21 results on '"Michael Niehle"'
Search Results
2. Publisher’s Note: 'Continuous tuning of two-section, single-mode terahertz quantum-cascade lasers by fiber-coupled, near-infrared illumination' [AIP Advances 7, 055201 (2017)]
- Author
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Martin Hempel, Benjamin Röben, Michael Niehle, Lutz Schrottke, Achim Trampert, and Holger T. Grahn
- Subjects
Physics ,QC1-999 - Published
- 2017
- Full Text
- View/download PDF
3. Selective Area Growth of High Quality Gan Nanocolumns on Si(001) by Plasma Assisted Molecular Beam Epitaxy
- Author
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Ana Bengoechea-Encabo, Steven Albert, Michael Niehle, and Achim Trampert
- Published
- 2023
4. Drastic effect of sequential deposition resulting from flux directionality on the luminescence efficiency of nanowire shells
- Author
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Achim Trampert, Ryan B. Lewis, Holger T. Grahn, Pierre Corfdir, Timur Flissikowski, Michael Niehle, Oliver Brandt, Lutz Geelhaar, and Hanno Küpers
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Condensed Matter - Materials Science ,Materials science ,Photoluminescence ,Condensed Matter - Mesoscale and Nanoscale Physics ,Nanowire ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Heterojunction ,Applied Physics (physics.app-ph) ,Physics - Applied Physics ,Epitaxy ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Crystallographic defect ,Molecular physics ,Condensed Matter::Materials Science ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,Quantum efficiency ,Quantum well ,Molecular beam epitaxy - Abstract
Core-shell nanowire heterostructures form the basis for many innovative devices. When compound nanowire shells are grown by directional deposition techniques, the azimuthal position of the sources for the different constituents in the growth reactor, substrate rotation, and nanowire self-shadowing inevitably lead to sequential deposition. Here, we uncover for In$_{0.15}$Ga$_{0.85}$As/GaAs shell quantum wells grown by molecular beam epitaxy a drastic impact of this sequentiality on the luminescence efficiency. The photoluminescence intensity of shell quantum wells grown with a flux sequence corresponding to migration enhanced epitaxy, i. e. when As and the group-III metals essentially do not impinge at the same time, is more than two orders of magnitude higher than for shell quantum wells prepared with substantially overlapping fluxes. Transmission electron microscopy does not reveal any extended defects explaining this difference. Our analysis of photoluminescence transients shows that co-deposition has two detrimental microscopic effects. First, a higher density of electrically active point defects leads to internal electric fields reducing the electron-hole wave function overlap. Second, more point defects form that act as nonradiative recombination centers. Our study demonstrates that the source arrangement of the growth reactor, which is of mere technical relevance for planar structures, can have drastic consequences for the materials properties of nanowire shells. We expect that this finding holds also for other alloy nanowire shells.
- Published
- 2021
5. Spatially-resolved luminescence and crystal structure of single core-shell nanowires measured in the as-grown geometry
- Author
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Ullrich Pietsch, Arman Davtyan, Tobias U. Schülli, Ryan B. Lewis, Michael Niehle, Hanno Küpers, Jonas Lähnemann, Florian Bertram, Danial Bahrami, Steven J. Leake, Ali AlHassan, and Lutz Geelhaar
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Materials science ,Scanning electron microscope ,Nanowire ,Physics::Optics ,FOS: Physical sciences ,Bioengineering ,Geometry ,Cathodoluminescence ,02 engineering and technology ,Applied Physics (physics.app-ph) ,010402 general chemistry ,01 natural sciences ,Condensed Matter::Materials Science ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,ddc:530 ,Electrical and Electronic Engineering ,Wurtzite crystal structure ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Mechanical Engineering ,Bragg's law ,Materials Science (cond-mat.mtrl-sci) ,Physics - Applied Physics ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,0104 chemical sciences ,Blueshift ,Mechanics of Materials ,Transmission electron microscopy ,0210 nano-technology ,Molecular beam epitaxy - Abstract
