Abstract
The optical transmission and electric field distribution of plasmonic nanostructures dictate their performance in nano-optics and nano-biosensors. Here, we consider the use of hollow, five-pointed, star-shaped nanostructures made of Al, Ag, Au or Cu. We use simulations based on finite-difference time-domain and the discrete dipole approximation to identify the strongest plasmon resonances in these structures. In particular, we were seeking plasmon resonances within the visible part of the spectrum. The silver pentagrams exhibited the strongest such resonance, at a wavelength of about 530 nm. The visible-light resonances of Au and Cu pentagrams were relatively weaker and red-shifted by about 50 nm. The main resonances of the Al pentagrams were in the ultra-violet. All the nanostars also showed a broad, dipolar-like resonance at about 1000 nm. Surprisingly, the maximum field intensities for the visible light modes were greatest along the flanks of the stars rather than at their tips, whereas those of the dipolar-like modes in the near-infrared were greatest at the tips of the star. These findings have practical implications for sensor design. The inclusion of a conformally hollow interior is beneficial because it provides additional ‘hot spots’.
Highlights
Plasmon resonances in nanostructures and nanoparticles have attracted interest because they can be exploited in many interesting new applications, including optical sensing [1,2], light guiding [3], biological sensors [4,5] and in the medical domain [6]
Studies of plasmonics are focused on structures made of gold (Au) or silver (Ag) because of their favoura‐ ble bulk dielectric properties [7]. Nanostructures made of these elements can support high-quality localized surface plasmon resonances (LSPRs) or long-lived surface plasmon polaritons (SPPs)
It is agreed that the attractive feature of nanostars is that they provide a greater number of locations of enhanced electric field than simpler shapes [21,22,23,24], there is certainly an optimum number of sharp points per particle beyond which overall electric field intensity declines again [23]
Summary
Plasmon resonances in nanostructures and nanoparticles have attracted interest because they can be exploited in many interesting new applications, including optical sensing [1,2], light guiding [3], biological sensors [4,5] and in the medical domain [6]. Studies of plasmonics are focused on structures made of gold (Au) or silver (Ag) because of their favoura‐ ble bulk dielectric properties [7] Nanostructures made of these elements can support high-quality localized surface plasmon resonances (LSPRs) or long-lived surface plasmon polaritons (SPPs). It is agreed that the attractive feature of nanostars is that they provide a greater number of locations of enhanced electric field than simpler shapes [21,22,23,24], there is certainly an optimum number of sharp points per particle beyond which overall electric field intensity declines again [23] Both three-dimensional [17,19,21,22,24] and two-dimensional [23,24] examples of nanostars have been studied. Star-shapes are obviously more complex than discs, rods or spheres, they can certainly be produced by focussed ion beam (FIB) milling [29], or by electron beam lithography (EBL) (Figure 1)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call