We investigate a two-fluid anisotropic plane symmetric cosmological model with variable gravitational constant G(t) and cosmological term Λ(t). In the two-fluid model, one fluid is chosen to be that of the radiation field modeling the cosmic microwave background and the other one a perfect fluid modeling the material content of the universe. Exact solutions of the field equations are obtained by using a special form for the average scale factor which corresponds to a specific time-varying deceleration parameter. The model obtained presents a cosmological scenario which describes an early acceleration and late-time deceleration. The gravitation constant increases with the cosmic time whereas the cosmological term decreases and asymptotically tends to zero. The physical and kinematical behaviors of the associated fluid parameters are discussed.

An improved Monte Carlo renormalization group method is established. Based on a new model, as well as the generalized Glauber dynamics, the first-order phase transition is studied in the Erd?s–Rényi network, which is used to represent the complex ferromagnet. Both static and dynamic critical exponents can be evaluated simultaneously, and the static critical exponents are evaluated to be independent of the dimension of the system. Thus by using the hyperscaling relation νd^{*}=2?α, the effective dimension d^{*} of complex networks can be found.

Using the model of Hindmarsh–Rose neurons, we study the synchronous behavior of the firing patterns in an uncoupled cell system. In this work, the membrane current I_{ext} is selected as a controllable parameter, whose initial values for all N cells are set to be near one of the bifurcation points randomly. It is found that the system will show un-synchronous state when the external stimuli is absent, otherwise, full synchrony will appear, even though without any coupling connection among these N neurons, indicating the occurrence of uncoupled synchrony. Moreover, similar behavior could also be observed when these neurons are set to be near other bifurcation points. The synchronous error is calculated for discussing this uncoupled synchrony behavior. Finally, we find that such synchrony may have some inherent relevance with the decrease of phase difference between different cells. Our results suggest that biological neuron systems may achieve an effective response to external feeble stimulus by the mode of uncoupled synchrony instead of only by the coupled scheme.

Generally speaking, the quark propagator is dependent on the quark chemical potential in the dense quantum chromodynamics (QCD). By means of the generating functional method, we prove that the quark propagator actually depends on p_{4}+iμ from the first principle of QCD. The relation between quark number density and quark condensate is discussed by analyzing their singularities. It is concluded that the quark number density has some singularities at certain μ when T=0, and the variations of the quark number density as well as the quark condensate are located at the same point. In other words, at a certain μ the quark number density turns to nonzero, while the quark condensate begins to decrease from its vacuum value.

The thermal widths for heavy quarkonia are calculated for both Coulomb gauge (CG) and Feynman gauge (FG), and the comparisons between these results with the hard thermal loop (HTL) approximation ones are illustrated. The dissociation temperatures of heavy quarkonia in thermal medium are also discussed for CG, FG and HTL cases. It is shown that the thermal widths, derived from the HTL approximation and used in many research studies, cause some errors in the practical calculations at the temperature range accessible in the present experiment, and the problem of gauge dependence cannot be avoided when the complete self energy is used in the derivation of potential.

The contribution of the quark loop to the gluon damping rate at zero momentum is calculated using the effective perturbative expansion technique developed by Braaten and Pisarski. It is shown that in the temperature range accessible in the present heavy-ion experiments, the contribution of the quark loop can not be ignored. The numerical results show that the quark loop provides an apparent contribution to the gluon damping rate at temperatures of experimental interest.

It is commonly accepted that the system undergoes a crossover at high temperature and low chemical potential beyond the chiral limit case, and the properties of the crossover region are important for researchers to understand the nature of strong interacting matters of quantum chromodynamics (QCD). Since at present there is no exact order of parameters of the phase transitions beyond the chiral limit, QCD susceptibilities are widely used as indicators. In this work various susceptibilities are discussed in the framework of Dyson–Schwinger equations. The results show that different kinds of susceptibilities give the same critical end point, which is the bifurcation point of the crossover region and the first order phase transition line of QCD. Nevertheless, different pseudo-critical points are found in the temperature axis. We think that defining a critical band is more suitable in the crossover region.

