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The microstructures of TiN/SiN(sub x) films were studies by means of a Monte Carlo method. The findings show that the average size of TiN grains decreases with volume fraction of SiN(sub x) approximately according to a power law with a time-dependent exponent decreasing with growth time.

A new approach is demonstrated for investigating charge and spin diffusion as well as surface and bulk recombination in unpassivated doped semiconductors. This approach consists in using two complementary, conceptually related, techniques, which are time-resolved photoluminescence (TRPL) and spatially resolved microluminescence (μPL) and is applied here to p+ GaAs. Analysis of the sole TRPL signal is limited by the finite risetime. On the other hand, it is shown that joint TRPL and μPL can be used to determine the diffusion constant, the bulk recombination time, and the spin relaxation time. As an illustration, the temperature variation of these quantities is investigated for p+ GaAs. [ABSTRACT FROM AUTHOR]

We have measured the temperature and field dependence of emission rates from five traps in electron damaged GaAs. Four of the traps have previously been identified as radiation defects. One of the traps, seen in higher doped diodes, has not been previously identified. We have fit the data to a multiphonon emission theory that allows recombination in GaAs to be characterized over a broad range of temperature and electric field. These results demonstrate an efficient method to calculate field-dependent emission rates in GaAs. [ABSTRACT FROM AUTHOR]

The temperature dependence of the spectral features in the vicinity of the direct band edge of mixed-crystals Mo(SxSe1-x)2 solid solutions is measured in the temperature range of 25-295K by using piezoreflectance (PzR). The near band-edge excitonic transition energies of Mo(SxSe1-x)2 solid solutions were determined accurately from a detailed line-shape fit of the PzR spectra. The near band-edge excitonic transition energies were found to vary smoothly with the increase of S content x, indicating that the natures of the direct band edges of Mo(SxSe1-x)2 solid solutions are similar. The temperature dependences of near band edge transition energies were analyzed using Bose-Einstein expressions in the temperature range from 25 to 295 K. The parameters that described the temperature variation of the energies and broadening function of the excitonic transitions were evaluated and discussed. [ABSTRACT FROM AUTHOR]

The polycrystalline BaTiO3 (BTO) thin films were grown on F-doped SnO2 substrates by pulsed laser deposition. The devices show a rectification at a small voltage, while bipolar resistive switching (RS) and negative differential resistance (NDR) appear at a large voltage. Furthermore, RS remains and NDR disappears when no positive bias is applied, while both RS and NDR behaviors improve when increasing the positive bias. The electrons trapped/detrapped by interface states at Au/BTO interface are proposed to understand the above behaviors. [ABSTRACT FROM AUTHOR]

The dependence of electron mobility on growth conditions and threading dislocation density (TDD) was studied for n--GaN layers grown by ammonia-based molecular beam epitaxy. Electron mobility was found to strongly depend on TDD, growth temperature, and Si-doping concentration. Temperature-dependent Hall data were fit to established transport and charge-balance equations. Dislocation scattering was analyzed over a wide range of TDDs (∼2×106 cm-2 to ∼2×1010 cm-2) on GaN films grown under similar conditions. A correlation between TDD and fitted acceptor states was observed, corresponding to an acceptor state for almost every c lattice translation along each threading dislocation. Optimized GaN growth on free-standing GaN templates with a low TDD (∼2×106 cm-2) resulted in electron mobilities of 1265 cm2/Vs at 296K and 3327 cm2/Vs at 113 K. [ABSTRACT FROM AUTHOR]

We have prepared the new amorphous superconductor MoxCyGazOδ with a maximum critical temperature Tc of 3.8K by the direct-write nano-patterning technique of focused (gallium) ion beam induced deposition (FIBID) using Mo(CO)6 as precursor gas. From a detailed analysis of the temperature-dependent resistivity and the upper critical field, we found clear evidence for proximity of the samples to a disorder-induced metal-insulator transition. We observed a strong dependence of Tc on the deposition parameters and identified clear correlations between Tc, the localization tendency visible in the resistance data and the sample composition. By an in-situ feedback-controlled optimization process in the FIB-induced growth, we were able to identify the beam parameters which lead to samples with the largest Tc-value and sharpest transition into the superconducting state. [ABSTRACT FROM AUTHOR]

Ion channeling technique using MeV C2+ ions and high resolution X-ray diffraction were used to study the crystal quality of an InAs/AlSb-based quantum wells. We found that the InAs quality has a strong dependence on the type of the interface used. With the addition of the InSb-like interface, the crystal quality of the InAs channel was greatly improved. The InAs lattice was fully strained and aligned with the lattice of the buffer layer without any lattice relaxation. On the other hand, if the interface was of the AlAs type, the lattice of the InAs quantum well was relaxed and the crystal quality was poor. This explains why a superior InAs quantum well with high electron mobility and good surface morphology can be achieved with the use of the InSb interface. [ABSTRACT FROM AUTHOR]

