Figure 1

Schematics of a cross section of crystallites grown at the surface of an fcc(111) substrate. Regular, untwinned crystallites appear as a stacking of green (light-gray) planes following an ABC sequence (left-inclined lines); twinned crystallites appear as a stacking of red (dark-gray) planes following a CBA sequence (right-inclined lines). Two types of lateral twin crystallite boundaries are shown: double positioning boundaries (dashed lines), separating crystallites that are 180${}^{ˆ}$ twinned one with respect to the other, as well as a stacking boundary (dotted line; see text for definition). A kink is also considered at one of the double positioning boundaries.Reuse & Permissions

Figure 2

(a–d) STM topographs illustrating characteristic features at different stages of homoepitaxy on Ir(111) after deposition of (a) 0.2 ML, (b) 0.9 ML, (c) 10 ML, and (d) 90 ML at 350 K. (e) Larger-scale STM topograph of a 90-ML film grown at 350 K. (f–i) STM topographs of the film shown in (e) after successive 180-s annealing steps at (f) 850 K, (g) 1025 K, (h) 1200 K, and (i) 1375 K. Image size: (a–d) $64\times 64$ nm; (e–i) $480\times 480$ nm; insets in (f) and (g), $120\times 120$ and $67\times 67$ nm, respectively. Small white arrows in (h) and (i) indicate the surface trace of emerging screw dislocation lines (junctions between up-and-down steps).Reuse & Permissions

Figure 3

(a) Grayscale STM topograph after deposition of a 90-ML film at 350 K and additional annealing to 1025 K for 180 s. Image size: $128\times 128$ nm. (b, c) Line scans along paths indicated in (a) illustrating full and fractional step heights as well as strain fields associated with fractional steps. (d) Three-dimensional visualization of the junction marked in (a).Reuse & Permissions

Figure 4

STM topographs after deposition of 90 ML at 350 K, subsequent annealing to 1200 K for 180 s, and final 0.2 ML Ir deposition at room temperature. The predominant orientation of the triangular envelope of the small dendritic islands allows one to identify the regular crystal matrix and twin crystallites, appearing in green (light gray) and red (dark gray), respectively. Image sizes: (a) $255\times 255$ nm and (b) $44\times 44$ nm.Reuse & Permissions

Figure 5

(a) Reciprocal space cut in the plane defined by the $[111]$ and $[\overline{2}11]$ directions of an fcc crystal. Green (medium-gray) circles depict the reciprocal lattice of the regular crystal; red (dark-gray) circles depict the reciprocal lattice of a twin crystal, that is, of a regular crystal rotated by 180${}^{ˆ}$ around the $[111]$ axis; yellow (light-gray) circles depict the reciprocal lattice of this twinned crystal, but additionally rotated by 180${}^{ˆ}$ around the $[\overline{5}11]$ direction of the initial regular crystal (twin-of-twin) that matches the $[\overline{1}11]$ direction of the twin crystal. For multitwin peaks, half- or quarter-circles are employed. Shaded areas represent truncated crystals: the gray crystal is terminated by a $(111)$ surface, while the yellow (light gray) one corresponds to the $(\overline{1}11)$ termination of the twin, that is, a $(\overline{5}11)$ surface in the frame of reference of the initial crystal. These truncated crystals produce CTRs that are displayed as solid gray or yellow (light-gray) lines. (b) Cross section depicting the facets and the corresponding orientations with respect to the regular crystal matrix. On the left (right) facet of the twin (regular) crystallite are shown two small crystallites, one with the same structure as the initial twin crystallite that is displayed with the same color, and one whose structure is twinned with respect to the initial twin crystallite. The latter two are the twin-of-twin and the twin and are shown in yellow and violet, respectively (light grays).Reuse & Permissions

Figure 6

(a–f) Integrated intensity scattered along six CTRs perpendicular to the $(111)$ surface, that is, along the $[111]$ direction, after deposition of 68 ML Ir on Ir(111) at 350 K. Filled circles represent the data, while solid lines correspond to the fit of the whole set of CTRs. (a) and (c) correspond to the CTRs marked (I) and (II) in Fig. 5a. Bragg reflections for the regular untwinned crystal are indicated in green (light gray). Positions for the twinned crystal are labeled “twin.” Vertical arrows point to positions where faint extra contributions are observed. The data set displayed in gray in (a) is the integrated scattered intensity for the substrate prior to the growth of the Ir thin film. (g) Integrated intensity at the left position marked “twin” in (b), as a function of the deposited amount. The dots represent the data, the solid line was computed through the parameters from the fit of the CTRs. (h) Fraction of twin regions in the Ir film as a function of the layer index, as deduced from the fit of the CTRs.Reuse & Permissions

Figure 7

(a, b) Intensity scattered along lines in the $[5\overline{1}\overline{1}]$ (a) and $[11\overline{1}]$ (b) directions, after deposition of 68 ML Ir on Ir(111) at 350 K. (a) Corresponds to CTRs marked (III) in Fig. 5a. In (a) Bragg reflections for the twinned crystal are labeled “twin”; in (b) those for the untwinned crystal are shown in green (gray). Vertical arrows point to positions of the twins-of-twins (a) and of the side-twins (b), which are better visible for scans (gray lines; shifted upward for clarity) corresponding to the scattered intensity after annealing at 750 K. The intensity measured off the peaks is a mixture between the lateral facet [$(5\overline{1}\overline{1})$ and $(11\overline{1})$] signals and that from the corresponding stacking faults. (c, d) Intensity at the central position marked by a vertical arrow in (a) and (b) as a function of the Ir deposit (see text).Reuse & Permissions

Figure 8

(a) Fraction of twinned surface area measured by LEED (filled squares) and lateral twin crystallite boundary length measured by STM (filled circles) for a 90-ML Ir film grown on Ir(111) at 350 K, as a function of the annealing temperature. (b) The x-ray scattered intensity from twins [filled squares; measured at the left position marked “twin” in Fig. 6b] and from twins-of-twins [filled circles; measured at the central location marked with a vertical arrow in Fig. 7a] as a function of the annealing temperature.Reuse & Permissions

Figure 9

(a) Models of possible double positioning boundaries involving low-index planes. Twin crystallites, shown in red (dark gray), are embedded in an untwinned matrix, shown in green (light gray), with (b) $\{112\}/\{112\}$ and (c) $\{111\}/\{115\}$ twin boundaries.Reuse & Permissions

Figure 10

Intensity map for a $\{112\}/\{112\}$ boundary between an untwinned and a twinned crystal of the same size, (a) without and (b) with a shift in the $(11\overline{1})$ lateral facet resulting in a height difference of one-third monolayer (see text). The fringes are due to the finite size of the crystallites considered for the calculation.Reuse & Permissions