Biomedical Engineering Reference
In-Depth Information
1.6.2 Scanned probe optics
Scanned probe optical systems utilize a molecularly sharp tip at the end of
a small cantilever beam to image the surface of the specimen. The probe is
attached to a piezoelectric scanner tube that raster scans the probe across
the selected area of the specimen surface. The probe interacts with the mor-
phological details of the surface and gathers information related to the
properties of the surface being scanned.
Image formation in the AFM
The AFM probe utilizes a molecularly sharp tip at the end of a small cantile-
ver beam. The probe is attached to a piezoelectric scanner tube which raster
scans the probe across the selected area of the specimen surface. The probe
interacts with the morphological details of the surface and gathers infor-
mation related to the properties of the surface being scanned. Inter-atomic
forces between the probe tip and the specimen surface cause the cantilever
to defl ect as the surface topography or other surface properties change. A
laser light refl ected from the back of the cantilever measures the defl ection
of the cantilever which is fed back to a computer. The defl ection data gen-
erate a map of topography or other property of interest. Various classes of
data are collected as the probe is raster scanned across the specimen and
analyzed by a computer to form a map of the measured property relative
to the
x-y
position. This surface map or image can be further manipulated
to extract the maximum amount of relevant information though the use
of image analysis software. Areas from 100 m
2
to less than 100 nm
2
can be
imaged. The various components of the AFM are shown in Fig. 1.12.
Detector and
feedback
electronics
Photodiode
Laser
Cantilever and tip
Sample surface
PZT scanner
1. 12
Components of an atomic force microscope (AFM).
