In the last 30 days

• Open/close Structural characterization of two-step growth of epitaxial ZnO films on sapphire substrates at low temperatures

  P Pant et al 2009 J. Phys. D: Appl. Phys. 42 105409 Tag this article

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  We have investigated two-step growth of high-quality epitaxial ZnO films, where the first layer—the buffer layer (nucleation layer template)—is grown at a low temperature (230–290 °C) to induce a smooth (two-dimensional) growth. This is followed by growth at a moderate temperature ~430 °C to form high-quality smooth ZnO layers for device structures. It was possible to reduce the growth temperature to 250–290 °C and obtain a smooth epitaxial template layer on sapphire (0 0 0 1) substrates with surface roughness less than 1 nm. After the high-temperature growth, the film surface undulations (roughness) increased to about 2 nm, but it is still quite smooth. The calculation of c and a lattice parameters by high-resolution x-ray diffraction shows that the a lattice parameter is fully relaxed at the growth temperatures but the c lattice parameter is dependent on the defect concentration in the growing film. A decoupling between a and c lattice parameters of the films is observed, which leads to abnormal Poisson's ratios ranging from 0.08 to 0.54. The decoupling of the lattice parameters is analysed based on growth characteristics and the presence of strain and defects in the grown films. We present our detailed studies on the nature of epitaxy, defects and interfaces by using comprehensive x-ray diffraction and high-resolution TEM studies.

• Open/close Charge accumulation by repeated contacts of metals to insulators

  J Lowell 1984 J. Phys. D: Appl. Phys. 17 1859 Tag this article

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  If a metal repeatedly touches an insulator the contact charge transferred gradually builds up even if contacts are made always to the same place. In some materials, this charge accumulation is undoubtedly a consequence of the 'insulator' being slightly conducting. The author shows that this mechanism cannot account for charge accumulation in polyethylene and polytetrafluoroethylene, so the phenomenon does not have a universal cause. He also shows that (in these polymers) charge accumulation is probably not a result of a gradual viscoelastic increase in area, nor a gradual area-increase due to inaccuracy in relocating the contact-point.

• Open/close Finite-size effects in fine particles: magnetic and transport properties

  Xavier Batlle and Amílcar Labarta 2002 J. Phys. D: Appl. Phys. 35 R15 Tag this article

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  Some of the most relevant finite-size and surface effects in the magnetic and transport properties of magnetic fine particles and granular solids are reviewed. The stability of the particle magnetization, superparamagnetic regime and the magnetic relaxation are discussed. New phenomena appearing due to interparticle interactions, such as the collective state and non-equilibrium dynamics, are presented. Surface anisotropy and disorder, spin-wave excitations, as well as the enhancements of the coercive field and particle magnetization are also reviewed. The competition of surface and finite-size effects to settle the magnetic behaviour is addressed. Finally, two of the most relevant phenomena in the transport properties of granular solids are summarized namely, giant magnetoresistance in granular heterogeneous alloys and Coulomb gap in insulating granular solids.

• Open/close Inactivation of a 25.5 µm Enterococcus faecalis biofilm by a room-temperature, battery-operated, handheld air plasma jet

  X Pei et al 2012 J. Phys. D: Appl. Phys. 45 165205 Tag this article

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  Effective biofilm inactivation using a handheld, mobile plasma jet powered by a 12 V dc battery and operated in open air without any external gas supply is reported. This cold, room-temperature plasma is produced in self-repetitive nanosecond discharges with current pulses of ∼100 ns duration, current peak amplitude of ∼6 mA and repetition rate of ∼20 kHz. It is shown that the reactive plasma species penetrate to the bottom layer of a 25.5 µm-thick Enterococcus faecalis biofilm and produce a strong bactericidal effect. This is the thickest reported biofilm inactivated using room-temperature air plasmas.

• Open/close Surface states and the contact electrification of polymers

  J Lowell 1977 J. Phys. D: Appl. Phys. 10 65 Tag this article

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  An experimental method is described for determining whether or not extrinsic surface states dominate the contact electrification of polymers; by 'extrinsic' surface states any kind of surface state which is not present on a freshly prepared surface of the polymer is meant. The experiments show conclusively that extrinsic surface states do not contribute to the contact electrification of polytetrafluoroethylene. In all probability, they are similarly unimportant in polyethyleneterephthalate, polyvinylchloride and polypropylene. On the other hand, the contact electrification of polyethylene is normally dominated by surface states which are formed when the polymer is exposed to the atmosphere.

• Open/close Decay and post-arc phases of a SF₆ arc plasma: a thermal and chemical non-equilibrium model

  J J Gonzalez et al 2000 J. Phys. D: Appl. Phys. 33 2759 Tag this article

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  After current zero in a high-voltage SF ₆ circuit breaker, the recovery voltage heats the remaining electrons, producing departures from thermal equilibrium that may modify the electrical conductivity of the medium and thus the interruption capability of the apparatus. In this study we present a two-temperature hydrodynamic model coupled with a kinetic model, applied to the extinction of a blown SF ₆ arc in a two-dimensional simplified geometry. The free decay and the post-arc phase with the recovery voltage have been studied. The kinetic part of the modelling allows us to calculate the evolution of the electron number density. A simplified turbulence model has been added to study its influence on the post-arc phase.

