Fabrication of Freestanding Graphene EdgeElectrodes for Single Molecule Experiments

• Main Authors: Chiu, Po-Kai, 邱柏凱
• Other Authors: Tsai, Tsung-Hui
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/79676863024208958249

碩士 === 國立臺灣海洋大學 === 光電科學研究所 === 104 === This thesis presents a method for single molecule experiment using the graphene probes for electrodes. Edges of these electrodes are sharp and a pair of electrodes were perpendicular to each other in order to increase possibility for linking a single molecule. The experimental measurement was recorded by scanning tunneling microscope (STM). Graphene is a 2D carbon material with atomic thickness. The advantage of using graphene electrodes owing to the carbon’s strong covalent bonds to form the linkage to molecules. Compare with metal electrodes, graphene electrodes have limited number of molecular bonding sites to contact single molecule. Our large area graphene was synthesized by chemical vapor deposition (CVD) method and mechanically pulled to form the freestanding graphene edge electrodes. To confirm the freestanding graphene edge structure, we used it as a new type of STM probe. Graphene probe is a ultra-thin film, so it is sharp and ideal for STM probe. Clear atomic structure of graphite surfaces were observed by using graphene probes and the image resolution was as good as metal probes. In addition, the differences between graphene and common metal probe was defined by scanning tunneling spectroscopy (STS) at -0.8V~0.8V range. Consequently, probes with freestanding graphene structure were selected as graphene electrodes. Finally, we used graphene electrodes to measure NPB and arachidic acid molecules. NPB is an important material for fabrication of organic light-emitting diode (OLED) used for the hole transport layer. Arachidic acid is molecular wire structure which is as a minor constituent of peanut oil and cocoa butter. The applications of arachidic acid are lubricant additives and surface active agents. Electrical transport of these two molecules were seldom studied in single molecular scale. From I-V and current-distance curves, we obtained the conductance information of graphene/molecule/graphene at molecular scale. Under 50 mV, the conductance of NPB was 1.5× 10−4 G 0 ~3.12× 10−4 G 0 and maximum pulling distance of molecules was 2 nm. Arachidic acid conductance was 7.58 × 10−2 G 0 ~ 2.58 × 10−4 G 0 and maximum pulling distance of molecules was 4 nm. According to experimental results, freestanding graphene edges are good for STM probes and electrodes for single molecule experiment.