IFIS - LITORAL   24734
INSTITUTO DE FISICA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Charla invitada. Surface diffusion mechanisms and growth mode.
Autor/es:
FERRON, J.
Lugar:
Natal
Reunión:
Conferencia; First Ibero-American Conference on Surface, Materials and Vacuum Applications (ICSMVA); 2014
Institución organizadora:
Brazilian Vacuum Association
Resumen:
Our comprehension of the
atomistic mechanisms related with the thin film growth has evolved in an
impressive way in the last years[1].
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[2],[3],
subsurface diffusion[4],[5],
and long jumps[6], including even memory
effects[7],
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[8],
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[9].
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[10]
(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[11] and insulators[12]
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,[13]. 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. All these systems
present particular characteristics related to the surface diffusion mechanisms
that largely influence the surface and interface develop.
[1]. G. Antczak and G. Erlich, Surface
Diffusion. Metals, Metal Atoms , and Clusters (Cambridge University Press 2010)
and references therein.
[2]. G. L. Kellogg and P.J. Feibelman, Phys.
Rev.
Lett. 64 (1990) 3143.
[3]. C. Chen and T.T Tsong,
Phys. Rev. Lett. 64 (1990) 3147.
[4]. R. Tromp, Nature Materials 2
(2003) 212.
[5]. J. Camarero, J. Ferrón, V. Cros, L. Gómez,
A.L. Vázquez de Parga, J.M. Gallego, J. E. Prieto, J.J. de Miguel and R.
Miranda, Phys. Rev. Lett. 81 (1998) 850.
[6]. G. Antczak and G. Ehrlich, Phys. Rev. Lett. 92
(2004) 166105.
[7]. J. Ferrón, L. Gómez, J.J. de Miguel and R.
Miranda, Phys. Rev. Lett. 93 (2004) 166107.
[8]. W.J. Egelhoff, P.J. Chen, C.J. Powell, M.D.
Stiles, R.D. McMichael, C.L. Lin, J. M. Sivertsen, J. H. Judy, K. Takano, and
A.E. Berkowitz, J. Appl. Phys. 80 (1996) 5183.
[9]. See F. Besenbacher, L. Pleth Nielsen and P. T.
Sprunger, in Growth and Properties of Ultrathin Epitaxial Layers, edited by D.
A. King and D. P. Woodruff, The Chemical Physics of Solid Surfaces Vol. 8
(Elsevier, Amsterdam, 1997), Chap. 6, and references therein.
[10]. G.
Ehrlich and F.G. Hudda, J. Chem. Phys. 44 (1966) 1039; R.L. Schwoebel and E.J.
Shipsey, J.Appl.Phys. 37 (1966) 3682.
[11]. L. Gómez, C. Slutzky, J. Ferrón, J. de la Figuera, J. Camarero, A.L.
Vázquez de Parga, J.J. de Miguel and R. Miranda, Phys. Rev. Lett. 84 (2000) 4397.
[12]. F.
Calleja, J.J Hinarejos, A.L. Vázquez de Parga, S.M. Suturin, N.S. Sokolov and
R. Miranda, Surface Sci. 582 (2005) 14. D. Farías, K.F. Braun, S. Fölsch, G. Meyer,
H.K. Rieder, Surface Sci. 470 (2000) L93.