Effects of electrode on resistance switching properties of ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> films deposited by magnetron sputtering

ZnMn₂O₄ films for resistance random access memory (RRAM) were fabricated with different device structures by magnetron sputtering. The effects of electrode on I-V characteristics, resistance switching behavior, endurance and retention characteristics of ZnMn₂O₄ films were investigated. The ZnMn₂O₄ films, using p-Si and Pt as bottom electrode, exhibit bipolar resistive switching (BRS) behavior dominated by the space-charge-limited conduction (SCLC) mechanism in the high resistance state (HRS) and the filament conduction mechanism in the low resistance state (LRS), but the ZnMn₂O₄ films using n-Si as bottom electrodes exhibit both bipolar and unipolar resistive switching behaviors controlled by the Poole-Frenkel (P-F) conduction mechanism in both HRS and LRS. Ag/ZnMn₂O₄/p-Si device possesses the best endurance and retention characteristics, in which the number of stable repetition switching cycle is over 1000 and the retention time is longer than 10⁶ seconds. However, the highest R _HRS/R _LRS ratio of 10⁴ and the lowest V _ON and V _OFF of 3.0 V have been observed in Ag/ZnMn₂O₄/Pt device. Though the Ag/ZnMn₂O₄/n-Si device also possesses the highest R _HRS/R _LRS ratio of 10⁴, but the highest values of V _ON,V _OFF, R _HRS and R _LRS, as well as the poor endurance and retention characteristics.     

Morphology study of oriented SmBCO film deposited by MOCVD

c-axis-oriented SmBa_2Cu_3O_7(SmBCO) films have been deposited on(100)- LaA1O_3(LAO)substrate by metal organic chemical vapor deposition(MOCVD) technique.The effects of deposition temperature(T_(dep)) and total pressure(P_(tot)) on the orientation and microstructure of SmBCO films were investigated.The orientation of SmBCO films transformed from α-axis to c-axis with increasing of T_(dep) from 900 to 1 100℃.At T_(dep)=1 050℃,SmBCO films had c-axis orientation and tetragon surface.At P_(tot)~(dep)=400-800 Pa and T_(dep)=1 050 ℃,totally c-axis-oriented SmBCO films were obtained.The R_(dep) of SmBCO films increased firstly and then decreased with increasing P_(tot).The surface of SmBCO films exhibited tetragon morphology at 1 050 ℃ and400 Pa.Maximum thickness of SmBCO film deposited was 1.2μm at P_(tot)= 600 Pa,and the corresponding R_(dep)was 7.2 μm·h~(-1).     

Effect of oxygen partial pressure on epitaxial growth and properties of laser-ablated AZO thin films

Al-doped ZnO (AZO) thin films were grown on c-sapphire substrates by laser ablation under different oxygen partial pressures (P _O2). The effect of PO2 on the crystal structure, preferred orientation as well as the electrical and optical properties of the films was investigated. The structure characterizations indicated that the as-grown films were single-phased with a wurtzite ZnO structure, showing a significant c-axis orientation. The films were well crystallized and exhibited better crystallinity and denser texture when deposited at higher P _O2. At the optimum oxygen partial pressures of 10 - 15 Pa, the AZO thin films were epitaxially grown on c-sapphire substrates with the (0001) plane parallel to the substrate surface, i e, the epitaxial relationship was AZO (000 1) // Al₂O₃ (000 1). With increasing P _O2, the value of Hall carrier mobility was increased remarkably while that of carrier concentration was decreased slightly, which led to an enhancement in electrical conductivity of the AZO thin films. All the films were highly transparent with an optical transmittance higher than 85 %.     

Probabilistic composition of cone-based cardinal direction relations

Composition tables play a significant role in qualitative spatial reasoning (QSR). At present, a couple of composition tables focusing on various spatial relations have been developed in a qualitative approach. However, the spatial reasoning processes are usually not purely qualitative in everyday life, where probability is one important issue that should be considered. In this paper, the probabilistic compositions of cone-based cardinal direction relations (CDR) are discussed and estimated by making some assumptions. Consequently, the form of composition result turns to be {(R ₁,P ₁), (R ₂,P ₂), ..., (R _n ,P _n )}, where P _i is the probability associated with relation R _i . Employing the area integral method, the probabilities in each composition case can be computed with the assumption that the target object is uniformly distributed in the corresponding cone regions.     

