We present a scheme for generating a ring magnetic waveguide on a single-layer atom chip. The wire layout consists of two interleaved Archimedean spirals of the same size. The waveguide avoids the trapping perturbation caused by the input and output ports, resulting in an enclosed guiding loop for neutral atoms in weak-field seeking states. Such a configuration can create a tight and deep trap potential with a small current. Taking the |F=2,m_{F}=2> state of ^{87}Rb as an example, the trap frequency and depth are estimated to be 18 kHz and 335 μK, respectively, with a dc current of 2 A.

The quantum correlation dynamics in an anisotropic Heisenberg XYZ model under decoherence are investigated with the use of concurrence C and quantum discord (QD). There is a remarkable difference between the time evolution behaviors of these two correlation measures: there is a entanglement-sudden-death phenomenon in the concurrence while there is none in QD, which is valid for all of the initial states of this system, and the interval time of the entanglement death is found to be strongly dependent on the initial states and the parameters B and Δ. With the long-time limit the steady entanglement (SC) and steady quantum discord (SQD) can be obtained. The magnitudes of SC and SQD are closely related to the parameters B and Δ, while the strength of the Dzyaloshinskii–Moriya interaction, D, has no influence. In addition, the effects of the parameters B and Δ on SC and SQD display such different and complicated features that one cannot obtain a uniform law about them, thus we give an analytical explanation of this phenomenon. Lastly, it can be noted that the value of SC is not always larger than SQD, which is strongly dependent on the parameters B and Δ.

We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of using the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a much easier manner. Our proposal overcomes the major drawback of the method used by Creffield et al. [Phys. Rev. Lett. 99 (2007) 110501], and can be implemented, in principle, in any one-dimensional optical lattice. Some potential applications of the scheme are also discussed.

We study the P–V critical behavior of a four-dimensional AdS black hole in an Einstein–Maxwell gravity with a conformal anomaly by treating the cosmological constant as a variable that is related to the thermodynamic pressure. It is shown that there will be no phase transition if k=0 or −1 are taken. When the charge q_{1} of the conformal field and the coefficient α satisfy a certain relation, the van de Waals like phase transition for the spherical black hole can occur where the temperature is lower than the small critical temperature or higher than the large one. We also evaluate the critical exponents of the phase transitions and find that the thermodynamic exponents associated with this four-dimensional AdS black hole coincide with those of the van de Waals fluid.

We calculate the energy distribution associated with a static spherically symmetric non-singular phantom black hole metric in Einstein's prescription in general relativity. As required for the Einstein energy-momentum complex, we perform the calculations in quasi-Cartesian coordinates. We also calculate the momentum components and obtain a zero value, as expected from the geometry of the metric.

We investigate the collective dynamics of network-organized identical excitable nodes. We theoretically analyze the stability of the rest state and propose that there are two different transition paths: the stationary path and the oscillatory path. We find that, although the onset of collective dynamics strongly depend on the network topology, the local dynamics and how local nodes interact with each other decide the transition path and the involved bifurcation.

A low gate voltage operated multi-emitter-dot gated lateral bipolar junction transistor (BJT) ion sensor is proposed. The proposed device is composed of an arrayed gated lateral BJT, which is driven in the metal-oxide-semiconductor field-effect transistor (MOSFET)-BJT hybrid operation mode. Further, it has multiple emitter dots linked to each other in parallel to improve ionic sensitivity. Using hydrogen ionic solutions as reference solutions, we conduct experiments in which we compare the sensitivity and threshold voltage of the multi-emitter-dot gated lateral BJT with that of the single-emitter-dot gated lateral BJT. The multi-emitter-dot gated lateral BJT not only shows increased sensitivity but, more importantly, the proposed device can be operated under very low gate voltage, whereas the conventional ion-sensitive field-effect transistors cannot. This special characteristic is significant for low power devices and for function devices in which the provision of a gate voltage is difficult.

