56
A. Hu et al.
of anther SWBNNT [232]. Green et al. reported a 160-kilo-byte molecular electronic
memory pattern, which fabricated by over 1400 Ti nanowires [233]. These molecular
device patterns were configured to form a fully functional random-access memory
circuit for storing and retrieving information.
Graphene is a typical 2D material providing valuable mechanical, electronic,
chemical, and optical properties. At the same time, graphene is recognized as an
ideal candidate for molecular junction [234, 235]. Wang et al. evident graphene as
the ideal electrode through a comparative study to PEDOT:PSS and gold in molecular
devices [235]. In their report, graphene has better transport characteristics and contact
conductance. Nowadays, graphene is extensively applied in multiple molecular electric devices, such as conducting electrode in memory devices [236], field-effect
transistors [236], and dye-sensitized solar cells [237].
1.6.4 Fabrication of Molecular Devices
In the process of molecular devices fabrication, pre-patterning, and precise manipulation of nanomaterials are required as very critical processes. Usually, e-beam
lithography and chemical vapor deposition for in situ growth are the main tools for
these procedures [238, 239]. With the development of molecular devices, some novel
approaches have been established. As aforementioned the laser as a tool for precision machining has considerably contributed to the nanoscale process, such as laserinduced plasmonic nano joining [5, 6], nanoscale ablation [240], and etching [141,
241]. The precision machining property of laser processing has also been applied
in molecular electrical devices as well. Maurice et al. reported a low-temperature
process for nanogap creating in graphene [242]. In this study, a tightly focused
femtosecond laser was used to induce a pre-patterned defect in graphene. After
the laser process, an electro-burn process was applied to generate a gap with tens
nanometer wide. During this process, the defected area could locally generate a
dynamic hot spot, further facilitate the burn of graphene and eventually yield a nanosize gap. As a result, the nanogap width is 36.4 ± 18.5 nm (as presents in Fig. 1.40).
A few nanometer gap as a basic architecture allows a single molecule to be inserted
to create molecular transistors [243, 244], DNA sequencers [245, 246], and sensors
[247]. Therefore, develop a nanogap fabrication process is essential in the field of
molecular electronics.
Currently, the development of molecular electronics using DNA molecules as the
building blocks or template for growth nanostructure has gained a huge interest.
The key to using DNA as a scaffold for electronic circuits is to effectively transform the DNA molecules into conductive wires, which is called DNA metallization
[248]. Typically, DNA-templated electronics is a two-step process; First, establish
metallic nucleation centers on DNA molecules, which can be approached by binding
metal ions or complexes to the DNA and their subsequent reduction, or by directly
placing small metallic particles to the DNA. Once metallic nucleation centers were
formed, using these centers as catalysts for selective deposition of metal along with
A. Hu et al.
of anther SWBNNT [232]. Green et al. reported a 160-kilo-byte molecular electronic
memory pattern, which fabricated by over 1400 Ti nanowires [233]. These molecular
device patterns were configured to form a fully functional random-access memory
circuit for storing and retrieving information.
Graphene is a typical 2D material providing valuable mechanical, electronic,
chemical, and optical properties. At the same time, graphene is recognized as an
ideal candidate for molecular junction [234, 235]. Wang et al. evident graphene as
the ideal electrode through a comparative study to PEDOT:PSS and gold in molecular
devices [235]. In their report, graphene has better transport characteristics and contact
conductance. Nowadays, graphene is extensively applied in multiple molecular electric devices, such as conducting electrode in memory devices [236], field-effect
transistors [236], and dye-sensitized solar cells [237].
1.6.4 Fabrication of Molecular Devices
In the process of molecular devices fabrication, pre-patterning, and precise manipulation of nanomaterials are required as very critical processes. Usually, e-beam
lithography and chemical vapor deposition for in situ growth are the main tools for
these procedures [238, 239]. With the development of molecular devices, some novel
approaches have been established. As aforementioned the laser as a tool for precision machining has considerably contributed to the nanoscale process, such as laserinduced plasmonic nano joining [5, 6], nanoscale ablation [240], and etching [141,
241]. The precision machining property of laser processing has also been applied
in molecular electrical devices as well. Maurice et al. reported a low-temperature
process for nanogap creating in graphene [242]. In this study, a tightly focused
femtosecond laser was used to induce a pre-patterned defect in graphene. After
the laser process, an electro-burn process was applied to generate a gap with tens
nanometer wide. During this process, the defected area could locally generate a
dynamic hot spot, further facilitate the burn of graphene and eventually yield a nanosize gap. As a result, the nanogap width is 36.4 ± 18.5 nm (as presents in Fig. 1.40).
A few nanometer gap as a basic architecture allows a single molecule to be inserted
to create molecular transistors [243, 244], DNA sequencers [245, 246], and sensors
[247]. Therefore, develop a nanogap fabrication process is essential in the field of
molecular electronics.
Currently, the development of molecular electronics using DNA molecules as the
building blocks or template for growth nanostructure has gained a huge interest.
The key to using DNA as a scaffold for electronic circuits is to effectively transform the DNA molecules into conductive wires, which is called DNA metallization
[248]. Typically, DNA-templated electronics is a two-step process; First, establish
metallic nucleation centers on DNA molecules, which can be approached by binding
metal ions or complexes to the DNA and their subsequent reduction, or by directly
placing small metallic particles to the DNA. Once metallic nucleation centers were
formed, using these centers as catalysts for selective deposition of metal along with