We investigate the anisotropic stress dependent magnetic and phonon behaviors in self-assembled CoFe2O4-PbTiO3 (CFO-PTO) nanostructures deposited on SrRuO3 buffered SrTiO3 substrates of various thickness. The increased vertical compressed stress with increasing thickness enhances the vertical magnetic anisotropy of CFO while gradually reducing the vertical polarization of PTO. By applying the magnetic-field dependent Raman scattering, the CFO-A1g and T2g(1) phonon frequencies shift oppositely because of the magnetostriction. Moreover, the PTO-A1 mode intensities anomalously enhance and the A1 and E mode frequencies, respectively, increase and decrease, which prove the existence of the stress-mediated magnetoelectric (ME) effect. This study shows that the ME transmission process is dominated by interfacial stress, which is critical for enhancing the ME efficiency. [ABSTRACT FROM AUTHOR]

To understand the origins of stress in thin films, we have used wafer curvature to measure the stress evolution during electrodeposition of Ni on lithographically patterned Si substrates. The stress is measured as the hemispherical islands grow and impinge upon each other, forming interfacial boundaries between them.We relate the results to a model for polycrystalline films in which the stress is attributed to competing processes occurring where the layers in adjacent grains grow into each other and form new segments of grain boundary. This model predicts that the stress in each layer depends on the rate at which the grain boundary is growing when that layer is incorporated into the film. The calculations agree with the measured stress vs thickness using a single set of fitting parameters for five different growth rates. [ABSTRACT FROM AUTHOR]

The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode-the shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5 μm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. Study of these devices by more advanced Monte Carlo techniques that simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5 μm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600 nm and 700 nm, respectively. The paper presents results of the first ever THz submicron planar Gunn diode fabricated in In0.53Ga0.47As on an InP substrate, operating at a fundamental frequency above 300 GHz. Experimentally measured rf power of 28 μW was obtained from a 600 nm long × 120 μm wide device. At this new length, operation in fundamental mode at much higher frequencies becomes possible-the Monte Carlo model used predicts power output at frequencies over 300 GHz. [ABSTRACT FROM AUTHOR]

Thins films are synthesized by deposition of size-selected Mon– cluster anions on an inert substrate. Scanning tunneling microscopy pictures indicate that the deposited material consists of individual particles with diameters corresponding to the size of the preformed clusters from the gas phase. Previous attempts to manufacture cluster materials from metals failed since these clusters coalesced at room temperature. Our data suggest the possibility to synthesize new nanomaterials from clusters of high fusing metals. This may prove to be the key to harness size-dependent and tuneable properties of clusters for creating novel classes of functional tailor-made materials. [ABSTRACT FROM AUTHOR]

We investigate the mechanism of deuterium retention by lithiated graphite and its relationship to the oxygen concentration through surface sensitive experiments and atomistic simulations. Deposition of lithium on graphite yielded 5%-8% oxygen surface concentration and when subsequently irradiated with D ions at energies between 500 and 1000 eV/amu and fluences over 1016 cm-2 the oxygen concentration rose to between 25% and 40%. These enhanced oxygen levels were reached in a few seconds compared to about 300 h when the lithiated graphite was allowed to adsorb oxygen from the ambient environment under equilibrium conditions. Irradiating graphite without lithium deposition, however, resulted in complete removal of oxygen to levels below the detection limit of XPS (e.g., <1%). These findings confirm the predictions of atomistic simulations, which had concluded that oxygen was the primary component for the enhanced hydrogen retention chemistry on the lithiated graphite surface. [ABSTRACT FROM AUTHOR]

The drain current fluctuation of ungated AlGaN/GaN high electron mobility transistors (HEMTs) measured in different fluids at a drain-source voltage of 0.5 V was investigated. The HEMTs with metal on the gate region showed good current stability in deionized water, while a large fluctuation in drain current was observed for HEMTs without gate metal. The fluctuation in drain current for the HEMTs without gate metal was observed and calculated as standard deviation from a real-time measurement in air, deionized water, ethanol, dimethyl sulfoxide, ethylene glycol, 1,2-butanediol, and glycerol. At room temperature, the fluctuation in drain current for the HEMTs without gate metal was found to be relevant to the dipole moment and the viscosity of the liquids. A liquid with a larger viscosity showed a smaller fluctuation in drain current. The viscosity-dependent fluctuation of the drain current was ascribed to the Brownian motions of the liquid molecules, which induced a variation in the surface dipole of the gate region. This study uncovers the causes of the fluctuation in drain current of HEMTs in fluids. The results show that the AlGaN/GaN HEMTs may be used as sensors to measure the viscosity of liquids within a certain range of viscosity. [ABSTRACT FROM AUTHOR]

