Vacuum synthesis of magnetic aluminum phthalocyanine on Au(111).

Air-unstable magnetic aluminum phthalocyanine (AlPc) molecules are prepared by an on-surface metalation reaction of phthalocyanine with aluminum (Al) atoms on Au(111) in ultrahigh vacuum. Experiments and density functional theory calculations show that an unpaired spin is located on the conjugated isoindole lobes of the molecule rather than at the Al position.

Spin Manipulation by Creation of Single-Molecule Radical Cations.

All-trans-retinoic acid (ReA), a closed-shell organic molecule comprising only C, H, and O atoms, is investigated on a Au(111) substrate using scanning tunneling microscopy and spectroscopy. In dense arrays single ReA molecules are switched to a number of states, three of which carry a localized spin as evidenced by conductance spectroscopy in high magnetic fields. The spin of a single molecule may be reversibly switched on and off without affecting its neighbors. We suggest that ReA on Au is readily converted to a radical by the abstraction of an electron.

Low-temperature scanning tunneling microscopy study of double-decker DyPc2 on Pb Surface.

Low-temperature scanning tunneling microscopy (STM), scanning tunneling spectroscopy and dI/dV mapping techniques have been applied to study double-decker DyPc2 molecules on Pb(111) films grown on silicon wafers. The DyPc2 molecules firstly self-assemble into a monolayer where two neighbouring molecules form an azimuthal angle of 6°. Scattered DyPc2 molecules in the second layer can be stabilized on top of the first self-assembled monolayer, adopting a co-axial alignment with the underlying molecules. With the reference to the new layer assembled by Pc molecules generated by the cracking of DyPc2 molecules on the substrate at or above room temperature, the molecular configuration can be directly deduced from STM imaging. The two Pc ligands in the same double-decker molecule rotate 45° with respect to each other. The dI/dV mapping of the individual DyPc2 molecules in the second layer shows that they can appear as either four-lobed or eight-lobed features in the STM images depending on the bias voltage employed.

Dynamical Coulomb blockade observed in nanosized electrical contacts.

Electrical contacts between nanoengineered systems are expected to constitute the basic building blocks of future nanoscale electronics. However, the accurate characterization and understanding of electrical contacts at the nanoscale is an experimentally challenging task. Here, we employ low-temperature scanning tunneling spectroscopy to investigate the conductance of individual nanocontacts formed between flat Pb islands and their supporting substrates. We observe a suppression of the differential tunnel conductance at small bias voltages due to dynamical Coulomb blockade effects. The differential conductance spectra allow us to determine the capacitances and resistances of the electrical contacts which depend systematically on the island-substrate contact area. Calculations based on the theory of environmentally assisted tunneling agree well with the measurements.

Ultrahigh vacuum deposition of organic molecules by electrospray ionization.

An electrospray apparatus for deposition of organic molecules on surfaces in ultrahigh vacuum is presented. The kinetic energy at the impact and mass to charge ratio of deposited ions can be controlled by an electrostatic quadrupole deflector and an in-line quadrupole mass spectrometer. With an ion funnel in the first two vacuum stages a high ion transmission is achieved. Experiments on porphyrin cations and deoxyribonucleic acid deposited on a Au(111) surface demonstrate the capabilities of the instrument.

Reduction of the superconducting gap of ultrathin Pb islands grown on Si(111).

The energy gap Delta of superconducting Pb islands grown on Si(111) was probed in situ between 5 and 60 monolayers by low-temperature scanning tunneling spectroscopy. Delta was found to decrease from its bulk value as a function of inverse island thickness. Corresponding T_{c} values, estimated using bulk gap-to-T_{c} ratio, are in quantitative agreement with ex situ magnetic susceptibility measurements, however, in strong contrast to previous scanning probe results. Layer-dependent ab initio density functional calculations for freestanding Pb films show that the electron-phonon coupling constant, determining T_{c}, decreases with diminishing film thickness.