RAS and STM investigations of pentacene molecules on metal and semiconductor surfaces
Carty, Darren (2004) RAS and STM investigations of pentacene molecules on metal and semiconductor surfaces. PhD thesis, Dublin City University.
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In this study the electronic surface states and surface reconstructions of an organic molecule on semiconductor and metal surfaces were investigated with Reflectance Anisotropy Spectroscopy (RAS), Scanning Tunnelling Microscopy (STM) and photoemission techniques.
The design, construction and operation of a Reflectance Anisotropy Spectrometer are described in detail. The RAS technique was applied to the investigation o f pentacene on the Au(110)-(2xl) surface. It was found that the pentacene molecules adsorbed on this surface shows three observable electronic transitions in the 1.6 eV-5 eV photon energy range. At monolayer coverage there are distinct changes in the RAS spectrum that can be associated with a change in the orientation of the molecule on the gold surface.
STM was applied to the investigation o f pentacene adsorbed on the Au(llO)- (2x1) and the A g /S i(lll)-(7 x 7 ) surface. It was found that on the Au(l 10)-(2xl) surface, below a monolayer the pentacene molecule adsorbs parallel to and between the Au rows in the [11 0] direction, While above a monolayer the molecule changes direction and preferentially adsorbs across the gold rows. This change in orientation accounts for the changes in the RAS spectra above a monolayer. The effect o f annealing on the molecular ordering was also studied. These interfaces were also studied by core level and valence band photoemission using a synchrotron light source. Deposition o f pentacene on the Ag/Si(l 11)-(V3 xy/3 ) surface produced three distinct ordered structures for coverages up to one monolayer. It is concluded from the RAS, STM, synchrotron studies that the molecule lies flat on the Au(110) and Ag/Si(l 11) surfaces.
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