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چكيده انگليسي :

Study of the Electronic Quantum Transport of Disordered Graphene Nanoribbons Mozhdeh Forouzandeh Hafshejani m forouzandeh@ph iut ac ir 22 02 2012 Department of Physics Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language PersianSupervisor Dr Farhad Fazileh fazileh@cc iut ac irAbstractGraphene is an allotrope of carbon Recently graphene has emerged as a fascinating system for funda mental studies in condensed matter physics The discovery of graphene and its remarkable electronicand magnetic properties initiated great research interest in this material The Nobel Prize in Physicsfor 2010 was awarded to Andre Geim and Konstantin Novoselov at the University of Manchester forgroundbreaking experiments regarding the two dimensional material graphene Graphene is a oneatom thick layer of graphite where low energy electronic states are described by the massless Diracfermion so that the unique features of graphene electronic properties arising from its gapless massless chiral Dirac spectrum are highlighted Furthermore Graphene nanoribbons are candidate materials forfuture applications in nanoelectronics and molecular devices due to their semiconducting properties Finite graphite systems having a zigzag edge exhibit a special edge state The corresponding energybands are almost flat at the Fermi level and thereby give a sharp peak in the density of states Thecharge density in the edge state is strongly localized on the zigzag edge sites No such localized stateappears in graphite system having an armchair edge Moreover the quality of the draphene deriva tives are so good that ballistic transport and quantum Hall effects QHE have been observed Amonggraphene derivatives graphene nanoribbons constitute a fascinating object due to a rich variety ofband gaps from metals to widegap semiconductors In particular the half filled zero energy statesemerge in all zigzag nanoribbons and hence they are metallic Another basic element of graphenederivatives is a graphene nanodisk It is a nanometer scale disk like material which has a closed edge It is also referred to as nanoisland nanoflake nanofragment or graphene quantum dot Nanoribbonsand nanodisks correspond to quantum wires and quantum dots respectively They are candidates offuture carbon based nanoelectronics and spintronics alternative to silicon devices In this project theelectronic quantum transport properties of graphene nanoribbons are studied Although these systemsshare the similar graphene electronic structure confinement effects are playing a crucial role Thelateral confinement of charge carriers could create an energy gap near the charge neutrality point depending on the width of the ribbon Then the conductance of metallic graphene nanoribbons withsingle defects and weak disorder at their edges is investigated in a tightbinding model We find thata single edge defect will induce quasilocalized states and consequently cause zero conductance dips The center energies and breadths of such dips are strongly dependent on the geometry of graphenenanoribbons Armchair graphene nanoribbons are more sensitive to a vacancy than zigzag graphenenanoribbons but are less sensitive to a weak scatter More importantly we find that with weak disor der that is modeled with the Anderson model zigzag graphene nanoribbons will change from metallicto semiconducting due to Anderson localization However weak disorder only slightly affects theconductance of armchair graphene nanoribbons near the Fermi energy Keywords Graphene nanoribbon Quantum transport Coherent transport Disordered systems Weak scatterer Vacancy Landauer formalism

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مطالعه ي هدايت الكتريكي در نانو روبان هاي گرافيتي بي نظم

ترابرد الكتريكي , تهي جاي , پراكندگي ضعيف , تابع گرين , فرمول لاندائر