Here you can find Answers to Frequently Asked Questions and some helpful tips and tricks …
Our SEM is delivered with a starter kit that includes most of the basic supplies you will need. However, each application has its own specific requirements to achieve the most optimal sample preparation and presentation of the sample with the SEM. That said, we are happy to recommend supplies to you that would be useful for your application based on our extensive background in sample prep. We feel like the best range for SEM supplies is available from Rave Scientific. We have listed a number of Electron Microscopy supply providers on our LINKS page.
Most desktop scanning electron microscopy systems (SEMs) and SEM systems, in general, utilize a standard tungsten filament that’s readily available in many microscopy consumable suppliers. While it’s adequate for many applications and has been the industry workhorse for a while, there are situations wherein a CeB6 electron source is the better choice.
Before proceeding, we need to note why Tungsten is the go-to choice as an electron source. Of all metals in pure form, Tungsten has the:
- Lowest vapor pressure
- Highest melting point
- Lowest thermal expansion and,
- Very high tensile strength
Although it has all these properties, Tungsten has fundamental disadvantages compared to a Cerium Hexaboride (CeB6) electron source in terms of the following:
When it comes to brightness, Tungsten supplies 106 A/cm2 sr. The lower work mechanism of a CeB6 filament yields higher beam currents at lower cathode temperatures, resulting in enhanced brightness at all acceleration voltages.
Tungsten gradually evaporates over time since it operates at white-hot temperatures. Here, the CeB6 source has the advantage since you can predict the end of its service life as it slowly degrades.
Overall, the average lifespan of Tungsten is about 100 hours depending on the vacuum, while a CeB6 source lasts 15 times longer, at approximately 1500+ hours.
Tungsten – elliptical in shape, with dimensions ranging from 50µm to 100µm
CeB6 – <25µm in dimension
These figures show that Tungsten requires a significant electron optic demagnification to achieve a small electron probe required by an SEM to have a high-quality resolution.
To recap, the advantages of a CeB6 source are:
- a more accurately predictable service life-ending
- higher brightness, and
- a steady output of high-resolution images
Its only disadvantage is the upfront cost. CeB6 filaments cost around $900 compared to $50-100 per Tungsten filament. However, note that the former lasts 15 times longer, making it less expensive in the long run. For these reasons, a CeB6 electron source is the more sensible investment between the two.
Magnification is the process of visually enlarging an object, but not physically. In many instances, it’s confused with “resolution,” which describes an imaging system’s ability to come up with a detailed display of the object that’s being imaged.
On the other hand, the distance between two distinguishable radiating points determines resolution. A microscopic imaging system may consist of numerous individual components, such as a lens, recording, and display components. Each of these factors, including the environment where the imaging is conducted, contributes to the system’s optical resolution. Optical systems are complex, and practical constraints often increase the distance between visible point sources.
While high magnification without high resolution may enable observers to view tiny microbes, it won’t allow them to identify between microbes or their sub-cellular sections. Therefore, it’s safe to say that microbiologists rely more on resolution because they want to distinguish between microbes and their subsections. However, to differentiate between two objects under a microscope, they must first magnify up to a point wherein resolution becomes relevant.
So, which of the two is more important? Magnification and resolution are two entirely different things. Although this is the case, they have an interdependent relationship.
Magnification is usually critical in scientific research, but only if the resolution is sufficient enough to see all of the fine detail in question.
Therefore, scientists need both magnification and resolution. Having the best resolution and precise magnification is always ideal for capturing the most incredible images possible.
How long does sample exchange require compared to the Phenom SEM?
Our SEM system’s have a medium size chamber that reaches its vacuum level in roughly 2.5 to 3 minutes. It can be opened in about 30 seconds from pressing “exchange” on the SEM’s front panel.
The Phenom SEM is able to exchange samples in around 30 seconds which on the surface, sounds attractive but this ability comes with a price. The Phenom SEM utilizes a unique design compared to standard SEM design by using both a column isolation valve to maintain column vacuum full-time, and a special sample holder design that is unlike any other SEM marketed.
As with many feature comparisons, there are caveats to consider. First, the SEC systems allow loading multiple samples at once while the Phenom Pro/ProX typically works with one sample at a time. So, while a single sample load time is faster with the Phenom, loading multiple samples would have the opposite result in total time required to images 4 or more samples for instance. Note that the Phenom Pro XL has ability to load multiple samples so this argument would not apply in that situation.
The Phenom Pro’s unique sample carriers are quite innovative but they also mean the maximum sample size is quite limited compared to other SEM’s with the exception of the Phenom XL which has a larger chamber. This smaller space for samples also means it is easier (faster) to evacuate that small chamber.
The CeB6 source of the Phenom requires a higher vacuum level and maintains the column at vacuum 24/7 which contributes to its ability of fast sample exchange times. See our other FAQ on Tungsten vs CeB6 sources for more info. Due to the high vacuum nature of the Phenom column, the column cannot be easily cleaned by the user. Particles from samples entering the column can be a concern for that reason and as such, Phenom suggests blowing and gentle tapping to remove loose particles on an SEM stub holding a powder or particle sample. Note though that this would then change the population statistics of a sample to be analyzed.
If your SEM workflow requires fast sample analysis, we encourage you to explain that process to your supplier. There are often alternatives and other factors to consider. If fast analysis is truly required, one possible solution is the use of a sample exchange device which can be even faster than Phenom’s exchange time. These are commonly used in large chamber SEMs. Once such device is offered by Quroum Technologies (LINK). This device allows keeping the SEM chamber at vacuum and utilizes and external sample exchange chamber. One advantage to this method is that the sample can be transported under an inert gas blanket at all times if necessary. This type of sample exchange system can be adapted to the SEC SEM systems.
Our SEM comes with a set of sample mounts that use a 9.5mm diameter connection to the sample stage. However, we routinely convert the base stage or provide parts so that you can utilize your favorite type of sample mount such as Pin Stubs, Hitachi M4 style mounts or Jeol style cylinder mounts. Our staff has indepth experience with adapting many types of mounting systems for SEM so please ask for our advice.