Work Function Modulation in 2D Carbon Allotropes via Defect Engineering for Field Emission Applications: A DFT Analysis

Two-dimensional (2D) materials from the carbon family, including γ-graphyne, holey graphyne, and biphenylene, are expected to exhibit remarkable properties such as adjustable band gaps, high surface-to-volume ratio, rapid carrier mobility, excellent thermal conductivity, and stability. The electronic properties of these materials exhibit distinct behavior in the presence of structural imperfections, such as vacancy defects. In this work, we explore the changes in the electronic properties of γ-graphyne, holey graphyne, and biphenylene monolayers after the introduction of periodic vacancy utilizing first-principles density functional theory. The work function of the defective structure is found to depend on the hybridization of the removed carbon atom. Double-vacancy defects in γ-graphyne lowered the work function from 5.39 to 5.17 eV. Removing an sp-hybridized carbon atom in holey graphyne reduced the work function from 5.56 to 5.29 eV, while removing an sp2 carbon atom increased the work function to 5.72 eV, indicating a strong correlation between carbon hybridization and work function. The band structure of defective structures shows interesting features like a flat bands. This investigation could offer valuable insights into how defect engineering in 2D materials can tailor electronic properties to achieve the desired characteristics, facilitating the design of field emission materials with reduced work functions.