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It was already demonstrated that Si hot implantation followed by high-temperature annealing induces the formation of Si nanocrystals (Si NCs) which when excited in a linear excitation regime present two photoluminescence (PL) bands (at 780 and 1000 nm). We have undertaken the present work in order to investigate three features: First, to determine the origin of each band. With this aim we have changed the implantation fluence and the high-temperature annealing time. Second, to investigate the influence of the postannealing atmosphere on the PL recovering process after bombarding the Si NCs. Third, we have annealed the as-produced Si NCs in a forming gas (FG) atmosphere in order to observe the PL behavior of each band. The results have shown that the 780 nm PL band has its origin in radiative interfacial states, while the 1000 nm one is due to quantum size effects. From the experiments we have concluded that the PL recovery after the Si NCs irradiation strongly depends on the type of postannealing atmosphere. Finally, it was found that the FG treatment strongly affects the line shape of the PL spectrum. [ABSTRACT FROM AUTHOR]

In this work we present a study of photoluminescence (PL) on Si nanocrystals (NC) produced by ion implantation on SiO2 targets at temperatures ranging between room temperature and 800 °C and subsequently annealed in N2 atmosphere. The PL measurements were performed at low excitation power density (20 mW/cm2) in order to avoid nonlinear effects. Broad PL spectra were obtained, presenting a line-shape structure that can be reproduced by two superimposed peaks at around 780 and 950 nm. We have observed that both PL intensity and line-shape change by varying the annealing as well as the implantation temperatures. Implantations performed at 400 °C or higher produce a remarkable effect in the PL line shape, evidenced by a strong redshift, and a striking intensity increase of the peak located at the long-wavelength side of the PL spectrum. In addition we have studied the PL dependence on the excitation power density (from 0.002 to 15 W/cm2). The samples with broad NC size distribution containing large grains, as revealed by transmission electron microscopy observations presented a PL spectrum whose line shape was strongly dependent on the excitation power density. While high excitation power densities (saturation regime) induce only the short-wavelength part of the PL spectrum, low excitation power densities bring out the appearance of the hidden long-wavelength part of the emission. The present results are explained by current models. [ABSTRACT FROM AUTHOR]

A systematic study of photoluminescence (PL) behavior of Si nanocrystals in SiO2 obtained by ion implantation in a large range of temperatures (-200 up to 800 °C), and subsequent furnace annealing in N2 ambient was performed. A PL signal in the wavelength range 650–1000 nm was observed. The PL peak wavelength and intensity are dependent on the fluence, implantation and annealing temperatures. It was found that after annealing at 1100 °C, both implantations of 1.5×1017 Si/cm2 at room temperature or 0.5×1017 Si/cm2 at 400 °C result in the same PL peak intensity. By varying the implantation temperature we can achieve the same PL efficiency with lower fluences showing that hot implantations play an important role for initial formation of the nanocrystals. The PL intensity evolution as a function of the annealing time was also studied. As the implantation temperature was increased, larger mean size Si nanocrystals were observed by means of dark-field transmission electron microscopy analysis. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A systematic study of photoluminescence (PL) behavior of Si nanocrystals in SiO2 obtained by ion implantation in a large range of temperatures (-200 up to 800 °C), and subsequent furnace annealing in N2 ambient was performed. A PL signal in the wavelength range 650–1000 nm was observed. The PL peak wavelength and intensity are dependent on the fluence, implantation and annealing temperatures. It was found that after annealing at 1100 °C, both implantations of 1.5×1017 Si/cm2 at room temperature or 0.5×1017 Si/cm2 at 400 °C result in the same PL peak intensity. By varying the implantation temperature we can achieve the same PL efficiency with lower fluences showing that hot implantations play an important role for initial formation of the nanocrystals. The PL intensity evolution as a function of the annealing time was also studied. As the implantation temperature was increased, larger mean size Si nanocrystals were observed by means of dark-field transmission electron microscopy analysis. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses a study which examined the iron-nitrogen phase transformations produced by the simultaneous use of temperature and ion bombardment. Principle behind nitrogen implantation; Description of the experimental setup; Findings.

The identification of 163 strains ofMycobacterium bovisby polymerase chain reaction (PCR) and microbiological tests was carried out on 252 tuberculous-like lesions (TLLs) collected from slaughtered cattle in south-east Brazil. This study compared the usefulness of three genotyping techniques, IS6110-restriction fragment length polymorphism (RFLP), polymorphic guanine-cytosine-rich sequence (PGRS)-RFLP and direct repeat (DR)-spoligotyping, as applied toM. bovisisolates. Based on IS6110-RFLP genotyping we selected a group of 23 isolates containing more than one IS6110copy, along with 16 samples containing one IS6110copy from different geographical areas, evenly distributed among dairy (eight) and beef cattle (eight). These selected isolates were analysed by PGRS-RFLP and DR-spoligotyping genotyping. Dairy cattle (17%) display a higher frequency of multiple IS6110copies than beef cattle (10%). A comparison between the genotype data obtained fails to show a correlation between the main clusters found by the three techniques. However, the clustering of each genotyping procedure revealed that the majority of strains are closely related. The RFLP-PGRS patterns showed a sizable group (20.5%) containing a 5.5 kb fragment and the predominant spoligotype is similar to that from the BCG vaccine strain. Unexpectedly, four strains (2.4%) showed drug resistance to 0.2 μg/ml isoniazid and 20 μg/ml ethionamide, but none of them was resistant to rifampicin or other antibiotics tested. [ABSTRACT FROM AUTHOR]

Ion-beam-assisted phase transformation in the Fe-N system has been studied in Fe samples implanted with N. By bombarding with Ar ions at temperatures in the 140oC < T < 420oC range, the epsilon-Fe2N -> epsilon-Fe2+xN + epsilon-Fe3.2N and epsilon-Fe3.2N + gamma-Fe4N phase transformations were induced. The ion-assisted phase transformations were studied as a function of firstly the temperature of the substrate, secondly the initial N concentration and thirdly the irradiation time. The results of the experiments show that the concomitant use of ion bombardment and temperature induces a given phase transformation at a temperature that is typically 40-50oC lower than that required for thermal annealing alone. [ABSTRACT FROM AUTHOR]