High Resolution Observations of Copper Vacancy Ordering in Chalcocite (Cu2S) and the Transformation to Djurleite (Cu1.97 to 1.94S)

Abstract

The technique of high resolution transmission electron microscopy (TEM) permits the first real space observations of the ordering of copper in the sulfur sublattices of chalcocite (Cu2S) and djurleite (Cu1.97 to 1.94S). Copper sulfide thin films formed by the ion exchange process in CdS single crystals are shown to be composed of small domains of the two phases (≈ 10 to 100 nm in diameter), separated by abrupt coherent interfaces. Strain calculations for these interfaces agree qualitatively with experimental observations. In addition, the chalcocite in the vicinity of chalcocite/djurleite interfaces is found to contain a high density of 1/4[010] faults. Structural considerations show that these faults are likely sites for copper vacancies.

Copper Sulfide Nanocrystal Level Structure and Electrochemical Functionality towards Sensing Applications

“…An interesting control parameter for the functionality of the copper sulfide nanocrystals is by stoichiometric tuning . Due to the low chemical potential of Cu in these systems, they show tendency towards stoichiometric diversity through the process of Cu vacancy creation, as reported in binary, ternary and quaternary metal chalcogenides and chalcopyrites . Furthermore, in nanomaterials, where surface effects are dominant, vacancy formation may be enhanced in comparison to the bulk materials, especially in processes involving small atoms diffusion to the interfaces.…”

“…The peak‐voltage down‐shift may be attributed to p ‐type doping in the oxidized Cu 2− x S nanocrystals, which takes place during oxidation of the copper(1+) ions . Accordingly, the decrease in potential required for copper‐ion oxidation may be assigned to a formation of an in‐gap state close to the valance band (VB) (see Scheme in Figure e).…”

“…[16,[19][20][21][22] Furthermore, in nanomaterials, where surface effectsa re dominant, vacancy formation may be enhanced in comparison to the bulk materials, especially in processes involvings mall atoms diffusion to the interfaces. There are various routes for forming Cu vacancies in copperc halcogenide nanocrystals including oxidation in ambient atmosphere, [5,17,23] chemicalt reatment [24,25] and also by moderate thermalt reatment. [7,8] In this context copperc halcogenides emerged as amodel system showing interesting development of aplasmon excitation upon Cu vacancy formation, serving as at est bed for studying correlated exciton-plasmoniceffects.…”

“…The peak-voltage down-shift may be attributed to p-type doping in the oxidized Cu 2Àx Sn anocrystals, which takes place duringo xidation of the copper(1 +)i ons. [17] Accordingly,t he decreasei np otential requiredf or copper-ion oxidation may be assigned to af ormation of an in-gap state close to the valance band (VB) (see Scheme in Figure 3e). To identify ap ossible ingap state(s)f ormation, and to provide an additional confirma- tion for the cyclic voltammetryo bservations, STS was applied.…”

Analytical modeling of localized surface plasmon resonance in heterostructure copper sulfide nanocrystals

“…12,13,16,21 Luther et al, 12 Kriegel et al, 16 and Hsu et al 21 have reported tunability of the LSPR frequency in Cu 2−x S nanocrystals through exposure to air, which introduces copper vacancies. 16,22 Other methods to control the LSPR frequency in semiconductor nanocrystals focus on synthetic routes or chemical treatments to selectively modify the geometry and size of the LSPR-supporting phase. Targeted phosphorus doping of Si nanowires has been shown to produce segmented nanowires consisting of alternating insulating and conducting regions.…”