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Silicon Carbide Materials Processing and Applications in Electronic Devices Part 2

Tham khảo tài liệu 'silicon carbide materials processing and applications in electronic devices part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | SiC Cage Like Based Materials 25 1.1.2 sp2 hybridization When the s orbital and two of the p orbitals for each carbon are mixed the hybridization for each carbon is sp2. The resulting geometry is the trigonal hexagonal planar geometry with the bond angle between the hybrid orbitals equal to 120 the additional p electron is at the origin of the n band. Fig. 2. how to build up graphite nanotube or fullerene from a graphene sheet after the original figure from Geim et al Geim and Novoselov 2007 Graphene is of importance both for its unusual transport properties and as the mother for fullerene and nanotube families figure 2 . Graphene can be defined as an infinite periodic arrangement of only six-member carbon ring polycyclic aromatic carbon. It can be looked at as a fullerene with an infinite number of atoms. Owing the theoretical unstability of 2D networks graphene sheets are stable over several microns enough for applications. Graphene has a two atom basis A and B per primitive cell arranged in a perfect hexagonal honeycomb. Except the center of the Brillouin zone r the structure can be entirely described by symmetry with the particular setpoints M K and K related by the relationship K -K . For each atom three electrons form tight bonds with neighbor atoms in the plane the fourth electron in the pz orbital does not interact with them leading to zero pz orbital energy Ez 0. It can be easily seen that the electron energy is zero at K and K graphene being a semiconductor with a zero bandgap. The most striking result is the linear relationship for the dispersion curve near K and K . Since the effective mass is related to the second derivation of the energy this implies a zero mass for the two electrons one by site A and B . As a consequence the classical picture of the Schrodinger equation must be replaced by the Dirac equation where Dirac spinors two component wave function are required in the mathematical description of the quantum state of the relativistic electron.