A 330–500 GHz zero?biased broadband monolithic integrated tripler is reported. The measured results show that the maximum efficiency and the maximum output power are 2% and 194 μW at 348 GHz. The saturation characteristic test shows that the output 1 dB compression point is about -8.5 dBm at 334 GHz and the maximum efficiency is obtained at the point, which is slightly below the 1 dB compression point. Compared with the conventional hybrid integrated circuit, a major advantage of the monolithic integrated circuit is the significant improvement of reliability and consistency. In this work, a terahertz monolithic frequency multiplier at this band is designed and fabricated.

Life science has a need for detection methods that are label-free and real-time. In this paper, we have selected staphylococcal protein A (SPA) and swine immunoglobulin G (IgG), and monitor the bindings between SPA and swine IgG with different concentrations, as well as the dissociations of SPA-swine IgG complex in different pH values of phosphate buffer by oblique-incidence reflectivity difference (OIRD) in a label-free and real-time fashion. We obtain the ON and OFF reaction dynamic curves corresponding to the bindings and dissociations of SPA and swine IgG. Through our analysis of the experimental results, we have been able to obtain the damping coefficients and the dissociation time of SPA and swine IgG for different pH values of the phosphate buffer. The results prove that the OIRD technique is a competing method for monitoring the dynamic processes of biomolecule interaction and achieving the quantitative information of reaction kinetics.

We calculate the quark number susceptibility (QNS) around the chiral critical end point (CEP). The CEP is found to be located at (μ_{c},T_{c}) = (80 MeV, 148 MeV) where μ_{c} and T_{c} are the critical chemical potential and temperature, respectively. The QNS is found to have the highest and sharpest peak at the CEP. It is also found that, when the chemical potential μ is in the range of 60 MeV ≤μ≤110 MeV, the QNS near the transition temperature is larger than the free field result, which indicates that the space-like damping mode dominates the degree of freedom of motion near the CEP.

Fusion power output is proportional not only to the fuel particle number densities participating in reaction but also to the fusion reaction rate coefficient (or reactivity), which is dependent on reactant velocity distribution functions. They are usually assumed to be dual Maxwellian distribution functions with the same temperature for thermal nuclear fusion circumstances. However, if high power neutral beam injection and minority ion species ICRF plasma heating, or multi-pinched plasma beam head-on collision, in a converging region are required and investigated in future large scale fusion reactors, then the fractions of the injected energetic fast ion tail resulting from ionization or charge exchange will be large enough and their contribution to the non-Maxwellian distribution functions is not negligible, hence to the fusion reaction rate coefficient or calculation of fusion power. In such cases, beam-target, and beam-beam reaction enhancement effect contributions should play very important roles. In this paper, several useful formulae to calculate the fusion reaction rate coefficient for different beam and target combination scenarios are derived in detail.

Ultrafast anisotropic decay is a prominent parameter revealing ultrafast energy and electron transfer; however, it is difficult to be determined reliably owing to the requirement of a simultaneous availability of the parallel and perpendicular polarized decay kinetics. Nowadays, any measurement of anisotropic decay is a kind of approach to the exact simultaneity. Here we report a novel method for a synchronous ultrafast anisotropy decay measurement, which can well determine the anisotropy, even at a very early time, as the rising phase of the excitation laser pulse. The anisotropic decay of the B850 in bacterial light harvesting antenna complex LH2 of Rhodobacter sphaeroides in solution at room temperature with coherent excitation is detected by this method, which shows a polarization response time of 30 fs, and the energy transfer from the initial excitation to the bacteriochlorophylls in B850 ring takes about 70 fs. The anisotropic decay that is probed at the red side of the absorption spectrum, such as 880 nm, has an initial value of 0.4, corresponding to simulated emission, while the blue side with an anisotropy of 0.1 contributes to the ground-state bleaching. Our results show that the coherent excitation covering the whole ring might not be realized owing to the symmetry breaking of LH2: from C_{9} symmetry in membrane to C_{2} symmetry in solution.

