Nanoplasmonics and surface enhanced spectroscopy

Dielectric function of a metal nanosphere covered with a layer of adsorbed molecules
Maniuk M.S.1, Smirnova N.A.1, Korotun A.V.1
1 National University ”Zaporizhzhia Polytechnic“,
Zhukovskogo st., 64, Zaporizhzhia, Ukraine.
E-mail: andko@zp.edu.ua

Currently, metal nanoparticles of various shapes, including spherical, due to their unique optical properties are widely used in biology and medicine [1]. Thus, the problem of determining the expansion of the plasmon resonance line of a spherical metal nanoparticle, the surface of which is covered with a layer of adsorbed molecules, is of considerable interest. In this case, the interface decay channel of surface plasmons makes a significant contribution to the surface relaxation rate.
This effect is due to an increase in the local density of states induced by adsorbed molecules near the Fermi level of nanoparticles. Note that the correct description of these factors requires consideration of interband and intraband transitions of electrons, as well as the tensor nature of the surface relaxation rate. Therefore, taking into account these considerations, in the expression for the effective parameter describing the degree of loss of coherence during electron scattering on the surface, it is necessary to take into account the term associated with the presence of the adsorbed molecular layer:
,				(1)
where  is the Fermi velocity of electrons;  is the corresponding lateral size of the nanoparticle, and
,				(2)
In formula (2), the first term is due to the scattering of electrons by the nanoparticle on its surface, and the origin of the second term is due to the presence of an adsorbed layer on the surface of the nanoparticle.

1.	Liu C., Xue N., Cai H., Sun J., Qi Z., Zhao P., Xiong F., Geng Z., Jiang L., Li L. Nanoparticles Enhanced Self-Driven Microfludic Biosensor // Micromachines.-2021.-11.-P. 350.