Effect of Surfactants on Shape of Gold Nanoparticles
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Effect of Surfactants on Shape of Gold Nanoparticles M. G. Spirina, b, *, S. B. Brichkina, b, E. S. Yushkovc, and V. F. Razumova, b,
d
aInstitute
of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia b Moscow Institute of Physics and Technology, Dolgoprudnyi, Moscow oblast, 141701 Russia c National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, 115409 Russia dMoscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received April 20, 2020; revised April 20, 2020; accepted April 20, 2020
Abstract—In a binary mixture of cetyltrimethylammonium bromide (CTAB) and benzyldimethyltetradecyl ammonium chloride (BDTAC), gold nanorods with a maximum absorption of longitudinal plasmon resonance up to 1600 nm have been obtained. It has been shown that the shape of the growing nanoparticles is determined by the CTAB/BDTAC molar ratio. The optimal conditions have been found for the synthesis of homogeneous nanorods with an aspect ratio of 1 : 7 in a high yield, providing their rapid formation with subsequent slow and uniform growth. The use of a CTAB/BDTAC mixture allows preventing the change in particle shape due to recrystallization during their long-term storage, as is observed in the presence of CTAB. Keywords: gold nanoparticles, nanorods, absorption spectra, near-infrared region, surfactants DOI: 10.1134/S0018143920050148
INTRODUCTION Rod-shaped gold nanoparticles (Au NRs) are of great interest to researchers due to their spectral properties determining by the presence of two absorption bands of localized surface plasmon resonance (LSPR). These bands are associated with the appearance of vibrations of conducting surface electrons under the action of light along the long (longitudinal resonance) and short (transverse resonance) axes of Au NRs [1, 2]. The position of the transverse resonance band is in the range of 500–540 nm, while for longitudinal resonance, it can be tuned from the visible to the near infrared region due to a change in the length/width ratio of Au NPs called the aspect ratio (AR). The most important property of Au NRs is their ability to concentrate and significantly enhance the electromagnetic field near their surface. Due to this, Au NRs can significantly increase Raman scattering [3] or fluorescence of closely spaced fluorophores [4], and can also be used as optical nanoantennas for photodetectors [5]. For the formation of nonspherical nanoparticles in an isotropic medium, it is necessary to create directed conditions for their anisotropic growth. Such conditions can be realized using hard or soft templates. Matrices with cylindrical pores, for example, in alumina, are used as hard templates [6]. Under certain conditions, surfactants are able to organize into nonspherical micelles [7], which can serve as soft templates for the synthesis of Au NRs [8]. Recently, the
seeding growth approach proposed back in 2001 [9] has been widely used to obtain gold nanorods. The essence of this method is t
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