Information Processing Schemes Based on Monolayer Protected Metallic Nanoclusters

Abstract

Nanostructures are potentially useful as building blocks to complement future electronics because of their high versatility and packing densities. The fabrication and characterization of particular nanostructures and the use of new theoretical tools to describe their properties are receiving much attention. However, the integration of these individual systems into general schemes that could perform simple tasks is also necessary because modern electronics operation relies on the concerted action of many basic units. We review here new conceptual schemes that can allow information processing with ligand or monolayer protected metallic nanoclusters (MPCs) on the basis of the experimentally demonstrated and theoretically described electrical characteristics of these nanostructures. In particular, we make use of the tunnelling current through a metallic nanocluster attached to the electrodes by ligands. The nanostructure is described as a single electron transistor (SET) that can be gated by an external potential. This fact permits exploiting information processing schemes in approximately defined arrays of MPCs. These schemes include: (i) binary, multivalued, and reversible logic gates; (ii) an associative memory and a synchronization circuit; and (iii) two signal processing nanodevices based on parallel arrays of MPCs and nanoswitches. In each case, the practical operation of the nanodevice is based on the SET properties of MPCs reported experimentally. We examine also some of the practical problems that should be addressed in future experimental realizations: the stochastic nature of the electron tunnelling, the relatively low operation temperatures, and the limited reliability caused by the weak signals involved and the nanostructure variability. The perspectives to solve these problems are based on the potentially high degree of scalability of the nanostructures.

Ideal Discrete Energy Levels in Synthesized Au Nanoparticles for Chemically Assembled Single-Electron Transistors

“…It is noted that another Coulomb diamond, 20 times less conductive than the main Coulomb diamonds, are superimposed in Figure a and b, and this result implies another Au NP (Au NP3 named in Supporting Information) is inserted in parallel with Au NP1. As the effect of Au NP3 is negligibly small, the SET can be considered as an SET consisting of Au NP1 as the Coulomb island and Au NP2 as the Coulomb box near Au NP1, which is similar to the other experimental results and theoretical proposals. − A detailed discussion about Au NP3 is in the Supporting Information. Consequently, the schematic spatial structure of the Au NPs and nanogap electrodes in this double-gate SET and the equivalent circuit are shown in Figure c and d, respectively, and the unique circuit parameters are evaluated as discussed above and listed in Table (a scanning electron microscopy image of typical electroless gold-plated nanogap electrodes is shown in Supporting Information Figure S2).…”

“…Chemical assembly is one of the promising candidates of fabrication processes for single-electron transistors (SETs). SETs are attractive components for high device density, high charge sensitivity, and low power consumption; − however, the reproducible fabrication of SETs is still a challenge. SETs consist of three (source, drain, and gate) electrodes, and a quantum dot as a Coulomb island has to be isolated by two tunneling junctions from source and drain electrodes.…”

Biologically Inspired Information Processing and Synchronization in Ensembles of Non-Identical Threshold-Potential Nanostructures

“…For example, the electrochemically determined capacitance of Au 225 (diameter 1.8 nm) is 0.6 aF approximately [30] and other particles like Pd 40 (diameter 1.2 nm) show a capacitance as low as 0.35 aF. The current–voltage curves of a single ligand-stabilized NP obtained by scanning tunneling spectroscopy can be described by SET equivalent circuits that give tunneling resistances and effective capacitances in the range 100 MΩ – 10 GΩ and 0.1 – 10 aF, respectively [2], [18]–[20], [22], [28]–[30]. A final, potentially useful characteristic of ligand-stabilized metallic nanoparticles is self-assembly in approximately defined nanoarchitectures [18], [19], [28]–[30].…”

“…At high temperatures, random electron tunneling makes it difficult to implement reliable information processing schemes for the system parameters mentioned above (1 aF for the NP capacitance and 10 GΩ for the charging resistance). However, higher temperatures can be considered by decreasing further the electrical capacitance, which can be achieved by reducing the NP size and introducing appropriate organic ligands [2], [18]–[20], [22], [29], [30]. Recently, Coulomb blockade effects have been observed up to 160 K in ligand-stabilized Au NP with nanoscale diameters [2].…”

“…To this end, we simulate the integrated response of ensembles of single-electron transistors (SET) whose threshold potentials suffer from a high individual variability [15], [16]. A particular experimental realization of a SET is the nanoparticle-based transistor [17]–[20] that mimics some of the spiking properties of biological synapses [15], [17], [21]. In these systems, the different shape and size distributions of metallic nanoparticles protected with organic ligands result in a significant variability in their threshold potentials [15], [22].…”