Focused Ion Beam Tomography Research Articles

Focused Ion Beam Tomography of Porous Titania Thin Films

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Focused Ion Beam as New Tool for Local Investigations of the Interaction of Microcracks with Grain Boundaries

Abstract So far the interaction of microcracks with microstructural elements like grain boundaries or phase boundaries is described qualitatively well by the models of Tanaka and Navarro and De Los Rios. However, an experimentally verified quantitative description is missing due to a lack of systematic experiments. The concept by Marx and Schaef introduced a combination of a focused ion beam technique with high resolution scanning electron microscopy. It is the first method to initiate artificial microcracks with idealized crack parameters relative to selected phase and grain boundaries. This combination of characterizing and manipulating techniques on a micro-scale enables for the first time a systematic investigation of the interaction between short cracks and micro-structural barriers to check the models quantitatively. However, the geometry of the active slip planes in the adjacent grains, their misorientation angle, and the position of the grain boundary is a three-dimensional problem. Therefore the geometry was reconstructed after the crack propagation measurements by focused ion beam tomography to measure the inclination angles between the surface, the crack plane, and the grain boundary. The results should lead to a better understanding of the physical mechanisms of crack propagation through grain and phase boundaries, which is fundamental to explain the huge scatter in the short crack behavior and to develop materials with fatigue resistant grain boundaries.

3D tomographic analysis of crack morphologies in alumina and glass using FIB microscopy

3D Focused Ion Beam tomography is increasingly being used for 3D characterisation of microstructures in the 50 nm −20 μm range. Here FIB tomography has been used to study crack morphologies under Vickers microindentations in R-cut alumina and in soda-lime-silicate glass samples. 3D tomographic reconstruction of crack distribution around 100g microindentation sites shows that the crack density in alumina is very much greater than glass. In addition the cracks observed are influenced by the location of the FIB milled surface trenches due to localised stress changes.

Evolution of residual stress and crack morphologies during 3D FIB tomographic analysis of alumina

Three-dimensional focused ion beam (FIB) tomography is increasingly being used for 3D characterization of microstructures in the 50 nm-20 microm range. FIB tomography is a destructive, invasive process, and microstructural changes may potentially occur during the analysis process. Here residual stress and crack morphologies in single-crystal sapphire samples have been concurrently analyzed using Cr3+ fluorescence spectroscopy and FIB tomography. Specifically, maps of surface residual stress have been obtained from optically polished single-crystal alumina [surface orientation (1 ī 0 2)], from FIB milled surface trenches, from Vickers micro-indentation sites (loads 50 g-300 g), and from Vickers micro-indentation sites during FIB serial sectioning. The residual stress maps clearly show that FIB sputtering generates residual stress changes. For the case of the Vickers micro-indentations, FIB sputtering causes significant changes in residual stress during the FIB tomographic serial sectioning. 3D reconstruction of the crack distribution around micro-indentation sites shows that the cracks observed are influenced by the location of the FIB milled surface trenches due to localized stress changes.

Interaction of Cracks and Dislocations with Grain Boundaries Investigated by Focus Ion Beam Microscopy and Nanoindentation Technique

Abstract In this paper new techniques and combinations of common techniques are presented for creating well defined experiments to study the interaction of dislocations and cracks with interfaces under different loading conditions. So far, our knowledge results mostly from macroscopic tests like tensile tests or Wöhler tests. However, failure mechanisms operate on the microscopic level. When experiments are done on the same scale we obtain local information of the operating mechanisms instead of average data. The presented techniques are used to proof well known models as well as to investigate the physical mechanisms in detail. One of these techniques is nanoindentation which in our case is used to measure the interaction of dislocations with grain boundaries. Another technique is electron channelling contrast imaging combined with orientation gradient mapping for a further understanding of the development of self organized ordered dislocation structures. Finally artificial crack initiation and focused ion beam tomography are used to investigate the propagation of microstructural short cracks which can not be described by common fracture mechanics.

Three-dimensional analysis of coalesced bainite using focused ion beam tomography

A coarse constituent resulting from the coalescence of platelets of bainite has recently been discovered in high-strength steel weld metals. The three-dimensional shape of coalesced bainite has been investigated by serial sectioning using a focused ion beam milling facility supplemented with observations made using field emission gun scanning electron microscopy and light optical microscopy. A compilation of the sections into a three-dimensional model revealed the shape of the coalesced bainite grain to be lath-like with a length in excess of 20 μm.

