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1. Novel nitride quantum structures for infrared sensing

   https://doi.org/10.1117/12.2608173  

   Malis, Oana ; Nguyen, Trang ; Cao, Yang ; Magill, Brenden A. ; Dzuba, Brandon ; McGill, Stephen ; Garcia, Carlos ; Khodaparast, Giti A. ; Manfra, Michael J. ( March 2022 , Proc. SPIE 12009, Quantum Sensing and Nano Electronics and Photonics XVIII)

   Razeghi, Manijeh ; Khodaparast, Giti A. ; Vitiello, Miriam S. (Ed.)

   Band structure, strain, and polarization engineering of nitride heterostructures open unparalleled opportunities for quantum sensing in the infrared. Intersubband absorption and photoluminescence are employed to correlate structure with optical properties of nonpolar strain-balanced InGaN/AlGaN nanostructures grown by molecular-beam epitaxy. Mid-infrared intersubband transitions in m-plane (In)AlxGa1-xN/In0.16Ga0.84N (0.19x0.3) multi-quantum wells were observed for the first time in the range of 3.4-5.1 μm (244-360 meV). Direct and attenuated total-reflection infrared absorption measurements are interpreted using structural information revealed by high-resolution x-ray diffraction and transmission electron microanalysis. The experimental intersubband energies are better reproduced by calculations using the local-density approximation than the Hartree-Fock approximation for the exchange-correlation correction. The effect of charge density, quantum well width, and barrier alloy composition on the intersubband transition energy was examined to evaluate the potential of this material for practical infrared applications. Temperature-dependent continuous-wave and time-resolved photoluminescence (TRPL) measurements are also investigated to probe carrier localization and recombination in m-plane InGaN/AlGaN quantum wells. Average localization depths of 21 meV and 40 meV were estimated for the undoped and doped structures, respectively. Using TRPL, dual localization centers were identified in undoped structures, while a single type of localization centers was found in doped structures. At 2 K, a fast decay time of approximately 0.3ns was measured for both undoped and doped structures, while a longer decay time of 2.2 ns was found only for the undoped sample. TRPL in magnetic field was explored to examine the effect of doping sheets on carrier dynamics. 

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2. Elimination of remnant phases in low-temperature growth of wurtzite ScAlN by molecular-beam epitaxy

   https://doi.org/10.1063/5.0118075  

   Dzuba, Brandon ; Nguyen, Trang ; Sen, Amrita ; Diaz, Rosa E. ; Dubey, Megha ; Bachhav, Mukesh ; Wharry, Janelle P. ; Manfra, Michael J. ; Malis, Oana ( November 2022 , Journal of Applied Physics)

   Growth of wurtzite Sc x Al 1−x N (x < 0.23) by plasma-assisted molecular-beam epitaxy on c-plane GaN at high temperatures significantly alters the extracted lattice constants of the material due to defects likely associated with remnant phases. In contrast, ScAlN grown below a composition-dependent threshold temperature exhibits uniform alloy distribution, reduced defect density, and atomic-step surface morphology. The c-plane lattice constant of this low-temperature ScAlN varies with composition as expected from previous theoretical calculations and can be used to reliably estimate alloy composition. Moreover, lattice-matched Sc 0.18 Al 0.82 N/GaN multi-quantum wells grown under these conditions display strong and narrow near-infrared intersubband absorption lines that confirm advantageous optical and electronic properties. 

