Facet‐Dependent Optical Properties Revealed through Investigation of Polyhedral Au–Cu₂O and Bimetallic Core–Shell Nanocrystals

Abstract

The ability to prepare Au–Cu2O core–shell nanocrystals with precise control over particle size and shape has led to the discovery of facet‐dependent optical properties in cuprous oxide crystals. The use of Au cores not only allows the successful formation of Au–Cu2O core–shell nanocrystals with tunable sizes, but also enables the observation of facet‐dependent optical properties in these crystals through the Au localized surface plasmon resonance (LSPR) absorption band. By tuning the Cu2O shell morphology from rhombic dodecahedral to octahedral and cubic structures, and thus the exposed facets, the Au LSPR band position can be widely tuned. Such facet‐dependent optical effects are not observed in bimetallic Au–Ag and Au–Pd core–shell nanocrystals with the same precisely tuned particle sizes and shapes. It is believed that similar facet‐dependent optical properties could be observed in other ionic solids and other metal–metal oxide systems. The unusually large degree of plasmonic band tuning covering from the visible to the near‐infrared region in this type of nanostructure should be quite useful for a range of plasmonic applications.

Highly Facet‐Dependent Photocatalytic Properties of Cu2O Crystals Established through the Formation of Au‐Decorated Cu2O Heterostructures

“…[29,36,37] The thin surfacel ayer with different degrees of band bending and band structures for the (100), (111), and (110) planeso fC u 2 O, and as ar esult supposedly different refractive indices, can also be used to explain the observed faceted-dependent optical properties of metal-Cu 2 Oc ore-shell nanocrystals discovered recently,i nw hich the optical absorption band positions of the metal cores and the Cu 2 Os hells are strongly dependent on the exposed Cu 2 Of acets. [31,[38][39][40][41] Thus, Cu 2 Oc rystals, and possibly many other semiconductors, can show variousf acet-dependent properties because they are all related. However,f ull understanding of these physicalp henomena still requires further studies and demonstrations.…”

Synthesis of Ultrasmall Cu2O Nanocubes and Octahedra with Tunable Sizes for Facet-Dependent Optical Property Examination

“…Facet-dependent optical properties of Cu 2 O nanocrystals were fi rst reported through the synthesis of AuCu 2 O cubes, cuboctahedra, octahedra, and rhombic dodecahedra, in which the Au surface plasmon resonance (SPR) absorption band position is fi xed despite large changes in the Cu 2 O shell thickness, but is dependent on the shape, or more precisely the exposed surface facets, of the core-shell particles. [9][10][11][12] More recently, Pd-Cu 2 O core-shell cubes and truncated octahedra have also displayed similar facet-dependent SPR absorption feature. [ 13 ] When the Cu 2 O shells are not single-crystalline or do not have sharp faces, absorption band from the plasmonic metal cores can shift progressively to the red with increasing shell thickness.…”

“…[1][2][3][4][5][6][7][8][9] Even heat transmission has been found to show facet dependence. [ 10 ] Unlike organocatalysis, which deals with only surface atoms, [4][5][6][7] photocatalytic, electrical, and optical properties involve with charge carriers or photons moving into or out of a crystal through the particle surfaces.…”

Strong Facet Effects on Interfacial Charge Transfer Revealed through the Examination of Photocatalytic Activities of Various Cu2O–ZnO Heterostructures

“…Successful syntheses of popular Cu 2 O nanocubes, octahedra, rhombic dodecahedra, and other polyhedral shapes have greatly advanced our knowledge of semiconductor nanocrystals by showing their electrical conductivity, photocatalytic activity, optical absorption, and heat transmission properties are strongly depended on the exposed surface facets . The observations of these unusual properties are not accidental and entirely unexpected, but nature led us to discover these material properties because they are all related manifestation of facet effects semiconductor nanocrystals possess.…”