Search results for " SEM"
showing 10 items of 1467 documents
Desarrollo y evaluación psicométrica de una forma abreviada de la escala de posicionamiento ante el diagnóstico enfermero
2013
El Position on Nursing Diagnosis (PND) es una escala que utiliza la técnica del diferencial semántico para medir las actitudes hacia el concepto diagnóstico enfermero. El estudio objetivó desarrollar una forma abreviada de la versión española de esta escala, evaluar sus propiedades psicométricas y eficiencia. Se utilizó un doble enfoque empírico-teórico para obtener una forma reducida del PND, el PND-7-SV, que fuera equivalente a la original. Mediante un diseño transversal a través de encuesta, se evaluó la fiabilidad (consistencia interna y fiabilidad test-retest), validez de constructo (análisis factorial exploratorio, técnica de grupos conocidos y validez discriminante) y de criterio (va…
Systematical, experimental investigations on LiMgZ (Z= P, As, Sb) wide band gap semiconductors
2011
This work reports on the experimental investigation of the wide band gap compounds LiMgZ (Z = P, As, Sb), which are promising candidates for opto-electronics and anode materials for Lithium batteries. The compounds crystallize in the cubic (C1_b) MgAgAs structure (space group F-43m). The polycrystalline samples were synthesized by solid state reaction methods. X-ray and neutron diffraction measurements show a homogeneous, single-phased samples. The electronic properties were studied using the direct current (DC) method. Additionally UV-VIS diffuse reflectance spectra were recorded in order to investigate the band gap nature. The measurements show that all compounds exhibit semiconducting be…
Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure
2016
The thermoelectric properties of n type semiconductor, TiNiSn is optimized by partial substitution with metallic, MnNiSb in the half Heusler structure. Herein, we study the transport properties and intrinsic phase separation in the system. The Ti1-xMnxNiSn1-xSbx alloys were prepared by arc-melting and were annealed at temperatures obtained from differential thermal analysis and differential scanning calorimetry results. The phases were characterized using powder X-ray diffraction patterns, energy dispersive X-ray spectroscopy, and differential scanning calorimetry. After annealing the majority phase was TiNiSn with some Ni rich sites and the minority phases was majorly Ti6Sn5, Sn, and MnSn2…
The enhancement of ferromagnetism in uniaxially stressed diluted magnetic semiconductors
2003
We predict a new mechanism of enhancement of ferromagnetic phase transition temperature $T_c$ in uniaxially stressed diluted magnetic semiconductors (DMS) of p-type. Our prediction is based on comparative studies of both Heisenberg (inherent to undistorted DMS with cubic lattice) and Ising (which can be applied to strongly enough stressed DMS) models in a random field approximation permitting to take into account the spatial inhomogeneity of spin-spin interaction. Our calculations of phase diagrams show that area of parameters for existence of DMS-ferromagnetism in Ising model is much larger than that in Heisenberg model.
Temperature dependence of spin depolarization of drifting electrons in n-type GaAs bulks
2010
The influence of temperature and transport conditions on the electron spin relaxation in lightly doped n-type GaAs semiconductors is investigated. A Monte Carlo approach is used to simulate electron transport, including the evolution of spin polarization and relaxation, by taking into account intravalley and intervalley scattering phenomena of the hot electrons in the medium. Spin relaxation lengths and times are computed through the D'yakonov-Perel process, which is the more relevant spin relaxation mechanism in the regime of interest (10 < T < 300 K). The decay of the initial spin polarization of the conduction electrons is calculated as a function of the distance in the presence of…
Heusler Compounds—A Material Class With Exceptional Properties
2011
The class of Heusler compounds, including the XYZ and the X2YZ compounds, has not only an endless number of members, but also a vast variety of properties can be found in this class of materials, ranging from semiconductors, half-metallic ferromagnets, superconductors, and topological insulators to shape memory alloys. With this review article, we would like to provide an overview of Heusler compounds, focusing on their structure, properties, and potential applications.
New Heusler Compounds and Their Properties
2013
Spintronics is a multidisciplinary field and a new research area. New materials must be found for satisfying the different types of requirement. The search for stable half-metallic ferromagnets and ferromagnetic semiconductors with Curie temperatures higher than room temperature is still a challenge for solid state scientists. A general understanding of how structures are related to properties is a necessary prerequisite for material design. Computational simulations are an important tool for a rational design of new materials. The new developments in this new field are reported from the point of view of material scientists.
Ab Initio Thermodynamics of Oxygen Vacancies and Zinc Interstitials in ZnO.
2015
ZnO is an important wide band gap semiconductor with potential application in various optoelectronic devices. In the current contribution, we explore the thermodynamics of oxygen vacancies and zinc interstitials in ZnO from first-principles phonon calculations. Formation enthalpies are evaluated using hybrid DFT calculations, and phonons are addressed using the PBE and the PBE+U functionals. The phonon contribution to the entropy is most dominant for oxygen vacancies, and their Gibbs formation energy increases when including phonons. Finally, inclusion of phonons decreases the Gibbs formation energy difference of the two defects and is therefore important when predicting their equilibrium c…
X-ray-absorption fine-structure study of ZnSexTe1−x alloys
2004
X-ray-absorption fine-structure experiments at different temperatures in ZnSexTe1−x (x=0, 0.1, 0.2, 0.55, 0.81, 0.93, 0.99, and 1.0) have been performed in order to obtain information about the structural relaxation and disorder effects occurring in the alloys. First and second neighbor distance distributions have been characterized at the Se and Zn K edges, using multiple-edge and multiple-scattering data analysis. The first neighbor distance distribution was found to be bimodal. The static disorder associated with the Zn–Te distance variance did not depend appreciably on composition. On the other hand, the static disorder associated with the Zn–Se distance increased as the Se content dimi…
Thickness scaling of space-charge-limited currents in organic layers with field- or density-dependent mobility
2006
An exact solution is provided for the current density-voltage (J –V) characteristics of space-charge limited transport of a single carrier in organic layers with field-dependent mobility of the type μ (E) = μ0 exp (γ √E. The general scaling relationship for field-dependent mobility occurs in terms of the variables JL and V /L. For the density-dependence of the mobility found in organic field-effect transistor measurements, the thickness scaling occurs in terms of different variables, J1/βL and V /L. The proposed scaling is a useful test for distinguishing field- and carrier density-dependent mobility in disordered organic semiconductors. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)