Molecular electronics

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Molecular electronics describes a further development of microelectronics in which the individual components are implemented in molecules by utilizing atomic interactions .

definition

The definition of the term “molecular electronics” is taken so broadly in many publications that in addition to conjugated organic and inorganic molecules such as fullerenes (e.g. as electromechanical amplifiers) also nanostructures such as carbon nanotubes (e.g. in the function of Transistors for logic circuits ) or one-dimensional crystallized metallic semiconductors in the form of nanowires (e.g. in the function of transistors, nanosensors or nano- light-emitting diodes ) as so-called "elements on a molecular scale". According to this convention (cf. e.g.), it is not the molecular character that is decisive for classification under the term “molecular electronics”, but rather the fact that there are individual nanoscopic elements that individually serve as a functional unit. The source references and examples in the following overview are limited to references to organic molecules in order to clarify their possible uses for electronics.

Classification

Monomolecular electronics

It is characteristic that each individual molecule acts as a functional element. The development of mono-molecular electronics is in the context of the miniaturization trend in the manufacture of electronic semiconductor systems and pursues the goal of extremely miniaturized nanoelectronics in this context.

The monomolecular functional elements that have been implemented so far include in particular molecular wires, switches (e.g. as information storage devices), diodes or molecular spin channels between quantum dots . Prominent techniques for contacting individual molecules are methods such as scanning probe microscopy , in which functionalized AFM tips or STM tips serve as counter-electrodes, as well as break junction or the self-assembly of monolayers between two electrode layers.

Supramolecular electronics

It is characteristic that delimited, non-covalent associations of molecules each act as an individual functional unit. The strategy of self-assembly of molecules into conductive supramolecular units is often in the context of the bottom-up approach to the generation of nanoelectronic structures and can be pursued with different approaches. In addition to direct self-assembly, these approaches also include co-assembly, hierarchical self-assembly or the self-assembly of different molecules to form a mechanically interlocking supramolecular unit.

Various prominent approaches to the generation of electronically active supramolecular units are based on the formation of liquid crystals with a columnar phase, in which electrically conductive supramolecular columns can in principle act as a single functional element. These approaches include: B. the self-assembly of functionalized hexabenzocoronen to conductive columns, which are proposed as mutually isolated supramolecular nanowires. Another approach pursues the generation of conductive supramolecular columns via the self-assembly of functionalized dendron molecules. Aromatic molecules in the core of the pillars ensure the mobility of charge carriers. Alternatively, a co-assembly of functionalized dendron molecules with polymers functionalized by aromatic molecules can be achieved in such a way that the polymer chains are incorporated in the center of the column via donor-acceptor interactions. In both cases, a conductive one-dimensional system results, so that individual columns can be used as elements (e.g. nanowires) for supramolecular electronics - provided they can be addressed independently.

An example of hierarchical self-assembly for the formation of conductive supramolecular units is an approach in which molecules that consist of two subunits - an oligomer as a semiconductor and a monomer as a coupling element - dimerize through hydrogen bonds between the coupling elements. These dimers in turn form helical columns through self-assembly, which are in principle suitable as supramolecular electronic functional elements. Approaches in which different molecules mechanically interlock and thereby form an electronically active supramolecular structure are based on e.g. B. on rotaxanes or catenanes. These supramolecular units - prototypes of artificial molecular machines - have the property of acting as individual electromechanical switches - a property that can be used for logical functions or information storage.

Individual evidence

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