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Type: Text × Subject: Raman spectroscopy × WGL Institute: IHP ×

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    A novel engineered oxide buffer approach for fully lattice-matched SOI heterostructures
    (College Park, MD : Institute of Physics Publishing, 2010) Giussani, A.; Zaumseil, P.; Seifarth, O.; Storck, P.; Schroeder, T.
    Epitaxial (epi) oxides on silicon can be used to integrate novel device concepts on the canonical Si platform, including functional oxides, e.g. multiferroics, as well as alternative semiconductor approaches. For all these applications, the quality of the oxide heterostructure is a key figure of merit. In this paper, it is shown that, by co-evaporating Y2O3 and Pr2O3 powder materials, perfectly lattice-matched PrYO3(111) epilayers with bixbyite structure can be grown on Si(111) substrates. A high-resolution x-ray diffraction analysis demonstrates that the mixed oxide epi-films are single crystalline and type B oriented. Si epitaxial overgrowth of the PrYO3(111)/Si(111) support system results in flat, continuous and fully lattice-matched epi-Si(111)/PrYO3(111)/Si(111) silicon-on-insulator heterostructures. Raman spectroscopy proves the strain-free nature of the epi-Si films. A Williamson-Hall analysis of the mixed oxide layer highlights the existence of structural defects in the buffer, which can be explained by the thermal expansion coefficients of Si and PrYO3. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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    Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites
    (Bristol : IOP Publishing, 2022) Spirito, Davide; Asensio, Yaiza; Hueso, Luis E.; Martín-García, Beatriz
    The continuous progress in the synthesis and characterization of materials in the vast family of hybrid organic-inorganic metal halide perovskites (HOIPs) has been pushed by their exceptional properties mainly in optoelectronic applications. These works highlight the peculiar role of lattice vibrations, which strongly interact with electrons, resulting in coupled states affecting the optical properties. Among these materials, layered (2D) HOIPs have emerged as a promising material platform to address some issues of their three-dimensional counterparts, such as ambient stability and ion migration. Layered HOIPs consist of inorganic layers made of metal halide octahedra separated by layers composed of organic cations. They have attracted much interest not only for applications, but also for their rich phenomenology due to their crystal structure tunability. Here, we give an overview of the main experimental findings achieved via Raman spectroscopy in several configurations and set-ups, and how they contribute to shedding light on the complex structural nature of these fascinating materials. We focus on how the phonon spectrum comes from the interplay of several factors. First, the inorganic and organic parts, whose motions are coupled, contribute with their typical modes which are very different in energy. Nonetheless, the interaction between them is relevant, as it results in low-symmetry crystal structures. Then, the role of external stimuli, such as temperature and pressure, which induce phase transitions affecting the spectrum through change in symmetry of the lattice, octahedral tilting and arrangement of the molecules. Finally, the relevant role of the coupling between the charge carriers and optical phonons is highlighted.