The Electrical Conduction at Early Stages of Cluster-Assembled Films Growth
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The Electrical Conduction at Early Stages of Cluster-Assembled Films Growth Emanuele Barborini1*, Gabriele Corbelli2 and Paolo Milani2 1
Tethis SpA, via Russoli 3, 20143 Milano, Italy
2
CIMAINA and Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano, Italy *
[email protected]
ABSTRACT Electrical conduction in Fe, Pd, Nb, W and Mo cluster-assembled films was investigated in-situ, during their growth by supersonic cluster beam deposition. We observed for clusterassembled films resistivity values several orders of magnitude larger than corresponding bulk, as well as an increase of resistivity by increasing the film thickness, in contrast to the behaviour of atom-assembled metallic films. This suggests that nanoscale morphology arising by growth dynamics of cluster-assembled films, such as the minimal cluster-cluster interconnection and the evolution of surface roughness with thickness, may play a crucial role in the observed behaviour. Theoretical models based on non-isotropic 3D distributions of clusters into the film would help for a deeper understanding of the behaviour of cluster-assembled films compared to atomassembled ones. Benefits are expected in the technological field of devices performing electrical read-out on active nanostructured layers, as in the case of chemoresistive sensors.
INTRODUCTION A powerful approach for the synthesis of nanostructured films with tailored properties consists in the deposition of atomic clusters produced in gas phase. The survival of the nanoscale building blocks during the deposition process (memory effect), as well as film growth dynamics, can both deeply influence the transport properties of cluster-assembled systems [1-3]. In particular their electrical conductivity may differ significantly respect to conductivity of atomassembled films, due to the presence of finite size effects, nanoscale disorder and peculiar topology evolution at early stages of film growth [4-7]. Although several studies on electrical conduction in cluster-assembled films at very low coverage [4-7], the role of cluster-surface interaction, fragmentation, diffusion, coalescence or sticking after the percolation onset and the first stage of 3D growth remains almost completely unexplored. A deeper knowledge in this field would provide benefits to many technological applications where the understanding of the influence of the nano- and mesostructure on transport properties are crucial. Examples are gas sensing through conductimetric microdevices, where the presence of chemical species in air is detected through variations of the electrical conduction of a nanostructured oxide film [8-12], as well as interconnections in highly integrated multi-layer electronics (3D electronics), where grain-boundary and surface scattering may affect
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electrical resistivity when the lateral dimensions are scaled down to nanometric length scales [13-16]. Cluster-assembled films have growth mechanism substantially different from atomassembled ones so different relationship bet
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