Controlling the band gap of ZnO by programmable annealing

TL;DR

This paper establishes a quantitative relationship between annealing conditions, grain size, and band gap in ZnO nanocrystals, revealing how thermal and cohesive energies influence electronic properties.

Contribution

It introduces a novel formulation linking annealing parameters to band gap tuning via critical size and energy considerations in ZnO nanocrystals.

Findings

Annealing condition determines critical size by energy balance.

Critical size influences local strain and quantum effects.

Formulation enables predictive control of nanomaterial properties.

Abstract

Annealing has been extensively used to control crystal growth and physical properties of materials with unfortunately unclear mechanism and quantitative correlations. Here we present the "annealing temperature - grain size - band gap" correlation for ZnO nanocrystals with experimental evidence. Findings revealed that the annealing condition determines the critical size by equating the thermal and the cohesive energy of the undercoordinated atoms in the surface skin, which in turn induce local strain and quantum entrapment, perturbing the Hamiltonian and hence the band gap. The formulation provides a general guideline for controlling crystal growth and performance of materials, and makes predictive design and fabrication of functional nanomaterials into reality.