Controllable formation of nanoscale patterns on TiO2 by conductive-AFM nanolithography.

We report on the nanopatterning of double-bond-terminated silane (5-hexenyltrichlorosilane, HTCS) molecules on titania (TiO2) using conductive atomic force microscopy (AFM). The influences of tip electrostatic potential and scanning velocity, relative humidity and of the repeated application of voltage on the topographic height, width, and hydrophilic and hydrophobic contrast of the resultant patterns were investigated. Tip voltage and tip velocity ( v) were applied between -10 V <or= V tip <or= +10 V and 100 nm/s <or= v <or= 2 microm/s during the lithography step(s), respectively. Average height and Lateral Force Mode (LFM) images of patterns were obtained with different values of (-10 V <or= V tip <or= -7 V) and v (100 nm/s <or= v <or= 2 microm/s). The average height of the patterns is seen to decrease for increasing v and decreasing V tip in both a single or repeated lithography step. No patterns were observed following a single or repeated lithography step for -5 V <or= V tip <or= +10 V. This conductive lithography technique results in nanoscale physiochemical manipulations of the HTCS molecules that are manifested as controllable step heights ranging from approximately 1-15 nm possessing different chemistries on the patterned and unpatterned areas. The use of conductive-AFM nanolithography for altering and manipulating double-bond-terminated molecules on TiO2 surfaces suggests a range of applications, including selective immobilization and assembly of functionalized inorganic nanoparticles and biomolecules.