The optical-beam-induced resistance-change-detection (OBIRCH) method has been improved by using a near-field optical probe as the heat source instead of a laser beam. The resulting NF-OBIRCH method has two advantages over the conventional OBIRCH method. (1) Its spatial resolution is higher. (2) The optical-beam-induced resistance change caused by heating can be observed when the aperture size is zero without interference from the photo current caused by electron-hole-pair generation. In the conventional OBIRCH method, the laser beam creates not only the resistance change, but also the photo current that can mask the resistance change signals.
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