Suppression of auxetic behavior in black phosphorus with sulfur substitution

TL;DR

This study uses first-principles calculations to show that sulfur substitution in black phosphorus suppresses its intrinsic auxetic behavior by distorting its structure and altering charge distribution, while also changing its mechanical and electronic properties.

Contribution

It provides a detailed atomic-level understanding of how sulfur doping affects the auxetic and electronic properties of black phosphorus, revealing the suppression mechanism.

Findings

Sulfur atoms distort the bow-tie structure responsible for auxeticity.

Sulfur substitution increases bulk modulus and Poisson's ratio, decreases Young's modulus and shear modulus.

Sulfur doping turns black phosphorus metallic, reducing semiconducting properties.

Abstract

Sulfur-doped black phosphorus (b-P) has recently emerged as a promising candidate for next-generation electronic and optoelectronic technologies owing to its enhanced environmental stability and tunable electronic properties. In this work, we systematically investigate the effects of sulfur substitution on the elastic, mechanical, and electronic properties of b-P, with a particular focus on its auxetic behavior (that is, negative Poisson's ratio), using first-principles density functional theory calculations. Our results unveil the fundamental origin of the intrinsic auxetic response in pristine b-P and elucidate how sulfur incorporation alters this behavior. We find that sulfur atoms distort the characteristic bow-tie structural motif responsible for the negative Poisson's ratio in b-P, thereby suppressing the in-plane auxeticity. Moreover, the resulting charge redistribution also effectively quenches the out-of-plane auxetic response of b-P. With increasing sulfur content, the bulk modulus and Poisson's ratio increase, whereas the Young's modulus, shear modulus, and Debye temperature decrease. Additionally, sulfur substitution suppresses the semiconducting properties of b-P, giving rise to metallicity. These findings highlight that although sulfur substitution enhances the environmental stability of b-P, it also substantially modifies its elastic and mechanical properties, particularly the auxetic behavior, which is an important consideration in the design of nanoscale electronic devices.