Conceptual description of the conventional NSOM (a) and proposed NSOM (b), where the sample loaded on the prong surface of a tuning fork is dithered but an optical fiber probe is not dithered.
Schematic of the proposed NSOM system. The tip-sample gap is controlled by the shear force feedback control method using a tuning fork. The side-illumination and collection mode is used to measure the near-field signal.
Frequency response curves of (a) a bare tuning fork, and tuning fork with the sample and (b) a tuning fork glued with a fiber probe. The Q factor of bare tuning fork changed slightly from 7783 to 7480 after loading the sample, and the Q factor of the tuning fork glued with a fiber probe decreased to 495.
(a) Description of anti-phase vibration of a tuning fork. (b) Approach curves showing the signal reduction of tuning fork when approaching the fiber probe tip to the sample. Three approach curves were measured: at the end (closed red circle), the center (open blue square), and close to the base (open green triangle) of the prong.
Topography and line profile of graphene sheets. (b) and (c) were observed with the conventional NSOM method (a). (e) and (f) were observed with the proposed NSOM method (d).
Topographic and near-field images of the neural cells, (b) and (c) were observed with the proposed method (a), and the images, (e) and (f), observed with the proposed method (d) having different direction of line scan.
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