3D optical, confocal, SEM microscopy and surface topography
NPL has recently set up a 3D microscopy facility that includes Optical, Confocal and Scanning Electron Microscopes (SEM) capabilities. This enables 3D imaging of surfaces to be obtained and analysed from a nominal magnification of x1 to over x50,000. NPL is actively working with the equipment suppliers to improve the capabilities of these instruments as well as to maintain our own capabilities.
Each of these techniques offer quick and cost effective method of obtaining surface topography information compared to scanned probe microscopy or surface profilometry. As these are non contact methods, the size of the probe is not an issue and surface contamination is not affected during image acquisition.
Each of the instruments can be used for characterising surfaces of materials:
- Profile Analysis, Profile, Form, Roughness, Waviness, Bearing Curve, Depth
- Areal Analysis
- Volume Analysis
The Alicona G4 Infinite Focus Microscope produces 3D datasets from which 3D images can be generated and surface topography characterised. The instrument has a maximum depth of field of 23.5 mm, maximum vertical resolution of 10 nm and lateral resolution of 0.4 mm. The image stitching also allows large areas to be scanned into a single image field. Images obtained are in true colour. A free viewer is available for the images to be viewed in 3D on a computer screen. Images can also be supplied as stereo pairs and as anaglyph images.
The Olympus LEXT OLS3100 is a confocal laser scanning microscope, which has a high lateral resolution of 0.12 mm and vertical resolution of 10 nm and fits in between the capabilities of optical and SEM techniques, but without the need for specimen preparation required by SEM. techniques. The LEXT is ideal for imaging featureless or very low contrast surfaces and also for transparent surfaces such as glass or ceramics. The instrument is also exceptional for locating the position of small features on the nano-scale such as graphene flakes, which cannot be easily found by conventional techniques.
The Zeiss Supra SEM is used to obtain images of the surface of interest at various tilt angles almost in the same way stereo pair images are obtained. The software can then be used to produce 3D images and measurements. The system is also very useful for studying and characterising the surfaces of the materials in the SEM while they are being tested, an example is that of deformation of surfaces during scratch testing as shown in the image above.
A few examples of the areas of use of 3D microscopy for material characterisation are:
- Quality assessment of indentors for hardness testing
- Assessment of probes for scratch testing and atomic force microscopes
- Measurement of scratch testing profiles and volumes
- Measurement of indents and surface pile up
- Imaging of fracture surfaces for analysis
- Measurement of wear, corroded and eroded surfaces
- Characterisation of biomaterial surfaces
- Measurement of edge chipping effects
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