Synthesis of mesoporous Si1−xGexO2 (0.10 ≤x≤ 0.31) using a nonionic block copolymer template

Abstract

We have successfully synthesized mesoporous silica-germania mixed oxide (Si 1Àx Ge x O 2 ) with x up to 0.31 by controlling the reaction to delay hydrolysis and condensation until the precursors have sufficiently ordered around the nonionic templating agent. Small-angle X-ray diffraction (SAXS) and transmission electron microscopy (TEM) reveal disordered worm-like mesopores for all germanium concentrations investigated, with pore periodicities of 9.8 and 10.5 nm for x z 0.10 and 0.20 respectively. We confirm that the germanium and silicon are homogenous on the nanoscale using scanning transmission electron microscopy (STEM) with energy dispersive X-ray (EDX) mapping. Attempts to convert the mixed mesoporous oxides to mesoporous Si 1Àx Ge x alloys via magnesiothermic reduction resulted in phase segregation.

Silicon-Based Thermoelectrics Made from a Boron-Doped Silicon Dioxide Nanocomposite

“…High-resolution synchrotron powder X-ray diffraction data (Figure a) for the clean, dry Si 90 Ge 10 powder indicate separate phases of germanium and silicon, with Le Bail fits giving an average germanium grain size of 8.5 nm and an average silicon grain size of approximately 200 nm. This phase segregation is in agreement with an observation made by Szczech et al…”

“…High-resolution synchrotron powder X-ray diffraction data (Figure 2a) for the clean, dry Si 90 Ge 10 powder indicate separate phases of germanium and silicon, with Le Bail fits giving an average germanium grain size of 8.5 nm and an average silicon grain size of approximately 200 nm. This phase segregation is in agreement with an observation made by Szczech et al 23 The average silicon grain size of 200 nm is about 15 times larger than the grain size obtained by groups that performed the reduction on silicon dioxide nanostructures; 16,24 however, this may be attributed to the oxide being in intimate contact with the magnesium powder (instead of the reduction relying upon Mg−vapor transport), the longer reduction time that we have used, and/or efficient crystal nucleation around the germanium nanoparticles, which form before the silicon dioxide starts to reduce. Since germanium dioxide can be reduced to germanium with hydrogen gas at temperatures below magnesium's melting point, 25 the germanium nanoparticles may act as seeds for the silicon crystallization.…”

Preparation of Mesoporous Sb‐, F‐, and In‐Doped SnO2 Bulk Powder with High Surface Area for Use as Catalyst Supports in Electrolytic Cells

“…[14d] The synthesized SnO 2 had very large specific surface area (211–339 m 2 g –1 ) at temperature from 400 to 600 °C, however these were barely unsuitable for the electrocatalyst supports because nonconductive silicon dioxide remained in the metal oxide structure. Furthermore, there are only a few reports about doped SnO 2 powder with high surface area and homogeneity, because the constituent metals of mixed metal oxide exhibit different hydrolysis and condensation kinetics . From these considerations and for all practical purposes, a more viable synthetic approach is required.…”

Solid‐State Route for the Synthesis of Scalable, Luminescent Silicon and Germanium Nanocrystals

“…The metallothermic reduction method reported here was applied to prepare Ge NCs. Mesoporous GeO 2 was prepared using a templated sol‐gel method . Pluronic 123 polymer was used as a template, which was removed by heating (Figure S6 in the ESI) to yield GeO 2 with average pore size of 5.8 nm (Figure A) as determined via N 2 adsorption isotherm measurements (Figure S7 in the ESI).…”