Initial growth stages of ultra-films of AlF3 on Cu(111): an STM study

ADRIANA CANDIA; J. C. MORENO-LÓPEZ; LILIANA GÓMEZ; R. A. VIDAL; M.C.G. PASSEGGI (H); J. FERRÓN

Santa Fe

Congreso; 14to SAM-CONAMET / IBEROMAT XIII / XIII SIMPOSIA MATERIA, Congreso Internacional de Metalurgia y Materiales; 2014

In this work, we characterize the initial growth stages of ultra-thin films of AlF3 on Cu(111) by means of scanning tunnelling microscopy (STM) and Metropolis Monte Carlo(MMC) with the aim of understanding the growth characteristic features based on kinetic and geometric factors. As well, we compare these results with previous ones obtained on Cu(100). The growth of AlF3 sub-monolayers (ML) on Cu(111) shows more differences than similarities regarding to the deposition on Cu(100). In both cases, we observe the formation of fractal islands, with very corrugated surfaces and similar heights, 0.25-0.30 nm. The stepedges on Cu(111) are not completely decorated as in the case of Cu(100), even at higher coverages (> 0.7 ML), the islands are bigger in size and the surface density smaller. For Cu(111), the distance average between AlF3 islands and the surface density for a coverage of 0.40 ML is 25 nm and 1.0×1011 islands/cm2, while for Cu(100) since 0.25 ML they had constant values of 17 nm and 1.5×1011 islas/cm2, respectively. The MMC calculation results show similarities with those of Cu(100) as far as isolated molecules and reconstructed bi-molecules is concerned. While the first ones show an isotropic diffusion by hopping, the bi-molecules diffuse over the surface along privilege directions, showing as well an important change in the diffusion length (2 magnitude orders in the number of MMC steps). Then, when bi-molecules are formed, they move along the three directions relative to the simmetry axis of the crystal triangular lattice; similar results have been observed for Cu(100), but in that case only along the two directions of simmetry of the crystal square lattice. Thus, for Cu(111) the bi-molecules exhibit high mobility, once the islands critic cores are formed, the potentiality of receiving new contributions is 50 % higher, justifying the bigger sizes and smaller surface density of the islands observed during the experiments.