We report the characterization of Bi 2 Te 2 Se crystals obtained by the modified Bridgman and Bridgman-Stockbarger crystal growth techniques. X-ray diffraction study confirms an ordered SeTe distribution in the inner and outer chalcogen layers, respectively, with a small amount of mixing.The crystals displaying high resistivity (> 1 Ωcm) and low carrier concentration (∼ 5×10 16 /cm 3 ) at 4 K were found in the central region of the long Bridgman-Stockbarger crystal, which we attribute to very small differences in defect density along the length of the crystal rod. Analysis of the temperature dependent resistivities and Hall coefficients reveals the possible underlying origins of the donors and acceptors in this phase.

We report the characterization of the layered rare-earth manganese oxyselenide La 2 O 3 Mn 2 Se 2 . The susceptibility data show a broad maximum near 350 K, indicating the existence of two-dimensional ͑2D͒ short-range ordering in this compound. A sharp feature associated with a short-range to long-range antiferromagnetic phase transition is seen at 163 K. A very small heat-capacity anomaly is detected around 163 K, indicating that most of the magnetic entropy is lost during the 2D ordering process. Both crystal and magnetic structures were studied by neutron powder diffraction at 300, 200, 150, 100, and 6 K. The structure was refined in space group I4 / mmm with a = 4.13 939͑3͒ Å and c = 18.8511͑2͒ Å at ambient temperature. No structural distortion was detected. The resulted magnetic structure is G-type with a propagation vector of k = ͑0,0,0͒ and an ordered magnetic moment of 4.147͑28͒ B / Mn along c is found at 6 K. Warren peak shape analysis of the neutrondiffraction data near 22°is employed to characterize the increase in correlation length in the 2D magnetic state on approaching the three-dimensional ordering transition.

In addition to the known effect of substrate on interfacial properties of perovskite films, here we show that bulk properties of Hybrid Lead Halide Perovskite films depend on the type of substrate used for film growth. Despite the relative large film thickness, ~600 nm, the roughness and nature of the substrate layer (glass, FTO, TiO 2 and PEDOT:PSS) affect not just the degree of preferential orientation and crystal grain size Raman peaks.The irreversible photoluminescence enhancement observed at low power with illumination time, also dependent on the substrate nature, is proposed to be due to the localization of the electron-hole excitons created in the vicinity of the light generated defects. The results shed light into the performance of the perovskite layer and help understanding how bulk processes, where ion migration is a conspicuous example, are severely affected by interfacial properties as those imposed by the substrate.

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The oxidation and corrosion of copper are fundamental issues studied for many decades due to their ubiquitous and transversal impact. However, the oxidation of copper used as catalyst for graphene synthesis has opened a singular problem not yet solved. Contradictory results are reported about the protecting or enhancing role of graphene in copper oxidation. We study short- and long-term oxidation of copper with different characteristics, such as oxygen content and morphology, with and without graphene, and in polycrystalline copper foils and almost totally textured (100) and (111) copper films on MgO and sapphire substrates, respectively. We propose a mechanism to explain the enhanced oxidation of polycrystalline copper originated by oxygen encapsulated by the graphene impermeable layer during graphene growth. The initial oxygen content and the existence of grain boundaries are the main factors that determine the relevance of this process. Graphene is shown to prevent oxidation from the atmosphere for any of the copper substrates but also promotes slow oxidation derived by the release of out-of-equilibrium encapsulated oxygen. The formation of bubbles after several months evidence this slow release. The occluded oxygen in graphene covered copper is demonstrated by comparing the oxygen to copper ratio at different depths using hard X-ray photoelectron spectroscopy for samples with and without graphene.

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