Date of Award

6-30-2016

Document Type

Open Access Dissertation

Department

Physics and Astronomy

First Advisor

Richard Webb

Abstract

Graphene, a two-dimensional semi-conductor material containing carbon atoms tightly bonded together in a hexagonal structure, was first isolated by mechanical exfoliation in 2004. Over the past decade, it has drawn huge research interest due to its outstanding mechanical, thermal, and electrical properties. These unique properties of graphene lead to very high carrier mobility. In particular, after an annealing treatment to remove the residual impurities, the suspended graphene mobility exceeds 200,000 cm2/Vs. However, this value is highly reduced to only a few thousand cm2 /Vs in supported graphene on SiO2 or SiC substrates, due to different sources of scattering. For example, thermally excited substrate surface polar phonon scattering is the major scattering mechanism in monolayer graphene, while Coulomb scattering becomes the most important scattering mechanism in bilayer or trilayer graphene.

There have been many synthesis methods developed to manufacture few-to-single layer of graphene, such as mechanical exfoliation, epitaxial growth on SiC, chemical vapor deposition (CVD) on Cu or Ni, etc. In our laboratory, graphene is synthesized by CVD method on Cu foils. With CVD grown graphene, temperature dependent carrier mobility and carrier concentration are carried out by the Hall-effect measurement performed in Physical Property Measurement System (PPMS) from temperature range of 300 to 10 K at three different situations: pristine graphene, 2 nm Pd deposited graphene, and Pd decorated graphene with H2 exposure. For 34 of 35 pristine graphene samples, the Hall mobility increases when temperature increases, indicating that the mobility is dominated by Coulomb scattering and those samples are bilayer graphene samples. Only one sample behaves as monolayer graphene and shows quantum Hall effect. After 2 nm Pd functionalization layer deposition on those bilayer graphene samples, the mobility decreases due to additional source of scattering induced by Pd functionalization layer. Furthermore, a significant mobility enhancement has been found in the Pd deposited graphene samples with 1000 ppm H2 exposure. Meanwhile, Coulomb scattering is damped and the dominant scattering mechanism switches to surface optical phonon scattering. All these changes are attributed to the hydrogenation of Pd. The nature of temperature dependent Hall mobility of Pd deposited graphene after H2 exposure completely matches with the model of semiconductor nanostructures sandwiched by high-κ dielectrics.

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