Microwave properties and surface topography of softmagnetic films with high resistivity

A single layer of CoFeB and a multilayer of CoFeB--MgO films are prepared by means of DC/RF magnetron sputter deposition. The excellent microwave properties and high electrical resistivity are simultaneously achieved in the discontinuous multilayer structure of [Co₄₄Fe₄₄B₁₂(0.7nm)/MgO(0.4nm)]_{40} film. This film has a high permeability ({μ \prime }) (larger than 100 below 2.1GHz), a high magnetic loss (μ') (larger than 100 in a range from 1.5 to 3.3GHz), a resistivity of 3.3× 10^*     

Judd-Oflet analysis of spectrum and laser performance of Ho：YAP crystal end-pumped by 1.91μm Tm：YLF laser

The Ho:YAP crystal is grown by the Czochralski technique.The room temperature polarized absorption spectra of Ho:YAP crystal was measured on a c cut sample with 1 at% holmium.According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10-20 cm2,Ω4 = 2.92 × 10-20 cm2,and Ω6 = 1.71 × 10-20 cm2,this paper calculated the fluorescence lifetime to be 6 ms for 5I7 →5 I8 transition,and the integrated emission cross section to be 2.24×10-18 cm2.It investigates the room temperature Ho:YAP laser end pumped by a 1.91 μm Tm:YLF laser.The maximum output power was 4.1 W when the incident 1.91 μm pump power was 14.4 W.The slope efficiency is 40.8%,corresponding to an optical to optical conversion efficiency of 28.4%.The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.     

Field theory,curdling, limit cycles,and cellular automata

It is suggested that the process of curdling is an important question for the science of fractals. A field equation which displays nucleation (curdling) of particles out of a pure radiation field is discussed. The particle formation arises naturally from the nonlinear character of the equation rather than from imposed quantization conditions. The relativistically invariant equation is $$div(\rho ^\mu (r,t,\Omega _1 )) = \int {[\rho _\mu (r,t,\Omega ),\rho ^\mu (r,t,\Omega _2 )]d} \Omega _2 $$ where ¦, ¦ denotes commutator.ρ ^μ (r,t,Ω) is both a 4-vector and a 2×2 matrix. It represents substance atr, t traveling with the velocity of light in direction Ω. A unique feature is that the scattering ofρ(Ω ₁) byρ(Ω ₂) as determined by the right-hand side of the above equation results in fields that persist at a given place even thoughρ itself represents substance traveling always at the speed of light. Explicit solutions are given for the case of one dimension. Fields representing particles are obtained and shown to have specially oscillatory structure with incipient fractal character.     

Oxygen-vacancy-related dielectric relaxation and conduction mechanisms in Bi5TiNbWO15 ceramics

This paper reports that the intergrowth ceramics Bi5TiNbWO15 （BW-BTN） have been prepared with the conventional solid-state reaction method. The dielectric and conductivity properties of samples were studied by using the dielectric relaxation and AC impedance spectroscopy in detail. Two distinct relaxation mechanisms were detected both in the plots of dielectric loss （tanδ） and the imaginary part （Z″） versus frequency in the frequency range of 10 Hz-13 MHz. We attribute the higher frequency relaxation process to the hopping process of the oxygen vacancies inside the grains, while the other seems to be associated with the space charges bound at the grain boundary layers. The AC impedance spectroscopy indicates that the conductivities at 625 K for bulk and grain boundary are about 1.12 × 10^-2 S/m and 1.43 × 10^-3 S/m respectively. The accumulation of the space charges in the grain boundary layers induces a space charge potential of 0.52 eV.     

Designing and manufacturing a piezoelectric tile for harvesting energy from footsteps

The objective of this research is to design a piezoelectric tile for harvesting energy from footsteps and to optimize the system for harvesting maximum energy. Because piezoelectric modules easily break when directly subjected to energy generated by human movements, we designed a tile that employs indirect energy transmission using springs and a tip mass. We aimed at matching the mechanical resonance frequency of the tile with that of the piezoelectric modules. The resonance frequency of a piezoelectric module with a 10-g tip mass was almost similar to the vibration frequency of the tile at 22.5 Hz when we dropped an 80-g steel ball from a 1-m height. We performed impedance matching and realized a matching value of 15 kΩ. Under these optimal mechanical and electrical conditions, we harvested 770-μW RMS and 55-mW peak output power.     

