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Journal ArticleDOI

XPS study of ion‐beam‐assisted formation of Si nanostructures in thin SiO2 layers

01 Dec 2002-Surface and Interface Analysis (John Wiley & Sons, Ltd)-Vol. 33, Iss: 12, pp 914-917
TL;DR: In this article, X-ray photoelectron spectroscopy (XPS) was used to monitor the composition changes caused in the layers by bombardment with 3 keV Ar ions at elevated temperatures.
Abstract: Thin thermally grown SiO 2 layers have been enriched with Si up to ∼15 at.% by Si ion implantation at room temperature. X-ray photoelectron spectroscopy (XPS) was used to monitor the composition changes caused in the layers by bombardment with 3 keV Ar ions at elevated temperatures. Argon ion irradiation of pure SiO 2 does not lead to the formation of Si nanoprecipitates. That was the case also for room-temperature Ar bombardment of Si-rich layers. Their'hot' irradiation with Ar ions was found to enhance considerably the formation of segregated Si nanophase inclusions. The process starts at ∼500°C and becomes strongly pronounced at 650°C. At this temperature ion-beam-induced crystallization of Si nanoprecipitates may be achieved. The results obtained are explained in the framework of the physical model, based on the irradiation-enhanced diffusion of excess Si atoms.
Citations
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Journal ArticleDOI
TL;DR: This sample shows an initial discharge capacity of 2279 mA h g(-1) with a Coulombic efficiency of 92% and displays 83% capacity retention after 50 cycles at 0.2C rate.
Abstract: Amorphous SiO2 coating layers with thicknesses of ca. 2, 7, 10, and 15 nm are introduced into bulk@nanowire core@shell Si particles via direct thermal oxidation at 650-850 °C. Of the coated samples, Si with a coating thickness of ca. 7 nm has the best electrochemical performance. This sample shows an initial discharge capacity of 2279 mA h g(-1) with a Coulombic efficiency of 92% and displays 83% capacity retention after 50 cycles at 0.2C rate.

233 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used X-ray photoelectron spectroscopy (XPS), depthprofiling, and spectroscopic ellipsometry (SE) to evaluate the surface/interface chemistry, Y-O bonding, and optical constants of the Y2O3 film surface and interface.
Abstract: Nanocrystalline yttrium oxide (Y2O3) thin films were made by sputter deposition onto silicon (100) substrates keeping the deposition temperature fixed at 300 °C. The surface/interface chemistry, Y–O bonding, and optical constants of the Y2O3 film surface and Y2O3–Si interface were evaluated by the combined use of X-ray photoelectron spectroscopy (XPS), depth-profiling, and spectroscopic ellipsometry (SE). XPS analyses indicate the binding energies (BEs) of the Y 3d doublet; i.e., the Y 3p5/2 and Y 3d3/2 peaks are located at 117.0 and 119.1 eV, respectively, characterizing yttrium in its highest chemical oxidation state (Y3+) in the grown films. The optical model is constructed based on the XPS depth profiles, which indicate that the Y2O3//Si heterostructure can be represented with Y2O3 film—YxSiyOz interfacial compound—Si substrate. Such a model accounts for the experimentally determined ellipsometry functions and accurately produces the dispersive index of refraction (n(λ)) of Y2O3 and YxSiyOz. The n(λ) ...

83 citations

Journal ArticleDOI
TL;DR: In this article, the authors designed anti-reflective coatings based upon multi-layers of TiO2 and SiO2 by magnetron sputtering on glass and silicon substrates at room temperature.

49 citations

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate a novel approach to wrap silicon nanoparticles in three-dimensional reduced graphene oxide (RGO) aerogel, which not only provides a porous network for entrapping SiNPs to accommodate the volume change during cycling but also facilitates electrolyte transport.
Abstract: The severe volume change and aggregation of silicon nanoparticles (SiNPs) when used as an anode for lithium ion batteries (LIBs) are the key issue. Here, we demonstrate a novel approach to wrapping SiNPs in three-dimensional reduced graphene oxide (RGO) aerogel. The RGO aerogel not only provides a porous network for entrapping SiNPs to accommodate the volume change during cycling, but also facilitates electrolyte transport. Furthermore, the continuous RGO network is favourable for electron transfer. The graphene-wrapped SiNPs were stable and displayed an excellent rate capacity, delivering a reversible capacity of about 2000 mA h g−1 after 40 cycles.

33 citations

Journal ArticleDOI
TL;DR: In this paper, a possible way to electrodeposit Si has been studied in trimethyln-hexylammonium bis(trifluoromethylsulfonyl)imide containing 0.1 mol L -1 SiCl 4.
Abstract: A possible way to electrodeposit Si has been studied in trimethyl-n-hexylammonium bis(trifluoromethylsulfonyl)imide containing 0.1 mol L -1 SiCl 4 . Cyclic voltammetry suggests that SiCl 4 should be reduced to form Si at around -2.0 V. Potentiostatic electrolysis at this potential forms a yellowish-brown film on a Ni substrate. X-ray photoelectron spectroscopy and Raman spectroscopy reveal that the electrodeposited film contains amorphous Si. It is also found from scanning electron microscopy observation and energy-dispersive X-ray spectroscopy analysis that a highly uniform and dense thin film can be obtained in the initial stage of electrodeposition and that the electrodeposited Si film becomes rougher and thicker with the progress of electrolysis.