Discrete Shannon entropy is applied to describe the information in a multiconfiguration Dirac–Fock wavefunction. The dependence of Shannon entropy is shown as enlarging the configuration space and it can reach saturation when there are enough configuration state wavefunctions to obtain the convergent energy levels; that is, the calculation procedure in multiconfiguration Dirac–Fock method is an entropy saturation process. At the same accuracy level, the basis sets for the smallest entropy are best able to describe the energy state. Additionally, a connection between the sudden change of Shannon information entropies and energy level crossings along with isoelectronic sequence can be set up, which is helpful to find the energy level crossings of interest in interpreting and foreseeing the inversion scheme of energy levels for an x-ray laser.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

We present a simple method to measure the topological charges of optical vortices with multiple singularities. Using a cylindrical lens, a vortex beam can decay into a light field distribution with multiple separated dark holes, whose number just equals the topological charge of the input beam. This conclusion is then verified via experiments and numerical simulations of the propagation of vortex beams with multiple singularities. This method is also reliable to measure the topological charges of broadband vortex beams with different distributions of singularities, which does not resort to multiple beam interferometric experiments.

We report on the room-temperature cw operation of a surface grating distributed feedback (DFB) quantum cascade laser (QCL) at λ～4.7 μm. Both grating design and material optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4-mm-long laser, high wall-plug efficiency of 6% is obtained at 20°C from a single facet producing over 1 W of cw output power. The threshold current density of DFB QCL is as low as 1.13 kA/cm^{2} at 10°C and 1.34 kA/cm^{2} at 30°C in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in the working temperature range of 20–50°C.

Wavelength-tunable ultrashort pulse source with high energy is highly desired for a lot of applications. The wavelength-tunable all-normal-dispersion (ANDi) mode-locked fiber laser, which can be compressed easily and amplified by an all-fiber structure, is a promising seed of such a source with compact structures. The pulse compression and amplification at different center wavelengths (from 1026 to 1058 nm) of the tunable ANDi Yb-doped mode-locked fiber lasers that we previously proposed are experimentally investigated in this work. It is found that, for different wavelengths, the duration and chirp of the direct output pulse from the oscillator vary considerably, however, the duration of compressed pulse fluctuates less. For the amplification process, due to the unflat gain spectrum of Yb-doped fiber, the gain at a short wavelength is larger than that at a long wavelength. Consequently, the trends of spectrum distortions induced by the amplification process are different for different wavelengths. These results and analyses will be helpful for the design of a high-energy and wavelength-tunable ultrashort pulse source based on an ANDi seed.

A single sheet of graphene exhibits the ability to turn polarization of light by several degrees in modest magnetic fields. Here we demonstrate that giant angle rotation in graphene in the terahertz range can be realized and further increased by the introduction of surface plasmon and constructive Fabry–Pérot interference with the supporting substrate. The maximum Kerr rotation angle is up to 15° in a single layer of graphene ribbons at 6 THz for the applied magnetic field 4 T. Such a magnification in magneto-optical Kerr effect can be realized in a fairly large incident angle.

We synthesize hollow-structured Ag@Au nanoparticles with single porous shell and Ag@Au/Ag@Au double shells by using the galvanic replacement reaction and investigate their linear and nonlinear optical properties. Our results show that the surface plasmon resonance wavelength of the hollow porous nanoparticles could be easily tuned in a wide range in the visible and near infrared region by controlling the volume of HAuCl_{4}. The nonlinear optical refraction of the double-shelled Ag@Au/Ag@Au nanoparticles is prominently enhanced by the plasmon resonance. Our findings may find applications in biosensors and nonlinear optical nanodevices.

A diode pumped Kerr-lens mode-locked femtosecond Yb:LSO laser is experimentally demonstrated for the first time. The 54 fs laser pulses at central wavelength of 1052 nm with a bandwidth of 22.5 nm are obtained at the repetition rate of 113 MHz. To the best of our knowledge, this is the shortest pulse duration ever produced from the Yb-doped orthosilicates lasers family.

