The Nanocell: A Chemically Assembled Molecular Electronic Circuit

Computing is one of the most demanding applications of integrated circuits (IC). It requires the highest possible speed to process information. Higher speeds imply smaller circuits and, therefore, higher densities of integration. Thus, the most effective way to make faster circuits is by "scaling down", i.e., reducing the device size proportionally. However, under present technology, miniaturization is mainly constrained by the amount of heat dissipated as the number of devices increases per unit area and by the ability of lithographic tools to chisel smaller details on bulk substrates; these are technical constraints. However, there are physical or natural constraints which are practically material independent (speed of light, size of atoms, response of the electron, and Planck constant). Two main scenarios have been proposed for using molecules or small group of atoms (clusters) to build devices able to perform logical operations, bypassing, to some extent, problems undermining miniaturization or scaling-down processes for IC. One approach is the crossbar; a promising technology that uses directed self-assembly to make nanoarrays similar in shape to those already fabricated at larger scales by standard electronics. The other approach is the nanocell, which is a complementary design in the sense that it builds up (bottom-up) from single molecules into precise and complex structures that can be approached by standard lithography. This paper focuses on the description, advances, and possibilities of the nanocell approach, which takes advantage of the great skills developed by chemists to synthesize molecules with precise arrangements of atoms in a molecule. The nanocell concept does not require a deterministic assembly or deposition of molecules and clusters, thanks to the recently discovered programmability feature of molecules. Thus, in this paper, it is shown that the nanocell is a feasible concept for the development of electronics beyond deterministic lithograph- - ic approaches presently used in the fabrication of IC. The great importance and advantage of having molecular size computing devices is their ability to interact directly with external agents or molecules producing a sensor device already attached to a nanoprocessor that is able to strongly help in the stand-off detection of chemical and biological agents