Department Of Physics

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    Ab Initio Modeling of the ZnO-Cu(111) Interface
    (American Chemical Society, 2021-12-31T00:00:00) Mondal, Krishnakanta; Megha; Banerjee, Arup; Fortunelli, Alessandro; Walter, Michael; Moseler, Michael
    The morphology at the catalytically active interfacial site of ZnO/Cu in the commercial ZnO/Cu/Al2O3 catalyst for CO2 hydrogenation to methanol is still an open question. In the present study, we employ ab initio density functional theory based methods to gain insight into the structure of the ZnO-Cu interface by investigating the morphology of supported ZnO nano-ribbons at the interface with the Cu(111) surface in the presence of hydrogen and water molecules. We find that the stabilities of free-standing ZnO nano-ribbons get enhanced when they are supported on the Cu(111) surface. These supported nano-ribbons are further stabilized by the adsorption of hydrogen atoms on the top of O atoms of the nano-ribbons. Interestingly, the hydrogenated nano-ribbons are found to be equally stable and they appear to be an array of independent chains of ZnOH motifs, suggesting that the hydrogenated nano-ribbons are structurally fluxional. The edge of these fluxional nano-ribbons is stabilized via a triangular reconstruction with a basic composition of Zn6O7H7 in the presence of water molecules. Such a triangular structure gets further stabilized when it is attached to a bulk-like part of the ZnO/Cu(111) system. Furthermore, we find that the triangular reconstruction is energetically favorable even at the methanol synthesis conditions. Therefore, we propose that, under methanol synthesis conditions, the motif Zn6O7H7 represents a stable form at the interface between the bulk-like part of ZnO and the Cu(111) surface in the ZnO/Cu/Al2O3 based commercial catalyst. � 2021 American Chemical Society
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    Thickness-dependent magnetic and transport properties of La0.5Sr0.5MnO3 thin films deposited by DC magnetron sputtering on the LaAlO3 substrate
    (Springer Verlag, 2018) Yadav, Kamlesh; Singh, H. K.; Maurya, K. K.; Varma, G. D.; Yadav, K.; Singh, H.K.; Maurya, K.K.; Varma, G.D.
    Thickness-dependent structural, magnetic and transport properties of La0.5Sr0.5MnO3 (LSMO) thin films have been studied. A series of the LSMO films with thickness 30, 60, 125 and 300?nm have been deposited on the LaAlO3 substrate using DC magnetron sputtering. The paramagnetic to ferromagnetic transition at TC is followed by antiferromagnetic ordering at TN in all films. It is also found that all LSMO films have TC lower than that of bulk LSMO. A small variation of TC is observed on increasing the film thickness. However, TN is found to rise with increase in the film thickness. The 60?nm-thick film shows a wide insulator to metal transition. The resistivity above 240?K of the films with various thicknesses is consistent with a small polaronic hopping conductivity. The polaronic formation energy EA rises with the increase of the film thickness except for 60?nm thin film, where a small decline in EA is observed. The correlation between observed structural, magnetic and electrical properties with the thickness of the films has been discussed in this paper. ? 2017, Springer-Verlag GmbH Germany, part of Springer Nature.