Self-assembled molecular structures formed on a bare Si(001) surface at high temperature have been studied by scanning tunneling microscopy (STM). Linearly arranged pyrazine (C 4 H 4 N 2 ) adsorbates were observed that had grown by self-assembly along the Si dimer bond direction on the heated Si(001) substrate. The degree of one-dimensional ordering of the molecules at elevated substrate temperatures (∼60−170 °C) was improved over that at room temperature. In cases of higher pyrazine dosage, well-ordered (2 × 2) molecular arrays were also observed by STM. We found that the molecules tend to adsorb on step edges and defect sites. Utilizing this selective adsorption near the step edge, pyrazine lines were successfully fabricated at regular spacing on the vicinal Si substrate. The local structure of the pyrazine adsorbate on the step edge is the same as that on the terrace. The ordering of molecules on the surface is closely related to the fact that the adsorbate can migrate without decomposition through metastable structures with a N−Si bond on the high-temperature substrate.Article pubs.acs.org/JPCC

We have studied the coverage-dependent energy transfer dynamics between hot electrons and CO on Cu(110) with femtosecond visible pump, sum frequency probe spectroscopy. We find that transients of the C-O stretch frequency display a red shift, which increases from 3 cm(-1) at 0.1 ML to 9 cm(-1) at 0.77 ML. Analysis of the transients reveals that the non-adiabatic coupling between the adsorbate vibrational motion and the electrons becomes stronger with increasing coverage. This trend requires the frustrated rotational mode to be the cause of the non-adiabatic behavior, even for relatively weak laser excitation of the adsorbate. We attribute the coverage dependence to both an increase in the adsorbate electronic density of states and an increasingly anharmonic potential energy surface caused by repulsive interactions between neighboring CO adsorbates. This work thus reveals adsorbate-adsorbate interactions as a new way to control adsorbate non-adiabaticity.

The coordination of CO to metalloporphyrins changes their electronic and magnetic properties. Here we locally desorb CO molecules from a single ruthenium tetraphenylporphyrin carbonyl (CO-RuTPP) on Cu(110) using STM. The desorption is triggered by the injection of holes into the occupied states of the adsorbate using an unusual two-carrier process.