Nanotechnology 31(21), 1-7 (2020). doi:10.1088/1361-6528/ab7590, We report on the direct correlation between the structural and optical properties of single, as-grown core-multi-shell GaAs/In$_{0.15}$Ga$_{0.85}$As/GaAs/AlAs/GaAs nanowires. Fabricated by molecular beam epitaxy on a pre-patterned Si(111) substrate, on a row of well separated nucleation sites, it was possible to access individual nanowires in the as-grown geometry. The polytype distribution along the growth axis of the nanowires was revealed by synchrotron-based nanoprobe x-ray diffraction techniques monitoring the axial 111 Bragg reflection. For the same nanowires, the spatially-resolved emission properties were obtained by cathodoluminescence hyperspectral linescans in a scanning electron microscope. Correlating both measurements, we reveal a blueshift of the shell quantum well emission energy combined with an increased emission intensity for segments exhibiting a mixed structure of alternating wurtzite and zincblende stacking compared with the pure crystal polytypes. The presence of this mixed structure was independently confirmed by cross-sectional transmission electron microscopy., Published by IOP Publ., Bristol
- Published
- 2020
- Full Text
- View/download PDF
6. The Interaction of Extended Defects as the Origin of Step Bunching in Epitaxial III–V Layers on Vicinal Si(001) Substrates
- Author
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Achim Trampert, Eric Tournié, Jean-Baptiste Rodriguez, Laurent Cerutti, Michael Niehle, Paul-Drude-Institut für Festkörperelektronik (PDI), Institut d’Electronique et des Systèmes (IES), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Composants à Nanostructure pour le moyen infrarouge (NANOMIR), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), and ANR-11-EQPX-0016,EXTRA,Centre d'Excellence sur les Antimoniures(2011)
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010302 applied physics ,Threading dislocations ,[PHYS]Physics [physics] ,Number density ,Materials science ,Condensed matter physics ,Material system ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Epitaxy ,01 natural sciences ,[SPI]Engineering Sciences [physics] ,Transmission electron microscopy ,Lattice (order) ,0103 physical sciences ,General Materials Science ,Nanometre ,0210 nano-technology ,Vicinal - Abstract
International audience; Several nanometer high steps are observed by (scanning) transmission electron microscopy at the surface and interfaces in heteroepitaxially grown III-Sb layers on vicinal Si(001) substrates. Their relations with antiphase boundaries (APBs) and threading dislocations (TDs) are elaborated. An asymmetric number density of TDs on symmetry-equivalent {111} lattice planes is revealed and explained according to the substrate miscut and the lattice misfit in the heteroepitaxial material system. Finally, a step bunching mechanism is proposed based on the interplay of APBs, TDs, and the vicinal surface of the miscut substrate.
- Published
- 2019
7. Ordered arrays of defect-free GaN nanocolumns with very narrow excitonic emission line width
- Author
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A. Fernando-Saavedra, D. López-Romero, Achim Trampert, Gordon Schmidt, Michael Niehle, E. Calleja, S. Albert, Juergen Christen, A. Bengoechea-Encabo, F. Bertram, Sebastian Metzner, and M.A. Sanchez-Garcia
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010302 applied physics ,Photoluminescence ,Materials science ,Exciton ,Stacking ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Molecular physics ,Inorganic Chemistry ,Transmission electron microscopy ,0103 physical sciences ,Materials Chemistry ,Emission spectrum ,Dry etching ,0210 nano-technology ,Nanopillar ,Molecular beam epitaxy - Abstract
Ordered arrays of very high quality, defect-free GaN nanocolumns were achieved by selective area growth following a two step process involving nanopillar dry etching (top down) and overgrowth by Molecular Beam Epitaxy (bottom up). A study by transmission electron microscopy, over more than 50 individual nanocolumns, confirmed the absence of extended defects, such as dislocations, polarity inversion domain boundaries and stacking faults. Low temperature (10 K) photoluminescence spectrum is dominated by a donor-bound exciton emission line at 3.472 eV with a line width of 0.5 meV. In addition, a distinct emission line from the free-exciton A is observed at 3.479 eV. No traces of emission lines, either at 2.3 eV (Yellow Band); 3.45 eV (also labeled as UX line and recently linked to polarity inversion domain boundaries); or 3.42 eV (stacking faults) were observed.