We compare the jet-path length and beam-energy dependence of the pion nuclear modification factor and a parton-jet nuclear modification factor at RHIC and LHC, and contrast the predictions based on a linear pQCD and a highly non-linear hybrid AdS holographic model of jet-energy loss. It is found that both models require a reduction of the jet-medium coupling from RHIC to LHC to account for the measured pion nuclear modification factor. In the case of the parton-jet nuclear modification factor, however, which serves as a lower bound for the LO jet nuclear modification factor of reconstructed jets, the extracted data can be characterized without a reduced jet-medium coupling at LHC energies. It is concluded that when the reconstructed jets are sensitive to both quarks and gluons and thus provide more information than the pion nuclear modification factor, their information regarding the jet-medium coupling is limited due to the superposition with NLO and medium effects. Hence, a detailed description of the underlying physics requires both the leading hadron and the reconstructed jet nuclear modification factor. Unfortunately, the results for both the pion and the parton-jet nuclear modification factor are insensitive to the jet-path dependence of the models considered.

An explicit evaluation of the deuteron spin asymmetry and the associated Gerasimov–Drell–Hearn (GDH) integral for coherent and incoherent π-photoproduction channels with inclusion of rescattering effects is presented. The helicity-dependent total inclusive photoabsorption cross section on the deuteron and the helicity-dependent semi-exclusive channels γd→π^{±}NN and γd→π^{0}X (X=pn or d) are explicitly evaluated up to 1.5 GeV. Our model calculations indicate that convergence of the GDH integral is reached for π^{0}-production, while it is not completely reached for π^{±}-production. For the sum of γd→πNN and γd→π^{0} d contributions to the finite GDH integral by explicit integration up to 1.5 GeV, a value of 249.73 μb is obtained. The extracted results are compared with available experimental data from MAMI and ELSA. We find that our predictions fairly well reproduce the data in the π^{±} NN case, while fail to predict the measured shape of the π^{0}X channel.

Within the isospin-dependent quantum molecular dynamics model, we investigate the nuclear collective flows produced in semi-central ^{197}Au+^{197}Au collisions at intermediate energies. The neutron–proton differential flows and difference of neutron–proton collective flows are sensitive to the momentum-dependent symmetry potential. This sensitivity is less affected by both the isoscalar part of nuclear equation of state and in-medium nucleon–nucleon cross sections. Moreover, this sensitivity becomes pronounced with increasing the rapidity cut.

We give a detailed examination of potential energy curves of the singlet and triplet states of CFCl correlated with the lowest three dissociation limits. The calculations are carried out at the internally contracted multi-reference configuration interaction/cc-pV(T+d)Z level with the other two geometric parameters fixed at the X? state equilibrium conformation. The vertical transition energy, the oscillator strength, the main configuration and the electron transition are also investigated at the same level.

The five longest tune-out wavelengths for the rubidium atom are predicted from existing experimental and theoretical information by using an approximation formula. The formula is derived from the analysis of a non-relativistic configuration-interaction plus core polarization (CICP) calculation of the tune-out wavelengths for rubidium. The differences between the wavelengths predicted from the approximation formula and the exact CICP calculation are at the 10^{?3} nm level. The predicted five longest tune-out wavelengths are 790.115 nm, 423.155 nm, 421.111 nm, 359.429 nm, and 359.022 nm, respectively.

We report on the production of large sodium Bose–Einstein condensates in a hybrid of magnetic quadrupole and optical dipole trap. With an optimized spin-flip Zeeman slower, 2×10^{10} sodium atoms are captured in the magneto-optical trap (MOT). A long distance magnetic transfer setup moves the cold atom over 46 cm from the MOT chamber to the UHV science chamber, which provides great optical access and long conservative trap lifetime. After evaporative cooling in the hybrid trap, we produce nearly pure condensates of 1×10^{7} atoms with lifetime of 80 s in the optical dipole trap.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

An efficient diode-end-pumped actively Q-switched Nd:YLF/SrWO_{4} Raman laser is demonstrated. The fundamental wave is 1047.0 nm and the corresponding first-Stocks wave is 1158.7 nm. With a pumping power of 10.5 W, the average output power of 2.2 W at 1158.7 nm is obtained, with the corresponding optical conversion efficiency of 20.9%. At a repetition rate of 6 kHz, the pulse width of the Raman laser is 8.7 ns and the peak power is calculated to be 42.1 kW. The beam quality factors M^{2} in horizontal and vertical directions are 1.3 and 1.5, respectively.