A benchmark model is developed to compute the three-dimensional acoustic field excited by a harmonic point source in a homogeneous wedge-shaped waveguide with impenetrable boundaries. A derivation of the exact solution is presented based on Fourier synthesis, which reduces the three-dimensional ideal wedge problem to a sequence of two-dimensional line-source ideal wedge problems, to which the analytical solution is well established. The details of the numerical implementation of this solution are also provided. Our numerical results indicate that this model is efficient and capable of providing accurate three-dimensional acoustic fields for arbitrary receiver locations, and hence can serve as a benchmark model for sound propagation in a continental shelf environment.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

The simple fluid model, an extended fluid model, and the fluid model with nonlocal ionization are applied for the calculations of static breakdown voltages, Paschen curves and current-voltage characteristics. The best agreement with the experimental data for the Paschen curve modeling is achieved by using the model with variable secondary electron yield. The modeling of current-voltage characteristics is performed for different inter-electrode distances and the results are compared with the experimental data. The fluid model with nonlocal ionization shows an excellent agreement for all inter-electrode distances, while the extended fluid model with variable electron transport coefficients agrees well with measurements at short inter-electrode distances when ionization by fast electrons can be neglected.

We investigate the dielectric and ferroelectric properties of Sr_{1?x}Bi_{x}Ti_{1?x}Fe_{x}O_{3} solid solutions (x=0, 0.05, 0.1, 0.15 and 0.2) together with their structures. Through the analysis of Rietveld refinement of powder x-ray diffraction, a cubic structure in space group Pm3m is determined for all the compositions. An obvious dielectric relaxation peak differing from SrTiO_{3} is observed in the present ceramics. The peak temperature T_{m} increases with increasing x, and it approaches room temperature at x=0.2. The Vogel–Fulcher law and Curie–Weiss law fittings further confirm the relaxor ferroelectricity in the present ceramics.

We theoretically and numerically demonstrate that a transmission-type electrically tunable polarizer can be realized by using graphene ribbons supported on a dielectric film with a graphene sheet behind. The polarization mechanism originates from the antenna plasmon resonance of graphene stripes. The results of full-wave numerical simulations reveal that transmittance of 0.70 for one polarization and 0.0073 for another polarization can be obtained at normal incidence. The transmission-type electrically tunable polarizer provides and facilitates a variety of applications, including filtering, detecting, and imaging.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

The mechanical properties and intrinsic hardness of the α-Ga boron phase (α-Ga-B) are studied by using the combination of first-principles calculations and a semiempirical macroscopic hardness model. It is found that α-Ga-B is mechanically stable and possesses higher bulk/shear modulus as compared with γ-B_{28}, a newly discovered high-pressure boron phase. The theoretical hardness of α-Ga-B is estimated to be 45 GPa, which is much higher than 38 GPa for γ-B_{28}. The results strongly indicate that α-Ga-B is a potential superhard boron phase. To further obtain insight into the superhard nature of α-Ga-B, we simulate stress–strain curves under tensile and shear deformation. Meanwhile, the microscopic mechanism driving the tensile and shear deformation modes in α-Ga-B is discussed in detail.

We study the stability and performance of Li absorption on the composite structure (B_{80}C_{72}) of boron fullerene and graphene by first-principles calculations. Our results show that the Li storage capacity of the composite structure is estimated to be at least Li_{54}B_{80}C_{72}, which is steady with improved dispersibility and electronic conductivity. The composite structure could have the potential application as the anode material of Li-ion batteries with high Li storage capacity and great mechanical property.

The temperature dependence of internal friction is first investigated to understand the microstructure transition during the sintering process for the green compact of aluminum powder. An internal friction (IF) peak is observed only during the first heating process while not in the subsequent cooling and repeated heating process. The temperature position of the peak is independent of the measuring frequency and the height decreases with the increasing frequency. The appearance of the peak is closely related to the weak bonding interfaces between deformed aluminum particles and increased dislocation density induced by the pressing. The appearance of the peak well responds to a recrystallization process of deformed particles and thus the formation of the grain boundary which is proven by the appearance of the grain boundary IF peak. The peak temperature position is rationalized with the onset of the recrystallization process during the sintering process.

