Quantum confinement of itinerant electrons in atomically smooth ultrathin lead films produces strong oscillations in the thickness-dependent film energy. By adding extra electrons via bismuth alloying, we showed that both the structural stability and the superconducting properties of such films can be tuned. The phase boundary (upper critical field) between the superconducting vortex state and the normal state indicates an anomalous suppression of superconducting order just below the critical temperature, Tc. This suppression varies systematically with the film thickness and the bismuth content and can be parametrized in terms of a characteristic temperature, Tc* (less than Tc), that is inversely proportional to the scattering mean free path. The results indicate that the isotropic nature of the superconductive pairing in bulk lead-bismuth alloys is altered in the quantum regime.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-002779.pdf

Tuning the Quantum Stability and Superconductivity of Ultrathin Metal Alloys

Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. However, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.

Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films.

In situ observation and control of ultrathin In layers on sublimated InP(100) surfaces

The structural and magnetic properties of TM13 and TM13@Au32 clusters (TM = Mn, Co) are studied by first-principles calculations. We find that the Au32 cluster can tune not only the magnetic moment but also the magnetic coupling properties between the TM atoms of the TM cluster. The Au32 cluster can increase the net magnetic moment of Mn13 clusters while reducing that of Co13 clusters. The interaction between Au and Mn atoms induces more Mn atoms to form spin parallel coupling, resulting in an increase of the total magnetic moment of Mn13 clusters, while for the Co13 clusters, the interaction between Au and Co atoms does not change the magnetic coupling states between the Co atoms, but reduces the magnetic moment of the Co atoms, leading to a decrease of the total magnetic moment of this system. Our findings indicate that the encapsulation of Au32 clusters can not only raise the chemical stability of TM clusters, but also can tune their magnetic coupling properties and magnetic moment, which enables such systems to be widely applied in fields of spintronics and medical science.

First-Principles Study of Magnetic Properties of TM 13 and TM 13 @Au 32 Clusters (TM=Mn, Co)

Metal nanoclusters featuring tunable luminescence and high biocompatibility are receiving attention as fluorescent markers for cellular imaging. The recently discovered ability of gold clusters to scavenge cytotoxic reactive oxygen species (ROS) from the intracellular environment extends their applicability to biomedical theranostics and provides a novel platform for realizing multifunctional luminescent probes with engineered anti-cytotoxic activity for applications in bio-diagnostics and conceivably cellular therapy. This goal could be achieved by using clusters of strongly reactive metals such as silver, provided that strategies are found to enhance their luminescence while simultaneously enabling direct interaction between the metal atoms and the chemical surroundings. In this work, we demonstrate a synergic approach for realizing multifunctional metal clusters combining enhanced luminescence with strong and lasting ROS scavenging activity, based on the fabrication and in situ protection of Ag nanoclusters with a supramolecular mantle of thiolated-Au atoms (Ag/Au-t). Confocal imaging and viability measurements highlight the biocompatibility of Ag/Au-t and their suitability as fluorescent bio-markers. ROS concentration tests reveal the remarkable scavenging activity of Ag-based clusters. Proliferation tests of cells in artificially stressed culture conditions point out their prolonged anti-cytotoxic effect with respect to gold systems, ensuring positive cell proliferation rates even for long incubation time.

/pdf/metal-nanoclusters-with-synergistically-engineered-optical-1prgqwy3zi.pdf

Metal Nanoclusters with Synergistically Engineered Optical and Buffering Activity of Intracellular Reactive Oxygen Species by Compositional and Supramolecular Design.

Quantum growth refers to the phenomena in which the quantum mechanically confined motion of electrons in metallic wires, islands, and films determines their overall structural stability as well as their physical and chemical properties. Yet to date, there has been a lack of a unified understanding of quantum growth with respect to the dimensionality of the nanostructures as well as the valency of the constituent atoms. Based on a first-principles approach, we investigate the stability of nanowires, nanoislands, and ultrathin films of prototypical metal elements. We reveal that the Friedel oscillations generated at the edges (or surfaces) of the nanostructures cause corresponding oscillatory behaviors in their stability, leading to the existence of highly preferred lengths (or thicknesses). Such magic lengths of the nanowires are further found to depend on both the number of valence electrons and the radial size, with the oscillation period monotonously increasing for alkali and group IB metals, and monoto...

Dimensionality and Valency Dependent Quantum Growth of Metallic Nanostructures: A Unified Perspective.

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Dimensionality and Valency Dependent Quantum Growth of Metallic Nanostructures: A Unified Perspective.