Electronic Contact Nanostructuring

We use the term electronic contact nano structuring to describe two dilferent types of nanostructuring techniques where the key role is played by the electronic contact between the tip and the substrate, yielding nanocativies on a surface. However, as we will see, the two alternatives seem to involve quite dilferent physical processes. 

The second procedure is different from the previous one in several aspects. First, the metallic substrate employed is Au, which does not show a remarkable dissolution under the experimental conditions chosen, so that no faradaic processes are involved at either the substrate or the tip. Second, the tip is polarized negatively with respect to the surface. Third, the potential bias between the tip and the substrate must be extremely small (e.g., -2 mV) otherwise, no nanocavity formation is observed. Fourth, the potential of the substrate must be in a region where reconstruction of the Au(lll) surface occurs. Thus, when the bias potential is stepped from a significant positive value (typically, 200 mV) to a small negative value and kept there for a period of several seconds, individual pits of about 40 nm result, with a depth of two to four atomic layers. According to the authors, this nanostructuring procedure is initiated by an important electronic (but not mechanical) contact between tip and substrate. As a consequence of this interaction, and stimulated by an enhanced local reconstruction of the surface, some Au atoms are mobilized from the Au surface to the tip, where they are adhered. When the tip is pulled out of the surface, a pit with a mound beside it is left on the surface. The formation of the connecting neck between the tip and surface is similar to the TILMD technique described above but with a different hnal result a hole instead of a cluster on the surface (Chi et al., 2000). 

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FIGURE 36.1 Schematic illustration of some electrochemical techniques employed for surface nanostructuring (a) tip-induced local metal deposition (b) defect nanostructuring (c) localized electrochemical nucleation and growth d) electronic contact nanostructuring. 

An alternative route to understanding the complications of disordered interfaces is to achieve functional control of intrinsically disordered materials interfaces as well. Such enhanced control can, for example, be achieved by construction of molecular sensitizers capable of binding in a functionally equivalent manner even to disordered nanostructured substrates. An important step in this direction is to find molecular sensitizers that can form interfaces with nanostructured substrates that display consistent interfacial electronic contacting capabilities, enabling systematic investigations of the distance dependence of surface electron transfer processes. 

An additional and very attractive aspect of molecular qubits is the fact that they are stable in solution, and that the ligand shell can be functionalized with specific chemical groups. In recent years, this has enabled depositing molecular clusters onto different substrates and grafting them to nanostructures or devices, such as carbon nanotube single electron transistors or point contacts [112]. These devices... 

Further increase in the density of nanoparticles leads to formation of close contacts between them, which leads to collectivization of electrons in ensembles of contacting particles. In the high-density limit, when each nanoparticle is in contact with all of its neighbors, the nanostructure becomes similar in its electrical properties to a thin metallic film and is characterized by a metallic type of conduction. 

Besides there are some other reasons for the LSPA band hybridization at binary close-packed arrays. For example, strong inhomogeneity of local fields in nanostructures under consideration changes the behavior of copper and silver valence electrons and makes easy the conditions of the interparticle charge carriers transport. A t th e area of cop per an d s ilver contact th e h ybrid li nks formation becomes possible. As a sum of these factors the modification of... 

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