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The thermophysical properties of liquid Zr–V alloys covering a whole composition range were systematically measured by an electrostatic levitation technique. A series of maximum undercoolings from 150 to 386 K (0.2 TL) was achieved for 11 different liquid alloys under containerless state and radiative cooling conditions, where Zr83.5V16.5 and Zr20V80 alloys displayed the strongest undercooling ability. The densities of liquid Zr–V alloys were measured over a wide temperature range from overheated to undercooled states, and the results exhibited a linear dependence on temperature for all 11 compositions. Two typical solidification pathways were observed for hypoeutectic alloys. Except for a slowing down of decreasing tendency near a eutectic Zr57V43 alloy, the liquid densities of Zr–V alloys almost decrease linearly with increasing V content. Accordingly, the thermal expansion coefficients of Zr–V alloys were also derived from containerless measurements, and they showed an increasing tendency with V content. Since thermal radiative dominated the heat transfer process, the ratio of isobaric specific heat to hemispherical emissivity was directly deduced from the thermal balance equation, leading to a quadratic relationship with temperature. It was found that the increase of V content enhanced the ability of radiative heat dissipation below 16.5 at. % V content. [ABSTRACT FROM AUTHOR]

The transmission properties for square potential barriers have been investigated and compared from graphene to a dice lattice via a variable coupling parameter. There are two limiting cases of pseudospin 1/2 and 1, respectively. The perfect Klein tunneling has been obtained for all parameter conditions. With the increase of the coupling parameter, the tunneling probability increases at oblique incidence. The tunneling shows little dependence on the number of barriers for the dice model. However, the barrier number is an effective factor to tune the transmission feature in graphene. The tunneling peaks can be analyzed from the energy band structure in the expanded periodic potential system and the wave function distribution in the well/barrier regions. The present findings are useful in the development of electronic devices based on quantum transport property with massless pseudospin particles. [ABSTRACT FROM AUTHOR]

Resistive random access memories with self-rectifying behaviors, in which the sneak-path issue in passive crossbar arrays can be alleviated without additional access devices, have been investigated recently. The applications of p-type transparent oxide semiconductors as a memory medium will pave the way for realizing all-transparent memories and integrating on the complementary metal-oxide-semiconductor devices. Here, Ag-based p-type delafossite AgCr 1 − x Mg x O 2 thin films were prepared onto n-Si wafers to investigate the resistive switching (RS) performance. Bipolar RS with self-rectifying behaviors were observed in the Au / AgCr 0.92 Mg 0.08 O 2 / n − Si sandwich structure, showing improved rectification ratio, On/Off ratio, and switching durability. The change of the oxygen vacancy concentration resulting from Mg doping plays a key role in determination of the RS. The intrinsic rectifying behavior in the low resistance state is attributed to the existence of a Schottky-like barrier in the AgCr 1 − x Mg x O 2 / n − Si p-n heterojunction. The RS behavior originates from the modification of the barrier, which is induced by the trapping/detrapping of charge carriers in oxygen vacancies at the interface. The results will provide novel RS devices based on p-type transparent delafossite thin films with a self-rectifying feature. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) titanium disulfide (TiS 2) is the lightest transition-metal dichalcogenide (TMD). It exhibits relatively better adsorption and diffusion of sodium (Na) and potassium (K) ions than other TMDs, such as MoS 2 (molybdenum disulfide) and ReS 2 (rhenium disulfide), making it a promising anode material for alkali-ion batteries. Previous studies have found that doping significantly enhances the adsorption and diffusion capabilities of 2D TMDs. For the first time, this work reports the adsorption of Na and K ions on doped TiS 2 monolayers using first-principles calculations, where the Ti atom is substituted by 3d-transition metals, including iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). Metal-atom doping induces remarkably stronger binding of alkali ions on the surface of TiS 2 , with adsorption energies ranging from − 2.07 to − 2.48 eV for Na and − 2.59 to − 3.00 eV for K. The diffusion barrier energies for alkali ions decrease in the proximity of the doping site and increase as the ions travel away from the doping site for Fe-, Co-, and Ni-doped TiS 2. The average open circuit voltage increases dramatically when Na ions are adsorbed on Fe-doped TiS 2 (by 62%) and Co-doped TiS 2 (by 61%), while K ions result in a moderate improvement of 9% and 8%, respectively. These findings suggest that metal-atom doping considerably improves the electrochemical properties of 2D TiS 2 , potentially enabling its use as anode materials in Na- and K-ion batteries. [ABSTRACT FROM AUTHOR]

