• Surface reconstructions induced by thin overlayers of indium on Si(111)

We have used the technique of impact collision ion scattering spectrometry (ICISS) to study the in‐plane geometry of both the 7/8 × 7/8 and 4×1 reconstructions of indium on Si(111). For the 7/8 × 7/8 reconstruction the In adatoms are generally thought to lie on either threefold hollow (H₃) sites or on fourfold atop (T₄) sites. Our ICISS polar‐angle scans agree with computer simulations of the T₄ model. Separations of the In and Si layers have also been determined from our experimental data, in agreement with predictions from total energy calculations. The 4×1 reconstruction is known to consist of double rows of adatoms running in 〈1̄10〉 directions, from scanning tunneling microscopy images. Assuming the top layer adatoms to be indium, we perform ICISS polar‐angle scans to determine whether the adatom positions lie in H₃ or T₄ sites. Our results show general agreement with the simulations for the H₃ sites in the 4×1 geometry.