We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase (i.e. isotropic–nematic phase transition). To improve the accuracy, precision, and efficiency of our computations, we attempt to employ the Wang–Landau NPT Monte Carlo algorithm in our simulations to calculate the function p(V) that gives the probability of arriving at the threshold density of the isotropic–nematic transition. Our results directly reveal that the nematic fluid phase, which is characterized by an ordered direction rather than an ordered configuration, appears and coexists with the isotropic phase when the aspect ratio α of the ellipsoid is located in a relatively narrow range of α=2.0–2.25, and it becomes dominant and is fully established when α≥α_{cut}=2.25. We find that our estimated α_{cut} is significantly lower than previously reported values of around 2.75. This prediction is further confirmed by the calculations of both the fluid reduced density and pressure of coexistence which show that the pressure grows up as the density increases and the probability function p(V) exhibits double peaks when the pressure enters the coexistence region. Based on these consistent results we are able to conclude that when α≥2.25 an ellipsoid fluid can fully display the nematic behavior. This study will place a useful and tight theoretical constraint on investigations of the isotropic–nematic phase transition in the future.

The highly charged ion Ar^{12+} with an energy of 3 MeV is used for irradiating metallic glass (Cu_{47}Zr_{45}Al_{8})_{98.5}Y_{1.5} and polycrystalline metallic W at the irradiation fluences of 1×10^{14} ions/cm^{2}, 1×10^{15} ions/cm^{2} and 1×10^{16} ions/cm^{2}. The main structure of metallic glass remains an amorphous phase under different irradiation fluences according to x-ray diffraction analysis. The scanning electron microscope observation on the morphologies indicates that no significant irradiation damage occurs on the surface and cross section of the metallic glass sample after different fluences of irradiation, while a large area of irregular cracks and holes were observed on the surface of metallic W at a fluence of 1×10^{16} ions/cm^{2}, with cracks and channel impairments at a certain depth from the surface. The root-mean-square (rms) roughness of metallic glass increases with increasing fluence of Ar^{12+}, while the reflectance decreases with increasing irradiation fluence. A nano-hardness test shows that the hardness of metallic glass decreases after irradiation. Under certain conditions, metallic glass (Cu_{47}Zr_{45}Al_{8})_{98.5}Y_{1.5} exhibits a higher capability of resistance to Ar^{12+} irradiation in comparison with polycrystalline W.

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

We study the adsorption of zigzag graphene nanoribbons (GNRs) on Si(001) substrates using the first-principles density functional theory, exploring the effects of the interface interaction on the structural and electronic properties of both GNRs and the substrate. By comparing the adsorption structures predicted by the local density approximation, the generalized gradient approximation, and the DFT-D2 approach, we confirm that both edge and inner C atoms of GNRs can form covalent bonds with the substrate. The GNR/substrate interaction destroys the antiferromagnetic coupling of the edge states in GNRs. The charge transfer from the substrate to GNRs exhibits a complicated pattern and is mainly localized near the C–Si bonds. We also observe a strong perturbation of the surface states and a surface reconstruction transition induced by the GNR adsorption.

The electronic structures and optical properties of the [110]?oriented Si_{1?x}Ge_{x} nanowires (NWs) passivated with different functional groups (?H, ?F and -OH) are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly: the band gap widths and types (direct or indirect) of the Si_{1?x}Ge_{x} NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si_{1?x}Ge_{x} NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si_{1?x}Ge_{x} NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.

We report ab initio calculations of the transport behavior of a phenyl substituted molecular motor. The calculated results show that the transport behavior of the device is sensitive to the rotation degree of the rotor part. When the rotor part is parallel with the stator part, a better rectifying performance can be found in the current-voltage curve. However, when the rotor part revolves to vertical with the stator part, the currents in the positive bias region decrease slightly. More importantly, the rectifying performance disappears. Thus this offers us a new method to modulate the rectifying behavior in molecular devices.