- Published
- 2019
8. On the origin of threading dislocations during epitaxial growth of III-Sb on Si(001): A comprehensive transmission electron tomography and microscopy study
- Author
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Eric Tournié, Laurent Cerutti, Michael Niehle, Jean-Baptiste Rodriguez, Achim Trampert, Institut d’Electronique et des Systèmes (IES), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Composants à Nanostructure pour le moyen infrarouge (NANOMIR), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), and Paul-Drude-Institut für Festkörperelektronik (PDI)
- Subjects
010302 applied physics ,Coalescence (physics) ,[PHYS]Physics [physics] ,Materials science ,Polymers and Plastics ,Condensed matter physics ,Metals and Alloys ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,[SPI.MAT]Engineering Sciences [physics]/Materials ,Crystallography ,[SPI]Engineering Sciences [physics] ,Electron tomography ,Transmission electron microscopy ,0103 physical sciences ,Microscopy ,Ceramics and Composites ,Partial dislocations ,0210 nano-technology ,Vicinal ,ComputingMilieux_MISCELLANEOUS ,Wetting layer - Abstract
Electron tomography and complementary (scanning) transmission electron microscopy (STEM) are applied to investigate the origin of threading dislocations in the large lattice misfit, heteroepitaxial system of III-Sb on vicinal Si(001). Buried AlSb islands of the initial wetting layer are revealed at the interface toward the substrate in the three-dimensionally reconstructed data. Locations of island coalescence are retrieved from the tomogram. Complementary (S)TEM measurements reveal the location of threading dislocations and the presence of antiphase boundaries at the same specimen area. The number density of threading dislocations emanating from the interface and their distribution are unexpected. It is shown that the presence of threading dislocations is not simply correlated to sites of AlSb-islands coalescence or to the film closure during the transition from a 3D to a 2D growth. Moreover, an interaction with antiphase boundaries is suggested by the presented observations. Consequently, the contemporary notion of threading dislocation formation is refined and, eventually, it is suggested that measures to avoid antiphase domains and such to reduce threading dislocations have to be balanced for future strategies to epitaxially grow sphalerite structure III-V semiconductors on Si or Ge.
- Published
- 2018
9. Structure and Composition of Isolated Core-Shell(In,Ga)N/GaNRods Based on Nanofocus X-Ray Diffraction and Scanning Transmission Electron Microscopy
- Author
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Achim Trampert, Michael Hanke, Zongzhe Cheng, Maik Kahnt, Christian G. Schroer, Andreas Waag, Lars Nicolai, Hergo-Heinrich Wehmann, Gerald Falkenberg, Hao Zhou, Michael Niehle, Jana Hartmann, and Thilo Krause
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010302 applied physics ,Diffraction ,Materials science ,Scattering ,Shell (structure) ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Rod ,0103 physical sciences ,X-ray crystallography ,Scanning transmission electron microscopy ,Relaxation (physics) ,Deformation (engineering) ,0210 nano-technology - Abstract
Nanofocus x-ray diffraction is used to investigate the structure and local strain field of an isolated ðIn; GaÞN=GaN core-shell microrod. Because the high spatial resolution of the x-ray beam is only 80 × 90 nm2, we are able to investigate several distinct volumes on one individual side facet. Here, we find a drastic increase in thickness of the outer GaN shell along the rod height. Additionally, we performed highangle annular dark-field scanning-transmission-electron-microscopy measurements on several rods from the same sample showing that (In,Ga)N double-quantum-well and GaN barrier thicknesses also increase strongly along the height. Moreover, plastic relaxation is observed in the top part of the rod. Based on the experimentally obtained structural parameters, we simulate the strain-induced deformation using the finiteelement method, which serves as the input for subsequent kinematic scattering simulations. The simulations reveal a significant increase of elastic in-plane relaxation along the rod height. However, at a certain height, the occurrence of plastic relaxation yields a decrease of the elastic strain. Because of the experimentally obtained structural input for the finite-element simulations, we can exclude unknown structural influences on the strain distribution, and we are able to translate the elastic relaxation into an indium concentration which increases by a factor of 4 from the bottom to the height where plastic relaxation occurs.
