1 Introduction to Laser Micro-to-Nano Manufacturing
53
the success welding of metallic nanowires [6, 206]. However, the further work to join
dissimilar nanowires, such as, metallic oxide nanowires still needs extensive research
[197].
1.6.2 Molecular Electronics
Transistor, which is one of the essential components in integrated circuits, controls
the flow of electrons by customizing the voltage that applied. In 2004 Ghost et al.
predicted to realize an evolutional solid-state molecular transistor by the electrostatic
regulation of the molecular orbital energy of a single molecule [207]. Electrostatic
and conformational interactions are two possible mechanisms for field-effect molecular transistors. Electrostatic component leads to the thermal limit in the absence of
tunneling. In their research, it shows that only if the molecular dipole moment μ
is close to qt ox , where t ox represents the thickness of the oxide isolation layer, the
conformational field effect can take a major role. Take advantage of that, if a large
molecular dipole along a suitable direction is established, the conformational transition can be achieved. Soon after, Ahm et al. [208] have suggested another approach,
in which internal electrostatic charge density can be adjusted by using an external
node to control the charge transfer across the metal electrodes and the molecules.
Transistor action can be achieved by aligning the molecular energy levels and the
Fermi level of the leads. Remarkably, researchers have developed molecular transistors by gold nanowire wires [209]. In this research, an approximately 100 nm
gold nanowire was patterned by electron beam lithography on top of an aluminum
gate electrode. As an active device, a 1,4-benzenedithiol (BDT) with a delocalized
aromatic ring as a π-conjugated molecule was coated on the gold nanowire surface,
which acted as a channel material.
Diodes are another crucial component of integrated circuits that conduct current
only in one direction when they are forward biased. Usually, a diode is composed of
two kinds of semiconductor materials to form a P-N junction. Currently, two types
of molecular diodes have been reported: rectifying diodes and resonant tunneling
diodes. In 1974, Aviram and Rater discussed the possibility of a rectifier, which
provided a foundation for current works on molecular rectifying diodes [210]. In their
research, a donor π -system and an acceptor π-system linked by a σ-bonded tunneling
bridge. This behavior has been identified by a hemi-quinone molecule, as shown in
Fig. 1.38 [211]. For resonant tunneling diodes (RTD), electrons can pass through
the resonant state at different energy levels; these diodes can be used as oscillators
and switches [212]. For molecular RTDs, methylene groups or aliphatic groups are
attached to both sides of a benzene ring, which leads to creating a potential barrier.
To create a functional device, electrodes need to be able to pass through this potential
barrier. However, the unoccupied energy level of the benzene ring does not match
the energy level of the electrode. In this case, the transistor remains in the “off” state.
The transistor can be turned to an “on” state, by varying the applied voltage [213]. To
design a proper molecule device, computation modeling is facile and time-effective.
53
the success welding of metallic nanowires [6, 206]. However, the further work to join
dissimilar nanowires, such as, metallic oxide nanowires still needs extensive research
[197].
1.6.2 Molecular Electronics
Transistor, which is one of the essential components in integrated circuits, controls
the flow of electrons by customizing the voltage that applied. In 2004 Ghost et al.
predicted to realize an evolutional solid-state molecular transistor by the electrostatic
regulation of the molecular orbital energy of a single molecule [207]. Electrostatic
and conformational interactions are two possible mechanisms for field-effect molecular transistors. Electrostatic component leads to the thermal limit in the absence of
tunneling. In their research, it shows that only if the molecular dipole moment μ
is close to qt ox , where t ox represents the thickness of the oxide isolation layer, the
conformational field effect can take a major role. Take advantage of that, if a large
molecular dipole along a suitable direction is established, the conformational transition can be achieved. Soon after, Ahm et al. [208] have suggested another approach,
in which internal electrostatic charge density can be adjusted by using an external
node to control the charge transfer across the metal electrodes and the molecules.
Transistor action can be achieved by aligning the molecular energy levels and the
Fermi level of the leads. Remarkably, researchers have developed molecular transistors by gold nanowire wires [209]. In this research, an approximately 100 nm
gold nanowire was patterned by electron beam lithography on top of an aluminum
gate electrode. As an active device, a 1,4-benzenedithiol (BDT) with a delocalized
aromatic ring as a π-conjugated molecule was coated on the gold nanowire surface,
which acted as a channel material.
Diodes are another crucial component of integrated circuits that conduct current
only in one direction when they are forward biased. Usually, a diode is composed of
two kinds of semiconductor materials to form a P-N junction. Currently, two types
of molecular diodes have been reported: rectifying diodes and resonant tunneling
diodes. In 1974, Aviram and Rater discussed the possibility of a rectifier, which
provided a foundation for current works on molecular rectifying diodes [210]. In their
research, a donor π -system and an acceptor π-system linked by a σ-bonded tunneling
bridge. This behavior has been identified by a hemi-quinone molecule, as shown in
Fig. 1.38 [211]. For resonant tunneling diodes (RTD), electrons can pass through
the resonant state at different energy levels; these diodes can be used as oscillators
and switches [212]. For molecular RTDs, methylene groups or aliphatic groups are
attached to both sides of a benzene ring, which leads to creating a potential barrier.
To create a functional device, electrodes need to be able to pass through this potential
barrier. However, the unoccupied energy level of the benzene ring does not match
the energy level of the electrode. In this case, the transistor remains in the “off” state.
The transistor can be turned to an “on” state, by varying the applied voltage [213]. To
design a proper molecule device, computation modeling is facile and time-effective.