Step Bunched Surfaces

Silicon etching in alkaline solutions has a long history [200] and has found numerous applications [201-203], and, accordingly, models of Si dissolution have been developed [204-206]. Dissolution is typically assumed to originate at an 

The distance of the respective arrows to the base line for deconvolution gives the maximum value of the 2ps/2 signal relative to the other deconvoluted signals (see also Table 2.1). 

Binding energy (AeV) Surface chemical species Relative contribution 

The lateral potential distribution across the surface has been measured by Kelvin probe AFM [214], which monitors contact potential differences across the surface and has been successfully applied, for instance, in the electrostatic 

Step edges. This property of the surface has been used for site-specific adsorption of heterodimeric enzymes in a precursor experiment for biologically inspired solar fuel generation systems [216]. 

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A series or bunch of m initially straight and parallel steps, between heights 0 and m, may be expected to relax with the same asymptotics as a pair of steps. Modifications may occur, already for a pair of steps, when step-step interactions are present in addition to the entropic step repulsion. Here, we merely refer to recent reviews on experiments and theoretical analyses " on the much studied phenomenon of step bunching for vicinal surfaces, which is accompanied by interesting phase transistions. 

In this paper we review some of our recent work on the dynamics of step bunching and faceting on vicinal surfaces below the roughening temperature, concentrating on several cases where interesting two dimensional (2D) step patterns form as a result of kinetic processes. We show that they can be understood from a unified point of view based on an approximate but physically motivated extension to 2D of the kind of ID step models studied by a number of workers. For some early examples, see refs. [1-5]. We have tried to make the conceptual and physical foundations of our own approach clear, but have made no attempt to provide a comprehensive review of work in this active area. More general discussions from a similar perspective and a guide to the literature can be found in recent reviews by Williams and Williams and BartelF. 

To proceed, we must describe the effective driving force and the effective interactions between steps on this mesoscopic scale. We focus here on two cases of recent experimental and theoretical interest current-induced step bunching on Si( 111) surfaces - " and reconstruction-induced faceting as seen a number of systems including the O/Ag(110) and Si(lll) surfaces" In both cases interesting 2D step patterns can arise from the competition between a driving force that promotes step bunching, and the effects of step repulsions, which tend to keep steps uniformly spaced. 

In the ID limit, Eqs. (7) and (8) and related equations have been used to analyze the relaxation of non-equilibrium step profile - and in a variety of other application We will not review this work here, but instead turn directly to two cases where characteristic 2D step patterns and step bunching are found as a result of the competition between the step repulsions and a driving force favoring step bunching. Perhaps the simplest application arises as a result of surface reconstmction. 

Figure 1 Free energies for unreconstructed surface f, and reconstructed surface f, vs slope s. The critical slope, sc, and the slope of the surface at step bunches, St, are given by Sc = ,/ , and St = The thick curve in (a) represents the free energy of a hypothetical system... 

Fig. 6 Step bunching mechanism forming macrosteps the photograph shows the typical macro steps (several microns) on the surface of a DAST single crystal.

V (cf. Figure 2.45 and the conditioning protocol) than at open circuit potential. Obviously, the product dissolution is still strongly enough inhibited to result in step bunching although the surface considered here had a nominal miscut of only 0.5° which yields a considerably lower initial step density than on a vicinal surface. 

Figure 2.53 Kelvin probe AFM experiment on a step bunched Si(l 11) surface. Top topographic features of the investigated step bunched sample bottom variation of the electrostatic potential.

H-terminated surface dashed-dotted curve, signal from Pt islands deposited onto a step bunched Si surface the latter are substantially smaller (see text). 

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