Temperature study of CVD graphene on Cu thin films: Competition between C catalysis and Cu dewetting
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Temperature study of CVD graphene on Cu thin films: competition between C catalysis and Cu dewetting G. Amato1, L. Croin1,2, G. Milano3 and E. Vittone3 1
The Quantum Research Laboratory, INRIM, strada delle Cacce 91, I-10135, Torino, Italy. Dept. of Applied Science and Technology, Polytechnic of Turin, Corso Duca degli Abruzzi 24, I-10129, Torino, Italy. 3 Physics Dept. and NIS center, University of Turin, Via Pietro Giuria 1, I-10125, Torino, Italy. 2
ABSTRACT In this paper we report on a systematic study of Cu thin film dewetting by the monitoring of the intensity of the infra-red emission from the film surface during Rapid Thermal Chemical Vapor Deposition of graphene. The time evolution of Cu coverage highlights three typical stages of dewetting which strongly depend not only on the temperature and film thickness, but also on the pressure and composition of the gas in chamber. Consequently, we demonstrate that the Cu surface can be effectively activated in films at temperatures lower than in foils and the process can be fully controlled by adjusting those parameters, in order to reach the optimal conditions for graphene growth. INTRODUCTION Chemical Vapor Deposition (CVD) in one of the most promising techniques for large area graphene production. The configuration that up to this time has been more studied is CVD on Cu foils used as catalyst. On the other hand, deposition of graphene onto Cu films could give many advantages related to the compatibility with current microelectronics technology, furthermore evaporated metals present less contaminations and there is much less copper to dissolve during transfer. However the main drawback of the synthesis of graphene on copper thin films is the dewetting of the substrate occurring at high temperature. This phenomenon is driven by surface energy minimization and can occur via surface diffusion under film’s melting temperature and consists in the agglomeration of the film forming holes and eventually islands. Dealing with polycrystalline thin films, dynamics is well studied [1][2] and consists in three different stages: hole formation, propagation and ligament breakup. The phenomenon occurs at the boundaries of three or more grains and evolves in time through the retracting of grains and the deepening of the grooves. The stage before hole opening can be defined as incubation stage. Such dynamics of the surface can be seen as a problem for a good CVD, so in order to increase the incubation time, what is usually done is to increase the thickness of the film (>500 nm) [3]–[5] approaching to the properties of the foil. On the other hand dewetting has also been proposed as a resource for a direct deposition of graphene on the substrate (usually SiO2) underlying the Cu thin film [6]. However, CVD of graphene is still not fully understood, but the condition, considered essential for a better catalysis, is the high mobility of the Cu surface atoms with behavior close to a liquid [7].
Here we report a study of the substrate dewetting and a possible approach to increase the
