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Characterization of Chromium Impurities in $β$-Ga$_2$O$_3$
Authors:
Mark E. Turiansky,
Sai Mu,
Lukas Razinkovas,
Kamyar Parto,
Sahil D. Patel,
Sean Doan,
Ganesh Pokharel,
Steven J. Gomez Alvarado,
Stephen D. Wilson,
Galan Moody,
Chris G. Van de Walle
Abstract:
Chromium is a common transition-metal impurity that is easily incorporated during crystal growth. It is perhaps best known for giving rise to the 694.3 nm (1.786 eV) emission in Cr-doped Al$_2$O$_3$, exploited in ruby lasers. Chromium has also been found in monoclinic gallium oxide, a wide-bandgap semiconductor being pursued for power electronics. In this work, we thoroughly characterize the behav…
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Chromium is a common transition-metal impurity that is easily incorporated during crystal growth. It is perhaps best known for giving rise to the 694.3 nm (1.786 eV) emission in Cr-doped Al$_2$O$_3$, exploited in ruby lasers. Chromium has also been found in monoclinic gallium oxide, a wide-bandgap semiconductor being pursued for power electronics. In this work, we thoroughly characterize the behavior of Cr in Ga$_2$O$_3$ through theoretical and experimental techniques. $β$-Ga$_2$O$_3$ samples are grown with the floating zone method and show evidence of a sharp photoluminescence signal, reminiscent of ruby. We calculate the energetics of formation of Cr from first principles, demonstrating that Cr preferentially incorporates as a neutral impurity on the octahedral site. Cr possesses a quartet ground-state spin and has an internal transition with a zero-phonon line near 1.8 eV. By comparing the calculated and experimentally measured luminescence lineshape function, we elucidate the role of coupling to phonons and uncover features beyond the Franck-Condon approximation. The combination of strong emission with a small Huang-Rhys factor of 0.05 and a technologically relevant host material render Cr in Ga$_2$O$_3$ attractive as a quantum defect.
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Submitted 31 December, 2024;
originally announced January 2025.
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Flow Driven Oil Recovery Enhanced with Structural Disjoining Pressure
Authors:
Shane Laibach,
Egor Vinogradov,
Jasper Stedman,
M G Guru Aravindan,
Myles Geise,
Viet Sang Doan,
Sangwoo Shin,
Craig Snoeyink
Abstract:
Nanofluids have the potential to enhance oil recovery through the structural disjoining pressure, a pressure developed when nanoparticles concentrate at the three-phase contact line. A model microfluidic porous network is used to measure the percentage of oil displaced from this channel as the volume fraction of a Triton X-100 micelle nanofluid is varied from 0 - 30%. The percentage of oil displac…
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Nanofluids have the potential to enhance oil recovery through the structural disjoining pressure, a pressure developed when nanoparticles concentrate at the three-phase contact line. A model microfluidic porous network is used to measure the percentage of oil displaced from this channel as the volume fraction of a Triton X-100 micelle nanofluid is varied from 0 - 30%. The percentage of oil displaced varies nearly linearly with micellar nanoparticle volume fraction starting with 39% using deionized water and 89% using a volume fraction of 30%. While the trend is clear, significant variability between experiments was observed for a fixed nanofluid volume fraction. This indicates that surface energy heterogeneity is important for the nanofluid oil displacement performance.
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Submitted 3 October, 2023;
originally announced October 2023.
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Shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids
Authors:
Viet Sang Doan,
Dong-Ook Kim,
Craig Snoeyink,
Ying Sun,
Sangwoo Shin
Abstract:
We present the diffusiophoresis of ellipsoidal particles induced by ionic solute gradients. Contrary to the common expectation that diffusiophoresis is shape independent, here we show experimentally that this assumption breaks down when the thin Debye layer approximation is relaxed. By tracking the translation and rotation of various ellipsoids, we find that the phoretic mobility of ellipsoids is…
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We present the diffusiophoresis of ellipsoidal particles induced by ionic solute gradients. Contrary to the common expectation that diffusiophoresis is shape independent, here we show experimentally that this assumption breaks down when the thin Debye layer approximation is relaxed. By tracking the translation and rotation of various ellipsoids, we find that the phoretic mobility of ellipsoids is sensitive to the eccentricity and the orientation of the ellipsoid relative to the imposed solute gradient, and can further lead to nonmonotonic behavior under strong confinement. We show that such a shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids can be easily captured by modifying theories for spheres.
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Submitted 17 May, 2023; v1 submitted 22 February, 2023;
originally announced February 2023.