D.E. Hole

Optical properties of silicon nanoclusters fabricated by ion implantation

A method for the fabrication of luminescent Si nanoclusters in an amorphous SiO2 matrix by ion implantation is reported. We have measured the dose (concentration of excess Si atoms) and annealing time dependence of the photoluminescence of Si nanoclusters in SiO2 layers at room temperature. The samples were fabricated by ion implantation and subsequent annealing. After annealing, a photoluminescence band below 1.7 eV has been observed. The peak energy of the photoluminescence is found to be almost independent of annealing time, while the intensity of the luminescence increases as the annealing time increases. Moreover, we found that the peak energy of the luminescence is strongly affected by the dose of implanted Si ions, especially in the high-dose range. We also show direct evidence of widening of the band-gap energy of Si particles of a few nanometers in size by employing photoacoustic spectroscopy. These results indicate that the photons are absorbed by Si nanoclusters, for which the band-gap energy i...

Luminescence from erbium-doped silicon nanocrystals in silica: Excitation mechanisms

We develop a model for the excitation of erbium ions in erbium-doped silicon nanocrystals via coupling from confined excitons generated within the silicon nanoclusters. The model provides a phenomenological picture of the exchange mechanism and allows us to evaluate an effective absorption cross section for erbium of up to 7.3×10−17 cm2: four orders of magnitude higher than in stoichiometric silica. We address the origin of the 1.6 eV emission band associated with the silicon nanoclusters and determine absorption cross sections and excitonic lifetimes for nanoclusters in silica which are of the order of 1.02×10−16 cm2 and 20–100 μs, respectively.

Evidence of energy coupling between Si nanocrystals and Er3+ in ion-implanted silica thin films

Silica thin films containing Si nanocrystals and Er3+ were prepared by ion implantation. Excess Si concentrations ranged from 5% to 15%; Er3+ concentration for all samples was 0.5%. Samples exhibited photoluminescence at 742 nm (attributed to Si nanocrystals), 654 nm (defects due to Er3+ implantation), and at 1.53 μm (intra-4f transitions). Photoluminescence intensity at 1.53 μm increased ten times by incorporating Si nanocrystals. Strong, broad photoluminescence at 1.53 μm was observed for λPump away from Er3+ absorption peaks, implying energy transfer from Si nanocrystals. Erbium fluorescence lifetime decreased from 4 ms to 1 ms when excess Si increased from 5% to 15%, suggesting that at high Si content Er3+ ions are primarily situated inside Si nanocrystals.

Annealing of ion implanted silver colloids in glass

Silvercolloids have been formed by ion implantation in float glass. Subsequent annealing methods alter the size distribution and optical reflectivity of the colloids.Furnaceanneals and rapid flameheating convert large colloids into smaller units but excimer laserannealing appears to cause a dissolution of silver into the glass network.

Mechanism of photoluminescence of Si nanocrystals in SiO2 fabricated by ion implantation: the role of interactions of nanocrystals and oxygen

A possible mechanism for the photoemission from Si nanocrystals in an amorphous SiO2 matrix fabricated by ion implantation is reported. We have measured the implantation dose and the temperature dependence as well as the oxidation effect of the photoluminescence behaviour of Si nanocrystals in SiO2 layers fabricated by ion implantation and a subsequent annealing step. After annealing, a photoluminescence band, peaking just below 1.7 eV was observed. The peak energy of the photoluminescence was found to be affected by the dose of implanted Si ions and the temperature during ion implantation, but to be independent of annealing time and excitation photon energy. We also present experimental results of an oxidation-induced continuous peak energy shift of the photoluminescence peak up to around 1.8 eV. This peak energy, however, was found to return to its previous position with re-annealing. These results indicate that whilst the excitation photons are absorbed by Si nanocrystals, the emission is not simply due to electron-hole recombination inside the Si nanocrystals, but is related to the presence of defects, most likely located at the interface between the Si nanocrystals and the SiO2, for which the characteristic energy levels are affected by cluster-cluster interactions or the roughness of the interface.

Formation of silver nanoparticles in soda–lime silicate glass by ion implantation near room temperature

The synthesis of silver nanoparticles in soda–lime silicate glass near room temperature is reported. Nanoparticles were prepared during 60 keV Ag-implantation with doses from 2 to 4×1016 ions/cm2 at a current density of 10 μA/cm2. Detailed evaluations were made of the dose contribution at the bulk-glass temperatures of 20°C, 35°C, 50°C and 60°C. The particle size distribution was assessed by monitoring optical reflectance from both the implanted and rear face of the samples. Depth data were provided by Rutherford backscattering analysis. Samples prepared with a high dose at 60°C were characterised by more complex reflectance spectra, with overlapping peaks, compared to reflectance data for room temperature implants. Additionally, comparisons between implants of the same dose and beam conditions for glass samples of different-thickness show the influence of surface heating and its influence on Ag nanoparticle formation. The factors, which influence the growth of metal nanoparticles and the differences in the observed optical properties are discussed.

Colloid size distributions in ion implanted glass

Abstract Ion implantation of silver ions at 60 keV into silicate glass produces metallic colloids. Colloid growth during implantation as recorded by in situ changes in optical reflectivity. Post implant analyses indluded optical absorption, Rutherford backscattering and transmission electron microscopy. The optical data imply there is a range of colloid sizes and the details of colloid size as a function of depth are determined by the TEM measurements of thinned samples. The factors influencing the changes in the optical data with ion dose and the depth dependence of the colloid size distribution are discussed.

Overview of material re-deposition and fuel retention studies at JET with the Gas Box divertor

in the period 1998-2001 the JET tokamak was operated with the MkII Gas Box divertor. On two occasions during that period a number of limiter and divertor tiles were retrieved from the torus and the ...

ENHANCEMENT OF LUMINESCENCE BY PULSE LASER ANNEALING OF ION-IMPLANTED EUROPIUM IN SAPPHIRE AND SILICA

Sapphire (Al2O3) and silica samples have been implanted with 400 keV europium ions at fluences between 5×1014 and 1×1016 ions cm−2. As‐implanted, samples show luminescence at 622 nm, and although the intensity may be increased by furnace anneals up to 1000 °C, higher temperatures, to 1200 °C, result in less emission, as the impurity ions form precipitate clusters. This problem can be avoided by the use of pulsed laser anneals which dissociate the clusters and quench in atomically dispersed ions. The luminescence intensity has been increased by factors of 95 and 85 for sapphire and silica, respectively, relative to the initial implanted signal. On comparing with furnace anneals at 1200 °C, the pulsed laser annealing is more effective, by factors of up to 45 times. Data for pulsed excimer and CO2 lasers are compared. Both types of laser appear to remove the ion‐implanted radiation damage, but in the case of silica, higher luminescence performance was obtained with the excimer anneals. There was no evidence ...

Reduction of the size of the implanted silver nanoparticles in float glass during excimer laser annealing

Silver nanoparticles have been synthesised by ion implantation in float glass at 60 keV to a dose of 7.0 = 10 16 ionrcm 2 and a current density of 10 mArcm 2 at a temperature of 508C. The size distribution of the metal particles was controlled by monitoring optical transmittance and reflectance together with atomic force microscopy measurements and Rutherford backscattering spectroscopy. A reduction in size of large silver nanoparticles and some dissolution of silver into the glass network has been made by pulse annealing with a high-power KrF excimer laser. The present study explores the possibilities of controlled size formation of metal nanoparticles within an insulator. Explanations of the observed modifications are proposed. q 1998 Elsevier Science B.V. All rights reserved.