  The main results of this study reinforce the conclusions obtained taking into account only the chemical non-equilibrium: the departures from equilibrium tend to decrease the interruption capability predicted by the model. This effect is due to the weak energy exchange by elastic collisions between the electrons and the heavy particles, leading to an electron temperature higher than the gas temperature which favours the ionization of the medium submitted to a recovery voltage.

• Open/close Improvements to the hierarchically structured ZnO nanosphere based dye-sensitized solar cells

  Yongzhe Zhang et al 2009 J. Phys. D: Appl. Phys. 42 085105 Tag this article

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  Hierarchically structured ZnO nanospheres are synthesized by a wet-chemical method and ZnO sphere-consisting films are applied to dye-sensitized solar cells (DSSCs). It is found that the overall light-to-electricity conversion efficiency (η) is significantly enhanced from 0.474% to 1.03% due to light scattering compared with the ZnO nanoparticle-based DSSC. However, the fill factor (FF) and open-circuit voltage ( V _oc) decrease obviously. After annealing the films in an oxygen environment and placing a ZnO blocking layer on the fluorine-doped SnO ₂ (FTO) conducting substrate, the FF and V _oc are greatly improved and η increases from 1.03% to 1.59% and 2.25%, respectively. According to the results of x-ray diffraction and photoluminescence, the significant improvements in the cell performances might be due to the suppression of the recombination and the decrease in the resistances existing in the cell.

• Open/close Structural transformation and magnetoelectric behaviour in Bi_1−xGd_xFeO₃ multiferroics

  V V Lazenka et al 2012 J. Phys. D: Appl. Phys. 45 125002 Tag this article

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  The crystal structure, dielectric, magnetic and magnetoelectric (ME) properties of Bi _{1− x}Gd _x FeO ₃ (BGFO, x = 0, 0.05, 0.1, 0.15, 0.2) multiferroic ceramics have been studied. The substitution of bismuth by gadolinium induces a phase structural transition at x > 0.1, which leads to the suppression of the spiral modulated spin structure and develops weak ferromagnetic properties in the BiFeO ₃-based materials. Through studying the temperature/magnetic field dependence of the ME coefficient, we have revealed the effect of the substitution of Gd ³⁺ ions on the ME properties, and have demonstrated the possibility of manipulating the electric state in BGFO multiferroics by applying magnetic field at room temperature.

• Open/close Hole-mediated ferromagnetic enhancement and stability in Cu-doped ZnOS alloy thin films

  Y F Li et al 2012 J. Phys. D: Appl. Phys. 45 075002 Tag this article

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  We report room temperature ferromagnetism enhancement of Cu-doped ZnOS (Zn _{1− x}Cu _x O _{1− y}S _y ) alloy thin films with high hole concentration. The Zn _0.91Cu _0.09O _0.92S _0.08 alloy thin films with a hole concentration of 4.3 × 10 ¹⁹ cm ⁻³ show the strongest magnetization of 1.5μ _B/Cu. First-principles calculation shows that high hole concentration stabilizes the ferromagnetic ordering in the Zn _{1− x}Cu _x O _{1− y}S _y system, indicating a strong correlation between ferromagnetic stability and hole concentration. These results suggest that the Zn _{1− x}Cu _x O _{1− y}S _y alloy with high hole concentration is promising to find applications in spintronic devices.

• Open/close Comparison of surface modification of polypropylene film by filamentary DBD at atmospheric pressure and homogeneous DBD at medium pressure in air

  Z Fang et al 2009 J. Phys. D: Appl. Phys. 42 085204 Tag this article

  Article References Full text PDF (1.15 MB)

  Non-equilibrium plasmas generated by a dielectric barrier discharge (DBD) are of great interest in material surface processing because of their convenience, effectiveness and low cost. In this paper, polypropylene (PP) films are modified using a non-equilibrium plasma generated by a DBD in air in homogeneous mode and in filamentary mode. The filamentary DBD is generated in ambient air, and the homogeneous DBD is generated at medium pressure with an operating pressure value of 3 kPa. The characteristics of homogeneous DBD are studied and compared with those of filamentary DBD by measuring their electrical discharge parameters and observing their light emission phenomena, and the surface properties of the PP films before and after the treatments are studied using contact angle and surface energy measurement, x-ray photoelectron spectroscopy and scanning electron microscopy. It is found that the homogeneous DBD is even and stable in the whole gas gap, which differs from the commonly filamentary DBD. The plasma treatments modify the PP surface in both morphology and composition. The PP films modified in both treatments show a remarkable decrease in the water contact angle and a remarkable increase in surface energy due to the introduction of oxygen-containing groups on the surface and the etching of the surface. The homogeneous DBD is more effective in PP surface modification than the filamentary DBD as it can make the contact angle decrease to a lower level by introducing more oxygen-containing groups. This effect could be explained by the evenly distributed plasma at a homogeneous DBD than at a filamentary DBD, and by the more efficient introduction of atomic oxygen to the PP surface in the case of homogeneous DBD.