Influence of O-vacancy concentration on the structural, electronic properties and quantum capacitance of monolayer Ti2CO2: A first-principles study

Abstract

First-principles calculations are used to systematically investigate the structural, electronic properties and quantum capacitance of Ti2CO2 monolayer with different oxygen vacancy concentration (OVC). The band unfolding technique is performed to obtain the effective band structure in the primitive cell. 32 configurations with OVC of 5.56%, 11.11%, and 16.67% are confirmed. Based on the binding energies and vacancy formation energy, three configurations with one oxygen vacancy at C site, two oxygen vacancies at (A, F) and three oxygen vacancies at (I, V, 5) are further investigated. Pristine Ti2CO2 is an indirect semiconductor with the band gap of 0.2871 eV. The introduction of two or three oxygen vacancies leads to the electronic phase transition from semiconductor to metal. The further analysis indicates that the red shift of Ti-d state results in the decrease of band gap for Ti2CO2 with OVC of 5.56%, while Ti-d and O-p states broadening result in the metallization of the systems with OVC of 11.11% and 16.67%. The introduction of oxygen vacancy can generally improve the quantum capacitance and surface storage charge of perfect Ti2CO2, especially for Ti2CO2 with OVC of 5.56%. The results could provide useful guidance for the practical applications of Ti2CO2 with different OVC in nanoelectronic devices.