Fabrication of sharp-needled conical polymer tip on the cross-section of optical fiber via two-photon polymerization for tuning-fork-based atomic force microscopy

Aiming at the use in tuning-fork-based atomic force microscopy (TF-based AFM), we propose and demonstrate fabrication methods of polymer tips on the cross-section of optical fibers by two-photon polymerization (TPP) using SCR500 resin. This method can be applied to any optical fibers or other bases regardless of the type. The specified polymer tips are fabricated with high reproducibility by this method. First, a conical polymer tip was fabricated via a continuous-scanning method and layer-by-layer accumulation of circular layers which reduce to a point along with the growth from the cross-section of optical fibers, by using a five-axis optical fiber mount combined with a two-photon nanofabrication system. A sharp-needled conical polymer tip of a 45 nm radius of curvature was fabricated with attachment of four voxels. These voxels were fabricated by the gradually-decreasing-exposure-time method on the apex of the simple conical tip. We have also designed and fabricated a triple-tapered polymer tip to demonstrate the feasibility of fabricating various tip shapes by the TPP method for the TF-based AFM. Moreover, the photoluminous polymer tip was fabricated using ORMOCER mixed with quantum dots. The sharp-needled polymer tip was utilized for the TF-based AFM using an optical fiber probe to investigate the performance of the polymer tip fabricated by the TPP method, and we have obtained a topographic image of a pitted sample. Finally, the near-field image of the 30-nm-thick gold layer with holes of 250-nm-radius was successfully obtained by the aluminum-coated NSOM probe fabricated on the TPP conical polymer tip with a radius of curvature of 45 nm in NSOM system.