Electron Optic Documents

Cryo-SEM imaging is a powerful tool in studying the structures of electron beam and vacuum sensitive materials. These materials include: fragile biological structures such as fungi, plants, cells, etc. as well as soft or volatile samples and even liquids. Cryo-SEM offers some clear advantages by rapidly freezing a sample prior to imaging, thus maintaining the sample as close as possible to its natural state. Long dehydration and chemical fixation steps can be avoided. Inhibiting dehydration helps maintain delicate structures without shrinkage. Moreover, volatile or even liquid samples are stabilized under the electron beam. Cryo fracturing techniques allow for study of the internal microstructure of these types of vulnerable materials as well. A few of the disadvantages are that for efficient freezing, the sample size must be small and the price may not be in everyone’s budget for a state-of-the-art cryo system with freezing station, cold stage, vacuum transfer system etc.

When a sample is exposed to the electron beam in a scanning electron microscope a variety of signals are generated. X-rays being one of those signals that can provide valuable insight into a materials chemical makeup. The collected X-ray signal includes background X-ray radiation and more importantly, X-rays of specific energies, that are characteristic of the elements present in the sample. For this reason, an energy dispersive X-ray detector (EDS) is one of the most common detectors that is added to a scanning electron microscope (SEM). It is used to not only determine the elements present in a sample but in many instances can give insight to the quantity as well as the spatial distribution of these elements over very small volumes.

The first commercially available SEM was introduced over 50 years ago and to this day there is still no internationally accepted standard procedure for determining the resolution in an SEM image. To add to the confusion, each SEM manufacturer relies on their own sample and methods for determining resolution. Defining the edge of a particle manually is also always subjective in nature; values will differ from one person to the next based on how that person interprets or ‘sees’ the edge of a particle.

SEM is an indispensable tool for studying the microstructure of a wide variety of materials. The images generated are inherently a 2 dimensional representation of the sample surface. Unlocking the 3rd dimension by reconstructing a 3D model from multiple SEM images can enhance our understanding of complex microstructure. This 3D view is often more intuitive and surface metrology characteristics can be calculated.

What makes the difference between a good SEM image and a stellar one? Imaging samples at the appropriate conditions, and that often means at very low accelerating voltage (low kV). It's time to give it a try! Every modern day scanning electron microscope (SEM) from the top of the line, ultra-high resolution field emission SEMs to the most economical entry level bench-top tungsten (W) thermionic SEMs have the capability of imaging samples at very low accelerating voltage (Low kV ). Low kV imaging has many benefits and this easily accessible function should not be overlooked.

Effortless sample navigation using JEOL’s Stage Navigation System (SNS). This system includes a high resolution, color CMOS camera mounted on the top of the SEM sample chamber, which captures a picture of the sample mounted on the stage. From this color picture, the user can control the position of the sample.

STEM-in-SEM (Scanning Transmission Electron Microscopy in an SEM) has become a popular technique for biologists, polymer scientists and materials scientists for its ease of use, cost effectiveness and high resolution. It is especially suited to investigating the internal structure of thin film (100-200nm) samples as well as size and shape of submicron to nanometer particles. With standard SEM imaging modes on bulk samples, there are limitations in the ultimate resolution that can be achieved due in part by the beam-sample interactions. With STEM-in-SEM, the sample is very thin and the interaction volume is small. Therefore, the resolution more closely approximates the diameter of the electron beam at the exit surface of the sample allowing for high resolution; using STEM with our state of the art FE SEMs, sub-nanometer resolution is easily achieved.

JEOL’s Three Dimensional Image Software is a program that takes stereo pair SEM images and constructs a three dimensional (3D) image of the sample surface. From this 3D image, height and contour maps can be created to provide cross sectional shape and height data. The easiest approach to creating stereo pair images is to take two images of the same area but at different tilt angles. Images can be taken with any detector, at any magnification, with high or low accelerating voltage and even in low vacuum mode. With this software, any offset to the stereo pair images can be corrected for automatically and an anaglyph image or 3D model of the surface created.