Controlled wrinkling of single-layer graphene (1-LG) at nanometer scale was achieved by introducing monodisperse nanoparticles (NPs), with size comparable to the strain coherence length, underneath the 1-LG. Typical fingerprint of the delaminated fraction is identified as substantial contribution to the principal Raman modes of the 1-LG (G and G’). Correlation analysis of the Raman shift of the G and G’ modes clearly resolved the 1-LG in contact and delaminated from the substrate, respectively. Intensity of Raman features of the delaminated 1-LG increases linearly with the amount of the wrinkles, as determined by advanced processing of atomic force microscopy data. Our study thus offers universal approach for both fine tuning and facile quantification of the graphene topography up to ~60% of wrinkling.

Abstract. We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al 2 O 3 /Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells.

The evolution of local ferroelectric lattice distortions in multiferroic Ge 1−x Mn x Te is studied by xray diffraction, x-ray absorption spectroscopy and density functional theory. We show that the anion/cation displacements smoothly decrease with increasing Mn content, thereby reducing the ferroelectric transition from 700 to 100 K at x = 0.5, where the ferromagnetic Curie temperature reaches its maximum. First principles calculations explain this quenching by different local bond contributions of the Mn 3d shell compared to the Ge 4s shell in excellent quantitative agreement with the experiments. I IntroductionMultiferroics combining ferroelectric (FE) and ferromagnetic (FM) order in one and the same material1,2 have triggered immense interest due to their unique properties that open promising avenues for device applications3,4. Materials combining ferroelectricity and ferromagnetism in a single phase are, however, very rare. In Ge 1−x Mn x Te these two properties coexist and couple to each other5. This is because ferroelectricity is induced by the huge lattice distortion of the GeTe host material, whereas ferromagnetism is caused by the local spins of the Mn ions that couple via the free carriers in the system. Due to high solubility of Mn in GeTe and the high hole concentration, FM transition temperatures up to Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts 190 K have been achieved5-9, which are amongst the highest of all ferromagnetic semiconductors10.While the ferromagnetic properties of Ge 1−x Mn x Te have been studied in detail5-9,11-14, the influence of Mn doping on the ferroelectric properties15, 16 are not yet understood. Ferroelectricity is due to the inversion symmetry breaking caused by the displacement of the anion and cation sublattice relative to each other17,18. For GeTe, this displacement is as large as ~ 0.3 Å17,18, which results in a high FE transition temperature of ~ 700 K19,20 and was shown to be connected with a softening of elastic parameters21. The strong ferroelectricity leads to a giant Rashba splitting of the bands22-24, making GeTe a prime member of ferroelectric Rashba semiconductors that provide additional features for spintronic devices22. For Ge 1−x Mn x Te, however, the driving force for the electric phase transitions as well as the multiferroic coupling have not been fully identified. Analogously to GeTe, in Ge 1−x Mn x Te a ferroelectric phase transition caused by a relative displacement of the anion/cation sublattice occurs. These displacements and their relation to the multiferroic properties has yet been largely unexplored since direct measurements of electric polarization have been hampered by the high carrier concentration25 needed for ferromagnetic interactions.In this work, we combine temperature dependent x-ray diffraction (XRD) and low temperature extended x-ray absorption fine structure spectroscopy (EXAFS) of high quality epitaxial Ge 1−x Mn x Te films to study the local lattice distortions of Ge and Mn atoms with respect to th...

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