XU Min, WANG Li-Min, PENG Rui, GE Qing-Qin, CHEN Fei, YE Zi-Rong, ZHANG Yan, CHEN Su-Di, XIA Miao, LIU Rong-Hua, Arita M., Shimada K., Namatame H., Taniguchi M., Matsunami M., Kimura S., SHI Ming, CHEN Xian-Hui, YIN Wei-Guo, KU Wei, XIE Bin-Ping, FENG Dong-Lai

Chin. Phys. Lett. 2015, 32 (02):
027401
.
DOI: 10.1088/0256-307X/32/2/027401

Employing the angle-resolved photoemission spectroscopy, we study the electronic structure of TaFe_{1.23}Te_{3}, a two-leg spin ladder compound with a novel antiferromagnetic ground state. Quasi-two-dimensional (2D) Fermi surface is observed, with sizable inter-ladder hopping. Moreover, instead of observing an energy gap at the Fermi surface in the antiferromagnetic state, we observe the shifts of various bands. Combining these observations with density-functional-theory calculations, we propose that the large scale reconstruction of the electronic structure, caused by the interactions between the coexisting itinerant electrons and local moments, is most likely the driving force of the magnetic transition. Thus TaFe_{1.23}Te_{3} serves as a simpler platform that contains similar ingredients to the parent compounds of iron-based superconductors.

Magneto-transport properties of insulating bulk states in Bi(111) films are systematically investigated under the parallel field (B_{||}). We find that the magnetotransport of the B_{||} field is a more powerful tool to distinguish the bulk states and the surface states. A large magnetoresistance (MR) up to 20% in the B_{||} field is induced by the insulating bulk states for the suppression of the backward scattering. With the increasing thickness, a positive MR(B_{||}) from magnetic induced boundary scattering appears in the semimetal films. As the thickness is reduced to 10 nm, the positive MR(B_{||}) is induced by weak anti-localization from the surface states.

Structural and magnetic properties are investigated for Fe_{1?x}Mn_{x}V_{2}O_{4} (0≤x ≤1) spinels. As orbital-active Fe^{2+} is substituted with Mn^{2+}, the cubic-to-tetragonal transition T_{S}1 and the tetragonal-to-orthorhombic transition T_{S}2 gradually decrease. These structural transitions originate from the Fe^{2+} ferro-orbital order (F-OO). Below Yafet–Kittel (YK) magnetic transition T_{N}2, V ^{3+} orbital order (V-OO) plays an important role on global structure. Here x=0.6 is a critical point. Fe^{2+} F-OO and V ^{3+} F-OO coexist for 0≤x ≤0.5. For x≥0.6, the orbital pattern of V ^{3+} is antiferro (AF)-OO, and Fe^{2+} F-OO disappears. Structural transition T_{S}3, accompanied by YK magnetic transition T_{N}2, decreases initially, and then increases at x=0.6. A scenario for the complex phase diagram arising from the cooperation or competition of Fe^{2+} and V ^{3+} orbitals is proposed.

Laser-induced damage often determines the effective lifetime of an optic in large high-energy laser facilities. We present the damage performance on the rear surface of a large-aperture KDP crystal for 351 nm, 5 ns laser pulses. Surface damage shows a lower threshold than bulk damage after conditioning. Craters initiated on the scratch are found to increase with the shot number before filling the scratch. The experimental results reveal that damage initiation is mainly caused by extrinsic nanoabsorbers buried in the surface during the large-aperture laser operation.

