Electronic properties of fluorine/hydrogen adsorbed two-dimensional tetrahex-carbon: A first-principles study

A recently proposed two-dimensional (2D) carbon allotrope, tetrahex-carbon, draws scientific attention due to its remarkable electronic and mechanical properties. This 2D carbon structure consists of tetragonal and hexagonal rings, and exhibits excellent semiconductor properties including a finite direct band gap and high carrier mobility, suggesting potential applications in semiconductor devices. In this paper, the electronic properties of fluorine/hydrogen adsorbed tetrahex-C was investigated via first-principles density-functional theory calculations. It demonstrates that its band structure can be significantly tuned and could be metallic with dangling bonds from F/H adsorption. With increasing F/H adsorption density, it shows semiconducting behavior and the band gap is widening, mainly due to the sp²-bonded carbon being gradually converted to sp³ hybridization. It was also found that effective masses of charge carriers along the zigzag-direction can largely reduce through adsorption of F/H, leading to potentially enhanced carrier mobility. Tetrahex-C shows prominent anisotropicity and the tunability of effective masses through F/H adsorption is remarkably dependent on the crystal orientation. In addition, it was found that, the work function of the F-adsorbed tetrahex-C increases while electron affinity decreases, compared to the pristine one. However, the H-covered carbon film shows significant reductions of both work function and electron affinity.