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Different from the extensive experimental investigations into the thermoelectric (TE) properties of the bulk IV–VI compounds, less attention has been paid to the TE properties of the monolayer IV–VI compounds. Here, we consider the TE transport properties including the Seebeck coefficient, electronic conductance, thermal conductance, power factor, and figure of merit Z T of the undoped and Bi-doped GeS monolayers. Our results show that for both the undoped and Bi-doped monolayers the anisotropy is widely observed in all their TE properties, and the maximum Z T at a certain temperature along the armchair direction is much greater than that along the zigzag direction. Moreover, Bi doping can lead to an increase of the maximum Z T , and there are more Z T peaks appearing near the zero chemical potential. This indicates that the Bi-doped GeS monolayer can work as a TE material at a lower bias voltage, and especially along the armchair direction it can work at zero bias voltage, which obviously strengthens the reliability of the TE devices. As the temperature increases, the maximum Z T will be uniformally increased along the armchair and zigzag directions for both the undoped and Bi-doped GeS monolayers. In the temperature scope from 300 to 800 K, the maximum Z T along the armchair direction of the Bi-doped GeS monolayer will increase from 3.39 to 4.85, which indicates that this Bi-doped GeS monolayer is a promising TE material in a wide-temperature zone. As an application, we have designed the GeS-based TE couples and found that their efficiencies can be greater than 27 % at large temperature differences. This research should be an important guidance for designing a low-voltage, wide-temperature-scope, and high-stability TE device. [ABSTRACT FROM AUTHOR]

With the increasing demand for energy, it has become imperative to investigate the thermoelectric properties that can be beneficial to directly converting heat into electric energy. Here, we theoretically study the thermoelectric transport of the Mn-doped blue phosphorene (blue-P) along the zigzag direction. We show that the spin-polarized electronic transport in the blue-P can be produced by the Mn-doping induced half-metallic energy band structure, and the Seebeck coefficients can take positive and negative values, indicating that the main carriers may be holes and electrons. Thus, the spin-down, spin, and charge Seebeck coefficients show a high peak and a deep valley, while the spin and charge thermoelectric figures of merit show two wide peaks. Moreover, the spin and charge thermoelectric figures of merit are found to be so large that the Mn-doped blue-P along the zigzag direction can be used as good thermoelectric materials. In addition, we consider the effect of the doping concentration on the electronic structure and thermoelectric transport properties. This research should be an important reference for designing spin caloritronic and thermoelectric devices. [ABSTRACT FROM AUTHOR]

The terahertz (THz) quantum cascade laser (QCL) provides a versatile tool in a plethora of applications ranging from spectroscopy to astronomy and communications. In many of these fields, compactness, single mode frequency emission, and low threshold are highly desirable. The proposed approach, based on line defects in a photonic crystal (PhC) matrix, addresses all these features while offering unprecedented capabilities in terms of flexibility, light waveguiding, and emission directionality. Nine line-defect QCLs were realized in a triangular lattice of pillars fabricated in the laser active region (AR), centered around ∼2 THz by tuning the photonic design. A maximal 36% threshold reduction was recorded for these ultraflat dispersion line-defect QCLs in comparison to standard metal-metal QCL. The mode selectivity is an intrinsic property of the chosen fabrication design and has been achieved by lithographically scaling the dimension of the defect pillars and by acting on the PhC parameters in order to match the AR emission bandwidth. The measured line-defect QCLs emitted preferentially in the single frequency mode in the propagation direction throughout the entire dynamic range. An integrated active platform with multiple directional outputs was also fabricated as proof-of-principle to demonstrate the potential of this approach. The presented results pave the way for integrated circuitry operating in the THz regime and for fundamental studies on microcavity lasers. [ABSTRACT FROM AUTHOR]

We used Raman scattering and time-resolved photoluminescence spectroscopy to investigate the molecular-beam-epitaxy (MBE) growth parameters that optimize the structural defects and therefore the internal radiative quantum efficiency of MBE-grown GaAs/AlGaAs double heterostructures (DH). The DH structures were grown at two different temperatures and three different As/Ga flux ratios to determine the conditions for an optimized structure with the longest nonradiative minority carrier lifetime. Raman scattering measurements show an improvement in the lattice disorder in the AlGaAs and GaAs layers as the As/Ga flux ratio is reduced from 40 to 15 and as the growth temperature is increased from 550 to 595 °C. The optimized structure is obtained with the As/Ga flux ratio equal to 15 and the substrate temperature 595 °C. This is consistent with the fact that the optimized structure has the longest minority carrier lifetime. Moreover, our Raman studies reveal that incorporation of a distributed Bragg reflector layer between the substrate and DH structures significantly reduces the defect density in the subsequent epitaxial layers. [ABSTRACT FROM AUTHOR]

High-resolution X-ray power diffraction was used to study magnetic field (MF) dependence of the phase separation (PS) in the manganites [Sm.sub.0.5][Sr.sub.0.5]Mn[O.sub.3] with [super 16]O and [super 18]O. The two compounds, having an identical structure show a significant difference in the PS region, where [super 16]O sample has a structural inhomogeneity in the from of two coexisting ferromagnetic (FM) and antiferromagnetic (AF) phases, while the [super 18]O sample phase separates into mixed AF and PM phases.

