Designs And Properties Studies Of Novel Carbon Materials By First Principles Calculations

Carbon,as one of the most abundant elements at the earth,exhibits flexible hybridizations,resulting in many of carbon materials with different dimensions,structures and particular properties.With the improvement of science and technology,the demand for novel functional materials is increasing day by day.Graphene,diamond,fullerene,carbon nanotubes and so on have stirred up the exiperimental and theoretical investigations for other carbon materials with fascinating structure and properties.At recent decades,more than one hundred of novel carbon allotropes have been theoretical or exiperimental proposed,as the candidate functional materials.However,only very few carbon allotropes proposed theoreticaly have been experimentally synthesized,which is far from enough to the needs of the new functional materials.Therefore,designing some novel carbon materials with unique structure and properties can provide more possible candidates for the corresponding applications and more choices for experimental synthesis.In this thesis,from twisted sp² and sp³ hybridizations as well as particular structure of black phosphorous,we successfully proposed three two-dimensional(2D)and two three-dimensional(3D)carbon allotropes using first-principles calculations,and we evaluated their theoretical reasibilities using four stabilties containing energetical,mechanical,thermal and dynamical stabilities.And we calculated and analyzed their electronic and mechanic properties,mobilities and so on.The main constents contain:1.From the twisted sp² bond model of carbon,we designed a 2D carbon allotrope Po-C32.Calculated cohesive energy,phonon band structure,elastic constants and ab intio molecular dynamic(AIMD)simulation demonstrate that it has good stabilities.The size of the biggest pore is 5.67?,close to that of graphenylene and exhibiting potential in absorption and catalysis fields.Based on the obtained elastic modulus,its mechanical properties have the similar results along x and y directions.Po-C32 is a semiconductor with a direct band gap of 2.05 e V.Stacking the structure of Po-C32,two 3D materials(Po-C24-3D and Po-C32-3D)can be obtained.Amond them,Po-C24-3D is a semiconductor with an indirect band gap of 1.02 e V,while Po-C32-3D possesses an indirect band gap of 3.90 e V.Simulated Raman,XRD,optical absorption and ¹³C NMR chemical shift reveal that they show different features,which can be used to identify them in the future.Po-C32 and its 3D derivative materials exhibit attractive structures,mechanical and electronic properties,applying in nanoelectronic devices,absorption,catalysis fields and so on.2.Owing to the lack of the study of all sp³-hybridized 2D carbon materials,combining the regular and twisted sp³-bonded models,we constructed a novel all sp³-hybridized 2D carbon allotrope,named as TTH-carbon.Based on first-principles calculations,we obtained its optimized structure and demonstrated its good stabilities.Then,we calculated its mechanical and electronic properties as well as carrier mobility and optical absorption.TTH-carbon has an indirect band gap of 3.23 e V,smaller than that of all sp³-bonded 2D TO-C₁₀.The mobilities of electrons and holes along y direction are about 3000 cm² V^-1 s^-1,while the mobilities along x direction is only?10² cm² V^-1 s^-1,revealing TTH-carbon can be applied in electronic devices.Its mechanical and optical properties display high anisotropy,and optical absoprtion can reach up to?10⁵ cm^-1.The proposed TTH-carbon can richen the family of 2D all sp³-bonded carbon allotropes,and its thin structure,outstanding electronic,mechanical and optical properties make it potential to apply in electronics,mechanics and optoelectronics.3.The dumbbell(DB)structures of Si/Ge/Sn exhibit fascinating structures and outstanding electronic properties,but the DB structures of carbon haven't been studied systematically to now.Therefore,we systematically investigated the structures and properties of two DB carbon allotropes(DB-C10-I and DB-C10-II).We also evaluated their stabilties,and then calculated their mechanical,electronic,optical properties and carrier mobilities.The calculation results demonstrate they have good stabilities.From their structures,all carbon atoms are sp³-hybridizations,richening the family of 2D all sp³-bonded carbon allotropes.DB-C10-I has an indirect band gap of2.68 e V and isotropic mechanical proeprties,while DB-C10-II possesses an indirect band gap of 3.65 e V and anisotropic mechanical properties.Meanwhile,they have high carrier mobilities and strong optical absorption(?10⁵ cm^-1).Two new allotropes can make up the lack of the investigations of the DB catbon structures,and their particular properties make them apply in electronics and optoelectronics.The existent[1.1.1]propellane molecule can be used as the precursor for possible experimental realization of two allotropes in the future,providing theoretical strategy for experimental synthesis.4.From the primitive cell of diamond and the twisted sp³-hybridized binding model in the above 2D carbon materials,we constructed a new carbon allotrope of diamond through moving a carbon atom,termed as TD-C8.The results using first-principles calculations demondstrate it have good stabilities.It has the similar structure with diamond,but smaller density of 2.67 g/cm³,close to that of graphite.The calculated Young's modulus and Vickers hardness are 314 and 27.5 GPa,respectively,much smaller than diamond and most of all sp³-bonded diamond-like allotropes.Additionally,TD-C8 has a moderate indirect band gap of 2.65 e V,and its optical absorption coefficient is?10⁵ cm^-1,exhibiting great potential in catalysis and optoelectronics.Simulated XRD spectra match well with the XRD model of the detonation soot(sample Alaska B),revealing it may be existed in the detonation soot.TD-C8 has lower density,smaller elastic modulus and more moderate band gap,applying in ultraviolet light absorption,mechanics and electronics.5.From the particular structure of black phosphorus,we substituted all phosphorus atoms using sp³-bonded carbon,and then made all carbon atoms bind with the adjacent atoms,resulting in a new all sp³-bonded 3D carbon allotrope(Ort-C8)with orthorhombic P2212 symmetry.Samely,we considered its cohesive energy,phonon band structure,AIMD simulation and elastic constants,which demonstrates it is stable.Electronic structure calculations display Ort-C8 has an indirect band gap of4.61 e V,belong to carbon material with the ultrawide band gap.Additionally,Ort-C8exhibits ultrahigh Young's modulus(1047 GPa)and Vickers hardness(93.2 GPa),close to that of diamond.Simulated XRD spectra show Ort-C8 has different characteristic peaks with other superhard materials(diamond,o C32,M-carbon and W-carbon),which can be used to experimentally identify them in the future.The proposed Ort-C8 richens the family of superhard carbon materials,which can be used as the candidate metamaterials.From the sp²-and sp³-hybridized bond models of carbon and the particular structure of black phosphorus,we successfully designed a series of carbon materials using first principles calculations,containing 2D Po-C32 with direct band gap,all sp³-bridized 2D TTH-carbon,2D Dumbell carbon DB-C10 with high mobilities,all sp³-bridized 3D diamond-like TD-C8 with moderate band gap and superhard 3D Ort-C8,which provides reliable strategies for designing other new functional materials.Moreover,these structures richened the family of carbon materials,and their unique structures and properties make them exhibit promissing applications in many fields like electronics,machanics,catalysis,adsorption and photoelectric devices.