Biomedical Engineering Reference
In-Depth Information
6.3.1
tem
TEM is one of the most popular tools for characterizing nanoparticles as it can
provide high-resolution images of particles ranging in size from less than one
nanometer to hundreds of nanometers. In a TEM, electrons are fired from an elec-
tron beam at voltages ranging from 20 kV to about 120 kV toward an ultrathin
sample (hundreds of nanometers or less) within a vacuum chamber, the electrons
interact with the sample, and an image is formed from the electrons that are trans-
mitted through the sample and are focused onto an imaging plane located below the
sample holder. an example of a TEM instrument is shown in figure 6.4. In most
modern TEMs, the focused image is collected using a CCD camera. as this tech-
nique utilizes electrons that have been transmitted through a sample, the image
produced is a two-dimensional (2D) profile, which for many particle samples
allows for easy measurement of particle diameter or edge length. However, as TEM
is a high-resolution technique, the field of view is very limited, making collection
of statistically relevant numbers of particle sizes a time-consuming task. for this
reason, TEM is most often used to confirm morphology and sizing results obtained
via different methods.
figure 6.4
Tecnai Spirit transmission electron microscope from fEI Company.
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