The Experts below are selected from a list of 84069 Experts worldwide ranked by ideXlab platform
Werner Seifert - One of the best experts on this subject based on the ideXlab platform.
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correlation lengths in stacked inas quantum dot systems studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2007Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, J M Ulloa, P Paul M Koenraad, Werner SeifertAbstract:We have studied the influence of the InP spacer layer thickness on stacked InAs/InP quantum dots, using cross-sectional Scanning Tunnelling Microscopy. We show that for a spacer layer thickness of up to 30 nm, the quantum dots are spatially correlated but for a separating distance of 50 nm the vertical ordering of the dots is lost. These values are the same as previously found for quantum dots in the InAs/GaAs system despite the large difference in lattice mismatch between the InAs/GaAs ( 7%) and InAs/InP ( 3%) systems. We show that the apparent similarities can be understood by a combination of intermixing in the dots and differences in dot size. Finally, we demonstrate that the size of the quantum dots is affected by their vertical correlation.
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stacked inas quantum dots in inp studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2004Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, Werner SeifertAbstract:We report on cross-sectional Scanning Tunnelling Microscopy (XSTM) measurements on vertically stacked InAs quantum dots in InP barriers. We have investigated two-, five- and tenfold stacked quantum dot structures,grown by low-pressure metal-organic vapour phase epitaxy. The XSTM images reveal that the quantum dots are generally vertically well aligned, and have a truncated pyramidal shape in agreement with similar studies of InAs dots in GaAs. STM images displaying atomic resolution indicate that the dots have a pure InAs stoichiometry, with intermixing only occurring in the top and bottom dot rows. Further, we have investigated various anomalies (considered as defects) as observed in the quantum dot stacks. The origins of these anomalies are discussed and compared to theoretical predictions available so far. (Less)
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direct imaging of the atomic structure inside a nanowire by Scanning Tunnelling Microscopy
Nature Materials, 2004Co-Authors: Anders Mikkelsen, Lassana Ouattara, Magnus T Borgstrom, Lars Samuelson, Werner Seifert, Niklas Skold, Jesper N Andersen, Edvin LundgrenAbstract:Semiconductor nanowires are expected to be important components in future nano-electronics and photonics1,2. Already a wide range of applications has been realized, such as high-performance field-effect transistors3, bio/chemical sensors4, diode logics5,6 and single-nanowire lasers7. As nanowires have small cross-sections and large surface-to-bulk ratios, their properties can be significantly influenced by individual atomic-scale structural features3,7,8,9, and they can have properties9 or even atomic arrangements10 with no bulk counterparts. Hence, experimental methods capable of directly addressing the atomic-scale structure of nanowires are highly desirable. One such method is Scanning Tunnelling Microscopy (STM), which, by direct imaging of the atomic and electronic structure of surfaces has revolutionized the perception of nanoscale objects and low-dimensional systems11,12. Here we demonstrate how combining STM with an embedding scheme allows us to image the interior of semiconductor nanowires with atomic resolution. Defect structures such as planar twin segments and single-atom impurities are imaged inside a GaAs nanowire. Further, we image an intriguing GaAs nanowire that is separated into two distinct nanocrystallites along the growth direction of the wire.
Lassana Ouattara - One of the best experts on this subject based on the ideXlab platform.
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correlation lengths in stacked inas quantum dot systems studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2007Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, J M Ulloa, P Paul M Koenraad, Werner SeifertAbstract:We have studied the influence of the InP spacer layer thickness on stacked InAs/InP quantum dots, using cross-sectional Scanning Tunnelling Microscopy. We show that for a spacer layer thickness of up to 30 nm, the quantum dots are spatially correlated but for a separating distance of 50 nm the vertical ordering of the dots is lost. These values are the same as previously found for quantum dots in the InAs/GaAs system despite the large difference in lattice mismatch between the InAs/GaAs ( 7%) and InAs/InP ( 3%) systems. We show that the apparent similarities can be understood by a combination of intermixing in the dots and differences in dot size. Finally, we demonstrate that the size of the quantum dots is affected by their vertical correlation.
