Electron Microscope vs. Light Microscope
Curious
smaller objects than a light microscope because "electrons are smaller
than photons".
How can this be?
I always thought photons are smaller than electrons.
OC
curious...@yahoo.com (Curious) wrote in message news:<34a4f456.04030...@posting.google.com>...
It is not a matter of "size", but of wave-length.
Visible light has a wave-length around 500 nm, which gives a maximum
resolution (in typical cases) of 100 nm (that is, one can distinguish
to points 100 nm apart).
An electron beam accelerated by a voltage of 10-20 kV can give a
resolution of 10 nm.
OC
Uncle Al
de Broglie wavelength. Charged massed particles at easily achieved
energies are manipulable by electrostatic and magnetic lenses at very
small de Broglie wavelengths. Light is not well handeled by lenses or
mirrors below about 200 nm wavelength. All leptons are literal point
particles - but they are clothed in Feynman diagrams.
Electron microscopes can achieve 1-10 angstrom resolutions. Doing
that in photons is out of the question except as a crystal structure.
What target reflects a 10 A photon or casts a meaningful shadow for
imaging?
--
Uncle Al
http://www.mazepath.com/uncleal/qz.pdf
http://www.mazepath.com/uncleal/eotvos.htm
(Do something naughty to physics)
c_ve...@spamyahoo.com
> My biology instructor said that an electron microscope can "see"
> smaller objects than a light microscope because "electrons are smaller
> than photons".
Well, your biology instructor doesn't know physics. Actually the
electrons and the photons are point-like particles (at least this is
what we think today), therefore there is no point in asking which one is
smaller.
The thing is that in forming an image of an object there is always
something called diffraction which limits the power of resolution of
your instrument. Now, the smallest distance between two points that can
be separated by your instrument is allways proportional to the
wavelength of photons or electrons, whichever you use. The wavelength
of the electrons can be modified by accelerating the electrons, and can
be made as small as you like. Therefore the electrons are better suited
for obtaining a more detailed picture than the photons.
Lubos Motl
The "size" (resolution) is determined by the wave properties of these
particles. A photon is a packet of an electromagnetic wave.
Electromagnetic waves have certain wavelength that determines the color.
The visible light's wavelength is about half a micrometer - the red light
has about 700 and the blue light about 400 nanometers. Infrared or even
radio waves are much longer, while the ultraviolet rays or even x-rays and
gamma rays are much much shorter.
OK, this means that using the visible light, you should not be able to see
finer details than a micrometer or so.
Electrons (but also shorter-wavelength electromagnetic waves, if they were
usable) can do much better because their typical wavelength is much
shorter. If they move almost by the speed of light, the wavelength is
called the Compton wavelength which is about 10^-13 meters. Slower
electrons have a longer associated "de Broglie's" wavelength - it is
lambda=hbar/p where "hbar" is Planck's constant and "p" is the momentum,
"p=mv" where "m" is the mass.
The typical size of the wave of the electrons inside the atom is
comparable to the size of the atom - a fraction of nanometer - and this
also determines the better resolution of electron microscopes.
In quantum mechanics it is true that the heavier particle you consider,
the shorter wavelength they can have, and therefore they can probe shorter
distances: lighter particles are much more "fuzzy" and "jittery" and
quantum mechanics is more important for them; for example the atoms are
much larger than the nuclei because the electrons are lighter than the
protons. For elementary particles this typical wavelength determines your
resolution, and therefore the heavier elementary particle you have, the
better resolution you can get. However composite particles, such as a
piece of dust ;-), of course do not have great resolution because it is
also reduced by the size of their internal structure, not just by the
wavelength.
______________________________________________________________________________
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and I'm not sure about the former. - Albert Einstein
Tim S
>
>
> curious...@yahoo.com (Curious) wrote in message
> news:<34a4f456.04030...@posting.google.com>...
>> My biology instructor said that an electron microscope can "see"
>> smaller objects than a light microscope because "electrons are smaller
>> than photons".
>>
>> How can this be?
>>
>> I always thought photons are smaller than electrons.
>
> It is not a matter of "size", but of wave-length.
>
> Visible light has a wave-length around 500 nm, which gives a maximum
> resolution (in typical cases) of 100 nm (that is, one can distinguish
> to points 100 nm apart).
Of course, there is electromagnetic radiation with much shorter wavelengths.
X-rays would be appropriate for imaging biological material, except for a
rather important difficulty: focussing them -- there are no X-ray lenses,
whereas electrons can be focussed using magnetic fields as lenses.