Magnetotransport measurements were performed on a series of nanostructured Bi1-xSbx alloy samples with an Sb content in the range between 0% and 60%. The samples were prepared by cold pressing and annealing of crystalline Bi1-xSbx nanoparticles, which were synthesized by mechanical alloying. The incorporation of Sb changes the band structure of these nanotextured alloys as well as their transport behavior. With increasing Sb content the band gap increases and reaches a maximum band gap of 42 meV at an Sb concentration of about 14% determined from temperature dependent resistivity measurements. For even higher Sb content, the band gap decreases again. The bands and thus the band gaps are shifted with respect to bulk material due to quantum confinement effects in the nanostructures. The change of the band structure with varying Sb content strongly affects the magnetoresistance behavior as well as the magnetic field dependence of the Hall-coefficient. Using a three band model in order to describe both properties, it was possible to determine the main band parameters of the nanostructured material as a function of the Sb content. [ABSTRACT FROM AUTHOR]

For n- and p-type semiconductors doped above the 1016 cm-3 range, simple analytical expressions for the surface recombination velocity S have been obtained as a function of excitation power P and surface state density NT. These predictions are in excellent agreement with measurements on p-type GaAs films, using a novel polarized microluminescence technique. The effect on S of surface passivation is a combination of the changes of three factors, each of which depends on NT: (i) a power-independent factor which is inversely proportional to NT and (ii) two factors which reveal the effect of photovoltage and the shift of the electron surface quasi Fermi level, respectively. In the whole range of accessible excitation powers, these two factors play a significant role so that S always depends on power. Three physical regimes are outlined. In the first regime, illustrated experimentally by the oxidized GaAs surface, S depends on P as a power law of exponent determined by NT. A decrease of S such as the one induced by sulfide passivation is caused by a marginal decrease of NT. In a second regime, as illustrated by GaInP-encapsulated GaAs, because of the reduced value of S, the photoelectron concentration in the subsurface depletion layer can no longer be neglected. Thus, S-1 depends logarithmically on P and very weakly on surface state density. In a third regime, expected at extremely small values of P, the photovoltage is comparable to the thermal energy, and S increases with P and decreases with increasing NT. [ABSTRACT FROM AUTHOR]

The anomalous appearance of a ferromagnetic moment in nominally antiferromagnetic nanoparticles has been known about since Néel, but never well understood. We present proof of the core/shell model of magnetism in antiferromagnetic NiO nanoparticles (NP) using neutron diffraction. Nickel oxide nanoparticles were produced in a large quantity by a novel continuous hydrothermal flow synthesis method. The antiferromagnetic nature of the nanoparticles allowed the structural and the magnetic diffraction peaks to be completely separated. Using both the microstructure option in "Fullprof" microstructure fitting suite and convolution techniques, we determined the NP consisted of an ordered antiferromagnetic core 5.2(2) nm in diameter surrounded by a disordered shell 0.7(2) nm thick. Further magnetic measurements showed that this disordered shell possess a significant polarisable magnetisation, up to a fifth that of pure nickel. They also indicate that two magnetic transitions occur between 400 and 10 K; around 350 K, there is a broad transition from paramagnetic to a form of superparamagnetism, then near 30 K there is a transition to a higher anisotropy state. Differences in field cooled and zero field cooled hysteresis loops were found, though with no evidence of exchange bias effects. [ABSTRACT FROM AUTHOR]

