Table of contents

The surface structure of cement paste has been investigated in humid air by contact mode atomic force microscopy (AFM). The samples have been prepared by the novel mica-replication-method (MRM). For relative humidities between 3% and 20%, a structure change from coarse to fine grains has been recognized. Above this range no further significant changes were found.

A new experimental procedure combining usual isothermal DC charging and discharging with non-isothermal current measurements has been recently proposed. It is mainly suitable for very high insulating polymers and it was successfully applied to the study of space charge trapping and transport in low-density polyethylene. The analysis of the isothermal currents revealed the presence of different traps whose characteristic (de)trapping times can be deduced. The isothermal procedures allowed the selective charging of the sample. By choosing the charging field and the ratio of charge/discharge times, non-isothermal analysis permitted the differentiation of three or four peaks (at ≈50 C, ≈65 C, ≈70 C and ≈85 C) associated with charge detrapping from surface or near-surface (<20 µm) traps. These traps have activation energies between 0.21 and 1.54 eV. The mobility at 30 C is around 5×10^-16 m² V^-1 s^-1. Samples had to be conditioned before each experiment in order to obtain reproducible results.

New methods have recently been developed to measure the carrier-envelope phase evolution of ultrashort optical pulses. These methods utilize a powerful combination of time-domain and frequency-domain techniques. The resulting ability to stabilize the carrier-envelope phase of the pulse train emitted by a mode-locked laser means that the absolute frequencies in the optical spectrum can be determined, which has had an immediate impact on optical frequency metrology and optical clocks. In the time domain, this establishes the basis for controlling and tailoring the electric field of ultrashort pulses, which will affect applications in extreme nonlinear optics and coherent control. This paper provides a detailed look at the correspondence between time and frequency that underlies these results and reviews the recent progress in the field.

High-quality superconducting thin films of Bi₂Sr₂CaCu₂O_Y have successfully been deposited on MgO (100) substrate using spray pyrolysis technique. Microbridge structures of various dimensions were patterned on the superconducting films using various techniques. A systematic study of the temperature dependence of the critical current (I_c) of the microbridges was carried out to understand the nature of the grain boundary Josephson weak links. These studies showed that the nature of the grain boundary weak links could vary from superconductor-normal metal-superconductor to superconductor-normal metal-insulator-superconductor to superconductor-insulator-superconductor, as the J_c of the microbridges is gradually decreased. The irradiation of microwaves on these microbridges led to the appearance of well-defined Shapiro steps in the I-V characteristics.

B-rich NdFeB base alloys with partial substitutions of Dy for Nd ((Nd_1-xDy_x)_4.5Fe₇₇B_18.5 (x = 0-0.4)) were chosen to study the influence of Dy on thermal behaviour and magnetic properties. It was found that partial substitution of Dy for Nd results in a dramatic enhancement of coercivity _jH_c from 183 to 261 kA m^-1 and of maximum magnetic product (BH)_max from 110.6 to 133.7 kJ m^-3. However, the saturation magnetization M_s only decreases about 22.8 kA m^-1 for every 0.1 increment of Dy content x. Differential thermal analysis traces show that the crystallization process of the initial amorphous ribbons is a three-peak process. X-ray diffraction and differential thermal analysis indicate that the three peaks correspond to the formation of crystalline Fe₃B, Nd₂Fe₁₄B, and α-Fe, respectively. With increase of Dy concentration, _jH_c increases to a maximum value at about x = 0.1, and then reduces gradually. The enhancement of coercivity arises from the increase of the anisotropy field for the hard magnetic phase. The reduction of intrinsic coercivity _jH_c is attributed to the emergence of α-Fe after annealing at the third peak and the reduction of the fraction of hard magnetic phase due to the Dy addition. In order to obtain the optimum magnetic properties, a special annealing method was used.

Ordered Ni-Cu alloy nanowire arrays embedded in the hexagonally ordered nanochannels of anodic alumina membranes (AAMs) were fabricated by electrodeposition. The x-ray diffraction, x-ray energy dispersion spectrum, scanning and transmission electron microscopy were utilized to characterize the Ni-Cu alloy nanowire arrays. The results reveal that single crystalline Ni-Cu alloy nanowires are single crystal and that the atomic composition of Ni and Cu is very close to a 1 : 1 stoichiometry. Magnetic hysteresis loop shows that the Ni-Cu alloy nanowire arrays embedded in AAMs have perpendicular magnetic anisotropy, indicating their potential applications in perpendicular magnetic recording.

