Evaluation of the capacitive force between an atomic force microscopy tip and a metallic surface

We propose a very simple method to determine the electrical tip-surface force in Atomic Force Microscopes used to study the electrical properties of metallic or insulating materials; the analysis of the measurements as well as determination of the appropriate experimental procedures requiring an analytical model of the tip-surface capacitance. The comparison of force expressions obtained by this method with those obtained by exact derivation in the case of the sphere-infinite plane system shows very good agreement. This method is then applied to determine the tip-surface force, the real shape of the tip being introduced in the derivation. The obtained expression is compared to experimental and numerical data. We emphasize that this method is very general and can be applied to any axially symmetric capacitor

Local triboelectricity on oxide surfaces

In triboelectric phenomena, electric charges are transferred when two materials are touched or rubbed together. We present in this paper a study of this effect performed on metallic oxides at the nanometric scale by an Atomic Force Microscope in the resonant mode. We show that following the electrification processes, positive or negative charges can be deposited. From our experimental data, we conclude that the charge transfer results in an equilibrium final state, the occupied states in the gap being "surface states" with large density and spread under the surface along a characteristic distance of about 100 nm

Magneto-optical Faraday imaging with an apertureless scanning near field optical microscope

We have developed an apertureless Scanning Near field Optical Microscope (SNOM) in transmission, devoted to near field magneto-optics. Our apertureless SNOM combines an inverted optical microscope, which has been adapted to Faraday effect imaging, with a commercial stand-alone Scanning Probe Microscope, used in Atomic Force Microscope (AFM) mode. Two different probes are validated as apertureless SNOM tips: a home-made etched tungsten wire and a commercial AFM silicon probe. We present and analyze preliminary images of the doMayn structure in iron garnets. They indicate a SNOM resolution clearly in the sub-micrometric range. Besides, the near field magneto-optical image presents some unexpected features, not revealed in far field images

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The Atomic Force Microscope used in resonant mode is a powerful tool to measure local surface properties : for example, the quantitative analysis of the electrical forces induced by the application of an electrical tension between a conductive microscope tip and a surface in front allows the determination of the tip/surface capacitance and of the local surface work fonction. However, this analysis needs a well adapted model for each type of surface. In this paper, we calculate, with a simple geometrical model, the tip-surface interaction for a metallic tip and a semiconducting surface and we describe its variation with the applied tension and the tip/surface distance. Our results show different kinds of behaviour that we are able to associate with the different semiconductor regimes (accumulation, depletion, inversion). Therefore, it is not possible to describe this tip-surface system as a passive capacitance.La Microscopie à Force Atomique en mode résonnant est un outil bien adapté à la mesure des caractéristiques locales des surfaces : par exemple, l'analyse quantitative des forces électriques créées par l'application d'une différence de potentiel entre la pointe conductrice du microscope et une surface en regard, permet de déterminer la capacité pointe/surface et le travail de sortie local de la surface. Toutefois cette analyse réclame un modèle adapté à chaque système. Cet article a pour but de calculer, dans un modèle géométrique simple, l'interaction pointe/surface dans le cas d'une pointe métallique et d'une surface semiconductrice et de décrire ses variations en fonction du potentiel appliqué et de la distance pointe-surface. Nos résultats montrent que ces forces présentent une grande richesse de comportements que nous avons associés aux différents régimes (accumulation, déplétion, inversion) du semiconducteur et que les modèles simples qui décrivent le système pointe/surface comme une capacité passive sont inappropriés