Plasmonic nanostructures have got a vast range of practical applications, which has caught the attention of many scientists hence leading to a lot of research over the past few years. Although several methods of fabricating the nanostructures are available, they have various shortcoming. For instance, the available methods are unaffordable and time consuming. Therefore, the need for a more simple, easy to implement and affordable method, which has remained a challenge especially in the fabrication of the nanogap-rich nanostructures, has been addressed.
A team of researchers at the University of Dayton in the United States: Ph.D. student Farzia Karim (Department of Electro-optics and Photonics), Professor Erick Vasquez (Department of Chemical and Materials Engineering) and Dr. Chenglong Zhao (Department of Physics, Department of Electro-optics and Photonics) demonstrated an efficient and cost-effective method of fabrication of the nanogap-rich structures. They also explained the benefits of using this method regarding the simple fabrication methods involved and the wide variety of applications of nanogap-rich structures produced using the stated method. Their work has been published in the journal, Optics Letters.
In their study, the team used gold nanoparticles as the primary source of heat hence generating optothermal surface bubbles. The gold nanoparticles also initiated the formation of nanogap-rich plasmonic structures by acting as their building blocks. Furthermore, the production of the surface bubbles led to the Marangoni convention which is useful in the deposition of the nanoparticles. To ensure protection of the sample from contamination and large consumption, the authors placed the nanoparticles in a nanoliter droplet before they were deposited.
The authors observed the rapid formation of the nanogap-rich structures due to the fast deposition of the nanoparticles. The rapid deposition was as a result of the formation of a sufficient convective flow that emanated from the heated optothermal surface bubbles.
According to the authors, the whole process is performed under favorable ambient conditions, therefore, reduces the cost and energy consumption. Furthermore, the fabrication is also performed inside a nanoliter droplet. This will lead to well-protected nanogap-rich structures free from unnecessary contamination and sample consumption. Additionally, it is time conservative as the other methods were prone to contamination which again required a lot of time to remove. Apart from mere fabrication, the method also allows for patterning of the nanostructures formed. Optothermal surface bubbles are still the useful tool in this area. However, the various sizes of the areas deposited is determined by the intensity of the heating laser.
The fabrication method also successfully proved to be economical and affordable because it does not limit the use of any specific substrates as in the cases of the other methods. This is because it is direct and forward, hence no need of absorptive layer as was seen in the other fabrication methods. Dr. Chenglong Zhao and colleagues are optimistic that this method will advance the field of nanogap-rich plasmonic structures fabrication which will, in turn, increase their application in several areas.
Karim, F., Vasquez, E., & Zhao, C. (2018). Fabricated nanogap-rich plasmonic nanostructures through an optothermal surface bubble in a droplet. Optics Letters, 43(2), 334.
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