Noncontact Atomic Force Microscopy - Yale School of Engineering ...

P.II-29
Local Dielectric Spectroscopy of Nanocomposite Materials Interfaces
M. Labardi 1 , D. Prevosto 1 , S. Capaccioli 1,2 , M. Lucchesi 1,2 and P.A. Rolla 1,2
1 INFM-CNR, LR polyLab, Largo Pontecorvo 3, 56127 Pisa, Italy
2 Dipartimento di Fisica, Università di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy.
Dielectric spectroscopy (DS) has revealed especially successful to disclose structural
properties of polymeric materials, like e.g. their glass transition and structural relaxation
phenomena. Local probe DS [1] combines the high spatial resolution of frequency
modulation electrostatic force microscopy (FM-EFM) with the physical insight typical of
DS, being firstly demonstrated on homogeneous poly-vinyl-acetate (PVAc) films under
vacuum [1]. In essence, a sinusoidal potential at frequency fmod is applied to a conductive
probe and the induced modulation of the resonant frequency shift Δfres is measured by
dual-phase lock-in technique, referenced at 2fmod. Phase delay indicates dielectric loss due
to polarization relaxation occurring with characteristic time τR ~ 1/ fmod [1].
We apply local DS to address the influence of inorganic inclusions on structural
relaxation of polymers. A PVAc thin film (30 nm) with a dispersion of a layered silicate
(montmorillonite, MMT) was spin-coated onto Au, and partially scratched away to
expose the metal, to obtain a reference surface (Fig. 1a). Presence of inorganic layers on
the surface is evident from the TappingMode TM phase image (Fig. 1b). Conventional FM-
EFM (Veeco Lift mode TM in controlled atmosphere [2] and temperature) shows materials
contrast (Fig. 1c), independent of T. In Fig. 1d-f, dielectric loss maps at T = 50, 60, 70°C
show highest contrast at T = 60°C for the used fmod = 130 Hz, corresponding to τR ~ 7-8
ms. Dielectric contrast at inclusions can also be studied (Fig. 1e, arrow).
Financial support from INFM-CNR “Seed 2007” project is acknowledged.
Figure 1: a) Topography of a PVAc/MMT thin film (left) on Au (right). b) Phase image showing
the location of inorganic layers (arrow). c) Δfres map. d)-f) Dielectric loss maps at T = 50,60,70°C.
[1] P.S. Crider, M.R. Majewski, J. Zhang, H. Oukris, N.E. Israeloff, Appl. Phys. Lett. 91, 013102 (2007).
[2] M. Lucchesi, G. Privitera, M. Labardi, D. Prevosto, S. Capaccioli, P. Pingue, J. Appl. Phys. 105,
054301 (2009).
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