Wide-range work function tuning in gold surfaces modified with fluorobenzenethiols toward application to organic thin-film transistors

Surface properties of Au electrodes modified by benzenethiol derivatives with a fluorine atom(s) have been methodically researched based on measurements of the work function and the contact angles. Benzenethiol derivatives with a fluorine atom(s) at ortho, meta, and/or para position were used for modification in this work. The measured work function was in a relatively wide range between 4.24-6.02 eV. The work function change from a bare Au surface was explained on the principle of dipole moments obtained by quantum chemical calculation. The water contact angle was found to vary between 64.8° and 97.7°. Furthermore, the surface tension was calculated from the measured contact angles of water and ethylene glycol. The calculated surface tension was reviewed from the perspective of the position of the substitute in the benzenethiol derivative. In addition, organic thin-film transistors (TFTs) with drain and source electrodes modified with 2-fluorobenzenethiol (2-FBT), 3-fluorobenzenethiol (3-FBT) or pentafluorobenzenethiol (PFBT) were characterized as other evaluations of the modified Au surface. The contact resistance in the TFT increased in the order of PFBT, 3-FBT and 2-FBT. The increase of the contact resistance was consistent with the decrease in the work function.