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Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate.

Patel NB, Tan B, Venkatakrishnan K - Nanoscale Res Lett (2013)

Bottom Line: We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst.It was found to be possible only in the presence of background nitrogen gas flow.We observed a clear transformation in the kind of nanotips that grew for the given laser conditions.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Aerospace Engineering, Ryerson University, Victoria Street, Toronto, ON M5B 2K3, Canada. tanbo@ryerson.ca.

ABSTRACT
Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions.

No MeSH data available.


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Schematic representation of the growth stages of plasma expansion and nanotips' stem formation.
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Figure 8: Schematic representation of the growth stages of plasma expansion and nanotips' stem formation.

Mentions: The repetition rate and dwell time affect the growth of nanotips in somewhat similar way since both control the number of laser pulses delivered to the target surface. After the breakdown of the target material has started, it requires a certain number of pulses according to the repetition rate and dwell time to ablate the required amount of target material into the plasma, as demonstrated in stages 1 to 3 in Figure 8. Before this point in time, the plume does not have enough monomers to start vapor condensation. Once the vapor condensation has started inside the plume, the vapor condensates begin to get deposited onto the hot target surface, as depicted in stage 3. If the machining is stopped little after reaching stage 3, there will not be any more incoming pulses that transfer energy to the plasma species to generate further turbulence. As a result, the plasma species start relaxing by cooling down and mixing with nitrogen gas molecules. The consequence of these phenomena will be that the pressure exerted due to the plasma species will be relieved and the internal pressure becomes much higher than the external pressure on the deposited plasma condensates due to the hot target surface. At the same time, the deposited condensates experience uneven cooling due to the random flow of nitrogen gas. As a result, the deposited droplets have regions of high and low surface tension over their entire surface. As a result, the imbalance of pressure pushes the material out of the volume of deposited droplets from regions of low surface tension resulting in the formation of the stem for the nanotips, as depicted in the side figures of stage 3 in Figure 8.


Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate.

Patel NB, Tan B, Venkatakrishnan K - Nanoscale Res Lett (2013)

Schematic representation of the growth stages of plasma expansion and nanotips' stem formation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3643873&req=5

Figure 8: Schematic representation of the growth stages of plasma expansion and nanotips' stem formation.
Mentions: The repetition rate and dwell time affect the growth of nanotips in somewhat similar way since both control the number of laser pulses delivered to the target surface. After the breakdown of the target material has started, it requires a certain number of pulses according to the repetition rate and dwell time to ablate the required amount of target material into the plasma, as demonstrated in stages 1 to 3 in Figure 8. Before this point in time, the plume does not have enough monomers to start vapor condensation. Once the vapor condensation has started inside the plume, the vapor condensates begin to get deposited onto the hot target surface, as depicted in stage 3. If the machining is stopped little after reaching stage 3, there will not be any more incoming pulses that transfer energy to the plasma species to generate further turbulence. As a result, the plasma species start relaxing by cooling down and mixing with nitrogen gas molecules. The consequence of these phenomena will be that the pressure exerted due to the plasma species will be relieved and the internal pressure becomes much higher than the external pressure on the deposited plasma condensates due to the hot target surface. At the same time, the deposited condensates experience uneven cooling due to the random flow of nitrogen gas. As a result, the deposited droplets have regions of high and low surface tension over their entire surface. As a result, the imbalance of pressure pushes the material out of the volume of deposited droplets from regions of low surface tension resulting in the formation of the stem for the nanotips, as depicted in the side figures of stage 3 in Figure 8.

Bottom Line: We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst.It was found to be possible only in the presence of background nitrogen gas flow.We observed a clear transformation in the kind of nanotips that grew for the given laser conditions.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Aerospace Engineering, Ryerson University, Victoria Street, Toronto, ON M5B 2K3, Canada. tanbo@ryerson.ca.

ABSTRACT
Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions.

No MeSH data available.


Related in: MedlinePlus