Magnetotransport in chemically reduced graphene oxide and gallium phosphide antimonide

• Main Authors: Hung-En Lin, 林弘恩
• Other Authors: 梁啟德
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/99089623646355400100

碩士 === 國立臺灣大學 === 物理研究所 === 99 === In this thesis, two materials, chemically reduced graphene oxide and GaPSb, were investigated for their magnetotransport behaviors under the influence of a magnetic fields up to 11.6 T at the temperatures between 4.5 K and 80 K. A brief summary of our discovery will be given in the following sections. 1. Magnetotransport in chemically reduced graphene oxide In recent years, transport behavior in chemically reduced graphene oxide (R-GO) has been widely investigated. However similar research in the presence of a magnetic field was rare. In chapter 4, the transport behavior in fully R-GO samples with a magnetic field up to 4 T at selected temperatures between 4.5 K and 80 K was studied. Negative magnetoresistance (NMR) was observed in all our R-GO samples. The magnitude of NMR was found to decrease with the increasing temperature and the increasing thickness of the R-GO film. A Mott hopping behavior, concluded from the data analyzed by using Sivan, Entin-Wohlman, and Imry (SE-WI) model, was found to be the dominant electron conducting mechanism for the NMR phenomenon. The magnetotransport features can be explained by a model based on the spin-coupling effect from vacancy-induced midgap states that facilitate the Mott variable range hopping (VRH) conduction in the presence of an external magnetic field. The origin of the staircase-like NMR revealed on the 3-nm-thick sample is not clear although it was also observed at a lower temperature from the dilute fluorinated graphene. Further investigations are required to elucidate the nature of this unusual behavior. 2. Magnetotransport in gallium phosphide antimonide The second part of this thesis was dedicated to the study of the transport behavior in a GaPSb sample in the presence of a perpendicular magnetic field at low temperatures. The Hall measurement indicated that the carrier concentration was about 1016 cm-3 and electrons were the dominant carriers in our sample. The NMR followed by PMR was observed along with the increase of a magnetic field up to 11.6 T. At the temperature regime between 40 K and 80 K, either three- or two-dimensional Mott VRH model or ES VRH model can be used to describe the electron transport behavior. To elucidate the ambiguity, the magnetoresistance theory in VRH regime was employed to analyze the transport behavior, showing that the transport behavior of the 720-nm-thick GaPSb is consistent with a two-dimensional Mott VRH conductance.