Ferroelectric size effect of BaTiO3 (BTO) tunnel junctions with metal Pt and/or oxide SrRuO3 (SRO) electrodes has been comprehensively investigated by the first-principle calculations. A vacuum layer is included in the supercell calculations, so that full-relaxation is achieved without artificial constraint on the supercell strains. We have constructed all of ten possible types of tunnel junctions with either symmetric or asymmetric geometries to systematically explore the influence of electrode/ferroelectric interfaces. The characteristics of atomic structure, polarization, charge density, and electrostatic potential for different geometries and sizes are revealed. It is found that the ferroelectric stability of a tunnel junction depends significantly on the details of the two electrode/ferroelectric interfaces, which present specific short- and long-range properties, e.g., local bonding environment, electronic screening, built-in field, etc. Result shows that Pt/BTO interfaces have strong coupling with ferroelectric distortion and thus play more dominant roles than the SRO/BTO interfaces in affecting the ferroelectric stability of the tunnel junctions. Particularly, it is found that Pt2/TiO2 interface can induce collective ferroelectric distortion in the initially non-distorted barrier. With a full-relaxation of the strains, an abnormal enhancement of ferroelectricity by Pt2/BaO interface due to Pt-O bonding effect is demonstrated, where a strong interfacial-bonding-related polarizing field is verified. Also importantly, polarization stability of asymmetric tunnel junctions is found dependent on direction, manifested with the appearing of a new critical thickness, below which the tunnel junction loses polarization bistability. Furthermore, it shows that the local features of a specific electrode/ferroelectric interface (e.g., the interfacial atomic structure, local polarization, charge transfer, and potential step) are well kept in different types of tunnel junctions. By analyzing and summarizing the results, our results suggest that traditional phenomenological models need several modifications in order to quantitatively reproduce the size effect of ferroelectric tunnel junctions. Our study provides a comprehensive picture of the ferroelectric size effect in BTO tunnel junctions as a function of electrode/ferroelectric interfaces and should have valuable implications for future studies and applications. [ABSTRACT FROM AUTHOR]

Research describing the fabrication of a tunable photonic band gap crystal is presented. Synthetic opal composed of silica spheres is infiltrated with nematic liquid crystal to produce the photonic band structures.

The study of band-gap energy of InAs(sub 1-x)Sb(sub x) digital superlattices and band alignment of InAs(sub 1-x)Sb(sub x)/AlSb quantum wells at 5 K is examined by using infrared photoluminescence. Results show that InAs(sub 1-x)Sb(sub x) digital alloys have a smaller effective band gap than the InAs(sub 1-x)Sb(sub x) random alloys.

For the initial growth of Si on Ge, three-dimensional Si quantum dots grown on the Ge surface were observed. With increasing Si thickness, the Si growth changes from three-dimensional to two-dimensional growth mode and the dots disappear gradually. Finally, the surface is smooth with the roughness of 0.26 nm, similar to the original Ge substrate, when 15 nm Si is deposited. More Ge segregation on the wetting layer leads to more open sites to increase the subsequent Si growth rate on the wetting layer than on the Si dots. The in-plane x-ray diffraction by synchrotron radiation is used to observe the evolution of tensile strain in the Si layer grown on Ge (100) substrate. [ABSTRACT FROM AUTHOR]

A large crack-free size of the GaN/AlN multilayers is expitaxially grown on the Si(111) substrate patterned with the Si(sub x)N(sub y) mesh. The stress relaxation is mainly attributed to the existence of the free surfaces (1011), (1122) and (1101) and the thermal-expansion coefficient difference among Si(sub x)N(sub y), GaN/AlN, and Si.

Metastable filamentary superconductivity with Tc = 10.2 K was observed in SrPt2Ge2. This is the highest Tc reported outside the iron-based 122-layer compounds. The stable phase for this compound is a non-superconducting monoclinic LaPt2Ge2-type structure with lattice parameters a = 0.4401(4) nm, b = 0.4435(4) nm, c = 0.9764(10) nm, β = 90.5°-90°. Weak diamagnetic shielding signal indicates that superconductivity is not from the major monoclinic phase, but from the minor BaFe2As2-type body-center-tetragonal (122-bct) phase with a=0.44 nm, c=0.98 nm,β=90°. Investigation on the pseudoternary system Sr(Pd1-xPtx)2Ge2 suggests that the stable bct to monoclinic structure phase transition occurs near x = 0.15. For x<0.15 with bct phase, bulk Tc increases from 3.2 K for SrPd2Ge2 to 3.6 K for SrPd1.8Pt0.2Ge2. For x>0.15 with metastable filamentary bct phase, Tc increases from 7.5 K for x = 0.5 to 9.2 K for x = 0.7 and reaches a Tc maximum of 10.2 K for SrPt2Ge2. High Tc is due to a strong quasi-2D Pt-Ge-Pt 5dxz,yz-4p-5dxz,yz hybridization in the Pt-Ge layer with squeezed-along-c-axis PtGe4 tetrahedral crystal field and Pt-5d8 spin-orbital interaction in the metastable filamentary bct phase and is another example of multi-band (dxz/dyz/dxy) non-conventional s-wave superconductor. [ABSTRACT FROM AUTHOR]

