Mass transport of In atoms and structural transformation of an In/Si(111) surface induced by PTCDA adsorption

초록

Adsorption of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules on various In-overlayer phases (root 3 x root 3, 2 x 2, and single-layer root 7 x root 3 (root 7 x root 3-SL)) on Si(111) was investigated using scanning tunneling microscope. On surfaces of all these phases, PTCDA molecules are initially adsorbed at defect sites. On root 3 x root 3, adsorbed molecules cover the surface disorderly and induce the development of small patches of 2 x 2. On the surface with mixed 2 x 2 and root 7 x root 3-SL phases, continued PTCDA adsorption increases the root 7 x root 3-SL area, and induces eventually the formation of a double-layer root 7 x root 3 phase. The adsorbed molecules aggregate, and some assemble on the root 7 x root 3-SL surface to form 2D molecular ordering in the herringbone structure. The development of new In-overlayer structures indicates that In atoms are additionally supplied to the surface by PTCDA adsorption, mass transported, and condensed to form higher-In-coverage phases. We propose that the adsorbed molecules displace or remove In atoms beneath them to bind more strongly to the underlying Si atoms than In atoms.

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