Shear Force Detection Using Single-Tine Oscillating Tuning Fork for Scanning Near-Field Optical Microscopy

We propose a new method to detect near-field by using a single-tine oscillating tuning fork with mechanically asymmetric excitation that exhibits the sensitivity and stability better than that by using a double-tine oscillating one. Comparison of shear forces for the two methods demonstrate that the single-tine oscillating tuning fork provides a simpler and more sensitive method for near-field measurements. A theoretical analysis is presented for explanation to the greater sensitivity. The method is demonstrated by imaging a sparse-packed layer of micro-spheres in size of 200 nm.