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2. EXPERIMENTAL METHODS These forces have its origin in three types of interaction and are connected with polar nature of matter and dipole moments. This attractive interaction has a 1/r6 dependence on the r distance between sample and the tip. Figure 2.11: Schematic view of AFM set-up - Basic components of atomic force microscope include cantilever with a sharp tip for scanning of the sample surface. Its movement is detected by a laser radiation reflected from the top of can- tilever and detected by a position sensitive photodiode. The signal is then converted by electronics and a feedback signal is sent to cantilever controller. The scanning movement is realized by piezoelectric elements connected either with the cantilever or the sample table. In contact mode the tip is so close to the surface that actually a direct contact is provided, and what follows electrical contact as well. This allows for measuring the electrical response of the sample to an applied potential and the variation of the method to do that is called Local Conductivity AFM (LC-AFM) or CAFM (Conductive AFM). In this set-up this is a two-contact method, one electrode being the sample surface and second being the scanning tip. When both elec- trodes are conducting, the applied voltage triggers flow of electric current which is measured by electronic system. In experimental setup application of positive (negative) bias voltage means that there is positive (negative) potential on the scanning tip and the electron current induced with the bias voltage flows from sample surface to tip (tip to sample surface). In fact, most often in LC-AFM method the sheet resistance of a thin film is measured. A sample, that is film on a substrate, is placed on a metal holder and clamped with a metallic element in order to prevent movement. The clamp is most often placed at the top of the sample, i.e. film’s surface. What follows is that the current between the two electrodes will go only in the strictly in the interface region. It is mainly due to a large gradient of potential drop from the 54PDF Image | Investigation of metal-insulator transition in magnetron sputtered samarium nickelate thin films
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