Mikroanalyse

Ohne Zusammenfassung     

Strain phase diagram and domain orientation in SrTiO3 thin films

SrTiO3 thin films were used as a model system to study the effects of strain and epitaxial constraint on structural phase transitions of perovskite films. The basic phenomena revealed will apply to a variety of important structural transitions including the ferroelectric transition. Highly strained SrTiO3 films were grown on different substrates, providing both compressive and tensile strain. The measured strain-temperature phase diagram is qualitatively consistent with theory; however, the increase in the phase transition temperature is much larger than predicted. Because of the epitaxial strain and substrate clamping, the SrTiO3 lattice is tetragonal at all temperatures. The phase transitions involve only changes in internal symmetry. The low temperature phase under tensile strain has a unique structure with orthorhombic Cmcm space group but a tetragonal lattice, an interesting consequence of epitaxial constraint.     

Determining the electron-phonon mass enhancement parameter λ on metal surfaces

We discuss various approaches for determining the strength of the electron-phonon coupling on metal surfaces by angle-resolved photoemission. The first is to extract the electron-phonon mass enhancement parameter directly from the re-normalization of the band dispersion very close to the Fermi level. The second is to use the temperature-dependence of photoemission spectra such as energy distribution curves (EDCs) or momentum distribution curves (MDCs). We illustrate the advantages and disadvantages of both methods with the help of simulated spectral functions. Using experimental data, we find =0.40(5) for Bi(111) by analyzing temperature-dependent MDCs. PACS 73.20.-r; 63.20.Kr; 71.18.+y; 79.60.Bm     

A revised assignment of the 13C NMR spectra of α- and β-pinenes

α-Pinene and β-pinene ¹³C enriched at the C-10 position were prepared by an unambiguous synthesis. ¹³C NMR spectral analysis provided evidence for a revised assignment for α-pinene at the C-9 and C-10 carbon atoms.