Modulated band structures of two-dimensional atomically thick (100) diamond nanofilms with surface functionalization

Using first-principles density functional theory calculations, we investigate the structural and electronic properties of layer number (n) dependent two-dimensional (2D) atomically thick (100) diamond nanofilms related to surface functionalization of hydrogen and fluorine. The nanofilms with functionalized surface are dynamically and thermally stable demonstrated by phonon dispersion curves and ab initio molecular dynamics simulations. The band gaps of semi-functionalized nanofilms are in the region of 2.41-2.65 eV almost unchanged related to n or surface functionalization, contributed by the electronic feature of the unfunctionalized side. For the cases of full-functionalization on both sides of the nanofilms, the band gaps are larger than that for the semi-functionalized 2D nanofilms. These band gaps decrease following a nonlinear inverse law of n, attributed to a quantum confinement effect. The fluorine-functionalized nanofilms present the larger band gaps with respect to the cases of hydrogen-functionalization. Moreover, the absorption spectra of these 2D nanofilms show an absorption edge at around 2.8 eV for semi-functionalized and upon 4.8 eV for full-functionalized nanofilms. Based on the theoretical results, the proposed nanofilms can inspire more efforts in practical applications and fabricating low-dimensional diamond-based optoelectronics devices.