Molecular Electronics: From Single‐Molecule to Large‐Area Devices

Abstract

This Minireview focuses on conductance measurements on molecular junctions containing few tens of molecules, which are carried out by using two approaches: 1) conducting atomic force microscopy to study self‐assembled monolayers on metal surfaces, and 2) tiny molecular junctions made of metal nanodots (diameter <10 nm), covered by fewer than 100 molecules and studied by conducting atomic force microscopy. In particular, this latter approach has new results to be obtained, or to previous results to be revisited which are reviewed here: 1) how the electron‐transport properties of molecular junctions are modified by mechanical constraint, 2) the role of intermolecular interactions on the shape of conductance histograms of molecular junctions, and 3) the demonstration that a molecular diode can operate in the microwave regime up to 18 GHz.

A review of oligo(arylene ethynylene) derivatives in molecular junctions

“…5. These and other methods have been thoroughly described in many reviews, [18][19][20][21][22][23][24][25][26] so will not be subject to detailed discussion here. Some aspects of their development are discussed in section 1.3.…”

Nanofabrication Techniques in Large-Area Molecular Electronic Devices

“…However, this methodology has so far been unsuccessful since the formation of clusters, or the penetration of metal ions from the solution or even metal wires through the defect sites in the monolayer are often observed-resulting in very low yield devices [84,359,360]. Although these problems-which are mainly associated with the existence of imperfections in the monolayer and the presence of free metal ions in the solution-have been able to be overcome or reduced [22,[361][362][363], still exits serious limitations in this approach. Only 1/3 of the monolayer is covered by the top metal layer; albeit this value can be increased until an almost completely covered SAM by repeating the adsorption-electrochemical reduction cycle in a metal ion free solution, but with the inconvenience of increasing the presence of short-circuits [364,365].…”

“…The official birth of molecular electronics is widely recognized as 1974, with the publication of the seminal paper from Aviran and Ratner that proposed (theoretically) that a single-molecule could act as a rectifier [15]. Intense work in the field for more than four decades has included the development of methodologies based on scanning tunneling microscopy (STM) or conducting atomic force microscopy (c-afm) for measuring the electrical properties of single-molecules and molecular assemblies [14,[16][17][18][19][20][21][22]. These studies have resulted in a growing understanding of the key parameters that determine the electrical properties of molecular junctions (molecular backbone [12,23], chemical anchoring groups [24][25][26], conformation [27], metal complexation [28], redox state [18,[29][30][31], electrode material [32][33][34][35], and if applicable, the characteristics of the medium: Solvent [36], pH [37], etc.…”

“…(v) Control of lateral interactions and aggregation effects in molecular assemblies. These lateral intermolecular interactions may have a decisive role in the electron transport properties of large-area devices based on π-conjugated materials [22]; (vi) Deposition of the top contact electrode avoiding the formation of short-circuits and/or damage of the functional organic molecules in the monolayer [84,85].…”

Porphyrins as building blocks for single-molecule devices

“…The study of single-molecule junctions is at the heart of molecular electronics and has been extensively reviewed already, for example in ref. [3][4][5][6] and references therein. In most cases fundamental structure-property relationships are reported extracted from a small set of synthesized molecules analyzed as single-molecule junctions in a particular experimental set-up.…”