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Electric Force-Distance Curves (EFDC) is one of the ways whereby electrical charges trapped at the surface of dielectric materials can be probed. To reach a quantitative analysis of stored charge quantities, measurements using an Atomic Force Microscope (AFM) must go with an appropriate simulation of electrostatic forces at play in the method. This is the objective of this work, where simulation results for the electrostatic force between an AFM sensor and the dielectric surface are presented for different bias voltages on the tip. The aim is to analyse force-distance curves modification induced by electrostatic charges. The sensor is composed by a cantilever supporting a pyramidal tip terminated by a spherical apex. The contribution to force from cantilever is neglected here. A model of force curve has been developed using the Finite Volume Method. The scheme is based on the Polynomial Reconstruction Operator-PRO-scheme. First results of the computation of electrostatic force for different tip-sample distances (from 0 to 600 nm) and for different DC voltages applied to the tip (6 to 20 V) are shown and compared with experimental data in order to validate our approach. [ABSTRACT FROM AUTHOR]

Techniques derived from the near-field microscopies and particularly the Atomic Force Microscopy (AFM) are presented as alternative techniques for space charge measurement compared to classical techniques due to their high sensitivity to the electrostatic force and an improved spatial resolution (few nanometers). One of the AFM derivative methods, which allow obtaining information on the charge state of the dielectric materials, is based on the measurement of Force Distance Curves (FDC) obtained by cycling approach and retraction of the AFM probe to the dielectric surface. In this paper, three-Dimensional (3D) simulation results for the electrostatic force between an AFM tip and the surface of a dielectric are presented for different AFM tip geometries. The first aim is to analyse the effect of tip shape on electrostatic contribution to force-distance curves. The second step consists in extracting cantilever contribution to electrostatic force. Finally, a model merging cantilever and tip shape contributions is developed. Simulation results are shown and compared with experimental data in order to validate our approach. [ABSTRACT FROM AUTHOR]

A numerical model for describing charge accumulation in electron-beam irradiated low density polyethylene has been put forward recently. It encompasses the generation of positive and negative charges due to impinging electrons and their transport in the insulation. However, the model was not optimized to fit all the data available regarding space charge dynamics obtained using up-to-date pulsed electro-acoustic techniques. In the present approach, model outputs are compared with experimental space charge distribution obtained during irradiation and post-irradiation, the irradiated samples being in short circuit conditions or with the irradiated surface at a floating potential. A unique set of parameters have been used for all the simulations, and it encompasses the transport parameters already optimized for charge transport in polyethylene under an external electric field. The model evolution in itself consists in describing the recombination between positive and negative charges according to the Langevin formula, which is physically more accurate than the previous description and has the advantage of reducing the number of adjustable parameters of the model. This also provides a better description of the experimental behavior underlining the importance of recombination processes in irradiated materials. [ABSTRACT FROM AUTHOR]