Search

The electronic stability of (001) and (110) surfaces of La2/3Ca1/3MnO3 (LCMO) capped with nanometric SrTiO3 (STO) layers in epitaxial heterostructures is addressed by (S)TEM electron energy loss spectroscopy. It is found that growth of STO on (001)LCMO promotes a significant electron doping of LCMO that extends a few nanometers deep into the film. In contrast, (110)LCMO appears to be electronically more robust and no electronic reordering has been observed. These results are in clear correlation with the distinct magnetic properties observed in those interfaces and illustrate that complex chemical phenomena take place at interfaces among multivalent oxides. [ABSTRACT FROM AUTHOR]

Epitaxial Fe/MgO heterostructures have been grown on Si(001) by a combination of sputtering and laser ablation deposition techniques. The growth of MgO on Si(001) is mainly determined by the nature of the interface, with large lattice mismatch and the presence of an amorphous layer of unclear origin. Reflection high energy electron diffraction patterns of this MgO buffer layer are characteristic of an epitaxial, but disordered, structure. The structural quality of subsequent Fe and MgO layers continuously improves due to the better lattice match and the burial of defects. A weak uniaxial in-plane magnetic anisotropy is found superimposed on the expected cubic biaxial anisotropy. This additional anisotropy, of interfacial nature and often found in Fe/MgO and Fe/ MgO/GaAs(001) systems, is less intense here due to the poorer MgO/Si interface quality compared with that of other systems. From the evolution of the anisotropy field with film thickness, magnetic anisotropy is also found to depend on the crystal quality. Kerr measurements of a Fe/MgO multilayered structure grown on Si show two different switching fields, suggesting magnetic coupling of two of the three Fe layers. Nevertheless, due to the little sensitivity to the bottom Fe film, independent switching of the three layers cannot be ruled out. [ABSTRACT FROM AUTHOR]

Focuses on the growth of heterostructures for application in high electron mobility transistors. Discussion on the partial and perfect dislocation nucleation at the onset of stress relaxation in active layers of high mobility transistors grown on indium phosphide; Importance of the determination of onset plastic relaxation of strained layers; Use of transmission electron microscopy in the study.

In this work, we present characterization methods for the analysis of nanometer-sized devices, based on silicon and III-V nitride semiconductor materials. These methods are devised in order to take advantage of the aberration corrected scanning transmission electron microscope, equipped with a monochromator. This set-up ensures the necessary high spatial and energy resolution for the characterization of the smallest structures. As with these experiments, we aim to obtain chemical and structural information, we use electron energy loss spectroscopy (EELS). The low-loss region of EELS is exploited, which features fundamental electronic properties of semiconductor materials and facilitates a high data throughput. We show how the detailed analysis of these spectra, using theoretical models and computational tools, can enhance the analytical power of EELS. In this sense, initially, results from the model-based fit of the plasmon peak are presented. Moreover, the application of multivariate analysis algorithms to low-loss EELS is explored. Finally, some physical limitations of the technique, such as spatial delocalization, are mentioned. [ABSTRACT FROM AUTHOR]