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12/29/04

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Focused Ion-Beam Tomography A.J. KUBIS, G.J. SHIFLET, D.N. DUNN, and R. HULL The focused ion beam (FIB) has become an important tool in materials science for studying and modifying materials systems at the micro and nanometer levels. The technique, due to its ability to perform precision in-situ milling, has been extended to studying three-dimensional structural and chemical relationships. With the help of computer algorithms for processing data and graphics packages for display, three-dimensional systems can easily be reconstructed and the structure interrogated to obtain both qualitative and quantitative information. It is possible to study features at spatial resolutions at the tens-of-nanometers level and volumes with dimensions of up to tens of microns. This allows the reconstruction of many systems in the size range important to nanotechnology. Practical aspects of FIB tomography will be presented, emphasizing data collection, image processing, creating threedimensional volumes, and extracting quantitative information.

I. INTRODUCTION

THE focused ion beam (FIB) allows the study of systems that have critical features with dimensions from tens of nanometers to tens of microns. This length range is increasingly important as interest in nanostructured systems grows. The FIB, in conjunction with secondary-ion mass spectrometry (SIMS) or energy-dispersive X-ray spectrometry, also allows the acquisition of elemental information from samples. The FIB uses serial sections to reconstruct three-dimensional features with the help of computer-aided rendering techniques. Since the ion beam can mill away material with close to nanometer precision and the sample can be rotated on a goniometric stage, in-situ sectioning can be performed. This eliminates the need to remove the sample from the instrument and to perform subsequent realignment. As a result, sequential slices can be obtained at smaller intervals relative to the minimum attainable when it is necessary to remove the sample from the instrument. This reduces the size of the features that can be reconstructed. With newer dual-beam instrumentation, the process can be automated, and imaging can be performed with an electron beam. Use of the electron beam reduces sample damage while automation allows the user more time to interpret data rather than perform repetitive operations. A number of factors need to be considered when performing three-dimensional reconstructions of materials by serial sectioning. 1. What is the size of the features being reconstructed relative to the instrumental resolution? 2. Some of the practical considerations in obtaining serial sections include the following. (a) Maintaining parallel slices (b) Precision in the slicing increment (c) Planarization of the surface A.J. KUBIS, Graduate Researcher, and G.J. SHIFLET and R. HULL, Professors, are with the Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904. Contact e-mail: ajk7s@ virginia.edu D.N. DUNN, formerly Post-Doc w