Table of contents

A range of mechanical properties of a coating/substrate system may be obtained using indentation tests, and with the emergence of continuously recording indentation testing with nanometre penetration (often called nanoindentation) the mechanical properties of very thin coatings (<1 µm) and surface treated layers may be measured. This paper reviews the deformation mechanisms which occur and the methods for extracting mechanical properties of coatings from nanoindentation load–displacement curves and introduces the differences observed when compared with the testing of bulk materials. The importance of the relative hardness of coating and substrate on the response of the system is highlighted, and the use of energy-based models for the prediction of the performance of single and multilayered systems is discussed.

A theoretical analysis of the combined analyser-based/propagation-based x-ray phase-contrast imaging of weak objects is presented in the case of partially coherent illumination. It takes into account the finite size and divergence of a polychromatic x-ray source as well as the detector point-spread function. The proposed formalism describes the diffraction of x-rays in the monochromator and analyser crystals and free-space propagations between various elements of the imaging system. As in the case of a monochromatic plane wave incident on the object, the intensity in the image is expressed in terms of the amplitude and phase transfer functions. Analytical expressions for the new 'polychromatic' transfer functions are obtained and compared with the corresponding 'monochromatic' transfer functions by numerical simulations. The crucial role of the monochromator is elucidated in the formation of the analyser-based phase-contrast images with polychromatic illumination.

In the paper, we study the dielectric barrier discharge (DBD) occurring in a metal–insulator–gas–insulator–metal system. We encounter these kinds of discharges in ozonator-type reactors used in gas electrochemistry. The experiments are done in air medium when the gap width value is 580 µm and the pressure is in the interval of 1–100 mbar. The schematic diagram of the experimental mechanism and the drawing methods of the characteristics are given, and it is determined that the barrier discharge has an impulse character. Experimentally, we determine that the voltage–current (v–i) and voltage–charge (v–q) characteristics of the discharge are linear for the case of (pl) < (pl)_cr and step shaped for the case of (pl) > (pl)_cr, and these cases are explained theoretically. Furthermore, the determination method of the ratio of the fading voltage depending on the width of the steps of the experimental v–i characteristic to the inception voltage is given in this paper.

A cylindrical inductively coupled plasma source (ICPS) is optimized for nitrogen atom production. How to operate in the bright mode (H-mode) in pure nitrogen at relatively low applied power is explained. Actinometry is developed for a quantitative determination of the nitrogen dissociation fraction in the ICPS. These results are compared with those obtained outside the ICPS by modulated beam mass spectrometry. A qualitative agreement is obtained between the nitrogen dissociative fraction inside and outside the ICPS. The higher magnitude of the dissociation fraction given by mass spectrometry compared with that derived from actinometry is explained by the contribution of dissociative recombination of near the exit hole of the ICPS. A dissociation fraction of up to 0.7 is observed by mass spectrometry. Some results are also reported for argon–nitrogen gas mixtures.

The power dissipation in radiofrequency (RF) discharges in N₂O–He mixtures was measured as a function of He dilution in N₂O at two different gas pressures and several RF voltages. The maximum of power dissipation as a function of the helium dilution was found to be dependent on both the gas pressure and the RF voltages. A particle model is used to analyse such a power variation in terms of the processes occurring between charged particles (i.e. electrons, negative ions: O⁻, NO⁻ and positive ions: N₂O⁺, He⁺) and the neutral gas mixture (N₂O and He). The electric model results bring out the importance of the elastic electron–He collisions on the position of maximum dissipated power.

Plasma based ion implantation for a planar target was simulated using the particle-in-cell model. The plasma sheath evolution and the ion implantation details (the incident ion flux, the ion impact angle and the ion impact energy) were studied for targets with different sizes, with an aim to investigate the dependence of dose uniformity on target size. The effect of plasma density and pulse width on dose distribution was studied as a plus. The simulation results show that a larger target leads to a faster and less cylindrical sheath expansion. By increasing the target size, a more uniform distribution of incident ion flux can be obtained and the normal impact effect can be improved, while the distribution of impact energy is slightly influenced. As a result, the ion implantation dose presents a better uniformity on a larger target. By increasing plasma density or pulse width, we get a higher ion implantation dose but worse dose uniformity.

The structure and thermal expansion of multi-walled carbon nanotubes (MWNTs) with different diameters, prepared through the catalytic decomposition of vaporized benzene, were studied by x-ray diffraction at different temperatures, combined with scanning electron microscopy, transmission electron microscopy and electron diffraction. In comparison with that of the as-grown MWNTs, decreasing d₀₀₂ and increasing L_c of MWNTs after high temperature treatment (HTT) were obvious. However, the smaller the diameter of MWNTs, the more difficult the graphitization. The structural strain ε_c representing the distribution of interlayer spacing increased with increasing nanotube diameter. Considering the observations of asymmetrical lattice fringe for small MWNTs and polygonization morphology for big MWNTs after HTT, the crystallite size L_c and the radial thermal expansion α_c of MWNTs with different diameters were comparatively analysed in view of the energy. Presumably 50 nm may be the critical diameter for polygonization of MWNTs. Based on these facts, the mechanism of the graphitization process for MWNTs was discussed and the structure models of the MWNTs before and after HTT were suggested.