- Published
- 2017
10. Electron tomography on III-Sb heterostructures on vicinal Si(001) substrates: Anti-phase boundaries as a sink for threading dislocations
- Author
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Laurent Cerutti, Achim Trampert, Jean-Baptiste Rodriguez, Michael Niehle, Eric Tournié, Paul-Drude-Institut für Festkörperelektronik (PDI), Institut d’Electronique et des Systèmes (IES), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Composants à Nanostructure pour le moyen infrarouge (NANOMIR), and Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
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Materials science ,02 engineering and technology ,01 natural sciences ,law.invention ,Condensed Matter::Materials Science ,Planar ,law ,0103 physical sciences ,Antimonide ,Scanning transmission electron microscopy ,General Materials Science ,ComputingMilieux_MISCELLANEOUS ,010302 applied physics ,Condensed matter physics ,Mechanical Engineering ,Metals and Alloys ,Heterojunction ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Laser ,[SPI.TRON]Engineering Sciences [physics]/Electronics ,Electron tomography ,Mechanics of Materials ,0210 nano-technology ,Vicinal ,Molecular beam epitaxy - Abstract
The three-dimensional arrangement of threading dislocations in a III-Sb based mid-infrared laser structure is studied by electron tomography (in a scanning transmission electron microscope). The stack of planar antimonide films which are grown by molecular beam epitaxy on vicinal Si(001) substrates, exhibits an inhomogeneous distribution of threading dislocations. A strong interaction of these line defects with planar defects is revealed. A significant number of dislocations appears to be trapped in anti-phase boundaries which are predominantly parallel to (110) lattice planes. Based on this finding, an explanation for the inhomogeneous distribution of dislocations is established.
- Published
- 2017
11. Rare-earth oxide superlattices on Si(1 1 1)
- Author
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André Proessdorf, Henning Riechert, Wolfgang Braun, Michael Niehle, Achim Trampert, Steffen Behnke, Sergiy M. Bokoch, and Frank Grosse
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Diffraction ,business.industry ,Chemistry ,Superlattice ,Oxide ,Substrate (electronics) ,Condensed Matter Physics ,Epitaxy ,Inorganic Chemistry ,chemistry.chemical_compound ,Optics ,Lanthanum oxide ,Transmission electron microscopy ,Materials Chemistry ,Optoelectronics ,business ,Molecular beam epitaxy - Abstract
Digital epitaxial rare-earth oxide layers are grown on Si(1 1 1) substrates by molecular beam epitaxy at substrate temperatures as low as 200 C. It is demonstrated by X-ray diffraction and transmission electron microscopy that coherent digital layers form with an abrupt interface to the substrate. Theoretical investigations employing density functional theory demonstrate the potential in designing physical properties by strain. The large lattice mismatch of 9% between La 2 O 3 and Lu 2 O 3 allows for an intentional variation of the internal strain in the layers over a wide range.
- Published
- 2011
12. Electron tomography on nanopores embedded in epitaxial GaSb thin films
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Achim Trampert and Michael Niehle
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Materials science ,General Physics and Astronomy ,Nanotechnology ,Heterojunction ,Cell Biology ,Epitaxy ,Focused ion beam ,Nanopore ,Electron tomography ,Structural Biology ,Scanning transmission electron microscopy ,General Materials Science ,Thin film ,Molecular beam epitaxy - Abstract
This work reports on the morphology of nanopores and their spatial position in group III-Sb based multilayer heterostructures grown by molecular beam epitaxy on Si(0 0 1) substrates. By using electron tomography based on dark-field scanning transmission electron microscopy, quantitative information in real space is obtained about individual nanopores unintentionally embedded in GaSb layers. For this purpose adequate needle-shaped samples have to be specifically prepared from the compact material system by focused ion beam. The three-dimensional reconstruction of the probed volume allows the determination of the spatial arrangement of the pores and the analysis of the detailed shape, i.e. the crystallographic facets. Based on these results, the nanopore's geometric shape is discussed with respect to the minimization of surface tension. The formation process can be explained by an agglomeration of vacancies which are generated during the heterostructure growth.