Enhanced Ferroelectric Polarization in Laser-ablated Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films by Controlling Preferred Orientation

Polycrystalline Bi₄Ti₃O₁₂ thin films with various fractions of a-axis, c-axis and random orientations have been grown on Pt(111)/Ti/SiO₂/Si substrates by laser-ablation under different kinetic growth conditions. The relationship between the structure and ferroelectric property of the films was investigated, so as to explore the possibility of enhancing ferroelectric polarization by controlling the preferred orientation. The structural characterization indicated that the large growth rate and high oxygen background pressure were both favorable for the growth of non-c-axis oriented grains in the Bi₄Ti₃O₁₂ thin films. The films with high fractions of a-axis and random orientations, i e, f (a-sxis) = 28.3% and f (random) = 69.6%, could be obtained at the deposition temperature of 973 K, oxygen partial pressure of 15 Pa and laser fluence of 4.6 J/cm², respectively. It was also noted that the variation of ferroelectric polarization was in accordance with the evolution non-c-axis orientation. A large value of remanent polarization (2Pr = 35.5 μC/cm²) was obtained for the Bi₄Ti₃O₁₂ thin films with significant non-c-axis orientation, even higher than that of rare-earth-doped Bi₄Ti₃O₁₂ films.     

Bimodal plate structures induced by pulsed laser in duplex-phase Zr alloy

A duplex-phase Zr-2.5Nb alloy was treated by pulsed laser, followed by careful microstructural characterization using field emission gun scanning electron microscope and attached electron backscatter diffraction. Beneath the modification zones with common uniform α-plate structures(UPS), a layer of unreported bimodal α-plate structures(BPS) featured by coarse(submicron)plates forming multiple cores surrounded by dense fine(nanoscale) plates was found. Presence of such BPS is attributed to non-equilibrium thermodynamic conditions induced by the pulsed laser treatments. Limited diffusion of Nb due to the short pulse during laser heating allows β phases with distinctly different Nb contents to be presented: Nb-enriched prior β films and Nb-depleted β phases, transforming into the fine and the coarse plates during cooling, respectively. Orientation analyses show that both types of plates in the BPS are aroused essentially from a single β orientation, suggesting epitaxial growth of the Nb-depletedβ phases from the preexisting β films.     

Density function theory study of electronic,optical and thermodynamic properties of CaN<Subscript>2</Subscript>, SrN<Subscript>2</Subscript> and BaN<Subscript>2</Subscript>

We put forward a first-principles density-functional theory about the impact of pressure on the structural and elastic properties of bulk CaN₂, SrN₂ and BaN₂. The ground state properties of three alkaline earth diazenides were obtained, and these were in good agreement with previous experimental and theoretical data. By using the quasi-harmonic Debye model, the thermodynamic properties including the debye temperature Θ _D, thermal expansion coefficient α, and grüneisen parameter γ are successfully obtained in the temperature range from 0 to 100 K and pressure range from 0 to 100 GPa, respectively. The optical properties including dielectric function ε(?), absorption coefficient α(?), reflectivity coefficient R(?), and refractive index n(?) are also calculated and analyzed.     

Effects of annealing processes on Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript> thin films

The Cu _x Si_1-x thin films have been grown by pulsed laser deposition (PLD) with in situ annealing on Si (001) and Si (111), respectively. The transformation of phase was detected by X-ray diffraction (XRD). The results showed that the as-deposited films were composed of Cu on both Si (001) and Si (111). The annealed thin films consisted of Cu + η”-Cu₃Si on Si (001) while Cu + η’-Cu₃Si on Si (111), respectively, at annealed temperature (T _a) = 300-600 °C. With the further increasing of T _a, at T _a= 700 °C, there was only one main phase, η”-Cu₃Si on Si (001) while η’-Cu₃Si on Si (111), respectively. The annealed thin films transformed from continuous dense structure to scattered-grain morphology with increasing T _a detected by field emission scanning electron microscope (FESEM). It was also showed that the grain size would enlarge with increasing annealing time (t _a).     

