Table of contents

We present proof-of-principle experiments and simulations that demonstrate a new biological assay technology in which microscopic tags carrying multi-bit magnetic codes are used to label probe biomolecules. It is demonstrated that these 'micro-barcode tags' can be encoded, transported using micro-fluidics and are compatible with surface chemistry. We also present simulations and experimental results which suggest the feasibility of decoding the micro-barcode tags using magnetoresistive sensors. Together, these results demonstrate substantial progress towards meeting the critical requirements of a magnetically encoded, high-throughput and portable biological assay platform. We also show that an extension of our technology could potentially be used to label libraries consisting of ∼10⁴ distinct probe molecules, and could therefore have a strong impact on mainstream medical diagnostics.

The reversible stress-induced magnetization (inverse magnetostriction or Villari effect) has been measured in a polycrystalline Ni–Fe–Ga–Co ferromagnetic martensite. The samples were mechanically excited using longitudinal resonant oscillations at frequencies close to 100 kHz, and experiments were performed over the temperature range 170–350 K under variable polarizing fields. It has been found that the reversible inverse magnetostriction changes its sign under low polarizing fields over a certain temperature range with its upper limit close to the Curie temperature. We argue that the variations of sign of the reversible inverse magnetostriction effect are related in the present experiments with the change in the sign of magnetostriction, as has additionally been verified in test measurements performed for pure Ni and Fe. The observed peculiarity of magnetoelastic coupling is also reflected in the temperature dependence of electrical resistance and even produces a minor effect in calorimetry scans. Possible origins of these features of magnetoelastic coupling are discussed.

The effect of a magnetic field on the current–voltage characteristics of Pr_0.6Ca_0.4MnO₃/Nb-doped SrTiO₃ heterojunctions was studied. An abnormal increase in diffusion voltage, break down voltage and ideality factor was observed at a low temperature. It was also found that the transport properties of these heterojunctions could be considerably influenced by external magnetic fields. When a magnetic field was applied, I–V curves were shifted to a lower bias voltage. Both ideality factor and saturation current were affected by the magnetic field. The magnetic field modulation was more significant at lower temperatures. The analysis showed that the current–voltage relation was dominated by tunnelling. The anomaly at low temperatures may be a result of temperature and electric field dependence of the dielectric constant of Nb : SrTiO₃. A magnetic field may also modify the work function and density of states of Pr_0.6Ca_0.4MnO₃, leading to a change in current–voltage characteristics.

We propose a new equation considering strain effect for the temperature dependence of bandgap transition of GaN films grown on sapphire. By using the chemical lift-off method the GaN films were separated from the sapphire substrate and we evaluated the energy shift of the bandgap transition due to the strain caused by the sapphire substrate quantitatively. The transition energies of the free exciton A (FX_A) in the GaN film at a finite temperature are described by the equation E(T) = E(0) − (αT²/(β + T)) + ΔE(0) + γ(TEC_film − TEC_sub)T, where α and β are the temperature coefficients, γ is the strain coefficient, and TEC_film and TEC_sub are thermal expansion coefficients of the film and the substrate, respectively. This equation is divided into an ordinary temperature component and an additional strain component of the hetero-epitaxial film. The temperature dependence of exciton transition energy of the strained GaN film should be expressed by the above equation with E(0) = 3.4774 eV, α = 0.93 meV K⁻¹, β = 1280 K, ΔE(0) = 10.87 meV and γ = 2.04 × 10⁻³ eV.

A zero-dimensional kinetic model has been developed to investigate the coupled electron and heavy-particle kinetics in Ar–O₂ surface-wave microwave discharges generated in long cylindrical tubes, such as those launched with a surfatron or a surfaguide. The model has been validated by comparing the calculated electron temperature and species densities with experimental data available in the literature for different discharge conditions. Systematic studies have been carried out for a surface-wave discharge generated with 2.45 GHz field frequency in a 1 cm diameter quartz tube in Ar–O₂ mixture at 0.5–3 Torr pressures, which are typical conditions found in different applications. The calculations have been performed for the critical electron density for surface-wave propagation, n_e = 3.74 × 10¹¹ cm⁻³.

It has been found that the sustaining electric field decreases with Ar percentage in the mixture, while the electron kinetic temperature exhibits a minimum at about 80%Ar. The charged and neutral species densities have been calculated for different mixture compositions, from pure O₂ to pure Ar, and their creation and destruction processes have been identified. The O₂ dissociation degree increases with Ar addition into O₂ and dissociation degrees as high as 60% can be achieved. Furthermore, it has been demonstrated that the dissociation degree increases with the discharge tube radius, but decreases with the atomic surface recombination of O-atoms. The density of O⁻ negative ions is very high in the plasma, the electronegativity of the discharge can be higher than 1, depending on the discharge conditions.