In this work, we attempt to show the differences between traditional qubit-based spintronic methodology for quantum computation and the possible ballistic quantum network implementations. Flux qubits can be considered topologically similar to the persistent currents possessed as the angular momentum in Aharonov-Bohm loops, which can be coupled and thus entangled together. Since entanglement is guaranteed for coupled quantum networks, starting from a point-contacted situation, we first investigate how varying the degree of entanglement strength can affect the superposition of the four possible states for two isolated flux qubits being brought together. In general, the superposition is destroyed once the degree of entanglement is altered from the point-contact situation. However, we show that for a specific network with maximum entanglement, a Bell state situation can be produced. We then examine the effects of varying the external perturbation strength on the readout capability in quantum networks by changing the coupling strength through the cross-sectional area ratio. From the analysis of our results, we are persuaded to believe that two universally accepted components for quantum computing are not valid in the quantum network approach: the need of a weak perturbation for measurement of computational results and the requirement of fixed entanglement among qubits. We show there is an interplay between the strength of the entanglement and that of the external perturbation for high-fidelity classical readouts. [ABSTRACT FROM AUTHOR]

We investigate the maximum available free electron carrier density in Al-doped n-type ZnO, based on density-functional theory calculations. The Coulomb interactions between the Al dopants and the Zn-vacancy native acceptors are found to limit the carrier density. In typical growth conditions, the n-type doping limit is found to be in the range of 1019 ∼ 1021 cm-3. [ABSTRACT FROM AUTHOR]

When biased in the negative differential resistance regime, electroluminescence (EL) is emitted from planar GaAs heterostructure Gunn diodes. This EL is due to the recombination of electrons in the device channel with holes that are generated by impact ionisation when the Gunn domains reach the anode edge. The EL forms non-uniform patterns whose intensity shows short-range intensity variations in the direction parallel to the contacts and decreases along the device channel towards the cathode. This paper employs Monte Carlo models, in conjunction with the experimental data, to analyse these non-uniform EL patterns and to study the carrier dynamics responsible for them. It is found that the short-range lateral (i.e., parallel to the device contacts) EL patterns are probably due to non-uniformities in the doping of the anode contact, illustrating the usefulness of EL analysis on the detection of such inhomogeneities. The overall decreasing EL intensity towards the anode is also discussed in terms of the interaction of holes with the time-dependent electric field due to the transit of the Gunn domains. Due to their lower relative mobility and the low electric field outside of the Gunn domain, freshly generated holes remain close to the anode until the arrival of a new domain accelerates them towards the cathode. When the average over the transit of several Gunn domains is considered, this results in a higher hole density, and hence a higher EL intensity, next to the anode. [ABSTRACT FROM AUTHOR]

Retardation effects in the valence electron energy-loss spectrum (EELS) of a Si slab are analyzed by angular-resolved EELS. The dispersion curves of the valence spectra excited in a slab are directly observed from a specimen area with several different thicknesses and are interpreted by performing a calculation of the dispersion relation using Kröger's formula. The dispersion curves observed below about 3 eV are attributed to guided modes coupled with Cˇerenkov radiation (CˇR). The coupling between guided modes and CˇR is found to be dependent on the sample thickness (t). For the sample with t > 150 nm, the intensity of the guided modes increased linearly with thickness, revealing the coupling with CˇR. For t < 150 nm, however, the intensity of the guided modes rapidly decreased due to a diminished coupling with CˇR, resulting from the thickness-dependent dispersion curves of the guided modes. [ABSTRACT FROM AUTHOR]

Based on the phase field simulations, effects of the surface charge screening and temperature on the vortex domain structure of the ferroelectric nanodot have been investigated. Our calculations show that the ferroelectric nanodot adopts a rhombohedral vortex domain pattern under an ideal open-circuit boundary condition. With the increase of the surface charge screening, the dipole vortex gradually rotates and appears rhombohedral-orthorhombic-tetragonal transformation. By adjusting the surface charge screening, the polar single domain and multi-vortices domain patterns with zero toroidal moment have been obtained near the phase transition temperature. More importantly, temperature and charge screening 'T-C' phase diagram has been summarized, which indicates an effective method to control the vortex domain structure in the low-dimensional ferroelectric nanostructures. [ABSTRACT FROM AUTHOR]

The properties of intersubband transition in AlGaN/GaN multi-quantum wells (MQWs) grown on different AlGaN templates by metalorganic chemical vapor deposition are investigated. The strain states of GaN wells are studied by Raman spectra and reciprocal space mappings, which shows that the GaN wells are compressively strained and the compressive strain is increased when the Al mole composition is varied from 0 to 0.3. The Fourier transform infrared spectrometer results show that the intersubband transition wavelength in the AlGaN/GaN MQWs can be tuned from 5.14 μm to 4.65 μm when the Al mole composition of the AlGaN template is increased. The results can be attributed to the quantum confined Stark effect. [ABSTRACT FROM AUTHOR]

