Heoretical Studies On The Structures And Properties Of Two-dimensional Diamond Nanofilms With Boron-termination

Since the discovery of graphene,the two-dimensional nanomaterials have been the focus of research,which are widely used in physics,chemistry,optoelectronics,biomedicine,sensors,supercapacitors and batteries.In this paper,based on density functional theory,the thickness-dependent structure stability,electrical properties,optical properties,and carrier mobility of boron-terminated diamond(111)nano films are systematically studied.Two-dimensional diamond nano film is a novel structure,whose surface relaxation reconstruction determine electrical properties.It has become one of the most active research directions in the diamond field.The main research results are summarized as follows:1.Based on first-principles calculation,two kinds of boron-terminated diamond(111)nanofilms model are considered.In the first model,one surface is substituted by B atoms and another side is passivated by H atoms(named as B-C-H structure).In the second model,both C surfaces are substituted by B atoms(named as B-C-B structure).The structural,electronic properties and optical properties of B-C-H and B-C-B diamond nanofilms are investigated.It is reasonably stated that the B-C-H structures with n?2 and B-C-B structures with n?3 are dynamically and thermally stable.The nano films have direct bandgap characteristic,and their bandgaps are tunable in a region of 2.0-2.7 eV.The bandgaps are narrower than that of bulk diamond,being mainly related to the surface termination of boron atoms.The valence band maximum is mainly contributed by the outmost surface C atoms and B atoms with the extended state in the plane,while the conductance band minimum levels are mainly contributed by the localized charge from the outmost B atoms perpendicular to the surface.2.Based on the deformation potential theory,the carrier mobility values of the B-C-H and B-C-B diamond nanofilms are calculated.The electron mobility of B-C-H and B-C-B nanofilms structures are 1.62-2.07×103 cm2·V-1·s-1 and 1.48-1.69×03 cm2·V-1·s-1,respectively,and the hole mobility are 4.05-6.40×102 cm2·V-1·s-1 and 3.33-6.59×102 cm2·V-1·s-1,respectively.The electron mobility is 3-4 times higher than the hole mobility,the distinguished carrier mobilities between electron and hole are favorable for enhancing the effective separation of electron-hole pairs.It has been proved that boron-termination can effectively increase the stability of diamond nanofilms and effectively modulate the electrical properties and transport properties,which provides a broad application field for the further preparation of diamond-based nanometer devices.