Anomalous hybridization in the In-rich InAs(001) reconstruction

The surface bonding arrangement in nearly all the confirmed reconstructions of InAs(001) and GaAs(001) have only two types of hybridization present. Either the bonds are similar to those in the bulk and the surface atoms are sp(3) hybridized or the surface atoms are in a tricoordinated bonding arrangement and are sp(2) hybridized. However, dicoordinated In atoms with sp hybridization are observed on the InAs(001), In-rich, room temperature and low temperature surfaces. Scanning tunneling microscopy (STM) images of the room temperature (300 K) InAs(001) surface reveal that the In-rich surface reconstruction consists of single-atom rows with areas of high electron density that are separated by similar to 4.3 angstrom. The separation in electron density is consistent with rows of undimerized, sp hybridized, In atoms, denoted as the beta 3'(4 x 2) reconstruction. As the sample is cooled to 77 K, the reconstruction spontaneously changes. STM images of the low temperature surface reveal that the areas of high electron density are no longer separated by similar to 4.3 angstrom but instead by similar to 17 angstrom. In addition, the LEED pattern changes from a (4 x 2) pattern to a (4 x 4) pattern at 77 K. The 77 K reconstruction is consistent with two (4 x 2) subunit cells; one that contains In dimers on the row and another subunit cell that contains undimerized, sp hybridized, In atoms on the row. This combination of dimerized and undimerized subunit cells results in a new unit cell with (4 x 4) periodicity, denoted as the beta 3(4 x 4) reconstruction. Density functional theory (DFT) and STM simulations were used to confirm the experimental findings. (C) 2009 Elsevier B.V. All rights reserved.