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UBC Theses and Dissertations

Tuning graphene’s electronic and transport properties via adatom deposition Khademi, Ali


This thesis investigates the effect of adatom deposition, especially alkali and heavy adatoms, on graphene’s electronic and transport properties. While there are many theoretical predictions for tuning graphene’s properties via adatom deposition, only a few of them have been observed. Solving this enigma of inconsistency between theory and experiment raises the need for deeper experimental investigation of this matter. To achieve this goal, an experimental set up was built which enables us to evaporate different metal adatoms on graphene samples while they are at cryogenic temperatures and ultra-high vacuum (UHV) conditions. The critical role of in situ high-temperature annealing in creating reliable interactions between adatoms and graphene is observed. This contradicts the commonly accepted assumption in the transport community that placing a graphene sample in UHV and performing in situ 400-500 K annealing is enough to provide a reliable adatom-graphene interaction. Even charge doping by alkali atoms (Li), which is arguably the simplest of all adatom effects, cannot be achieved completely without in situ 900 K annealing. This observation may explain the difficulty many groups have faced in inducing superconductivity, spin-orbit interaction, or similar electronic modifications to graphene by adatom deposition, and it points toward a straightforward, if experimentally challenging, solution. The first experimental evidence of short-range scattering due to alkali adatoms in graphene is presented in this thesis, a result that contradicts the naive expectation that alkali adatoms on graphene only cause long-range Coulomb scattering. The induced short-range scattering by Li caused decline of intervalley time and length (i.e., enhancement of intervalley scattering). No signatures of theoretically predicted superconductivity of Li doped graphene were observed down to 3 K. Cryogenic deposition of copper increased the dephasing rate of graphene. This increase in dephasing rate is either a sign of inducing spin-orbit interaction or magnetic moments by copper. No similar effect was observed for indium.

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