Carbon Electrodes in Molecular Electronics

Edited by Richard C. Alkire, Philip N. Bartlett and Jacek Lipkowski. 

Si-SiOx) or physisorption n-n, S-Au, etc.), which can exert a controlling influence on junction behavior. Upon application of voltage across the junction, current flows across the molecular layer. However, the system should be treated as whole, as the thickness and electronic properties of the molecule are not the only factors that will dictate conductivity. 

Even though this article did not contain experimental data, as the methods and techniques that have become commonplace in constructing molecular electronic devices were not developed until more than a decade later, it has served as motivation for many of the experimental efforts that followed. Thus, theoretical molecular electronics preceded experiments by approximately two decades while some experiments had been done in the 1980s, it was not until the mid-1990s that experimental molecular electronics came into its own. 

With respect to motivators, electronics are ubiquitous in modern society. Given the enormous value of the global consumer electronics market place, it is not surprising that concerted efforts toward realizing the potential of exploiting molecules in electronic devices are ongoing. Part of the reason for the success 

While size represents perhaps the most commonly cited motivator in molecular electronics, there are other reasons to study MJ systems. Moreover, it should not be mistaken that shrinking device size represents the actual goal much of 

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In this regard, we compared Au, Ru, and carbon nanotube (CNT) electrodes on molecular electronic devices. (This sub-chapter is mainly based on Ref. [28].) These are a few materials among the employed as an electrode in experiments. Au is the most popular in molecular electronics [29]. Tulevski et al. studied the Ru surface to which a carbon atom was bound by forming a multiple covalent bond [30]. Guo et al. studied CNT electrodes with an amide linkage [31]. Au, CNT, and Ru also represent a material mainly having s, p, and d band characters in the vicinity of their Fermi energies, respectively. 

In the following chapters of this textbook, different aspects of electrochemical research on carbon materials will be discussed in detail, including carbon electrodes in different applications (fuel cells, molecular electronics, sensing, etc.) using various methods (surface modification, carbon paste, carbon fiber, etc.), and electrochemistry of different carbon materials (graphene, HOPG, carbon nanotube, diamond, etc.). 

This chapter discusses the use of carbon-based electrode materials in the construction of MJs and the use of carbon-based materials in related studies (such as electrochemical experiments and in the construction of other electronic devices). The methods for making MJs are first outlined, followed by the use of the more novel allotropes of carbon. These materials have interesting electronic properties that provide additional opportunities for their application in molecular electronics relative to more conventional carbon materials. Finally, some ofthe considerations that dictate charge transport across molecular layers in MJs are discussed before we leave with some future prospects. 

This section focuses on the electronic properties of other, novel carbon materials as relevant to their use in molecular electronics. The appropriate background regarding properties and preparation methods is discussed, while an interested reader may refer to Chapters 1-4 for more details on electrochemistry of highly oriented pyrolytic graphite (HOPG), graphene, and CNTs. Here, we specifically consider electrodes made of confined sp2 carbon layers, and limit the discussion to graphene and CNTs as prominent examples. 

In addition to traditional carbon materials, novel allotropes of carbon have unique electronic properties that may be exploited to provide some advantages to electronic device fabrication. These may serve as electrode materials in molecular electronics, or may form the basis of extant electronic devices with specifications that exceed those of existing electronics. In any case, carbon electrodes provide a rich area of study for molecular electronic systems. 

In the SECM measurement (Figure 18), a small microelectrode (typically a metal or carbon electrode) is rastered across the surface of interest, and the current resulting from a Faradaic reaction is mea-sured. 220 q-j g experiment is arranged such that the tip current is proportional to the local concentration of a redox species, which in turn may reflect molecular transport rates within a porous matrix (Figure ISa) or the electron-transfer activity at an electrode (Figure 18b). 

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