(There's also the fact that biological matter is typically rather
transparent to X-rays. Biological matter is also transparent to visible
light, but over the period since the early nineteenth century a lot of
excellent specific dyes have been developed which highlight biologically
significant materials or structures. X-ray dyes are rather harder to come
by!
However, this is less of a problem than focussing. Biological matter also
needs a lot of serious preparation to make good electron images.)
Tim
Steve McGrew
<Uncl...@hate.spam.net> wrote:
>Curious wrote:
>>
>> My biology instructor said that an electron microscope can "see"
>> smaller objects than a light microscope because "electrons are smaller
>> than photons".
>>
>> How can this be?
>>
>> I always thought photons are smaller than electrons.
>
>de Broglie wavelength. Charged massed particles at easily achieved
>energies are manipulable by electrostatic and magnetic lenses at very
>small de Broglie wavelengths. Light is not well handeled by lenses or
>mirrors below about 200 nm wavelength. All leptons are literal point
>particles - but they are clothed in Feynman diagrams.
>
>Electron microscopes can achieve 1-10 angstrom resolutions. Doing
>that in photons is out of the question except as a crystal structure.
>What target reflects a 10 A photon or casts a meaningful shadow for
>imaging?
And then there are the other possibilities: scanning probe
microscopes of various kinds. There are near-field optical scanning
probe microscopes that achieve resolutions way better than
diffraction-limited optical microscopes; and scanning tunneling
microscopes, atomic force microscopes, etc., can "see" single atoms.
Steve
Mr. B
"Lubos Motl" <mo...@feynman.harvard.edu> wrote in message
news:Pine.LNX.4.31.040304...@feynman.harvard.edu...
> On Wed, 3 Mar 2004, Curious wrote:
>
> > My biology instructor said that an electron microscope can "see"
> > smaller objects than a light microscope because "electrons are smaller
> > than photons".
> >
> > How can this be?
> > I always thought photons are smaller than electrons.
>
> The "size" (resolution) is determined by the wave properties of these
> particles. A photon is a packet of an electromagnetic wave.
> Electromagnetic waves have certain wavelength that determines the color.
> The visible light's wavelength is about half a micrometer - the red light
> has about 700 and the blue light about 400 nanometers. Infrared or even
> radio waves are much longer, while the ultraviolet rays or even x-rays and
> gamma rays are much much shorter.
>
> OK, this means that using the visible light, you should not be able to see
> finer details than a micrometer or so.
>
> Electrons (but also shorter-wavelength electromagnetic waves, if they were
> usable) can do much better because their typical wavelength is much
> shorter. If they move almost by the speed of light, the wavelength is
> called the Compton wavelength which is about 10^-13 meters. Slower
> electrons have a longer associated "de Broglie's" wavelength - it is
> lambda=hbar/p where "hbar" is Planck's constant and "p" is the momentum,
Could protons be used instead of electrons in order to achieve even better
resolution?
Mr. B.
Uncle Al
You could use a fluid electrode to beam gallium ions. What do you
think happens to the target at high beam energies and high fluences?
Where does the stuff in the beam go after hitting the target? You
have to capture it to form an image - without ruining the detector.
The Devil lays in the details.
Danny Ross Lunsford
Uncle Al wrote:
>>Could protons be used instead of electrons in order to achieve even better
>>resolution?
>
>
> You could use a fluid electrode to beam gallium ions. What do you
> think happens to the target at high beam energies and high fluences?
> Where does the stuff in the beam go after hitting the target? You
> have to capture it to form an image - without ruining the detector.
> The Devil lays in the details.
Very nice! Is this a standard thing in industrial semiconductor (say)
processes?
-danny
David Winsemius
> There's also the fact that biological matter is typically rather
> transparent to X-rays. Biological matter is also transparent to visible
> light, but over the period since the early nineteenth century a lot of
> excellent specific dyes have been developed which highlight biologically
> significant materials or structures. X-ray dyes are rather harder to come
> by!
>
That is what I was taught 35 years ago, but haven't things changed a bit?
http://www-cxro.lbl.gov/microscopy/
It would seem fairly straight-forward to load up some monoclonal antibodies
against an interesting epitope with as much iodine as they can carry and
image away. I also think you may have forgotten to mention phase contrast
microscopy.
--
David "just an old country doctor" Winsemius, MD
If the statistics are boring, then you've got the wrong numbers.
-Edward Tufte