Synthesis of Nanoamorphous Germanium and Its Transformation to Nanocrystalline Germanium

Abstract

A simple reaction between a mild reducing agent such as a trialkoxysilane and GeIV species such as germanium tetraalkoxides in a room‐temperature water/alcohol solution produces silica‐coated ultrasmall (2–3 nm) amorphous germanium nanoparticles (na‐Ge/SiO2). The initial reaction involves the straightforward hydrolysis and condensation of the precursors, Ge(OCH2CH3)4 and (CH3CH2O)3SiH, where the reaction rate depends on the water concentration in the reaction medium. These processes can be further accelerated by adding acid to the reaction medium or carrying out the reaction at higher temperatures. At low water contents (up to 50% water/ethanol) and low acid concentrations, the reaction proceeds as a clear solution, and no precipitation is observed. The initially colorless clear solution progressively changes to pale yellow, yellow, orange, red, and finally dark red as the na‐Ge particles grow. Evaporation of the solvent yields a reddish‐brown powder/monolith consisting of na‐Ge, embedded in an encapsulating amorphous silica matrix, na‐Ge/SiO2. The formation of na‐Ge proceeds extremely slowly and follows a first‐order dependence on both water concentration and diameter of the na‐Ge particles under the reaction conditions used. Annealing of the na‐Ge/SiO2 powder under an inert atmosphere at 600 °C produces ultrasmall germanium nanocrystals (nc‐Ge) embedded in amorphous silica (nc‐Ge/SiO2). Freestanding, colloidally stable nc‐Ge is obtained by chemical etching of the encapsulating silica matrix.

Ultrasmall particles and nanocomposites: state of the art

“…In addition, a simple reaction between a mild reducing agent such as a trialkoxysilane and Ge IV species such as Ge tetraalkoxides in a r.t. H 2 O-alcohol solution produced SiO 2coated ultrasmall (2-3 nm) amorphous germanium nanoparticles (na-Ge/SiO 2 ). 67 The formation of na-Ge proceeded extremely slowly and follows a rst-order dependence on both H 2 O concentration and diameter of the na-Ge particles under the reaction conditions used. Annealing of the na-Ge/SiO 2 powder under an inert atmosphere at 600 C produced ultrasmall Ge nanocrystals (nc-Ge) embedded in amorphous SiO 2 (nc-Ge/SiO 2 ).…”

Solution Synthesis, Surface Passivation, Optical Properties, Biomedical Applications, and Cytotoxicity of Silicon and Germanium Nanocrystals

“…Owing to the low toxicity of both silicon precursor and reducing agents, these reactions have unlocked the gram‐scale production of silicon NCs . The use of germanium alkoxides to synthesize germanium NCs has been limited to sol–gel processes, which can have reaction times of up to several days and require high‐temperature treatment to form crystalline particles . There is an opportunity to modify the syntheses reported by the group of He to synthesize Ge NCs from Ge alkoxide precursors.…”

Investigation of the photophysical properties of energy-relevant inorganic nanocrystals

“…88 Indeed, all reports on the preparation of Ge nanocrystals where XPS was performed show strong peaks for Ge 0 and small contributions from oxidized species, whether they are attributed to surface ligands and/or surface oxidation (GeO2). 62,72,108 The photoluminescence (PL) properties of Ge-based materials are highly sensitive to the resultant size of the nanocrystals as well as other properties such as the capping ligand used. 46-47, 61, 96, 109 Lee et al prepared Ge nanocrystals stabilized with 1-octadecene that exhibited luminescence maxima from 900 to 1400 nm for diameters 3.2 to 4.0 nm.…”