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.

The ability to obtain three-dimensional information has always been important to gain insight and understanding into material systems. Three-dimensional reconstruction often reveals information about the morphology and composition of a system that can otherwise be obscured or misinterpreted by two-dimensional images. In this article, we describe tomographic measurements with 10nm scale resolution, combining focused ion-beam processing with field-emission scanning electron microscopy to obtain a series of high-resolution two-dimensional cross-sectional images. The images were then concatenated in a computer and interpolated into three-dimensional space to assess and visualize the structure of the material. The results of this research demonstrate the use of tomographic reconstruction of Si–Si∕Ge and θ′ Al2Cu samples to reproduce the three-dimensional morphology with sub-10nm resolution.

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Buried layers in quantum dot (QD) superlattices influence the position of QDs in the subsequently grown layers through strain field interactions. Since the strain interactions are complex, a three-dimensional reconstruction of the superlattice can enhance the fundamental understanding of self-organization mechanisms. We have studied the three-dimensional relationship of QDs using focused ion beam tomography. Analysis of the reconstruction is consistent with earlier models for self-organization. QDs on successive layers form above buried QDs. In certain cases, successive QDs in a column decrease in size, resulting in the elimination of the column while QDs in other columns grow in size.

It is well documented that buried layers in quantum dot (QD) superlattices influence the position of quantum dots in the subsequently grown layers through strain field interactions (e.g.1,2, 3,4). Using the Focused Ion Beam (FIB) tomographic technique we have reconstructed the 3D relationship of successive layers of coherent Ge QDs separated by epitaxial Si capping layers - a “QD superlattice”.Techniques such as Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) can only look at a single surface layer of QDs or, in the case of Transmission Electron Microscopy (TEM), look at a two-dimensional projection of a three-dimensional volume so that 3D relationships need to be inferred. Since the strain interactions are complex, an enhanced fundamental understanding of these self-organization mechanisms can more directly be obtained from full 3D reconstructions of these structures.By capping with Si at 300°C we were able to grow QD superlattices with QDs tens of nanometers in height. This places them within the resolution of the FIB tomographic technique to reconstruct. Using the FIB we performed in-situ serial sectioning of the QD superlattice and then reconstructed the QD superlattice. The reconstruction was then analyzed to investigate the ordering of the QDs.Results from a reconstruction of a superlattice matrix will be presented with analysis of the self-ordering of the QDs. Observations of a novel self-limiting (in height) morphology, the quantum mesa, associated with the capping technique used will also be discussed.