Coverage-dependent structures of cobalt-phthalocyanine molecules adsorbed on Cu(001) surface.

The morphologies, self-assembly structures, and stability of cobalt-phthalocyanines (CoPc) molecules adsorbed on Cu(001) with coverage ranging from 0.2 monolayer (ML) to 1.6 ML are investigated by ultrahigh-vacuum low-temperature scanning tunneling microscopy (UHV LT-STM) at liquid nitrogen temperature. Upon increasing the deposition of CoPc molecules various structures, such as isolated adsorption, quasi-hexagonal structure, square root(29) x square root(29) structure, are well characterized by the corresponding high-resolution STM images. The CoPc-CoPc intermolecular interaction and CoPc-substrate interfacial interaction dominate the structural evolutions. For the coverage higher than 1 ML, CoPc molecules preferentially locate on top of the molecules underneath and organize into square root(58) x square root(58) structure. As more and more CoPc molecules adsorb on the first layer, in some square root(58) x square root(58) regions molecular insertion leads to the formation of the square root(29) x square root(29) domain to effectively decrease the energy of the whole system.

The initial stage of the dissociative adsorption and the surface electronic state evolution of NH3 on Si(111)-(7 × 7).

Adsorption of NH3 molecules on Si(111)-(7 × 7) has been studied by scanning tunneling microscopy. We find that the dissociative adsorption is site-selective and exhibits two adsorption structures resulting from different reaction channels: [Formula: see text] and [Formula: see text]. To explain the dissociation processes, an adsorption model for these reactions is given. Furthermore, the evolution of the local electronic structures is investigated by means of atomically resolved scanning tunneling spectroscopy to clarify the effect of different fragments on the surface states. Finally, we discuss the adsorption position of H atoms from the NH3 dissociation.