Graphene, an atom-thick sheet of carbon, is a novel two-dimensional material in which the low-energy electrons behave as massless Dirac fermions. This thesis explores the effects of adsorbates on the electronic properties graphene by adsorption in controlled environment in ultra-high vacuum (UHV), coupled with in situ measurement of transport properties. Two types of adsorbates on graphene are investigated. First, the effects of charged impurity scattering are studied by controlled adsorption of potassium on bilayer graphene at low temperature in UHV. The results indicate that the magnitude of charged-impurity scattering in bilayer graphene is similar to that in single layer graphene, and in good agreement with theory. The widely observed lower mobility in bilayer graphene on SiO2 is likely due to another source of disorder. Second, the dielectric screening of bilayer graphene is modified by deposition of ice overlayers at low temperature in UHV. No screening effect is observed in pristine bilayer graphene. However, ice overlayers significantly increase the mobility of potassium-doped bilayer graphene through screening of potassium ions. Together, the ice deposition experiments demonstrate the existence of screening effect in bilayer graphene and support that charge impurities are not the dominant scatters in pristine bilayer graphene on SiO2. The screening of adsorbed potassium ions on single-layer graphene is also investigated both experimentally and theoretically. The increase in mobility upon ice deposition is much larger than expected assuming ice's bulk relative dielectric constant of 3.2. A simple model assuming stronger local screening near potassium ions is proposed which can explain the experimental observations. Temperature-dependent studies of electronic transport in the system of coadsorbed potassium and ice show that graphene's resistivity is sensitive to phase transitions in overlayers as well as desorption, opening new opportunities to study surface phases with electronic measurements.
|Advisor:||Fuhrer, Michael S.|
|Commitee:||Cullen, William G., Einstein, Theodore L., Ouyang, Min, Reutt-Robey, Janice E.|
|School:||University of Maryland, College Park|
|School Location:||United States -- Maryland|
|Source:||DAI-B 74/03(E), Dissertation Abstracts International|
|Subjects:||Condensed matter physics|
|Keywords:||Adsorbates, Electronic properties, Graphene|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be