Table of contents

Modern society relies on readily available refrigeration. Magnetic refrigeration has three prominent advantages compared with compressor-based refrigeration. First, there are no harmful gases involved; second, it may be built more compactly as the working material is a solid; and third, magnetic refrigerators generate much less noise. Recently a new class of magnetic refrigerant-materials for room-temperature applications was discovered. These new materials have important advantages over existing magnetic coolants: they exhibit a large magnetocaloric effect (MCE) in conjunction with a magnetic phase-transition of first order. This MCE is larger than that of Gd metal, which is used in the demonstration refrigerators built to explore the potential of this evolving technology. In the present review we compare the different materials considering both scientific aspects and industrial applicability. Because fundamental aspects of MCE are not so widely discussed, we also give some theoretical considerations.

Ferroelectric switching in unipolar (CH₃NH₃)₅Bi₂Br₁₁ crystal has been studied by optical observation of the domain structure in low electric fields and switching current registration in high fields. We discuss investigations on the temporal behaviour of the electric polarization in static electric fields as well as polarization decay after removal of the electric field. The backswitching process appears to have a correlation to a defect-induced internal field in the crystal. For the interpretation of experimental data we utilize the classical nucleation and growth model of phase transformation (e.g. Avrami–Kolmogorov theory). An analysis assuming a statistical distribution of the characteristic domain growth times is proposed to explain and to find the functional form of the experimental data.

Experiments of inserting an ultra thin layer of DCJTB at three different levels in a blue emitter layer of a blue device, ITO/CuPc/NPB/TBADN/Alq/LiF/Al, were carried out. The spectra of these devices indicate that the recombination zone is chiefly located near the NPB/TBADN interface, implying that TBADN is capable of electron transport. The inserted DCJTB at TBADN/Alq interface has no contribution to emission, leaving only the blue emission from TBADN, even at high voltage. However, it improved the stability of the device; the half lifetime was prolonged twice more and the rise of applied voltage during ageing was suppressed from 3 V to 0.4 V.

The electron paramagnetic resonance (EPR) parameters (g factors g_∥, g_⊥ and zero-field splitting D) of the approximately tetragonal defect centre in cubic ZnS crystal are calculated from high-order perturbation formulae based on the two spin-orbit coupling parameter model for the EPR parameters of the 3d⁷ ion in tetragonal symmetry. From the calculations, we suggest that the associated defect X (which is at the interstitial site on a ⟨100⟩ axis, but its origin and nature remain unknown) in this centre has a negatively charged state (i.e. an anion). The slightly monoclinic distortion of this defect centre is attributed to a further anion S²⁻ vacancy Vs²⁻ in the vicinity of defect X owing to charge compensation. The defect model is discussed.

Formaldehyde is a major indoor air pollutant and can cause serious health disorders in residents. This work reports the removal of formaldehyde from gas streams via alumina-pellet-filled dielectric barrier discharge plasmas at atmospheric pressure and 70 °C. With a feed gas mixture of 140 ppm HCHO, 21.0% O₂, 1.0% H₂O in N₂, ∼92% of formaldehyde can be effectively destructed at GHSV (gas flow volume per hour per discharge volume) of 16 500 h⁻¹ and E_in = 108 J l⁻¹. An increase in the specific surface area of the alumina pellets enhances the HCHO removal, and this indicates that the adsorbed HCHO species may have a lower C–H bond breakage energy. Based on an examination of the influence of gas composition on the removal efficiency, the primary destruction pathways, besides the reactions initiated by discharge-generated radicals, such as O, H, OH and HO₂, may include the consecutive dissociations of HCHO molecules and HCO radicals through their collisions with vibrationally- and electronically-excited metastable N₂ species. The increase of O₂ content in the inlet gas stream is able to diminish the CO production and to promote the formation of CO₂ via O-atom or HO₂-radical involved reactions.

A single-stage pulsed inductive plasma accelerator was modelled as an inductive mass-driver, with the plasma treated as a rigid slug that acts as the armature. We derive a set of coupled dynamic-circuit equations, with dimensionless coefficients. The functional form of the mutual inductance profile, M(z), was calculated using the magnetic field solver QuickField; an exponential form for M(z) was found to be accurate for a variety of coil-slug geometries. A parametric study of the solutions to the equations was performed in order to determine the conditions that yield high coupling efficiency. High inductance, multi-turn drive-coils yield the highest efficiency for a single-stage device. Using inductive recapture, coupling efficiencies in excess of 90% are possible; without it, the peak efficiency is much lower, η ≦ 55%. We conclude that inductive recapture will be required in order to achieve the high efficiency required of an electric thruster. The efficiency scales favourably with increasing power, although this does not preclude operation at lower power with acceptable efficiency. The presence of an imbedded bias flux in the slug improves the dynamic efficiency for devices without inductive recapture, but offers little improvement when used with inductive recapture.

