Combined Scanning Tunneling Microscopy and High-Resolution Electron Energy Loss Spectroscopy Study on the Adsorption State of CO on Ag(001)

Abstract

The adsorption site and vibrational energies of CO on a clean Ag(001) surface were determined using scanning tunneling microscopy, inelastic electron tunneling spectroscopy with a scanning tunneling microscope, and high-resolution electron energy loss spectroscopy. The CO molecules were found to adsorb on the atop site of the Ag(001) surface, which was similar to their adsorption on the Cu(001) surface. The vibrational energy of the CO internal stretching mode was found to be 263 meV, which is only 3 meV less than that of CO in the gas phase. This result indicates that the CO molecules chemisorb very weakly on the Ag(001) surface.

Binding Behavior of Carbonmonoxide to Gold Atoms on Ag(001)

“…The value of 16 meV for the FR mode of CO on Ag(001) is fully in line with the value reported in the literature [16]. The value for the FR mode of CO atop of a single Au on Ag(001) found in our experiment (around 10 meV) is nearest to the case of CO on single Fe atoms on Ag(110) where the CO molecule on top of the Fe atom is believed to have a slightly tilted on top configuration [14].…”

“…Moreover, IETS reveals different low-energy vibrational energies observed between tunneling voltages of 10 and 30 meV for the two adsorption sites of CO to Au as compared to the one at 16 meV for the single CO molecule bound to Ag(001). The latter value corresponds closely to the one reported previously [16], identified as the frustrated rotational mode of CO. DFT calculations of the adsorption energies, the diffusion barriers, and the vibrational frequencies of the CO molecule on the different adsorption sites contribute to a quantitative insight into the CO adsorption behaviour on single Au adatoms.…”

“…Of considerable significance for the present investigation of the CO binding behaviour to individual Au atoms on Ag(001) are the reports concerning (I) the adsorption of CO on Ag(001) [16] and (II) the observation of metal carbonyl formation on individual Cu and Fe adatoms on Ag(110) [10,14]. CO on Ag(001) is found to be very weakly bound and is still mobile at temperatures of 6 K [16].…”

“…The IET spectrum for the clean Ag(001) surface (bottom spectrum, black curve) is featureless, pointing to a metallic tip without a CO functionalization. With a CO functionalized tip the low-lying vibrational excitation observed for CO on Ag(001) (top spectrum, blue line) is present [16] (spectrum not shown). As expected, the IET spectrum obtained on top of a Au adatom (yellow) is also featureless within the chosen bias voltage range.…”

“…A technique that has proven very useful in this respect is inelastic electron tunneling spectroscopy, IETS [8][9][10][11]. Here we study the adsorption of CO on or near Au atoms supported on a Ag(001) surface [12][13][14][15][16].…”