Morphological and SERS Properties of Silver Nanorod Array Films Fabricated by Oblique Thermal Evaporation at Various Substrate Temperatures

Abstract

Aligned silver nanorod (AgNR) array films were fabricated by oblique thermal evaporation. The substrate temperature during evaporation was varied from 10 to 100 °C using a home-built water cooling system. Deposition angle and substrate temperature were found to be the most important parameters for the morphology of fabricated films. Especially, it was found that there exists a critical temperature at ~90 °C for the formation of the AgNR array. The highest enhancement factor of the surface-enhanced Raman scattering (SERS), observed in the Ag films coated with benzenethiol monolayer, was ~6 × 107. Hot spots, excited in narrow gaps between nanorods, were attributed to the huge enhancement factor by our finite-difference time-domain (FDTD) simulation reflecting the real morphology.

Surface Enhanced Raman Scattering Substrates Made by Oblique Angle Deposition: Methods and Applications

“…Coupled with their FDTD calculations, it was found that the pores formed from deposition at 140 K to generate hotspots for SERS enhancement which is consistent with their experimental observations. This suggests that making SERS substrates at lowered temperatures will generate greater enhancements, however, the opposite was found to be true in the study by Oh et al [43]. In their study, it was found that substrates made at higher temperatures had higher SERS enhancements than substrates made at lower temperature.…”

“…The effect of substrate temperature has been a topic of interest for SERS researchers, particularly those using the oblique angle deposition configurations [16,43,59]. Compared to other materials typically used in OAD, silver and gold tend to have significantly lower surface diffusion activation energies, this means adatoms can more readily take part in thermally activated effects.…”

“…Oskooi et al's interactions with other photonics researchers found that FDTD codes were developed to address their needs, this would be time consuming and so open-source packages such as MEEP (MIT Electromagnetic Equation Propagation) enable easier access to FDTD calculations [40]. FDTD studies are typically done to find the electric fields around the nanostructures in order to understand the SERS EF from an EM perspective [43,44]. A notable application of 3D-FDTD for understanding SERS enhancements was in a study by Liu et al [44].…”

SERS Activity of Silver Nanosphere, Triangular Nanoplates, Hexagonal Nanoplates and Quasi-Spherical Nanoparticles: Effect of Shape and Morphology

“…The Raman scattering enhancement is attributed to the generation of local electromagnetic field "hotspots", due to the surface roughness of the materials and the shape of nanoparticles, coupled with LSPR excitation [16]. In fact, the high curvature surface, irregular surface and sharper edges exhibit a great enhancement of the Raman scattering by generating a local high electromagnetic field enhancement, demonstrating the importance of metal nanoparticles synthesis [11,12,16,17]. In this sense, silver nanostars, nanocubes, prisms, or nanoparticles with defects have demonstrated high sensitivity and high enhancement of the Raman signals showing higher potential, with respect to spherical nanoparticles with the same dimensions [12,[18][19][20][21][22][23].…”

Long-Standing Stability of Silver Nanorod Array Substrates Functionalized Using a Series of Thiols for a SERS-Based Sensing Application

“…20 A detailed study of morphology and SERS response of the AgNR array substrates fabricated at various substrate temperatures are presented elsewhere. 18 The crystallinity of a fabricated AgNR array was studied by investigating the obtained XRD spectrum presented in nature with a stronger (111) phase suggesting dominant out-of-plane growth along this crystal orientation. 21 Thus, these Ag nanorods fabricated via thermal evaporation technique are free from crystallographic contaminations as no counterfeiting diffraction is observed.…”