Scanning Electron Microscope (SEM) Laboratory
掃瞄式電子顯微鏡實驗室

Acknowledgements: This equipment is financially supported by the Science and Technology Development Fund (FDCT) of Macau SAR through research project FDCT 018/2008/A. Support from the infrastructure and facility of The Institute for the Development and Quality, Macau (IDQ) is also acknowledged.

Objective

The major functions of SEM/EDS systems are to analyse the materials in the areas including microstructural analysis, failure analysis, fractography, qualitative and quantitative compositional analysis of coatings, powders, fibers and bulk materials. The SEM can allow undergraduate and research students with an interest in Materials Science to study the surface characterization and elemental compositions of materials.

Facilities

1. Scanning Electron Microscope (SEM, Hitachi S-3400N, Type I)

SEM is a microscope which uses electrons to form an image. It is one of the most versatile instruments for investigating the microstructure of a wide range of materials. Compared with optical microscope, SEM can offer many advantages such as larger depth of field, higher resolution and higher magnification.

Features:

• Resolution: 3 nm at 30 kV, WD = 5 mm, high vacuum mode
• Magnification range: 5 X – 300,000 X
• Specimen size: 200 mm diameter (max.)
• Max. height: 35 mm at WD = 10 mm
• SE & BSE detectors

2. Energy Dispersive X-ray Spectroscopy (EDS, Horiba EX-250)

Compositional analysis in the SEM is performed by measuring the energy and intensity distribution of X-ray signal generated by a focused electron beam on the specimen. With the attachment of EDS, the precise elemental compositions of materials can be obtained with high spatial resolution.

Features:

• Quantitative analysis of elements down to boron with Si(Li) detector
• Qualitative analysis of elements by mapping and line analysis

3. Ion sputter (Hitachi E1010)

For the SEM observation of non-conductive specimens such as ceramics and polymers, gold coating is required for avoiding specimens charging and keeping a high quality image. Thin layer of gold can be deposit on the specimens by the ion sputter for electrical conduction.

Experiments

Observation of multi-walled CNT SEM is a basic tool for observation and development of novel materials. With very wide magnification range (5 X to 300,000 X), it is very suitable for observing microstructure and even nanostructure of the materials. The image indicates that diameter of the carbon nanotubes is about 30 nm.
Microstructural analysis Fine cellular and dentritic patterns are observed in the laser-alloyed mild steel 1050 with Nanosteel SHS717 powder (FeCrMoMnWCB). After laser surface alloying, the microstructure consists of ferrite reinforced with fine boro-carbides and its hardness is increased.
Coating thickness measurement In many applications that involved processing of materials, the coating thickness, size and shape of grains, particles and inclusions needs to be determined. The image shows the cross-sectional view of bioactive hydroxyapatite coating (resembles the mineral constituents of human bones) on a body implant alloy Ti6Al4V fabricated by electrophoretic deposition. The thickness of the coating is about 10 µm.
Wear surface and particles analysis The images show the wear surface (upper) and debris (lower) of high-copper alloy CuCrZr used for overhead contact wires. The presence of parallel and continuous scratches in the direction of motion on the wear surface is due to the action of the dislodged debris which has the size of about 20 µm. The combined effects of friction and electric current lead to electro-mechanical wear.
Failure Analysis SEM is a versatile and useful tool for failure analysis due to the advantages of high resolution, wide magnification range, large depth of field, and possibility of compositional analysis. The image of the sensitized surface of a failed heating element (made of stainless steel 316L) reveals ditches at grain boundaries. The failure is attributed to intergranular corrosion.
EDS analysis of corrosion products Elemental composition analysis is one of the most important task for identifying the materials. The image shows incrustation and corroded surface of a stainless steel heating element used in hot potable water. High contents of Ca and O are detected indicating that compound of Ca and O is present on the surface.

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