An electrostatic force microscope (EFM) and a Kelvin probe are used to characterize the charges embedded in thin anodic alumina layers of thickness ranging from 100 to 400 nm. Introducing a method for obtaining self-supported alumina layers, we exhibit the presence of positive charges at the metal/oxide interface of anodic alumina layers. These positive charges, together with the negative charges present at the surface of the anodic layer, induce a true polarization of the layer. The magnitude of this polarization depends on the conditions of preparation of the layers and can be well controlled. As a second step, we show the influence of this polarization on charge injection in these layers with EFM: charges of both signs may be injected in unpolarized layers whereas one cannot inject negative charges in polarized layers, which thus exhibit a diode-like behavior.

We shall demonstrate in this article that characterization of the charge distribution by electrostatic force microscopy is not straightforward: we will stress the important role played by the electrostatic images of the scanned charge distribution in the tip and by the operating mode in the formation of extra features in images obtained with this instrument. To illustrate this, we will describe two models that correspond to the scanning of small and extended charge distributions. These models will be compared with experimental images.

We report the observation in the direct space of the transport of a few thousand charges submitted to a tunable electric field along the surface of a silicon oxide layer. Charges are both deposited and observed using the same Electrostatic Force Microscope. During the time range accessible to our measurements (i.e. t = 1 ∼ 1000 s), the transport of electrons is mediated by traps in the oxide. We measure the mobility of electrons in the "surface" states of the silicon oxide layer and show the dispersive nature of their motion. It is also demonstrated that the saturation of deep oxide traps strongly enhance the transport of electrons under lateral electric field. c EDP Sciences

In order to clarify the mechanisms of charge transfer on insulating surfaces by contact electrification, we performed charge-transfer experiments on high-K oxides using the tip of an electrostatic force microscope. In particular, we investigated the influence of the applied voltage between the tip and the surface and the contact duration on the amount of transferred charges on Al2O3. The electronic motion in the insulating material is analyzed in terms of hopping processes assisted by the electric field created by the tip inside the oxide. We show that this electric field must be described by a three-dimensional model. In this frame, the transfer mechanism is analyzed as an instantaneous wetting of the surface by the charges—the surface being a region of large trap concentration—followed by a progression of the charges inside the oxide.

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