We have synthesized a red fluorescent dye of 4-dicyanomethylene- 2,6-di-(4-dimethylaminobenzaldehyde)-γ-pyran (DCDM), and fabricated electroluminescent devices of glass/indium-tin oxide/N,N'-diphenyl-N, N'-(3-methyphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), doped with different concentration of DCDM and 2.5wt.% of 9-cyanoanthracene (CNA), 50 nm/2,9-dimethy-4,7-diphenyl-1,10-phenanthroline (BCP), 40 nm/tris-(8-hydroxyquiniline) aluminium (Alq₃), 5 nm/Ag : Mg, 500 nm/Ag cap, 100 nm. The Commission International de 1' Eclairage (CIE) colour coordinates traverses along a straight line in the CIE chromaticity diagram with the concentration of DCDM. By adjusting the concentration of the fluorescent dyes, the pure white light emission was obtained at the CIE coordinates of x = 0.34 and y = 0.35.

Recent work indicating the determination of the electron temperature versus pressure×plasma dimension (pL) characteristic for electronegative gases with a single negative ion is combined with other recent work describing plasmas with more than one negative ion species. Using CF₄ as the exemplar gas, the characteristic is obtained for the range 1 mTorr cm to 10 Torr cm and comparison is made between the case when both F^- and CF₃^- are taken into account and that where the generation of CF₃^- is suppressed. Comparison is also made with experimental measurements on the positive column in CF₄.

A fluid model of the homogeneous barrier discharge is constructed for nitrogen at atmospheric pressure. The primary excitation and ionization processes specific for this discharge are pointed out. The calculations show that, in a wide range of external conditions, the homogeneous barrier discharge in nitrogen has a form of Townsend discharge which is easy to study. The influence of different mechanisms of electron emission from dielectric barriers and surface recombination over the electrical characteristics of a barrier discharge is studied. Introduction of a finite lifetime at the surface for adsorbed electrons allows us to obtain the results qualitatively corresponding to the experimental data.

Current waveforms of first negative corona pulses have been measured in N₂-SF₆ mixtures over a pressure range extending from 30 to 60 kPa and various overvoltages. Effects of changing cathode secondary electron emission were studied using a copper cathode coated by CuI and graphite. For a given set of experimental conditions, it is concluded that in the mixtures containing less than approximately 10% of SF₆ the negative corona pulse is associated with the formation of a cathode-directed streamer-like ionizing wave in the immediate vicinity of the cathode. In the mixtures containing more than 10% of SF₆ the ionizing wave is quenched and, consequently, the discharge is governed by the Townsend ionization mechanism fed by cathode photoemission processes. The results indicate that using the graphite-coated cathode, field emission processes play an important role in the corona pulse formation, especially at higher concentrations of SF₆.

An assessment of the boundary conditions for pulsed laser ablation is presented in the case where a thermal sputtering mechanism is relevant at the surface of the molten pool formed by the effect of irradiation. This paper deals with, in particular, the evaporation and boiling mechanisms when superheating effects are allowed to occur. The non-equilibrium character of the process at fluences enabling superheating plays a critical role in the rise of a large temperature gradient and subsurface temperature maximum even in the presence of surface boiling by vapour bubble nucleation.

This paper reports on the applications of analytical electron microscopy to the study of cathodic arc deposited CrN coating on a Ti(6% Al, 4% V) substrate. Particular attention is given to analysis of the coating/substrate interface. Electron energy loss spectroscopy is used to show that the Cr sputter cleaning of the Ti(6% Al, 4% V) results in penetration of Cr into the substrate giving a bcc alloy layer whose composition varies from Ti(6% Al, 4% V) at the substrate interface to almost pure Cr at the coating interface. Subsequent deposition of CrN results in an initial deposition of sub-stoichiometric Cr₂N followed by sub-stoichiometric CrN with a { 022} texture and a columnar structure. The degree of sub-stoichiometry of the nitrides depends on the substrate bias and the substrate orientation relative to the cathode.

Ion implantation is commonly used as a method to modify the surface or near-surface properties of materials and to improve their mechanical properties. In this paper, nanocrystalline diamond films, prepared by a microwave plasma enhanced chemical vapour deposition, were implanted using 110 keV nitrogen ions under a fluence ranging from 1×10¹⁶ to 1×10¹⁷ ions cm^-2. The friction and wear properties of the nanocrystalline diamond films in ambient atmosphere, and the surface structure and chemical state of the films, without and with the implantation were investigated. The results showed that adhesive friction took place between the nanocrystalline diamond film without ion implantation and a ruby ball in the friction process, which caused high friction coefficient and wear of the ruby ball. Ion implantation changed the surface chemical state of the nanocrystalline diamond films. A layer of oxygen-containing groups on the nanocrystalline diamond films produced by the high fluence nitrogen implantation played an important role in reducing the adhesive friction between the films and the ruby ball, and decreasing the friction and wear of the ruby ball.

