Rough silver films for surface plasmons generation and SERS optical properties study

We used electron microscopy and AFM, ellipsometry, and Raman microscopy to investigate dielectric and optical properties of rough silver films fabricated by electrodeposition from a cyanide-thiocyanate electrolyte and... [ view full abstract ]

We used electron microscopy and AFM, ellipsometry, and Raman microscopy to investigate dielectric and optical properties of rough silver films fabricated by electrodeposition from a cyanide-thiocyanate electrolyte and modified by electrochemical and physicochemical treatment. We studied spectral reflectance of p-polarized light of silver films manufactured with/without anodic dissolution (AD). This work presents experimental results and simulation calculations of the dielectric functions of silver surfaces with varying roughness, manufactured with/without AD. A juxtaposition of the theoretical distribution and the experimentally measured function ε(ω) allowed to establish the bandgap width of the rough surfaces. The width ranged from 0.7 eV, which is close to the band values characteristic of Ag₂O (1.4 eV). We identified the bandgap width for AD silver surfaces, which had been modified by the silver NPs from a borohydride sol. The bandgap width amounted to 0.13 eV. It was established experimentally that the dissolution of the oxide layer of a rough silver surface with an ammonia solution translated into a significant reduction in the band gap width (to E₀≈0.05 eV). We studied the Raman scattering spectra (RSS) of silver films treated at different anodic dissolution rates and of AD surfaces with adsorbed nanoparticles of borohydride silver. Upon laser excitation at 532 and 632 nm, the intensity of RSS of silver films differed, since the maximum of the spectra of plasmon resonance of rough silver surfaces is at 405 nm. After the dissolution of the samples’ oxide layers with an ammonia solution, the RSS intensity decreased by an order of magnitude. This has practical importance for the manufacture of plasmon resonance-based optical sensors. We calculated Purcell factors, which describe the processes of local electromagnetic field enhancement under Raman light scattering in micro- and nanocavities of different rough surfaces.The established up to 10⁴-fold factor of Raman scattering enhancement on rough silver surface manufactured using the above metal electrodeposition techniques can contribute to obtaining surface-enhanced Raman scattering in creating biosensors with different molecular systems.

The reported study was carried out within Russian Academic Excellence Project "5-100".