Microscopical Study of Au Nanocrystals Self-Assembled on (100)Si and SiO2/(100)Si Substrates
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Microscopical Study of Au Nanocrystals Self-Assembled on (100)Si and SiO2/(100)Si Substrates Emanuela Piscopiello1, Leander Tapfer1, Marco Vittori Antisari2, Pasquale Paiano3, Paola Prete4, and Nicola Lovergine3 1 Dept. Advanced Physics Technology and New Materials (FIM), ENEA, Strada Statale Appia, Brindisi, I-72100, Italy 2 Dept. Advanced Physics Technology and New Materials (FIM), ENEA, Via Anguillarese 301, Roma, I-00060, Italy 3 CNISM-Research Unit of Lecce and Dept. of Innovation Engineering, University of Lecce, via Arnesano, Lecce, I-73100, Italy 4 IMM-Institute for Microelectronics and Microsystems, CNR, via Arnesano, Lecce, I-73100, Italy
ABSTRACT This work reports on the structural characterization of Au nanocrystals directly prepared on the surface of (100)Si and 150 nm-thick SiO2 deposited (100)Si substrates, by a physical selfassembly method, consisting in the UHV evaporation of a thin Au film and its successive high temperature annealing. The morphology, orientation, and crystalline structure of Au nanocrystals were characterized by scanning and high-resolution transmission electron microscopy and X-ray diffraction, respectively. Experimental results show that the nature of the substrate strongly influences the process of Au nanocrystal formation upon heat treatment, by affecting the interaction of deposited Au with the underlying material. In the case of clean (100)Si substrates the Au strongly interacts with Si, so that Au nanoislands are obtained with a well defined epitaxial relationships with the substrate, i.e. [100]Au[110]Si and [110]Au[311]Si. The nanoisland shape is affected by faceting at the Au/Si interface, the Au nanocrystal being limited by the {111}, {311}, {711} and {-111} planes of Si. In the case of SiO2/(100)Si substrates spherical shaped Au nanoparticles with random crystal orientation are instead, produced. INTRODUCTION The controlled fabrication of size-selected metal nanocrystals on various semiconductor surfaces has both great scientific and technological interests. In recent years this field has attracted considerable attention due to its technological relevance in the fabrication by self-assembly methods of quasi 1-dimensional (1D) semiconductor nanostructures (so called nanowires and related 1D heterostructures) [1, 2] that may lead to the creation of the next generation of nanoelectronic devices. In addition to this, the optical properties of Au nanoparticles deposited onto suitable solid surfaces can be used to detect hybridization processes of specific DNA sequences. DNA functionalization and subsequent hybridization of Au nanoparticles immobilized on Si substrates can be exploited to fabricate specific biosensors devices in solid phase [3]. In this context, the achievement of these goals is strictly related to the capability to
observe and understand the mechanisms involved in the formation of metallic nanostructures on semiconductor surfaces. Different methods have been used to produce Au nanocrystals on Si substrates. Most of them are based on the s
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