Electron microscopy techniques are dependent on the transfer of electrons between sample and microscope. For conductive samples, this can easily be achieved. However, it is necessary to coat non-conductive or poorly conducting samples with an electrically conductive coating to generate usable images.
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A high-quality coating is crucial when attempting to acquire high-quality images. Quorum Technologies has developed the Q Plus Series to offer researchers a dynamic and high-performance coating to compete with major manufacturers without the associated price tag.
The Role of Coatings in Electron Microscopy
Scanning Electron Microscopes (SEM) and Transmission Electron Microscopes (TEM) function similarly to Optical Microscopes, but instead of probing materials using light, they utilize electrons. As a result, they are the most powerful microscopy techniques in the world.
Optical microscopes are diffraction-limited (to a maximum resolution of about 200 nm). In contrast, electron microscopes can generate beams of electrons with significantly smaller wavelengths1 and exceed the resolving power of optical microscopes by several orders of magnitude.
However, utilizing the power of electrons rather than light presents a new set of challenges. Both techniques (SEM and TEM) are dependent on the transfer of electrons between sample and microscope. Thus, it can be tricky (or near impossible) to acquire a usable image signal from samples with little to no conductivity.
This is particularly true of SEM, where samples are inundated with an electron beam: poorly conductive or non-conductive samples will accumulate charge under these conditions rapidly, resulting in image distortion in addition to thermal and radiation damage to the sample.
In exceptional circumstances, the sample may accumulate sufficient charge to decelerate the primary beam, acting as an “electron mirror” and impeding any image acquisition altogether.2
To ger around this issue, a thin layer of carbon or metal is applied to poorly conducting samples. This coating makes the surface conductive, eradicating charge accumulation and facilitating a better signal which the microscope can obtain.
Coating techniques are used extensively for imaging biological or organic samples since these are generally non-conductive and damaged easily by the electron beam.
While the principal role of coating in SEM is to enhance electrical conductivity and prevent “charging,” it also has a number of other useful effects:
- A thin layer of carbon can hold in place and mechanically stabilize particulate matter and fragile organic samples.
- Coating organic samples that contain trapped gas or moisture protects both sample and microscope from being contaminated by off-gassing.
- Metallic coatings can be used to significantly reduce the volume of penetration of the electron beam, localizing scanning to the very surface of a sample. This can also increase the emission of secondary and backscattered electrons remarkably.
- Using a thermally conductive material to coat a sample, such as gold, silver, copper or aluminium, can limit thermal damage from the primary electron beam.
The Impact of Coating Quality
When working with a coated sample in an electron microscope, the coating itself is directly imaged. Therefore, the quality of the coating means that there is a limit on the quality of the images that can be acquired.
When imaging extremely small structures (such as electrospinning fibers doped with nanocrystals), applying a coating that is too thick can restrict access to useful information. It is, therefore, crucial that coating thickness can be controlled precisely and tailored to the features under assessment.3
In the worst-case scenario, poor quality coating equipment presents contamination issues that may damage samples irreparably. Researchers typically opt for cheap coaters to reduce costs, to find at the end that their costs increase due to additional microscope time and damaged samples.
The Q Plus Series from Quorum Technologies no longer makes it necessary to pay a premium to acquire advanced, cutting-edge coatings.
The Q Plus Series: Affordable and High-Quality Coating
The Q Plus Series is the latest iteration of Quorum’s world-leading range of coaters, offering state-of-the-art sputter and evaporation coating in an individual, easy-to-use platform.
Quorum’s turbomolecular-pumped coaters are appropriate for both oxidizing and non-oxidizing metals, while the company’s low-cost rotary-pumped sputter coaters are good for noble metals.
The Q Plus Series is also suitable for sputter coating and evaporating carbon coating for SEM, FE-SEM and TEM applications.
This new range of coaters has been developed to provide researchers with the capacity to exercise precise control over coating thickness, regardless of their application requirements.
For optimum performance, the Q150V Plus supplies an ultimate vacuum of 10-6 mbar, eliminating oxygen, nitrogen and water vapour from the chamber and eradicating chemical reactions throughout the sputtering process.
The Q150V Plus also facilitates the production of finer grain size and thinner coatings for ultra-high-resolution applications (beyond 200,000x magnification). Low scattering allows for the formation of high-purity amorphous carbon films of high density.
All models in the Q Plus Series come equipped with a touch-screen interface as well as status LEDs and audio notifications for intuitive and streamlined control. Integrated 16 GB memory means that over 1000 recipes can be stored, and a USB port facilitates easy upgrades and downloads of log files.
To discover more about the Q Plus Series of coaters, view the brochure or contact Quorum today.
References
- The Diffraction Barrier in Optical Microscopy. Nikon’s MicroscopyU https://www.microscopyu.com/techniques/super-resolution/the-diffraction-barrier-in-optical-microscopy.
- Goldstein, J. I. et al. Coating Techniques for SEM and Microanalysis. in Scanning Electron Microscopy and X-Ray Microanalysis: A Text for Biologist, Materials Scientist, and Geologists (eds. Goldstein, J. I. et al.) 461–494 (Springer US, 1981). doi:10.1007/978-1-4613-3273-2_10.
- Ahire, J. J., Neveling, D. P. & Dicks, L. M. T. Polyacrylonitrile (PAN) nanofibres spun with copper nanoparticles: an anti-Escherichia coli membrane for water treatment. Appl Microbiol Biotechnol 102, 7171–7181 (2018).
This information has been sourced, reviewed and adapted from materials provided by Quorum Technologies Ltd.
For more information on this source, please visit Quorum Technologies Ltd.