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Formation of Gold Microparticles by Ablation with Surface Plasmons

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ABSTRACT

The formation of gold microparticles on a silicon substrate through the use of energetic surface plasmons is reported. A laser-assisted plasmonics system was assembled and tested to synthesize gold particles from gold thin film by electrical field enhancement mechanism. A mask containing an array of 200 nm diameter holes with a periodicity of 400 nm was prepared and placed on a silicon substrate. The mask was composed of 60 µm thick porous alumina membrane sputter-coated with 100 nm thin gold film. A Nd:YAG laser with 1064 nm wavelength and 230 µs pulse width (free-running mode) was then passed through the mask at an energy fluence of 0.35 J/cm2. The extraordinary transmission of laser light through alumina/gold micro-hole optical antenna created both extended and localized surface plasmons that caused the gold film at the bottom of the mask to fragment into microparticles and deposit on the silicon substrate that is in direct contact with the mask. The surface plasmon method is simpler, quicker, more energy efficient, and environmentally safer than existing physical and chemical methods, as well as being contamination-free, and can be extended to all types of materials that will in turn allow for new possibilities in the formation of structured surfaces.

No MeSH data available.


SEM image of the mask after laser irradiation.
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nanomaterials-03-00592-f005: SEM image of the mask after laser irradiation.

Mentions: In experimental setups 1–3, the alumina membrane was completely destroyed in the irradiated area due to the high intensity of SPs. The pore structure of the alumina in this area was damaged and only fragmented pieces of alumina and gold remained in the exposed area. In experimental setups 4 and 5, a noteworthy result occurred. In these trials, the laser beam irradiated the alumina membrane resulting in clean ablation and subsequent deposition of gold particles on the surface of the silicon substrate. The pore structure of the alumina membrane in this case was undamaged while the gold underneath the alumina in the exposed area was removed and deposited onto the wafer’s surface. Figure 4 shows the microparticles embedded on silicon. Figure 5 shows the SEM image of the mask after laser irradiation. The intriguing aspect of this experiment is the low energy fluence and long pulse width of the laser beam in setup 5 that was needed for the fragmentation of the gold thin film. Various studies of nanosecond pulsed laser ablation in gas or liquid media indicate that threshold fluence required for gold thin films is approximately 5–8 J/cm2 [3]. For the femtosecond pulsed laser ablation, threshold fluence is approximately 1.5 J/cm2 [26]. For long pulses such as microseconds, threshold fluence is expected to be much higher. In the described work, 0.35 J/cm2 was sufficient to ablate a significant amount of gold in the exposed area. A comparison with direct laser ablation suggests that surface plasmons substantially reduced the threshold fluence for ablation of gold. To further validate this result, setup 5 was repeated several times under the same conditions while irradiating different sections of the gold/alumina mask. Each of these new tests yielded the same result as before with the formation of gold microparticles on the surface of the substrate and no visible damage to the pore structure of the alumina membrane.


Formation of Gold Microparticles by Ablation with Surface Plasmons
SEM image of the mask after laser irradiation.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5304590&req=5

nanomaterials-03-00592-f005: SEM image of the mask after laser irradiation.
Mentions: In experimental setups 1–3, the alumina membrane was completely destroyed in the irradiated area due to the high intensity of SPs. The pore structure of the alumina in this area was damaged and only fragmented pieces of alumina and gold remained in the exposed area. In experimental setups 4 and 5, a noteworthy result occurred. In these trials, the laser beam irradiated the alumina membrane resulting in clean ablation and subsequent deposition of gold particles on the surface of the silicon substrate. The pore structure of the alumina membrane in this case was undamaged while the gold underneath the alumina in the exposed area was removed and deposited onto the wafer’s surface. Figure 4 shows the microparticles embedded on silicon. Figure 5 shows the SEM image of the mask after laser irradiation. The intriguing aspect of this experiment is the low energy fluence and long pulse width of the laser beam in setup 5 that was needed for the fragmentation of the gold thin film. Various studies of nanosecond pulsed laser ablation in gas or liquid media indicate that threshold fluence required for gold thin films is approximately 5–8 J/cm2 [3]. For the femtosecond pulsed laser ablation, threshold fluence is approximately 1.5 J/cm2 [26]. For long pulses such as microseconds, threshold fluence is expected to be much higher. In the described work, 0.35 J/cm2 was sufficient to ablate a significant amount of gold in the exposed area. A comparison with direct laser ablation suggests that surface plasmons substantially reduced the threshold fluence for ablation of gold. To further validate this result, setup 5 was repeated several times under the same conditions while irradiating different sections of the gold/alumina mask. Each of these new tests yielded the same result as before with the formation of gold microparticles on the surface of the substrate and no visible damage to the pore structure of the alumina membrane.

View Article: PubMed Central - PubMed

ABSTRACT

The formation of gold microparticles on a silicon substrate through the use of energetic surface plasmons is reported. A laser-assisted plasmonics system was assembled and tested to synthesize gold particles from gold thin film by electrical field enhancement mechanism. A mask containing an array of 200 nm diameter holes with a periodicity of 400 nm was prepared and placed on a silicon substrate. The mask was composed of 60 µm thick porous alumina membrane sputter-coated with 100 nm thin gold film. A Nd:YAG laser with 1064 nm wavelength and 230 µs pulse width (free-running mode) was then passed through the mask at an energy fluence of 0.35 J/cm2. The extraordinary transmission of laser light through alumina/gold micro-hole optical antenna created both extended and localized surface plasmons that caused the gold film at the bottom of the mask to fragment into microparticles and deposit on the silicon substrate that is in direct contact with the mask. The surface plasmon method is simpler, quicker, more energy efficient, and environmentally safer than existing physical and chemical methods, as well as being contamination-free, and can be extended to all types of materials that will in turn allow for new possibilities in the formation of structured surfaces.

No MeSH data available.