We report studies of bimetallic nanoparticles with 15%–16% atomic crystal parameters size mismatch. The degree of alloying was probed in a 2-nm Pt core (smallest attainable core size) of Pt–Ag nanoparticles (completely immiscible in bulk) and 20-nm-diameter Pd–Ag nanowires (completely miscible in bulk). Particles were synthesized radiolytically, and depending on the initial parameters, they assume spherical or cylindrical (nanowire) morphologies. In all cases, the metals are seen to follow their bulk alloying characteristics. Pt and Ag segregate in both spherical and wire forms, which indicates that strain due to crystallographic mismatch overcomes the excess surface free energy in the small particles. The Pd–Ag nanowires alloy similar to previously reported spherical Pd–Ag particles of similar diameter and composition.

Articles you may be interested inTheoretical description of X-ray absorption spectroscopy of the graphene-metal interfaces J. Chem. Phys. 138, 154706 (2013); 10.1063/1.4801501Near-edge x-ray absorption fine structure spectroscopy studies of charge redistribution at graphene/dielectric interfaces J.We have measured x-ray absorption fine structure of pre-and post-ultraviolet͑UV͒-irradiated gold ͑Au͒ deposited-titania (TiO 2 ) nanocomposites in order to study the effect of UV irradiation on the charge state and local structures around Au in TiO 2 . Our results indicate a positive oxidation state of Au in TiO 2 following UV irradiation and, in addition, a remarkable change is observed in the local environment between these samples as an effect of UV irradiation. The environment around Au, which is comprised mostly of Ti and O atoms prior to UV illumination, is seen to form Au clusters following UV illumination. The photoinduced chemical transformation established in this study demonstrates the nature of semiconductor/metal interface under UV irradiation, and its role in dictating long-term photoelectrochemical performance of nanocomposite photocatalysts.

Structural and electronic properties of BiFeO3 clusters were studied using first-principles electronic structure calculations. The main aim of this work is to unveil the role of structural modifications in developing ferromagnetism in nano-BiFeO3. We have found that the ferromagnetic ground state is energetically more favorable than the antiferromagnetic ground state for this cluster. In a relaxed cluster, there are large distortions for BiO6 octahedra, comparatively small distortion but large rotation (20°) for FeO6 octahedra, and large reduction of Fe–O–Fe coupling angle (153° → 133°) compared to bulk BiFeO3. A large charge transfer from Bi-s states is predicted for cluster which may be responsible for the observed structural changes. These results are in consistent with recent experimental observation of Bi sublattice melting for small BiFeO3 nanoparticles (<18 nm). Also, a large charge transfer from Bi-s states explains why small BiFeO3 nanoparticles cannot sustain ferroelectricity. Applying a crystal chemistry perspective, we have shown that the ferromagnetism in BiFeO3 cluster is originates from Fe–O–Fe angle changes. Now, by changing Fe–O–Fe angle in BiFeO3 crystal, we have shown that there is a magnetic phase transition (antiferromagnetic to ferromagnetic) near ∠FeOFe = 133°. Therefore, we conclusively shown that the key structural parameter responsible for ferromagnetism in nano-BiFeO3 is the Fe–O–Fe coupling angle. These results are also important for device fabrication which often uses nano-BFO/BFO-films where it is possible to change the Fe–O–Fe coupling angle easily by applying some strains.

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Structural transformations at the TiO2Pt and TiO2Ir interfaces during UV-irradiation have been probed by X-ray absorption spectroscopy. Oxidation by the photogenerated holes results in the intercalation of Pt and Ir into the Titania matrix. The structural transformations observed with Pt and Ir nanoparticles anchored on TiO2 is different than the clustering of gold atoms observed in the TiO2/Au system. Implications of such structural transformations on the photocatalytic activity of semiconductor photocatalyts are discussed.