Improved enzyme immobilization for enhanced bioelectrocatalytic activity of porous electrodes

Porous electrodes with increased surface area have been prepared using a template route via colloidal crystals. The ordered porous structure and the interconnections between the pores have been quantitatively characterized by Focused Ion Beam Tomography. The internal surfaces of the electrodes have been biofunctionalized with two enzymatic systems for glucose oxidation. In order to increase significantly the stability, the biocatalysts have been immobilized either by crosslinking or by incorporation in an electrodeposition paint. The modified porous electrodes show an increased overall signal and therefore a better detection limit and a higher sensitivity when used as sensors, and a potentially higher power output when employed in biofuel cells.

Investigation of small crack behaviour under cyclic loading in a dual phase steel with an FIB tomography technique

ABSTRACTDamage accumulation is investigated in the early stage of fatigue life in a ferritic martensitic dual phase steel. Microcrack initiation and propagation are influenced by microstructure, such as grain boundaries, grain orientation and/or phase distribution morphology. The dominant crack initiation pattern is one in which microcracks are generated in a ferrite grain along slip bands inclined at a certain angle with respect to the loading direction. Subsurface observation with a focused ion beam (FIB) device and additional crystallographic characterization by means of the electron backscatter diffraction (EBSD) technique show that a slip system having a high Schmid factor value is activated and results in a crack nucleus. The FIB tomography technique with the help of EBSD measurement allows a three‐dimensional investigation of small crack behaviour to be performed.

Three-Dimensional Microstructural Characterization Using Focused Ion Beam Tomography

AbstractThis article reviews recent developments and applications of focused ion beam (FIB) microscopes for three-dimensional (3D) materials characterization at the microscale through destructive serial sectioning experiments. Precise ion milling—in combination with electron-optic—based imaging and surface analysis methods—can be used to iteratively section through metals, ceramics, polymers, and electronic or biological materials to reveal the true size, shape, and distribution of microstructural features. Importantly, FIB tomographic experiments cover a critical size-scale gap that cannot be obtained with other instrumentation. The experiments encompass material volumes that are typically larger than 1000 μm3, with voxel dimensions approaching tens of nanometers, and can contain structural, chemical, and crystallographic information. This article describes the current state of the art of this experimental methodology and provides examples of specific applications to 3D materials characterization.

Focused ion beam tomography of a microelectronic device with sub-2-nm resolution

A method for implementing focused ion beam tomography with two dimensional images separated by less than 2nm per slice has been developed. The calculated resolution of the voxel dataset is estimated to be less than 1×1×2nm3 ∼2nm3. A programed antifuse structure in a field programable gate array antifuse structure was analyzed using this method of imaging, showing the individual nanoscale components of the antifuse structure and the fusing region.

Interaction of cracks with precipitates and grain boundaries: Understanding crack growth mechanisms through focused ion beam tomography

Focused ion beam tomography is a new powerful tool to investigate the three-dimensional (3-D) spreading of microcracks. In this study, the interaction between a fatigue microcrack with a grain boundary decorated by carbide precipitates in a directionally solidified Ni base alloy is investigated. The carbide precipitates strongly influence crack growth by initiating geometrically necessary steps in the crack plane. 3-D reconstruction shows that the sub-surface orientation of grain boundaries is an important factor for interpreting crack growth rate at the surface.

Analysis of the three-dimensional ordering of epitaxial Ge quantum dots using focused ion beam tomography

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.

Focused ion-beam tomography

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 three-dimensional volumes, and extracting quantitative information.

Analysis of the Three-Dimensional Nanoscale Relationship of Ge Quantum Dots in a Si Matrix Using Focused Ion Beam Tomography.

AbstractIt 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.

3D determination of grain shape in a FeAl-based nanocomposite by 3D FIB tomography

The 3D shapes of individual grains in an extruded FeAl nanocomposite have been determined by a new method of 3D focused ion beam (FIB) tomographic analysis. Sequential 2D sectioning and imaging of grains using a FIB, and computer reconstruction can locate the grain boundaries with better than 100 nm precision.

Nickel and molybdenum contact allergies in patients with coronary in-stent restenosis

ZrO2-10 mol.% SiO2 composite coatings has been produced on 316L stainless steel, surface treated using mechanical polishing, electropolishing and anodic oxidizing procedures. For this purpose, the composite particles were prepared using sol-gel processing method, electrophoretically deposited on pre-treated substrate and then sintered at 1100 °C. The evaluations confirmed firm attachment of the coating deposited on the oxidized 316L surface, providing a dual-structure interface including dense and porous layer. Focused ion beam tomography technique was applied to study the interface. In this regard, the interface structure was reconstructed and a model was proposed based on acquired three dimensional images to describe the interlayer formation mechanism on the anodic oxidized substrate. Corrosion studies in a simulated body fluid solution indicated that the highest barrier effect was obtained on anodically oxidized surface post coating. This sample revealed the lowest corrosion current density of 0.95 nA cm−2 after 24 h immersion.