Nanoscale physics

Plasmon effect in DMAAS ferroelectric crystal with silver nanoparticles on their surface
Semak S.I., Rudko M.S., Kapustianyk V.B., Turko B.I., Bolesta I.M.
Ivan Franko Lviv National University of Lviv. Dragomanova, 50, Lviv-79005, Ukraine. 
E-mail: rudko_mykola@ukr.net

The two types of silver nanoparticles were obtained on a surface of NH2(CH3)2Al(SO4)2×6H2O (DMAAS) ferroelectric crystal: the smaller nanoparticles with characteristic dimensions of 60 nm and the larger nanoelements with an average diameter of 450 nm, which may be called "nanowells". The model  describing formation of these nanowells on a crystal surface is proposed. Is is based on the previous studies of DMAAS crystal doped with chromium [1].
Presence of silver nanoparticles on a surface of DMAAS single crystal is accompanied by appearance of a surface plasmon resonance (SPR) band in the wavelength range of 360-460 nm. The temperature evolution of this plasmon absorption band in vicinity of the ferroelectric phase transition at Tc = 152 K [2] was studied. All parameters of the SPR band, in particular the position of the band maximum, the maximum absorption coefficient, the area under the contour of the plasmon peak, and the half-width of the peak, reveal anomalies in vicinity of the ferroelectric phase transition temperature. 
The anomalous behavior of the SPR band parameters at Tc is associated with the formation of dipole clusters with a certain orientation of the total dipole moment in respect to the crystal surface. The arising local electric fields cause polarization of the silver nanoparticles in a plane parallel to the crystal surface.  

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