Radially resolved line-of-sight intensities of the 254 nm resonance line of Hg were measured for cold spot temperatures between 16 °C and 50 °C. The observed normalized intensities agree with line-of-sight intensities predicted by our improved 1D Boltzmann/non-local radiation transport model for fluorescent lamps. An additional comparison with model predictions employing the conventional Holstein theory showed that the latter is inadequate for describing the radiation transport of resonance lines in fluorescent lamps.

The high frequency fluctuations of the burning voltage of cathodic vacuum arcs have been investigated in order to extract information on cathode processes, especially concerning evolution in time after arc ignition. Eight cathode materials (W, Ta, Hf, Ti, Ni, Au, Sn, Bi) were selected covering a wide range of cohesive energy. The voltage noise was recorded using both a broad-band voltage divider and an attenuator connected to a fast oscilloscope (limits 1 GHz analog and 5 GS s⁻¹ digital). Fast Fourier transform revealed a power spectrum that is linear in log–log presentation, with a slope of 1/f ², where f is the frequency (brown noise). The amplitude of the spectral power of the voltage noise was found to scale with the cohesive energy, in agreement with earlier measurements at lower resolution. These basic results do not depend on the time after arc initiation. However, lower arc current in the beginning of the pulse shows greater voltage noise, suggesting an inverse relation between the noise amplitude and number of emission sites (cathode spot fragments).

Extreme ultraviolet (EUV) radiation with wavelengths of 11–14 nm is seen as the most promising candidate for a new lithographic technology. In the development of our Z-pinch plasma EUV source, xenon (Xe) is used for the background gas discharges and a solid tin (Sn) rod is used as target material due to its potential for high conversion efficiency (CE) from input electric energy to EUV radiation. The Z-pinch plasma was driven by pulsed current with amplitude of 30 kA and pulse duration of 110 ns. Pinhole imaging, an EUV spectrograph and an in-band EUV energy monitor were used to characterize the EUV emission from the Z-pinch discharge. Previously reported experimental analyses by Horita et al have demonstrated that the CE was as high as 3%.

An analytical solution is obtained for the classical heat conduction problem for a solid film with a surface that is simply deformed and irradiated by repetitive laser pulses. Convective heat losses from the surface and the film–substrate interface are taken into account. The solution, evaluated for large times, shows that the surface deformation increases the average surface temperature. This increase is pronounced when the absorption length of the laser radiation is less than the film thickness (even in the case when the amplitude of surface deformation is much less than its wavelength). At any point on a deformed surface the temporal dependence of temperature is characterized by narrow spikes, which are repeated with the period of pulse repetition. The spatial dependence of surface temperature follows surface deformation.

A three-dimensional (3D) energy-dependent kinetic Monte Carlo technique is developed to simulate thin film growth with deposition of energetic atoms. We incorporate the effects of the incident kinetic energy and the incident angle of atomic fluxes into the conventional vapour phase deposition model. The atom reflection, the biased diffusion and the athermal diffusion caused by the incident energy and the incident angle are included in our study. We simulate the film morphology and the surface roughness of homoepitaxial Cu films on a Cu(001) substrate with various incident energies and incident angles. The simulation results show that the energetic atoms can enhance the smoothness of the surface. This effect is very significant at a low substrate temperature or a high deposition rate. For a fixed incident energy, there exists a transition angle where the surface roughness is a minimum. In addition, the surface morphology of the Cu film in sputtering deposition is also studied and the approximate energy and angle distributions of the sputtered atoms are used. The results are in agreement with the experimental results.

The electrical behaviour of Ta₂O₅ layers rf sputtered on nitrided silicon surface has been studied. The incorporation of nitrogen in Si substrate is performed by plasma immersion ion implantation. The conduction mechanisms and charge trapping in the structures are investigated. A high density of trapped negative charge near the Ta₂O₅-nitrided Si interface is found. It is established that the trapping/detrapping of negative charge in the structures is asymmetric for the two gate polarities that reveals a non-homogeneous spatial distribution of the traps. The charge trapping influences the electron conduction in the layers and modifies the main Poole–Frenkel conduction mechanism in the structure.

Composite coatings were fabricated by laser alloying of titanium alloy Ti-6Al-4V with nitrogen gas and silicon powder. An XRD spectrum indicates that the coating mainly contains Si₃N₄, Ti₅Si₃, Ti₂N, etc compounds. EPMA and SEM micrographs show that the compounds in the coatings are not well-developed dendritic with round tips. Compared with laser nitriding of Ti-6Al-4V, the addition of Si not only improves the sliding wear resistance but also impedes the formation of the well-developed dentritic compounds and thus facilitates the reduction of crack formation in the coatings. In addition, the test results also demonstrate that the coatings have better wear and oxidation resistance than the as-received sample and the enhancing mechanism is briefly discussed.

