Surface morphology analysis of HgI2 and PbI2 with interference microscopy - the challenges of measuring fragile materials and deep surface roughness

The surface morphology of lead iodide and mercuric iodide, materials being developed for use in nuclear detectors, has been measured with interference microscopy. This is not easy, since these materials are soft and brittle and present a large surface roughness (<80 μm), localised regions of thin surface films and in certain cases an evolution of the surface structure over time. These different factors can contribute to errors in the measured position of the surface. We have developed our own automated interference microscopy system, based on scanning white light interferometry and Mirau type interference objectives and adapted it for use on these difficult surfaces. Results are shown of typical signals associated with these materials to illustrate the difficulties. Some initial solutions are proposed for improving measurement accuracy, through careful use of the microscope parameters, improved algorithms and the development of a high speed, low noise, and intelligent CCD camera.