Modulation Of The Electronic And Transport Properties Of Two-dimensional Quantum Systems

Recently, extensive experimetal and theoretically studies have been carried out on modulating the electronic properties and electronic transport properties of the two dimension material. Developing approach to effectively control the electronic and magnetic properties of those materials, such as chemical decoration, stress, external electronic field and magnetic field, is important to promote the application of these two dimensional magnetic material. In this work, we considered the modulation effect of chemical decoration and external electronic field on the electronic and transport properties of two dimensional materials by using the density functional theory in combination with none-quilibrium Green’s method. The main content and conclusions of this thesis are as follows:1. We systematically study the modulation effect of chemical decoration including hydrogenation, fluorination, and oxidization on the surface work function of graphene and two-dimensional hexagonal boron nitride. The chemical decoration is effective approach to modulate the surface work function, which expands the space to design diverse nano-devices based on graphene. Moreover, we also find some un-expectation chemically decorated cases which do not follow the traditional rule of “electronegative(electropositive) adsorbates, which increase(decrease) the work function of the surface”.Such a phenomenon is mainly derived from the charge redistribution induced by the bonding process between adsorbates and carbon atoms along with the chemical decoration;2. We study the electronic properties and tunneling magnetoresistance(TMR) of magnetotunnel junctions(MTJs) based on Co/Fe intercalated bilayer graphene(bi-Gr),bilayer hexagonal boron nitride(bi-h-BN), and bilayer Gr-h-BN(bi-GBN). The spin-polarized bands around the Fermi energy of the two dimensional bilayer sheets are modulated by the intercalated cobalt. The TMR ratio reaches 169.94% and 173.00% for cobalt and iron intercalated Ni|bi-GBN|Ni MTJs, respectively. We observe that the Co/Fe intercalated bi-GBN is a promising candidate as a spacer in MTJs for spintronics;3. We investigate the tunneling magnetoresistance(TMR) of the magnetotunnel junctions(MTJs) based on one quintuple layer(QL) Bi2Se3 and its response to external electrical field. The TMR oscillates with the externally applied field because of the spin resolved charge redistribution. Our results indicate that the one QL Bi2Se3 is a promising candidate for the spacer of MTJs because of the weak interaction of one QL Bi2Se3 to Feelectrode. Moreover, its TMR ratio can be modulated by external electrical field;4. We perform a first principles study of transition metal atom doped in graphane.Based on density functional theory(DFT) plus the self-consistent Hubbard U approach,we explore the influence of the external electronic field effects on the electronic and magnetic properties of transition metal embedded graphane(TM-Grane, TM= Mn, Co).Our studies give clear evidence that the charge transfer between the carbon atom and TM atom or the electronic states within the TM atom is the main reason for the magnetic variation in these TM-Grane systems. An externally applied electric field could tailor the magnetic properties of Mn-Grane.