Reflection high-energy electron diffraction (RHEED) is a versatile technique for surface and interface analysis during film growth. Analysis of RHEED patterns during film growth is helpful for the understanding of the properties of both surface and interface. The geometrical arrangement of RHEED patterns can be derived from diffraction theory, and the in-plane and out-of-plane lattice constants are computed from the streaky or spotty patterns. During epitaxial growth of SrTiO₃/SrTiO₃, MgO/SrTiO₃ and MgO/LaAlO₃ with lattice mismatch of 0%, 7.8% and 11%, respectively, the changes of lattice constants are recorded as a function of film thickness. The in-plane lattice constant oscillates along with the oscillation of RHEED intensity in the case of SrTiO₃ homoepitaxial growth. During the MgO cube-on-cube deposition on SrTiO₃, the in-plane lattice constant is relaxed due to positive mismatch, and the MgO lattice is distorted into tetragonal phase at the same time. For the in-plane 45° rotation system of MgO/LaAlO₃, relaxation behaviour is observed suffering from negative mismatch. The measured in-plane orientation and lattice relaxation correlate well with a two-dimensional nearly coincident site lattice model, in which the match relation of MgO/LaAlO₃ growing with a 5 : 4 lattice ratio can result in negative mismatch.

The interconnection between the geometry of biological tissue (BT) structure and their polarization properties has been studied. It has been shown that for physiologically normal BT, the polarization properties of radiation scattered on architectonic nets formed by protein fibrils have a fractal character. Pathological changes of BT architectonics are accompanied by the transformation of self-similar structure of 2D Mueller-matrix elements into stochastic and statistic ones.

CaCu₃Ti₄O₁₂ (CCTO) film is attractive for microelectronic device applications due to its high dielectric constant. However, its dielectric loss has to be lowered. In this study, a thin layer SiO₂ was inserted into the CCTO films prepared on Pt/Ti/SiO₂/Si substrates by the pulsed laser deposition method, in an effort to reduce the dielectric loss. The SiO₂ thin layers are located in the bottom, middle and top of the films, respectively. Compared with the single layer CCTO films, the CCTO/SiO₂ multilayers exhibit lower dielectric loss while maintaining an adjustable dielectric constant. Both the microstructure and dielectric properties were found to be strongly dependent on the position of the SiO₂ thin layer, showing that the SiO₂ thin layer acts not only as a barrier layer but also an initial nucleation layer of the CCTO thin films. The CCTO film with a SiO₂ layer in the middle shows the lowest dielectric loss (0.06 at 100 kHz) and leakage current (4.4 × 10⁻⁶ A cm⁻² at 100 kV cm⁻¹), while the dielectric constant is 171 at 100 kHz.

The understanding of atomic and electronic structures is crucial for designing devices. The surface properties of bimetallic systems have been widely studied due to the possibility of applications in different areas, such as catalysis, magnetism, microelectronics and electrochemistry. The objective of this work is studying thin (10 nm) Pd and Ni films on polycrystalline Ni and Pd substrates (Pd/Ni and Ni/Pd), respectively, grown by dc magnetron sputtering. The film structure was investigated by x-ray diffraction (XRD), morphology, by atomic force microscopy and surface composition, and by x-ray photoelectron spectroscopy. The XRD indicated that the Ni/Pd film did not present an ordered structure, while the Pd/Ni had a nanocrystalline structure with a slight structural distortion. Oxide formation was detected for the Ni film, but not for the Pd film.

Measurements of the times of arrival of the primary shock produced by the explosion of a nominal 20 tn propane–oxygen mixture have been analysed to provide the variation of the peak hydrostatic overpressure as a function of distance. The results have been scaled to those for a charge of unit mass at normal temperature and pressure, based on the masses of the propane and oxygen and of the propane alone. The scaled results are compared with those produced by the explosion of a hemispherical unit mass of TNT to provide the TNT equivalence factor as a function of overpressure and distance. For overpressures greater than 1 atm there is a strong dependence on the distance from the centre of the explosion, but at lower overpressures the equivalence factors have almost constant values of 0.55 for the propane–oxygen mixture and 1.95 for the propane alone. The significance of these findings, in relationship to vapour cloud explosions and boiling liquid expanding vapour explosions, is discussed.

The demand for compact power sources with high energy density is increasing. A microthermophotovoltaic (micro-TPV) power generator is a renewable energy source with high power density and without moving parts. A thin layer of platinum was successfully deposited on the inner surface of the microcombustor as catalyst by reducing platinum from H₂PtCl₆, which is able to improve the flame structure in the microcombustor and increase the output power density of the micro-TPV system. The output electrical power of the system with platinum as catalyst is increased by 11–23.8% compared with that without platinum.

This article discusses whether the production of radioisotopes by high-intensity laser pulses is a breakthrough which will soon provide a cost-effective source of medically interesting nuclides or is merely a modest proof of principle without direct practical applications.