CCI Newsletter, No. 29, June 2002

The Science of Conservation: CCI's New Variable-pressure Scanning Electron Microscope with X-ray Spectrometers

by Ian N.M. Wainwright, Manager, Analytical Research Laboratory

Scanning electron microscopy and X-ray microanalysis are important techniques in conservation. They can provide information on the composition, morphology, and structure of a wide range of materials and artifact samples,¹ and are essential for many of the projects CCI undertakes.

The Institute has had a scanning electron microscope (SEM) since 1973. The first one was replaced in 1985, and funding was recently received from the Department of Canadian Heritage to replace the now-aging 1985 system. The new microscope (an Hitachi S-3500N variable-pressure SEM) was delivered in March 2002; the old one (an Hitachi S530) has been loaned to the Canadian Museum of Nature where it will be used in the museum's research and public programs.

The new SEM is equipped with Oxford Instruments X-ray energy and X-ray wavelength spectrometers, a Robinson backscattered electron detector, an environmental secondary electron detector, a 5-axis motorized stage, and a cooling stage. The X-ray wavelength spectrometer is a more sensitive detector for chemical elements and also has much better X-ray spectral resolution than the X-ray energy spectrometer. The two detectors combined provide sensitive, accurate, and fast analyses of chemical elements with atomic number 5 (boron) and higher in the periodic table of elements. The variable-pressure SEM also allows samples to be examined without having to be coated with a conductive layer — a procedure that is required with conventional, high-vacuum SEMs. This means that a wider variety of samples can be examined, including entire artifacts. With the cooling stage, even wet or viscous samples can be studied.

The manufacture, acquisition, delivery, and installation of this system was a success thanks to the collaboration of Hitachi High-Technologies Canada (Hitachi Scientific Instruments), Oxford Instruments, Canberra-Packard Canada, Public Works and Government Services Canada, and CCI's procurement, financial, and building services staff.

1. 1. Wainwright, I.N.M. "Scanning Electron Microscopy and X-Ray Microanalysis at CCI." CCI Newsletter No. 12 (September 1993), pp. 8-9. [Also published as « Microscopie électroni-que à balayage et micro-analyse aux rayons X à l'ICC », in the same issue.]