SCANNING PROBE MICROSCOPY.BASIC PRINCIPLES ,SCANNING TUNNELING MICROSCOPY .ATOMIC FORCE MICROSCOPY.

1. THE INSTITUE OF SCIENCE .
TOPIC :Scanning probe
microscopy.
-sana shaikh
m.sc(physical chemistry)
Paper-2.

2. Scanning probe microscopy (SPM),
• First scanning probe microscope invented in 1981
by Binning and Roher ,for which they received the
Nobel prize.
• The family of SPM uses no lenses ,but rather a
probe that interacts with the sample surface.
• Simple design.
• Low cost .
• Easy to handle
• Automatically resolves images

4. Most used SPM technique.

5. Basic principles of SPM.

6. SPM.
For the techniques to provide
information on the surface
structure at the atomic level:
• the position of the tip with
respect to the surface must
be very accurately controlled
(to within about 0.1 Å) by
moving either the surface or
the tip.
It is possible to accurately
control the relative positions
of tip and surface by ensuring
good vibrational isolation of
the microscope and using
sensitive piezoelectric
positioning devices.
• the tip must be very sharp -
ideally terminating in just a
single atom at its closest point
of approach to the surface.

8. STM.
• It has metal needle that scans sample by
moving back and forth over it, gathering
information about the curvature of the
surface.
• STM uses sharp conducting tip with bias
voltage applied between the tip and the
sample.
• When the tip is brought within about 10A of
the sample ,electrons from the sample being
to “tunnel” through the 10 A gap into the tip
or vice versa depending upon the sign of the
bias voltage.
• The resulting current varies with the tip-to-
sample spacing and it is the signal used to
create an STM image.
• STM is designed to scan a sample in either of
two modes
• Constant –height mode
• Constant –current mode.

10. AFM.
• The AFM probes the surface of
sample with a sharp tip, a couple
of microns long often less than
100A in diameter .the tip is
located at the free end of the
cantilever that is 100 to 200 Um
long.
• Force between tip and the
sample surface causes the
cantilever to bend or deflect.
• A detector measures the
cantilever deflection allow a
computer to generate a map of
surface topography .
• Can be used to study insulators
and semi conductors as well as
electrical conductors.

12. Advantages.
• The resolution of the microscopes is not limited by
diffraction, only by the size of the probe-sample
interaction volume .
• Hence the ability to measure small local differences in
object height (like that of 135 picometres steps on <100>
silicon) is unparalleled. Laterally the probe-sample
interaction extends only across the tip atom or atoms
involved in the interaction.
• The interaction can be used to modify the sample to create
small structures (Scanning probe lithography).
• Unlike electron microscope methods, specimens do not
require a partial vacuum but can be observed in air at
standard temperature and pressure or while submerged in
a liquid reaction vessel.

13. Disadvantages
• The detailed shape of the scanning tip is sometimes
difficult to determine. Its effect on the resulting data is
particularly noticeable if the specimen varies greatly
in height over lateral distances of 10 nm or less.
• The scanning techniques are generally slower in
acquiring images, due to the scanning process. As a
result, efforts are being made to greatly improve the
scanning rate.
• The maximum image size is generally smaller.
• Scanning probe microscopy is often not useful for
examining buried solid-solid or liquid-liquid interfaces.

14. Reference:-
• Skoog D A, West D M , Fundamentals of
Analytical Chemistry, Thomson
• Asia Pvt ltd., 8 th Ed, (2004)
• 2) Skoog, Holler, Nieman, Principles of
Instrumental Analysis
• http://teachers.stanford.edu/activities/SPMRe
ference/SPMReference.pdf
• http://slideplayer.com/slide/4959102/