Secondary electron emission often appears as a parasitic physical process in systems that either use electrons of a few hundred eV, or that can evolve in an environment where low energy electrons are present [1]. In certain cases, by an avalanche phenomenon, electrons can multiply to a level that can disturb the functioning of sensitive equipments (multipactor) [1] or lead to catastrophic effects such as corona discharges. Multipacting is an issue for space systems that undergo electrons trapped in the earth radiation belts [2]. The satellite’s power chain is particularly sensitive to this physical mechanism. In this context, the risk associated with the electron secondary emission can be mitigated by surface treatments [3] of the walls of the Radio Frequency (RF) devices. The Total Electron Emission Yield (TEY) is closely dependent to the surface state and to the nature of the coating deposited on the material. For instance, the chemical state of the surface is modified by the irradiation in a way that the TEY can be reduced. It is known that irradiations can polymerize organic molecules present at the surface of the material and fix on it a layer of graphite. Since graphite has a low emission yield, the presence of a layer of a few nanometres thick is sufficient to drive and reduce the TEY [4]. This has been shown experimentally [4], but, few numerical simulations of such behaviour have already been performed. The objective of the work presented here, is to study numerically the impact of thin carbon layers of different thicknesses, on the SEY of Ag and Cu substrates, using Monte Carlo simulations [5-[8].