Elimination of Voids at Interface of <Emphasis Type="Italic">β</Emphasis>-SiC Films and Si Substrate by Laser CVD

Void-free β-SiC films were deposited on Si(001) substrates by laser chemical vapor deposition using hexamethyldisilane (HMDS) as the precursor. The effect of the time of introducing HMDS, i e, the substrate temperature when HMDS introduced (T_in), on the preferred orientation, surface microstructure and void was investigated. The orientation of the deposited SiC films changed from <001> to random to <111> with increasing T_in. The surface showed a layer-by-layer microstructure with voids above T_in ? 773 K, and then transformed into mosaic structure without voids at T_in= 298 K. The mechanism of the elimination of voids was discussed. At T_in =298 K, Si surface can be covered by an ultrathin SiC film, which inhibits the out-diffusion of Si atoms from substrate and prohibites the formation of the voids.     

Spontaneous Magnetic Transitions and Corresponding Magnetoelastic Properties of Intermetallic Compounds <Emphasis Type="Italic">R</Emphasis>Mn<Subscript>2</Subscript>Ge<Subscript>2</Subscript> (<Emphasis Type="Italic">R</Emphasis>=Gd,Tb and Dy)

The spontaneous magnetic transitions and corresponding magnetoelastic properties of intermetallic compounds RMn₂Ge₂ (R=Gd, Tb and Dy) were investigated by using the X-ray diffraction method and magnetic measurement. The results showed that the compounds experience two magnetic transitions, namely the second-order paramagnetic to antiferromagnetic transition at temperature T_N (T_N=368, 423 and 443 K for GdMn₂Ge₂, TbMn₂Ge₂ and DyMn₂Ge₂, respectively) and the first-order antiferromagnetic - ferrimagnetic transition at temperature T_t (T_t=96, 80 and 40 K for GdMn₂Ge₂, TbMn₂Ge₂ and DyMn₂Ge₂, respectively) as the temperature decreases. The temperature dependence of the lattice constant a(T) displays a negative magnetoelastic anomaly at the second-order transition point T_N and, at the first-order transition T_t, a increases abruptly for GdMn₂Ge₂ and TbMn₂Ge₂, Δa/a about 10^-3. Nevertheless, the lattice constant c almost does not change at these transition points indicating that such magnetoelastic anomalies are mainly contributed by the Mn-sublattice. The transitions of the magnetoelastic properties are also evidenced on the temperature dependence of magnetic susceptibility χ. The first-order transition behavior at T_t is explained by the Kittel mode of exchange inversion.     

Statistical study of magnetotail flux ropes near the lunar orbit

Flux-rope/TCR events near the magnetotail lunar orbit(-67R_E GSM X* -39RE) were studied using magnetic-field and plasma data measured by THEMIS B and C between January 2011 and March 2012. The aberrant coordinate GSM*, where the X* axis is rotated 4° relative to GSM-X, was used to count the occurrence rate. The number ratio of earthward to tailward events was about 3:5. Moreover, the event occurrence rate distribution showed a clear dawn-dusk asymmetry distribution, with dusk-side events accounting for 57.98%. A superposed epoch analysis of the flux-rope events showed that earthward events had a shorter duration in the leading than in the trailing part. Earthward events also displayed a lower temperature and a lower flow speed than tailward events. We studied the relationship between the event occurrence rate and geomagnetic activity level even further. The occurrence rate of tailward flux-rope/TCR events increases with increasing AE-index, whereas earthward events occur mainly in the relatively quiet period of geomagnetic activity(AE ~ 100–300 n T). Flux-rope/TCR events identified within a 10 mm time frame were treated as belonging to a single reconnection event. By comparing the occurrence rates of earthward and tailward events along X*, we estimated the most likely location of the near-Earth reconnection site as X* = -36R_E.     

Low temperature synthesis of amorphous La<Subscript>0.7</Subscript>Zn<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> films grown on p<Superscript>+</Superscript>-Si substrates and its resistive switching properties

Amorphous La_0.7Zn_0.3MnO₃ (LZMO) films were deposited on p⁺-Si substrates by sol-gel method at low temperature of 450 °C. The Ag/LZMO/p⁺-Si device exhibits invertible bipolar resistive switching and the R _HRS/R _LRS was about 10⁴-10⁶ at room temperature which can be kept over 10³ switching cycles. Better endurance characteristics were observed in the Ag/LZMO/p⁺-Si device, the V _Set and the V _Reset almost remained after 10³ endurance switching cycles. According to electrical analyses, the conductor mechanism was in low resistor state (LRS) governed by the filament conductor and in the high state (HRS) dominated by the traps-controlled space-charge-limited current (SCLC) conductor.     

