Determination of InP(001) surface reconstructions by STM and infrared spectroscopy of adsorbed hydrogen

The atomic structure of the InP(001) reconstructions has been identified by scanning tunneling microscopy and infrared spectroscopy of adsorbed hydrogen. The four phases, in order of decreasing phosphorous coverage, are c(2X2)/p(2X2), theta(P)=2.0 ML; (2X1), theta(P)=1.0 ML; sigma(2X4), theta(P)=0.25 ML, and delta(2X4), theta(P)=0.125 ML. The (2X2) consists of phosphorous dimers adsorbed onto a layer of P atoms. Removal of the P adatoms at 300 degrees C, produces the (2X1), which is terminated with a complete layer of buckled phosphorous dimers. Further annealing at 400 to 500 degrees C, yields the indium-rich sigma(2X4) and delta(2X4) reconstructions. The sigma(2X4) reconstruction comprises a single phosphorous dimer in the top layer and four indium dimers in the second layer. The delta(2X4) differs from the sigma(2X4) reconstruction in that one of the P atoms is replaced with an In atom to make an In-P heterodimer. This difference is evident by comparison of the intensities of P-H, In-H, and In-H-In stretching vibrations for the two surfaces.