Scanning electron microscope

In summary, optical devices are limited in the level of detail they can show because of the size of the wavelength of visible light. The smallest thing that can be seen with an optical device is limited by the length of the light wave. Electron microscopes, such as the SEM, use electrons with shorter wavelengths and can achieve higher resolution. The highest resolution devices are scanning transmission microscopes. The best resolution achieved by an optical microscope so far is around 10 nm. PMMA is a type of organic resist used in electron microscopy, and can be removed using solvents such as IPA and acetone.
  • #1
Will
I know that optical devices are limited in the detail that can be seen because of the size of the wavelength of visible light. What is the limit, the smallest thing that can be seen with an optical device? Is the level of detail directly proportional to the wavelength? So what is the wavelength used by the SEM? Is this the device that can show the highest detail?
 
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  • #2
Hello Will,

I posted this once upon a time back in PF2. So far as I know this was/is the most powerful optical microscope ever built (The Universal Microscope);

http://www.rife.de/mscope/mscope1.htm
 
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  • #3
So, what is the resolution of this microscope? Wavelength? Half wavelength? Quater?
 
  • #4
SEM

SEM's today use electrons with anywhere from 2 - 50 KeV of energy and you can get ~5 nm resolution, or better, with them quite easily. The highest resolution devices are scanning transmission microscopes.

JMD
 
  • #5
Is Rife microscope a SEM?
 
  • #6
Originally posted by Alexander
Is Rife microscope a SEM?
Alexander,
Have you clicked on the link I provided?
 
  • #7
Yes. It does not say what is the resolution of Rife microscope (say, 0.1 micron for blue light, or half wavelength for visible, or anything like this).

So, the question - what is best resolution of optical microscope achieved so far - is still open.
 
  • #8
In the 1870s, a man named Ernst Abbe explained why the resolution of a microscope is limited. He said that since the microscope uses visible light and visible light has a set range of wavelengths. The microscope can't produce the image of an object that is smaller than the length of the light wave.

More details here;
http://hypertextbook.com/facts/1999/GeetikaKumar.shtml
 
  • #9
Basically, as light waves hit really small objects, they experience diffraction, and also interference. This limits the resolution you get from it. You can decrease the wavelength of you em waves to get better resolution, but then you have another problem - you have weak signal intensity because then the waves tend to go THROUGH the object, or THROUGH the receiver.
By using electrons, you can get better resolution because the debroglie wavelength of electrons are much smaller than the wavelength of standard em radiation. Hence, you experience less diffraction, less interference and hence better quality.
 
  • #10
On a good day, the SEM in our lab can resolve 10 nm. Of course, we can use it to write lines typically ~40 nm thick on a PMMA surface.

eNtRopY
 
  • #11
What is PMMA? Do you write lines to make a mask for photolithography?
 
  • #12
PMMA is polymethyl methacrylate, it's an organic resist. When PMMA is exposed to electrons, bonds between molecules is broken. So the exposed areas have a lower molcular weigth than the unexposed areas. You then use MIBK(Methyl Isobutyl Ketone) and IPA to devlop, or remove the exposed areas of PMMA. Then you can evaporate metal unto the wafer, then remove rest of the PMMA, leaving only the pattern you exposed made with a thin layer of metal.
 
  • #13
Cool. How do you remove PMMA from under metal (gold, I presume)?
 
  • #14
IPA breaks it down and removes it. Acetone also works, but not as well.

JMD
 

What is a scanning electron microscope?

A scanning electron microscope (SEM) is a type of microscope that uses a beam of electrons to create high-resolution images of the surface of a sample. It provides a detailed view of the surface, allowing scientists to study the shape, size, and composition of the sample at a nanometer scale.

How does a scanning electron microscope work?

In a scanning electron microscope, a beam of electrons is focused onto the sample using electromagnetic lenses. As the beam scans across the surface of the sample, secondary electrons are emitted and collected by detectors. These signals are then translated into an image on a screen, creating a highly magnified view of the sample.

What are the advantages of using a scanning electron microscope?

One of the main advantages of a scanning electron microscope is its high resolution, which allows for detailed imaging of the sample's surface. It also has a large depth of field, meaning that multiple layers of the sample can be in focus at the same time. Additionally, SEMs are non-destructive, meaning that the sample can be imaged without being damaged.

What are the limitations of a scanning electron microscope?

One limitation of SEMs is that they can only be used to image conductive samples, as non-conductive samples would build up a charge and distort the image. Additionally, the sample must be placed in a vacuum chamber, which can limit the types of samples that can be studied.

How is a scanning electron microscope different from other types of microscopes?

Unlike optical microscopes, which use light to create an image, SEMs use electrons. This allows for much higher resolution and magnification. Additionally, SEMs are capable of producing 3D images of the sample, while other types of microscopes typically only produce 2D images.

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