Thermally Induced Evolution of “Ge(OH)₂”: Controlling the Formation of Oxide-Embedded Ge Nanocrystals

Abstract

Germanium nanocrystals (GeNCs) hold great promise as active materials in many applications including solar cells, biological imaging, Bragg reflectors, light-emitting diodes, and nonvolatile memory devices. However, because of the size-, shape-, and composition-dependent nature of their properties, it is essential that methods affording high-purity, well-defined GeNCs be developed. Herein, we report a systematic investigation of a series of “Ge­(OH)2” precursors using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and solid-state 73Ge NMR and correlate their properties with the GeNCs obtained from their thermal processing. This study provides important insights into the role of the Ge­(OH)2 internal structure and will allow for future rational design and practical application of GeNCs.

Recent progress in solid‐state nuclear magnetic resonance of half‐integer spin low‐γ quadrupolar nuclei applied to inorganic materials

“…The surrounding matrix remains too broadened to detect. [218] For halogen-containing inorganic germanium compounds, 73 Ge experimental NMR data and GIPAW DFT calculations were reported from GeX 4 and GeX 2 germanium halides and revealed a wide range of C Q of 0.16 to 35 MHz (Table 9). [219] For the GeX 4 series δ iso could be correlated with the halide electronegativity.…”

Synthesis of germanium nanocrystals from solid-state disproportionation of a chloride-derived germania glass

“…The XRD pattern of the hydrolyzed GeCl 2 Ádioxane (prior to annealing) exhibits broad amorphous features centered around 31.41 and 50.81 2y. Previous studies from Javadi et al 24,25 and Sun et al 23 also reported amorphous features from GeO 2 -derived GeO prior to annealing; however these amorphous scattering features were at slightly lower angles (27.51 and 501 2y) and were attributed to amorphous germanium. 24,25 The different positions of the amorphous features in the precursors indicate that our samples may possess a different composition from the previous studies.…”

“…Previous studies from Javadi et al 24,25 and Sun et al 23 also reported amorphous features from GeO 2 -derived GeO prior to annealing; however these amorphous scattering features were at slightly lower angles (27.51 and 501 2y) and were attributed to amorphous germanium. 24,25 The different positions of the amorphous features in the precursors indicate that our samples may possess a different composition from the previous studies. Differential scanning calorimetry (DSC) reveals an exotherm that we hypothesized to coincide with the decomposition of the precursor and formation of Ge nuclei around 250 1C (Fig.…”

“…7,22 Very recently, there have been reports of solid state approaches using a Ge(OH) 2 precursor. [23][24][25] These approaches used Ge(OH) 2 that was derived from GeO 2 , followed by thermal annealing to induce dehydration and disproportionation, ultimately resulting in Ge NCs suspended within a germania matrix.…”

“…This is different from the observation of Javadi et al of a clear increase in nanocrystal size with increasing annealing temperature. 25 The Ge NCs are polydisperse and have different morphologies, which could be caused by the twostep heating procedure. 5 The presence of unreacted precursors and amorphous species are also observed in the vicinity of Ge NCs, the presence of which decreases with increasing reaction temperature (Fig.…”