Surface Adsorption and Vacancy in Tuning the Properties of Tellurene

The emerging two-dimensional tellurene has been demonstrated to be a promising candidate for photoelectronic devices. However, there is a lack of comprehensive insight into the effects of vacancies and common adsorbates (i.e., O₂ and H₂O) in ambient conditions, which play a crucial role in semiconducting devices. In this work, with the aid of first-principles calculations, we demonstrate that H₂O and O₂ molecules behave qualitatively differently on tellurene, while water adsorption can be remarkably promoted by adjacent preadsorbed O₂. Upon the formation of Te vacancies, the adsorption of both O₂ and H₂O molecules is enhanced. More importantly, the existence of H₂O and Te vacancies can dramatically facilitate the dissociation of O₂, suggesting that tellurene may be readily oxidized in humid conditions. In addition, it is found that the electronic properties of tellurene are well preserved upon either H₂O or O₂ adsorption on the surface. In sharp contrast, vacancies enable significant modification on the band structure. Specifically, an indirect-to-direct band gap transition is found at a vacancy concentration of 5.3%.