- Published
- 2015
13. Fano-like resonances sustained by Si doped InAsSb plasmonic resonators integrated in GaSb matrix
- Author
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Jean-Baptiste Rodriguez, Achim Trampert, Eric Tournié, Thierry Taliercio, Vilianne Ntsame Guilengui, Michael Niehle, F. Barho, Maria-José Milla Rodrigo, Laurent Cerutti, F. Gonzalez-Posada, Institut d’Electronique et des Systèmes (IES), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Composants à Nanostructure pour le moyen infrarouge (NANOMIR), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), and Paul-Drude-Institut für Festkörperelektronik (PDI)
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Materials science ,business.industry ,Doping ,Surface plasmon ,Physics::Optics ,Substrate (electronics) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Atomic and Molecular Physics, and Optics ,[SPI.TRON]Engineering Sciences [physics]/Electronics ,Condensed Matter::Materials Science ,Resonator ,Semiconductor ,Optics ,Optoelectronics ,business ,Plasmon ,ComputingMilieux_MISCELLANEOUS ,Localized surface plasmon ,Molecular beam epitaxy - Abstract
By using metal-free plasmonics, we report on the excitation of Fano-like resonances in the mid-infrared where the Fano asymmetric parameter, q, varies when the dielectric environment of the plasmonic resonator changes. We use silicon doped InAsSb alloy deposited by molecular beam epitaxy on GaSb substrate to realize the plasmonic resonators exclusively based on semiconductors. We first demonstrate the possibility to realize high quality samples of embedded InAsSb plasmonic resonators into GaSb host using regrowth technique. The high crystalline quality of the deposited structure is confirmed by scanning transmission electron microscopy (STEM) observation. Second, we report Fano-like resonances associated to localized surface plasmons in both cases: uncovered and covered plasmonic resonators, demonstrating a strong line shape modification. The optical properties of the embedded structures correspond to those modeled by finite-difference time-domain (FDTD) method and by a model based on Fano-like line shape. Our results show that all-semiconductor plasmonics gives the opportunity to build new plasmonic structures with embedded resonators of highly doped semiconductor in a matrix of un-doped semiconductor for mid-IR applications.
- Published
- 2015
14. Continuous tuning of two-section, single-mode terahertz quantum-cascade lasers by fiber-coupled, near-infrared illumination
- Author
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Achim Trampert, Martin Hempel, Michael Niehle, Lutz Schrottke, Holger T. Grahn, and Benjamin Röben
- Subjects
010302 applied physics ,Physics ,Facet (geometry) ,business.industry ,Terahertz radiation ,Near-infrared spectroscopy ,Single-mode optical fiber ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,lcsh:QC1-999 ,law.invention ,Optics ,Cascade ,law ,0103 physical sciences ,Optoelectronics ,Fiber ,0210 nano-technology ,business ,Quantum ,lcsh:Physics - Abstract
The dynamical tuning due to rear facet illumination of single-mode, terahertz (THz) quantum-cascade lasers (QCLs) which employ distributed feedback gratings are compared to the tuning of single-mode QCLs based on two-section cavities. The THz QCLs under investigation emit in the range of 3 to 4.7 THz. The tuning is achieved by illuminating the rear facet of the QCL with a fiber-coupled light source emitting at 777 nm. Tuning ranges of 5.0 and 11.9 GHz under continuous-wave and pulsed operation, respectively, are demonstrated for a single-mode, two-section cavity QCL emitting at about 3.1 THz, which exhibits a side-mode suppression ratio better than −25 dB.
- Published
- 2017
15. Oxygen-deficient oxide growth by subliming the oxide source material: The cause of silicide formation in rare earth oxides on silicon
- Author
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Achim Trampert, Frank Grosse, Oliver Bierwagen, Michael Niehle, Max Klingsporn, and André Proessdorf
- Subjects
Silicides ,Materials science ,Interface instability ,Silicon ,Vacuum ,Inorganic chemistry ,Oxygen deficiency ,Sublimation ,Oxide ,chemistry.chemical_element ,Oxygen ,chemistry.chemical_compound ,Rare earth oxide ,Rare-earth silicides ,Silicide ,Rare earths ,Interfaces (materials) ,Stoichiometric films ,General Materials Science ,Oxide thin film growth ,Thin film ,Oxide films ,Oxygen stoichiometry ,General Chemistry ,Condensed Matter Physics ,Silicide formation ,chemistry ,Phase transitions ,Vapors ,Sublimation (phase transition) ,Molecular beam epitaxy ,Stoichiometry - Abstract
The fundamental issue of oxygen stoichiometry in oxide thin film growth by subliming the source oxide is investigated by varying the additionally supplied oxygen during molecular beam epitaxy of RE2O3 (RE = Gd, La, Lu) thin films on Si(111). Supplying additional oxygen throughout the entire growth was found to prevent the formation of rare earth silicides observed in films grown without an oxygen source. Postgrowth vacuum annealing of oxygen stoichiometric films did not lead to silicide formation thereby confirming that the silicides do not form as a result of an interface instability at growth temperature in vacuum but rather due to an oxygen deficiency in the source vapor. The average oxygen deficiency of the rare-earth containing species in the source vapor was quantified by the 18O tracer technique and correlated with that of the source material, which gradually decomposed during sublimation. Therefore, any oxide growth by sublimation of the oxide source material requires additional oxygen to realize oxygen stoichiometric films.