Temperature dependences of the piezoelectric modulus d₃₁ and complex elastic compliance have been measured for a lithium niobate single crystal grown by the high temperature top-seeded solution growth technique. The results obtained have shown that the imaginary part of the elastic coefficient is probably sensitive to the lithium ion and proton migration inside the crystal. X-ray photoelectron spectroscopy has revealed the existence of some defects in the crystal structure. While these imperfections only weakly control the magnitude of the piezoelectric coefficients, they influence the elastic properties, even in the relatively low temperature range. It was found that the temperature dependence of the elastic properties is stable as long as a temperature of ∼90 °C is not reached.

I investigated the molecular structure of natural wax from Japanese bees (Apis cerana japonica) in its native state (neither purified nor recrystallized) by ¹³C and ¹H solid-state NMR. Two strong ¹³C peaks at 32.9 and 34.0 ppm were attributed to signals from internal-chain methylene carbons [int-(CH₂)] in two types of crystal form. The peak at 32.9 ppm was assigned to an orthorhombic crystal form, and that at 34.0 ppm was assigned to a triclinic or monoclinic form. In both crystalline regions, bi-exponential decay of ¹³C spin-lattice relaxation [T₁(C)] for the crystalline peaks due to chain diffusion was observed. ¹H spin-lattice relaxation [T₁(H)] values for protons of the CH₃ group and for int-(CH₂) in the crystalline and amorphous regions were identical; this was interpreted as being due to averaging of the T₁(H) relaxation rates via spin diffusion. In contrast, although the decay curves for protons of the CH₃ group and for int-(CH₂) in the amorphous and orthorhombic forms were almost identical, those of the triclinic or monoclinic forms were different. This unhomogeneous character of was interpreted as resulting from differences in the molecular composition of each crystal form. Moreover, two components with long and short ¹H spin–spin relaxation [T₂(H)] values, arising from the mobile and rigid phases, respectively, were observed at above about −30 °C.

Powders consisting of 44 Å Cd_1−xMn_xS (x = 0; 0.05; 0.1; 0.15; 0.3) quantum dots (QDs) were synthesized using the colloidal chemistry method and characterized by Raman scattering measurements. The dominant Raman line of the 44 Å Cd_1−xMn_xS QDs was at about 300 cm⁻¹ showing asymmetric broadening for ω < 300 cm⁻¹. A significant change in the intensity of the first harmonic for different x and excitation energies was noticed. Also, the second harmonic of confined Raman modes was experimentally observed. A theoretical model was used to calculate the relative contributions of the confined Raman scattering modes for the 44 Å CdS QDs and satisfactory agreement with experimental results was found.

The diffractive–refractive optical device consisting of four crystals in (+, −, −, +) setting with longitudinal parabolic grooves has a geometrical aberration which influences the achievable focus size. This aberration is discussed analytically by using a new, more precise formula for the calculation of focusing distance, which respects the finite distance between optical elements. The calculation of the intensity distribution surrounding the focus is illustrated by a ray-tracing method based on the dynamical theory of diffraction. It demonstrates an achievable focus size. Finally we discuss that this aberration may be suppressed by the slight narrowing of the groove profile. In particular, the parameter a in the equation of parabola has to slightly grow with x. A practical application may require an ultra-precise fabrication of the grooves.

Depth resolved positron annihilation measurements were carried out on 85 keV and 1 MeV nitrogen ion implanted InP samples. The defect sensitive S-parameter and R-parameter values for the low energy implantations confirm the presence of monovacancies up to a dose of 10¹⁵ cm⁻² and coexistence of monovacancies and divacancies for 10¹⁶ cm⁻² dose sample. Corroborative glancing incidence x-ray diffraction measurements on the highest dose sample revealed that the sample is amorphized. For high energy implantation, it is found that vacancy-defects are present right from the near-surface region and these defects are identified to be monovancancies, based on the observed S- and R-parameters. A comparison of the results for the low and high energy implantations is made.

Glass forming ability (GFA), magnetic properties and the microstructure of an Nd₆₀Al₂₀Fe₂₀ as-cast rod were investigated in comparison with as-spun ribbons. The as-cast rod with a diameter of 3 mm and as-spun ribbons exhibit typical amorphous characters in x-ray diffraction patterns and distinct glass transition in differential scanning calorimetry traces. However, glass transition, crystallization behaviours and magnetic properties of an as-cast rod are different from that of as-spun ribbons. Microstructural investigations have revealed that a few nano-crystalline particles are embedded randomly in an amorphous matrix of the as-cast rod while the as-spun ribbons are fully amorphous. The formation of these nano-crystalline particles with a structure and composition similar to the A_x phase, as well as its effect on the magnetic properties and apparent GFA of Nd₆₀Al₂₀Fe₂₀ glass forming alloys, were investigated.

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