Electron Microscopy (EM) is used for seeing otherwise invisible worlds of microspace (1 m = 10-6 m) and nanospace (1 nm = 10-9 m). By using a beam of high energy electrons, EM reveals levels of detail and complexity inaccessible by light microscopy (LM). EM provides the user with several advantages over LM, of which spatial resolution is perhaps the most eye-catching and appealing. Spatial resolution can be defined as the smallest distance between two closely opposed points, at which they may be recognized as two separate entities. The best lateral resolution possible in a LM is about 200 nm, whereas an EM can resolve features in the range of a couple of nm down to sub nm level, depending on which kind of EM is used.
Scanning Electron Microscopy (SEM)
is a very widely used technique to study surface morphology. SEMs can magnify an object from about 10 times up to over 500000 times. Essentially, the way an SEM “looks” at the surface is by scanning the object of investigation by a finely focused electron beam. An ultimate spatial resolution of approx. 2 nm with 3D appearance is easily achievable at MAC-Twente.
Dual beam Focused Ion Beam (FIB)
enables reseachers and developers to create, modify and characterize complex structures below 100 nanometers. It combines ultra-high resolution field emission scanning electron microscopy (SEM) and precise focused ion beam (FIB) etch and deposition to complement existing technology in Mesa+ NanoLab and extend many application with nanoscale prototyping, machining, 2D and 3D-characterization and RAMAN analysis. Structures such as photonic crystal prototyping, laser on a chip prototyping, nano-stamping and modification of MEMS devices like AFM tips have been created with our db-FIB. Analysis of these and other structures is enabled via several FIB-methods like cross-sectioning and TEM preparation. Combined with its SEM's ultra high resolution in-lens backscattered electron imaging phase contrast characterization, secondary ion imaging for grain contrast and STEM for nm-sized characterization makes the db-FIB one of the most versatile instruments in the MESA+NanoLab.
Transmission Electron Microscopy (TEM),
on the other hand, is used to produce images from a thin specimen by illuminating it with very high energy electrons and detecting the electrons that are transmitted through the specimen. “Transmission” means “to pass through”. In this way the internal structure of a material can be investigated. Ultimately, using TEM we can “see” columns of atoms present in crystalline samples, yielding TEM images with near atomic spatial resolution. Specimen thickness, or “thinness” is crucial for high-Q TEM imaging. As a general rule of thumb, the electron transparent TEM specimen should have a thickness less than 100 nm. For high-resolution lattice imaging, however, 30 – 50 nm or even much less, is required. Our lab is equipped with instruments to bring samples down to the required electron transparency with a minimum of damage. This can be done by mechanical polishing followed by argon ion etching, or by means of FIB.
SEM, FIB and TEM at MAC-Twente provide the user with options in these key areas:
- High spatial resolution, in combination with a large depth of field (SEM)
- Imaging and nanostructuring using electrons and ions (FIB)
- · Compositional micro and nano analysis, structural information
- · Crystal structure of solids by Electron Diffraction (ED); in SEM known as Electron Backscatter Diffraction (EBSD)
- · Large variety of imaging modes and analytical options to choose from
Henk van Wolferen
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