Diffusion properties of chalcogens (S, Se, Te) into pure silica
ABSTRACT The diffusion properties of chalcogens (S, Se, Te) implanted into SiO2 were studied via secondary ion mass spectroscopy (SIMS) profiling between room temperature and the glass transition temperature (800–950 °C). Annealing of Te-containing samples leads directly to precipitation of metallic tellurium nanocrystals within the implantation profile. The S and Se concentration profiles were fitted by using a simple diffusion model in order to provide estimates of the diffusion constant and approximate solubility of these fast moving chemical species. A comparison of their differing diffusion behavior with complementary data on these systems suggests that (i) their oxidation states play a crucial role and (ii) the chalcogen propagation mechanism actually involves complex chemical interactions.
- Reviews in Mineralogy and Geochemistry 06/2011; 73(1):79-111. DOI:10.2138/rmg.2011.73.4 · 3.57 Impact Factor
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ABSTRACT: Ion beam synthesis has played a significant role in fabricating metallic or semiconducting nanocrystal arrays in glass for their optical or magnetic properties, but basic questions remain unanswered. What are the microscopic mechanisms that control nanocluster growth, determine their density and size distributions? To what extent can we control these processes in order to tailor the properties? We demonstrate the role of chemistry (redox properties; charge state equilibrium modified by irradiation) in Ag nanocluster nucleation and growth processes in glasses and extend the conclusions to PbS nanocluster synthesis. In the latter case, we show how charge state differences affect diffusion and growth and devise a strategy that produces PbS quantum dots emitting intense photoluminescence at 1.5 μm. In the course of this work, we also showed that the lognormal shape of cluster size distributions signals a loss of information as to the formation process and hence loss of property control.Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 04/2007; 1020(1-2-257):1-5. DOI:10.1016/j.nimb.2006.12.110 · 1.19 Impact Factor
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ABSTRACT: Lead chalcogenide (PbS, PbSe, and PbTe) nanocrystals were synthesized by sequential implantation of Pb and one of the chalcogen species into pure silica. The implantation energy and fluence were chosen so that the implantation profiles practically overlap at a depth approximately 150 nm with a maximum concentration of about 0.3 atom %. Annealing for 1-8 h at 850-900 degrees C triggers nanocrystal growth, which is monitored by high-resolution (HRTEM) and conventional transmission electron microscopy (TEM), secondary-ion mass spectrometry (SIMS), and Rutherford backscattering spectrometry (RBS). Striking differences are found in the depth distributions and microstructures of the resulting nanocrystals. We show that the differing chemical interactions of Pb and chalcogens (between each other and with silica) play a crucial role in chalcogenide nucleation and growth. Using available information on chalcogen redox states in silicate glass, we propose a nonclassical nucleation and growth mechanism consistent with our experimental results. The complex chemistry involved at the microscopic level is shown to impair control over the nanocrystal size distribution. Finally, PbS nanocrystal-doped silica is shown to emit intense photoluminescence (PL) in the 1.5-2 microm wavelength range, an effect that we relate to the above nucleation and growth scheme.The Journal of Physical Chemistry B 11/2005; 109(41):19148-55. DOI:10.1021/jp0527047 · 3.38 Impact Factor