Role of Quantum-Confinement in Anatase Nanosheets

TL;DR

This study uses ab initio calculations to explore how quantum confinement and surface orientation influence the electronic and optical properties of anatase nanosheets, revealing localized excitons and their impact on photoconversion efficiency.

Contribution

It provides a detailed theoretical analysis of quantum confinement effects and surface orientation on anatase nanosheets' properties, which was previously not well understood.

Findings

Localized excitons along the (001) direction explain optical differences.

Surface orientation affects electronic and optical properties.

High (001) facet percentage improves photoconversion efficiency.

Abstract

Despite most of the applications of anatase nanostructures rely on photoexcited charge processes, yet profound theoretical understanding of fundamental related properties is lacking. Here, by means of ab initio ground and excited-state calculations, we reveal, in an unambiguous way, the role of quantum confinement effect and of the surface orientation, on the electronic and optical properties of anatase nanosheets (NSs). The presence of bound excitons extremely localized along the (001) direction, whose existence has been recently proven also in anatase bulk, explains the different optical behavior found for the two orientations (001) and (101) when the NS thickness increases. We suggest also that the almost two-dimensional nature of these excitons can be related to the improved photoconversion efficiency observed when a high percentage of (001) facet is present in anatase nanocrystals.