Photoluminescence (PL) is commonly used for investigations of Cu2ZnSnS(e)4 [CZTS(e)] and Cu(In,Ga)Se2 (CIGS) thin film solar cells. The influence of interference effects on these measurements is, however, largely overlooked in the community. Here, it is demonstrated that PL spectra of typical CZTS absorbers on Mo/glass substrates can be heavily distorted by interference effects. One reason for the pronounced interference in CZTS is the low reabsorption of the PL emission that typically occurs below the band gap. A similar situation occurs in band gap graded CIGS where the PL emission originates predominantly from the band gap minimum located at the notch region. Based on an optical model for interference effects of PL emitted from a thin film, several approaches to reduce the fringing are identified and tested experimentally. These approaches include the use of measured reflectance data, a calculated interference function, use of high angles of incidence during PL measurements as well as the measurement of polarized light near the Brewster angle. [ABSTRACT FROM AUTHOR]

The field-orientation dependence of magnetization reversal and spin wave modes in nanorings has been investigated by focused magneto-optical Kerr effect spectroscopy, Brillouin spectroscopy, and micromagnetic simulations. The samples studied are periodic arrays of 150 nm wide Ni80Fe20 rings with long axes of 850, 1200, and 1500 nm, and respective short axes of 550, 700, and 900 nm. For the smallest ring, the onion-to-vortex transition is observed for both the applied magnetic field directed along, and 5° from its magnetization easy axis. In contrast for the two larger rings, this transition is not observed for the field in the latter orientation. Splitting of spin wave modes is observed for the transition from the onion to vortex state. Micromagnetic simulations of magnetization reversal and spin waves are in good agreement with experiments. The simulated temporal recording of magnetization distributions during transition reveals that different switching mechanisms result from different applied magnetic field orientations. [ABSTRACT FROM AUTHOR]

We studied magnetic anisotropic properties, interlayer coupling, and spin wave relaxation in ten periods of CoFeB/Cr/CoFeB films grown on seed layers of Cu with a Co:Fe:B composition ratio of 2:2:1. The measurements were taken in samples with 50 Å layers of CoFeB using the ferromagnetic resonance technique. The thickness of the Cr interlayers was varied from 4 to 40 Å for understanding the mechanisms of interlayer coupling. We investigated the magnetic anisotropy parameters by rotating the sample with respect to the microwave magnetic field from in plane to perpendicular to the plane. We identify both the acoustic branch and the optical branch in the spin wave resonance spectra. The effective interlayer coupling constant and the out-of-plane anisotropy show an oscillatory change, while the uniaxial in-plane anisotropy increases monotonically with increasing the thickness of the spacing layers. Moreover, we show that the spin wave relaxation can be optimized by adjusting the interlayer exchange interactions. [ABSTRACT FROM AUTHOR]

We investigated the magnetic anisotropic properties and the spin wave relaxation in trilayer films of CoFe/PtMn/CoFe grown on the seed layer Ru or NiFeCr with CoFe compositions being Co–16 at. % Fe. The measurements were taken in samples with the ferromagnetic layers of CoFe varying from 10 to 500 Å by the ferromagnetic resonance (FMR) technique. The magnetic anisotropic parameters were investigated by rotating the field aligned axis with respect to the spectral field in the configurations of both in plane and out of plane. We determine the effective in-plane anisotropy field of ∼0.005 T, the uniaxial out-of-plane anisotropy of ∼-0.3 T, and the exchange stiffness D of ∼512 meV Å2. Moreover, spin wave damping was estimated by analyzing the FMR linewidth and line shape as a function of the angle between the external field and easy axis and as a function of the thickness of the CoFe layers. We identify an extrinsic contribution of the damping parameter dominated by two-magnon scattering in addition to the intrinsic Gilbert term with a damping parameter, α=0.012. Further, we reveal that a significant linewidth broadening could also be caused by the overlap of the surface and the uniform spin wave excitations. The FMR lines show a strong dependence of the surface anisotropy contribution of free energy in trilayer films. [ABSTRACT FROM AUTHOR]

