Electrodeposited Quantum Dots. 3. Interfacial Factors Controlling the Morphology, Size, and Epitaxy

Abstract

Electrodeposition of CdSe from nonaqueous solutions is shown to produce epitaxial, 5 nm diameter quantum dots (QDs) on evaporated {111}Au substrate and diffraction-amorphous QDs on evaporated Pd substrate. The QDs were characterized using bright-field and dark-field transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. It is shown that similar short-range-order elements are present in both the crystalline QDs on Au and the amorphous QDs on Pd. An epitaxial size-limiting mechanism is proposed for the CdSe QDs on Au, on the basis of growing mismatch-induced strain energy upon increase in the QD size, giving rise to arrays of “self-assembled” QDs. We show that this concept, previously demonstrated using MBE and MOCVD techniques, can be successfully applied to electrochemical deposition, resulting in homogeneous QDs of considerably smaller size.