Dear Nemat Amirjani,

There are very clear advantages and disadvantages on both sides of the microscopic methods mentioned that speak for themselves.

SEMicroscopy - advantages:

-- extremely high resolution down to the nanometer range.

-- extremely sharp images of tiny sections.

-- Quantitative chemical analysis

SEM - disadvantages:

-- Only surfaces are considered and analyzed.

-- The penetration depth of the electrons is extremely short.

-- You only see black and white or artificially generated false color images.

-- The specimen can only be viewed and magnified in a high vacuum.

-- The size of the object is limited to a few cm.

-- The automated movement of the object and the sample change only happen very slowly and in a very limited manner.

-- A SEM device is super expensive

Optical microscopy - advantages:

-- All natural colors of the spectrum of white light are shown.

-- Extreme variety of methods:

-- Transmitted light microscopy

-- Polarized light microscopy

-- The determination of amorphous and crystalline status

-- Reflected light microscopy

-- Dispersed light (dark-field) microscopy

-- Ultraviolet fluorescence microscopy

-- Confocal microscopy

-- Stereo microcroscopy

-- Raman microspectroscopy

-- phase contrast microscopy

-- The methods mentioned above can be combined as required in one device.

-- The object can be moved and the sample can be changed at any speed.

Optical microscopy – disadvantages

-- Resolution limited

-- No quantitative multi-element chemical analysis possible.

Conclusions

Optical microscopy is used at the beginning of all higher resolution (electronic) methods. I don't know of any engineer or scientist who would limit himself to just one of the two methods. Since 55 years I am using both optical as well as SEM microscopes.

Best regards,

Guenter Grundmann

Hello

In which field are you talking about characterization of microstructures, ? Biology, material?

SEM is for scanning electron microscope and it exists since 1930's, not so emerging.

And for OM, it exists now super-resolution microscopes, going beyond the light diffraction limit.

Nowadays, OM and EM are also combined to analyze the same sample, which started as correlative light electron microscopy (CLEM). Correlative microscopy now includes AFM, microCT...

Dear Nicolas Barois

Thank you for your response. We discuss this question in the field of materials engineering. Regarding emerging SEM, my point is to consider new SEMs as a replacement for OM and my point is not to mention its history. However, you did not make a clear statement about your answer. Imagine you have only one option, OM or SEM. Which one will you choose and why? Are there criteria you consider for choosing?

You are a bit late speaking about "emerging SEM". SEMs are used since 1965, for 55 years already. There should be not a question "which one microscope is better", but for what task one of them is better. There is no battle of microscopes, we just have different tools for different tasks. About one hundred years ago it was said, that one "can drive in nails with a microscope", but old hammer is still suited better for the task. SEM is indispensable in materials science, but good old OM still has its use when working with polished and etched cross sections for measuring grain size and such.

Dear Vladimir Dusevich

Thank you for your response. As I mentioned in the text, I meant the new types of SEMs with higher resolution and so forth. My main idea of discussing this question is to respond to some Journals which do not recently accept papers with OM figures and they emphasize the SEM figures. As a result, this issue has forced me to bring up this question and ask the experts' opinion of it. I have the same viewpoint on the OM since it can conduct a contrast between microstructures and make it easier for recognition of them.

Dear Nemat Amirjani,

There are very clear advantages and disadvantages on both sides of the microscopic methods mentioned that speak for themselves.

SEMicroscopy - advantages:

-- extremely high resolution down to the nanometer range.

-- extremely sharp images of tiny sections.

-- Quantitative chemical analysis

SEM - disadvantages:

-- Only surfaces are considered and analyzed.

-- The penetration depth of the electrons is extremely short.

-- You only see black and white or artificially generated false color images.

-- The specimen can only be viewed and magnified in a high vacuum.

-- The size of the object is limited to a few cm.

-- The automated movement of the object and the sample change only happen very slowly and in a very limited manner.

-- A SEM device is super expensive

Optical microscopy - advantages:

-- All natural colors of the spectrum of white light are shown.

-- Extreme variety of methods:

-- Transmitted light microscopy

-- Polarized light microscopy

-- The determination of amorphous and crystalline status

-- Reflected light microscopy

-- Dispersed light (dark-field) microscopy

-- Ultraviolet fluorescence microscopy

-- Confocal microscopy

-- Stereo microcroscopy

-- Raman microspectroscopy

-- phase contrast microscopy

-- The methods mentioned above can be combined as required in one device.

-- The object can be moved and the sample can be changed at any speed.

Optical microscopy – disadvantages

-- Resolution limited

-- No quantitative multi-element chemical analysis possible.

Conclusions

Optical microscopy is used at the beginning of all higher resolution (electronic) methods. I don't know of any engineer or scientist who would limit himself to just one of the two methods. Since 55 years I am using both optical as well as SEM microscopes.

Best regards,

Guenter Grundmann

Dear Nemat Amirjani,

please find enclosed two documents illustrating the striking differences between SEM and reflected light digital images. In a direct comparison of the two methods, you can see the polished section of a rare selenium ore from Bolivia with the typical differences in resolution and colors, width of images ca. 2 mm. Make your own judgment.

Best regards,

Guenter Grundmann

Dear Guenter Grundmann

Let me express my thanks due to your prompt and careful response. So far, based on my experience, the biggest advantage of OM is the contrast between microstructures which makes the recognization easier. My judgment about the attached figures is the latter fact that I mentioned.

Regards,

Nemat.

Dear Nemat,

Since the direct comparison between SEM (BSE) and reflected light images of the same section clearly shows the microstructures in different ways, I have here another example from Bolivia with the very rare selenium mineral species grundmannite (light-brown), watkinsonite (creme), clausthalite (off white) and krutaite (blueish- to brownish-gray). Just for fun!

Best regards,

Guenter

Dear Guenter Grundmann

Wow, outstanding!

There is no doubt these figures are a practical example of OM and; accordingly, it makes the judgment, as you mentioned above, easier for individuals. Thanks a lot for your contribution, again!

Dear Guenter Grundmann , you show pictures where SEM has advantage. What Nemat Amirjani and I are talking about is where OM has clear advantage - high contrast, good for automatic image analysis, as for calculating grain size from pictures like this one

https://static1.olympus-ims.com/data/Image/appnotes/GrainSizeAnalysis_AppNote_img1.jpg?rev=37C7