A novel scheme of fully immersing water cooling is proposed for a Nd:glass radial slab laser. The slab medium is entirely immersed in the circulating water filling the pumping cavity, which enables much lower temperature and reasonably smaller thermal gradient in the slab medium. The radial slab is symmetrically and synchronously pumped by eight flash lamps, and produces multi-output beams with a total energy of 469 mJ. Incoherent beam combination property of the multi-output beams is also investigated. The approach suggested here provides a way of scaling the slab lasers to much higher output levels and also a convenience for beam combinations.

Phase modulation is first introduced into aperture-scanning Fourier ptychography. A series of images are acquired with an aperture scanning the Fourier plane of an optical system with a phase modulator. Then the reported algorithm synthesizes the captured images in the frequency domain to recover a high-resolution complex object wavefront. The leading results are considerably improved in robustness against the noises and shift errors, with a much faster convergence speed compared with the conventional scheme without phase modulation.

We report the observed photon bunching statistics of biexciton cascade emission at zero time delay in single quantum dots by second-order correlation function g^{(2)}(τ) measurements under continuous wave excitation. It is found that the bunching phenomenon is independent of the biexciton binding energy when it varies from 0.59 meV to nearly zero. The photon bunching takes place when the exciton photon is not spectrally distinguishable from the biexciton photon, and either of them can trigger the 'start' in a Hanbury–Brown and Twiss setup. However, if the exciton energy is spectrally distinguishable from the biexciton, the photon statistics will become asymmetric and a cross-bunching lineshape can be obtained. The theoretical calculations based on a model of three-level rate-equation analysis are consistent with the result of g^{(2)}(τ) correlation function measurements.

Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss (TL) data in the shadow zone of deep water. We propose a multiple-step TL inversion method to invert sound speed, density and attenuation in deep water. Based on a uniform liquid half-space bottom model, sound speed of the bottom is inverted by using the long range TL at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea (SCS) in summer 2014. Meanwhile, bottom density is estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the TL data in the shadow zones by using the known sound speed and density as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. The inverted bottom parameters can be used to forecast the transmission loss in the deep water area of SCS very well.

A geoacoustic inversion method is proposed based on the modal dispersion curve of two-wideband explosive signals for range-dependent environment. It is applied to the wideband explosive sound source data from the South China Sea in 2012. The travel time differences of different modes at various frequencies and distances are extracted by warping transform. The mean bottom acoustic parameters are inverted by matching the theoretical modal time differences to that of the experimental data. The inversion results are validated by using other explosive signals at different distances.

Based on the fact that the evolution trace in incident angle and frequency of the resonance zeros of the reflection coefficient function for a water charged layered medium is equivalent to its guided wave mode dispersion, the interfacial adhesion of a three-layer aluminum–adhesive–aluminum bonding structure is characterized nondestructively by determining the interface shear stiffness k_{t} associated with the interfacial strength. The resonance reflection function is obtained experimentally by the V(z) inversion technique using an ultrasonic focused transducer of wide-band and large angular aperture (up to ±45^{°}). The dispersion curves are numerically calculated, adjusting the parameter k_{t} so that the difference between the dispersion curves and the angular-frequency tracing of the reflection zeros is minimum. The parameter k_{t} at an interface of weakly adhered aluminum epoxy-resin is estimated to be 10^{14} N/m^{3}.