The InAlN alloy system has bandgap energies that span the entire visible range and is a promising candidate for bandgap engineering. To facilitate bandgap engineering, the bandgap bowing for the entire composition range must be well characterized. In rich InxAl1−xN (x > 0.60), films were grown via plasma assisted molecular beam epitaxy on freestanding GaN substrates. The InxAl1−xN film compositions were determined using high resolution X-ray diffraction. On-axis 0002 ω-2θ scans were used to determine the c spacing of the films, reciprocal space maps of the 1 ¯ 015 peaks were used to determine that the films were completely relaxed, and the film compositions were calculated from that information assuming Vegard's law. The bandgaps were independently measured using absorbance spectroscopy and fitting to the linear region of a Tauc plot (dependence of α2 hν on hν) as determined by interpolating the second derivative of the data and selecting a region of low curvature. Compared with the literature, the data were fit to a composition-independent bandgap bowing model, and a bowing parameter of b = 4.0 ± 0.2 eV was calculated, which is consistent with previous results. [ABSTRACT FROM AUTHOR]

A calculation is presented for the direct conversion of a measured luminescence signal to the implied open circuit voltage. The effects of re-absorption, spectral dependence, and interference with front and back interfaces are all included, so long as the optical properties of the structure are known. The method is validated through a comparison of the terminal open-circuit voltage with the photoluminescence intensity of Cu(In,Ga)Se2 solar cells, each as a function of illumination intensity. [ABSTRACT FROM AUTHOR]

Room-temperature non-radiative recombination is studied at single dislocations in Ga0.5In0.5P quantum wells grown on metamorphic templates using cathodoluminescence and electron channeling contrast imaging. An analysis of the light emission intensity profiles around single dislocations reveals that the average recombination strength of a dislocation decreases by a factor of four and seven as a result of decreasing growth temperature of the GaInP quantum well from 725 to 675 and 625 °C, respectively. This reduction occurs despite little change in the diffusion length, precluding the prospect of inducing carrier localization by ordering and phase separation in GaInP at lower growth temperatures. These observations are rationalized by the premise that point defects or impurities are largely responsible for the recombination activity of dislocations, and the extent of decoration of the dislocation core decreases with temperature. Preliminary evidence for the impact of the Burgers vector is also presented. The lowest growth temperature, however, negatively impacts light emission away from dislocations. Carrier recombination in the bulk and at dislocations needs to be considered together for metamorphic devices, and this work can lead to new techniques to limit non-radiative recombination. [ABSTRACT FROM AUTHOR]

The refractive index of LiNiO2 thin films is complex and exhibits both dielectric and metallic properties. With LiNiO2 thin films coated on or inserted in photonic crystals (PCs), it is possible to enhance the absorptance in the designed (AB)nLiNiO2(BA)m PC structures. One-way absorption in the photonic bandgap of (AB) PCs has been observed via changing the optical transmitting direction. The positions, width, and strength of the absorption peaks depend on the thickness of the LiNiO2 films, the incident angles, and the transverse electric/transverse magnetic modes. The photonic band structure can be employed to determine the allowed and forbidden photonic modes and the related optical properties for (AB) PC and (AB)nLiNiO2 PCs. These novel absorption characteristics can enrich the optoelectric properties of LiNiO2 thin films. [ABSTRACT FROM AUTHOR]