We present the results of a systematic characterization of the magnetization reversal mechanism of arrays of elongated Ni80Fe20 nanorings using focused magneto-optical Kerr effect measurements. The long axis of the rings was varied from 850 nm to 1.60 μm while the aspect ratio, ring width, and thickness were fixed at 2, 150 nm, and 25 nm, respectively. We observed an increase in the range of stability of the intermediate vortex state with both increasing length (l) of the ring and varying field orientations. Interestingly, for l>lcrit, the reversal process drastically changes from a two-step switching to a single step switching without the formation of a vortex state and from a one-step switching to a double step switching with the formation of a vortex state when the applied field is (±5°) away from the easy and hard axes of the ring, respectively. There is a good agreement between the experimental results and micromagnetic simulations. [ABSTRACT FROM AUTHOR]

In situ time-of-flight neutron diffraction and high-energy x-ray diffraction techniques were used to reveal the preferred reselection of martensite variants through a detwinning process in polycrystalline Ni–Mn–Ga ferromagnetic shape memory alloys under uniaxial compressive stress. The variant reorientation via detwinning during loading can be explained by considering the influence of external stress on the grain/variant orientation-dependent distortion energy. These direct observations of detwinning provide a good understanding of the deformation mechanisms in shape memory alloys. [ABSTRACT FROM AUTHOR]

In this work, we examine the valence band offset of hafnium aluminate (HfAlO), a material of interest for use as a high dielectric constant (high-k) gate oxide, following postdeposition annealing. It is observed that annealing leads to a change in the band offset between the high-k oxide and the semiconductor. Our results conclusively show that the change is due to the existence of an electrostatic dipole field at the interface between HfAlO and the silicon substrate. This provides evidence to partly account for the observed flatband voltage shifts in high-k dielectric stack structures in the literature. The origin of the dipole field is also discussed in terms of the interfacial permittivity. [ABSTRACT FROM AUTHOR]

The three-dimensional structure of oleic acid-capped CdSe and thiol-capped CdTe nanocrystals used as quantum dots has been determined by total synchrotron radiation x-ray diffraction and atomic pair distribution function analysis. Both CdSe and CdTe are found to exhibit the zinc-blende-type atomic ordering. It is only slightly distorted in CdSe implying the presence of nanosize domains and very heavily distorted in CdTe due to the presence of distinct core-shell regions. The results well demonstrate the great potential of the experimental approach and thus encourage its wider application in quantum dot research. [ABSTRACT FROM AUTHOR]

We report here that the ball-milling process induces the phase transformation from the tetragonal structure to the disordered face-centered-cubic structure in Ni2MnGa ferromagnetic shape-memory alloys. The in situ high-energy x-ray diffraction analyses reveal that an intermediate phase, which is characterized by amorphous structure, controls the transformation kinetics during the postannealing process. Completely different from their coarse-grained counterparts, the ferromagnetic Ni2MnGa nanoparticles undergo various sequences of structural transitions that are tailored by the crystallite size, atomic order, and intrinsic magnetic structure. [ABSTRACT FROM AUTHOR]

Anomalous hysteresis loops measured by longitudinal and polar magneto-optical Kerr effects (MOKE) were observed in a Co/NiO/Cu/Co/Cu structure. After excluding other possible mechanisms, we explain the anomalous hysteresis loops in terms of the opposite rotation angles for the top- and bottom-Co layers. Ultimately, the opposite rotation angles are likely caused by the different incidence angles for the top- and bottom-Co layers. [ABSTRACT FROM AUTHOR]

Magnetic field (MF) dependence of the phase separation (PS) in the manganites Sm0.5Sr0.5MnO3 with 16O and 18O was studied using high-resolution high-energy x-ray powder diffraction in the temperature range from 4.2 to 240 K and with the MF up to 6 T. Although the two compounds have an identical structure [a paramagnetic (PM) phase with the Pbnm symmetry] at room temperature, they show a significant difference in the PS region below Tps∼110 K, where the 16O sample has a structural inhomogeneity in the form of two coexisting ferromagnetic (FM) and antiferromagnetic (AF) phases, while the 18O-sample phase separates into mixed AF and PM phases. The 16O→18O isotope substitution appears to prevent the formation of the FM phase at low temperature. The application of a magnetic field significantly enhances the FM phase by converting other phases, leading to a homogeneous structure. The effects on the microscopic structure of the oxygen isotope substitution and external magnetic field play the key role in the physics behind the colossal magnetoresistance effect. [ABSTRACT FROM AUTHOR]

