Nanografting of N-vinyl-2-pyrrolidone molecules on a graphite surface with a scanning tunneling microscope

Experimental evidence that STM tips can induce grafting of N-vinyl-2-pyrrolidone (NVP) molecules on a graphite surface from a solution of NVP is presented. Such a process depends mainly on the bias voltage (V-t) applied to graphite. For V-t < 2.9 V, the graphite surface remains unchanged while, at V-t = 3 V, NVP islands are detected. When V-t > 3.4 V and applied for 100, islands are formed together with holes in the graphite surface. For V-t = 3 V, islands with a diameter which varies from 0.3 to 4.5 nm are formed. They exhibit a similar thickness (similar to 0.4 nm). High-resolution STM images show that the electronic structure of the graphite is perturbed around these islands. Some islands appear made of units which have a diameter of 0.5-0.6 nm, in agreement with the known diameter of a single NVP molecule. A mechanism for the grafting is proposed.