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stacked inas quantum dots in inp studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2004Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, Werner SeifertAbstract:We report on cross-sectional Scanning Tunnelling Microscopy (XSTM) measurements on vertically stacked InAs quantum dots in InP barriers. We have investigated two-, five- and tenfold stacked quantum dot structures,grown by low-pressure metal-organic vapour phase epitaxy. The XSTM images reveal that the quantum dots are generally vertically well aligned, and have a truncated pyramidal shape in agreement with similar studies of InAs dots in GaAs. STM images displaying atomic resolution indicate that the dots have a pure InAs stoichiometry, with intermixing only occurring in the top and bottom dot rows. Further, we have investigated various anomalies (considered as defects) as observed in the quantum dot stacks. The origins of these anomalies are discussed and compared to theoretical predictions available so far. (Less)
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direct imaging of the atomic structure inside a nanowire by Scanning Tunnelling Microscopy
Nature Materials, 2004Co-Authors: Anders Mikkelsen, Lassana Ouattara, Magnus T Borgstrom, Lars Samuelson, Werner Seifert, Niklas Skold, Jesper N Andersen, Edvin LundgrenAbstract:Semiconductor nanowires are expected to be important components in future nano-electronics and photonics1,2. Already a wide range of applications has been realized, such as high-performance field-effect transistors3, bio/chemical sensors4, diode logics5,6 and single-nanowire lasers7. As nanowires have small cross-sections and large surface-to-bulk ratios, their properties can be significantly influenced by individual atomic-scale structural features3,7,8,9, and they can have properties9 or even atomic arrangements10 with no bulk counterparts. Hence, experimental methods capable of directly addressing the atomic-scale structure of nanowires are highly desirable. One such method is Scanning Tunnelling Microscopy (STM), which, by direct imaging of the atomic and electronic structure of surfaces has revolutionized the perception of nanoscale objects and low-dimensional systems11,12. Here we demonstrate how combining STM with an embedding scheme allows us to image the interior of semiconductor nanowires with atomic resolution. Defect structures such as planar twin segments and single-atom impurities are imaged inside a GaAs nanowire. Further, we image an intriguing GaAs nanowire that is separated into two distinct nanocrystallites along the growth direction of the wire.
Edvin Lundgren - One of the best experts on this subject based on the ideXlab platform.
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correlation lengths in stacked inas quantum dot systems studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2007Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, J M Ulloa, P Paul M Koenraad, Werner SeifertAbstract:We have studied the influence of the InP spacer layer thickness on stacked InAs/InP quantum dots, using cross-sectional Scanning Tunnelling Microscopy. We show that for a spacer layer thickness of up to 30 nm, the quantum dots are spatially correlated but for a separating distance of 50 nm the vertical ordering of the dots is lost. These values are the same as previously found for quantum dots in the InAs/GaAs system despite the large difference in lattice mismatch between the InAs/GaAs ( 7%) and InAs/InP ( 3%) systems. We show that the apparent similarities can be understood by a combination of intermixing in the dots and differences in dot size. Finally, we demonstrate that the size of the quantum dots is affected by their vertical correlation.
