Miscut

The dynamics of upd reactions have also been examined by STM. The formation of the ordered copper/sulfate layer [354] and copper chloride layer [355] on Au(lll) was examined in a dilute solution of Cu where the reaction was under diffusion control so that growth proceeded on a time scale compatible with STM measurements [354]. In another study, the importance of step density on nucleation was examined and the voltammetric and chronoamperometric response for Cu upd on vicinal Au(lll) was shown to be a sensitive function of the crystal miscut, as... 

The Ni surfaces used in these experiments were nominally within 1 of (100) and (110) so that they undoubtedly had a fairly large density of the type of background steps described in figure 1. The temperature range used may have sparmed that of terrace roughening but the presence of so many steps due to the miscut probably masked any effect of spontaneous step creation on the terraces. Under such experimental conditions it is extremely unlikely that extensive facets at the extrema have strong effects on the mode of decay. 

Figure 7. STM4 image showing the crossing steps(due to the miscut ) at a maximum of a 1-D grating on a surface near Si(OOl). Due primarily to the difference in free energies of the two step types they occur in pairs[28]. It is believed that the amplitude decay occurs by the motion of such crossing steps along the extrema.

Periodic surface profiles on vicinal surfaces have received considerable attention in the past, both from a continuum as well as an atomistic point of view [8-18], Here we describe briefly some recent work for surfaces of miscut a (about 3-10°) based on continuum mechanics specifically designed to take the anisotropy of y(0) into account [18], The approach is based on eq. (1) and the excess chemical potential given by [2]... 

Eqs. (3), (5) and (6) depend on the particular form of eq.( 1). If the main step interaction term in eq.(l) is proportional to rather than p, the expressions for E( /) would be different, particularly for the Mf = izH case. Whereas the variation of B(ji/2) with miscut a isstrong(atan a/cos a) for p dependence, it is weak a 1 /cos a) for p dependence. Thus a measurement of B(n/2) for several miscut surfaces, although tedious, would be a means to distinguish between those dependences. The anisotropy factor, eq.(6), would also exhibit a weaker variation with miscut for p dependence. 

When the small slope approximation is not fulfilled, the profile shape is expected to deviate from a sine wave and the decay kinetics are not necessarily exponential. Numerical calculations for / = 0 orientations and for not so small slopes show profiles with flattened maxima and minima as well as non-exponential decay behavior [18]. Examples of amplitude decay for several miscuts a are plotted in fig. 3. Calcnlations for f nearn/2 are also possible bnt have not been carried out as yet. 

Figure 3. Calculated decay rate of profile orientation t / = 0 versus amplitude for several miscuts a. 

Figure 5. Profiles z(x, f) of a grating below the roughening transition temperature, at increasing time, of the standard SOS model with 80 x 320 sites and a miscut of a few lattice spacings, using evaportion kinetics in Monte Carlo simulations (full symbols). For comparison, a sinusoid is shown (open symbols). The initial amplitude of the grating is five lattice spacings.

The effect of a miscut of the surface in the case of surface diffusion has been recently studied, which seems to be important in interpreting experiments. ... 

Thus, depending on the mode of transport which is operative on the length and time scales of interest, any value for the dynamic exponent z between 5 and 8 can be expected for the surface diffusion case. Smaller values of z are also conceivable if the rare-event dominated top terrace dissociation or a miscut enters the game. A detailed analysis, however, is beyond the scope of present article. 

Figure 2 STM images of vicinals of Au ll0) (courtesy ofM.S. Hoogeman, L. Kuipers and J.W.M. Frenken, AMOLF Amsterdam). The area shown is 90nm x 20nm aX T = 550K, with a miscut angle of 0.07 degrees.

Deposition of Au onto this surface leads to the nucleation of Au islands at the intersection of clean Cu stripes thus leading to a square island lattice with a period of 50 A [83,86-88]. The N-covered Cu(100) surface has also been used for the growth of so far less well-ordered lattices of Fe and Cu [89], Co [90-92], Ag [93,94], and Ni [95], We note that square lattices can in principle also be created on Au(f4,f5,f5) since this miscut leads to 70 A step distance, which is equal to the reconstruction period. However, the steps are already far apart reaching the limit of the elastic step repulsions which may render global order difficult. Finally we note that another interesting alternative square template, although with smaller lattice constant, is presented by the (3 /3 x 5)-phase of V-oxide on Rh(lll) [96]. 

Si(100). (c) STM image of cyclopentene on a vicinal (100) surface obtained by a miscut of 4°. The molecules remain ordered across double-height steps. Reprinted from [42] with permission from the American Chemical Society. 

As well as the lattice mismatch between the layer and the substrate, other factors influence the FWHM of the RC, including thickness of the buffer layer, miscut of the substrate, substrate quality, growth conditions etc. For example, Warren Weeks et al [16] reported 00.2 FWHMs of 58 and 151 arc sec for 1.4 pm GaN layers grown on on-axis and off-axis (3 - 4° toward the <11.0>) SiC substrates, respectively. The corresponding FWHMs for the 0.1 pm AIN buffer layers were approximately 200 and 400 arc sec. For a thicker GaN layer of 2.7 pm, the off-axis sample also exhibited an FWHM of 66 arc sec. 

For (00.1) oriented sapphire substrates, application on surfaces miscut up to 10° with respect to the <00.1> has been shown to be of little help in improving the overall quality of the epitaxial layers [26],... 

The growth of (00.1) oriented GaN layers on a-plane (11.0) sapphire was reported by Fatemi et al [26], The authors presented a comprehensive study on the influence of the substrate miscut on the structural... 

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