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Optical Near-Field Imaging Using the Kelvin Probe Technique

In the force detection of the evanescent field using a semiconductor tip, the force gradient is affected not only by the surface potential change due to the evanescent field, but also by the contact potential difference (CPD) between the tip and the sample which is not uniform on the surface. In this paper, we propose a novel method to measure the evanescent field without the CPD effect using the Kelvin probe technique. Simultaneous images of the topography, the CPD and the force gradient due to the evanescent field were obtained on a 15-nm thickness sputtered Au surface. These images showed no correlation in several areas. The lateral resolution of the force gradient due to the evanescent field was better than 15 nm (λ/33).