The magneto-Seebeck (MS) effect, which is also called magneto-thermo-power, was observed in Co/Cu/Co and NiFe/Cu/Co spin valves. Their Seebeck coefficients in the parallel state were larger than those in the antiparallel state, and the MS ratio defined as (SAP -SP)/SP could reach –9% in our case. The MS effect originated not only from trivial giant magnetoresistance but also from spin current generated due to spin-polarized thermoelectric conductivity of ferromagnetic materials and subsequent modulation of the spin current by different spin configurations in spin valves. A simple Mott two-channel model reproduced a –11% MS effect for the Co/Cu/Co spin valves, qualitatively consistent with our observations. The MS effect could be applied for simultaneously sensing the temperature gradient and the magnetic field and also be possibly applied to determine spin polarization of thermoelectric conductivity and the Seebeck coefficient of ferromagnetic thin films. [ABSTRACT FROM AUTHOR]

In this work, using the transfer-matrix method, the optical transport process is investigated, with graphene inserted into multilayer dielectric structures, theoretically and numerically in the THz regime. When the incident frequency is lower than the graphene Fermi energy, the optical intra-band transitions provide the main contribution to the graphene surface current. The absorptance can be enhanced to about 50% with only one graphene/dielectric layer in air. When increasing the number of dielectric layers coated with graphene, the absorption increases. Periodic absorption peaks are observed in multilayer structures. The positions of the absorption peaks as a function of the frequency and the incident angle are in accordance with the positions of the abrupt change in the reflection coefficient phase and of the imaginary solution of the Bloch wavevector in expanding periodic structures using Bloch theorem. [ABSTRACT FROM AUTHOR]

CdSeTe/CdMgTe double heterostructures were produced with both n-type and unintentionally doped absorber layers. Measurements of the dependence of photoluminescence intensity on excitation intensity were carried out, as well as measurements of time-resolved photoluminescence decay after an excitation pulse. It was found that decay times under very low photon injection conditions are dominated by a non-radiative Shockley-Read-Hall process described using a recombination center with an asymmetric capture cross section, where the cross section for holes is larger than that for electrons. As a result of the asymmetry, the center effectively extends photoluminescence decay by a hole trapping phenomenon. A reduction in electron capture cross section appeared at doping densities over 1016cm-3. An analysis of the excitation intensity dependence of room temperature photoluminescence revealed a strong relationship with doping concentration. This allows estimates of the carrier concentration to be made through a non-destructive optical method. Iodine was found to be an effective n-type dopant for CdTe, allowing controllable carrier concentrations without an increased rate of non-radiative recombination. [ABSTRACT FROM AUTHOR]

Pointed magnetic elements are introduced as an improvement upon rectangular strips currently employed in composite element magnetic barcodes. The coercivity of these elements, as measured using the magneto-optic Kerr effect, is found to strictly adhere to a single power law relationship with the element width, where the power law exponent is dependent on the length of the pointed region and takes values between − 0.98 and − 0.91. The steeper gradients here, along with the absence of the crossover region seen in rectangular devices, present these structures as a strict improvement in terms of potential device applications. These improvements are found to be present for all structures where the pointed region is as long as, or longer than, the magnetic element is wide. The remanent magnetization configuration, imaged using photo-emission microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM), is compared to the results of micromagnetic simulations. It is found to cant inward in the pointed section of the strip, aligning with the edges of the point, pinning the magnetization and giving a consistent magnetization reversal behavior for all element widths investigated. [ABSTRACT FROM AUTHOR]

The electronic and magnetic properties of tetravalent-ion-doped La0.85Zr0.15MnO3 (LZMO) thin films that were epitaxially grown on SrTiO3 (STO) and MgO substrates were studied using temperature-dependent x-ray diffraction (XRD), x-ray absorption near-edge structure, x-ray linear dichroism, and x-ray magnetic circular dichroism at the Mn L3,2- and K-edge. XRD studies reveal that the LZMO thin films have compressive and tensile strains (along the c-axis) on the STO and MgO substrates, respectively. As the temperature is reduced from room temperature to below magnetic transition temperature, the preferentially occupied Mn majority-spin eg orbital changes from the in-plane dx2-y2 to the out-of-plane d3z2-r2 orbital for LZMO/STO, and vice versa for LZMO/ MgO. Experimental results suggest that the new hopping path that is mediated by the Mn2+ ions triggers a stronger d3z2-r2 orbital ordering of Mn3+ ions and enhances the ferromagnetic coupling between the Mn spin moments of t2g electrons in LZMO/STO, whereas the strong tensile strain stabilizes the dx2-y2 orbital by inducing lattice distortions of the MnO6 octahedra in LZMO/MgO. [ABSTRACT FROM AUTHOR]