- Published
- 2013
- Full Text
- View/download PDF
16. Nanofocus x-ray diffraction and cathodoluminescence investigations into individual core–shell (In,Ga)N/GaN rod light-emitting diodes
- Author
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Manfred Burghammer, Martin Rosenthal, Hao Zhou, Hergo-Heinrich Wehmann, Michael Niehle, Achim Trampert, Michael Hanke, Zongzhe Cheng, Johannes Ledig, Andreas Waag, Thilo Krause, and Jana Hartmann
- Subjects
Diffraction ,Materials science ,chemistry.chemical_element ,Bioengineering ,Cathodoluminescence ,02 engineering and technology ,01 natural sciences ,law.invention ,Optics ,law ,0103 physical sciences ,General Materials Science ,Electrical and Electronic Engineering ,010302 applied physics ,Beam diameter ,business.industry ,Scattering ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Wavelength ,chemistry ,Mechanics of Materials ,X-ray crystallography ,0210 nano-technology ,business ,Indium ,Light-emitting diode - Abstract
Employing nanofocus x-ray diffraction, we investigate the local strain field induced by a five-fold (In,Ga)N multi-quantum well embedded into a GaN micro-rod in core-shell geometry. Due to an x-ray beam width of only 150 nm in diameter, we are able to distinguish between individual m-facets and to detect a significant in-plane strain gradient along the rod height. This gradient translates to a red-shift in the emitted wavelength revealed by spatially resolved cathodoluminescence measurements. We interpret the result in terms of numerically derived in-plane strain using the finite element method and subsequent kinematic scattering simulations which show that the driving parameter for this effect is an increasing indium content towards the rod tip.
- Published
- 2016
17. Strain dynamics during La2O3/Lu2O3 superlattice and alloy formation
- Author
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Peter Rodenbach, Michael Niehle, Frank Grosse, Achim Trampert, Michael Hanke, and André Proessdorf
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010302 applied physics ,Materials science ,Condensed matter physics ,Superlattice ,General Physics and Astronomy ,02 engineering and technology ,Crystal structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallographic defect ,Dark field microscopy ,Condensed Matter::Materials Science ,Crystallography ,Transmission electron microscopy ,0103 physical sciences ,Scanning transmission electron microscopy ,0210 nano-technology ,High-resolution transmission electron microscopy ,Molecular beam epitaxy - Abstract
The dynamics of strain relaxation and intermixing during molecular beam epitaxy of La2O3 and Lu2O3 superlattices and alloys consisting of both binaries on Si(111) have been studied by real-time in situ grazing incidence x-ray diffraction and high resolution transmission electron microscopy. The presence of both hexagonal and cubic polymorphs of La2O3 influences the epitaxial formation within the superlattice. The process of strain relaxation is closely related to the presence of a (La,Lu)2O3 alloy adopting a cubic symmetry. It is formed by interdiffusion of La and Lu atoms reducing internal lattice mismatch within the superlattice. An interface thickness dominated by interdiffusion regions of about 3 monolayers is determined by high-angle annular dark field scanning transmission electron microscopy.
- Published
- 2016
18. Delayed crystallization of ultrathin Gd2O3 layers on Si(111) observed by in situ X-ray diffraction
- Author
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Vladimir M. Kaganer, Achim Trampert, Michael Niehle, Michael Hanke, and Oliver Bierwagen
- Subjects
Diffraction ,Reflection high-energy electron diffraction ,Materials science ,Nano Express ,Analytical chemistry ,Nanotechnology ,Condensed Matter Physics ,Epitaxy ,Bixbyite ,law.invention ,Condensed Matter::Materials Science ,Materials Science(all) ,Electron diffraction ,law ,X-ray crystallography ,General Materials Science ,Crystallization ,Electron backscatter diffraction - Abstract
We studied the early stages of Gd2O3 epitaxy on Si(111) in real time by synchrotron-based, high-resolution X-ray diffraction and by reflection high-energy electron diffraction. A comparison between model calculations and the measured X-ray scattering, and the change of reflection high-energy electron diffraction patterns both indicate that the growth begins without forming a three-dimensional crystalline film. The cubic bixbyite structure of Gd2O3 appears only after a few monolayers of deposition.
