IFIS - LITORAL   24734
INSTITUTO DE FISICA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Charla invitada. Surface diffusion mechanisms and growth mode.
Conferencia; First Ibero-American Conference on Surface, Materials and Vacuum Applications (ICSMVA); 2014
Brazilian Vacuum Association
Our comprehension of the atomistic mechanisms related with the thin film growth has evolved in an impressive way in the last years. The way an adatom diffuses over a surface reaching either defects, steps or another diffusing adatom to nucleate, determines the basic paths of growing. These diffusing mechanisms can be either simple as one atom jumping from one equilibrium site to the nearest one, or they can also involve more complicated processes like atomistic exchange,, subsurface diffusion,, and long jumps, including even memory effects, for mention some of the last startling discoveries. The increasing needs of growing flat and structurally almost perfect layers, coming from the requirements involving the fabrication of elaborated artificial structures, such as magnetic superlattices, lead to the develop of new methods for obtaining flatter surfaces and sharper interfaces. However, the layer by layer growth (LbL), where no atomic level starts to growth before the preceding atomic monolayer (ML) is completely filled, is the exception rather than the rule. Intermixing, even between (in bulk) immiscible materials, and defect generation, for mention a couple of facts, may lead to roughness developing from the very beginning of the growth. The diffusion of an adatom on a flat surface is by far the most important kinetic process in film growth. Smooth, uniform films could not be formed without enough surface mobility. In the extreme case of zero mobility parallel to the surface, an adatom stays where it lands, and the resulting growth front is very rough. The island nucleation is, on the other hand, the only possible growing mechanism over a perfectly plane surface. However, a real surface is composed by flat terraces limited by steps. While ascending steps constitute nucleating sites, descending ones usually act as atom mirrors, since the Erlich Schwoebel barrier (the energy needed for the adatoms to overcome the steps, falling down to the lower terrace) is too high as compared to the energy needed to return to the inner terrace. Whereas decoration of steps at the upper side is clearly disfavored in metals and insulators due to this mechanism, it has been observed in few cases. However, these cases involve the modification of the nature of the step by the interaction with the adatoms11,. Thus, a competition between on terrace and at (ascending) steps nucleation is established. For large atomic/molecular diffusion lengths as compared to terrace size, adatoms have time enough to reach the steps nucleating there; otherwise they may nucleate over the terrace. The growth of insulator films is a physical phenomenon even more important than metallic growth due to technological requeriments and certainly more complicated from the basic physics point of view. In this work we analyze different systems from experimental and theoretical point of views, using different experimental and theoretical techniques. The analyzed systems include metal ? metal, homo (Cu on Cu (100) and Cu(111)) and heteroepitaxial (Co/Cu(111)) growth, and insulator-metal film growth (AlF3 on Cu(100) and Cu(111)). We also studied film growth using ion implantation techniques, as in NCu on Cu(100) and Graphene on Cu(111). Among the experimental tools, we used thermal energy atom spectroscopy (TEAS), scanning tunneling microscopy (STM), electron energy loss (ELS), Auger (AES), xray photoelectron (XPS) and ion scattering (ISS) spectroscopies. The analysis is complemented by Metropolis Montecarlo and Molecular Dynamics simulations, and Density Functional Theory calculations. 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