Abstract
The use of a functional molecular unit acting as a state variable provides an attractive alternative for the next generations of nanoscale electronics. It may help overcome the limits of conventional MOSFETd due to their potential scalability, low-cost, low variability, and highly integratable characteristics as well as the capability to exploit bottom-up self-assembly processes. This bottom-up construction and the operation of nanoscale machines/devices, in which the molecular motion can be controlled to perform functions, have been studied for their functionalities. Being triggered by external stimuli such as light, electricity or chemical reagents, these devices have shown various functions including those of diodes, rectifiers, memories, resonant tunnel junctions and single settable molecular switches that can be electronically configured for logic gates. Molecule-specific electronic switching has also been reported for several of these device structures, including nanopores containing oligo(phenylene ethynylene) monolayers, and planar junctions incorporating rotaxane and catenane monolayers for the construction and operation of complex molecular machines. A specific electrically driven surface mounted molecular rotor is described in detail in this review. The rotor is comprised of a monolayer of redox-active ligated copper compounds sandwiched between a gold electrode and a highly-doped P+ Si. This electrically driven sandwich-type monolayer molecular rotor device showed an on/off ratio of approximately 104, a read window of about 2.5 V, and a retention time of greater than 104 s. The rotation speed of this type of molecular rotor has been reported to be in the picosecond timescale, which provides a potential of high switching speed applications. Current-voltage spectroscopy (I-V) revealed a temperature-dependent negative differential resistance (NDR) associated with the device. The analysis of the device I–V characteristics suggests the source of the observed switching effects to be the result of the redox-induced ligand rotation around the copper metal center and this attribution of switching is consistent with the observed temperature dependence of the switching behavior as well as the proposed energy diagram of the device. The observed resistance switching shows the potential for future non-volatile memories and logic devices applications. This review will discuss the progress and provide a perspective of molecular motion for nanoelectronics and other applications.
Highlights
Miniaturization has been one of the driving forces of the semiconductor industry based on the well-known Moore’s law since Richard Feynman stated in his famous talk ‘there is plenty of room at the bottom’ in 1959
The above scenario provides an opportunity for exploring molecular machines and nanomachines which can be functionalized as nanoscale electronic devices
These devices based on functional molecular units acting as state variables are attractive due to their potential ultimate small size, low-cost, low variability, highly integratable characteristics and the ability to self-assemble themselves [1,2,3,4,5,6]
Summary
Miniaturization has been one of the driving forces of the semiconductor industry based on the well-known Moore’s law since Richard Feynman stated in his famous talk ‘there is plenty of room at the bottom’ in 1959. The above scenario provides an opportunity for exploring molecular machines and nanomachines which can be functionalized as nanoscale electronic devices. These devices based on functional molecular units acting as state variables (e.g., rotation and motor) are attractive due to their potential ultimate small size, low-cost, low variability, highly integratable characteristics and the ability to self-assemble themselves [1,2,3,4,5,6]. We will focus on a specific electrically driven surface mounted molecular rotor because of its potential capability of integration with standard semiconductor fabrication technologies, which provides the realization possibility in the near future. This review will concentrate on a real prospect of integrating a bottom-up approach, based on molecular design and micro-fabrication, in order to construct molecular electronic devices that can store information with very high densities
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