Wednesday, October 22, 2008 2:00 – 3:00 pm
Room 610, M&M Building
Dr. Paul Mainwaring
5794 West Las Positas Blvd.
Pleasanton, CA 9458
The great advantage of X-ray microscopy is the ability to image the internal structure ofspecimens compared to the surface information obtained by SEM imaging. The two techniquescombine to deliver the maximum amount of structural information of the specimen. A SEMhosted X-ray ultra microscope consists of a metallic target material mounted on a high precisionsoftware-controlled positioning arm which is placed beneath the electron beam to produce apoint source of X-rays, a sample holder and a CCD camera for signal detection. Thesecomponents are fully compatible with the SEM working environment and allow switchingbetween SEM and X-ray imaging modes. The X-ray energy used can be “tuned” to increasevisibility of certain low contrast specimens. In general, spatial resolution of 200 – 400 nm can beachieved for 2D imaging.
X-ray microscopy allows the sample to be always in focus and the depth of focus enables stereo imaging and 3D micro-tomography to be carried out. Image contrast from the specimen is the result of both X-ray absorption and phase contrast mechanisms. Phase contrast arises from refraction and diffraction rather than absorption, and patented algorithms have been developed to extract this information. Variations in refractive index can occur in samples that present little variation in density and show little absorption contrast in the image. This allows fine detail,especially in low density materials which would be otherwise invisible, to be imaged using the phase contrast component of the total transmitted signal.
Recent improvements include custom built cameras for X-ray detection, robust phase contrast extraction algorithms, fast tomographic acquisition and very fast 3D reconstruction.Examples of the use of the X-ray microscope to image polymers, metal and graphite foams andbiological materials will be given.
Dr. Mainwaring received a Ph.D degree in geochemistry from the University of Toronto, Canada. In hisearly career, he joined the Canadian federal government Labs in the Department of Energy and built up a modernelectron beam and X-ray diffraction laboratory with SEMs, electron microprobe instruments and image analysissystems for materials characterization. Since 1995 he has been involved in the development of electronbackscattered diffraction systems with Oxford Instruments and EDAX/TSL. Dr. Mainwaring is now at Gatan Inc. asProduct Manager for Cathodoluminescence and X-ray Microscopy, both growing fields in the biological andmaterials research areas.