Surface Electron Transfer Dynamics in the Presence of Organic Chromophores [article]

Lars Gundlach, Universitätsbibliothek Der FU Berlin, Universitätsbibliothek Der FU Berlin
The dynamics of heterogeneous electron transfer between photoexcited organic adsorbate molecules and single crystal surfaces are investigated by means of time-resolved two-photon photoemission spectroscopy (TR-2PPE). Whereas, the focus of this work is set on different chemically modified perylene chromophores attached to the (110) surface of TiO2 rutile crystals, other combinations of organic molecules on semiconductor and metal surfaces are investigated. The necessary time resolution for
more » ... E measurements is achieved via a novel setup consisting of two non-collinear optical parametric amplifiers operated simultaneously at a repetition rate of 150 kHz delivering a crosscorrelation function with 35 fs FWHM. The preparation of the adlayers is performed by chemisorption from solution in a special preparation chamber allowing for switching between ultra-high vacuum and inert gas conditions. The adsorbate covered as well as the bare single crystal surfaces are characterized by means of standard surface science techniques like UPS, XPS and LEED. Transient absorption spectroscopy is carried out on some of the samples for comparison with the TR-2PPE experiments. The well ordered organic adsorbate layers with sub-monolayer coverages formed on the surface of TiO2 enable the determination of the binding geometry of the molecules for two different anchor groups, i.e. carboxylic and phosphonic acid. The adsorption geometry is deduced from angular and polarization dependent 2PPE measurements by applying Fresnel equations. Time dependent 2PPE measurements of perylene chromophores equipped with long rigid spacer groups yield the expected slow injection times in contrast to earlier measurements of the same molecules attached to colloidal TiO2 films via transient absorption spectroscopy. The latter gave unreasonable short injection times as a result of the narrow pores in the colloidal film. TR-2PPE measurements of perylene chromophores equipped with short anchor groups enable the investigation of electron transport in the surf [...]
doi:10.17169/refubium-5604 fatcat:kyfl33qexzffrkv33kfhqyiqja