Coarsening of Unstable Surface Features during Fe(001) Homoepitaxy

Abstract

The evolution of the surface potential during homoepitaxial growth of Fe(001) is studied by scanning tunneling microscopy and reflection high energy electron diffraction. The observed morphology exhibits a non-self-affine collection of moundlike features that maintain their shape but coarsen as growth proceeds. The characteristic feature separation I. is set in the submonolayer regime and increases with thickness t as L(t) -to'"-o" . During the coarsening phase, the mounds are characterized by a magic slope and a lack of reflection symmetry. These observations are shown to be described by a continuum growth equation without capillarity. PACS numbers: 68.55.Jk, 05.70.Ln, 61.16.ChThe basic mechanisms of epitaxial growth onto Hat single crystal surfaces have been known for over fifty years [1]. In the absence of surface defects, growth occurs by the nucleation, growth, and coalescence of two-dimensional (single atom height) islands. Atoms from an external beam arrive at the surface, transfer the heat of condensation to the substrate, and begin activated surface diffusion. Pairs of migrating atoms collide randomly over the surface and may bind to form dimers. The dimers may or may not dissociate thermally before other atoms diffuse to join them. Eventually, stable nuclei form that grow in size as other atoms arrive and attach. Individual island growth continues until nearby islands begin to impinge upon one another and coalesce. Layer completion occurs as freshly deposited particles fill in the gaps between coalesced islands. In principle, this scenario repeats for each layer so that the surface roughness varies periodically in time. But in fact, shot noise in the deposition Aux randomly induces nucleation of new stable nuclei on top of existing islands before layer completion occurs. The progressive roughening of the growth front implied by this picture has been the subject of numerous experimental and theoretical studies in recent years [2,3]. Part of the impetus for many of these studies has been the theoretical expectation [4] that noise-induced roughening during crystal growth might lead to self-affine surfaces [5]. Very recently, however, experimental data obtained from GaAs(001) [6],Cu(001) [7],Ge(001) [8], and Pt (111) [9] have revealed that a completely different morphological scenario can occur for homoepitaxy onto high quality single crystal surfaces. The surface morphology here takes the form of a collection of fairly regular three-dimensional mounds characterized by a well-defined separation distance L(t). The mere existence of the single scale length L(r) implies that these surfaces are not self-affine. According to Villain [10], the origin of this behavior can be traced to an intrinsic instability of the Oat surface that occurs in the island nucleation and coalescence regime whenever energy barriers to the transport of diffusing atoms downward over step edges exceed the usual surface diffusion barrier on a Oat terrace. Since atoms on an incomplete layer that recoil from these barriers are more likely t...

Self-organized nano-structuring of CoO islands on Fe(001)

“…This is clearly not the case here, since the morphology of the growing film is regular on a characteristic length scale (see below). The growth mode shows instead many similarities with the wedding cake model [55], in particular concerning the fact that the spatial distribution of the mounds is substantially determined by the positions of the islands nucleated on the first layer [55,56]. In this case, they are those formed after the development of the misfit dislocation network.…”

Surface roughening during plasma-enhanced chemical-vapor deposition of hydrogenated amorphous silicon on crystal silicon substrates

“…9 Unfortunately, experimental studies of even the simplest homoepitaxial growth systems reveals a complexity beyond current physical models. [10][11][12][13][14] Schwoebel-Ehrlich step-edge diffusion barriers can have major consequences for epitaxial growth. 15 The present case of an amorphous material is free of this type of effect, providing an opportunity to investigate the interplay of shadowing, surface diffusion, and chemical potential in film growth.…”

Kink dynamics in a one-dimensional growing surface

“…To our knowledge, the current (10) has not been formerly studied. The closest model is the one considered by Stroscio et al [18] in two dimensions, where the Mullins term (Km ′′ (x)) is replaced by a higher order one (Km ′′′′ (x)) and the resulting equation is studied numerically. Clearly, in two dimensions analytical treatments are much more difficult; anyway, neither a numerical solution of the model studied in the present paper is available at the moment.…”

“…It is not clear if such process is effective in presence of a flux F . For example, Stroscio and Pierce [17] state that thermal detachment is negligible in the homoepitaxial growth of Fe (at least at room temperature) and therefore they do not write [18] such a term in the current. Anyway, it has been shown [6,16] that the current (8) may derive also from nonequilibrium effects: nucleation noise and diffusion noise.…”