5321

4991

كارشناسي ارشد

فيزيك

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1388

[هشت]،79ص.:مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

فرهاد شهبازي

اكبر جعفري

13/4/89

فيزيك

ID4991

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Numerical Study of the Effect of Disorder in Bilayer Graphene and Bilayer Graphene Nano Flakes Mohammad Hossein Zare mh zare@ph iut ac ir Date of Submission March 7 2010 04 24 Depatment of Physics Isfahan University of Thechnology Isfahan 84156 83111 Iran Degree M Sc Languege Farsi Farhad Shahbazi Shabazi@cc iut ac ir Abstract In this thesis we investigate localization behavior of electronic states in bilayer graphene and bilayer graphene nanoribbon formed with the Bernal stacking in presence of diagonal disorder within the tight binding model Bilayer graphene is a semi metal consisting of two coupled hexagonal lattices with inequivalent sites and on the bottom and top graphene sheets Early proposals for the control of the electronic properties in graphene such as the opening of gaps were based on controlling its geometry by reducing it to nanoribbons Nevertheless current lithographic techniques that can produce such nanostructures do not have enough accuracy to cut graphene to Angstrom precision As a result graphene nanostructures unavoidably have rough edges which have strong effects in transport properties of nanoribbons This can be accomplished in a bilayer graphene with an electric field applied perpendicular to the plane It was shown theoretically and demonstrated experimentally that a bilayer graphene is the only material with semiconducting properties that can be controlled by electric field Effect of disorder is similar to the applied electric field to the plane We use the kernel polynomial method KPM which based on the expansion of spectral functions in terms of a complete set of polynomials to numerically study the effect of disorder in bilayer graphene This accurate numerical method enables us to study very large lattices The intrinsic Gibbs oscillation in this method can be damped with the Gibbs factors We obtain local density of state LDOS numerically and evaluat discrimination parameter DP The DP is a criterion which can distinguish localized states from extended ones We find critical disorder strength which is the onset of Anderson localization in bilayer graphene The results of our calculation are presented in the weak and strong disordered regimes In the weak disordered regime all of states are delocalized and they contribute to transport but in the strong disordered regime the states start to get localized start from the boundaries of the energy spectrum With increasing disorder all states eventually become localized beyond a critical strength of disorder and a metal to insulator transition take place Keywods Graphene Anderson Transition Diagonal Disorder Kernel polynomial Method Local Density of State

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