Page 114 - How It Works - Book of Amazing Answers To Curious Questions, 12

� AMAZIG ANSWERS TO CURIOUS QUESTIONS

earth is How do A steady beam of
What on Electron gun
high-energy electrons is
created either by thermal
electron electrical fields
that? fired into the machine,
energy (thermionic guns) or
(field-emission guns) .
microscopes Lenses
•
A series of magnetic lenses
bend and focus the beam
into a precise spot to
Guitar string operate? ensure only a specific part
Magnification: x75 of the sample is hit by the
Here, you can see the inside of a beam at any one time.
'super-wound' guitar string under a
scanning electron microscope.
We put these marvellous magnification
machines under the microscope

hen the scanning The core principle of an SEMis that it
electron microscope uses a 'tracing' technique to produce
W ISEM) was unveiled in a replicated 3D image of the original
1935, its reception was lukewarm at sample being studied. It does this by
Fly eye best. Despite the potential to scanning its electron beam over an
Magnification: xlBO
This is a scanning electron microscope magnify objects up to 30o,ooo object and measuring the electrons
image of the drosophilidae compound times, scientists struggled to see a given off at a particular point. Using
eye of a fruit fly.
commercial use for the bulky and this process it can create a 'trace' of
Sweep
expensive machines. However, the object, and output an amplified
Scanning electromagnetic
their application was vastly image to a display. This is made coils move the focused
underestimated, and today more possible byscanningcoils, which beam across the sample
in rows, so that the whole
than 50,000 are in use worldwide, create a magnetic field that moves the sample is subjected to
largely for industrial purposes. beam across the surface of the the beam.
SEMs have a variety of modern-day sample. The smaller the area the
uses, from forensics to microchip beam sweeps across the larger the
Snowflake production and insect observation. magnification will be, and vice versa.
Magnifzcation: xlOO SEMs have many advantages over One of the most important
Computer-generated colours have been
used on this snowflake to highlight its other methods of magnification aspects of using an SEM is
crystalline structure. such as optical microscopes. For preparing a sample for observation
example, they do not rely on light and ensuring that there is nothing
for their images, which isa major that could hinder the final image.
drawback of their optical Samples must be thoroughly
counterparts. Light is unpredictable cleaned to get rid of any dust, debris
as it can diffract and bend around or alien material not native to the
objects, potentially making sample that could skew results. The
observations very difficult. As sample must also be able to conduct
Moth their name suggests, scanning electricity. If it can't, electrons will
Magnification: x75 electron microscopes instead rely not leave its surface when struck by
In this close-up view of a pyralidae moth on the release of electrons to the beam. Objects that aren't
you can see the side of its head, including
its compound eye and its proboscis. make observations. already conductive will be coated in
Inside a scanning electron a fine layer of gold or platinum in a
microscope's casing are an electron process known as 'sputter coating'.
gun, several coils, and condensing This also prevents the sample
lenses that work together to observe a becoming damaged by the beam
target sample in super-fine detail. during observation.
Bad vibrations
'' SEMs have a variety of modem­ The sample is placed on a
stage inside a chamber of
Peacock mite day uses, from forensics to microchip the machine. This must be
Magnification: x260 kept extremely still as
Here's a pest commonly found in the SEMs are very sensitive
tropics known as a peacock mite, production and insect observation '' to vibrations.
imaged here on a tea stem.

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