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UBC Theses and Dissertations
Tuning graphene’s electronic and transport properties via adatom deposition Khademi, Ali
Abstract
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.
Item Metadata
Title |
Tuning graphene’s electronic and transport properties via adatom deposition
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2017
|
Description |
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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Genre | |
Type | |
Language |
eng
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Date Available |
2017-08-14
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0354245
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2017-09
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Rights
Attribution-NonCommercial-NoDerivatives 4.0 International