Resolution-enhanced polarization imaging with focused thermal pulses

Abstract

The non-destructive measurement of electrical polarization and space charge densities is a key technique in electret research. The principal idea behind these methods is a non-uniform deformation or heating, which gives rise to a short-circuit current that can be recorded in the time or frequency domain, and which carries information about the polarization depth profile. In recent years, thermal pulses and thermal waves have been used successfully to obtain three-dimensional polarization maps in polymeric electrets by scanning the beam of a pulsed or intensity-modulated cw laser across the sample surface. However, the polarization maps in these experiments were reconstructed using a relatively simplistic one-dimensional heat diffusion model that does not take into account lateral heat diffusion in the metal electrode. A two-dimensional “coupled neighbors” model was developed, where the current signal from several adjacent beam pointings along a scan line is coupled together, and a Monte Carlo method is used for the deconvolution. Simulations show that the new approach enhances the lateral resolution by a factor of 2−3×, since it avoids the information loss occurring when three-dimensional polarization measurements are processed with a one-dimensional thermal model. We also present an augmented, low-noise thermal-pulse instrument where thermal pulses are initiated by a pulse-modulated diode laser.

Space charge distributions in insulating polymers: A new non-contacting way of measurement

“…[36][37][38][39][40][41][42] The first results showed that non-contacting measurements were possible, provided that significant currents can be extracted from noise. In this case, they are representative of an internal space charge (or polarization) in the sample that can be calculated by mathematical inversion of the electrostatic problem.…”

Contributed Review: Review of thermal methods for space charge measurement

“…35 a metal-oxide-semiconductor (MOS) structure with thickness of several hundreds of nanometers was tested. The TPM has been recently adapted by Mellinger and Aryal for both 2D 36 and 3D measurements. 36,37 …”