Electron Spin Injection at a Schottky Contact

We investigate theoretically electrical spin injection at a Schottky contact between a spin-polarized electrode and a non-magnetic semiconductor. Current and electron density spin-polarizations are discussed as functions of barrier energy and semiconductor doping density. The effect of a spin-dependent interface resistance that results from a tunneling region at the contact/semiconductor interface is described. The model can serve as a guide for designing spin-injection experiments with regard to the interface properties and device structure.Comment: 4 pages, 4 figure

Spin-Polarized Electron Transport at Ferromagnet/Semiconductor Schottky Contacts

We theoretically investigate electron spin injection and spin-polarization sensitive current detection at Schottky contacts between a ferromagnetic metal and an n-type or p-type semiconductor. We use spin-dependent continuity equations and transport equations at the drift-diffusion level of approximation. Spin-polarized electron current and density in the semiconductor are described for four scenarios corresponding to the injection or the collection of spin polarized electrons at Schottky contacts to n-type or p-type semiconductors. The transport properties of the interface are described by a spin-dependent interface resistance, resulting from an interfacial tunneling region. The spin-dependent interface resistance is crucial for achieving spin injection or spin polarization sensitivity in these configurations. We find that the depletion region resulting from Schottky barrier formation at a metal/semiconductor interface is detrimental to both spin injection and spin detection. However, the depletion region can be tailored using a doping density profile to minimize these deleterious effects. For example, a heavily doped region near the interface, such as a delta-doped layer, can be used to form a sharp potential profile through which electrons tunnel to reduce the effective Schottky energy barrier that determines the magnitude of the depletion region. The model results indicate that efficient spin-injection and spin-polarization detection can be achieved in properly designed structures and can serve as a guide for the structure design.Comment: RevTex

Tailoring the efficiency of an active catalyst for CO abatement through oxidation reaction: The case study of samarium-doped ceria

In the present study, for the first time we tailored organic chemistry traditional synthesis tools towards preparation of CexSm1-xO2 (x = 0.2, 0.5, 0.8, 1) fluorite-type mixed oxides which are used for CO abatement. In this study, microwave radiation has been used as stand-alone heating method (conventional microwave), in the presence of oxalic acid acting as complexing agent (OX), or it has been coupled with simultaneous air cooling (AC), reflux (RE) and on/off cycles of the magnetron power (C1 and C5) in the so called enhanced microwave synthesis (EMW) approach. The EMW methods were applied in the case of Ce0.5Sm0.5O2 composition and enlightened different aspects of the rational design of its morphology (flower-like, rod-shaped, random aggregates), as well as the engineering of its oxygen vacant sites. CO oxidation reaction, in the presence and absence of H2, was used as a model probe reaction towards the evaluation of the catalysts. Different characterization techniques, namely, XRD, BET, ICP-MS, Raman, SEM, FTIR, TEM, XPS, H2-TPR, and CO2-TPD, have been employed to understand the synthesis −structure-properties relationship of the catalysts. Interestingly, the EMW synthesis conditions affect the crystalline structure of the catalysts (XRD), and the crystal growth, giving rise to CexSm1-xO2 particles with a crystallite size in the range of 8–26 nm. A rational manipulation of the morphology of the CexSm1-xO2 was achieved under the different EMW synthesis conditions and reported herein for the first time in such a systematic way, where the Ce0.5Sm0.5O2 catalyst was crystallized in octahedral rods (RE), random aggregates (C1 and C5), and elongated flower-like shapes (AC). The co-presence of Ce3+ and Sm3+ in the metal oxides (XPS studies) facilitates the presence of oxygen vacant sites, as confirmed by the Raman spectra (550–590 cm‐1), the mobility of which, though, differs as has been proved by H2-TPR, following the order: Ce0.5Sm0.5 (RE) > Ce0.5Sm0.5 (AC) > Ce0.5Sm0.5 (C1). A tensile lattice strain in the 0.6–2.4% range of the cubic CexSm1-xO2 lattice was found to be strongly correlated with the CO oxidation performance. Two of the enhanced microwave methods, RE and AC, led to catalysts with improved catalytic performance, lowering the T50 by 130 °C (or 27%) and 30 °C (or 6%), respectively, compared to the Ce0.5Sm0.5O2 (OX). The superior performance is discussed in terms of oxygen vacancies, oxygen mobility, lattice strain and CO2-affinity of the surfaces involved.KP would like to acknowledge the financial support from Abu Dhabi Educational Council (ADEC B3111 ) and Khalifa University Internal Research Fund ( L1KUIRF-210103 ) for supporting this research. KP thanks Khalifa University Core Nanocharacterization Facilities and acknowledges KU and CNCF staff support. AFZ acknowledges the support of the grant number NPRP 6-351-1-072 from the Qatar National Research Fund (a member of Qatar Foundation). Work done by AFI was done at Cornell University CCMR and Brookhaven National Lab CFN, supported by US Department of Energy . This work made use of the Cornell Center for Materials Research Shared Facilities which are supported through the NSF MRSEC program (DMR-1719875). This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.Scopu

Transverse correlations and plasticity in the CDW conductor NbSe3_{3} studied by X-ray microbeam diffraction

In whisker-like samples of the quasi-1D conductor NbSe$_{3}$, the presence of longitudinal steps causes shearing of the CDW, and leads to a loss of transverse correlations. We use a microdiffraction setup with a spatial resolution of 300 nm and an angular sensitivity of 5 mdeg to image the resulting CDW contrast between thick and thin portions of the sample. Microdiffraction in the b* - c* plane shows that depinning on the thick, weakly pinned side is accompanied by the loss of diffraction intensity, demonstrating a loss of correlations in qualitative agreement with previous X-ray diffraction topography measurements$^{1}$, but with an order-of-magnitude improvement in spatial resolution. Microdiffraction images in the a* - b* plane reveal a sharp increase in the full width at half maximum in an approximately 1 micron thick region near the step edge and a rotation of the CDW wavevector that varies with applied field. We use the extremal value of the CDW wavevector rotation to estimate the shear modulus of this electronic crystal