Verification of nano-particle absolute height position measurement from a surface with invisible reference tilt resin by multi-wavelength evanescent fields

Abstract

Some nanoscale technologies are being employed without a full understanding of the underlying phenomena. Both static and dynamic observations of nanoparticles are essential for investigating these phenomena. While there are several methods for static observation such as scanning electron microscopy typically in a vacuum environment, however, there are few methods for dynamic observation. One of the dynamic observation methods is to observe nanoparticles using an evanescent field, a unique field that emerges only near the surface being observed. The dynamic observation method has been proposed for measuring the three-dimensional positions of moving nano-particles in liquid using a multi-wavelength evanescent field. However, the absolute height of the nano-particles remains unexplored in this study. Hence, to establish this method, it is necessary to confirm the absolute distance or the height from the surface being observed at the same position by other reference measurement methods. In this paper, an optical resin with a refractive index close to the water was formed as an invisible reference tilt surface that was thinner than 200 nm in height. We also constructed a compact interferometric optical system to utilize optical interferometry that can measure the height of the tilt resin without contact and with nanoscale accuracy. Polystyrene standard nano-particles suspended in water were deposited onto the water-invisible tilt resin and was measured the height at each position on the tilt resin by a multi-wavelength evanescent field. As a result, it was confirmed that the 3D position measurement of particles using multi-wavelength evanescent fields tends to follow the resin surface height well. At the heights under approximately 100 nm, the differences in height were less than 5 nm between multi-wavelength evanescent fields and interferometry measurement, and the precision (2σ) also was approximately 5 nm.

Keywords

• height measurement
• evanescent field
• nano-particle
• interferometry
• invisible resin
• tilt surface