arXiv subjects

Brinthan Kanesalingam

Publications and source records attributed to Brinthan Kanesalingam.

3 recordsLinked to original sources

arXiv2026

Dynamical diffraction formalism for imaging time-dependent diffuse scattering from coherent phonons with Dark-Field X-ray Microscopy

Coherent acoustic phonons, whose damping sets the upper bound of quality factors in acoustic resonators, play a critical role in advanced telecommunication and quantum information technologies. Yet, probing their decay in the GHz regime remains challenging using conventional surface-based techniques. Dark-field X-ray microscopy (DFXM) offers a solution by enabling through-depth, non-destructive and full-field imaging of strain fields and dislocations inside bulk materials with high spatial and angular resolution. We previously used kinematic diffraction theory to describe DFXM signals based on how the Bragg peak shifts due to the strain wave, allowing us to reconstruct the frequency spectrum of coherent phonons as a function of depth through the sample. The approach of tracking the Bragg peak shifts to study phonon dynamics, however, places an upper-bound to the highest phonon frequency that can be studied, determined by the spatial resolution of the measurement. In this work, we discuss how coherent phonon dynamics can be studied with DFXM from time-dependent intensity oscillation sidebands. This approach simultaneously allows studying coherent phonon dynamics in real and reciprocal space, overcoming frequency resolution limits imposed by the real-space resolution of Bragg-peak tracking. Using Takagi-Taupin dynamical diffraction formalism, we establish the spatial and reciprocal space resolution achievable for studying the coherent phonon dynamics and evaluate conditions for observing long-lived intensity oscillations. We close by proposing experimental strategies to optimize excitation bandwidths and reciprocal-space selectivity. The formalism in the paper enables the design of DFXM experiments for quantitative, frequency-resolved measurements of acoustic phonon decay and phonon-defect interactions in bulk crystalline materials.

cond-mat.mes-hall↗

arXiv2025

Computation and Sensitivity Analysis of the Deformation-Gradient Tensor Reconstruction in Dark-Field X-ray Microscopy

Spatially resolved strain measurements are crucial to understanding the properties of engineering materials. Although strain measurements utilizing techniques such as transmission electron microscopy and electron backscatter diffraction offer high spatial resolution, they are limited to surface or thin samples. X-ray diffraction methods, including Bragg Coherent Diffraction Imaging and X-ray topography, enable strain measurements deep inside bulk materials but face challenges in simultaneously achieving both high spatial resolution and large field-of-view. Dark-field X-ray Microscopy (DFXM) offers a promising solution with its ability to image bulk crystals at the nanoscale while offering a field-of-view approaching a few hundred $μ$m. However, an inverse modeling framework to explicitly relate the angular shifts in DFXM to the strain and lattice rotation tensors is lacking. In this paper, we develop such an inverse modeling formalism. Using the oblique diffraction geometry, enabling access to noncoplanar symmetry-equivalent reflections, we demonstrate that the reconstruction of the full deformation gradient tensor ($\mathbf{F^{(g)}}$) is possible. We also develop the computational framework to both forward calculate the anticipated angular shifts and reconstruct the average $\mathbf{F^{(g)}}$ for an individual pixel from DFXM experiments. Finally, utilizing the established formalism and computational framework, we present methods for sensitivity analysis to relate individual components of the rotation or strain tensor to specific angles of DFXM. The developed sensitivity analysis also enables explicit computation of the errors associated with the reconstruction of each component. The formalism, the computational framework, and the sensitivity analysis established in this paper should assist both the interpretation of past DFXM experiments and the design of future DFXM experiments.

cond-mat.mtrl-sci↗

arXiv2025

Planar 3$ω$ and 2$ω$ Method for Increased Sensitivity to Through-Plane Thermal Properties

Accurately measuring the thermal properties of buried interfaces is crucial for understanding heat transport in multilayered materials, particularly in applications such as batteries and integrated circuits. The conventional 3$ω$ method, which uses a line heater, has limited sensitivity to through-plane thermal properties due to lateral heat spreading, especially when a highly conductive layer overlays a resistive one. Additionally, when using a line heater, there is a lower limit to the frequency of heating, below which the analytical solution assuming infinite lateral dimension is not valid. This limits analytical interpretation of 2$ω$ temperature oscillation at lower frequencies where the sensitivity to the conductivity of a buried layer is greater. To overcome these limitations, we propose a planar 3$ω$ and 2$ω$ method that enhances the sensitivity to buried layers by ensuring planar heat flow. We implement this technique using a planar metallic heater across the entire sample and validate it experimentally against the analytical solution using Feldman's algorithm. We also discuss the practical implementation details of the approach, including ensuring uniform current distribution and the required sensor layout. Our results demonstrate improved measurement sensitivity for polymer layers in silicon stacks and buried interfaces in battery electrodes, with sensitivity improvements by factors of 2-5 compared to conventional technique using a line heater.

physics.app-ph↗