Déformation photoinduite dans les films minces contenant des ...

Chapter 2. Experimental setup and sample preparation 27(x, y, z)scan piezodither piezo(shear force)optical fibertipOPTICAL FIBERzxyC pr pzV 0HT gainR pRCR cr cComputer(labview)rTOPOGRAPHYIMAGE(z control input)VV’+-V zG ! "VBW = 100 KHzG = 100G CRlock-in(G LI )e1/G cV SFV in+-V Cprocessingpastel-00527388, version 1 - 19 Oct 2010filmy xsubstrateFigure 2.6: Shear-force microscopy: detection electronics and feedback.end, the optical fiber is connected to a photomultiplier.The (x, y, z) scan piezo tube has four external electrodes and one internal electrode,driven by a voltage between 0 and 400 V , which allow a maximum excursion of 30 µmalong the x, y axis and 2 µm along the z-axis. The head is mounted on a translationstage driven by a step motor, every step corresponding to a 200 nm displacement alongthe z-axis, which allows a precise setting of the tip-to-sample distance within the rangeof the (x, y, z) piezotube extension. This is achieved first, by a visually controlled coarseapproach and, subsequently, by an automatic approach based on the shear-force feedback,that we will detail later.The sample is mounted in front of the head, on a sample holder equipped with manualtranslational stages along the x and z directions of the sample surface plane, having aprecision of 10 µm.2.1.3 Shear-force microscopyThe shear-force topography measurement is based on the detection of the vibrationamplitude of a tip oscillating along the x-axis. In our system (Figure 2.6), this oscillationis obtained by means of an alternating voltage V 0 applied to the dither piezotube. The electrical behavior of the dither piezo tube is essentially capacitive. Usinga Wheatstone bridge we detect the variation of this capacitance due to the mechanicalconstraints imposed on the dither piezo tube by the tip. Driving the tip at a resonant