Theoretical Study Of Surface Structures And Electronic Properties Of Nitrogen-terminated Diamond

Diamond has excellent physical and chemical properties,such as high hardness,high excitation electric field,high carrier mobility and chemical inertness,which make it be applied to high-power and high-frequency electronic devices.Surface functionalization in diamond can improve the structural stability and modulate electronic properties,such as band gap and electron affinity.At present,diamond surface is generally terminated by hydrogen or oxygen.The study show that the hydrogen-terminated diamond surface has p-type surface conductivity and presents negative electron affinity.The oxygen terminal greatly enhances the stability of the structure,adjusts the diamond hydrophobicity to hydrophilicity,and the electron affinity changes from negative to positive.In addition,nitrogen-terminated diamonds have been experimentally realized on single-crystal and polycrystalline diamond by N-plasma treatment.Due to the difference of electronegativity between nitrogen and carbon atoms,nitrogen-terminated diamond surface is expected to show positive electron affinity,and it is potential to apply in nano-sensing and quantum information.Some theoretical works have proved that nitrogen-terminated diamond provides an ideal electronic environment for near-surface color centers for sensing and quantum information applications.However,in previous work,the nitrogen-terminated diamond surface structures were obtained by directly substituting surface carbon atoms with nitrogen atoms,then the structures are simple.Therefore,we use CALYPSO to systematically predict the nitrogen-terminated diamond(100)and(111)surface structures,and calculate their stability and electronic properties through first-principles calculation,and discuss their possible applications.The main research results are as follows:1.The three types of 1 monolayer(ML)coverage nitrogen-terminated diamond(100)surfaces were obtained by crystal structure prediction method,and the stability and electrical properties were calculated by first principles.The surfaces of three nitrogen-terminating diamonds(100)have dynamically and thermally stability.The electron local function indicates covalent bonds between surface nitrogen atoms.The three types of nitrogen-terminated diamonds(100)surfaces have positive electron affinity(3.03,2.87 and 2.64 e V),which can be used to maintaining the negative charge states of silicon-vacancy and nitrogen-vacancy near the diamond surface,so that it has potential applications in nano-sensing technology and quantum information processing.Bader charge analysis shows that more charge accumulation gives the material higher electron affinity potential.In addition,the band structures of the three configurations show semiconducting characteristics,and surface states caused by nitrogen atoms exist in the diamond band gap.The electron states near the Fermi level are mainly contributed by the surface C and N atoms,and the 2p orbitals of C and N atoms are hybridized.2.The three types of 1 ML coverage nitrogen-terminated diamonds(111)surface structures were obtained by crystal structure prediction method,and the stability and electrical properties were calculated by first principles.The three types of nitrogen-terminated diamonds have thermally stability.The electron local function indicates covalent bonds between surface atoms.The three types of nitrogen-terminated diamonds(111)surfaces have positive electron affinity(1.39,1.37 and 1.95 e V),which can be used in nano-sensing and quantum information processing.Surface states caused by nitrogen atoms exist in the diamond band gap.The electron states near the Fermi level are mainly contributed by the surface C and N atoms,and the 2p orbitals of C and N atoms are hybridized.This work provides theoretical guidance for the design and fabrication of nitrogen-terminated diamond-based electronic devices.