We have performed the x-ray photoemission experiments in the colossal magnetoresistive manganites Re0.7Ca0.3MnO3 with Re=La, Pr, and Nd in order to study the Re dependence of electronic structures in this system. The samples are epitaxial films grown on LaAlO3 substrates with pulsed laser deposition system. It is found that the binding energies of Mn 2p3/2 are 641.7 and 643.1 eV for La0.7Ca0.3MnO3 and Nd0.7Ca0.3MnO3, respectively. The shift of this energy level is related to the change in bond angle and/or bond length between Mn and oxygen. Moreover, two lines of O 1s core level are assigned as Mn–O (530 eV) and Re–O (533 eV). The intensity ratio of these two lines in Nd0.7Ca0.3MnO3 is different from those in La0.7Ca0.3MnO3 and Pr0.7Ca0.3MnO3, suggesting that the ion redistribution between Re–O and Mn–O sites occurs with the Re substitution in these films. [ABSTRACT FROM AUTHOR]

Two Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers with different thickness ratios are fabricated and the spin-injection effects are investigated. The NCMO/YBCO samples have thicknesses of 100 nm/200 nm and 200 nm/200 nm, which are denoted as N/Y(1) and N/Y(2), respectively. It is shown that the current-induced suppression rate of superconducting transition temperature (dTc/dI) in YBCO is enhanced by four to six times of magnitude in N/Y(1) and N/Y(2) compared with that in pure YBCO. Furthermore, dTc/dI in N/Y(2) is larger than that in N/Y(1), which suggests that the thickness of NCMO has influence on the pair breaking in YBCO. [ABSTRACT FROM AUTHOR]

Magnetic properties, microstructure, and phase evolution of (Ce1-xPrx)9.5Febal.CoyTi2B10 (x=0–1 and y=0, 2.5) nanocomposites have been investigated. A progressive substitution of Pr for Ce enhances the remanence (Br), intrinsic coercivity (iHc), and maximum energy product [(BH)max] of the ribbons effectively. In addition, the Curie temperature of 2:14:1 phase also increases with increasing Pr concentration. For Co-free (Ce1-xPrx)9.5Febal.Ti2B10 ribbons, magnetically hard 2:14:1 phase and two soft phases, α-Fe and Fe3B, are found in the ribbons with x=0, 0.3, 0.4, and 0.7, while Fe3B phase disappears in the ribbons with x=1. On the other hand, the value of Br, (BH)max, temperature coefficient α, and Curie temperature of 2:14:1 and α-Fe are improved with a slight substitution of 2.5 at. % Co for Fe. The magnetic properties of Br=8.5 kG, iHc=7.5 kOe, (BH)max=13.5 MGOe, α=-0.185%/°C, and β=-0.54%/°C can be achieved in (Ce0.5Pr0.5)9.5Febal.Co2.5Ti2B10 nanocomposites. [ABSTRACT FROM AUTHOR]

Images of the steady-state luminescence of passivated GaAs self-standing films under excitation by a tightly focussed laser are analyzed as a function of light excitation power. While unipolar diffusion of photoelectrons is dominant at very low light excitation power, an increased power results in a decrease of the diffusion constant near the center of the image due to the onset of ambipolar diffusion. The results are in agreement with a numerical solution of the diffusion equations and with a physical analysis of the luminescence intensity at the centre of the image, which permits the determination of the ambipolar diffusion constant as a function of electron concentration. [ABSTRACT FROM AUTHOR]

The comprehensive investigation on the effect of dislocation edge stress for Si N-type metal-oxide-semiconductor field-effect transistors is presented in this work by the experimental measurement and proposed simulation model. The accurate stress measurement in Si OD region with and without dislocation edge stress treatment is extracted by atomic force microscope-Raman technique with the nanometer level space resolution. Less compressive stress in Si OD region on the real transistor with dislocation edge stress treatment is observed successfully and has its corresponding higher electron carrier mobility, agreed with the strained Si theory. Main reasons for the less compressive stress in the device with dislocation edge stress treatment are the more stress relaxation of the STI intrinsic compressive stress in modern CMOS process and one layer Si atom missing near the source and drain region along the dislocation line. The measured stress from AFM-Raman spectra experimentally, the simulated stress from proposed finite element method, and its corresponding electrical characteristics agrees well with each other in this work. After the comprehensive understanding and calibrated model for the dislocation edge stress, the relationship between channel stress and dislocation edge shapes, including the angle and length of dislocation lines is simulated and investigated clearly. It can be found that longer dislocation line and smaller dislocation angle can relax the intrinsic STI compressive stress more and should have the better electron carrier mobility and device performance for N-MOSFETs. [ABSTRACT FROM AUTHOR]

