Copper Oxide Nanocrystals

TLDR

Inorganic nanocrystals serve as benchmark models for nanotechnology, and copper(I) oxide is a promising semiconductor for solar energy conversion and catalysis, though phase‑transformation volume changes can induce crystal twinning. The study develops a method to produce highly uniform, monodisperse Cu₂O nanocrystals to understand the Cu/Cu₂O/CuO system at the nanoscale. The method involves first forming Cu nanocrystals, then oxidizing them to highly crystalline Cu₂O, demonstrating a generalized approach for synthesizing transition‑metal‑oxide nanocrystals. Spectroscopic analysis revealed a thin (~5 Å) epitaxial CuO layer on Cu₂O nanocrystals that blue‑shifts with decreasing size, and the Cu(I) oxide phase remains surprisingly well‑stabilized at this scale.

Abstract

It is well-known that inorganic nanocrystals are a benchmark model for nanotechnology, given that the tunability of optical properties and the stabilization of specific phases are uniquely possible at the nanoscale. Copper (I) oxide (Cu2O) is a metal oxide semiconductor with promising applications in solar energy conversion and catalysis. To understand the Cu/Cu2O/CuO system at the nanoscale, we have developed a method for preparing highly uniform monodisperse nanocrystals of Cu2O. The procedure also serves to demonstrate our development of a generalized method for the synthesis of transition metal oxide nanocrystals. Cu nanocrystals are initially formed and subsequently oxidized to form highly crystalline Cu2O. The volume change during phase transformation can induce crystal twinning. Absorption in the visible region of the spectrum gave evidence for the presence of a thin, epitaxial layer of CuO, which is blue-shifted, and appears to increase in energy as a function of decreasing particle size. XPS confirmed the thin layer of CuO, calculated to have a thickness of ∼5 Å. We note that the copper (I) oxide phase is surprisingly well-stabilized at this length scale.