In this work, non-stoichiometric silicon oxide (SiO
x
) films and (SiO
x
/SiO
y
) junctions, as-grown and after further annealing, are characterized by different techniques. The SiO
x
films and (SiO
x
/SiO
y
) junctions are obtained by hot filament chemical vapor deposition technique in the range of temperatures from 900°C to 1,150°C. Transmittance spectra of the SiO
x
films showed a wavelength shift of the absorption edge thus indicating an increase in the optical energy band gap, when the growth temperature decreases; a similar behavior is observed in the (SiO
x
/SiO
y
) structures, which in turn indicates a decrease in the Si excess, as Fourier transform infrared spectroscopy (FTIR) reveals, so that, the film and junction composition changes with the growth temperature. The analysis of the photoluminescence (PL) results using the quantum confinement model suggests the presence of silicon nanocrystal (Si-nc) embedded in a SiO
x
matrix. For the case of the as-grown SiO
x
films, the absorption and emission properties are correlated with quantum effects in Si-nc and defects. For the case of the as-grown (SiO
x
/SiO
y
) junctions, only the emission mechanism related to some kinds of defects was considered, but silicon nanocrystal embedded in a SiO
x
matrix is present. After thermal annealing, a phase separation into Si and SiO2 occurs, as the FTIR spectra illustrates, which has repercussions in the absorption and emission properties of the films and junctions, as shown by the change in the A and B band positions on the PL spectra. These results lead to good possibilities for proposed novel applications in optoelectronic devices.PACS61.05.-a; 68.37.Og; 61.05.cp; 78.55.-m; 68.37.Ps; 81.15.Gh
The present work explores electron diffraction methods for studying the structure of metallic clusters stabilized with thiol groups, which are susceptible to structural damage caused by electron beam irradiation. There is a compromise between the electron dose used and the size of the clusters since they have small interaction volume with electrons and as a consequence weak reflections in the diffraction patterns. The common approach of recording individual clusters using nanobeam diffraction has the problem of an increased current density. Dosage can be reduced with the use of a smaller condenser aperture and a higher condenser lens excitation, but even with those set ups collection times tend to be high. For that reason, the methods reported herein collects in a faster way diffraction patterns through the scanning across the clusters under nanobeam diffraction mode. In this way, we are able to collect a map of diffraction patterns, in areas with dispersed clusters, with short exposure times (milliseconds) using a high sensitive CMOS camera. When these maps are compared with their theoretical counterparts, oscillations of the clusters can be observed. The stability of the patterns acquired demonstrates that our methods provide a systematic and precise way to unveil the structure of atomic clusters without extensive detrimental damage of their crystallinity.Electronic supplementary materialThe online version of this article (doi:10.1186/s40679-016-0026-x) contains supplementary material, which is available to authorized users.
Although the diffusion control and dopant activation of Ge p-type junctions are straightforward when using B+ implantation, the use of the heavier BF2+ ions or even BF+ is still favored in terms of shallow junction formation and throughput—because implants can be done at higher energies, which can give higher beam currents and beam stability—and thus the understanding of the effect of F co-doping becomes important. In this work, we have investigated diffusion and end-of-range (EOR) defect formation for B+, BF+, and BF2+ implants in crystalline and pre-amorphized Ge, employing rapid thermal annealing at 600 °C and 800 °C for 10 s. It is demonstrated that the diffusion of B is strongly influenced by the temperature, the presence of F, and the depth of amorphous/crystalline interface. The B and F diffusion profiles suggest the formation of B–F complexes and enhanced diffusion by interaction with point defects. In addition, the strong chemical effect of F is found only for B in Ge, while such an effect is vanishingly small for samples implanted with F alone, or co-implanted with P and F, as evidenced by the high residual F concentration in the B-doped samples after annealing. After 600 °C annealing for 10 s, interstitial-induced compressive strain was still observed in the EOR region for the sample implanted with BF+, as measured by X-ray diffraction. Further analysis by cross-sectional transmission electron microscopy showed that the {311} interstitial clusters are the majority type of EOR defects. The impact of these {311} defects on the electrical performance of Ge p+/n junctions formed by BF+ implantation was evaluated.
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