Helios G4 PFIB UXe DualBeam for Materials Science

Abstract: Micro- and nanomachining of diamond using focused ion beam (FIB) continues to generate interest in applications such as diamond anvil cells, photonic devices, micro-cantilevers and tools for imprinting applications. However, the milling rate of diamond by FIB is approximate 4X slower when compared to silicon using 30 kV Ga+ FIB. Recent instrumentation using PFIB technology and Xe+ ions offer increased milling rates because of their ability to deliver up to 30X more current compared to Ga+ FIBs. While the sputter rate of diamond using Ga+ and Xe+ differs only slightly (0.07 µm3 /nC [Ga] and 0.09 µm3 /nC [Xe]), the ability to use more current for micromachining will allow users to increase throughput significantly. Therefore, it is of interest to understand the amount of amorphous damage introduced into a sidewall of diamond. Previous results indicate that for a glancing angle ~0 degrees, up to 35 nm of amorphous damage is introduced by Ga+ FIB in single crystal diamond.

Abstract: The moderately high lateral RS gradients (on the order of tens of MPa/μm) near shot peened notches in conjunction with the shallow treatment depth (some hundreds of microns) limit the application of far-field and/or high resolution synchrotron diffraction residual stress measurement techniques. Recently proposed Focused Ion Beam - Scanning Elecron Microscope - Digital Image Correlation (FIB-SEM-DIC) based micro mechanical stress relaxation methods for the measurement of residual stress at the micron scale became suitable techniques for local evaluation of residual stresses and stress gradients in shot peened specimens. In this paper ultra-high resolution (~0.5-0.8 μm depth and 5-10 μm lateral resolution) mechanical relaxation stress measurements were used to evaluate the stress variation local to individual peening dimples in ceramic (60-120 μm diameter beads) shot peened Al-7075-T651 double notched samples having 0.15, 0.5 and 2.0 mm radii using Micro-Hole Drilling (μHD), Micro-Slot Cutting (μSC) and micro X-ray Diffraction (μXRD) methods. The micron-sized sampling volumes enabled the stress to be evaluated in individual impact craters (dimples) showing significant point-to-point variation (~ +/−150 MPa) (with certain dimples even recording tensile stresses). After around 30 μm of layer removal the heavily deformed region had largely been removed and the stress profile became much more homogeneous. At this depth the μHD and μSC results were in good accord with those from μXRD measurements which sample over a much larger volume (~40 μm depth × 50 μm laterally) showing an in-plane compressive stress of around 150 MPa far from the notches with the residual stress rising to about 200 MPa at a blunt (2 mm) notch and 500 MPa for a sharp (0.15 mm) one. Further, these recorded variations of residual stresses were correlated with microstructural features, e.g. grains, networks of sub-surface cracks, intermetallics and highly deformed sub-surface regions, revealed by large volume Serial Sectioning Tomography using Plasma Xe+ Focus Ion Beam - Scanning Electron Microscope (PFIB-SEM), EDS and EBSD maps. This allowed for the first time characterize large volume (100 × 66 × 30 μm3) of shot peened regions with resolution of dozens of nanometers and correlate residual stress depth profiles with 3D microstructural features. Finally, in (Benedetti et al. 2016, Int. J. Fatigue) these RS measurements are used to reconstruct the RS field through finite element (FE) analyses.

Abstract: Ga+ Focused Ion Beam-Scanning Electron Microscopes (FIB-SEM) have revolutionised the level of microstructural information that can be recovered in 3D by block face serial section tomography (SST), as well as enabling the site-specific removal of smaller regions for subsequent transmission electron microscope (TEM) examination. However, Ga+ FIB material removal rates limit the volumes and depths that can be probed to dimensions in the tens of microns range. Emerging Xe+ Plasma Focused Ion Beam-Scanning Electron Microscope (PFIB-SEM) systems promise faster removal rates. Here we examine the potential of the method for large volume serial section tomography as applied to bainitic steel and WC-Co hard metals. Our studies demonstrate that with careful control of milling parameters precise automated serial sectioning can be achieved with low levels of milling artefacts at removal rates some 60× faster. Volumes that are hundreds of microns in dimension have been collected using fully automated SST routines in feasible timescales (<24 h) showing good grain orientation contrast and capturing microstructural features at the tens of nanometres to the tens of microns scale. Accompanying electron back scattered diffraction (EBSD) maps show high indexing rates suggesting low levels of surface damage. Further, under high current Ga+ FIB milling WC-Co is prone to amorphisation of WC surface layers and phase transformation of the Co phase, neither of which have been observed at PFIB currents as high as 60 nA at 30 kV. Xe+ PFIB dual beam microscopes promise to radically extend our capability for 3D tomography, 3D EDX, 3D EBSD as well as correlative tomography.