Three-dimensional ion micro-tomography

The technique of ion micro-tomography (IMT) provides three-dimensional dist ribution information about a sample's mass density and elemental compositio n. The required data are obtained by doing a scanning transmission ion micr oscopy (STIM) tomography experiment followed by a particle-induced X-ray em ission (PIXE) tomography experiment. The experiment times have been vastly reduced now that data are collected with MicroDAS, the new fast data acquis ition system. Moreover, the experiment is easier to perform because sample manipulation is automated via computer control. To obtain comparable spatia l resolutions between the STIM and PIXE data, the PIXE tomography experimen t is performed by implementing a large solid angle between the sample and X -ray detector. To correct for the inherent three-dimensional nature of such an experimental setup, a specially developed tomographic reconstruction te chnique is used to combine the STIM and PIXE tomography data sets to create an accurate quantitative tomogram of the sample. The efficacy of the entir e IMT process is tested with a characterised "standard" sample. The calcula ted data agree well with the quantitative and structural information known about the sample. To interpret the three-dimensional distribution informati on, a special volume rendering program is used to visualise various aspects of the tomogram. Each aspect is colour coded to facilitate the easy visual isation of multiple complex three-dimensional structures. (C) 2001 Elsevier Science B.V. All rights reserved.