High efficient surface textured SiGe-based solar cell is proposed by the designed top nano-level surface trench structure and the optimized SiGe/Si type-II substrate hetero-junction design. The surface reflectance rate of solar cell can be successfully reduced about 3 times (totally from 32% to ∼10%) by the nano-surface textured structure with obvious photonic crystal effect, simulated by finite differential time domain simulation. With different top surface trench spacing (d) structure design on the nanometer level, broadband antireflection and total absorption rate can be realized and enhanced greatly, respectively. Moreover, SiGe/Si hetero-structure substrate is also implemented to enhance an additional solar cell efficiency about 3% in this work, not only due to the originally higher absorption rate in SiGe-based material but also due to optimized SiGe/Si type-II hetero-structure substrate design. The offset and discontinuousness of the energy band between n+-Si and grown fully strained Si0.9Ge0.1 type-II hetero-junction structure can prevent hole diffusion into the n+-Si layer and have the larger Voc. With the integration of these two key technologies including nano-level surface trench structure design and SiGe/Si type-II hetero-structure optimization, the high efficient (∼18% for the stable production and 21% for the peak record) nano-surface textured SiGe-based solar cell can be achieved and demonstrated in this work. [ABSTRACT FROM AUTHOR]

Here we show that the configuration of an inhabited area controls the time required by all the pedestrians to vacate the space. From the minimization of the global evacuation time emerges the optimal configuration of the area. This is a fundamental principle for designing living spaces with efficient evacuation quality, and it is demonstrated here with several simple building blocks that can be used as components of more complex living structures: single walkway, corner, and T-shaped walkway. We show analytically and numerically that the ratio of the widths of the stem and branches of the T-shaped walkway has an optimal value that facilitates the evacuation of all the inhabitants. This result is fundamental, and is the crowd-dynamics equivalent of the Hess-Murray rule for the ratio of diameters in bifurcated ducts with fluid flow. [ABSTRACT FROM AUTHOR]

Intraband absorption in quantum-dot-in-a-well (DWELL) mid-infrared photodetectors is investigated using photocurrent spectroscopy and computationally cost-effective modeling linked to experimental data. The DWELL systems are challenging for modeling the electronic structure, which involves both discrete levels and the continuum energy spectrum. We show that the latter can be successfully approximated by a quasi-continuum in a large three-dimensional (3D) 'quantum box' in which the electronic structure is calculated in the effective mass approximation using the finite element method. Experimental and simulated spectra show good agreement with each other, which justifies using the modeling for analysis of the experimental data. In particular, the origin of the peaks and the dot parameters, such as composition are deduced. Effects of dot composition and shape on the intraband absorption spectra are also predicted. Our model proves to be a useful tool in designing and analyzing advanced DWELL structures for any realistic 3D quantum dot geometry. [ABSTRACT FROM AUTHOR]

The positions of the electronic levels of an intrinsic bistable defect have been measured using deep level transient spectroscopy (DLTS) in n- and p-type damaged silicon bipolar transistor diodes after minority carrier injection and thermal annealing. The kinetic rates observed during conversion of this defect have been determined using both DLTS and transistor gain measurements on devices irradiated with electrons and neutrons. First order conversion kinetics are observed during both injection and thermal annealing of this defect in electron damaged transistors, but more complicated, stretched-out kinetics are seen in neutron irradiated devices. The latter behavior can be successfully modeled as a small spread in the energy barriers for atomic displacements of this defect probably due to strain or electrostatic variations expected in damage clusters. The measured injection bias dependence of the recombination-driven transition to the bistable state of this defect is unlike that seen for generation-recombination currents at deep trap levels, but it is consistent with Shockley-Read-Hall predictions for recombination at shallow states. This latter behavior is expected from the lone shallow peak seen in DLTS measurements of the stable state of this center. Some comparisons of the present results with existing models of this defect are made. [ABSTRACT FROM AUTHOR]

A simple critical thickness for generating lattice misfits is insufficient to describe the onset strain relaxation in InAs quantum dots (QDs). A predominant dot family is shown to relieve its strain by In/Ga interdiffusion, rather than by lattice misfits, at the onset of strain relaxation. This argument is based on photoluminescence spectra, which show the emergence of a fine blueshifted transition at the onset of strain relaxation, along with a low-energy transition from a dot family degraded by lattice misfits. From the analysis of the temperature-dependent blueshift and energy separation between the ground and excited-state transitions, the blueshift is attributed to In/Ga interdiffusion. Transmission electron microscopy suggests a relaxation-induced indium migration from the interdiffused dot family to the dislocated dot family. Post-growth thermal annealing can further relieve strain by inducing more In/Ga interdiffusion in the interdiffused dot family and more dislocations in the dislocated dot family. This study explains the co-existence of strong carrier confinement in the QDs and enormous misfit-related traps in the capacitance-voltage spectra, and an elongated QD electron-emission time. [ABSTRACT FROM AUTHOR]

