Discharges in heptane in pin-to-plate configuration are produced between a platinum wire and a (100)-oriented silicon wafer coated by a carbon nanotube (CNT) carpet. This carpet is used to simulate the behavior of a nanostructured surface in electro-discharge machining (EDM) where small protrusions on the surface could play a similar role. CNTs behave like simple electrical conductors between the discharge and the silicon wafer. They act as if they would focus the current on smaller areas. The average diameter of impacts is about five times smaller if the silicon wafer is coated by a CNT carpet. The underlying silicon surface is heated by the plasma and melts, forming a central spot surrounded by a serrated trailing edge. The current density being about one order of magnitude larger when a CNT carpet is present, the induced magnetic field stirs the molten silicon, creating serrations all around the impact. Hot nanoparticles of carbon coming from the plasma fall and roll randomly on the silicon surface where they create wavy micro-channels. Nanowires that are detached from the surface are covered by nanoparticles of platinum in the plasma and embedded within an amorphous carbon layer deposited on the nanotube. However, these effects can only be observed if the current density is high enough (>approximate to 10A mu m(-2) depending on the material) like in micro-EDM but not in nano-EDM.