- Published
- 2012
19. Epitaxial polymorphism of La2O3 on Si(111) studied by in situ x-ray diffraction
- Author
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Michael Hanke, Michael Niehle, Vladimir M. Kaganer, F. Grosse, Oliver Bierwagen, André Proessdorf, and Achim Trampert
- Subjects
Diffraction ,Crystallography ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Transmission electron microscopy ,X-ray crystallography ,Crystal growth ,High-resolution transmission electron microscopy ,Epitaxy ,Bixbyite ,Surface energy - Abstract
The phase formation of La2O3 epitaxial films during growth on Si(111) is investigated by synchrotron-based in situ grazing incidence x-ray diffraction and high resolution transmission electron microscopy. We find that first a 2–4 nm thick cubic bixbyite La2O3 layer grows at the interface to Si(111) substrate, followed by a hexagonal La2O3 film. Hence, to keep a cubic on cubic heteroepitaxy and to achieve high quality epitaxial nanostructures or multi-layers, the thickness of the interfacial La2O3 layer has to be restricted to 2 nm. The larger formation energy of the cubic phase can only partially be compensated by the biaxial strain in the epitaxial film based on density functional perturbation theory. Hence, the stabilization of the cubic phase is not due to bulk strain but could be related to a lower surface or interface free energy, or to kinetic effects.
- Published
- 2014
20. Atomic interface structure of bixbyite rare-earth sesquioxides grown epitaxially on Si(1 1 1)
- Author
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Michael Niehle and Achim Trampert
- Subjects
Lanthanide ,Materials science ,Acoustics and Ultrasonics ,Oxide ,Analytical chemistry ,Condensed Matter Physics ,Bixbyite ,Epitaxy ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Crystallography ,chemistry ,Transmission electron microscopy ,Lattice (order) ,Thin film ,High-resolution transmission electron microscopy - Abstract
High-resolution transmission electron microscopy (HRTEM) is applied to thin crystalline films of (Gd1−x Lu x )2O3 and (La1−x Lu x )2O3 on Si(1 1 1). Electron micrographs confirm that an atomically smooth and chemically abrupt interface of epitaxially grown rare-earth thin films is feasible. This work demonstrates an unambiguous recognition of cubic bixbyite, which is the common cubic phase of rare-earth sesquioxides at room temperature except for the light lanthanoids. This serves as prerequisite to analyse the atomic configuration of the cubic oxide lattice at the interface to the Si(1 1 1) surface. Two new configurations which have not been considered yet, are proposed and proved by comparison of experimental HRTEM images and contrast simulations.
- Published
- 2012
21. Nanofocus x-ray diffraction and cathodoluminescence investigations into individual core–shell (In,Ga)N/GaN rod light-emitting diodes.
- Author
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Thilo Krause, Michael Hanke, Zongzhe Cheng, Michael Niehle, Achim Trampert, Martin Rosenthal, Manfred Burghammer, Johannes Ledig, Jana Hartmann, Hao Zhou, Hergo-Heinrich Wehmann, and Andreas Waag
- Subjects
X-ray diffraction ,CATHODOLUMINESCENCE ,LIGHT emitting diodes ,OPTICAL properties of gallium nitride ,SCATTERING (Physics) ,FINITE element method ,WAVELENGTHS ,KINEMATICS - Abstract
Employing nanofocus x-ray diffraction, we investigate the local strain field induced by a five-fold (In,Ga)N multi-quantum well embedded into a GaN micro-rod in core–shell geometry. Due to an x-ray beam width of only 150 nm in diameter, we are able to distinguish between individual m-facets and to detect a significant in-plane strain gradient along the rod height. This gradient translates to a red-shift in the emitted wavelength revealed by spatially resolved cathodoluminescence measurements. We interpret the result in terms of numerically derived in-plane strain using the finite element method and subsequent kinematic scattering simulations which show that the driving parameter for this effect is an increasing indium content towards the rod tip. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
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