Annealing Induced Morphology of Silver Nanoparticles on Pyramidal Silicon Surface and Their Application to Surface-Enhanced Raman Scattering

Abstract

This paper reports on a simple and cost-effective process of developing a stable surface-enhanced Raman scattering (SERS) substrate based on silver (Ag) nanoparticles deposited on silicon (Si) surface. Durability is an important issue for preparing SERS active substrate as silver nanostructures are prone to rapid surface oxidation when exposed to ambient conditions, which may result in the loss of the enhancement capabilities in a short period of time. Here, we employ the galvanic displacement method to produce Ag nanoparticles on Si(100) substrate prepatterned with arrays of micropyramids by chemical etching, and subsequently, separate pieces of such substrates were annealed in oxygen and nitrogen environments at 550 °C. Interestingly, while nitrogen-annealed Si substrates were featured by spherical-shaped Ag particles, the oxygen annealed Si substrates were dominated by the formation of triangular shape particles attached with the spherical one. Remarkably, the oxygen-annealed substrate thus produced shows very high SERS enhancement compared to the either unannealed or nitrogen annealed substrate. The hitherto unobserved coexistence of triangular morphology with the spherical one and the gap between the two (source of efficient hot-spots) are the origin of enhanced SERS activity for the oxygen-annealed Ag particle-covered Si substrate as probed by the combined finite-difference time domain (FDTD) simulation and cathodoluminesensce (CL) experiment. As the substrate has already been annealed in an oxygen environment, further probability of oxidation is reduced in the present synthesis protocol that paves the way for making a novel long-lived thermally stable SERS substrate.

Metal Nanoparticle-Decorated Silicon Nanowire Arrays on Silicon Substrate and their Applications

“…The HRTEM image (Fig. 3e) from the region marked by black square in Figure 3d shows interplanar spacing of 2.35 Å, which is close to Ag (111) plane spacing (Ghosh et al, 2014; Roy et al, 2017) and it also shows Si (111) planes of spacing 3.14 Å. These two are rotated by 32.4° relative to each other with a layer of SiO 2 between them which is also confirmed from the fast Fourier transform (FFT) image taken from the same region, where the diffraction spots correspond to Ag and Si are marked by red and yellow circles, respectively (Fig.…”

“…The Ag nanoparticles form a continuous network. A detailed study on the interface of this Ag thin film and Si substrate is reported in our previous report (Roy et al, 2017). Figure 2c shows the XTEM image of Ag on P-Si.…”

“…Figure 6a shows the normal Raman spectra of 10 −1 M R6G on P-Si and SERS spectra of 10 −5 M R6G on different substrates. The characteristic Raman spectra of R6G are observed clearly (Hildebrandt & Stockburger, 1984; Roy et al, 2017). The in-plane xanthene ring deformation and out of plane C–H bonding are responsible for the peaks at 609 and 775 cm −1 , respectively.…”

Autocatalytic Metallization of Fabrics Using Si Ink, for Biosensors, Batteries and Energy Harvesting

“…Scanning electron micrographs (SEM) recorded from a sample, predeposition (Si only), after 40 s and after 20 min autocatalytic metallization with Ag ( Figure A) also confirm that small Ag nuclei form on the Si crystals soon after immersion into the bath (40 s). After prolonged deposition, these nuclei grow into large crystals and then coalesce into even larger crystals (to reduce their surface energy) with a smooth surface . By inspecting the cross‐section of a Si‐wafer plated autocatalytically in a 1 m bath of AgNO 3 (SEM image in Figure S4, Supporting Information), we estimate the Ag layer thickness increases at ≈2 µm min −1 .…”

Direct Laser Annealing of Surface‐Enhanced Raman Scattering Substrates

“…However, annealing is an indispensable process in the fabrication procedures, where both the substrates and the colloidal film have to be heated together. The hot substrates allow long‐range aggregation of the molten gold to form large particles with large separation distance or gap widths between them . This makes it difficult to control the preparation conditions precisely, in particular, the closely packed nanoparticles can be produced only in a small range of the annealing temperatures.…”