CORDIS - EU research results

Single molecule on surfaces: manipulation and study of chemical, electronic and vibrational properties with a low temperature ultra high vacuum scanning tunnelling microscopy

Final Activity Report Summary - SMS-STM (Single molecule on surfaces: manipulation and study of chemical, electronic and vibrational properties with Ultra High Vacuum Scanning Tunnelling microscopy)

The central idea of the project has been the study of chemical, electronic and vibrational properties of adsorbates on metals studied at a single-molecule level. This information can only be obtained by means of low temperature scanning tunnelling microscopy (LT-STM). Two different LT-STM systems have been used throughout the project, both with an optimised design for performing single-molecule manipulation and spectroscopy. The first one, home-built by the same author, and a second commercial one installed in the returning institution.

The first study has been focused on a detailed understanding of the adsorption configuration and stability of water on the clean and C and O precovered Ru(0001) surface. The results clarify long standing controversies about whether water adsorbs intact or dissociatively on the clean surface and its exact configuration. The most recent predictions of a thermally activated partial dissociation were confirmed. In addition, molecular-resolution images revealed an intriguing and complex structure of the mixed water-hydroxyl phase, which provides crucial information about the reaction details. By acquiring an atomic level picture of the configuration and energy of water adsorption for different pre-adsorbed O coverage we have been able to explain the mechanism for the O coverage dependent transition from thermally activated dissociation to intact adsorption. Within this study, individual water molecules have been manipulated by exciting internal vibrational modes by inelastic electrons coming from / to the tip. In this way we could induce diffusion, dissociation, desorption, and controlled tip-surface transfer of the molecule. This controlled chemistry not only represents an elegant way of manipulating matter at the atomic scale, but also provide us with essential information about the energetics, adsorption sites and reaction products of the different paths involved in the reactions.

The second study has been carried out in the returning institution, and consisted on the study of the electronic properties of different molecular and atomic adsorbates deposited on metallic surfaces. In particular, we have focused on the many-body interaction between the spin-polarised localised states of magnetic adsorbates and the free electrons of the host substrate, known as the Kondo effect.

As magnetic adsorbates, we have studied atomic Co impurities and metallorganic molecules such as Co or Fe phthalocyanines (Co / Fe-Pc). By doing local spectroscopic measurements, we have studied the lateral localization of the Kondo related peak along the magnetic impurity, and the effect of the adsorption configuration and the presence of other impurities on the Kondo interaction. In particular, we have been able to follow the evolution of the Kondo feature as we chemically transform the molecule with the STM tip. These experiments are part of a more general study consisting on the controlled modification of the electronic and magnetic properties of atoms and molecules adsorbed on a surface.