C₂₀ Cluster-assembled Solids And Adsorption Of C₂₀ On 2D Materials

The discovery of fullerene C60 stimulated extensive theoretical and experimental studies of carbon clusters,because of its excellent properties such as high temperature carbon superconductivity.The possibility of superconductivity arising from electron-phonon coupling,and vibronic coupling becomes large as the cluster size decreases.So,tremendous attention has been focused to explore the smallest fullerenes.Among a variety of carbon clusters,C20 is the smallest and the simplest fullerene structure with the largest curvature.As a result,it can be predicted that the condensed form of the smallest fullerene C20 is the best potential candidate for high temperature superconductors because of its stronger electron phonon coupling than that of C60 fullerene.Thus in this dissertation,we have investigated various prospects of C20 based clustered assembled solid.Moreover,after the rise of graphene,two dimensional honeycomb lattices are recently materials of interest due to their unique properties as compared to their bulk counterparts.In addition to the studies on the intrinsic properties of these pure 2D materials,a great attention has also been paid to the effect of adsorbed guest atoms or molecules on some of these 2D materials.And the hybrid systems consisting of graphene and various two-dimensional materials would provide more opportunities for achieving desired electronic and/or optoelectronic properties.Moreover,fullerene based hetero-structure(C20/2D)requires understanding on the nature of the adsorption of C20 on various two-dimensional materials because their interface interaction and bonding properties play important roles in molecular functionality in hetero-structure nanomaterials.Thus we have studied adsorption of C20 cluster on 2D structures,such as graphene,silicene,germanene,stanene,BN and MoS2,by using first principal calculations based on density functional theory(DFT).In part 1,the studies are mainly focused on solid made out of C20 cluster.By performing first-principles calculations based on the density functional theory,we have investigated the optimized structures,cohesive energies and electronic properties of crystalline solids made of C20 clusters.Two cases in one-dimensional(1D)with different orientations of C20 are studied.We found that 1D molecular solid could be formed when clusters are head to head.C20 arranged in 2D graphene structure are also investigated.Our results show that,in this 2D case,C20 units are distorted and interlinked by covalent bonds,exhibiting metallic character which are supported by the corresponding calculated band structures and DOS profiles.In the 3D case,C20 arrangement in the face-centered cubic(fcc)and diamond structure are calculated.The optimized diamond structure composed of C20 molecules yields dimered C20'S,i.e.,(C20)2,which are condensed by weak van der Waals interaction between(C20)2 dimers.The band structures along with DOS calculations also suggest that molecular solid is formed in this case which is a semiconductor.However,for C20 in the fcc structure,there is significant coalescence of neighboring C20 fullerenes that makes system metallic rather than insulating.In part 2,we have studied the interaction of C20 with 2D materials,e.g,graphene,silicene,garmanene,stanene,BN and MoS2.We considered the geometric and electronic properties of C20 molecule adsorbed on these two-dimensional(2D)substrates by using first-principles calculations based on the density functional theory(DFT)with van der Waals correction.For each case,we have considered three adsorption configurations of C20 molecule,i.e.top-site(T),hallow-site(H)and bridge site(B),respectively.Our results show that.C20'S are strongly bound to silicene,germanene and stanene,however,the adsorbed C20 molecules have only weak interactions with graphene,BN and MoS2 substrates.Moreover,charge density plot implies substantial charge transfer taking place between the constituents of C20 and the substrate of silicene,germanene and stanene.Results indicate that the buckling structure of the 2D material plays important role in determining the reactivity of a 2D substrate.