Plasmonic sensor: Towards parts-per-billion level sensitivity

We have developed a plasmonic gas sensing system using transmissive (metal hole array) and scattering (rough surface of Au film) plasmonic materials in an integrating sphere geometry. The combination of transmissive and reflective plasmonic materials significantly enhances the detection threshold by way of surface-enhanced infrared absorption. Here, we first investigate the individual sensing enhancement contributions for each of the plasmonic materials and reveal the path towards applications in high-sensitivity gas detection

Thermal to electrical energy converter based on black Si

Photo-thermal - to - electrical converter is demonstrated by using a commercial Peltier Bi-Te element with a hot contact made out of nanotextured Si (black-Si). Black-Si with colloidal Au nanoparticles is shown to further increase the efficiency of thermal-to-electrical conversion. Peculiarities of heat harvesting using black-Si with plasmonic Au nanoparticles at different gold densities are analyzed. Solar radiation absorption and electric field enhancement in plain and Au nanoparticle decorated black-Si was simulated using finite difference time domain (FDTD) method. Thermal conduction in nanotextured black-Si was explained using phonon Monte-Carlo simulations at the nanoscale. Strategies for creating larger thermal gradient on Peltier element using nanotextured light absorbers is discussed

Nanotextured CuO: sensing and light harvesting platform

Rapid and cost effective fabrication of nano-textured surfaces of CuO and Cu2O by chemical bath process was used to fabricated large surface areas with cross sections in centimeters. Through chemical etching and oxidation induced nano-texturation Cu foils are rendered black and their surface area is increased by two orders of magnitude. Magnetronic Au sputtering was used to coat the nano-textured CuxO features with nano-granular metal films which were found to be conformal for the range of 5-50 nm layer thicknesses. The Au coated substrates of CuxO were tested for surface enhanced Raman scattering (SERS) performance and showed one of the best sensitivity enhancements when compared with other nano-textured surfaces. Application potential of the black-Cu2O for SERS sensing and for solar cell applications is discussed

3D micro-optical elements for generation of tightly focused vortex beams

Orbital angular momentum carrying light beams are usedfor optical trapping and manipulation. This emerging trend provides new challenges involving device miniaturization for improved performance and enhanced functionality at the microscale. Here we discus a new fabrication method based on combining the additive 3D structuring capability laser photopolymerization and the substractive sub-wavelength resolution patterning of focused ion beam lithography to produce micro-optical elements capable of compound functionality. As a case in point of this approach binary spiral zone pattern based high numerical aperture micro-lenses capable of generating topological charge carrying tightly focused vortex beams in a single wavefront transformation step are presented. The devices were modelled using finite-difference time-domain simulations, and the theoretical predictions were verified by optically characterizing the propagation properties of light transmitted through the fabricated structures. The resulting devices had focal lengths close to the predicted values of f = 18 µm and f = 13 µm as well as topological charge ℓ dependent vortex focal spot sizes of ~ 1:3 µm and ~ 2:0 µm for ℓ = 1 and ℓ = 2 respectively

Nanoscale precision in ion milling for optical and terahertz antennas

Plasmonics and nanoscale antennas have been intensively investigated for sensors, metasurfaces and optical trapping where light control at the nanoscale enables new functionalities. To confine and manipulate the light in tiny spaces sub-wavelength antennas should be used with dimensions from micro- to nano-meters and are still challenging to make. Direct fabrication/modification of nanostructures using focused ion beam (FIB) milling is demonstrated for several types of antennas. Arrays of identical nanoparticles were fabricated in a single step by (i) milling gold films or (ii) by modifying structures which were already defined by electron beam or mask projection lithography. Direct FIB writing enables to exclude resist processing steps, thus making fabrication faster and simpler. Sensor areas of 25x25 μm2 of densely packed nanoparticles separated by tens-of-nanometers were fabricated in half an hour (103 μm2/h throughput at 90 nm resolution). Patterns of chiral nanoparticles by groove inscription is demonstrated. The processing speed and capability to mill complex 3D surfaces due to depth of focus not compromised over micrometers length, makes it possible to reach sub-50 nm resolution of direct write. FIB technology is practical for emerging applications in nano-fabrication/photonic/fluidic/magnetic applications