This is a (3 x 3)R30 structure

**Rationale**

The rotated unit cell is illustrated below - note, the hexagonal symmetry of the substrate is also evident in the overlayer structure.

The vectors **b _{1}** and

This is easily proved by noting

- that the
**b**vector corresponds to moving between the heads of the arrows representing the_{2}**a**and_{1}**a**vectors_{2}

- |
**b**| = |_{1}**b**| = b ; |_{2}**a**| = |_{1}**a**| = a_{2}

The length of the **b** vectors may therefore be obtained by
considering an isosceles triangle with an angle of 120 degrees
between the two sides which are of identical length (a), and applying
the cosine rule to find the length of the third side (b).

b^{2} = a^{2} + a^{2}
- 2.a.a cos 120 = 3 a^{2} ⇒ **b
= ****3
a**

The angle between the **b _{2}** and

Hence, this is a (3 x 3)R30 structure.