ZhiGang Zeng

Polarization fatigue in ferroelectric vinylidene fluoride and trifluoroethylene copolymer films

In this letter polarization fatigue in ferroelectric polymers has been reported. Experimental results indicate that the driving voltages with lower frequency and higher amplitude should correspond to higher fatigue rates. A universal scaling behavior with N∕f, where N is the number of switching cycles and f is the frequency, is found in the frequency dependence of polarization fatigue. The profile of driving voltages is also found to affect the fatigue behavior. It is believed that the trapped charges, injected from electrodes into films, should make the major contribution to polarization fatigue.

EFFECT OF CRYSTALLINITY ON POLARIZATION FATIGUE OF FERROELECTRIC P(VDF-TrFE) COPOLYMER FILMS *

The dependence of polarization fatigue on crystallinity of vinylidene fluoride and trifluoroethylene copolymer films was studied. Experimental data indicated that the higher the crystallinity of the film was, the slower the fatigue rate of the film became. A possible explanation was put forward, and it was regarded that the space charges, trapped at the boundaries of crystallites and/or captured by the defects lying both in amorphous and crystalline phases, should make the major contribution to polarization fatigue.

A simple method for AFM tip characterization by polystyrene spheres

An AFM image would not be the true topography of a surface because of the limitation of a finite size of the tip. The true topography of the surface can be deduced if we can know the tip shape. In this paper a simple method has been established to determine the profile of an AFM tip. A geometrical model for the tip and a spherical object has been proposed to show the procedure for deducing the tip shape from AFM images. Isolated spheres and closely packed spheres with different diameters have been observed to confirm the tip shape by this method. It is a non-destructive method to determine the tip shape and the results can be used for future reconstruction of an AFM image.

Observation of asymmetric ferroelectric switching in fatigued ferroelectric vinylidene fluoride and trifluoroethylene copolymer films

In this paper, we illuminated the observation of asymmetric ferroelectric switching phenomena in fatigued P(VDF-TrFE) copolymer films. Two types of asymmetric switching were observed: one was the occurrence of switching dual peaks obtained from films with asymmetric electrode structure and the other was the jump of remanent polarization during fatigue process, as was obtained mostly from films with asymmetric electrodes and occasionally from films with symmetric electrodes. No evidence indicated the dependence between the switching dual peaks and the jump of remanent polarization. The possible mechanism of such asymmetric phenomena was also discussed.

The role of space charges on polarization fatigue in ferroelectric P(VDF-TrFE) copolymer films

Recently, in our lab we have performed some systemic studies on polarization fatigue in ferroelectric polymers and four possible contributing factors (applied voltages, operation temperature, film crystallinity and electrode structure) are characterized by a homemade sawyer-Tower circuit. All fatigue phenomena observed in these experiments seem to imply the effect of space charges, which are injected from electrodes into ferroelectrics and trapped at the boundaries of crystallites or/and by defects. We believe that the interaction between trapped charges and electric dipoles in ferroelectrics has inhibited ferroelectric switching in polymers and induced the occurrence of polarization fatigue.

The preparation of uniform Ag-TCNQ electrically bistable films with nano-grains for ultrahigh density data storage

The Ag-TCNQ films with smooth surface and uniform tiny grains in nanometer scale were prepared by an improved vacuum evaporation method in which the deposition temperature of TCNQ films was increased from room temperature to 100degC. It is an ideal medium for ultrahigh density data storage with SPM-based techniques. Storage dots were recorded by applying voltage pulses between the tip of a scanning tunneling microscopy (STM) and the substrate under ambient condition. A recording pattern with six storage dots was obtained. The average diameter of recording dots was ~20nm, which corresponds to a data storage density of 0.5 Tbit/cm2