Crossover from metastable to unstable facet growth on Si(111)

Abstract

Vicinal SiC 111) surfaces misoriented towards the [211] direction facet reversibly upon cooling through the (1x1) to (7x7) reconstructive phase transition. We have used low-energy electron microscopy to examine the kinetics of this phase separation. Nucleation and growth of facets occur when the surfaces are quenched just below the phase boundary. However, at lower temperatures we find evidence for the existence of a spinodal which divides the faceting kinetics into unstable and metastable regions. The location of the spinodal is consistent with previous measurements of Si (111) step energetics.PACS numbers: 68.35.Md, 61.16.Bg, 81.60.Cp, 82.65.Dp As surfaces are becoming better characterized, the importance of surface morphology in determining surface characteristics is becoming increasingly evident [1][2][3][4][5][6]. A dramatic manifestation of the variability of surface morphology is "faceting" in which a flat surface breaks into a hill-and-valley structure, thus increasing total area. One of the most thoroughly studied of the faceting systems is vicinal SiC 111) [2,3]. Here surfaces which consist of a uniform array of steps at high temperature facet into singular (111) regions and step "bunches" at low temperature. The faceting is initiated by a change in the surface structure [from (lxl) to (7x7) periodicity], which occurs in a strongly first-order transition at about 870 °C on singular, unstepped surfaces. This faceting is reversible, and there is a well-defined temperature-orientation phase diagram [2] which determines the temperature dependence of the average spacing between steps in a step bunch. In this paper we discuss our low-energy electron microscopy (LEEM) observations of the kinetics of the faceting of these Si surfaces.The principal result of this paper is that the analogy of faceting with phase separation extends also to the kinetics. In previous work we have focused on the nucleation and growth of facets near the thermodynamic phase boundary, comparing observations with the predictions of the classical theories of nucleated facet growth by Mullins [7,8]. However, in systems which phase separate there is often a sharp transition between temperature regimes in which regions of a second phase nucleate and grow within the first, and lower temperatures where the system is unstable with respect to spontaneous decomposition everywhere into two phases [9]. The line separating these two kinetic regimes is called the spinodal The existence of a spinodal is particularly important in explaining the decomposition of metal alloys [10]. For example, microscopy studies often show marked changes in the morphology of phase separation as a function of quench conditions [11]. Here we present evidence for the existence of a spinodal for vicinal SiC 111).We emphasize at the outset that we expect our observations and arguments to apply generally. From a thermodynamic perspective, faceting induced by the formation of a surface reconstruction is very similar to faceting induced by impurity adsorption. Faceting of sy...

Zipping process on the step bunching in the vicinal surface of the restricted solid-on-solid model with the step attraction of the point contact type

“…So far, it has been known that the step bunching is caused by the various mechanisms [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. One is the Schwoebel effect [1], and others are the effect of impurities [2][3][4][5], the effect of the electromigration [6][7][8] on the vicinal surface, the effect of the phase transition on the surface reconstruction [9][10][11][12], the effect of strain [13], the long range inter-step attraction [14], and the short range adsorbates mediated inter-step attraction [15][16][17].…”

Evolution of surface morphology of vicinal Si(111) surfaces after aluminum deposition

“…bunches of steps [7]. The height of the step bunches is of course determined by the macroscopic Al was evaporated from an Al 2 O 3 crucible that was heated by a tungsten filament wrapped around miscut angle.…”

Interactions between Fluctuating Steps on Vicinal Surfaces: Edge Energy Effects in Reconstruction Induced Faceting

“…While reconstruction can lower the free energy of a flat terrace on which it occurs, it generally makes defects such as steps that disturb the reconstruction energetically more costly [3,16]. This suggests that reconstruction should occur on a stepped surface only for sufficiently wide terraces above some "critical" terrace width w c , as seen in many experiments [11,13,14].…”