Introducing a thin InGaN interlayer with a relatively lower indium content between the quantum well (QW) and barrier results in a step-like In_{x}Ga_{1?x}N/GaN potential barrier on one side of the QW. This change in the active region leads to a significant shift in photoluminescence (PL) and electroluminescence (EL) emissions to a longer wavelength compared with the conventional QW based light-emitting diodes. More importantly, an improvement against efficiency droop and an enhancement in light output power at the high-current injection are observed in the modified light-emitting diode structures. The role of the inserted layer in these improvements is investigated by simulation in detail, which shows that the creation of more sublevels in the valence band and the increase of hole concentration inside QWs are the main reasons for these improvements.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

A high quality of GaAs crystal growth in nanoscale V-shape trenches on Si(001) substrates is achieved by using the aspect-ratio trapping method. GaAs thin films are deposited via metal-organic chemical vapor deposition by using a two-step growth process. Threading dislocations arising from lattice mismatch are trapped by laterally confining sidewalls, and antiphase domains boundaries are completely restricted by V-groove trenches with Si {111} facets. Material quality is confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution X-ray diffraction. Low temperature photoluminescence (PL) measurement is used to analyze the thermal strain relaxation in GaAs layers. This approach shows great promise for the realization of high mobility devices or optoelectronic integrated circuits on Si substrates.

We report a back-gated metal-oxide-ferroelectric-metal (MOFM) field-effect transistor (FET) with lead zirconate titanate (PZT) material, in which an Al doped zinc oxide (AZO) channel layer with an optimized doping concentration of 1% is applied to reduce the channel resistance of the channel layer, thus guaranteeing a large enough load capacity of the transistor. The hysteresis loops of the Pt/PZT/AZO/Ti/Pt capacitor are measured and compared with a Pt/PZT/Pt capacitor, indicating that the remnant polarization is almost 40 μC/cm^{2} and the polarization is saturated at 20 V. The measured capacitance-voltage properties are analyzed as a result of the electron depletion and accumulation switching operation conducted by the modulation of PZT on AZO channel resistance caused by the switchable remnant polarization of PZT. The switching properties of the AZO channel layer are also proved by the current-voltage transfer curves measured in the back-gated MOFM ferroelectric FET, which also show a drain current switching ratio up to about 100 times.

We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor (1T1R) resistance random access memory (RRAM) device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state (HRS) under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament (CF) formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state (LRS) can be easily changed by removing a few trapping states from the conducting path. Hence, a higher HRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.

In finite population games with weak selection and large population size, when the payoff matrix is constant, the one-third law serves as the condition of a strategy to be advantageous. We generalize the result to the cases of environment-dependent payoff matrices which exhibit the feedback from the environment to the population. Finally, a more general law about cooperation-dominance is obtained.

We find that a conserved mutation residue Glu to residue Asp (E303D), which both have the same polar and charged properties, makes Kir2.1 protein lose its function. To understand the mechanism, we identify three interactions which control the conformation change and maintain the function of the Kir2.1 protein by combining homology modeling and molecular dynamics with targeted molecular dynamics. We find that the E303D mutation weakens these interactions and results in the loss of the related function. Our data indicate that not only the amino residues but also the interactions determine the function of proteins.

The calculated and experimental research of sheet resistances of crystalline silicon solar cells by dry laser doping is investigated. The nonlinear numerical model on laser melting of crystalline silicon and liquid-phase diffusion of phosphorus atoms by dry laser doping is analyzed by the finite difference method implemented in MATLAB. The melting period and melting depth of crystalline silicon as a function of laser energy density is achieved. The effective liquid-phase diffusion of phosphorus atoms in melting silicon by dry laser doping is confirmed by the rapid decrease of sheet resistances in experimental measurement. The plateau of sheet resistances is reached at around 15 Ω/?. The calculated sheet resistances as a function of laser energy density is obtained and the calculated results are in good agreement with the corresponding experimental measurement. Due to the successful verification by comparison between experimental measurement and calculated results, the simulation results could be used to optimize the virtual laser doping parameters.

The power conversion efficiency (PCE) of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC_{61}BM) based organic solar cells (OSCs) is significantly improved by using benzyl acetate (BA), an organic compound without any halogen or sulphur atom, as a processing additive to control the blend morphology. The solar cells show PCE of 3.85% with a fill factor (FF) of 65.22%, which are higher than those of the common thermal annealing device (PCE 3.30%, FF 60.83%). The overall increased PCE depends upon the enhanced crystallinity of P3HT and good carriers transport, with a high balanced charge carrier mobility.