29 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the authors investigated visible photoluminescence excited by an Ar-ion laser (488 nm, 2.54 eV) at room temperature from Si+implanted silica glass, as-implanted and after subsequent annealing in vacuum.
Abstract: We have investigated visible photoluminescence excited by Ar‐ion laser (488 nm, 2.54 eV) at room temperature from Si+‐implanted silica glass, as‐implanted and after subsequent annealing in vacuum. We found two visible luminescence bands: one peaked around 2.0 eV, observed in as‐implanted specimens and annealed completely after heating to about 600 °C, the other peaked around 1.7 eV observed only after heating to about 1100 °C, the temperature at which Si segregates from SiOx. It was found that the 2.0 eV band anneals parallel to the E’ centers, as detected by electron spin resonance studies. It was also found that Raman lines around 520 cm−1, due to Si—Si bonds, grow and that interference patterns are induced by annealing Si+‐implanted silica glass. Based on these studies, we ascribe the 2.0 eV band to the electron‐hole recombination in Si‐rich SiO2 and the 1.7 eV band to the electron‐hole recombination in the interface between the Si nanocrystal and the SiO2 formed by segregation of crystalline Si from SiOx.

379 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reported the observation of visible light emission at room temperature from high fluence (0.3-3×1017 cm−2) Si+ implanted thermal SiO2 layers grown on silicon substrates.
Abstract: We report the observation of visible‐light emission at room temperature from high fluence (0.3–3×1017 cm−2) Si+ implanted thermal SiO2 layers grown on silicon substrates. Significant blue‐light emission and an intense broad luminescent band with a peak beyond 750 nm are observed after annealing at high temperature (T≥1000 °C). The red‐light emission, present only in the highest fluence implant, is attributed to the luminescence emitted from silicon nanocrystals produced by silicon precipitation. The presence of silicon nanocrystals is confirmed by transmission electron microscopy. Significant blue‐light emission is visible after thermal annealing in the 1×1017 cm−2 fluence implant. The peak position shifts from 490 to 540 nm by increasing the annealing cycles temperature.

282 citations

Journal ArticleDOI
TL;DR: In this article, the principal features in the Auger electron spectrum from a SiO2 surface are presented, and the effects of these parameters on the dissociation have been studied.
Abstract: The principal features in the Auger electron spectrum from a SiO2 surface are presented. The primary electron beam bombarding the SiO2 surface has a profound influence on its composition, in that it dissociates the surface leaving it enriched in elemental silicon. The main parameters affecting the dissociation are found to be the electron‐beam current density, the beam energy, the presence of impurities on the surface, and the residual gas pressure of oxygen. The effects of these parameters on the dissociation have been studied and some suggestions to minimize the dissociation are made. The results of the present study do not agree with the mechanism proposed by Lineweaver for oxygen release from electron‐irradiated glass.

177 citations

Journal ArticleDOI
TL;DR: In this paper, the photoluminescence of Si-rich SiO2 films has been measured for the as-deposited and annealed films, showing that the gap between the highest occupied and lowest occupied molecular orbitals decreases as the size increases, causing the redshift of the luminescence peak.
Abstract: Si-rich SiO2 films have been prepared by a rf cosputtering method and their photoluminescence, as well as infrared absorption and Raman spectra, has been measured for the as-deposited and annealed films. Photoluminescence spectra very similar to those of porous Si were observed for the sample with a relatively low Si content. Redshift of the luminescence peak was observed upon annealing. Results of infrared and Raman measurements strongly suggest that Si clusters are embedded in the as-deposited sample, and that their size increases upon annealing. The photoluminescence is thus thought to arise from the Si clusters, in which the gap between the highest-occupied and lowest-unoccupied molecular orbitals decreases as the size increases, causing the redshift of the photoluminescence peak. A sample containing well-grown Si microcrystals was also prepared by increasing the Si content. No detectable photoluminescence signal was observed for this sample.

139 citations

Journal ArticleDOI
TL;DR: In this paper, the 2.2 eV band was investigated in 60Co γ-irradiated (dose < 1 MGy) oxygen-deficient type amorphous SiO2 (a•SiO2) excited by 2.4 eV photons.
Abstract: Visible photoluminescence (PL) bands around 2 eV were studied in 60Co γ‐irradiated (dose<1 MGy) oxygen‐deficient‐type amorphous SiO2 (a‐SiO2) excited by 2–4 eV photons. In addition to the well‐known 1.9 eV PL band due to nonbridging oxygen hole centers, another PL band was observed at 2.2 eV when excited by 3.8 eV photons. The intensity of the 2.2 eV band increases with decreasing oxygen partial pressure during the sample preparation. Electron‐spin‐resonance measurements show that the intensity of the 2.2 eV band is correlated with the concentration of the Eδ′ center, a paramagnetic state of a cluster of silicons. After much higher γ irradiation with a dose up to 10 MGy, a new PL band was induced at 1.75 eV under excitation by 2.5 eV photons, as well as the 1.9 and 2.2 eV PL bands. By comparing its spectral shape and excitation energy with known PL band in Si‐implanted a‐SiO2, it is suggested that the 1.75 eV band is associated with Si nanocrystals formed from Si clusters in a‐SiO2 by the high‐dose γ irra...

117 citations