How Does SEM Imaging Work?

SEM Imaging stands for scanning electron microscopy imaging, a tool that has become widely used in recent years. Instead of light, SEM imaging uses electrons to create an image and finds use in the medical and physical science communities. This article will outline how the process is carried out and some of the main applications.

The Process of SEM Imaging

SEM imaging involves an electron gun firing beams and then these accelerate down the SEM column. Throughout this process, electron beams move through a range of apertures and lenses to focus the beam.

This process takes place under vacuum conditions, stopping atoms and molecules already present in the microscope column from interacting with the electron beam. This then means that the image quality is much higher, protecting the electron source from noise and vibrations.

Electron beams scan the sample in lines from side to side, top to bottom. On the surface of the sample, the electrons interact with atoms creating signals in the form of secondary electrons which is a characteristic of the sample.

SEM Imaging Components

SEM Imaging instruments include:

  • Electron source – Generates electrons at the top of the microscope column
  • Condenser lens – Controls the size of the beam, determining the levels of electrons in the beam. The size defines the resolution of the image.
  • Anode – positive charge, attracting electrons to create a beam
  • Scanning coil – deflect the beam along the x and y axes to make sure it scans in a raster pattern above the sample surface
  • Objective lens – this is the last lens in the lens sequence, creating an electron beam. Because it is closest to the sample it focuses the beam to a very small spot on the sample.

Electrons are not able to move through the glass and as such, SEM imaging lenses are electromagnetic and are formed of coil wires in a metal pole.

Currents pass through these coils creating a magnetic field to which the electrons are extremely sensitive. This enables the lenses in the microscope to control them.

Key Differences Between SEM Imaging and Optical Microscopy

Optical microscopy uses a range of lenses and light to magnify an image. Optical microscopy allows the user to view small objects such as cells however there are limits to the magnification and thus the materials that can be analyzed.

SEM Imaging can overcome the limitations of optical microscopes as they have shorter wavelengths, producing a higher resolution image.

SEM Imaging from Raith

PIONEER Two from Raith is a brilliant solution for scientists that require both SEM imaging and EBL, integrated into one turnkey system. It is user-friendly, robust, and versatile for applications in life sciences and materials.

Photo of the SEM imaging and EBL tool PIONEER Two

With a variety of secondary and backscattered electron detectors in different configurations, PIONEER Two allows the most flexible operation with a large application bandwidth. Additionally, with the integrated Laser Interferometer Controlled Stage, it delivers much better positioning and pattern placement accuracies in the nm range than an SEM – pattern generator combo. Furthermore, the Laser Interferometer Stage allows the mapping of sample areas exceeding a single field of view to nm precision by stitching SEM images together.