Growth, thermal desorption and low dose ion bombardment damage of C60 films deposited on Cu(111)

Abstract

Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED) and Reflection Electron Energy Loss Spectrometry (REELS) were used to characterize the growth and thermal stability of C60 films deposited on Cu(111). By means of LEED we found that while C60 grows in an ordered fashion up to the first monolayer (ML) at room temperature (RT), it turns amorphous beyond that point. On the other hand, when the substrate temperature is kept at 450K films up to two ML with crystalline structure are obtained. For substrate temperatures beyond 570K thick films (more than 1 ML) do not grow at all. By using AES, we found that a thick C60 film starts to desorb at a temperature around 470K but the first monolayer remains stable up to temperatures as high as 900K. A monolayer with a better crystalline order is obtained after desorption than that growth with the substrate at RT or higher temperatures. When the substrate is heated at 970K, the first monolayer is not fully removed but the C60 molecular structure is altered or molecules break up into smaller pieces. The ion induced damage on C60 on Cu(111) films was studied for typical ions, incoming energies and irradiation doses used in Low Energy Ion Scattering (LEIS) experiments. The D-value of C(KLL) Auger spectra and the -plasmon of REELS, were monitored to characterize the damage caused to the film. We found that, at low doses ( 1014 ions/cm2), damage is only detectable for massive ions like Ar, but not for H and He in the 2-8 keV range.