Preparation and magnetic properties of Mn-Zn ferrites by the Co-precipitation method

Mn-Zn ferrites (Mn_1?x Zn _x Fe₂O₄) with different compositions were prepared by the coprecipitation method, and the influences of such synthesis conditions as pH value, composition and volume ratio (R) of the mixed solution and NH₄HCO₃ solution on their microstructures and magnetic properties were discussed. The samples were characterized by X-ray diffraction (XRD) and magnetization measurement instrument. Lattice parameters and average crystalline size of the synthesized materials were calculated from the corresponding XRD patterns with the related software Jade.5. For samples of different pH values, only one phase was found when pH values were 7.0, 8.0 and 9.0. The sample with pH value of 7.0 exhibited the highest saturation magnetic induction, the lowest coercive force, and crystallized best. For samples of different R values with pH value of 7.0, only one phase was observed in all samples, and the sample with R value of 2.3 exhibited the highest saturation magnetic induction and the lowest coercive force. The composition has mainly afected the magnetic properties, and the saturation magnetic induction increases with the increase of the content of Zn (x), but decreases when x is beyond 0.6. The trend of coercive force is on the contrary. However, no magnetism is exhibited when the x value is up to 0.8.     

Parameter sensitivity and inversion analysis of a concrete faced rock-fill dam based on HS-BPNN algorithm

Considering the complex nonlinear relationship between the material parameters of a concrete faced rock-fill dam(CFRD) and its displacements, the harmony search(HS) algorithm is used to optimize the back propagation neural network(BPNN), and the HS-BPNN algorithm is formed and applied for the inversion analysis of the parameters of rock-fill materials. The sensitivity of the parameters in the Duncan and Chang's E-B model is analyzed using the orthogonal test design. The case study shows that the parameters φ0, K, Rf, and Kb are sensitive to the deformation of the rock-fill dam and the inversion analysis for these parameters is performed by the HS-BPNN algorithm. Compared with the traditional BPNN, the HS-BPNN algorithm exhibits the advantages of high convergence precision, fast convergence rate, and strong stability.     

Preparation and piezoelectric properties of CuO-added (Ag<Subscript>0.75</Subscript>Li<Subscript>0.1</Subscript>Na<Subscript>0.1</Subscript>K<Subscript>0.05</Subscript>)NbO<Subscript>3</Subscript> lead-free ceramics

CuO-doped (Ag_0.75Li_0.1Na_0.1K_0.05)NbO₃ (ALNKN-xCuO, x = 0–2mol%) lead-free piezoelectric ceramics were prepared by the solid-state reaction method in air atmosphere. The effects of CuO addition on the phase structure, microstructure, and piezoelectric properties of the ceramics were investigated. The experimental results show that the ALNKN ceramics without doping CuO possess rhombohedral phase along with K2Nb6O16-type phase and metallic silver phase. For all of the CuO-doped ALNKN ceramics, a pure perovskite structure with the orthorhombic phase was obtained by enclosing the samples in a corundum tube. A homogeneous microstructure with the grain size of about 1 μm was formed for the ceramics with 0.5mol% CuO. The grain size increases with increasing amount of CuO. The temperature dependence of dielectric properties indicates that the ferroelectric phase of the ALNKN-xCuO ceramics becomes less stable with the addition of CuO. The ceramics with x = 1mol% exhibit relatively good electrical properties along with a high Curie temperature. These results will provide a helpful guidance to preparing other AN-based ceramics by solid-state reaction method in air atmosphere.     

UV disinfection of Staphylococcus aureus in ballast water: Effect of growth phase on the disinfection kinetics and the mechanization at molecular level

This work aimed to study the inactivate kinetics of Staphylococcus aureus (S. aureus) in artificial seawater by ultraviolet radiation, establish relationships between model parameters and growth phases, and explain the mechanization of UV disinfection by molecular biological detection. Investigations were carried out for the validation of Chick-Watson, Collins-Selleck, Hom and Biphasic models when S. aureus was in stationary phase (t=14 h). The results showed that the Biphasic kinetic model’s R² turned out to be the highest one (R²=0.9892) and RMSE was less than 0.5 (RMSE =0.2699). The Biphasic kinetic model was better fit for ultraviolet disinfection than the other three models under the circumstance of this experiment and chosen to fit the ultraviolet disinfection curves for microorganisms at three growth phases. The sensitivity of microorganisms under ultraviolet radiation was in the following order: in exponential phase > in stationary phase > in lag phase by comparing the indexes of the Biphasic model (k₁ and x). Besides, agarose gel electrophoresis was used in order to directly assess the damage to DNA of microorganisms that were exposed to the different dose of UV irradiation. The results revealed that DNA damage caused by UV radiation was an important reason for the microorganism inactivation and as the UV dose increased, there was greater damage caused in DNA.     