The efficiency of organic light-emitting diodes that utilize the principle of thermally activated delayed fluorescence (TADF) depends sensitively on the host material in which the TADF emitter molecules (guests) are embedded. Potential loss processes are "deconfinement," the transfer of excitons from the guest to the host, and "dissociation," the formation of intermolecular charge-transfer states. We investigate how both processes can be suppressed by studying the photoluminescence efficiency, emission spectrum, and time-resolved emission intensity of eight thin-film systems in which 5 mol. % of the sky-blue TADF emitter 4-carbazolyl-methylphthalimide (abbreviated here as CzPIMe) is embedded in various host materials. Deconfinement is found to be entirely suppressed if the triplet energy of the host is 0.25 eV or more above that of the guest. For systems allowing for deconfinement, the dependence on the energy difference is consistent with a recent theoretical analysis [C. Hauenstein et al., J. Appl. Phys. 128, 075501 (2020)]. Dissociation, due to hole transfer to a host molecule, is found to be suppressed if the host's highest occupied molecular orbital energy is not more than about 0.2 eV higher than that of the guest. Otherwise, we observe an efficiency loss, a spectral redshift, and the disappearance of distinct prompt and delayed emission regimes. A comprehensive rate-equation model is developed from which we study the sensitivity of these observations to the energy level structure, the intermolecular interaction rates, and the photophysical rates that follow from a fit to the experimental data for the CzPIMe:TCTA[ tris (4 - carbazoyl - 9 - ylphenyl) amine ] system. [ABSTRACT FROM AUTHOR]

In this study, a 300 °C-annealed 3 × 4 V/ZnO multilayer structure demonstrates the lowest resistivity (3.82 × 10−3 Ω cm) and the highest mobility (18 cm2/V s) among the studied V/ZnO multilayer structures. By measuring the energy bandgap (Eg), work function (Φ), and electron affinity (χ) by ultraviolet photoelectron spectroscopy and photoluminescence analysis, the corresponding energy band diagram at the ZnVxOy/ZnO interface can be constructed. A potential is observed at the ZnVxOy/ZnO interface, which induces the two-dimensional electron gas (2DEG) effect, and this is attributed to the high-mobility conduction path. The potential well directly relates to the Φ difference between the ZnO and ZnVxOy layers, which is determined to be 0.22, 0.46, and −0.1 eV for the as-deposited, 300 °C-annealed, and 500 °C-annealed V/ZnO multilayer structures, respectively. The 300 °C-annealed V/ZnO multilayer structure could possibly have the largest depth in the potential well. This supports the 2DEG mechanism for the high mobility of the 300 °C-annealed V/ZnO multilayer structure. [ABSTRACT FROM AUTHOR]

An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices. [ABSTRACT FROM AUTHOR]

Size-selected Mon-, Wn-, and Fen - cluster anions are deposited on a weakly interacting substrate (highly oriented pyrolytic graphite) and studied ex-situ using atomic force microscopy. Depending on size, three growth modes can be distinguished. Very small clusters consisting of less than 10-30 atoms behave similar to atoms and coalesce into 3-dimensional bulk-like islands. Medium sized clusters consisting of hundreds of atoms do not coalesce and follow a Stanski-Krastanov growth pattern. At low coverage, an almost perfect monolayer is formed. This is a new finding different from all previous studies on deposited metal clusters. For clusters with several thousands of atoms, the growth pattern again changes. At low coverage, the substrate is dotted with individual clusters, while at high coverage, the surface becomes extremely rough. [ABSTRACT FROM AUTHOR]