A unified theory of matter. II. Derivation of the fundamental physical law

The equation for the fundamental field quantity ? is obtained. It is Div \(\rho ^\mu (\Omega _1 ) = \operatorname{h} \int {[\rho _\mu (\Omega _1 ),\rho ^\mu (\Omega _2 )]_ - \operatorname{d} \Omega _2 } \) ,where h is an arbitrary function oft andr, and [,]_? is the commutator. The derivation requires the following hypotheses:(1) All of physical reality is completely described by the field ?.(2) Relativistic covariance of the equations governing ?.(3) Principle of continguous action.(4) Conservation of total amount of ?. The equation appears to be unique. It is suggested that the physical world corresponds to ? being a2×2 matrix. A close correspondence between the basic equation and Maxwell's equation is displayed. The electromagnetic vector potential A^μ is identified with ε ρ^μ dΩ. Conservation laws on various measures of ? are obtained. The symmetry groups of the basic equation are derived. A preliminary attempt to connect the field ? to the metric is made via Einstein's gravitational equation G_μυ =_KT_μυ.     

Eine neue Methode zur Berechnung der elektrischen Leitfähigkeit von Halbleitern in starken homogenen elektrischen Feldern

The Boltzmann equation for electrons in a semiconductor is assumed to be of the form $$\frac{{\partial f}}{{\partial t}} + F \cdot \frac{{\partial f}}{{\partial k}} = \frac{{h - f}}{{\tau _0 }} + \frac{1}{{\tau \left( k \right)}} \cdot \frac{1}{{4\pi }}\int {d\Omega 'w\left( \theta \right)\left( {f\left( {k,\vartheta '} \right) - f\left( {k,\vartheta '} \right)} \right)} $$ whereh is the Maxwell-Boltzmann distribution. The energy surface structure of the lattice electronsE(k) is assumed to be spheric. The stationary solutions for strong electric fields show a concentration of electrons into the field direction (field orientation), if the elastic collision frequency is not too large. This means, at least for large energies, that nearly all electrons are in a cone with small aperture around the field direction. Every transport problem whose collision operator can be reduced to the upper form at least for large energies, can be solved by a perturbation method whose zeroth order is the ideal field orientation. The conditions for a field orientation of the electron distribution to exist will be investigated.     

In‐situ series connection of an amorphous silicon photovoltaic tandem module

Local shading during thin film deposition monolithically interconnects thin film solar cells into photovoltaic modules. This in‐situ series connection method is, for the first time, applied to an amorphous silicon tandem cell structure. Sequential maskingand mask‐shifting forms the electrical series connection in‐situ, i.e. during the sputtering and plasma depositions of the contact and semiconductor layers of the thin film solar cell structure. The resulting photovoltaic module consists of five amorphous silicon tandem cells with a total module area A_{\rm m} =12.5\mathop {\;{\rm cm}}\nolimits^2. The module exhibits a fill factor {\rm FF}_{\rm m} > 72% and a total area efficiency \eta _{\rm m} =6.2%. Thermographic imaging proves successful patterning by local shading and attributes low shunt resistances of some component cells to single pinhole formation. The dark‐shunt resistance of each cell of the module amounts to R_{{\rm sc}{\rm,dark}{\rm,cell}} > 13\;{\rm k\Omega }\;{\rm cm}^{2} and for the complete module to R_{{\rm sc}{\rm,dark}{\rm,module}} =454\;{\rm k\Omega }\;{\rm cm}^{2}. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of deposition pressure and plasma power on the growth and properties of boron-doped microcrystalline silicon films

Using diborane as doping gas, p-doped μc-Si：H layers are deposited by using the plasma enhanced chemical vapour deposition （PECVD） technology. The effects of deposition pressure and plasma power on the growth and the properties of μc-Si：H layers are investigated. The results show that the deposition rate, the electrical and the structural properties are all strongly dependent on deposition pressure and plasma power. Boron-doped μc-Si：H films with a dark conductivity as high as 1.42 Ω^-1·cm^-1 and a crystallinity of above 50% are obtained. With this p-layer, μc-Si：H solar cells are fabricated. In addition, the mechanism for the effects of deposition pressure and plasma power on the growth and the properties of boron-doped μc-Si：H layers is discussed.     

