arXiv subjects

Shantal Adajian

Publications and source records attributed to Shantal Adajian.

4 recordsLinked to original sources

arXiv2026

Reversible Modulation of Thermal Conductivity in GaN through Strain-Field Screening around Dislocations

Crystalline defects are generally regarded as static phonon scatterers that irreversibly suppress thermal transport. Here we show that elastic strain can reversibly modify dislocation-associated strain fields and strongly alter heat conduction. Using in situ strain-dependent time-domain thermoreflectance measurements, we observe a reversible enhancement of thermal conductivity in GaN by 23% under only 0.21% uniaxial strain. High-resolution X-ray diffraction reveals progressive narrowing of the symmetric (0002) reflection, indicating a reduction in the distribution of lattice rotations and heterogeneous strain. High-resolution electron backscatter diffraction directly shows that the spatial autocorrelations of multiple strain components decay over progressively shorter distances with applied strain, providing real-space evidence for enhanced screening of long-range strain fields. Raman spectroscopy further shows a non-monotonic evolution of the $E_{2}^{\mathrm{high}}$ phonon linewidth near the onset of the thermal-conductivity increase. Together, these results support a picture in which elastic strain reversibly reconfigures pinned dislocation lines and shortens the spatial range of their heterogeneous strain fields, thereby reducing phonon scattering. Our work establishes defect-associated strain correlations as a tunable degree of freedom for controlling thermal transport in crystalline solids.

cond-mat.mtrl-sci↗

arXiv2025

Electric-Field-Dependent Thermal Conductivity in Fresh and Aged Bulk Single Crystalline $\mathrm{BaTiO_3}$

Active thermal management requires advances in thermal switching materials, whose thermal conductivity responds to external stimuli. The electric field, as one of the most convenient and effective stimuli, has shown great potential in tuning the thermal conductivity of ferroelectric materials. While previous studies on electric-field-induced ferroelectric thermal switching have primarily focused on thin films and bulk solid solutions with strong extrinsic interface and defect scatterings, bulk single crystals, which can offer clear insights into intrinsic thermal switching mechanisms, have received comparatively less attention. Here, we demonstrate electric-field-induced thermal switching in bulk single-crystalline $\mathrm{BaTiO_3}$ (BTO) at room temperature and elucidate the critical role of domain evolution and aging in governing heat transport. Using a customized steady-state platform with in-situ electric fields up to $\pm$10 kV/cm, we observe a modulation of thermal conductivity up to 35% in fresh BTO driven by polarization reorientation and domain restructuring. First-principles finite-temperature lattice-dynamics calculations confirm that the switching behavior primarily originates from anisotropic phonon transport associated with domain configuration rather than strain-induced changes in phonon velocities. We further reveal that both ambient aging and controlled thermal aging can enhance the switching contrast through the formation and alignment of defect dipoles that modulate phonon-defect scattering. These results establish defect-domain interactions as a powerful design parameter for ferroelectric thermal switches and demonstrate a versatile experimental platform for exploring field-tunable heat transport and phase behavior in bulk functional materials.

cond-mat.mtrl-sci↗

arXiv2025

Fast nanothermometry based on direct electron detection of electron backscattering diffraction patterns

Accurate temperature measurement at the nanoscale is crucial for thermal management in next-generation microelectronic devices. Existing optical and scanning-probe thermometry techniques face limitations in spatial resolution, accuracy, or invasiveness. In this work, we demonstrate a fast and non-contact nanothermometry method based on temperature-induced changes in electron backscattering diffraction (EBSD) patterns captured by a high-performance direct electron detector within a scanning electron microscope (SEM). Using dynamical electron simulations, we establish the theoretical temperature sensitivity limits for several semiconductors (Si, Ge, GaAs, and GaN), showing that thermal diffuse scattering (TDS) leads to a measurable smearing of Kikuchi bands in the EBSD patterns. We develop a Fourier analysis method that captures these subtle changes across the full diffraction pattern, achieving a simulated temperature sensitivity of approximately 0.15\% per K. Experimental results on silicon confirm a sensitivity of 0.14\% per K and achieve a 13-K temperature uncertainty with a 10-second acquisition time, and enable spatial temperature mapping under thermal gradients. Our approach offers a pathway toward practical and high-resolution thermal mapping directly in SEMs, expanding the toolbox for device-level thermal diagnostics.

cond-mat.mtrl-sci↗

arXiv2024

Room-temperature Magnetic Thermal Switching by Suppressing Phonon-Magnon Scattering

Thermal switching materials, whose thermal conductivity can be controlled externally, show great potential in contemporary thermal management. Manipulating thermal transport properties through magnetic fields has been accomplished in materials that exhibit a high magnetoresistance. However, it is generally understood that the lattice thermal conductivity attributed to phonons is not significantly impacted by the magnetic fields. In this study, we experimentally demonstrate the significant impact of phonon-magnon scattering on the thermal conductivity of the rare-earth metal gadolinium near room temperature, which can be controlled by a magnetic field to realize thermal switching. Using first-principles lattice dynamics and spin-lattice dynamics simulations, we attribute the observed change in phononic thermal conductivity to field-suppressed phonon-magnon scattering. This research suggests that phonon-magnon scattering in ferromagnetic materials is crucial for determining their thermal conductivity, opening the door to innovative magnetic-field-controlled thermal switching materials.

cond-mat.mtrl-sci↗