1,720,980 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
Quantitative analysis of mixed self-assembled monolayers using ToF-SIMS
No full textThe spacing of chemical functional groups on self-assembled monolayers (SAMs) plays an important role in controlling the density of biomolecules in biochips and biosensors. In this sense, a mixed SAM made of two different terminal groups is a useful organic surface since spacing can be easily controlled by changing a relative mole fraction in a mixture solution. In this study, an acetylene-OCH(2)O(EG)(3)(CH(2))(11)S-S(CH(2))(11)(EG)(3)OCH(2)O-propene (Eneyne) SAM and mixed SAMs made by a mixture of (S(CH(2))(11)(EG)(3)O-CH(2)O-acetylene)(2) (Diyne) and (S(CH(2))(11)(EG)(3)OCH(2)O-propene)(2) (Diene) were produced on gold substrates and measured by using ToF-SIMS. The secondary ion yield ratio of [Au center dot S(CH(2))(11)(EG)(3)O-11(EG)(3)OCH(2)O-acetylene] to [Au center dot S(CH(2))(11)(EG)(3)OCH(2)O-propene] was measured for each mixed SAM and plotted as a function of the mole fraction of Diyne to Diene in a SAM solution. The ion yield ratio of a mixed SAM produced from a solution with a mole fraction of 0.5 (i.e., 1:1 mixture) was 0.3, which corresponded well to the ion yield ratio measured from an Eneyne SAM. A time-dependent experiment of Eneyne SAM formation and immersion experiment of Eneyne SAM into Diyne solution or into Diene solution were performed. The relative ion yield ratio of 0.3 was due to a different secondary ion formation and not due to the difference in the amount of adsorbates on the surface, nor to the different binding strengths onto the gold surface. Our study shows that a mixed SAM with well-controlled spacing can be produced and quantified by using the ToF-SIMS technique. (C) 2008 Elsevier B. V. All rights reserved
Strain-induced anisotropic Ge diffusion in SiGe/Si superlattices
No full textAnisotropic diffusion of Ge induced by nonuniform strain in SiGe/Si interfaces in the range of 700-850 degreesC is directly observed with medium-energy ion-scattering spectroscopy through its composition and strain profiles of atomic-layer depth resolution. For SiGe/Si interfaces with identical composition profiles but with different strain distributions, the anisotropic diffusion of Ge can be clearly correlated with the anisotropic relaxation of the nonuniform strain in the near-surface layer of several nm depth. The results suggest that atomic-scale strain control is critical to maintain abrupt SiGe/Si interfaces under thermal budget. (C) 2002 American Institute of Physics
Strain-induced diffusion in a strained Si1−xGex/Si heterostructure
Full text linkDiffusivity of a strained heterostructure was theoretically investigated, and general diffusion equations with strain potential were deduced. There was an additional diffusivity by the strain potential gradient as well as by the concentration gradient. The strain-induced diffusivity was a function of concentration, and its temperature dependence was formulated. The activation energy of the strain-induced diffusivity was measured by high-resolution transmission electron microscopy. This result can be generally applied for the investigation of the diffusion in strained heterostructures. (C) 2000 American Institute of Physics. [S0003- 6951(00)02247-6]
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
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
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