Interactions of Functional Groups with Surfaces
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- Institutt for fysikk 
The adsorption of atoms and molecules is a key step in a wide range of technologically important areas including catalysis, adhesion, corrosion, electrochemistry and microelectronics. Investigations of well-defined systems can contribute to better understanding of processes within these areas. This thesis presents studies of different functional groups adsorbed on NiAl alloys and semiconductor surfaces by means of high resolution photoemission spectroscopy (HR-PES), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The combination of experimental techniques and theorectical calculations has proven to be a powerful tool for obtaining a more complete picture of the interactions between adsorbates and surfaces. HR-PES measurements of methanol (CH3OH) on Ni3Al(111) and NiAl(110) revealed the formation of two adsorption products upon exposure at low temperatures, which were identified as methanol and methoxy species, producing a new contribution shifted by 0.48 eV relative to the Al 2p bulk contribution. After methanol adsorption on NiAl(110), a contribution at the low binding energy side relative to the Al 2p bulk contribution was observed. This was attributed to surface Al atoms not bonded to methanol or methoxy. Further decomposition to methoxy was observed upon heating to 200 K. DFT calculations predict that methanol adsorbs preferentially in the Al on-top site on both Ni3Al(111) and NiAl(110), whereas methoxy prefers a 2Ni+Al hollow site on Ni3Al(111) and a slightly off Al bridge site on NiAl(110). Methylamine adsorption on Ni3Al(111) and NiAl(110), caused one new contribution to appear at the high binding energy side relative to the Al 2p bulk contribution on both surfaces. Mainly molecular desorption was observed upon heating. However, a small fraction of methylamine decomposed, possibly forming CN upon heating. DFT calculations showed contradicting results for the adsorption of methylamine on Ni3Al(111) and NiAl(110) favouring the Ni on-top and Al on-top sites, respectively. Calculated core level shifts in the Al 2p spectra, due to methylamine adsorbed in the Al on-top site on both surfaces agree with the experimental results. HR-PES measurements of carbon monoxide (CO) adsorbed on Ni3Al(111) and NiAl(110) indicate that two different CO species are present at both surfaces high CO coverage. Preliminary DFT calculations predict that CO adsorbs in Ni dominated sites. However, the surface Al atoms are affected by the adsorption of CO. An additional contribution is observed in the Al 2p spectra from Ni3Al(111), whereas the contribution associated with the surface component on NiAl(110) is reduced upon exposure to CO. Another technological important element is silicon. In the present work we have studied the adsorption of 1,1-dichloroethene (Cl2C=CH2) on the Si(111)–7×7 surface. The HR-PES measurements showed that 1,1-dichloroethene dissociates upon adsorption at room temperature by breaking one or both C–Cl bonds resulting in Cl, 1-chlorovinyl (CCl=CH2) and vinylidene (>C=CH2). The dissociation products occupy different adatoms and restatom sites at Si(111)–7×7 as observed by STM.