Significant efforts towards understanding bi-magnetic core-shell nanoparticles are underway currently as they provide a pathway towards properties unavailable with single-phased systems. Recently, we have demonstrated that the magnetism of c-Fe2O3/CoO core-shell nanoparticles, in particular, at high temperatures, originates essentially from an interfacial doped iron-oxide layer that is formed by the migration of Co2+ from the CoO shell into the surface layers of the γ-Fe2O3 core [Skoropata et al., Phys. Rev. B 89, 024410 (2014)]. To examine directly the nature of the intermixed layer, we have used high-resolution transmission electron microscopy (HRTEM) and first-principles calculations to examine the impact of the core-shell intermixing at the atomic level. By analyzing the HRTEM images and energy dispersive spectra, the level and nature of intermixing was confirmed, mainly as doping of Co into the octahedral site vacancies of γ-Fe2O3. The average Co doping depths for different processing temperatures (150 °C and 235 °C) were 0.56 nm and 0.78 nm (determined to within 5% through simulation), respectively, establishing that the amount of core-shell intermixing can be altered purposefully with an appropriate change in synthesis conditions. Through first-principles calculations, we find that the intermixing phase of γ-Fe2O3 with Co doping is ferromagnetic, with even higher magnetization as compared to that of pure γ-Fe2O3. In addition, we show that Co doping into different octahedral sites can cause different magnetizations. This was reflected in a change in overall nanoparticle magnetization, where we observed a 25% reduction in magnetization for the 235 °C versus the 150 °C sample, despite a thicker intermixed layer. [ABSTRACT FROM AUTHOR]

This paper develops a discrete optimal control based on the multi-rate observer method for electromagnetic suspension systems in order to levitate the vehicle, maintaining the desired gap. The proposed multi-rate compensator consists of two parts which are the discrete Kalman filter and the optimal control law. The Kalman filter estimates all states with fast sampling rate time, using a slowly measured output from the gap sensor. The optimal control law is determined by linear matrix inequality optimization for the discrete time multiple input system obtained by the lifting operator. The proposed multi-rate controller has the advantages to guarantee the stability of the slow-rate optimal control and maintain the performance of fast-rate control. The simulation and experiment show the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Robustness of the geometric phase (GP) with respect to different noise effects is a basic condition for an effective quantum computation. Here, we propose a useful quantum system with real physical parameters by studying the GP of a pair of Stokes and anti-Stokes photons, involving Raman emission processes with and without photonic band gap (PBG) effect. We show that the properties of GP are very sensitive to the change of the Rabi frequency and time, exhibiting collapse phenomenon as the time becomes significantly large. The system allows us to obtain a state which remains with zero GP for longer times. This result plays a significant role to enhance the stabilization and control of the system dynamics. Finally, we investigate the nonlocal correlation (entanglement) between the pair photons by taking into account the effect of different parameters. An interesting correlation between the GP and entanglement is observed showing that the PBG stabilizes the fluctuations in the system and makes the entanglement more robust against the change of time and frequency. [ABSTRACT FROM AUTHOR]

We outline the procedure of extending the Thévenin equivalence principle for classical electric circuits to reducing Aharonov-Bohm-based quantum networks into equivalent models. With examples, we show from first principles how the requirements are related to the electron band structure's Fermi level and the lattice spacing of the network. Quantum networks of varying degrees of coupling strength from four basic classifications of single and double entangled loops sharing symmetry and highly correlated band structures are used to demonstrate the concept. We show the limitations of how the principle may be applied. Several classes of examples are given and their equivalent forms are shown. [ABSTRACT FROM AUTHOR]

The results of the growth of thin (~3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation. [ABSTRACT FROM AUTHOR]

