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Controllable assembly of silver nanoparticles induced by femtosecond laser direct writing

View Article: PubMed Central - PubMed

ABSTRACT

We report controllable assembly of silver nanoparticles (Ag NPs) for patterning of silver microstructures. The assembly is induced by femtosecond laser direct writing (FsLDW). A tightly focused femtosecond laser beam is capable of trapping and driving Ag NPs to form desired micropatterns with a high resolution of ∼190 nm. Taking advantage of the ‘direct writing’ feature, three microelectrodes have been integrated with a microfluidic chip; two silver-based microdevices including a microheater and a catalytic reactor have been fabricated inside a microfluidic channel for chip functionalization. The FsLDW-induced programmable assembly of Ag NPs may open up a new way to the designable patterning of silver microstructures toward flexible fabrication and integration of functional devices.

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Schematic illustration of FsLDW-induced controllable assembly of Ag NPs. The laser beam was tightly focused by a ×100 oil immersion objective lens with a high numerical aperture NA = 1.45; the moving stage (PZT: piezoelectric transducer) was controlled by computers.
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Figure 2: Schematic illustration of FsLDW-induced controllable assembly of Ag NPs. The laser beam was tightly focused by a ×100 oil immersion objective lens with a high numerical aperture NA = 1.45; the moving stage (PZT: piezoelectric transducer) was controlled by computers.

Mentions: The obtained Ag NPs have been used for FsLDW directly without the use of any photosensitive reagents. Figure 2 shows the schematic illustration of the FsLDW of Ag NPs. When a tightly focused femtosecond laser beam irradiated into the Ag NP suspension, three radiation pressures including absorption force, scattering force, and gradient force were exerted on the tiny particles. Generally, absorption force and scattering force were proportional to laser intensity, which were applied in the direction of laser beam, whereas gradient force was proportional to the gradient of laser intensity, being toward the focus [59]. Although detailed theories to calculate these forces are still under development, it is very clear that the light–matter interaction is dominated by particle sizes, refractive index, and dielectric constant of target NPs [60–62]. In this experiment, considering the metallic Rayleigh particles (diameter d ≪ wavelength λ) are much smaller than the wavelength of laser (here d ≈ 2.5 nm; λ ≈ 800 nm), a gradation force proportional to the polarizability of an NP and the square of optical electric field vector dominates the assembly of Ag NPs, whereas absorption force and scattering force push the Ag NPs along the laser beam direction, leading to the enrichment of Ag NPs in the focal region. Together with the Ag NP deposition, mass transfer was performed by concentration diffusion of the Ag NPs solution. At the same time, due to the extremely high transient power density of the femtosecond laser, the aggregated Ag NPs have been sintered together. Since the near-infrared femtosecond laser beam is not absorbed by the solution, the beam penetrates deeply into the Ag NP solution with very small power loss. By scanning the laser focus along a preprogrammed trace, the desired silver micropatterns could be fabricated accordingly.


Controllable assembly of silver nanoparticles induced by femtosecond laser direct writing
Schematic illustration of FsLDW-induced controllable assembly of Ag NPs. The laser beam was tightly focused by a ×100 oil immersion objective lens with a high numerical aperture NA = 1.45; the moving stage (PZT: piezoelectric transducer) was controlled by computers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036472&req=5

Figure 2: Schematic illustration of FsLDW-induced controllable assembly of Ag NPs. The laser beam was tightly focused by a ×100 oil immersion objective lens with a high numerical aperture NA = 1.45; the moving stage (PZT: piezoelectric transducer) was controlled by computers.
Mentions: The obtained Ag NPs have been used for FsLDW directly without the use of any photosensitive reagents. Figure 2 shows the schematic illustration of the FsLDW of Ag NPs. When a tightly focused femtosecond laser beam irradiated into the Ag NP suspension, three radiation pressures including absorption force, scattering force, and gradient force were exerted on the tiny particles. Generally, absorption force and scattering force were proportional to laser intensity, which were applied in the direction of laser beam, whereas gradient force was proportional to the gradient of laser intensity, being toward the focus [59]. Although detailed theories to calculate these forces are still under development, it is very clear that the light–matter interaction is dominated by particle sizes, refractive index, and dielectric constant of target NPs [60–62]. In this experiment, considering the metallic Rayleigh particles (diameter d ≪ wavelength λ) are much smaller than the wavelength of laser (here d ≈ 2.5 nm; λ ≈ 800 nm), a gradation force proportional to the polarizability of an NP and the square of optical electric field vector dominates the assembly of Ag NPs, whereas absorption force and scattering force push the Ag NPs along the laser beam direction, leading to the enrichment of Ag NPs in the focal region. Together with the Ag NP deposition, mass transfer was performed by concentration diffusion of the Ag NPs solution. At the same time, due to the extremely high transient power density of the femtosecond laser, the aggregated Ag NPs have been sintered together. Since the near-infrared femtosecond laser beam is not absorbed by the solution, the beam penetrates deeply into the Ag NP solution with very small power loss. By scanning the laser focus along a preprogrammed trace, the desired silver micropatterns could be fabricated accordingly.

View Article: PubMed Central - PubMed

ABSTRACT

We report controllable assembly of silver nanoparticles (Ag NPs) for patterning of silver microstructures. The assembly is induced by femtosecond laser direct writing (FsLDW). A tightly focused femtosecond laser beam is capable of trapping and driving Ag NPs to form desired micropatterns with a high resolution of ∼190 nm. Taking advantage of the ‘direct writing’ feature, three microelectrodes have been integrated with a microfluidic chip; two silver-based microdevices including a microheater and a catalytic reactor have been fabricated inside a microfluidic channel for chip functionalization. The FsLDW-induced programmable assembly of Ag NPs may open up a new way to the designable patterning of silver microstructures toward flexible fabrication and integration of functional devices.

No MeSH data available.


Related in: MedlinePlus