Browsing by Subject "Oblique angle deposition"

Now showing 1 - 2 of 2

Open Access
Shape and deposition angle control of silver film-over-nanosphere SERS substrates
(Institute of Physics Publishing, 2021-10-06) Esmaeilzad, Nasim Seyedpour; Demirtaş, Özge; Demir, Ahmet Kemal; Bek, Alpan
Thin metallic films on dielectric nanospheres are demonstrated to have a high potential for the fabrication of cost-effective SERS substrates. In addition to the morphological advantages that nanospheres offer for attaining a high density of hot spots, possessing shape adjustability by uncomplicated thermal treatment makes them an attractive platform for tuneable SERS substrates. Furthermore, when combined with the oblique angle metal deposition technique, adjustable gaps at a high density and adjustable shape of metal films, such as Ag films, can be achieved on nanospheres. Applying small changes in deposition angle can provide means for fine adjustment of the Raman enhancement factor (EF), resulting in EF up to 108 measured using crystal violet dye molecule as a Raman analyte. This practice paves the way for the fabrication of high EF SERS substrates at a reasonable cost using a monolayer of self-organized nanosphere patterns. An ultra-thin Ag film coated at 5° tilt is shown to be an excellent substitute for a film deposited at 0° with double the thickness. There is a strong agreement between the experimental results and finite-elements-method-based Maxwell simulations exhibiting expected field enhancements up to 109 at a tilt angle of 5°.
Open Access
Ultra-broadband near-unity light absorption by disjunct scattering resonances of disordered nanounits created with atomic scale shadowing effect
(Springer, 2020) Özbay, İmre; Ghobadi, Amir; Özbay, Ekmel
Metamaterial perfect absorbers have been the subject of many studies in recent years. Near-unity light harvesting in an ultra-broadband frequency range is the prime goal in many applications such as photoconversion systems. While the most common designs for achieving this goal are periodic plasmonic architectures, this work reveals the unprecedented potential of random designs for ultra-broadband light absorption. A metal-insulator-metal (MIM) structure with a periodically patterned top layer has discrete translational symmetry. The proposed theory, supported by numerical simulations, unveils the fact that breaking this symmetry in the top layer introduces multiple resonant units with separate spectra, and the superposition of these separate resonances broaden the overall response. The random absorber is realized using the oblique angle deposition-induced atomic scale shadowing effect. Based on the experimental results and numerical calculations, the proposed disorder plasmonic design can propose unity absorption (> 90%) over the spectral range from 520 to 1270 nm.