Domain formation mechanism of the Si(110) “$16\times 2$” reconstruction

The main factor that determines which of the two domains forms upon reconstruction of the Si(110) “$16\times 2$” surface has been investigated. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) images showed that the domain orientation was independent of the heating current direction used to induce the Si(110) “$16\times 2$” reconstruction. Reciprocal-space lattice models of the reconstruction allowed for the correct identification of domain orientations in the LEED images, and they confirmed that the reconstruction is two dimensionally chiral. It is proposed that the domain orientation upon surface reconstruction is determined by the direction of monatomic steps present on the Si(110) plane. This is determined in turn by the direction at which the surface is polished off-axis from the (110) plane.

Figure 1

Schematic diagram of the double domain structure of the Si(110) “$16\times 2$” reconstruction. The gray and white segments correspond to the periodic channel structure with “pairs of pentagons” on both levels. The channels on the left are in the $\left[\overline{1}12\right]$ direction, and the other set is in the $\left[1\overline{1}2\right]$ direction.

Figure 2

Diagrams of the front and back of two types of Si(110) samples, $A$ and $B$, used in the experiments. The top figure defines the front of the samples, and the bottom defines the back of the samples. The angle $\theta$ indicated on the diagram is $54.7^{\circ }$.

Figure 3

STM images of (a) sample type $A$ and (b) sample type $B$ showing the Si(110) “$16\times 2$” reconstruction. Both images show channels in the $\left[1\overline{1}2\right]$ direction, and the current was applied approximately in the horizontal $\left[1\overline{1}1\right]$ and $\left[\overline{1}11\right]$ directions, respectively. The images were taken at a bias voltage of $1.6\mathrm{V}$ and a tunneling current of $0.9\mathrm{nA}$.

Figure 4

Line profile taken between $X$ and $Y$ on the inserted STM image of sample type $A$ showing the Si(110) “$16\times 2$” reconstruction. This shows step bunching present on the surface with seven steps with a separation of $\sim 2.5\mathrm{nm}$ and a height difference of $\sim 0.15\mathrm{nm}$ [16].

Figure 5

(a),(b) LEED images of the “$16\times 2$” reconstruction for Si(110) surfaces with the sample short axes along $\left[\overline{1}12\right]$ and $\left[1\overline{1}2\right]$, respectively. Both images show the fractional-order spots in the $\left[\overline{1}11\right]$ direction. (c),(d) $1\times 1$ surface LEED patterns for the samples in (a) and (b), respectively. All directions shown are real-space directions. The unit cells of the LEED patterns for the $1\times 1$ surfaces are shown by white rectangles. Parts (a)–(c) were obtained at a primary energy of $67\mathrm{eV}$, whereas (d) was obtained at $56\mathrm{eV}$. (a) Sample type A, (b) Sample type B, (c) Sample type A, and (d) Sample type B.

Figure 6

Diagrams showing the unit-cell parallelograms for the two possible domains of the “$16\times 2$” reconstruction. For the front face, the $G$ and $G^M$ matrices represent the channels in the $\left[\overline{1}12\right]$ and $\left[1\overline{1}2\right]$ directions, respectively. The angle $\theta =54.7^{\circ }$.

Figure 7

(a),(b) The reciprocal-space lattices of the two possible domains for the “$16\times 2$” reconstruction calculated using $G^M$ and $G$, respectively; $R$ is the lattice constant of silicon. The blue circles were generated using ${\mathit{r}}_s^{*}$ and the red squares were generated using ${\mathit{r}}^{*}$, which correspond to the reciprocal-lattice vectors of the reconstructed and bulk-terminated surfaces, respectively.

Figure 8

$1\times 1$ LEED patterns from Figs. 5 and 5 rotated through an angle of $+{55}^{\circ }$ for (a) and $-{55}^{\circ }$ for (b). (a) Sample type A and (b) Sample type B.

Figure 9

“$16\times 2$” LEED patterns from Figs. 5 and 5 rotated through an angle of $+{55}^{\circ }$ for (a) and $-{55}^{\circ }$ for (b). (c) The LEED pattern of the Si(110) “$16\times 2$” reconstruction for sample type $A$ with an off-axis polish angle changed to $0.5^{\circ }$ about the $\left[\overline{1}12\right]$ rotation axis. The $1\times 1$ LEED pattern for the same sample in (c) reveals it to be the back face.

Figure 10

Crystal direction diagrams showing the orientations of (a) the (17 15 1) and (b) the (15 17 1) planes relative to the (110) plane. The angle between the [17 15 1] and [110] directions is $4.3^{\circ }$. The same applies for the [15 17 1] and the $\left[110\right]$ directions.