This paper is an experimental study of a pulsed filamentary plasma discharge inside liquid water in pin-to-plane electrode configuration. Time-resolved electrical and imaging diagnostics have been performed. The initiation and the propagation of the discharge have been studied for several experimental parameters. The propagation is continuous and is followed by reilluminations at low water conductivity. The measured propagation velocity of the plasma discharge is 30 km s⁻¹ for the secondary positive mode. This velocity was found to be surprisingly constant whatever the experimental parameters and especially as a function of the water conductivity.

The conventional model of near-cathode space-charge sheath with ions entering the sheath from the quasi-neutral plasma may not be applicable to discharges burning in cathode vapour, e.g. vacuum arcs, where ionization of emitted atoms may occur inside the sheath with some of the produced ions returning to the cathode and others moving into the plasma. In this connection, a simple model is considered of a sheath formed by electrons and positive ions injected into the sheath with a very low velocity and moving from the sheath into the plasma. It is shown that such a sheath is possible provided that the sheath voltage is equal to or exceeds approximately 1.256kT_e/e. This limitation is due to the space charge in the sheath and is in this sense analogous to the limitation of ion current in a vacuum diode expressed by the Child–Langmuir law. The ions leave the sheath and enter the plasma with a velocity equal to or exceeding approximately 1.585u_B.

It is shown that Steenbeck's principle of minimum power, or voltage, for discharges with fixed current is not a corollary of the principle of minimum entropy production, in contrast to what is frequently assumed; besides, the latter principle itself does not provide a reasonable approximation in gas discharge physics. Similarly, Steenbeck's principle is not a corollary of mathematical models of gas discharges. Hence, this principle contradicts the mathematical models. A methodically correct evaluation of the error caused by the use of Steenbeck's principle requires a comparison of a solution obtained with the use of this principle with an exact solution to the same problem, rather than with experimental results or results deemed reasonable from the point of view of common sense. Such a comparison is performed for two examples from the theory of a cylindrical arc column. The examples show that the error incurred by the usage of Steenbeck's principle is uncontrollable and may be unacceptably high.

An interfacial buffer layer has been developed to improve the silicon oxide (SiO_x) hard coating adhered to a flexible plastic substrate through a consecutive plasma-enhanced chemical vapour deposition process, using the same organosilicon precursor. The adhesion of the hard coating structure, correlated with the buffer layer thickness, was rated by the standard tape-peeling test. An excellent adhesion (rank 5B) was available for the hard coating structure with an interfacial buffer layer deposited on polycarbonate and polymethylmethacrylate substrates. The degree of adhesion strength for the hard coating structures was measured by the standard scratch test. The increase in the critical loads determined from the scratch test was well correlated with the tape-peeling test results. The hard coating structure showed excellent adhesion and also corresponded to a minimum residual stress. The mechanisms responsible for the adhesion enhancement were linked to the specific chemical bonds of the hydrocarbon C–H bond, and cross-linking Si–C bond appeared in the interfacial buffer layer. The C–H bond was recognized as a hydrophobic group that was favourable for minimizing the adsorption of ambient contaminants potentially arising during deposition, while the cross-linking Si–C bond functioned to compensate the large tensile stress residing in the SiO_x hard coating. As a consequence, a close contact and progressive morphology resulting in excellent adhesion were observed at the interface of the hard coating structure with an interfacial buffer layer.

It is shown, by DFT calculations, that the uniform functionalization of the upper layer of graphite by hydrogen or fluorine does not change essentially its bonding energy with the underlying layers, whereas the functionalization by phenyl groups decreases the bonding energy by a factor of approximately ten. This means that the functionalized monolayer in the latter case can be easily separated by mild sonication. According to our computational results, such layers can be cleaned up to pure graphene, as well as functionalized further up to 25% coverage, without much difficulty. The energy gap within the interval from 0.5 to 3 eV can be obtained by such one-side funtionalization using different chemical species.

The time-resolved crystallization dynamics of as-deposited amorphous AgInSbTe thin films induced by single picosecond laser pulses has been studied. The crystallization process was shown to be a threshold-dependent multi-stage process. For the same film structure, the total crystallization time does not change significantly with different fluences in a broad fluence range. The total crystallization time can be effectively shortened by an additional thermally conductive silver underlayer. After the film has been primed with a low-fluence single ∼30 ps laser pulse, the crystallization process can be simplified to be a monotonic process with a markedly reduced crystallization time.

