Tapping modeHeight and phase image of polymer coating on inside
of aluminum beverage can.
Introduction
The Atomic Force Microscope (AFM) is being used to
solve processing and materials problems in a wide range of technologies
affecting the electronics, telecommunications, biomedical, chemical,
automotive, aerospace, and energy industries. The materials under
investigation include thin and thick film coatings, ceramics,
composites, glasses, synthetic and biological membranes, metals,
polymers, and semiconductors. The AFM is being applied to studies
of phenomena such as abrasion, adhesion, cleaning, corrosion,
etching, friction, lubrication, plating, and polishing. The real-world
examples presented on our web page indicate the breadth of AFM
applications for problem solving; yet they represent only a fraction
of our experience at Advanced Surface Microscopy.
Technical Capabilities
AFM images show critical information about surface
features with unprecedented clarity. The AFM can examine any rigid
surface, either in air or with the specimen immersed in a liquid.
"Minor" (and major) differences between "smooth"
surfaces are shown dramatically. On one hand, the AFM can resolve
very tiny features, even single atoms, that were previously unseen.
On the other hand, the AFM can examine a field of view larger
than 125 microns (0.005 inch), so that you can make comparisons
with other information, e.g. features seen in the light microscope
or hazes seen by eye. The AFM can also examine rough surfaces,
since its vertical range is more than 5 microns. Our analytical
reports of AFM results include three-dimensional images and quantitative
data analysis (such as feature sizes, surface roughness and area,
and cross-section plots), integrated and interpreted in the context
of your problem.
Large samples fit directly in the microscope without
cutting. We can examine any area on flat specimens up to 8"
(20 cm) in diameter and up to 0.5" (12.7 mm) thick. We have
designed custom adapters to accommodate SEM stubs, microtomed
blocks, metallurgical mounts, and other odd shapes and sizes (up
to 1.5" thick and 42" wide). We can quickly find and
document the location of interest using the built-in optical microscope
(with magnification up to 2000x). For comparative studies using
different probes and scanning modes, we can find the spot within
one micron.
How the AFM makes a 3-D image
A tiny stylus gently contacts the specimen. As the
XYZ translator scans either the specimen or the stylus horizontally
in a raster pattern (XY), the stylus rides up and down the surface
hills and valleys. The deflection of the stylus is registered
by the laser/photodiode sensor and the XYZ translator adjusts
stylus or specimen (depending on microscope) up or down (Z) to
restore the stylus to its original orientation. The computer stores
the vertical position at each point and assembles the image.
For image display, we select the vertical (Z) and
horizontal (XY) ranges independently, to best present the surface
structure. Using "dual magnification," the AFM combines
the wide field view of a Scanning Electron Microscope (SEM) with
vertical resolution which exceeds that of a Transmission Electron
Microscope (TEM). The ratio of the vertical to horizontal magnification
can be very large (1000 or more) to allow easy perception of differences
between very smooth surfaces.
Topographic results can be enhanced by simultaneously
using other modes of AFM data capture, such as phase imaging.
In the left image (above), we see the many interesting surface
features of the coating. When combined with the phase image (right),
we can now tell which features are of similar chemical composition.
This allows determining whether surface features may be the result
of a residue or specific chemical component, or whether the surface
is homogeneous.
See what you've been missing
In addition to its superior resolution, the AFM has these key advantages:
Another mode of operation which can be useful when combined with topography is friction imaging. In the height image above (left), there are several areas where the topography appears higher and rougher than the bulk surface. When combined with a friction image (right), we see that there is a contaminant on the surface which appears dark in the image. Therefore the contaminant has a lower coefficient of friction than the underlying surface. This can be helpful in determining the source of the contaminant.
updated 04/09/2007