Search results for "superlattice"
showing 10 items of 83 documents
Controlling the intralayer structure of Co/Pt superlattices
1999
Abstract The effect of the surface quality of MgO (1 1 1) substrates seeded by a 3 nm thick Pt layer on the intralayer and interlayer structure of Co/Pt (1 1 1) superlattices was investigated. The superlattices were grown by DC magnetron sputtering. Pre-growth processing of the MgO shows that intensive polishing using a specific H 2 O/SiO 2 suspension prior to growth is mandatory for obtaining long-range structural coherence in the films. The comparison between superlattices grown on re-polished and as-supplied substrates shows that the substrate treatment enhances the crystalline in-plane orientation and suppresses abc / acb twin formation. Magnetization measurements were performed using t…
Coarsening of Antiferromagnetic Domains in Multilayers: The Key Role of Magnetocrystalline Anisotropy
2002
The domain structure of an antiferromagnetic superlattice is studied. Synchrotron Mössbauer and polarized neutron reflectometric maps show micrometer-size primary domain formation as the external field decreases from saturation to remanence. A secondary domain state consisting mainly of at least 1 order of magnitude larger domains is created when a small field along the layer magnetizations induces a bulk-spin-flop transition. The domain-size distribution is reproducibly dependent on the magnetic prehistory. The condition for domain coarsening is shown to be the equilibrium of the external field energy with the anisotropy energy.
Interface properties of magnetic tunnel junctionLa0.7Sr0.3MnO3/SrTiO3superlattices studied by standing-wave excited photoemission spectroscopy
2010
The chemical and electronic-structure profiles of magnetic tunnel junction (MTJ) La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical and core-hole multiplet theoretical modeling. Epitaxial superlattice samples consisting of 48 and 120 bilayers of LSMO and STO, each nominally four unit cells thick, and still exhibiting LSMO ferromagnetism, were studied. By varying the incidence angle around the superlattice Bragg condition, the standing wave was moved vertically through the interfaces. By comparing experiment to x-ray optical c…
Size-filtering effects by stacking InAs/InP (001) self-assembled quantum wires into multilayers
2002
Multilayer structure containing vertically stacked InAs/InP self-assembled quantum wires have been successfully grown by molecular-beam epitaxy. The influence of the InP spacer layer thickness on the structural and optical properties of the wire superlattice has been studied by means of transmission electron microscopy and photoluminescence. The coherent propagation of the strain field in the sample with a 5-nm-thick spacer determines by a size filtering effect a good homogeneity and uniformity of the wire stacks, and hence a good optical quality. The exciton recombination dynamics in the wire superlattice cannot be related to thermal escape of carriers out to the barriers, as occurs in sin…
Depth profiling of optical and vibrational properties in GaN/AlN quantum dot superlattices
2009
Spatially resolved confocal μ-Raman and μ-photoluminescence experiments were performed to analyze the vibrational and optical properties of GaN/AlN quantum dots as a function of depth. Two approaches have been followed. First, spectra were taken by defocusing the microscope objective at various depths on the sample surface. In a second set of experiments a bevel at an angle of 20° with respect to the surface normal was prepared by mechanical polishing of the surface, and spectra were taken across the bevel. The E2h vibrational modes ascribed to the GaN QDs and the AlN spacer redshift towards the surface, indicating the progressive relaxation of the QDs and a considerable increase of the ten…
Residual crystalline silicon phase in silicon-rich-oxide films subjected to high temperature annealing
2002
Structural properties of silicon rich oxide films (SRO) have been investigated by means of micro-Raman spectroscopy and transmission electron microscopy (TEM). The layers were deposited by plasma enhanced chemical vapor deposition using different SiH4/O2 gas mixtures. The Raman spectra of the as-deposited SRO films are dominated by a broad band in the region 400-500 cm-1 typical of a highly disordered silicon network. After annealing at temperatures above 1000°C in N2, the formation of silicon nanocrystals is observed both in the Raman spectra and in the TEM images. However, most of the precipitated silicon does not crystallize and assumes an amorphous microstructure. © 2002 The Electrochem…
Phase-separation-induced changes in the magnetic and transport properties of the quaternary Heusler alloyCo2Mn1−xTixSn
2010
The quaternary Heusler compound ${\text{Co}}_{2}{\text{Mn}}_{1\ensuremath{-}x}{\text{Ti}}_{x}\text{Sn}$ with $x=0$, 0.2, 0.4, 0.5, 0.6, 0.8, and 1 shows a phase separation into the two Heusler compounds, ${\text{Co}}_{2}\text{MnSn}$ and ${\text{Co}}_{2}\text{TiSn}$. Only at the edges of the composition range a slight admixture of Mn and Ti to the respective other phase is observed. This phase separation leads to a distinct microstructure which can be altered by the composition of the material. Pronounced changes in the magnetic and electronic properties take place with varying composition. Two magnetic transitions occur which indicate different Curie temperatures for both phases. The reduct…
MgO surface microstructure and crystalline coherence of Co/Pt superlattices
1998
We report the growth of Co/Pt(111) superlattices sputtered onto MgO(111) substrates of different surface quality. Long-range structural coherence in the Pt-seed layers and the superlattices could only be obtained on specially re-polished substrates. In seed layers and superlattices grown on miscut re-polished substrates suppression of abc versus acb stacking was observed.
Substantial enlargement of angular existence range for Dyakonov-like surface waves at semi-infinite metal-dielectric superlattice
2012
We investigated surface waves guided by the boundary of a semi-infinite layered metal-dielectric nanostructure cut normally to the layers and a semi-infinite dielectric material. Using the Floquet-Bloch formalism, we found that Dyakonov-like surface waves with hybrid polarization can propagate in dramatically enhanced angular range compared to conventional birefringent materials. Our numerical simulations for an Ag-GaAs stack in contact with glass show a low to moderate influence of losses. This research was funded by the Qatar National Research Fund under the project NPRP 09-462-1-074, by the Spanish Ministry of Economy and Competitiveness under the project TEC2009-11635, and by the Serbia…
Superior Electrocatalytic Activity of MoS2-Graphene as Superlattice
2020
[EN] Evidence by selected area diffraction patterns shows the successful preparation of large area (cm x cm) MoS2/graphene heterojunctions in coincidence of the MoS2 and graphene hexagons (superlattice). The electrodes of MoS2/graphene in superlattice configuration show improved catalytic activity for H-2 and O-2 evolution with smaller overpotential of +0.34 V for the overall water splitting when compared with analogous MoS2/graphene heterojunction with random stacking.