The formation of chains of aligned carbon nanofibres (CNFs) in polymers is a subject of great interest in the field of multifunctional nanocomposites. The mechanism of CNF chain assembly and growth in a low viscosity epoxy is investigated by developing a finite element model of a chain attached to an electrode. The model examines the combined effects of electrostatic and electrohydrodynamic forces on chain morphology. The electrohydrodynamic forces are modelled using the theory of ac electro-osmosis. The predictions of the model are supported by experimental results. The experiments were conducted on a CNF/epoxy/amine mixture by applying an ac field at frequencies ranging from 100 to 100 000 Hz. The predictions of the model qualitatively capture the variations of chain morphology and growth rate as functions of ac frequency. Higher frequencies promote a more uniform and denser network of chains. The rate of growth of chains is highest at an intermediate frequency. A uniform network of chains was observed at frequencies of 1 kHz and greater in the experiments. The rate of growth of chains was maximized at a frequency of 1 kHz for a liquid viscosity of 0.03 Pa s.

Semilocalized transition (SLT) kinetic models for thermoluminescence (TL) contain characteristics of both a localized transition (LT) and of a single trap model. TL glow curves within SLT models typically contain contain two TL peaks; the first peak corresponds to the intra-pair luminescence due to LTs and the second TL peak corresponds to delocalized transitions involving the conduction band (CB). The latter delocalized TL peak has also been found to exhibit non-typical double-peak structure, in which the main TL peak is accompanied by a smaller peak called the displacement peak. This paper describes the simulation of isothermal luminescence signals using a previously published SLT model. It is found that these simulated isothermal signals exhibit several unusual time characteristics. Isothermal signals associated with the LTs follow first order kinetics and are therefore described by single decaying exponentials. However, isothermal signals associated with delocalized transitions show a non-typical complex structure characterized by several time regions with different decay characteristics. For certain values of the parameters in the SLT model the isothermal signals can also exhibit non-monotonic behaviour as a function of time. Another notable result from the simulations is that isothermal currents (which are proportional to the concentration of electrons in the CB) can persist for very long periods of time, even after the apparent termination of the isothermal luminescence signals. It is concluded that isothermal processes described by the SLT model depend strongly on the presence of SLTs, in contrast to previous studies using Monte Carlo simulations, which showed a weak interdependence of these phenomena. The simulations in this paper suggest that isothermal experiments offer a sensitive method for detecting the presence of SLTs in a dosimetric material.

A frequency-tunable cloak with semiconducting constituents has been proposed by modifying the dielectric constant by externally controlling the free-carrier density. We have theoretically studied that the cloaking frequency of a single-layer shell consisting of intrinsic InSb can be tuned by varying the temperature based on the Mie scattering theory. The calculated results show that this tunable cloak has a large bandwidth of over 0.3 THz, a tunability of cloaking frequency of 17 GHz K⁻¹ with temperature and a dramatic reduction in the total scattering cross section of 90% at cloaking frequencies. It is also possible to realize a tunable cloak of extrinsic semiconductor Ge by changing the impurity density with current injection.

It was observed that when polarized by an intense electric field, water is able to self-arrange into macroscopic cylindrical wires that can hang up and remain floating against gravity. This phenomenon is now known as a 'water bridge'. Several attempts have been made to give an explanation of this apparently unusual behaviour of water. A number of experiments have been performed with the aim of probing any possible structural change of bulk water, after application of the electric field. None of the available findings appear conclusive at the moment.

Here we report the results of the first Raman scattering experiment on floating water bridges. The inter-molecular OH-stretching band has been investigated and the results have been compared with those from bulk water. Some changes in the scattering profiles after application of the electric field are shown to have a structural origin. The bridges have been obtained, for the first time, in a vertical geometry and under application of an alternating field. The adopted geometry has allowed us to reveal a clear asymmetry between opposite direct current biasing, which can be related to the nature of the charge carriers.

Mechanical depolarization of poled lead titanate zirconate (PZT) ceramics was conducted at a series of temperatures from 25 to 180 °C in a temperature-controlled silicon oil tank. Both the longitudinal strain and polarization of the bar-shaped PZT samples were measured during uni-axial compression up to 400 MPa. It is found that both the stress-induced switchable polarization and the switchable strain of the poled PZT samples decrease steadily with increasing temperature. Unpoled PZT samples were also tested and the switchable strains follow a rule similar to the poled ones but of smaller magnitude. By measuring the P–E hysteresis loops, polarization variations and strain variations of a compression-free, poled PZT sample during a full cycle of heating–cooling, it is found that at elevated temperatures, the reduced switchable polarization by stress is caused by the pyroelectric effect and the reduced switchable strain is mainly due to the decreasing tetragonality (c/a). Furthermore, it was found that both the poled and unpoled PZT ceramics show a recoverable thermal shrinkage effect within the measurement temperature range.

The caption for figure 4 on page 3 is incorrect. The corrected figure is given in the attached PDF file.