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5.3 Experimental Analysis  181
                                  (a)                       (b)
                                                               Photodiode  Substrate
                                          10mm                       Al wire



                                       Photodiode


                            Fig. 5.13. Photograph of photocantilever, in which top photodiode (PD)is fabri-
                            cated (a), and sketch of that (b)


                            (a)                                (b)
                                                                               Optical head
                                       Microscope
                                                                     Photocantilever
                                                                           Prism
                                               Optical head
                                               Cylindrical PZT       Cylindrical PZT




                                               He–Ne laser
                            Fig. 5.14. Photograph of AFM/SNOM setup mounted on a vibration-damped table




                            placed very close to the probe tip [5.22]. Figure 5.13 shows a photograph of a
                            photocantilever (a), and a sketch of that (b). The photocantilever is attached
                            to a piezoelectric transducer (PZT) allowing z distance regulation. The pho-
                            tocantilever is moved close to the sample surface and the distance between
                            the cantilever and the surface is detected from the focus error signal of the
                            optical head placed above the cantilever.


                            Experimental Setup

                            Figure 5.14 shows a photograph of an AFM/SNOM setup mounted on a
                            vibration-damped table. An He–Ne laser (this side) incident to a prism and
                            a microscope (other side) are used to observe the sample and the cantilever
                            tip, which is helpful in aligning the setup. An evanescent light is produced at
                            the prism surface by the total internal reflection arrangement. The prism is
                            mounted on a cylindrical PZT, allowing xyz movement. The z movement is
                            used for the gap (distance) control and xy for 2-D scanning. Since the piezo-
                            electric transducer has characteristics of creep and hysteresis, it is driven by a
                            small voltage or with feedback control. Figure 5.15 shows a sketch of the main
                            part of the setup usingthe photocantilever.
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