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High-resolution transmission electron microscope (hrtem)

There are high-resolution TEM (HRTEM) which have been built. In fact the resolution is sufficient to show carbon atoms in diamond separated by only 89 picometers and atoms in silicon at 78 picometers. This is at magnifications of 50 million times. The ability to determine the positions of atoms within materials has made the HRTEM a very useful tool for nano-technologies research. It is also very important for the development of semiconductor devices for electronics and photonics.

Transmission electron microscopes produce two-dimensional images.

Scanning electron microscope (sem)

The Scanning Electron Microscope (SEM) produces images by hitting the target with a primary electron beam which then excites the surface of the target. This causes secondary electrons to be emitted from the surface which are then detected. So the electron beam in the SEM is moved (or scanned) across the sample, while detectors build an image from the secondary electrons.

Generally, the transmission electron microscope's resolution is about an order of magnitude better than the SEM resolution. However, because the SEM image relies on surface processes rather than transmission it is able to image bulk samples (unlike optical microscopes and TEM which require the samples to be thin) and has a much greater depth of view, and so can produce images that are a good representation of the 3D structure of the sample.

Disadvantages of an electron microscope

Electron microscopes are expensive to buy and maintain. They are also very sensitive to vibration and external magnetic fields. This means that special facilities are required to house microscopes aimed at achieving high resolutions. Also the targets have to be viewed in vacuum, as the electrons would scatter off the molecules that make up air.

Scanning electron microscope (sem)

Scanning electron microscopes usually image conductive or semi-conductive materials best. A common preparation technique is to coat the target with a several-nanometer layer of conductive material, such as gold, from a sputtering machine; however this process has the potential to disturb delicate samples.

The targets have to be prepared in many ways to give proper detail. This may result in artifacts purely as a result of the treatment. This gives the problem of distinguishing artifacts from material, particularly in biological samples. Scientists maintain that the results from various preparation techniques have been compared, and as there is no reason that they should all produce similar artifacts, it is therefore reasonable to believe that electron microscopy features correlate with living cells.

Interesting fact

The first electron microscope prototype was built in 1931 by the German engineers Ernst Ruska and Max Knoll. It was based on the ideas and discoveries of Louis de Broglie. Although it was primitive and was not ideal for practical use, the instrument was still capable of magnifying objects by four hundred times. The first practical electron microscope was built at the University of Toronto in 1938, by Eli Franklin Burton and students Cecil Hall, James Hillier and Albert Prebus.

Although modern electron microscopes can magnify objects up to two million times, they are still based upon Ruska's prototype and his correlation between wavelength and resolution. The electron microscope is an integral part of many laboratories. Researchers use it to examine biological materials (such as microorganisms and cells), a variety of large molecules, medical biopsy samples, metals and crystalline structures, and the characteristics of various surfaces.

Uses of electron microscopes

Electron microscopes can be used to study:

  • the topography of an object - how its surface looks.
  • the morphology of particles making up an object - their shapes and sizes.
  • the composition of an object - the elements and compounds that the object is composed of and the relative amounts of them.
  • the crystallographic information for crystalline samples - how the atoms are arranged in the object.

End of chapter exercises

  1. If the following particles have the same velocity, which has the shortest wavelength: electron, hydrogen atom, lead atom?
  2. A bullet weighing 30 g is fired at a velocity of 500 m · s - 1 . What is its wavelength?
  3. Calculate the wavelength of an electron which has a kinetic energy of 1 . 602 × 10 - 19  J.
  4. If the wavelength of an electron is 10 - 9  m what is its velocity?
  5. Considering how one calculates wavelength using slits, try to explain why we would not be able to physically observe diffraction of the cricket ball in the first worked example.

Questions & Answers

what does the word emitted mean?
Mwinga Reply
to be ejected or released
Ok thanks
what are the hooke laws
Tyriek Reply
what do really asked in exam
Leiyo Reply
hi please help me how to balance redox reactions?
Brian Reply
Which equation do u wanna balance
i tried to write it but my phone just can't write it Cr2 O72-(aq) + H2S (aq) Cr3 (aq) + S(s)
show is the equation
hello. what is the difference between a primary, secondary and tertiary alcohol
Thokozani Reply
primary the C=bonded to 1 Carbon atom.... secondary=bonded to 2 carbon atoms tertiary=bonded to 3 carbon atoms
I hope you're answered
thanks Christina
My pleasure
Thank you Christina. This is very helpful 😀👍👍💯
Anytime Thokozani
How to calculate pH?
thank you guys i didn't know about the primary, secondary and tertiary alcohols
thank you Christina
Hey guys which topic does AC nd DC generator falls
thank you
can somebody help me with functional isomers
Baningi Reply
function isomer has the same molecular formula but different functional group
what's momentum
Luvelo Reply
the product of an objects mass times velocity. it is mainly prevalent in collisions.
in order to produce an interference pattern, the waves used must be what?
Methane contains C and H. This compound is
Juan Reply
ketones's functional group
Moloi Reply
Why does the carboxyl group have acidc properties?
Evi Reply
carboxylic acids
Besides improving appearance what is another reason why medal is electro plated
Elizabeth Reply
it is made of metal
what is different between Dependent variable and independent variables
difference between A.c and D.c
AC has slip rings DC has split rings commutator
to avoid rust and to improve strength and conductivity
the variable whose value doesn't depend on other is known as independent variable ex time
are UV rays dangerous?
Khathutshelo Reply
what's this?
if there is extensive exposure, it can lead to skin cancer
yes depend upon their intensity
i hv a problem with this chapter because i also have problem with Newton's laws of motion
Kearabetswe Reply
I have a problem with calculation in Newton's law of motion
me also VuyokAzi
what's the question
Which area in particular?
just get the hang if free body diagrams,know the directions.
I know how to draw free diagram I have a problem with calculation in second law
what is the wave model of atom ?
Trazy Reply
guys what is momentum
@Luvelo... Momentum is the product of an object's mass and its velocity.
the model based on wave nature of electron
Can you state the Doppler effect in words
Nombuyiselo Reply
State Coulomb's law in words
the magnitude of the electrostatic force exerted point on each other is directly proportional to the product on magnitude of charges and inversely proportional to the square distance between them
the change in frequency of the sound detected by a listener because sound source and listener have different velocity

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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