Ni3Fe/(Ni, Fe)O thin films with bilayer and nanocrystallite dispersion morphologies are prepared with a dual ion beam deposition technique permitting precise control of nanocrystallite growth, composition, and admixtures. A bilayer morphology provides a Ni3Fe-to-NiO interface, while the dispersion films have different mixtures of Ni3Fe, NiO, and FeO nanocrystallites. Using detailed analyses of high resolution transmission electron microscopy images with Multislice simulations, the nanocrystallites' structures and phases are determined, and the intermixing between the Ni3Fe, NiO, and FeO interfaces is quantified. From field-cooled hysteresis loops, the exchange bias loop shift from spin interactions at the interfaces are determined. With similar interfacial molar ratios of FM-to-AF, we find the exchange bias field essentially unchanged. However, when the interfacial ratio of FM to AF was FM rich, the exchange bias field increases. Since the FM/AF interface 'contact' areas in the nanocrystallite dispersion films are larger than that of the bilayer film, and the nanocrystallite dispersions exhibit larger FM-to-AF interfacial contributions to the magnetism, we attribute the changes in the exchange bias to be from increases in the interfacial segments that suffer defects (such as vacancies and bond distortions), that also affects the coercive fields. [ABSTRACT FROM AUTHOR]

This paper reports the electronic transport measurements of the single crystal Pr1.2Sr1.8Mn2O7 and Pr1Sr2Mn2O7 under pressure. The measurements in the ab plane for Pr1.2Sr1.8Mn2O7 show that the pressure induces a phase transition from a semiconducting state to a metallic state at 0.5 GPa, and then the transition temperature decreases rapidly with increasing pressure, indicating the pressure favors the paramagnetic semiconducting state and suppresses the ferromagnetic metallic state after the occurring of the transition. Moreover, for Pr1Sr2Mn2O7, the semiconducting-metallic state transition occurs at ambient pressure and the pressure favors the paramagnetic semiconducting state and suppresses the antiferromagnetic metallic state. [ABSTRACT FROM AUTHOR]

The solar-energy absorption material β-In2S3 was characterized using temperature-dependent photoconductivity (PC) measurements in the temperature range between 30 and 340 K in this study, and thermoreflectance (TR) and photoluminescence (PL) measurements were carried out to identify near-band-edge transitions in the β-In2S3 tetragonal crystal. The experimental analyses of PL, PC, and TR confirmed that β-In2S3 is a direct semiconductor with a band gap of 2.073 eV at 30 K and 1.935 eV at 300 K. The PL and PC spectra manifest some defect-related features in the β-In2S3 single crystal. Two defect emissions and two band-edge luminescences were simultaneously detected in the PL spectrum at 30 K, and the temperature-dependent PC spectra of β-In2S3 from 160 to 300 K reveal an additional defectlike or band-to-band feature with an energy located above the conduction band edge (EC). The temperature dependences of the PC transition features in the β-In2S3 defect crystal were analyzed. The origin and mechanism of all defect states and band-edge transitions in the β-In2S3 single crystal are evaluated and discussed. [ABSTRACT FROM AUTHOR]

200-nm-thick La- and Sm-doped BaTiO3 thin films with A/B ratio of unity fabricated by magnetron sputtering on the Pt/Ti/SiO2/Si substrate have been characterized. The effects of post-annealing and the amount of dopant on structure and electrical properties were studied. X-ray diffraction studies reveal that the films annealed at 750 °C show tetragonal BaTiO3 crystal structure without any detectable second phase formation. X-ray photoelectron spectroscopy results confirm that La substitutes the A site and Sm is in the B site in lightly doped films. La2O3 or Sm2O3 is present in the BaTiO3 structure when the dopant content is more than 1.4 at. % La or 1.0% Sm. The permittivity increases with increasing annealing temperature up to 750 °C due to the coarse grains and better crystallinity. The leakage current property is found to vary with the type of dopant. [ABSTRACT FROM AUTHOR]

