Development of a novel scanning near field microscope with a facility of simultaneous shear stress measurement

Abstract

This project is about building a near-field optical microscope which can simultaneously measure evanescent fields as well as lateral shear forces. Possibility of quantify the lateral shear forces through a special q-plus arrangement using a theoretical model from Manhee et al. and simultaneously measure evanescent field make this instrument unique. This instrument is built mainly to study water in between two surfaces separated by nanometers. We know very little about this nano-confined water. In-order to get a clear molecular picture of confined water we can look at the diffusion coefficient of a particle through it. By measuring the intensity fluctuations of the light from a fluorescent molecule in this confined water, we can measure it’s diffusion coefficient. This instrument can do such a measurement along with measuring mechanical shear response forces. The instrument uses a tuning fork as the force sensor and a special optical probe for sensing near field light. The optical probe is a tapered optical fibre with 100 nm aluminium coat everywhere except at the tip. In this project along with these optical probes necessary electronics like PI feedback controller, high voltage amplifiers were made. For making optical probes, first a fibre pulling method is optimised and an aluminium coating process is optimised. A probe holder is designed and tuning fork with optical probe is attached on it. A separate piezo-tube assembly is made for the actuation of this probe. Few LabVEW programs are written to automate this assembly and electronics. These programs are tested and optimised. Also an optical set-up is assembled to illuminate the sample with evanescent field. There was some delay in getting FIB facility to prepare optical probe. But at the end we managed make those probes. Now the instrument works like an AFM and obtained some AFM images. The images shows that the motion control and LabVIEW programs are working as expected. The optical probe will be attached with PMT to finish the instrument.