Scanning Electron Microscopy

What is an SEM?

What is an SEM? A Scanning Electron Microscope is an instrument that investigates the surfaces of solid samples by using a beam of electrons in a vacuum.

What is an SEM? A Scanning Electron Microscope is an instrument that investigates the surfaces of solid samples by using a beam of electrons in a vacuum. The image is generated by the secondary emissions from the sample.

Advantages of using an SEM instead of a light microscope

Advantages of using an SEM instead of a light microscope Imaging high resolution (because of short wavelength) - >1.4nm

Advantages of using an SEM instead of a light microscope Imaging high resolution (because of short wavelength) - >1.4nm Secondary electron imaging for topology

Advantages of using an SEM instead of a light microscope Imaging high resolution (because of short wavelength) - >1.4nm Secondary electron imaging for topology Backscatter electron imaging for chemistry

Advantages of using an SEM instead of a light microscope Imaging high resolution (because of short wavelength) - >1.4nm Secondary electron imaging for topology Backscatter electron imaging for chemistry High depth of field

Advantages of using an SEM instead of a light microscope Imaging high resolution (because of short wavelength) - >1.4nm Secondary electron imaging for topology Backscatter electron imaging for chemistry High depth of field Elemental Analysis – EDXS (Energy-dispersive X-ray analysis)

Advantages of using an SEM instead of a light microscope Imaging high resolution (because of short wavelength) - >1.4nm Secondary electron imaging for topology Backscatter electron imaging for chemistry High depth of field Elemental Analysis – EDXS (Energy-dispersive X-ray analysis) Structural Analysis – EBSD (Electron Back-scatter Diffraction analysis)

Advantages of using an SEM instead of a light microscope Imaging high resolution (because of short wavelength) - >1.4nm Secondary electron imaging for topology Backscatter electron imaging for chemistry High depth of field Elemental Analysis – EDXS (Energy-dispersive X-ray analysis) Structural Analysis – EBSD (Electron Back-scatter Diffraction analysis) Ease of sample preparation since most SEMs only require the sample to be conductive.

Sample Constraints

Sample Constraints Must fit in chamber (!)

Sample Constraints Must fit in chamber Must be compatible with vacuum (even for ESEM samples)

Sample Constraints Must fit in chamber Must be compatible with vacuum (even for ESEM samples) Must have conductive surface (not necessary for ESEM samples)

JEOL 5910 General-Purpose SEM

FEI XL30 FEG-ESEM

JEOL 6320 High-resolution SEM

Secondary Electron Images Give information about sample's topography

Give information about sample's chemistry BSE Images Give information about sample's chemistry

Give information about sample's composition EDS Spectra Give information about sample's composition

Give information about elemental distribution in the sample X-Ray Maps Give information about elemental distribution in the sample SE Cu Pb Sn

Electron beam strikes a crystalline material tilted at 70° Backscatter patterns composed of intersecting bands Indexable patterns Scanning Electron Microscope (SEM) strikes a crystalline material mounted at an incline around 70°, the electrons disperse beneath the surface, and diffract among the crystallographic planes. The diffracted beam produces electron backscatter patterns composed of intersecting bands, These patterns are imaged by placing a phosphor screen very close to the sample in the SEM sample chamber. The bands in the pattern are directly related to the crystal lattice structure in the sampled region. Analyzing of the pattern and bands can provide key information about the crystal structure for the measured phase such as: The symmetry of the crystal lattice is reflected in the pattern. The width and intensity of the bands are directly related to the spacing of atoms in the crystal planes. The angles between the bands are directly related to the angles between planes in the crystal lattice. Indexable patterns can be obtained from about 0.2 microns with a tungsten filament SEM and from about 0.05 microns with a field emission source.

The data obtained can be processed to create Orientation Imaging Micrographs, providing a visual representation of the crystallographic microstructure. Each point can be assigned a color or gray scale value based on a variety of parameters such as orientation, image quality, confidence index, phase, etc. Crystals with their 111 axis normal to the surface of the sample will be blue, and so on. Grain boundary Map can be obtained by comparing the orientation between each pair of neighboring points in an orientation imaging microscopy (OIM) scan. A line is drawn separating a pair of points if the difference in orientation between the points exceeds a given tolerance angle. These figures illustrate a side-by-side comparison of optical and OIM micrographs of an intergranular stress corrosion crack in a nickel- based super alloy

Center for Materials Science and Engineering Electron Microscopy SEF Location: 13-1012 Normal Working Hours: 8:30 am – 4:45 pm on M-F 24 hr accessible for evening/weekend users (not for undergraduates) Staff: Dr. Anthony (Tony) Garratt-Reed (TEM, SEM, STEM) Dr. Yong Zhang (TEM, SEM, STEM) Mr. Patrick Boisvert (SEM, Microtome)