We have calculated magnetostatic fields from transverse and vortex magnetic domain walls in a planar Ni81Fe19 nanowire using micromagnetic simulations. Magnetic fields were calculated either side of the wire in the wire plane. Asymmetries in the stray field from the two types of domain walls can be understood in terms of monopole, dipole and quadrupole contributions. These calculations indicate the required sensitivity of a nearby sensor for domain wall detection or being able to distinguish domain wall character. We demonstrate this by modeling the electrical response of a magnetoresistive multilayer element to a domain wall in a nearby magnetic nanowire. [ABSTRACT FROM AUTHOR]

The characteristics and dispersion of the distinct surface acoustic waves (SAWs) propagating in ZnO/GaAs heterostructures have been studied experimentally and theoretically. Besides the Rayleigh mode, strong Sezawa modes, which propagate confined in the overlayer, arise due to the smaller sound velocity in ZnO than in the substrate. The design parameters of the structure providing the strongest piezoelectric field at a given depth within the layered system for the different modes have been determined. The piezoelectric field of the Rayleigh mode is shown to be more than 10 times stronger at the interface region of the tailored ZnO/GaAs structure than at the surface region of the bulk GaAs, whereas the same comparison for the first Sezawa mode yields a factor of 2. This enhancement, together with the capacity of selecting waves with different piezoelectric and strain field depth profiles, will facilitate the development of SAW-modulated optoelectronic applications in GaAs-based systems. [ABSTRACT FROM AUTHOR]

A series of Co/Pt multilayers with perpendicular magnetic anisotropy has been grown by magnetron sputtering and characterized using magneto-optical Kerr effect measurements with a view to optimizing samples for current-driven domain motion applications. The influence of the thickness of both Co and Pt layers on the coercivity and switching behavior has been systematically investigated. The coercivity was found to depend strongly on the thickness of the Co layer and clear perpendicular magnetic anisotropy was observed in multilayer stacks with Co thickness ranging from 3 to 7 Å. Upon increasing the Co thickness further the magnetization reverts to the in-plane direction and both the coercivity and the remanence drop rapidly, with the former becoming dominated by shape anisotropy. Increasing the thickness of the Pt buffer layer leads to improved perpendicular magnetic anisotropy with higher coercive fields. In contrast, the thickness of the Pt capping layers does not appear to have any systematic influence on the anisotropy in the range of 22-62 Å. The coercivity can be further affected by the number of repeat Co layers in the stack due to exchange and magnetic coupling between adjacent Co layers. Upon increasing the thickness of the intermediate Pt spacer layer beyond 27 Å, a transition from a coherent single-unit-like reversal to a sequential layer-by-layer reversal was observed. Structures with sharp switching fields and medium coercivity (50-150 Oe) have Co thickness fractions in the range 5 ∼ 7% of the total stack height and should be well optimized for studying current-driven domain motion at low current densities. [ABSTRACT FROM AUTHOR]

We show that it is possible to obtain large field transmission through a periodic structure at frequencies where the field is lossy in a finite temperature superconductor. The feat is accomplished by using thin superconducting layers. This makes the superconductor photonic crystal useful for transmitting signals over larger distances at higher temperature. Narrow transmission resonances due to surface plasmon effect are damped more quickly with increasing temperature than broader transmission bands. The temperature dependence is useful, particularly for developing optothermal sensors in terahertz and far infrared regimes. [ABSTRACT FROM AUTHOR]

We investigated several classes of two coupled Aharonov-Bohm rings that share a finite center common path, where the phase of the electron wave function can be modulated by two distinct magnetic fluxes. The coupling is similar to two coupled atoms. The behavior of charge accumulation along the center common path or, equivalently, the bonding and anti-bonding of the two rings can be achieved as the two applied fluxes are varied. Thus, when three external terminals are connected to such coupled rings, the behavior of the electron transport is divided into several classes, depending on the number of atoms in each ring and the locations of the terminals. The results are presented here. The applicable electron wave computing circuits are discussed. In particular, a half-adder construction is shown here by employing the symmetric and anti-symmetric properties of the transmission of a given terminal when the sign of the flux is changed. The analogy of two coupled rings with respect to two spins allows one to make a further connection with traditional spintronics-based schemes. [ABSTRACT FROM AUTHOR]