1,720,968 research outputs found
Influence of sub-nm scale dimensional control on the Er3+ luminescence properties of Er-dopedSi/SiO2 superlattices
No full textThe Er3+ photoluminescent properties of Er-doped Si/SiO2 superlattices in which the location of Er atoms and layer thickness were controlled with sub-nm precision are investigated. The superlattices were deposited either by ultra-high vaccum(UHV) ion beam sputter deposition or electron-cyclotron resonance plasma-enhanced chemical vapor deposition(ECR-PECVI) method with a subsequent anneal at 950 degreesC. Er was doped only into the SiO2 layers whose thickness was fixed. The Er-carrier interaction was controlled by either depositing nm-thin buffer layers of pure SiO2 or by varying the thickness of the Si layers from 0.6 to 3.6 nm. The structure and the composition of the films were confirmed using transmission electron microscopy(TEM) and medium energy ion scattering spectroscopy(MEIS). We find that the Er3+ luminescence increases very strongly as the buffer layer thickness is increased, even though the excitation of Er3+ ions occurs through carriers generated in Si layers. Furthermore, Er3+ luminescence can be increased even further by decreasing the Si layer thickness down to the limit of one monolayer of Si. This demonstrates that with sub-nm scale dimensional control on the environment of Er atoms, we can achieve substantial enhancement in Er3+ luminescence
The electronic energy loss of 100 keV heavy ions in medium energy ion scattering analysis of a Ta2O5 ultrathin film
No full textTo optimize the depth resolution of Medium Energy Ion Scattering Spectroscopy (MEIS), a 10 nm Ta2O5 thin film on a Si(100) substrate was analyzed by MEIS using H+ and heavy ions such as Li+, N+ and Ne+ ions. The use of heavy ions such as Li+ and N+ increased the electronic stopping powers 2-3 times but it also increased the electronic straggling compared to H+ ions, For Nef ions, the ion neutralization problem was so severe that the scattering ion intensity from the subsurface layer was attenuated very rapidly and a strong doubly ionized Ne++ peak was observed. For 100 keV N+ and Ne+ ions, multiple scattering peaks were observed.The work is supported financially from the center for molecular science, south korea
Low sputter damage of metal single crystalline surfaces investigated with medium energy ion scattering spectroscopy
No full textIt was observed clearly that the sputter damage due to Ar+ ion bombardment on metal single crystalline surfaces is extremely low and the local surface atomic structure is preserved, which is totally different from semiconductor single crystalline surfaces. Medium energy ion scattering spectroscopy (MEIS) shows that there is little irradiation damage on the metal single crystalline surfaces such as Pt(111), Pt(100), arnd Cu(111), in contrast to the semiconductor Si(100) surfaces, for the ion energy of 3-7 keV even above 10(16)-10(17) ions/cm(2) ion doses at room temperature. However, low energy electron diffraction (LEED) spots became blurred after bombardment. Transmission Electron Microscopy (TEM) studies of a Pt polycrystalline thin film showed formation of dislocations after sputtering. Complementary MEIS, LEED and TEM data show that on sputtered single-crystal metal surfaces, metal atoms recrystallize at room temperature after each ion impact. After repeated ion impacts, local defects accumulate to degrade long range orders. (C) 1999 Elsevier Science B.V. All rights reserved.Financial supports from Ministry of Science and
Technology, Korea through Nanostructure Technology
Project and Center for Molecular Science, Korea
are appreciated
A medium energy ion scattering analysis of the Si-SiO2 interface formed by ion beam oxidation of silicon
No full textThe Si-SiO2 interface formed by 3 keV O-2(+) ion bombardment on silicon at room temperature and 600 degrees C was studied by in situ medium energy ion scattering spectroscopy (MEIS). The amorphization process at the initial stage of the oxygen ion bombardment and the subsequent formation of the suboxide layer and the disordered silicon layer at the Si-SiO2 interface were studied as a function of the ion dose from 2.5 X 10(15) atoms/cm(2) to 5 X 10(17) atoms/cm(2) at room temperature and 600 degrees C. After reaching the steady state, below a similar to 6 nm SiO2 layer, a similar to 2 nm suboxide layer and a similar to 3 nm disordered Si layer were observed at the Si-SiO2 interface. The annealing effect at 600 degrees C decreased the number of disordered silicon atoms and the suboxide silicon atoms, which make the Si-SiO2 interface more abrupt, was more clearly observed at the initial stage of the bombardment.Financial supports from the Center for Molecular
Science, Korea, and the Ministry of Science and
Technology, Korea, are appreciated
Atomic scale investigations of the Co/Pt(111) interface structure and magnetic properties
No full textThe interface structure of an ultrathin Co overlayer on a Pt(111) crystal was investigated with atomic-layer resolution medium-energy ion scattering spectroscopy and surface magneto-optical Kerr effect (SMOKE). For a 7 ML Co, interdiffusion begins at 673 K to form a heavily distorted Co-Pt surface alloy layer with little change in SMOKE intensity. However, annealing at 773 K formed a 30 atomic-layer-thick Co-Pt substitutional alloy with 3.7% maximum tensile strain, at which the SMOKE intensity increased more than 200%. The enhancement of the Kerr intensity is discussed with the interface alloy formation. (C) 2001 American Institute of Physics.This work was supported in part by MOST of Korea
through the National Research Laboratory program and the
Creative Research Initiatives project
Relaxation of the Si lattice strain in the Si(001)-SiO2 interface by annealing in N2O
No full textIt was clearly observed with medium energy ion scattering spectroscopy that the strain in the Si(001)-SiO2 interface of thermal oxides is relaxed by annealing in N2O. The strain relaxation could be correlated with the improved hot-electron hardness of the nitrided oxides compared with the thermal oxides. Based on the direct observation of the strain relaxation, it is suggested that the incorporated N atoms at the interface release the strain and increase the immunity of trap generation under the current stress. (C) 1999 American Institute of Physics. [S0003-6951(99)04523-4].Financial support from the Center for Molecular Science,
Korea, and the Ministry of Science and Technology,
Korea through Nanostructure Technology Project is acknowledge
Ultrathin Co films on Pt(111) and the Co-Pt interface investigated by surface magneto-optical Kerr effect and medium-energy ion scattering spectroscopy
No full textMagnetic anisotropy evolution of ultrathin Co films grown on a Pt(111) single-crystal surface is investigated by a UHV in situ surface magneto-optical Kerr effect (SMOKE) measurement. Perpendicular magnetic anisotropy in ultrathin Co films is found to be persistent up to a thickness of 12 ML where the easy magnetization axis changes its orientation to an in-plane direction. The interface structure of an ultrathin Co overlayer on Pt(111) was investigated with atomic-layer resolution medium-energy ion scattering spectroscopy. For 7-ML Co, interdiffusion begins at 673 K to form a heavily distorted Co-Pt surface alloy layer with little change in SMOKE intensity. However, annealing at 773 K formed a 30-atomic-layers thick Co-Pt substitutional alloy with tensile strain, at which the SMOKE intensity increased by more than 200%. The enhancement of the Kerr intensity is discussed with the interface alloy formation.This work was supported by MOST of Korea through the
Creative Research Initiative Project and the National Research
Laboratory Program
A medium energy ion scattering analysis of the Si-SiO2 interface formed by ion beam oxidation of silicon
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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