We demonstrate that colloidal Cu2–xSe nanocrystals exhibit a well-defined infrared absorption band due to the excitation of positive charge carrier oscillations (i.e., a valence band plasmon mode), which can be tuned reversibly in width and position by varying the copper stoichiometry. The value of x could be incrementally varied from 0 (no plasmon absorption, then a broad peak at 1700 nm) to 0.4 (narrow plasmon band at 1100 nm) by oxidizing Cu2Se nanocrystals (upon exposure either to oxygen or to a Ce(IV) complex), and it could be incrementally restored back to zero by the addition of a Cu(I) complex. The experimentally observed plasmonic behavior is in good agreement with calculations based on the electrostatic approximation.

Reversible Tunability of the Near-Infrared Valence Band Plasmon Resonance in Cu2–xSe Nanocrystals

Stoichiometric copper(I) selenide nanoparticles have been synthesized using the hot injection method. The effects of air exposure on the surface composition, crystal structure, and electronic properties were monitored using X-ray photoelectron spectroscopy, X-ray diffraction, and conductivity measurements. The current−voltage response changes from semiconducting to ohmic, and within a week a 3000-fold increase in conductivity is observed under ambient conditions. The enhanced electronic properties can be explained by the oxidation of Cu+ and Se2− on the nanoparticle surface, ultimately leading to a solid-state conversion of the core from monoclinic Cu2Se to cubic Cu1.8Se. This behavior is a result of the facile solid-state ionic conductivity of cationic Cu within the crystal and the high susceptibility of the nanoparticle surface to oxidation. This regulated transformation is appealing as one could envision using layers of Cu2Se nanoparticles as both semiconducting and conducting domains in optoelectronic...

Cu2Se Nanoparticles with Tunable Electronic Properties Due to a Controlled Solid-State Phase Transition Driven by Copper Oxidation and Cationic Conduction

Copper selenide thin films by chemical bath deposition

CuxS thin films with a wide range of sheet resistances (rSquare Operator ) and optical transmittance (T%), indicating different composition x, have been obtained from chemical baths constituted from copper(II) chloride, triethanolamine and thiourea at appropriate pH (10-12). Depending on the deposition parameters, a range of combination of rSquare Operator approximately=30 Omega to 1 M Omega and T% (500 nm) approximately=1 to 65 and a range of colour of reflected daylight (golden yellow, purple, blue, green, etc.) can be obtained. The films have been found to be stable with respect to electrical and optical properties on storage under ambient. Various possible large area applications such as in architectural glazing, photothermal and photovoltaic conversions are discussed.

https://iopscience.iop.org/article/10.1088/0268-1242/4/3/009/pdf

Chemical bath deposition of CuxS thin films and their prospective large area applications

This paper presents the preparation of unique copper sulfide flakes in CTAB/n-C5H11OH/n-C6H14/water microemulsions under hydrothermal conditions at 130 °C. With the pre-addition of n-dodecanethiol to the microemulsions, much smaller hexagonal Cu2S nanodisks resulted, which self-assembled into a superlattice. The crystal phases, absorption properties, and morphologies were characterized. The formation mechanism of the unique crystals is also discussed.

L. Fabick

Papers

Research on polycrystalline thin-film photovoltaic devices