Magnetic field (MF) dependence of the phase separation (PS) in the manganites Sm0.5Sr0.5MnO3 with 16O and 18O was studied using high-resolution high-energy x-ray powder diffraction in the temperature range from 4.2 to 240 K and with the MF up to 6 T. Although the two compounds have an identical structure [a paramagnetic (PM) phase with the Pbnm symmetry] at room temperature, they show a significant difference in the PS region below Tps∼110 K, where the 16O sample has a structural inhomogeneity in the form of two coexisting ferromagnetic (FM) and antiferromagnetic (AF) phases, while the 18O-sample phase separates into mixed AF and PM phases. The 16O→18O isotope substitution appears to prevent the formation of the FM phase at low temperature. The application of a magnetic field significantly enhances the FM phase by converting other phases, leading to a homogeneous structure. The effects on the microscopic structure of the oxygen isotope substitution and external magnetic field play the key role in the physics behind the colossal magnetoresistance effect. [ABSTRACT FROM AUTHOR]

Studies on the distribution of the electric field produced by a thermal poling process in a layer of Ge-doped silica on silicon substrate, by using secondary electron emission yield (SEEY) measurements (δ) are presented. Comparing δ0 between poled and unpoled areas, the SEEY at the origin of electron injection, we pointed out an electric field 0.5 μm below the surface for our poling conditions and directed in the same direction as the external field applied during the poling process. Then, the dependence of δ on the injected dose of electrons allows us to deduce that the poling process disturbs the glass structure strongly enough for leading to a weak conductivity. It is then easy to display the poled areas. We have also pointed out an effect of the electric properties of the glass on the measurements obtained with the Electron Probe for MicroAnalysis. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magneto-optical Kerr effect measurements are used for characterizing the magnetization reversal mechanism of arrays of elongated [Ni.sub.80][Fe.sub.20] nanorings. An increase is observed in the range of stability of the intermediate vortex state with both increasing length (l) of the ring and varying field orientations.

A study reports the observation of anomalous hysteresis loops for Co/NiO/Cu/Co/Cu in longitudinal and polar magneto-optical Kerr effects (MOKE) measurements. The anomalous hysteresis loops are explained in terms of the opposite rotation angles for the top- and bottom-Co layers, which are caused by the different incidence angles for the top- and bottom-Co layers.

We report on our recent study of confined spin wave excitations in a 200 Å CoFe/PtMn/CoFe trilayer film by ultrafast Kerr-rotation experiments. Coherent magnetization precessions were generated and detected by subpicosecond laser pulses. Three precession modes are observed when a magnetic field is oriented in the film plane. The frequencies of two modes increase with the field, while one mode shows no field dependence. The modes are assigned to the exchange-dominated spin wave excitations and the nonhomogeneous dipole mode. We used a comprehensive model of the magnetic eigenmodes and their coupling to light to gain values of the exchange, bulk, and surface anisotropy constants. Further, we investigated spin wave relaxation as a function of the applied field. We calculated an effective damping constant for the uniform precession to be α∼0.012. [ABSTRACT FROM AUTHOR]

The magnetic properties of the ultrathin Fe/Co/Cu(100) films grown at 110 K with Co underlayer thickness below 2 monolayers (ML) are investigated by means of the in situ magneto-optical Kerr effect. The spin reorientation transitions (SRT) from out-of-plane to in-plane influenced by the Co underlayer are observed. A simplified bilayer growth mode of Co is introduced to fit the experiment results, obtaining that the true critical Fe thickness of a SRT if without structural transformation for a fct Fe on Cu(001) is about 4.6 ML, the same value as the previous Co capping experiment. [ABSTRACT FROM AUTHOR]

We report on time-resolved pump-probe measurements of spin-dependent dynamics in strained Nd[sub 0.67]Sr[sub 0.33]MnO[sub 3] thin films grown on three different substrates: LaAlO[sub 3] (001), SrTiO[sub 3] (001), and NdGaO[sub 3] (110). The temperature dependence of the long-lived spin-relaxation component is represented well by a power-law decay of long-range correlations, clearly showing the transition from quasilong-range ferromagnetic order to a disordered paramagnetic phase. The "disordering" temperature, T[sub M], where the intermediate phase of quasilong-range order appears, varies according to the creation of static-distortion waves under different strain forces. [ABSTRACT FROM AUTHOR]

Presents a study of the electronic structure and magnetic properties of iron-rich ternary compounds. Electronic structure; Results and discussion; Conclusions.

Deals with a study that detailed magnetic measurements for iron-rich ternary alloys with certain compositions. Description of ternary alloys; Impact of the use of light rare earth on the alloy; Use of rapid-quenching techniques in the production of single-phase 10:1:1 alloys.

Presents a study which reported the electronic and magnetic structure and surface reactivity for R[sub2]T[sub14]B compounds. Description of the electronic structure of R[sub2]T[sub14]B crystals; Overview of the representative Auger spectra for the Nd[sub2]Fe[sub14]B surface; Oxidation of rare-earth alloys exposed to ambient atmosphere.

Presents a study which examined the pressure dependence of magnetic ordering temperature for linear-chain charge-transfer ferromagnetic salt, decamethylferrocenium tetracyanoethanide. Experimental methods; Results; Discussion.