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.