Optical transmittance spectra of In₂O₃ : Sn (ITO) films were simulated with a computer program based on dielectric modelling. The films were prepared by radiofrequency sputtering under various oxygen fluxes such that the carrier density varies from 3×10¹⁹ to 1.5×10²¹ cm^-3. The dielectric function used is the sum of three types of electronic excitations: intraband transitions of free electrons (Drude model), band gap transitions, and interband transitions into the upper half of the conduction band. The parameters of these excitations are evaluated as a function of the carrier density. The damping in the Drude term was modelled frequency-dependent to account for the low extinction coefficient observed in the visible spectral range. The parameters resulting from the optical measurements were compared with those from the electrical measurements. Both the optical mobility and carrier density are found to be higher than those of the respective electric parameters. These discrepancies are attributed to a pronounced microstructure with badly conducting grain boundaries. The refractive index at 550 nm decreases linearly with increasing electron concentration. This is due both to the shift of the plasma edge and the Burstein-Moss shift of the band edge. All band gap transitions go up to the Fermi level.

A new model is presented of the electroformed metal-insulator-metal structure which explains its various properties including electron emission, electroluminescence, memory effects and, for the first time, a complete account of the differential negative resistance. The model is based upon experiments which identify the conduction process to be trap-controlled thermally activated tunnelling between metal islands produced in the forming process. The implications for the production of commercial electroformed devices are discussed.

Mixed former effect (MFE) and transport property studies on a new fast Ag⁺ ion conducting silver boro-molybdate glass system - 0.7[0.75AgI : 0.25AgCl] : 0.3[Ag₂O : { xB₂O₃ : (1-x)MoO₃} ] - are reported. A `quenched [0.75AgI : 0.25AgCl] mixed system/solid solution' has been used as the host salt in place of the traditional AgI host. The glass former compositions were varied from x = 0 to x = 0.9 in molar weight fraction, while the Ag⁺ ion salt concentration was kept constant. The composition 0.7[0.75AgI : 0.25AgCl] : 0.3[Ag₂O : { 0.7B₂O₃ : 0.3MoO₃} ] exhibited highest conductivity (σ_27°C = 6×10^-3 S cm^-1) at room temperature, and has been referred to as the optimum conducting composition (OCC). The conductivity enhancement in OCC, approximately 6 times from the pure molybdate glass system, has been found to be due to an increase in the Ag⁺ ion mobility. This has been attributed purely as a consequence of MFE. Temperature dependence on some important ion transport parameters such as conductivity (σ), mobility (µ), mobile ion concentration (n), ionic transference number (t_ion) and drift velocity (v_d) were done for the OCC samples only, and energies involved in the different thermally activated processes were evaluated from the respective Arrhenius-type plots. The ion transport mechanism has been discussed in the light of models suggested for superionic glasses.

The group velocity of the zero-order symmetric Lamb wave mode (S₀) has been measured on metal sheet as a function of angle to the rolling direction. Generation and detection of the Lamb wave was achieved using wideband non-contact ultrasonic electromagnetic acoustic transducers (EMATs). The EMATs were relatively small in size and employed permanent NdFeB magnets. The angular dependent velocity of the S₀ mode was measured on both aluminium and stainless steel (316) sheet. The entire system was computer controlled and the data were processed as acquired. The generation EMAT was driven with a current pulse of 270 A (peak value). This high current level gave rise to a more powerful generation source than is usually obtained with EMATs, enabling measurements to be made on stainless steel sheet which is much less efficient for EMAT generation of S₀ mode Lamb waves than aluminium sheet.

To form a smooth solid layer of the hydrogen isotope inside a microshell, a new approach is in progress where the basic principles of fabrication of fine dispersed compounds (solid solutions) with low doping are employed. This approach is shown to be applied experimentally using the H₂/HD mixture with the HD concentration less than 1%. As a result, a transparent solid layer is formed inside a 500 µm glass shell. The layer keeps its transparency under cycling heating treatment from 5 to 16-20 K. The technique developed can be applied for fabrication of cryogenic targets used in the inertial confinement fusion.