Nanoscale surface charge detection in epoxy resin materials using electrostatic force spectroscopy

D El Khoury,R Arinero,J C Laurentie,J Castellon

doi:10.1063/1.4944953

Abstract

Electrostatic force spectroscopy (EFS) operated in a conventional force gradient detection method allows determining local surface charges in epoxy samples. This is made possible through a detailed analysis of gradient versus DC voltage curves. The parabolic dependence of these curves is closely related to the charge density. Both maximum and origin-ordinate are key data from which it is possible to extract quantitative information on the detected charge. The study is based on the combined use of numerical and analytical simulations of the probe sample interaction. Excellent sensitivities to very low surface charge densities are reported.

Highlights

While a biased atomic force microscopy probe is scanned over a sample surface, it is possible to generate an image contrast related to nanoscale electric or dielectric surface properties
For an applied voltage ranging from -8V to +8V, we only observe a single branch of the parabola and one notices that the maximum is not reached
A zero charge boundary condition was selected for this area and at symmetry boundaries where the potential is known to be symmetric with respect to the boundary

Summary

INTRODUCTION

While a biased atomic force microscopy probe is scanned over a sample surface, it is possible to generate an image contrast related to nanoscale electric or dielectric surface properties. EFM is, for example, routinely used to determine surface potentials of doped semiconductors[3]; such measurements are possible under vacuum thanks to the excitation of higher order harmonics, that allow reducing the stabilization time (transient regime) of the oscillating sensor.[4] EFM is widely used in the form of the Kelvin Probe Force Microscopy (KPFM) variant[5] which can be sensitive to the composition and electronic state of the local structure up to atomic or molecular scales.[6,7] An important advance in EFM technique was achieved by Crider et al.[8,9] and Riedel et al.[10] who developed the so-called local dielectric spectroscopy (LDS), based on the detection of the phase shifts of AC gradients under vacuum which allowed studying dielectric losses in thin polymer layers. To the previously mentioned methods, we show in this paper that it is possible to detect a surface charge without preliminary injection

EXPERIMENTAL AND THEORETICAL BACKGROUNDS

EXPERIMENTAL RESULTS AND NUMERICAL SIMULATIONS

CONCLUSION