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stacked inas quantum dots in inp studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2004Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, Werner SeifertAbstract:We report on cross-sectional Scanning Tunnelling Microscopy (XSTM) measurements on vertically stacked InAs quantum dots in InP barriers. We have investigated two-, five- and tenfold stacked quantum dot structures,grown by low-pressure metal-organic vapour phase epitaxy. The XSTM images reveal that the quantum dots are generally vertically well aligned, and have a truncated pyramidal shape in agreement with similar studies of InAs dots in GaAs. STM images displaying atomic resolution indicate that the dots have a pure InAs stoichiometry, with intermixing only occurring in the top and bottom dot rows. Further, we have investigated various anomalies (considered as defects) as observed in the quantum dot stacks. The origins of these anomalies are discussed and compared to theoretical predictions available so far. (Less)
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direct imaging of the atomic structure inside a nanowire by Scanning Tunnelling Microscopy
Nature Materials, 2004Co-Authors: Anders Mikkelsen, Lassana Ouattara, Magnus T Borgstrom, Lars Samuelson, Werner Seifert, Niklas Skold, Jesper N Andersen, Edvin LundgrenAbstract:Semiconductor nanowires are expected to be important components in future nano-electronics and photonics1,2. Already a wide range of applications has been realized, such as high-performance field-effect transistors3, bio/chemical sensors4, diode logics5,6 and single-nanowire lasers7. As nanowires have small cross-sections and large surface-to-bulk ratios, their properties can be significantly influenced by individual atomic-scale structural features3,7,8,9, and they can have properties9 or even atomic arrangements10 with no bulk counterparts. Hence, experimental methods capable of directly addressing the atomic-scale structure of nanowires are highly desirable. One such method is Scanning Tunnelling Microscopy (STM), which, by direct imaging of the atomic and electronic structure of surfaces has revolutionized the perception of nanoscale objects and low-dimensional systems11,12. Here we demonstrate how combining STM with an embedding scheme allows us to image the interior of semiconductor nanowires with atomic resolution. Defect structures such as planar twin segments and single-atom impurities are imaged inside a GaAs nanowire. Further, we image an intriguing GaAs nanowire that is separated into two distinct nanocrystallites along the growth direction of the wire.
Anders Mikkelsen - One of the best experts on this subject based on the ideXlab platform.
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correlation lengths in stacked inas quantum dot systems studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2007Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, J M Ulloa, P Paul M Koenraad, Werner SeifertAbstract:We have studied the influence of the InP spacer layer thickness on stacked InAs/InP quantum dots, using cross-sectional Scanning Tunnelling Microscopy. We show that for a spacer layer thickness of up to 30 nm, the quantum dots are spatially correlated but for a separating distance of 50 nm the vertical ordering of the dots is lost. These values are the same as previously found for quantum dots in the InAs/GaAs system despite the large difference in lattice mismatch between the InAs/GaAs ( 7%) and InAs/InP ( 3%) systems. We show that the apparent similarities can be understood by a combination of intermixing in the dots and differences in dot size. Finally, we demonstrate that the size of the quantum dots is affected by their vertical correlation.
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stacked inas quantum dots in inp studied by cross sectional Scanning Tunnelling Microscopy
Nanotechnology, 2004Co-Authors: Lassana Ouattara, Anders Mikkelsen, Edvin Lundgren, Magnus T Borgstrom, Lars Samuelson, Werner SeifertAbstract:We report on cross-sectional Scanning Tunnelling Microscopy (XSTM) measurements on vertically stacked InAs quantum dots in InP barriers. We have investigated two-, five- and tenfold stacked quantum dot structures,grown by low-pressure metal-organic vapour phase epitaxy. The XSTM images reveal that the quantum dots are generally vertically well aligned, and have a truncated pyramidal shape in agreement with similar studies of InAs dots in GaAs. STM images displaying atomic resolution indicate that the dots have a pure InAs stoichiometry, with intermixing only occurring in the top and bottom dot rows. Further, we have investigated various anomalies (considered as defects) as observed in the quantum dot stacks. The origins of these anomalies are discussed and compared to theoretical predictions available so far. (Less)
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direct imaging of the atomic structure inside a nanowire by Scanning Tunnelling Microscopy
Nature Materials, 2004Co-Authors: Anders Mikkelsen, Lassana Ouattara, Magnus T Borgstrom, Lars Samuelson, Werner Seifert, Niklas Skold, Jesper N Andersen, Edvin LundgrenAbstract:Semiconductor nanowires are expected to be important components in future nano-electronics and photonics1,2. Already a wide range of applications has been realized, such as high-performance field-effect transistors3, bio/chemical sensors4, diode logics5,6 and single-nanowire lasers7. As nanowires have small cross-sections and large surface-to-bulk ratios, their properties can be significantly influenced by individual atomic-scale structural features3,7,8,9, and they can have properties9 or even atomic arrangements10 with no bulk counterparts. Hence, experimental methods capable of directly addressing the atomic-scale structure of nanowires are highly desirable. One such method is Scanning Tunnelling Microscopy (STM), which, by direct imaging of the atomic and electronic structure of surfaces has revolutionized the perception of nanoscale objects and low-dimensional systems11,12. Here we demonstrate how combining STM with an embedding scheme allows us to image the interior of semiconductor nanowires with atomic resolution. Defect structures such as planar twin segments and single-atom impurities are imaged inside a GaAs nanowire. Further, we image an intriguing GaAs nanowire that is separated into two distinct nanocrystallites along the growth direction of the wire.
