62
A. Hu et al.
nanostructures [274]. Compared with the direct laser writing method, they demonstrated that the use of STED nanolithography can greatly reduce the lateral size of the
line. Using optically STED lithography, sub-diffraction-limited acrylate nanoanchors
were prepared [275]. Acrylic nanopatches with a diameter of 60–70 nm prepared by
STED enhanced two-photon polymerization are easily functionalized by antibodies
at the single-molecule level. He proposed a control method of 45 nm wire based on
direct laser writing with STED, which has a rod-shaped effective focal point. In traditional standard direct laser writing, a donut-shaped depletion focus is usually used,
and the minimum line width is limited to 55 nm. In this work, they push this limit to
the sub-50 nm size with a rod-like effective focal point, which is a combination of
Gaussian excitation focusing and twin-oval depletion focusing [276]. Furthermore,
Gan has demonstrated deep sub-diffraction optical beam lithography with a 9 nm
feature size based on the STED mechanism [277].
1.8 Summary and Outlooks
A laser is a crucial tool for precise micro-to-nano manufacturing. For various applications the understanding of fundamentals between the laser and material interaction
is basic. With the development of ultrafast laser available for a shorter pulse, higher
peak power, and tunable wavelength at a wider band, the laser manufacturing enables
versatile processing with a higher precision beyond the optical diffraction limit.
The basic interaction of laser and materials involves in energy absorption. At
a micro-to-nanoscale, this physical procedure includes surface plasmon excitation
and surface electron excitation. At a periodic approximately equal to or shorter than
the electron-lattice coupling time, typically a couple of picoseconds, the so-called
Coulomb explosion, and nonthermal melting will occur due to the surface electron
vaporization. This localizes the thermal effect to the size similar to the optical penetration depth. This is the current physical basis for precision manufacturing using an
ultrafast laser.
At a nanoscale, the physical properties of materials will be quite different from
their bulk counterparts. The micro-to-nano manufacturing leads to the mass transfer
at these scopes. The surface properties will be dominant due to the size effect and the
scaling laws. The nanoparticles can be melt and sintered at a pretty low temperature,
even close to room temperature. The involved surface liquid phase and enhanced
surface diffusion will bring new mechanisms to the manufacturing and materials
science.
Due to these new features, laser-based micro-to-nanomanufacturing is especially
effective and powerful for printed electronics, such as flexible/stretchable electronics,
3D microprinting for portable electronics at current big data, Internet of things,
next-generation computation and artificial intelligent era. It will create extensive
opportunities in energy, environment, sensing, and biomedical applications.
With the further development of laser-based micro-to-nano manufacturing, it can
be expected that molecular devices with high manufacturing and manipulation will
A. Hu et al.
nanostructures [274]. Compared with the direct laser writing method, they demonstrated that the use of STED nanolithography can greatly reduce the lateral size of the
line. Using optically STED lithography, sub-diffraction-limited acrylate nanoanchors
were prepared [275]. Acrylic nanopatches with a diameter of 60–70 nm prepared by
STED enhanced two-photon polymerization are easily functionalized by antibodies
at the single-molecule level. He proposed a control method of 45 nm wire based on
direct laser writing with STED, which has a rod-shaped effective focal point. In traditional standard direct laser writing, a donut-shaped depletion focus is usually used,
and the minimum line width is limited to 55 nm. In this work, they push this limit to
the sub-50 nm size with a rod-like effective focal point, which is a combination of
Gaussian excitation focusing and twin-oval depletion focusing [276]. Furthermore,
Gan has demonstrated deep sub-diffraction optical beam lithography with a 9 nm
feature size based on the STED mechanism [277].
1.8 Summary and Outlooks
A laser is a crucial tool for precise micro-to-nano manufacturing. For various applications the understanding of fundamentals between the laser and material interaction
is basic. With the development of ultrafast laser available for a shorter pulse, higher
peak power, and tunable wavelength at a wider band, the laser manufacturing enables
versatile processing with a higher precision beyond the optical diffraction limit.
The basic interaction of laser and materials involves in energy absorption. At
a micro-to-nanoscale, this physical procedure includes surface plasmon excitation
and surface electron excitation. At a periodic approximately equal to or shorter than
the electron-lattice coupling time, typically a couple of picoseconds, the so-called
Coulomb explosion, and nonthermal melting will occur due to the surface electron
vaporization. This localizes the thermal effect to the size similar to the optical penetration depth. This is the current physical basis for precision manufacturing using an
ultrafast laser.
At a nanoscale, the physical properties of materials will be quite different from
their bulk counterparts. The micro-to-nano manufacturing leads to the mass transfer
at these scopes. The surface properties will be dominant due to the size effect and the
scaling laws. The nanoparticles can be melt and sintered at a pretty low temperature,
even close to room temperature. The involved surface liquid phase and enhanced
surface diffusion will bring new mechanisms to the manufacturing and materials
science.
Due to these new features, laser-based micro-to-nanomanufacturing is especially
effective and powerful for printed electronics, such as flexible/stretchable electronics,
3D microprinting for portable electronics at current big data, Internet of things,
next-generation computation and artificial intelligent era. It will create extensive
opportunities in energy, environment, sensing, and biomedical applications.
With the further development of laser-based micro-to-nano manufacturing, it can
be expected that molecular devices with high manufacturing and manipulation will