Boendgen, Gisela; (2000) Quantum dynamics of STM and laser induced desorption of atoms and molecules from surfaces. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The manipulation of atoms and molecules at solid surfaces by electronic excitations with electrons (or holes) emitted from the tip of a scanning tunneling microscope (STM) or with laser radiation is both of applied and fundamental interest, e.g. for micro- and nanostructuring of materials, the clarification of elementary (catalytic) reaction mechanisms and for the question of how to treat the quantum dynamics of a laser or STM driven "system" (the adsorbate) in contact with a dissipative (energy-withdrawing) "bath" (the substrate). Desorption induced by electronic transitions (DIET) and its variant DIMET (M = multiple) are among the simplest possible "reactions" of adsorbate-surface systems; usually involving extremely short-lived electronically excited intermediates. In this thesis, the ultra-short dynamics of directly (localised to the adsorbate-substrate complex) and indirectly (i.e., through the substrate) stimulated DIET and DIMET processes was studied for Si(100)-(2x1):H(D) and Pt(111):NO. Isotope effects and the influence of substrate temperature and applied electric fields on the desorption yields were examined and possibilities to actively control the outcome (e.g. yields, isotope ratios), for example by laser shaping techniques, were investigated. For that purpose, time-dependent wave packet methods and open system density matrix theory were used to account for energy dissipation and thus resulting ultrashort lifetime of the electronically excited states involved.

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