An alternative extension to the Gaussian-beam expansion technique is provided to simplify the computation of the Fresnel field integral for rectangular symmetric sources. From a known result that the circle or rectangle function is approximately decomposed into a sum of Gaussian functions, the cosine function is similarly expanded by the Bessel–Fourier transform. Two expansions are together inserted in this field integral, it is then expressible in terms of the simple algebraic functions. As examples, the numerical results for the sound pressure field are presented for the uniform rectangular piston transducer, in a good agreement with those directly evaluated from the Fresnel integral. A wide applicability of this approach is discussed in treatment of the ultrasonic field radiation problem for a large and important group of piston sources in acoustics.

The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

We compare three different methods to extract coherent modes from Doppler backscattering (DBS), which are center of gravity (COG) of the complex amplitude spectrum, spectrum of DBS phase derivative (phase derivative method), and phase spectrum, respectively. These three methods are all feasible to extract coherent modes, for example, geodesic acoustic mode oscillation. However, there are still differences between dealing with high frequency modes (several hundred kHz) and low frequency modes (several kHz) hiding in DBS signal. There is a significant amount of power at low frequencies in the phase spectrum, which can be removed by using the phase derivative method and COG. High frequency modes are clearer by using the COG and the phase derivative method than the phase spectrum. The spectrum of DBS amplitude does not show the coherent modes detected by using COG, phase derivative method and phase spectrum. When two Doppler shifted peaks exist, coherent modes and their harmonics appear in the spectrum of DBS amplitude, which are introduced by the DBS phase.

Three-wave resonant parametric decay instability of extraordinary wave decay into two upper hybrid waves in an inhomogeneous plasma is studied theoretically. Analytical expressions of the local absolute growth rate, convective amplification factor and threshold intensity are obtained. The calculated results show that the effects of magnetic field and k_{y} (k_{y} is the component of the wavenumber of upper hybrid wave perpendicular to pump wave k_{0}) on the growth rate, amplification factor and threshold intensity are extremely dependent on their strength. The absolute growth rate and convective amplification factor increase with the plasma density while the threshold decreases. Moreover, the expression indicates that the inhomogeneity scale length of density and linear damping will reduce the convective amplification factor.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

We present the numerical simulation results of a model granular assembly formed by spherical particles with Hertzian interaction subjected to a simple shear in the athermal quasi-static limit. The stress-strain curve is shown to separate into smooth, elastic branches followed by a subsequent plastic event. Mode analysis shows that the lowest-frequency vibrational mode is more localized, and eigenvalues and participation ratios of low-frequency modes exhibit similar power-law behavior as the system approaches plastic instability, indicating that the nature of plastic events in the granular system is also a saddle node bifurcation. The analysis of projection and spatial structure shows that over 75% contributions to the non-affine displacement field at a plastic instability come from the lowest-frequency mode, and the lowest-frequency mode is strongly spatially correlated with local plastic rearrangements, inferring that the lowest-frequency mode could be used as a predictor for future plastic rearrangements in the disordered system jammed marginally.

The calculated Raman spectra disclose that alumina polymorphs of nordstrandite, gibbsite, diaspore, boehmite, bayerite and α-Al_{2}O_{3} display different phonon behaviors, which can be attributed to their internal crystal structure changes. The strongest Raman peaks of nordstrandite, gibbsite, diaspore, boehmite, bayerite and α-Al_{2}O_{3} are located at 214.2 cm^{?1}, 3314.4 cm^{?1}, 2298.6 cm^{?1}, 747.7 cm^{?1}, 3484.6 cm^{?1} and 529.2 cm^{?1}, respectively. The characterizations in Raman spectra of those polymorphs are obviously different, which can be used in fingerprints to identify the alumina polymorphs structure.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

The fabrication and characterization of 1700 V 7 A 4H-SiC vertical double-implanted metal-oxide-semiconductor field-effect transistors (VDMOSFETs) are reported. The drift layer is 17 μm in thickness with 5×10^{15} cm^{?3} n-type doping, and the channel length is 1 μm. The MOSFETs show a peak mobility of 17 cm^{2}/V?s and a typical threshold voltage of 3 V. The active area of 0.028 cm^{2} delivers a forward drain current of 7 A at V_{GS}=22 V and V_{DS}=15 V. The specific on-resistance (R_{on,sp}) is 18 mΩ?cm^{2} at V_{GS}=22 V and the blocking voltage is 1975 V (I_{DS}<100 nA) at V_{GS}=0 V.

