It consists of a piezoelectric scanner and a probe with tungsten
tip. The sample is placed in sample holder. The voltage is applied between the
sample and the tip and the signal that comes out from tip is being tunnelled
with the amplifier using tunnelling current amplifier. This tunnelling current
amplifier amplifies the current that is coming from tunnelling effect between
tip and the sample. There is a control scanning unit present in it which
controls the scanning property and data can be recorded using CPU.
Force Microscopy (AFM):
The AFM operates by measuring the interaction force between the
tip and the sample. The probe carries a cantilever and a tip which moves on the
top of the surface of the material, thus analyzing and imaging the material. In
AFM, the sample is mounted on the piezoelectric scanner. The cantilever is
attached with the probe and monitors the force. The probe can act as spring
which measures the deflection or bens of the cantilever. Atomic force
microscopy has three modes of operations. They are Contact mode, non-contact
mode, tapping mode.
This is the mode in which the tip is almost placed on the
material and is run throughout the surface of the material and imaging it. The
tip remains in the repulsive region of the intermolecular force curve.
The tapping mode is where the tip is oscillated at a high
frequency of around 500,000 tapping’s/seconds and the deflection in the
oscillations are observed and processed into the image.
In this mode, the tip is placed outside the sample in the
Near field optical Microscope (SNOM):
Scanning near field
optical microscope (SNOM) is a microscopic technique which is used in
determining the nanostructure which cracks the far field resolution using
evanescent wave property. The main instrumentation part of scanning near field
optical microscopy consists of light source, feedback loop, scanning tip,
detector and piezoelectric stage.
The major difference
between the atomic force microscopy (AFM) and Scanning near field optical
microscopy (SNOM) includes:
The probe used in AFM is force. The probe
used in SNOM is near optic field.
In AFM, surface topography can be
determined with physical contact to the sample, whereas in SNOM we could able
to determine the surface topography without having physical contact.
AFM does not able to determine the inner
structure of the sample. SNOM can determine the inner structure of the sample.
AFM cannot able to distinguish the sample
composition with respect to size and shape. SNOM can distinguish between the
identical component of sample.