Hidemi Shigekawa - One of the best experts on this subject based on the ideXlab platform.
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probing ultrafast spin dynamics with optical pump probe Scanning Tunnelling Microscopy
Nature Nanotechnology, 2014Co-Authors: Shoji Yoshida, Yuta Aizawa, Zihan Wang, Ryuji Oshima, Yutaka Mera, Eiji Matsuyama, Haruhiro Oigawa, Osamu Takeuchi, Hidemi ShigekawaAbstract:Studies of spin dynamics in low-dimensional systems are important from both fundamental and practical points of view. Spin-polarized Scanning Tunnelling Microscopy allows localized spin dynamics to be characterized and plays important roles in nanoscale science and technology. However, nanoscale analysis of the ultrafast dynamics of itinerant magnetism, as well as its localized characteristics, should be pursued to advance further the investigation of quantum dynamics in functional structures of small systems. Here, we demonstrate the optical pump-probe Scanning Tunnelling Microscopy technique, which enables the nanoscale probing of spin dynamics with the temporal resolution corresponding, in principle, to the optical pulse width. Spins are optically oriented using circularly polarized light, and their dynamics are probed by Scanning Tunnelling Microscopy based on the optical pump-probe method. Spin relaxation in a single quantum well with a width of 6 nm was observed with a spatial resolution of ∼ 1 nm. In addition to spin relaxation dynamics, spin precession, which provides an estimation of the Lande g factor, was observed successfully.
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laser combined Scanning Tunnelling Microscopy for probing ultrafast transient dynamics
Journal of Physics: Condensed Matter, 2010Co-Authors: Yasuhiko Terada, Shoji Yoshida, Osamu Takeuchi, Hidemi ShigekawaAbstract:The development of time-resolved Scanning Tunnelling Microscopy (STM), in particular, attempts to combine STM with ultrafast laser technology, is reviewed with emphasis on observed physical quantities and spatiotemporal resolution. Ultrashort optical pulse technology has allowed us to observe transient phenomena in the femtosecond range, which, however, has the drawback of a relatively low spatial resolution due to the electromagnetic wavelength used. In contrast, STM and its related techniques, although the time resolution is limited by the circuit bandwidth (∼100 kHz), enable us to observe structures at the atomic level in real space. Our purpose has been to combine these two techniques to achieve a new technology that satisfies the requirements for exploring the ultrafast transient dynamics of the local quantum functions in organized small structures, which will advance the pursuit of future nanoscale scientific research in terms of the ultimate temporal and spatial resolutions.
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ultrafast photoinduced carrier dynamics in ganas probed using femtosecond time resolved Scanning Tunnelling Microscopy
Nanotechnology, 2007Co-Authors: Yasuhiko Terada, Osamu Takeuchi, Masahiro Aoyama, Hiroyuki Kondo, Atsushi Taninaka, Hidemi ShigekawaAbstract:The combination of Scanning Tunnelling Microscopy (STM) with optical excitation using ultrashort laser pulses enables us, in principle, to simultaneously obtain ultimate spatial and temporal resolutions. We have developed the shaken-pulse-pair-excited STM (SPPX-STM) and succeeded in detecting a weak time-resolved Tunnelling current signal from a low-temperature-grown GaNAs sample. To clarify the underlying physics in SPPX-STM measurements, we performed optical pump‐probe reflectivity measurements with a wavelength-changeable ultrashort-pulse laser. By comparing the results obtained from the two methods with an analysis based on the nonlinear relationship between the photocarrier density and Tunnelling current, we obtained a comprehensive explanation that the photocarrier dynamics is reflected in the SPPX-STM signal through the surface photovoltage effect. (Some figures in this article are in colour only in the electronic version)