YAN Jun-Da, WANG Quan, WANG Xiao-Liang, XIAO Hong-Ling, JIANG Li-Juan, YIN Hai-Bo, FENG Chun, WANG Cui-Mei, QU Shen-Qi, GONG Jia-Min, ZHANG Bo, LI Bai-Quan, WANG Zhan-Guo, HOU Xun

Chin. Phys. Lett. 2015, 32 (12):
127301
.
DOI: 10.1088/0256-307X/32/12/127301

Direct?current transfer characteristics of (InGaN)/AlGaN/AlN/GaN heterojunction field effect transistors (HFETs) are presented. A drain current plateau (I_{DS}=32.0 mA/mm) for V_{GS} swept from +0.7 V to -0.6 V is present in the transfer characteristics of InGaN/AlGaN/AlN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) in InGaN/AlGaN/AlN/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when I_{DS}–V_{GS} scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.

The transport properties of a Dirac semimetal quantum wire with two side gates are theoretically studied by adopting the lattice Green function method. It is found that a residual conductance quantum contributed from the surface states can be switched on or off by tuning the electron energy or the side gates voltage. This ideal switching effect for the surface Dirac electron results from the transversal quantum confinement of the quantum wire in combination with the electrostatic potential induced by the side gates. These findings may provide useful guidance for designing all-electrical topological nanoelectronic devices.

We investigate the conductance and shot noise properties of quasi-particle transport through a superconducting barrier in graphene. Based on the Blonder, Tinkham, and Klapwijk (BTK) formulation, the theory to investigate the transport properties in the superconductive graphene is developed. In comparison, we consider the two cases which are the transport in the presence and absence of the specular Andreev reflection. It is shown that the conductance and shot noise exhibit essentially different features in the two cases. It is found that the shot noise is suppressed as a result of more tunneling channels contributing to the transport when the superconducting gate is applied. The dependences of the shot noise behavior on both the potential strength and the width of the superconducting barrier in the two cases are different. In the presence of the specular Andreev reflection, the shot noise spectrum is more sensitive to both the potential strength and the width of the superconducting barrier. In both cases, total transmission occurs at a certain parameter setting, which contributes greatly to the conductance and suppresses the shot noise at the same time.

A new thermoelectric material Ag_{8}SnS_{6}, with ultra?low thermal conductivity in thin film shape, is prepared on indium tin oxide coated glass (ITO) substrates using a chemical process via the electrodeposition technique. The structural, thermal and electrical properties are studied and presented in detail, which demonstrate that the material is of semiconductor type, orthorhombic structure, with a band gap in the order of 1.56 eV and a free carrier concentration of 1.46×10^{17} cm^{?3}. The thermal conductivity, thermal diffusivity, thermal conduction mode, Seebeck coefficient and electrical conductivity are determined using the photo-thermal deflection technique combined with the Boltzmann transport theory and Cahill's model, showing that the Ag_{8}SnS_{6} material has a low thermal conductivity of 3.8 Wm^{?1}K^{?1}, high electrical conductivity of 2.4×10^{5} Sm^{?1}, Seebeck coefficient of -180 μVK^{?1} and a power factor of 6.9 mWK^{?2}m^{?1}, implying that it is more efficient than those obtained in recently experimental investigations for thermoelectric devices.

