68 research outputs found
Control of magnetic anisotropy by orbital hybridization in (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattice
The asymmetry of chemical nature at the hetero-structural interface offers an
unique opportunity to design desirable electronic structure by controlling
charge transfer and orbital hybridization across the interface. However, the
control of hetero-interface remains a daunting task. Here, we report the
modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n
superlattices by manipulating the periodic thickness with n unit cells of
SrTiO3 and n unit cells La0.67Sr0.33MnO3. The easy axis of magnetic anisotropy
rotates from in-plane (n = 10) to out-of-plane (n = 2) orientation at 150 K.
Transmission electron microscopy reveals enlarged tetragonal ratio > 1 with
breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n
interface, and electronic charge transfer from Mn to Ti 3d orbitals across the
interface. Orbital hybridization accompanying the charge transfer results in
preferred occupancy of 3d3z2-r2 orbital at the interface, which induces a
stronger electronic hopping integral along the out-of-plane direction and
corresponding out-of-plane magnetic easy axis for n = 2. We demonstrate that
interfacial orbital hybridization in superlattices of strongly correlated
oxides may be a promising approach to tailor electronic and magnetic properties
in device applications
Impact of N on the atomic-scale Sb distribution in quaternary GaAsSbN-capped InAs quantum dots
The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure
Strong enhancement of phonon scattering through nanoscale grains in lead sulfide thermoelectrics
We present nanocrystalline PbS, which was prepared using a solvothermal method followed by spark plasma sintering, as a
promising thermoelectric material. The effects of grains with different length scales on phonon scattering of PbS samples, and
therefore on the thermal conductivity of these samples, were studied using transmission electron microscopy and theoretical
calculations. We found that a high density of nanoscale grain boundaries dramatically lowered the thermal conductivity by
effectively scattering long-wavelength phonons. The thermal conductivity at room temperature was reduced from 2.5 W m1K 1
for ingot-PbS (grain size 4200 lm) to 2.3 W m1K 1 for micro-PbS (grain size 40.4 lm); remarkably, thermal conductivity
was reduced to 0.85 W m1 K 1 for nano-PbS (grain size B30 nm). Considering the full phonon spectrum of the material, a
theoretical model based on a combination of first-principles calculations and semiempirical phonon scattering rates was
proposed to explain this effective enhancement. The results show that the high density of nanoscale grains could cause
effective phonon scattering of almost 61%. These findings shed light on developing high-performance thermoelectrics via
nanograins at the intermediate temperature range.This contribution was supported primarily by the startup of the South
University of Science and Technology of China, supported by the Shenzhen
government, and the national 1000 plan for young scientists. This work was
also partially supported by a grant-in-aid of ‘985 Project’ from Xi’an Jiaotong
University, the National Natural Science Foundation of China (Grant No.
21201138 and 11204228), the National Basic Research Program of China
(2012CB619402 and 2014CB644003) and the Fundamental Research Funds for
the Central UniversitiesS
High-Resolution Electron Microscopy of Semiconductor Heterostructures and Nanostructures
This chapter briefly describes the fundamentals of high-resolution electron microscopy techniques. In particular, the Peak Pairs approach for strain mapping with atomic column resolution, and a quantitative procedure to extract atomic column compositional information from Z-contrast high-resolution images are presented. It also reviews the structural, compositional, and strain results obtained by conventional and advanced transmission electron microscopy methods on a number of III–V semiconductor nanostructures and heterostructures
Measurement of the displacement field of dislocations to 0.03 Å by electron microscopy
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