Entanglement in a generalized Jaynes--Cummings model

We investigate the pairwise entanglement and global entanglement in a generalized Jaynes--Cummings model, which can be used to realize Greenberger--Horne--Zeilinger (GHZ) entangled state (Zheng S B 2001 {\it Phys. Rev. Lett.} {\bf 87} 230404). Our results show that the W-type entangled states cannot be generated based on the model. The dependences of entanglement on Rabi frequency $\lambda$ and dipole--dipole coupling strength ${\it \Omega}$ are given. It is found that there exists the quantum phase transition when $\lambda={\it \Omega}$. For typical experimental data, the critical temperature for pairwise entanglement is on the order of $10^{-6}$\,K. Based on these results, two strategies that overcome decoherence are proposed.     

Millimeter-wave Detectors Based on Antenna-coupled Low-barrier Schottky Diodes

The principles of construction of millimeter wave detectors based on low-barrier Schottky diodes and planar antennas are discussed. The modified planar slot antenna with low beam spillover at the resonant frequency of 94 GHz has been developed. Experiments have been carried out to investigate detecting characteristics of the diodes with differential contact resistances at zero bias. Experimental data are well correspond to calculations in a simple model of detector. At the maximum of rf-to-dc voltage sensitivity - more than 10000 V/W - is obtained. At lower values of a better noise equivalent power (NEP), around 10⁻¹² W Hz^−1/2, is predicted.     

The research on suspended ZnO nanowire field-effect transistor

This paper reports that a novel type of suspended ZnO nanowire field-effect transistors (FETs) were successfully fabricated using a photolithography process, and their electrical properties were characterized by I--V measurements. Single-crystalline ZnO nanowires were synthesized by a hydrothermal method, they were used as a suspended ZnO nanowire channel of back-gate field-effect transistors (FET). The fabricated suspended nanowire FETs showed a p-channel depletion mode, exhibited high on--off current ratio of ～10⁵. When V_DS=2.5 V, the peak transconductances of the suspended FETs were 0.396 μS, the oxide capacitance was found to be 1.547 fF, the pinch-off voltage V_TH was about 0.6 V, the electron mobility was on average 50.17 cm²/Vs. The resistivity of the ZnO nanowire channel was estimated to be 0.96× 10²Ω cm at V_GS = 0 V. These characteristics revealed that the suspended nanowire FET fabricated by the photolithography process had excellent performance. Better contacts between the ZnO nanowire and metal electrodes could be improved through annealing and metal deposition using a focused ion beam.     

On quantum analogue of dynamical stabilisation of inverted harmonic oscillator by time periodical uniform field

Quantum analogue of stabilised forced oscillations around an unstable equilibrium position is explored by solving the non-stationary Schrödinger equation (NSE) of the inverted harmonic oscillator (IHO) driven periodically by spatial uniform field of frequency \(\Omega \), amplitude \(F_{0}\) and phase \(\phi \), i.e. the system with the Hamiltonian of \(\hat{{H}}=(\hat{{p}}^{2}/2m)-(m\omega ^{2}x^{2}/2)-F_0 x\sin \) \(\left( {\Omega t+\phi } \right) \). The NSE has been solved both analytically and numerically by Maple 15 in dimensionless variables \(\xi = x\sqrt{m\omega /\hbar }\hbox {, }f_0 =F_0 /\omega \sqrt{\hbar m\omega }\) and \(\tau =\omega t\). The initial condition (IC) has been specified by the wave function (w.f.) of a generalised Gaussian type which suits well the corresponding quantum IC operator. The solution obtained demonstrates the non-monotonous behaviour of the coordinate spreading \(\sigma \left( \tau \right) \hbox { =}\sqrt{\big ( {\overline{\Delta \xi ^{2}\big ( \tau \big )} } \big )}\) which decreases first from quite macroscopic values of \(\sigma _{0} =2^{12,\ldots ,25}\) to minimal one of \(\sim \!(1/\sqrt{2})\) at times \(\tau <\tau _0 =0.125\ln \!\left( {16\sigma _0^4 +1} \right) \) and then grows back unlimitedly. For certain phases \(\phi \) depending on the \(\Omega /\omega \) ratio and \(n=\log _2\!\sigma _0 \), the mass centre of the packet \(\xi _{\mathrm {av}}( \tau )= \overline{\hat{{x}}(\tau )} \cdot \sqrt{m\omega /\hbar }\) delays approximately two natural ‘periods’ \(\sim \!(4\pi /\omega )\) in the area of the stationary point and then escapes to ‘\(+\)’ or ‘?’ infinity in a bifurcating way.  For ‘resonant’ \(\Omega =\omega \), the bifurcation phases \(\phi \) fit well with the regression formula of Fermi–Dirac type of argument n with their asymptotic \(\phi ( {\Omega ,n\rightarrow \infty } )\) obeying the classical formula \(\phi _{\mathrm {cl}} ( \Omega )=-\hbox {arctg} \, \Omega \) for initial energy \(E = 0\) in the wide range of \(\Omega =2^{-4},...,2^{7}\).     

