Thiol-Capped Germanium Nanocrystals: Preparation and Evidence for Quantum Size Effects

Abstract

Applications of Ge nanocrystals (NCs) are limited by the stability and air reactivity of the Ge surface. In order to promote stability and increase the diversity of ligand functionalization of Ge NCs, the preparation of thiol-passivated Ge NCs via a ligand exchange process was investigated. Herein a successful replacement of oleylamine ligands on the surface of Ge NCs with dodecanethiol is reported. The successful ligand exchange was monitored by FTIR and NMR spectroscopy and it was found that dodecanethiol provided a better surface coverage, leading to stable Ge NC dispersions. Dodecanethiol capping also enabled band gap determination of the NCs by surface photovoltage (SPV) spectroscopy. The SPV measurements indicated an efficient charge separation in the ligand-exchanged Ge NCs. On the other hand, oleylamine-terminated Ge NCs of similar sizes exhibited a very small photovoltage, indicating a poorly passivated surface.

Europium chalcogenide magnetic semiconductor nanostructures

“…Although the II-VI semiconductor nanoparticle syntheses have been highly refined, syntheses of covalent semiconductors, such as Si and Ge, remain challenging in terms of yield and size control [48]. Even within metal chalcogenide nanoparticles, size control as well as crystallinity appear to be notably better for thiophilic metals.…”

Probing Electronics as a Function of Size and Surface of Colloidal Germanium Nanocrystals

“…This reaction has been expanded to include thiol ligands as capping agents. 8 3 NCs with a narrow size distribution are most desired for applications in optoelectronic devices, and precise knowledge of the optical and electronic bandgap is crucial for studying properties such as electron transfer. 9 UV-vis spectroscopy is commonly employed to determine the optical bandgap of NCs, but to determine the energy level of the VB and CB other methods must be used.…”

Direct Evaluation of the Quantum Confinement Effect in Single Isolated Ge Nanocrystals

“…16,21 It is not surprising then that surface passivation of Ge NCs by ligands has drawn much attention; 48 however, to date its impact on QC has not been addressed. For example, a previous attempt to utilize the ligandcapped Ge-NCs was based on the quasi-optical measurement of the surface photovoltage, 18 but the extrapolation of the spectra …”