Introduction To Atomic Force Microscopy - AFM Workshop LS-AFM User Manual

1.

Introduction to Atomic Force Microscopy

In an AFM (atomic force microscope), a probe is scanned
over a surface and the motion of the probe is monitored
to create a three-dimensional image of the surface.
These unique instruments are capable of measuring
high-resolution images in both ambient air and liquids,
with surface features of only a few nanometers in size.
The three-dimensional motion of the sample (or
probe) is generated by piezoelectric ceramics. These
sensitive ceramics allow motions as small as a frac-
tion of a nanometer. Typically, the sample (or probe) is
moved in a raster pattern as the probe glides across
the surface.
A light lever sensor is used for controlling the force of
the probe on the surface while the sample is scanned.
The light lever reflects a laser beam off the surface of
a cantilever into a photo-detector. As the probe inter-
acts with a surface, the cantilever deflects, and this
motion is sensed by the photo-detector.
With this light lever, forces as small as a pico-new-
ton are possible. With such small forces, very small
probes may be used. With micro-machining methods,
probes can have diameters of only a few nanometers.
The light lever can be made more sensitive by vibrat-
ing the cantilever with a small piezoelectric ceramic
and modulating the light. When the vibrating probe
interacts with the surface, the amplitude of vibration
may be monitored and used to control the probe's
force on the surface.
Modern atomic force microscopes include not only a
probe and piezoelectric scanner, but additional hard-
ware for bringing the probe rapidly into the proximity
of a surface. A video optical microscope is very help-
ful for operating an AFM. The video microscope helps
with aligning the light lever and probe approach, and
for finding features for scanning.
For an in-depth description of AFM instrumentation,
we recommend the book Atomic Force Microscopy
by Peter Eaton and Paul West. This book provides a
complete theoretical, as well as practical explanation
for the design and application of AFMs.
V 1.1 / LS-AFM Users Guide Section 1-1