We studied the evolution of the current voltage behavior of a doped Si tip on 1-octadecanethiol coated Au film on mica to understand the impact of current on material modification for negative tip biases up to 10 V. The resistance is non linear ranging from a 550 kΩ to essentially infinite resistance at tip bias of 250 mV to as low as 6–10 kΩ for tip biases of 10 V. The measured resistance is shown to be primarily due to the contact resistance. The tip radius increases with repeated exposure to 10 V tip bias. The oxide layer on the tip initially decreases but then increases with repeated exposure to 10 V tip bias. We performed heat transfer analysis of the tip-substrate interface to show that the measured powers are sufficient to raise the temperature at the interface to as high as 200–1100 °C which is sufficient to cause rapid tip oxidation of bare Si tip in an ambient environment and can cause diffusion or melting of organic or inorganic thin coatings from coated Si tips [Liu and Miller, J. Phys. Chem. C 111, 10758 (2007) and Liu and Miller, Nanotechnology 20, 055303 (2009)]. We observed 5–20 nm high bumps on the gold surface for negative tip bias >5.5 V. The bumps frequently disappeared with repetitive scanning leaving a 2–10 nm deep pit behind and the bumps created in high humidity (>60%) were more easily removed.