Low-energy surface vibration measurements on the alpha-quartz (0001) surface
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Despite the enormous range of usages, only little is known about the dynamic and structural properties of quartz (SiO2) surfaces on the atomic scale. The main reason for this is probably that quartz is an insulator, with the outermost surface layer consisting entirely of oxygen atoms. This means that it is difficult to investigate quartz with most surface science techniques which investigates the material on the atomic level. Three years ago, the first paper on the low-energy surface phonons on the alpha-quartz (0001) surface were published. The paper presented results measured using helium scattering as well as a theoretical prediction of the phonon spectra. The experimental results presented only partially agreed with the theoretically predicted energy spectrum, and in particular there were no phonon measurements fitting into the lower energy band predicted at around 5 meV. The main aim for this thesis was to investigate if the predicted low-energy surface phonons, not found from earlier experiments, are in fact present at the surface. For that, new measurements at different surface conditions and with a higher energy resolution than previously used, were performed using helium atom scattering. The results were analyzed using a new fitting procedure. The main outcome of this thesis is that lower phonon energy bands could be found. For the Gamma-K-direction of the Brillouin zone the dispersionless phonon mode was found at (2,3 +/- 0,6) meV and higher overtones at (6,1 +/- 0,5) meV and at (10,9 +/- 1,5) meV. For the Gamma-M-direction of the Brillouin zone the dispersionless phonon mode was found at (2,9 +/- 0,4) meV, higher overtones at (6,6 +/- 0,6) meV and at (10,8 +/- 1,5) meV.
PublisherThe University of Bergen
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