Composition dependence of phase structure and electrical properties of (1−y)Bi1−xNdxFeO3−yBiScO3 ceramics

In this work, we have studied a new lead-free ceramic of(1-y)Bi_(1-x)Nd_xFeO_(3-y)BiScO_3(0.05≤x≤0.15 and 0.05≤y≤0.15) prepared by a conventional solid-state method, and the influences of Nd and Sc content on their phase structure and electrical properties were investigated in detail. The ceramics with 0.05≤x≤0.10 and 0.05≤y≤0.15 belong to an R3 c phase, and the rhombohedral-like and orthorhombic multiphase coexistence is established in the composition range of 0.125≤x≤0.15 and y=0. The electrical properties of the ceramics can be enhanced by modifying x and y values. The highest piezoelectric coefficient(d33~51 p C/N) is obtained in the ceramics with x=0.075 and y=0.125, which is superior to that of a pure BiFeO_3 ceramic. In addition, a lowest dielectric loss(tan δ~0.095%, f=100 k Hz) is shown in the ceramics with x=0.15 and y=0 due to the involvement of low defect concentrations, and the improved thermal stability of piezoelectricity at 20–600oC is possessed in the ceramics. We believe that the ceramics can play a meaningful role in the high-temperature lead-free piezoelectric applications.     

YIG thin film for RF integrated inductor

The yttrium iron garnet(YIG) thin films prepared by the sol-gel method and rapid thermal annealing(RTA) process for integrated inductor are investigated. The X-ray diffraction(XRD) results indicate that the YIG film annealed above 650 ℃ is poly-crystalline with single-phase garnet structure. Moreover, it can be found that the initial permeability μi, saturation magnetization M_S and coercivity H_c of these YIG films increase with increasing RTA temperature. Low temperature annealing after crystallization can further improve the magnetic properties of YIG film. Thereby, a planar integrated inductor in the presence of Si substrate/SiO_2 layer/Y_(2.8)Bi_(0.2)Fe_5O_(12) thin film/Cu spiral coil structure is fabricated successfully by the standard IC processes. Due to the magnetic enhancement originated from YIG film, the inductance L and quality factor Q of the inductor with YIG film are improved in a certain frequency range.     

A statistical approach to fit Gaussian part of full-energy peaks from Si(PIN) and SDD X-ray spectrometers

A new statistical fitting approach,named Statistical Distribution-Based Analytic(SDA)method,is proposed to fit single Gaussian-shaped Kαand KβX-ray peaks recorded by Si(PIN)and silicon drift detector(SDD).In this method,we use the discrete distribution theory to calculate standard deviation of energy resolutionσ.The calibration ofσand energy(E)for two detectors between the energy ranges of 4.5–26 keV are also completed by measuring characteristic X-ray spectra of nineteen types of pure elements.With the spectrum fraction(SF)parameter proposed in this paper,the SDA method can be used to resolve overlapping peaks.In measured spectra,the Gaussian part of X-ray peaks can be fitted by a Gaussian function with two parameters,σand SF.This new fitting approach is simpler than traditional methods and it achieves relatively good results when fitting the complex X-ray spectra of national standard alloy samples detected by Si(PIN)and SDD detectors.The2r values are obtained for each spectrum to assess fitting results,and the SDA fitting method gives a preferable fit for the SDD detector.     

Electronic structure and transport coefficients of the thermoelectric materials Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> from first-principles calculations

The electronic structures of bulk Bi₂Te₃ crystals were investigated by the first-principles calculations. The transport coefficients including Seeback coefficient and power factor were then calculated by the Boltzmann theory, and further evaluated as a function of chemical potential assuming a rigid band picture. The results suggest that p-type doping in the Bi₂Te₃ compound may be more favorable than n-type doping. From this analysis results, doping effects on a material will exhibit high ZT. Furthermore, we can also find the right doping concentration to produce more efficient materials, and present the “advantage filling element map” in detail.