Scanning Electron Microscopy

	PhenomXL G2 SEM	Phenom ProX G5 SEM
Magnification Range:	160x to 200,000x	40,000x to 100,000x
Accelerating Voltages:	4.8kV to 20kV (advanced mode)	5, 10, or 15kV
Feature Resolution:	< 50nm	< 500nm
Detectors:	Secondary (SED) & Backscatter (BSD)	Backscatter only
Capabilities:	EDS, AIM, 3DRR	EDS
Sample Dimensions:	< 10cm in diameter, <4cm tall	< 2.5cm in diameter, <3cm tall

Scanning electron microscopy (SEM) rasters an electron beam across a specific area on a sample, allowing for much higher magnifications compared to optical microscopy. The electrons are either elastically or inelastically reflected off the sample, then captured by detector(s) to yield an image.

Electron Microscopy Theory

Electron and optical microscopy share many fundamental components—specifically, a lens used to focus a specific type of source, and after either reflecting from or transmitting through the sample, a “signal” is then captured by a detector which processes inputs and spits out an image. In optical microscopy, an optical glass lens focuses photons from a lamp into either a digital camera or your eye. In electron microscopy, a series of variable magnetic fields serve as condenser lenses to focus an electron beam generated from an electron gun.

Similar to optical microscopy, electron microscopy also has both reflection and transmission modes—these are two separate imaging techniques known as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), respectively.

Types of Electron Guns

There are 2 main types of electron guns used in electron microscopy: thermionic (Schottky) emission and cold field emission. Both types required an electron source—typically this is either a single crystal of tungsten, lanthanum hexaboride (LaB₆), or cerium hexaboride (CeB₆).

Both Phenom SEMs at the MILL use thermionic emission guns with a CeB₆ source.

Related Techniques

• Optical Microscopy
• Transmission electron microscopy (TEM)