretation for large electrostrictive strain in these copolymers.

This paper reports theoretical optical properties of composite metal (Cu, Ag, Au, Ni, Pd and Pt) nickel oxide thin films, aiming to create a new electrochromic material. Selective absorption was verified only in composites with metals belonging to the IB column of the periodic table. In particular, emphasis was given to the spectral transmission, reflection and absorption, between 0.4 and 2.5 µm, of Au–NiO composite thin films, that showed the narrowest absorption band in the visible spectrum. Au–CoO films presented similar results. The calculations were based on the Maxwell–Garnett effective medium theory, with Au fill factors, f, varying from 0.0 to 0.2. The Au configurations were modelled to be isolated single spheres (ISS), isolated double spheres, single linear chain (SLC), double linear chain and fcc clusters (FCCs). Independent of the aggregate state, the increase in the fill factor enhances the selective absorption and broadens the absorption band of the films. Films with different thicknesses (0.1–0.3 µm), but with the same amount of Au particles per unit area and aggregate state, showed distinct interference patterns in the transmission and reflection spectra. The absorption spectra were almost insensitive to thickness, being very dependent on the gold content and configuration. The tailoring of the optical properties in the visible region of the Au–NiO films was achieved by controlling the Au configuration. A combination of ISS (25%), SLC (25%) and FCC (50%) was also simulated.

We studied the structure and magnetic properties of as-deposited and subsequently annealed Co_xC_100−x granular films fabricated by a DC facing-target magnetron sputtering system at room temperature using atomic force microscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy and a vibrating sample magnetometer. The average roughness, R_α, of the as-deposited Co_xC_100−x granular films is smaller than that of the Si(100) substrates. XRD and TEM analyses indicate that the as-deposited Co_xC_{100 − x} granular films are composed of ∼2 nm amorphous cobalt grains dispersed in an amorphous carbon matrix, and their morphology is composition independent. The high resolution TEM image of the as-deposited Co₃₀C₇₀ film shows that cobalt and carbon have already separated during the deposition, even if the aggregation of cobalt is not complete. Annealing at 300–450°C causes the crystallization of amorphous cobalt followed by an increase in grain size and the graphitization of the amorphous carbon matrix. The constriction arising from the structural environment results in the coexistence of the hcp and fcc Co phases at temperatures higher than the phase transformation point of 425°C. Magnetic measurements reveal that the coercivity of the as-deposited Co_xC_100−x granular films decreases with the increase in cobalt concentration, and increases with decrease in film thickness. The enhanced coercivity can be attributed to the weakened intergrain interaction because of the increased percolation threshold and/or the destruction of long-range domain structures caused by the reduction in film thickness.

Europium doped LiNaSO₄ in its nanocrystalline form has been prepared and its thermoluminescence (TL) properties are studied. The TL glow curve of the phosphor has been found to have a simple structure with a single peak at 432 K. Though the highly sensitive, commercially available TL phosphor LiF : Mg, Cu, P (TLD-700H) is about 1.5 times more sensitive than the nanocrystalline material, the sensitivity of the concerned nanomaterial is much higher (∼10 times) than the other standard phosphor TLD-100 (LiF : Mg, Ti). Compared to the conventional LiNaSO₄ : Eu phosphor (prepared through a melting procedure and having particle size of 125 µm), the nano-sized phosphor has a lesser TL sensitivity. However, this reduction in TL sensitivity on decreasing the particle size from micrometres to nanometres gives a better understanding of the TL phenomenon. The order of TL kinetics for the concerned nanomaterial is also found to be different from that of the conventional material. Photoluminescence studies that have been performed on these materials throw light on the reasons for such a change in the order of kinetics. Further, fading and reusability of the concerned nanomaterial has also been studied and it has been found that the phosphor is quite suitable for radiation dosimetry.

The dynamic Faraday cup is an electrostatic device used to measure the charge and velocity of a moving charged particle. In this paper, the interaction between a charged particle and a dynamic Faraday cup is described analytically, including the difficult case where the particle is close to but not in the cup. A summation method is used to extract information from the slowly converging series that results from the approximation that we use, and we are able to determine the charge distribution and mutual capacitance of the system. An example of the calculated and measured responses of a typical Faraday cup is provided. The agreement between the calculated and measured response of the cup, given in terms of the standard deviation, is from 4.5 × 10⁻³ to 9.4 × 10⁻³ for the inside of the cup and from 3.3 × 10⁻² to 3.6 × 10⁻² for the outside of the cup.

Using linear elasticity theory and thermodynamics, a thermodynamic criterion for equilibrium contact between two solid surfaces in atomic force microscopy (AFM) was established, in which the cantilever beam and tip of the AFM were modelled as an elastic spring and a microparticle, respectively. The elastic energy stored in the spring was included in the calculation of system energy. A new relation between the adhesion energy and the displacement of the microparticle at the separation was established, which could be used to calculate the adhesion energy between solid surfaces.

A new and (simple) versatile high-density sub-micron liquid spray source has been developed and examined for use in laser–plasma interaction studies. Sub-micron sized water droplets were produced in a spray by hypersonic expansion of superheated water vapour through a nozzle into vacuum. Employing Mie scattering and transmission measurement of the spray, the size of individual droplets were determined to a diameter of d = (0.15 ± 0.01) µm. The droplet number density varied from (1.6 ± 0.5) × 10¹¹ up to (7.5 ± 0.7) × 10¹⁰ droplets cm⁻³ depending on the position below the nozzle while the maximum mean atomic density was >10¹⁸ atoms cm⁻³. This water spray target system provides a six to eight times higher x-ray emission at photon energies below 10 keV compared to a single droplet (15 µm diameter) source where both were irradiated with ultrafast (35 fs) 20 TW Ti : Sa laser pulses.