arXiv subjects

M. Haroon Qaiser

Publications and source records attributed to M. Haroon Qaiser.

3 recordsLinked to original sources

arXiv2026

Characterizing Dislocation Substructures in Creep-Deformed Olivine Using Electron Channeling Contrast Imaging

Olivine is the dominant mineral in Earth's upper mantle and therefore controls mantle rheology and the mechanics of plate tectonics. The constitutive laws for dislocation-mediated deformation of olivine depend on the nature, density, and arrangements of dislocations within crystals. Hence, imaging and characterizing these defects is important, albeit challenging. Traditional imaging approaches involve (1) transmission electron microscopy (TEM), which samples small areas and requires extensive preparation and (2) oxidation decoration methods that have low spatial resolution and cannot distinguish dislocations of opposite Burgers vectors. Here, we apply electron channeling contrast imaging (ECCI) to unlock insight into the deformation structures within olivine, and combined with electron backscatter diffraction (EBSD) and weighted Burgers vector (WBV) mapping as an informative route to characterize dislocation substructures in bulk materials. Specifically, we have used an ECCI workflow based on selected-area electron channeling patterns (SA-ECPs) and we apply this workflow to a single crystal of San Carlos olivine that was deformed by creep at high temperature. ECCI micrographs reveal subgrain boundaries, surface threading dislocations, and dislocation loops across representative areas. The observations demonstrate that this workflow can reliably reveal the complexity of subgrain boundaries in olivine, which can host multiple dislocation types and exhibit non-planar geometries. Despite the limited number of slip systems in olivine, subgrain boundaries can form complex, mixed assemblies. Overall, such observations can provide a variety of constraints on dislocation types, morphologies, and distributions, which are required to parameterize and calibrate models of transient and steady-state dislocation creep in olivine and other materials.

cond-mat.mtrl-sci↗

arXiv2026

Channeling-in channeling-out revisited: selected area electron channeling and electron backscatter diffraction

Scanning electron microscopy combined with electron backscatter diffraction (EBSD) and electron channeling provides rich crystallographic contrast, but the mutual influence of channeling-in and channeling-out is often simplified or neglected in quantitative analyses. In this work, we use selected-area electron channeling patterns (SA-ECPs) acquired from a single-crystal silicon wafer while recording an EBSD pattern at every incident beam direction, thereby directly probing how channeling-in affects the EBSD signal. We show that common Hough-based quality metrics (pattern quality, band contrast, and band slope), pattern-matching cross-correlation coefficients, and Fourier-based signal-to-noise ratios all exhibit strong crystallographic modulations that follow the underlying ECP, in both raw and background-corrected patterns. Similar wide-angle channeling features are also visible in conventional, low-magnification EBSD maps, indicating that channeling-in effects are relevant under routine mapping conditions and not only in specialized ECP experiments. These observations highlight that channeling-in can significantly bias quality-based interpretation of EBSD data, with consequences for methods such as pattern blurring analysis, high-resolution strain mapping, and emerging statistical or machine-learning approaches that rely on subtle variations in diffraction patterns. The combined SA-ECP and EBSD strategy presented here offers a practical framework to visualize and potentially control channeling-in/channeling-out coupling in the SEM, suggesting new routes to design experiments and detector configurations that either mitigate or intentionally exploit these dynamical effects.

cond-mat.mtrl-sci↗

arXiv2025

AstroECP: towards more practical Electron Channeling Contrast Imaging

Electron channeling contrast imaging (ECCI) is a scanning electron microscopy (SEM) based technique that enables bulk-sample characterization of crystallographic defects (e.g. dislocations, stacking faults, low angle boundaries). Despite its potential, ECCI remains underused for quantitative defect analysis as compared to transmission electron microscope (TEM) based methods. Here, we overcome barriers that limit the use of ECCI including optimizing signal-to-noise contrast, precise determination of the incident beam vector with calibrated and easy to use simulations and experimental selected area electron channeling patterns (SA-ECP). We introduce a systematic ECCI workflow, alongside a new open-source software tool (AstroECP), that includes calibration of stage tilting, SA-ECP field of view, and the energy that forms the ECP/ECCI contrast using dynamical simulations. The functionality of this workflow is demonstrated with case studies that include threading dislocations in GaAs and the cross validation of precession based ECCI-contrast, which is otherwise known as Electron Channeling Orientation Determination (eCHORD). To assist the reader, we also provide best practice guidelines for ECCI implementation to promote high-resolution defect imaging in the SEM.

cond-mat.mtrl-sci↗