Abstract
Conventional nano-sphere lithography techniques have been extended to the fabrication of highly periodic arrays of sub-wavelength nanoholes in a thin metal film. By combining the dry etching processes of self-assembled monolayers of polystyrene colloids with metal physical deposition, the complete transition from increasing size triangular nanoprism to hexagonally distributed nanoholes array onto thin metal film has been gradually explored. The investigated nano-structured materials exhibit interesting plasmonic properties which can be precisely modulated in a desired optical spectral region. An interesting approach based on optical absorbance measurements has been adopted for rapid and non-invasive inspections of the nano-sphere monolayer after the ion etching process. By enabling an indirect and accurate evaluation of colloid dimensions in a large area, this approach allows the low-cost and reproducible fabrication of plasmonic materials with specifically modulated optical properties suitable for many application in biosensing devices or Raman enhanced effects.
Highlights
IntroductionAn extensive interest towards plasmonic nano-structures has been established owing to their capability to confine and manipulate electromagnetic waves at the nanoscale level [1], as well as for their potential applications in several research fields, such as surface-enhanced spectroscopies [2,3], chemical or biosensors [4,5,6,7,8].Innovative metamaterials characterized by exotic optical and physical properties have been proposed [9] for applications as ultrasensitive bio-chemical sensors exploiting surface plasmon resonance (SPR) properties [10].Surface plasmons (SPs) are collective charge density oscillations that can be excited at a metal-dielectric interface [1,11]
With a blue laser, of the close-packed array (CPA) deposited onto a transparent substrate, a diffraction pattern characterized by hexagonal geometry can be generated
A clear hexagonal diffraction pattern should be observed with well-defined maxima, suggesting the presence of long-range structural ordering in the area illuminated by the laser beam
Summary
An extensive interest towards plasmonic nano-structures has been established owing to their capability to confine and manipulate electromagnetic waves at the nanoscale level [1], as well as for their potential applications in several research fields, such as surface-enhanced spectroscopies [2,3], chemical or biosensors [4,5,6,7,8].Innovative metamaterials characterized by exotic optical and physical properties have been proposed [9] for applications as ultrasensitive bio-chemical sensors exploiting surface plasmon resonance (SPR) properties [10].Surface plasmons (SPs) are collective charge density oscillations that can be excited at a metal-dielectric interface [1,11]. SPPs experience a relatively deep penetration into the surrounding medium, creating large active volumes, while metal nanostructures supporting LSPR tend to tightly confine the enhanced electromagnetic field into subwavelength regions as small as a few nanometers. To this purpose, the variations in the refractive index of the surrounding external environment could be probed in a different manner, depending on the near field properties of the generated plasmonic field and taking into account that the sensitivity parameters are strictly related to the spatial distribution of the electric field intensity near the metal surface [15], allowing the detection of biorecognition events occurring at its interface. Plasmonic EM field amplification on a metal surface can be exploited for several applications like the enhancement of local
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