LEEM images

FigurelO. LEEM images of 2-D gratings following annealing at 980C and at 1060C. The980C sample shown in a) is symmetrical with respect to maxima and minima and the saddle point features( bow-tie shapes) are approximately 4-fold symmetric hypocycloids. In the 1060C sample the minima have extensive (001) facets and the saddle point features are elongated in the directions between maxima note also that a particular reconstructed domain is preferred at the saddle points[31,34].

Figure 11. Series of LEEM images[31,35] showing a short sequence in the disappearance of islands at a maximum of a 2-D grating on Si(OOl) at 950C the relative annealing times are indicated. At this temperature the behavior of the holes at the minima is essentially the same. Note that the islands are elliptical when separated from the rest of the stack.

The Saddle Point Features of the 2-D Gratings For an ideal 2-D sinewave the saddle point features should appear to have 4-fold symmetry when viewed in LEEM images. From the sketch of figure 13 it can be seen that the hypocycloid shaped terrace at the saddle point has the same type of monoatomic step on all four sides due to the difference in the free energies of the two steps, Sa and Sb, on Si(OOl) there should be a strong preference for Sa steps and hence each maximum would prefer to be flanked by two white domains and two "black ones as is the case in figure 10. (A similar conclusion follows if the the saddle point terrace is surrounded by two Sa steps and two double steps of Db type[31]). 

Fig. 5 LEEM images showing domain pattern evolution as a function of Pb coverage at 673 K. The images correspond to Pb coverages of (a) 0.33, (b) 0.39, and (c) 0.48 ML. The evolution from droplets to stripes to inverted droplets is evident. Figure from Ref. [68].

Representative LEEM images from the initial stages of Pb deposition on Cu(lOO) at 410 K are shown in Fig. 9. Prior to deposition the only feature in the... 

Fig. 9 LEEM images showing the changes in surface morphology that take place during initial deposition of Pb on Cu(lOO) at 410 K. (a) 0.05 ML, (b) 0.15ML, (c) 0.23 ML. The field of view is 4.5 pm. Figure from Ref. [82].

The addition of more Pb to the c(4x4) surface alloy causes the surface to dealloy resulting in a c(2x2) overlayer phase at 0.5 ML. LEEM images recorded during transition from the c(4x4) to c(2x2) surface structures are shown in Figs. 10(a) and 10(b). In these images the conditions are chosen such that the c(2x2) phase appears bright. The starting surface is pure c(4x4) with small islands... 

LEEM images taken during conversion of the surface from the c(2x2) to c(5V2xV2)R45 phases at 400 K provide further evidence that Cu is incorporated... 

In the case of the c(4x4) structure, LEEM observations [88] imply a first-order phase transition. Bright-field LEEM images clearly show a nucleation and growth process as the temperature is lowered through the transition. However, the LEEM results for the value for the temperature of the transition (-513 K) are... 

Low-energy electron microscopy (LEEM) image single monolayer of graphene on SiC(OOOI), diameter 20 pm. Reprinted with permission from Physical Review B 78 (2008), 245403. 2008 American Physical Society (Virojanadara etal., 2008). 

Figure 9.29 Bright-field LEEM image ob- terrace side of the step edges [62]. Depend-...

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