A combination of normal-incidence x-ray standing-wave ͑NIXSW͒ spectroscopy, x-ray photoelectron spectroscopy ͑XPS͒, scanning tunneling microscopy ͑STM͒, and density-functional theory ͑DFT͒ has been used to investigate the interaction of a number of phthalocyanine molecules ͑specifically, SnPc, PbPc, and CoPc͒ with the Ag͑111͒ surface. The metal-surface distances predicted by the DFT calculations for SnPc/Ag͑111͒ ͑2.48 Å͒ and CoPc/Ag͑111͒ ͑2.88 Å͒ are in good agreement with our NIXSW experimental results for these systems ͑2.31Ϯ 0.09 and 2.90Ϯ 0.05 Å, respectively͒. Good agreement is also found between calculated partial density-of-states plots and STM images of CoPc on Ag͑111͒. Although the DFT and Pb 4f NIXSW results for the Pb-Ag͑111͒ distance are similarly in apparently good agreement, the Pb 4f core-level data suggest that a chemical reaction between PbPc and Ag͑111͒ occurs due to the annealing procedure used in our experiments and that the similarity of the DFT and Pb 4f NIXSW values for the Pb-Ag͑111͒ distance is likely to be fortuitous. We interpret the Pb 4f XPS data as indicating that the Pb atom can detach from the PbPc molecule when it is adsorbed in the "Pb-down" position, leading to the formation of a Pb-Ag alloy and the concomitant reduction in Pb from a Pb 2+ state ͑in bulklike films of PbPc͒ to Pb 0 . In contrast to SnPc, neither PbPc nor CoPc forms a well-ordered monolayer on Ag͑111͒ via the deposition and annealing procedures we have used. Our DFT calculations show that each of the phthalocyanine molecules donate charge to the silver surface, and that back donation from Ag to the metal atom ͑Co, Sn, or Pb͒ is only significant for CoPc.

The atomistic structure of the tip apex plays a crucial role in performing reliable atomic-scale surface and adsorbate manipulation using scanning probe techniques. We have developed an automated extraction routine for controlled removal of single hydrogen atoms from the H:Si(100) surface. The set of atomic extraction protocols detect a variety of desorption events during scanning tunneling microscope (STM)-induced modification of the hydrogen-passivated surface. The influence of the tip state on the probability for hydrogen removal was examined by comparing the desorption efficiency for various classifications of STM topographs (rows, dimers, atoms, etc). We find that dimer-row-resolving tip apices extract hydrogen atoms most readily and reliably (and with least spurious desorption), while tip states which provide atomic resolution counter-intuitively have a lower probability for single H atom removal.

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Articles you may be interested inOptimal design and fabrication of three-dimensional calibration specimens for scanning probe microscopy Rev. Sci. Instrum. 83, 053708 (2012); 10.1063/1.4719661 TSP based Evolutionary optimization approach for the Vehicle Routing Problem AIP Conf.We describe the development and application of an imaging protocol, which evolves a scanning probe's atomic structure in parallel with automated optimization of the scan parameters. Our protocol coerces the system into a state that produces a specific atomic resolution image type without human involvement.