SAW characteristics of AlN films sputtered on silicon substrates

This article is focused on the analysis of the electroacoustic response of surface acoustic wave (SAW) filters made of aluminium nitride (AlN) thin films on various types of Si wafers. AlN films with (00.2) orientation were deposited by RF reactive sputtering of an Al target in Ar and N(2) admixtures on Si(100) and (111) wafers with resistivities ranging between 10 and 2000 Omega cm. The electroacoustic response of SAW filters with an acoustic wavelength of 40 microm was analysed by measuring the Sij parameters with a network analyser. We have determined that the out-of-band loss is directly related to the Si substrate resistivity, varying from 26 dB for 10 Omega cm to 55 dB for 2000 Omega cm. The SAW velocity depends on the orientation of the Si wafer, being approximately 4700 m/s for Si(111) and 5100 m/s for Si(100). The electroacoustic responses of the SAW filters were fitted by computations based on a simple circuital model that takes into account parasitic effects such as airborne electromagnetic coupling and conduction through the substrate. This procedure provides accurate values of the electromechanical coupling factor k2 even for devices with poor characteristics. Good quality SAW filters of AlN on high resistivity Si(100) wafers with k2 larger than 0.12% are demonstrated.     

LD泵浦Nd∶YAG多波段激光器

为了获得高效率多波段激光输出,通过高重复频率驱动声光调Q技术和LD侧面泵浦技术,获得高功率高重频窄脉宽1.06 m激光输出。利用起偏器件获得垂直和水平两束1.06 m线偏振光,一束垂直线偏振光泵浦非线性晶体周期极化钽酸锂（PPLT）,实现1.46 m与3.9 m激光输出后与另一束1.06 m水平线偏振光合束,实现三波段共轴激光输出。在电源输入电流35 A、调Q驱动频率10 kHz的条件下,获得140 W的1.06 m激光。分束后泵浦PPLT获得最高功率为6.3 W的3.9 m和8.6 W的1.46 m激光,差频转化效率为21.3%。试验结果表明:通过高重频声光调Q技术和LD侧面泵浦技术,可以实现高重频窄脉宽1.06 m光输出,泵浦PPLT可获3.9 m和1.46 m激光输出。     

Unusual microwave response of dirac quasiparticles in graphene

Recent experiments have proven that the quasiparticles in graphene obey a Dirac equation. Here we show that microwaves are an excellent probe of their unusual dynamics. When the chemical potential is small, the intraband response can exhibit a cusp around zero frequency Omega and this unusual line shape changes to Drude-like by increasing the chemical potential |mu|, with width linear in mu. The interband contribution at T=0 is a constant independent of Omega with a lower cutoff at 2mu. Distinctly different behavior occurs if interaction-induced phenomena in graphene cause an opening of a gap Delta. At a large magnetic field B, the diagonal and Hall conductivities at small Omega become independent of B but remain nonzero and show a structure associated with the lowest Landau level. This occurs because in the Dirac theory the energy of this level, E0 = +/-Delta, is field independent in sharp contrast to the conventional case.     

Absence of long-range order in one-dimensional spin systems

For a one-dimensional Ising model with interaction energy $$E\left\{ \mu \right\} = - \sum\limits_{1 \leqslant i< j \leqslant N} {J(j - i)} \mu _\iota \mu _j \left[ {J(k) \geqslant 0,\mu _\iota = \pm 1} \right]$$ it is proved that there is no long-range order at any temperature when $$S_N = \sum\limits_{k = 1}^N {kJ\left( k \right) = o} \left( {[\log N]^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} } \right)$$ The same result is shown to hold for the corresponding plane rotator model when $$S_N = o\left( {\left[ {{{\log N} \mathord{\left/ {\vphantom {{\log N} {\log \log N}}} \right. \kern-\nulldelimiterspace} {\log \log N}}} \right]} \right)$$