The vibrational, electronic, and crystalline properties of n-type chlorine-doped ZnSe (ZnSe:Cl) layers with a carrier concentration from 8.2×1015 to 1.8×1018 cm-3 are studied by Raman spectroscopy. The spectral line shapes of the longitudinal-optical-phonon and plasmon coupling mode are analyzed using the Raman scattering efficiency and the dielectric function to obtain the electron densities and mobility. The splitting of the transverse-optical (TO) phonon and the redshift of the chlorine-related impurity vibration mode are clearly observed when pressure is applied. The semiconductor-to-metal phase transition pressure of ZnSe:Cl layers declines as the carrier concentration increases, indicating that n-type doping reduces crystal stability. Additionally, the pressure-induced weakening of the longitudinal-optical-phonon-plasmon coupling efficiency suggests that pressure tends to degrade the n-type characteristic of ZnSe:Cl because of the emergence of the new deep donorlike state. [ABSTRACT FROM AUTHOR]

We have studied the effect of the thickness of catalytic Ni film for the growth of vertically aligned carbon nanofibers (VA-CNFs) on glass substrates coated with a conductive underlayer of Cr. Both the pretreatment process through which the catalytic Ni nanoparticles were formed and the growth of well-aligned CNFs were carried out in an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. The VA-CNFs were characterized by scanning electron microscopy, Raman spectroscopy, as well as field emission measurements. The results of VA-CNF growth shows that as the Ni film thicknesses decrease, not only the length but also the density of the CNFs drop, although the density of catalytic Ni nanoparticles increases. The variation of CNF density with Ni film thicknesses is believed to be a result of the detachment of the CNFs from the substrate, caused by the electrostatic force produced by the plasma sheath electric field, as well as an ion-enhanced chemical etching effect due to atomic/ionic hydrogen, during the ICP-CVD growth. A field emission measurement apparatus based on a metallic probe of spherical anode structure was also constructed in this study. An electrostatic image model was employed to determine the electric field distribution on the cathode surface. Along with the standard F-N field emission model, the dependence of field emission current density on the cathode surface electric field, as well as an effective field enhancement factor, were extracted from the current-voltage measurement results. The threshold electric field (Ethreshold, for a current density of 1 mA/cm2) increases from 9.2 V/μm to 13.1 V/μm, and then drops to 11.5 V/μm for the CNFs with Ni film thicknesses of 20 nm, 30 nm, and 40 nm, respectively. The electrostatic model results also indicate that the 20 nm case has the greatest space-charge effect on the emission current, consistent with the growth results that the 20 nm case has the lowest CNF density. On the other hand, the CNF length of the 40 nm case is longer than that of the 30 nm one, while the densities are nearly the same; as a result, Ethreshold for the 30 nm case is higher. [ABSTRACT FROM AUTHOR]

This work systematically investigates the influence of InAs growth conditions and superlattice parameters on the optical properties of InAs/GaAs quantum dot (QD) superlattice structures grown by molecular beam epitaxy. Using surface photovoltage spectroscopy, one directly obtains the absorption spectra up to the highest confined QD levels at room temperature. Based on photoluminescence measurements at different excitation wavelengths, a feature below the fundamental transition is attributed to the transition from uncoupled dots in the bottom layers. The QD transition energy shift was found to be correlated with material intermixing, driven by enhanced strain strength with the increase of layer number and the decrease of spacer thickness, and the growth rate of InAs. A blueshift observed in low growth rate samples is indicative of greatly enhanced intermixing. For QD superlattices grown at a relatively high deposition rate of InAs, the material intermixing effect is gradually enhanced with increasing layer numbers, which will compensate the electronically coupled effect and will prevent further energy shift toward the lower energy side. The absorption wavelengths in 10- and 30-period InAs/GaAs QD superlattices with higher growth rates are near 1.32 μm. The results suggest that these QD superlattice structures can be used as promising active media for long-wavelength QD lasers operating at room temperature. [ABSTRACT FROM AUTHOR]

300⊗300 μm2 crack-free GaN/AIN multilayers of 2 μm in thickness have been successfully grown on the Si(111) substrate patterned with the SixNy mesh by metal-organic chemical-vapor deposition. The in-plane stress exhibits a U-shape distribution across the ‘window’ region, supported by the Raman shift of the GaN E2(TO) mode. This indicates a stress relaxation abruptly occurring near the edge of the window region due to the freestanding surface (1101) or (1122). The in-plane stress is almost relaxed at the corner of the window region due to three freestanding surfaces (1101), (1122), and (1011). The maximum in-plane stress is located near the surface of the multilayers at the center of the window region, supported by the Raman measurements and the failure observations. The role of the SixNy mesh in the stress relaxation is discussed. [ABSTRACT FROM AUTHOR]

