Surface modification of ZnO on the Zn-polar 0001 face by self-assembled triptycene-based polar molecules along with an increase of electric conductance

Abstract

The application of self-assembled monolayers (SAMs) is a representative method of surface modification for tuning material properties. In this study, we examine the influence of the surface modification by coating the Zn-polar 0001 surface of ZnO single crystal with a SAM of triptycene-based polar molecules in our own technique and investigated temperature dependences of the sheet conductance of the surface with and without the SAM. The sheet conductance at 70 K with the SAM is increased by an order of magnitude, compared to the case without the SAM. We infer that the additional electrons are introduced at the surface by the polar triptycene molecules, whose electropositive hydroxyl groups are supposed to face toward the Zn-polar surface of ZnO. The present result implies that the molecular orientation of the triptycene SAM plays a critical role in the surface properties of oxide semiconductors.