Abstract
An experimental investigation of Ag and Ni nanoparticles (NPs) deposited on Silicon with its native oxide, on highly oriented pyrolytic graphite and on graphene flakes is reported. The NPs were physically synthesized with a magnetron based gas aggregation source and the produced beam was mass-filtered and deposited in vacuum on the substrates. The study was concentrated on the morphology for the different cases, shedding some light on the interaction of pre-formed NPs with surfaces, a crucial aspect both of technological and scientific relevance. The nature of adhesion can be strongly influenced by the intrinsic properties of the surface (like for instance the energetics of interaction between the NP surface atoms and the first layers of the substrate) and/or the extrinsic properties, like the presence of defects, step edges, impurities and other irregularities. After adhesion, the NPs mobility and their mutual interaction are very relevant. In this work, the study was concentrated on NP/surface morphology, by using atomic force microscopy, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy.Article highlightsMorphology of physically synthesized metal Nano-Particles (NPs) on Si, HOPG and Graphene was investigated. The NPs were pure Ag and Ni. Coalescence, diffusion and self-aggregation and preferential adhesion were observed, with possible applications in sensor technology.Possible explanations are: NP softness, NP/surface bonding interaction and presence of contaminant species molecules between NP.
Highlights
Synthesis and manipulation of metal nanoparticles (NPs) is a research subject of tremendous impact in nanotechnology [1,2,3,4]
The bottom-up techniques for NP production includes the vast area of chemical synthesis [5], of self-assembling at surfaces [6], and of physical vapor deposition (PVD) techniques, like Molecular Beam Epitaxy (MBE) [7], pulsed laser ablation [8] and magnetron sputtering followed by gas aggregation [3, 4, 9,10,11]
Bardotti et al [17] demonstrated experimentally that large Sb clusters could diffuse and selfaggregate on Highly Oriented Pyrolitic Graphite (HOPG) surface. They observed that clusters of an average diameter < d > = 5 nm gave rise to ramified islands, an aggregation mode that was a clear proof of diffusion of Sb NPs on such a surface. They simulated with the Montecarlo method the interaction of Sb NPs on the surface, by assuming that it occurs in three different steps: landing, diffusion and aggregation, and they found an excellent agreement with the experiment
Summary
Synthesis and manipulation of metal nanoparticles (NPs) is a research subject of tremendous impact in nanotechnology [1,2,3,4]. It was demonstrated that the cluster impact energy and the surface material can give rise to different degrees of adhesion, so it is possible to create areas where the islands density is significantly different [24, 25], with potential applications in the development of new sensors and electronic devices. These classes of experiments have never been performed on Ni nanoclusters. The study was concentrated on NP/surface morphology, by using Atomic Force Microscopy (AFM), SEM, Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS)
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