The objective of this work was to understand the effect of the movable electrode (the tip of an atomic force microscope) on a piezoelectric-induced (PEI) image. Local polarization is induced on a lead zirconate titanate (PZT) thin film using an atomic force microscope (AFM), by applying dc voltage between the movable electrode and the Pt bottom electrode. The polarized PZT film is then characterized by the AFM using a two-pass method, in which both the topography and PEI image are obtained. The surface morphology is recorded in the first pass under contact mode with a fixed setpoint. A PEI image is obtained in the second pass in piezo-response mode. In this mode, the sample surface is scanned by applying ac voltage between the AFM tip and the Pt bottom electrode at sample displacement. PEI images of various sample displacement, corresponding to different stress exerted by the tip on the sample surface, are obtained and analyzed using force–sample displacement curves. It is found that PEI images can be detected if the tip adheres to the sample. The asymmetry of the A cos θ signal is improved as the force changes from repulsive to attractive. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the origin of temperature-sensitive hole current at low voltage regime in ultrathin gate oxide. Correlation of the gate and source/drain currents at low gate voltage regime; Dependence of the currents on temperature above 250 Kelvin; Observation of the temperature dependence on both negative and positive polarities.

Presents a study which proposed a method to measure the lifetime of excess electron-hole pairs generated by laser beams. Importance of the lifetime of the excess carriers in a semiconductor; Measurement principles; Components of the noise measurement system.

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]

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]

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]

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]

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]

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]

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]

We found that the exciton-phonon coupling in the Zn1-xMgxO powders (0.01 <= x <= 0.07) is greatly influenced by the crystalline-size. Two well-resolved photoluminescence (PL) bands due to recombination of free exciton and its longitudinal optical (LO)-phonon replicas enable us to analyze the relative intensities among free excitons, one-LO-phonon replicas, and two-LO-phonon replicas. As crystalline size increases, a larger enhancement of the PL-intensity ratio of a free exciton to its LO-phonon replicas was found compared to that of two LO-phonon replica to one-LO-phonon replica. [ABSTRACT FROM AUTHOR]

Vertical microcavity surface-emitting lasers employing quantum wells and small aperture buried-oxide current and field confinement are demonstrated with wider mode spacing and faster spontaneous carrier recombination (enhanced Purcell factor), lower threshold current, larger side mode suppression ratio (SMSR), and higher photon density and temperature insensitivity. The result is a microcavity laser that achieves higher microwave modulation bandwidth (f-3dB = 15.8 GHz) at ultra-low power consumption (1.5 mW) with a slope for the modulation current efficiency factor (MCEF) = 17.47 GHz/mA-1/2, as well as a better quality eye diagram in high-speed data transmission. The microwave behavior model for the microcavity laser is used to estimate the enhanced recombination and reduced lifetime. [ABSTRACT FROM AUTHOR]

We have investigated the InGaAs/GaAsSb/InAlGaAs/InAlAs type-II 'W' quantum wells (QWs) grown on InP substrates by molecular beam epitaxy. The photoluminescence (PL) emission wavelength longer than 2.56 μm at room temperature (RT) is demonstrated for the first time in this material system. The PL emission peaks of our designed samples can cover a wide range from 2 to 2.5 μm at cryogenic temperature. The samples show good optical quality that the reduction in integrated PL intensity is only around one order of magnitude from 35 K to RT. We found that the integrated PL intensity decreased as the emission wavelength increased, which is due to the reduction in the electron-hole wave function overlap. This is consistent with the calculated result. In the power dependent PL measurements, the emission peak of 'W' type QWs show blue shifts with the excitation power (Pex) but does not follow the Pex1/3 rule as predicted by type-II band bending model. The localized states filling effect gives reasonable explanations for the observed phenomena. [ABSTRACT FROM AUTHOR]