A convenient, aqueous-based synthesis of stable HgTe nanocrystals with widely size-tunable room temperature emission between wavelengths of 1.2 to 3.7 mum is demonstrated. By the choice of the thiols, applied as stabilizers, we optimized the growth dynamics, the luminescence quantum yields (up to 40%), and a ligand-exchange procedure, required to transfer the nanocrystals from water to nonpolar organic solvents. The latter is greatly improved and facilitated by the use of mercaptoethylamine as initial stabilizer. The possibility to tune the HgTe nanocrystal sizes from 3 to 12 nm and to control their surface functionalities (hydrophobic and hydrophilic) makes them very promising for the development of infrared optical devices, emitting in the wavelength region between the telecommunications and the molecular vibrations.

Stranski-Krastanow island growth is demonstrated for tensile strained silicon epilayers on Ge (001) substrates over a wide range of growth temperatures. Small, Si-rich islands show sidewall faces near {1,1,10}, whereas larger islands are {113}-terminated truncated pyramids with an aspect ratio near 0.1. In contrast to compressively strained Ge on Si, we find for Si on Ge a significantly thicker wetting layer of >8 ML and coexistence of islands and dislocations.

A highly tunable lateral quantum dot realized in InGaAs/InP by an etching technique

We studied the nucleation and ordering mechanism of Ge islands on hill-patterned Si (001) templates. Like in the case of pit-patterned substrates, the initial Ge wetting layer decorates the inclined surfaces of the hill pattern with corrugations consisting entirely of {105} faceted prisms and {001} terraces. Upon further Ge deposition, islands nucleate as pairs in the V-shaped troughs between neighboring hills, and subsequently merge into a single island near the center of each trough. Finite element calculations show that island nucleation and the subsequent movement toward the center of the trough are governed by elastic energy minimization.

Stranski–Krastanow growth, modified by the presence of submonolayer coverages of carbon or antimony, is investigated for tensile strained silicon epilayers on Ge(001) substrates. We find a reduction in the wetting layer thickness from >10 monolayers without surfactant, to 7.5 and 4.5 monolayers, respectively, with Sb and C predeposition. Very small islands with an aspect ratio of 0.05 and a narrow size distribution were found for Sb-mediated growth. For both adatom species the wetting layer is free of dislocations, whereas the Si islands are almost completely strain relaxed, mainly via sessile 90° misfit dislocations. We show that early dislocation nucleation is an inherent property of a (001) oriented cubic heterosystem under tensile strain.