Twinned silicon and germanium nanocrystals: Formation, stability and quantum confinement

Abstract

Although twins are often observed in Si/Ge nanocrystals (NCs), little theoretical investigation has been carried out to understand this type of important planar defects in Si/Ge NCs. We now study the twinning of Si/Ge NCs in the frame work of density functional theory by representatively considering single-twinned and fivefold-twinned Si/Ge NCs. It is found that the formation of twinned Si/Ge NCs is thermodynamically possible. The effect of twinning on the formation of Si NCs is different from that of Ge NCs. For both Si and Ge NCs twinning enhances their stability. The quantum confinement effect is weakened by twinning for Si NCs. Twinning actually enhances the quantum confinement of Ge NCs when they are small (<136 atoms), while weakening the quantum confinement of Ge NCs as their size is large (>136 atoms). The current results help to better understand the experimental work on twinned Si/Ge NCs and guide the tuning of Si/Ge-NC structures for desired properties.

Topological Identification Criteria, Stability, and Relevance of Pentagonal Nanochannels in Amorphous Ice

“…Recent investigations on ice crystallized on surfaces have confirmed the presence of pentagonal rings in a variety of mesoscopic environments. , Metastable ice clusters, known as clathrate hydrates, also contain cages formed by planar pentagonal and hexagonal rings, which are stabilized by trapped gas molecules . Planar pentagonal ring structures in a fivefold symmetric environment have also been found in amorphous silicon, amorphous germanium, as well as ice crystallized from supercooled liquid. − …”