Buy Electron Microscopes After Considering These Points

Electron microscopes are a major investment. Purchasing one calls for a comprehensive plan that’ll help ensure you’re choosing the right system that’ll address both your current and future needs while preserving your budget and accelerating your research programs. 

In this article, we will discuss the considerations that you shouldn’t overlook when you buy electron microscopes. Note that each of these buying points is interlinked with each other, thus very relevant when you’re deciding which make and model to buy and the eventual performance you can expect from your new device. 

Microscope Type 

The initial step in purchasing electron microscopes is to decide what type of imaging you require in your facility. The types of samples you’ll analyze and specific information to be collected (i.e., internal features and sample surface information) should help you decide the type of imaging you’ll carry out. 

At present, there are three microscope options available commercially, namely: 

Transmission Electron Microscope (TEM)

TEMs are the original type of electron microscope that creates a magnified image of a sample by directing a high voltage electron beam towards a specimen to illuminate it. Electron beams are produced using an electron gun which is usually equipped with a tungsten filament cathode that serves as the electron beam’s source. 

Once the electron beam passes through the specimen, it gets scattered then produces an image of the specimen’s microscopic structure that you can view through the objective lens. 

TEMs are primarily designed to process image samples in transmission. Thus, you need to ensure the samples you’ll use are thin or electron transparent. 

The need for very thin specimen samples (approx less than 100) nm is the most significant drawback of the TEM. Since this is the case, a good number of biological specimens have to be dehydrated and chemically fixed to be embedded in a polymer resin so that they can be viewable with a TEM.  

Scanning Electron Microscope/Focused Ion Beam (FIB) 

An FIB setup resembles a Scanning Electron Microscope, but while SEMs employ a focused beam of electrons to capture image samples, it uses a focused beam of ions instead. This beam of ion can be operated at high beam currents for specific milling or sputtering and low beam currents for imaging. 

FIB systems are produced primarily for large semiconductor manufacturers. Most of these manufacturers feature field emitter electron sources, but cold cathode emission sources are also available.

Scanning Electron Microscope (SEM)

SEMs utilize a technique known as raster scanning to come up with magnified images of a specimen. They work by directing a focused electron beam across the rectangular area of the specimen and are specifically designed to image the surface of bulk samples, as well as cryo (hydrated) and dehydrated specimens. 

SEMs are advantageous because they employ surface processes, thus create large sample images that has a greater field depth and up to a couple of centimeters in size. Therefore, SEM images are considered a good representation of what the real shape of the specimen looks like. 

Electron Source 

After deciding on the type of imaging you require, the next part of the decision process is to determine the image resolution requirements. There are two types of emitters to choose from: 

• Thermionic emitter 
• Field emitter 

They essentially establish the system resolution. Hence is reflected in the price and added complexity of the machine. 

Thermionic Gun

A thermionic gun is ideal for imaging large specimen areas because of the large beam cross-over diameter that it features. It has stable emission and a consistent current density, making it ideal for analysis techniques like Energy-Dispersive X-ray Analysis (EDX).  

Field Emitter Gun 

A field emission gun is used to produce electron beams that are smaller in diameter. It’s more coherent and can cater to a maximum of three orders of magnitude greater current density or brightness compared to traditional thermionic emitters. As a result, spatial resolution and signal-to-noise ratio are vastly improved while providing more life and reliability than thermionic devices. 

Between the two, the field emitter gun comes with a heftier price tag, but it provides a higher resolution and performance. Since it’s a high-resolution system, certain factors, such as environmental conditions, influence machine performance. In addition to considering the specific location of the machine, you should also factor in peripheral system requirements, such as scroll pumps, water chillers, continuous power supply, and additional lab space complete with high-performance sample preparation equipment. 

Other Practical Considerations

After deciding on the machine type and detectors for sample analysis, there are specific areas to consider further before finally narrowing down your choice of manufacturer and model. These areas and the key practical issues you should evaluate when choosing an electron microscope are as follows: 

Machine Build 

Most users operate microscopes in spaces with considerations for optimal imaging conditions. However, there are instances when said devices are required to operate in harsh conditions. Thus, the primary consideration you need to look at is the robustness of the outer skeleton and the ability of the device to withstand heavy use. True enough, machines vary in design depending on the manufacturer. Specific designs are more robust than others, and the technology featured by a particular model becomes a critical factor. 

At this point, you should take a close look at key factors, including the age of the technology for the electron source, vacuum system, and lenses. On top of these, you should also consider other factors, such as: 

• Sample size
• Stage load capacity 
• Stage tilt
• Precision and stability in x, y, z 
• Stage eucentricity for dual beam systems 

These factors are primarily dependent on the type of sample and imaging that your research requires. 

Machine Environment

Several factors influence the performance of an electron microscope, including, but are not limited to, barometric pressure changes, variations in room temperature, variations in water chiller temperature, magnetic fields, vibrations, etc. It’s necessary to go over the manufacturer’s requirements to minimize adverse ambient conditions and maximize the performance of your device.   

It’s also important to consider the building location and the room where you’ll house the instrument as they are significant determinants of machine performance. Meanwhile, air buffeting within the room, vibrations from the surrounding floor, and stray magnetic fields all negatively impact your machine’s performance.

The most practical and effective way to address this problem is to isolate the machine from the factors mentioned.  

Key Takeaways 

Buying a new electron microscope can be stressful as you try to maximize your investment over a limited time span because changes in technology occurs at such a rapid pace. 

Deciding on which machine to procure requires developing a standardized and impartial testing method and a whole lot of research to help narrow down your machine choices.

You should base your choices on particular criteria that include: 

• Environmental condition requirements
• Imaging capacity and performance
• Hardware and software associated with the machine
• Sales support and servicing, among others. 

Having a general guideline that’s organized as a flow diagram showing the steps in the purchasing process should help you purchase an electron microscope that provides a problem-free optimal performance in its lifetime.