Nanoplasmonics and surface enhanced spectroscopy

Gold nanoparticles arrays formation on charged substrate
Stetsenko M.O.1,2,*, Maksimenko L.S.2, Hreshchuk O.M.2, Vityuk N.V.3, Serdega B.K.2, Junle Qu1, Mukha Iu.P.3
1 Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Physics and Optoelectronic Engineering, Shenzhen University, 518060, Shenzhen, PR China. 
E-mail: stetsenko@szu.edu.cn, StetsenkoMax@gmail.com
2 V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 03680, Kyiv, Ukraine.
3 Chuiko Institute of Surface Chemistry, NAS of Ukraine, 03164, Kyiv, Ukraine.

Development of sensors and SERS substrates based on gold nanoparticles (Au NPs) received considerable attention due to effectiveness. For spherical Au NPs, aggregation is needed in order to increase the magnitude of the SERS effect. In its turn, close proximity of Au NPs could be achieved by immobilization of nanoparticles on a solid substrate. 
The gold nanoparticles arrays were prepared by prolonged adsorption of previously formed Au NPs on positively charged glass slides produced by Superfrost® Plus (Menzel) from colloid during different time intervals (1, 3, 8 days). Optical characteristics of prepared samples were studied by UV-vis and modulation polarization spectroscopies. Angular dependencies of internal reflection coefficients of s- and p-polarized light and polarization difference parameter were measured in Kretschmann geometry (Stokes polarimetry) [1].
Absorption bands of localized surface plasmon resonance (LSPR) of gold were presented in measured UV-vis spectra their maxima were located in the wavelength range of 516-530 nm. The long-wavelength shoulder in the absorption spectra at 600-700 nm is associated with aggregation of nanoparticles on the substrate. For registration of transformation/changes in morphology (formation of aggregates) we used Stokes-polarimetry with 520 nm and 650 nm wavelength for experiments. The correlation between LSPR band characteristics and optical-polarization spectra/data were shown depending on morphology features/changes of Au NPs arrays. The formation of different aggregates of Au NPs arrays for samples with different time of immersion in colloidal solution was discussed. 
1.	Stetsenko M. et al. Optical Properties of Gold Nanoparticle Assemblies on a Glass Surface// Nanoscale Res. Let. - 2017.- 12-P.348-358