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Title: Aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy studies of epitaxial Fe/MgO/(001)Ge heterostructures

Abstract

Aberration correction in the scanning transmission electron microscope combined with electron energy loss spectroscopy allows simultaneous mapping of the structure, the chemistry and even the electronic properties of materials in one single experiment with spatial resolutions of the order of one Angstrom. Here the authors will apply these techniques to the characterization of epitaxial Fe/MgO/(001)Ge and interfaces with possible applications for tunneling junctions, and the authors will show that epitaxial MgO films can be grown on a (001)Ge substrates by molecular beam epitaxy and how it is possible to map the chemistry of interfaces with atomic resolution. Epitaxial growth of insulator oxides on semiconductors constitutes a key issue within the field of electronics, and a considerably large effort has been devoted to harness the growth of high-k oxides on Si. Ge, due to its high electronic and hole mobility, is a very interesting alternative as a potential substrate for future high performance complementary metal-oxide-semiconductor field-effect transistors. However, a major issue is to avoid the high resistivity at the source and drain contacts ensuing from the pinning of the Fermi level at the valence-band maximum. It has been suggested that this problem could be fixed by depositing a thin insulating tunnelingmore » barrier between the Ge substrate and the metal contacts. In this case, single crystal epitaxy would represent an additional benefit, since it would lead to a reduction of interfacial defects and improved performance of the tunneling barrier. MgO has been suggested to fulfill such requisites. Furthermore, MgO has been demonstrated to be a good substrate for epitaxial growth of transition metals thin films, such as Fe and Co, thus avoiding the potential problem of chemical reactivity with Ge. In such a scenario, epitaxial deposition of high quality MgO films on Ge substrates is highly desirable. But in addition, successful epitaxial growth of MgO on a semiconductor would also constitute a plus for applications in spintronics, since the injection of a spin polarized current from a ferromagnetic electrode to a non-magnetic semiconductor requires the presence of a potential barrier. MgO represents a convenient choice because the symmetry filtering properties at the interface with transition metals would allow an efficient spin filtering effect. For this approach to succeed, a suitable semiconducting substrate where MgO can be grown epitaxially must be found. And again, while GaAs and Si have been investigated for such role, Ge has not received much attention so far. In this study the authors report on the atomic resolution characterization of high quality interfaces in Fe/MgO/(001)Ge heterostructures. The study of the defects, the inhomogeneities and the interface structure of such junctions is a must to pave the way toward future applications. For this aim, the combination of scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) is a most useful tool, since it allows these features to be probed with atomic resolution. Spherical aberration correction in the STEM allows for increased contrast, allowing even single atoms to be detected both in imaging and spectroscopy.« less

Authors:
 [1];  [1];  [2];  [2];  [2];  [2];  [2]
  1. ORNL
  2. Politecnico di Milano
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1018970
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Journal of Materials Science
Additional Journal Information:
Journal Volume: 46; Journal Issue: 12; Journal ID: ISSN 0022--2461
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHEMISTRY; DEFECTS; ELECTRODES; ELECTRON MICROSCOPES; ELECTRONS; ENERGY-LOSS SPECTROSCOPY; EPITAXY; FERMI LEVEL; GEOMETRICAL ABERRATIONS; HOLE MOBILITY; MOLECULAR BEAM EPITAXY; MONOCRYSTALS; OXIDES; RESOLUTION; SPATIAL RESOLUTION; SPECTROSCOPY; SPIN; SUBSTRATES; THIN FILMS; TRANSITION ELEMENTS; TRANSMISSION ELECTRON MICROSCOPY; TUNNELING

Citation Formats

Gazquez Alabart, Jaume, Varela del Arco, Maria, Petti, D., Cantoni, M., Rinaldi, C., Brivio, S., and Bertacco, R. Aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy studies of epitaxial Fe/MgO/(001)Ge heterostructures. United States: N. p., 2011. Web. doi:10.1007/s10853-011-5248-7.
Gazquez Alabart, Jaume, Varela del Arco, Maria, Petti, D., Cantoni, M., Rinaldi, C., Brivio, S., & Bertacco, R. Aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy studies of epitaxial Fe/MgO/(001)Ge heterostructures. United States. doi:10.1007/s10853-011-5248-7.
Gazquez Alabart, Jaume, Varela del Arco, Maria, Petti, D., Cantoni, M., Rinaldi, C., Brivio, S., and Bertacco, R. Sat . "Aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy studies of epitaxial Fe/MgO/(001)Ge heterostructures". United States. doi:10.1007/s10853-011-5248-7.
@article{osti_1018970,
title = {Aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy studies of epitaxial Fe/MgO/(001)Ge heterostructures},
author = {Gazquez Alabart, Jaume and Varela del Arco, Maria and Petti, D. and Cantoni, M. and Rinaldi, C. and Brivio, S. and Bertacco, R.},
abstractNote = {Aberration correction in the scanning transmission electron microscope combined with electron energy loss spectroscopy allows simultaneous mapping of the structure, the chemistry and even the electronic properties of materials in one single experiment with spatial resolutions of the order of one Angstrom. Here the authors will apply these techniques to the characterization of epitaxial Fe/MgO/(001)Ge and interfaces with possible applications for tunneling junctions, and the authors will show that epitaxial MgO films can be grown on a (001)Ge substrates by molecular beam epitaxy and how it is possible to map the chemistry of interfaces with atomic resolution. Epitaxial growth of insulator oxides on semiconductors constitutes a key issue within the field of electronics, and a considerably large effort has been devoted to harness the growth of high-k oxides on Si. Ge, due to its high electronic and hole mobility, is a very interesting alternative as a potential substrate for future high performance complementary metal-oxide-semiconductor field-effect transistors. However, a major issue is to avoid the high resistivity at the source and drain contacts ensuing from the pinning of the Fermi level at the valence-band maximum. It has been suggested that this problem could be fixed by depositing a thin insulating tunneling barrier between the Ge substrate and the metal contacts. In this case, single crystal epitaxy would represent an additional benefit, since it would lead to a reduction of interfacial defects and improved performance of the tunneling barrier. MgO has been suggested to fulfill such requisites. Furthermore, MgO has been demonstrated to be a good substrate for epitaxial growth of transition metals thin films, such as Fe and Co, thus avoiding the potential problem of chemical reactivity with Ge. In such a scenario, epitaxial deposition of high quality MgO films on Ge substrates is highly desirable. But in addition, successful epitaxial growth of MgO on a semiconductor would also constitute a plus for applications in spintronics, since the injection of a spin polarized current from a ferromagnetic electrode to a non-magnetic semiconductor requires the presence of a potential barrier. MgO represents a convenient choice because the symmetry filtering properties at the interface with transition metals would allow an efficient spin filtering effect. For this approach to succeed, a suitable semiconducting substrate where MgO can be grown epitaxially must be found. And again, while GaAs and Si have been investigated for such role, Ge has not received much attention so far. In this study the authors report on the atomic resolution characterization of high quality interfaces in Fe/MgO/(001)Ge heterostructures. The study of the defects, the inhomogeneities and the interface structure of such junctions is a must to pave the way toward future applications. For this aim, the combination of scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) is a most useful tool, since it allows these features to be probed with atomic resolution. Spherical aberration correction in the STEM allows for increased contrast, allowing even single atoms to be detected both in imaging and spectroscopy.},
doi = {10.1007/s10853-011-5248-7},
journal = {Journal of Materials Science},
issn = {0022--2461},
number = 12,
volume = 46,
place = {United States},
year = {2011},
month = {1}
}