We perform systematic thermal conductivity measurements on heavily hole-doped Ba_{1?x}K_{x}Fe_{2}As_{2} single crystals with 0.747≤x ≤0.974. At x=0.747, the κ_{0}/T is negligible, indicating a nodeless superconducting gap. A small residual linear term κ_{0}/T (≈0.035 mW?K^{?2}cm^{?1}) appears at x=0.826, and it increases slowly up to x=0.974, followed by a substantial increase of more than 20 times to the pure KFe_{2}As_{2} (x=1.0). This doping dependence of κ_{0}/T clearly shows that the nodal gap appears near x=0.8, possibly associated with the change of Fermi surface topology. The small values of κ_{0}/T from x=0.826 to 0.974 are consistent with the ?-shaped nodal s-wave gap recently revealed by angle-resolved photoemission spectroscopy experiments at x=0.9. Furthermore, the substantial increase of κ_{0}/T from x=0.974 to 1.0 is inconsistent with a symmetry-imposed d-wave gap in KFe_{2}As_{2}, and a possible nodal gap structure in KFe_{2}As_{2} is discussed.

The effect of an external magnetic field on the structural and magnetic properties of bond frustrated ZnCr_{2}Se_{4} at low temperatures is investigated using magnetization, dielectric constants and thermal conductivity experiments. With an increase in the magnetic field H, the antiferromagnetic transition temperature T_{N} is observed to shift progressively toward lower temperatures. The corresponding high temperature cubic (Fd3m) to low temperature tetragonal (I4_{1}amd) structural transition is tuned simultaneously due to the inherent strong spin-lattice coupling. In the antiferromagnetic phase, an anomaly at H_{C}_{2} defined as a steep downward peak in the derivative of the M–H curve is clearly drawn. It is found that T_{N} versus H and H_{C}_{2} versus T exhibit a consistent tendency, indicative of a field-induced tetragonal (I4_{1}amd) to cubic (Fd3m) structural transition. The transition is further substantiated by the field-dependent dielectric constant and thermal conductivity measurements. We modify the T–H phase diagram, highlighting the coexistence of the paramagnetic state and ferromagnetic clusters between 100 K and T_{N}.

Textured Bi and MnBi/Bi thin films are prepared by the pulsed laser deposition method. The highly c-axis textured MnBi films are obtained by annealing the bilayer consisting of textured Bi and Mn films. The coercivities of the MnBi/Bi film are 1.5 T and 2.35 T at room temperature and at 373 K, respectively, showing a positive temperature coefficient. Microstructural investigations show that the textured MnBi film results from the orientated growth induced by the textured Bi under-layer.

We report the first nuclear magnetic resonance (NMR) study on single crystals of staircase Kagomé antiferromagnet PbCu_{3}TeO_{7} (T_{N}_{1}∼36 K). A Curie constant Θ ∼−140 K is obtained by a Curie–Weiss fit to the high-temperature Knight shift of ^{125}Te. The hyperfine coupling constant is estimated to be ^{125}A_{hf}=−67 kOe/μ_{B}, and a strong interlayer coupling among staircase Kagomé planes is suggested with such a large hyperfine coupling, according to the lattice structure. The ^{63, 65}Cu NMR spectra are found by the zero-field (ZF) NMR at T=2 K, and the internal hyperfine fields are estimated to be 10.3 T and 9.6 T, for Cu(1) and Cu(2) sites, respectively, in the lattice. A second type of ZF NMR signal with a large rf enhancement is also seen after field-cycling through a high magnetic field.

Simple models are proposed for the calculation of refractive index n and electronic polarizability α of A^{I}B^{III}C_{2}^{VI} and A^{II}B^{IV}C_{2}^{V} groups of chalcopyrite semiconductors from their energy gap data. The values of n and α for 2 compounds of A^{I}B^{III}C_{2}^{VI} family and 12 compounds of A^{II}B^{IV}C_{2}^{V} family are calculated for the first time in this work. The proposed models are applicable for the whole range of energy gap materials. The calculated values are compared with the available experimental and reported values. A fairly good agreement between them is obtained.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Ag_{3}PO_{4} microcrystals with highly enhanced visible light photocatalytic activity are prepared by a facile and simple solid state reaction at room temperature. The composition, morphology and optical properties of the as-prepared Ag_{3}PO_{4} microcrystals are characterized by x-ray diffraction, scanning electron microscopy and UV-vis diffuse reflectance spectra. The photocatalytic properties of Ag_{3}PO_{4} are investigated by the degradation of both methylene blue and methyl orange dyes under visible light irradiation. The as-prepared Ag_{3}PO_{4} microcrystals possess high photocatalytic oxygen production with the rate of 673 μmolh^{?1}g^{?1}. Moreover, the as-prepared Ag_{3}PO_{4} microcrystals show an enhanced photoelectrochemistry performance under irradiation of visible light.

