Simultaneous measurement on full electric field intensity of a nano-structure in near-field

Abstract

A micro- or nano-antenna has attracted great attention since it can control either near-field or far-field. Antenna well-couples to freely propagating light and enables electric field concentration within ultra-small volume. Due to such near-field properties, there have been numerous researches conducted in bio-chemistry or bio-imaging. Besides employing near-field properties, studies related to visualizing near-field information itself have been also carried out. Since near-field is confined and decays rapidly, it cannot be detected by conventional microscopy. Thus, a new type of microscopy was developed, i.e. near-field scanning optical microscopy (NSOM). NSOM uses either aperture or apertureless probe tip to detect excited near-field by perturbing it. Thanks to the new technique, there was a boost in the research field to measure all electric or magnetic field components of a micro- or nano-structure. A various tip designs have been introduced and employed to demonstrate the amplitude and phase measurement of all electric field components. However, there has been little demonstration on simultaneous measurement of the fields of a nano-structure. In this research, a tip design to detect all the electric fields is introduced and its functionality was investigated. A commercial aperture probe was combined with a sharp tip, fabricated right next to the aperture for out-of-plane electric field detection. Electron beam-induced deposition (EBID) technique was implemented for apertureless tip construction. The NSOM measurement was carried out on an Au grating structure followed by an inverse nano-rod antenna. The result shows that an EBID probe clearly works as an Ez-field scatterer which means that the designed EBID-NSOM tip is capable of detection on the all the electric field components. By implementing finite-domain time-difference simulation and convolution, the measured height and tip response can be estimated. From this research, the intensity measurement on all the electric field components of a nano-structure was successfully demonstrated. If phase measurement is also conducted, we expect that magnetic field can be derived from Maxwell equations, and then Poynting vector distribution cal be also mapped.