A pseudoplastic metal nanoparticle fluid (PMNF) is used in nanoimprint to fabricate semiconductors and functional devices. The evaporation of the solvent and the sintering of the Au PMNF are investigated. The key parameters, which influence the morphology of patterning, such as the radius of metal particles, the concentration of metal particles, the Hamaker constant of the solvent, viscosity of the fluids and the evaporation velocity, are analyzed. Based on a two-sphere sintering model, the equations are derived, which represent the relationships between the relative shrinkage and radius of the metal particles, sintering temperature and time. The optimal parameters for the heat treatment are provided in nanoimprint.

The objective of this study is to find an effective method to improve V_{oc} without J_{sc} loss for Cu_{2}ZnSnSe_{4} (CZTSe) thin film solar cells, which have been fabricated by the one step co-evaporation technique. Surface sulfurization of CZTSe thin films is carried out by using one technique that does not utilize toxic H_{2}S gas; a sequential evaporation of SnS after CZTSe deposition and the annealing of CZTSe thin films in selenium vapor. A Cu_{2}ZnSn(S,Se)_{4} (CZTSSe) thin layer is grown on the surface of the CZTSe thin film after the annealing. The conversion efficiency of the completed device is improved due to the enhancement of V_{oc}, which could be attributed to the formation of a hole-recombination barrier at the surface or the passivation of the surface and grain boundary by S incorporation.

We design and fabricate 4H-SiC UV avalanche photodiodes (APDs) with positive beveled mesa, which exhibit low leakage current and high avalanche gain when working in the Geiger mode. The single photon counting performance of the SiC APDs is studied by using a passive-quenching circuit. A new method to determine the exact breakdown voltage of the APD is proposed based on the initial emergence of photon count pulses. The photon count rate and dark count rate of the APD are also evaluated as a function of quenching resistance.

Single and dual δ-doped GaAs/AlGaAs two-dimensional electron gas (2DEG) Hall devices for low magnetic field detection at room temperature are prepared. The sensitivity and noise spectrum of the Hall devices are measured for evaluating the signal-to-noise ratio performance. It is observed that the dual δ-doped Hall devices achieve a minimum detectable magnetic field as low as 303 nT, which is better than the single δ-doped Hall device prepared under the same growth condition.

We design and fabricate a parallel system with 10 high speed side-illuminated evanescently coupled waveguide photodetectors (ECPDs). The 10 ECPDs exhibit a uniform 3 dB bandwidth of 20 GHz and low dark current of about 1 nA at 2 V reverse bias. The 10 ECPDs also exhibit uniform photo-responsivity of about 0.23 A/W with an active region of 5×25 μm^{2}. The photodetector array has a total bandwidth of more than 200 GHz and can be integrated with other optoelectronic devices.

The influence of a node in a network can be characterized by its macroscopic properties such as eigenvector centrality. An issue of significant theoretical and practical interest is to modify the influence or roles of the nodes in a network, and recent advances indicate that this can be achieved by just controlling a subset of nodes: the so-called controllers. However, the relationship between the structural properties of a network and its controllability, e.g., the control of node importance, is still not well understood. Here we systematically explore this relationship by constructing scale-free networks with a fixed degree sequence and tunable network characteristics. We calculate the relative size (n_{C*}) of the minimal controlling set required to control the importance of each individual node in a network. It is found that while clustering has no significant impact on n_{C*}, changes in degree–degree correlations, heterogeneity and the average degree of networks demonstrate a discernible impact on its controllability.