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3. Charge-clustering induced fast ion conduction in 2LiX-GaF 3 : A strategy for electrolyte design

   https://doi.org/10.1126/sciadv.adj9930  

   Patel, Sawankumar V. ; Lacivita, Valentina ; Liu, Haoyu ; Truong, Erica ; Jin, Yongkang ; Wang, Eric ; Miara, Lincoln ; Kim, Ryounghee ; Gwon, Hyeokjo ; Zhang, Rongfu ; et al ( November 2023 , Science Advances)

   2LiX-GaF₃(X = Cl, Br, I) electrolytes offer favorable features for solid-state batteries: mechanical pliability and high conductivities. However, understanding the origin of fast ion transport in 2LiX-GaF₃has been challenging. The ionic conductivity order of 2LiCl-GaF₃(3.20 mS/cm) > 2LiBr-GaF₃(0.84 mS/cm) > 2LiI-GaF₃(0.03 mS/cm) contradicts binary LiCl (10⁻¹²S/cm) < LiBr (10⁻¹⁰S/cm) < LiI (10⁻⁷S/cm). Using multinuclear⁷Li,⁷¹Ga,¹⁹F solid-state nuclear magnetic resonance and density functional theory simulations, we found that Ga(F,X)_npolyanions boost Li⁺-ion transport by weakening Li⁺-X⁻interactions via charge clustering. In 2LiBr-GaF₃and 2LiI-GaF₃, Ga-X coordination is reduced with decreased F participation, compared to 2LiCl-GaF₃. These insights will inform electrolyte design based on charge clustering, applicable to various ion conductors. This strategy could prove effective for producing highly conductive multivalent cation conductors such as Ca²⁺and Mg²⁺, as charge clustering of carboxylates in proteins is found to decrease their binding to Ca²⁺and Mg²⁺.

    

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4. Infrared-active phonon modes and static dielectric constants in α -(Al x Ga 1− x ) 2 O 3 (0.18  ≤ x  ≤ 0.54) alloys

   https://doi.org/10.1063/5.0085958  

   Stokey, Megan ; Gramer, Teresa ; Korlacki, Rafał ; Knight, Sean ; Richter, Steffen ; Jinno, Riena ; Cho, Yongjin ; Xing, Huili Grace ; Jena, Debdeep ; Hilfiker, Matthew ; et al ( March 2022 , Applied Physics Letters)

   We determine the composition dependence of the transverse and longitudinal optical infrared-active phonon modes in rhombohedral α-(Al_xGa_1−x)₂O₃alloys by far-infrared and infrared generalized spectroscopic ellipsometry. Single-crystalline high quality undoped thin-films grown on m-plane oriented α-Al₂O₃substrates with x =  0.18, 0.37, and 0.54 were investigated. A single mode behavior is observed for all phonon modes, i.e., their frequencies shift gradually between the equivalent phonon modes of the isostructural binary parent compounds. We also provide physical model line shape functions for the anisotropic dielectric functions. We use the anisotropic high-frequency dielectric constants for polarizations parallel and perpendicular to the lattice c axis measured recently by Hilfiker et al. [Appl. Phys. Lett. 119, 092103 (2021)], and we determine the anisotropic static dielectric constants using the Lyddane–Sachs–Teller relation. The static dielectric constants can be approximated by linear relationships between those of α-Ga₂O₃and α-Al₂O₃. The optical phonon modes and static dielectric constants will become useful for device design and free charge carrier characterization using optical techniques.

    

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5. Peculiarities of crystal structures and photophysical properties of Ga III /Ln III metallacrowns with a non-planar [12-MC-4] core

   https://doi.org/10.1039/c9qi01647c  

   Nguyen, Tu N. ; Eliseeva, Svetlana V. ; Chow, Chun Y. ; Kampf, Jeff W. ; Petoud, Stéphane ; Pecoraro, Vincent L. ( March 2020 , Inorganic Chemistry Frontiers)

   A new series of gallium( iii )/lanthanide( iii ) metallacrown (MC) complexes ( Ln-1 ) was synthesized by the direct reaction of salicylhydroxamic acid (H 3 shi) with Ga III and Ln III nitrates in a CH 3 OH/pyridine mixture. X-ray single crystal analysis revealed two types of structures depending on whether the nitrate counterion coordinate or not to the Ln III : [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 4 (NO 3 )](py) 2 (Ln = Gd III , Tb III , Dy III , Ho III ) and [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 5 ](NO 3 )(py) (Ln = Er III , Tm III , Yb III ). The representative Tb-1 and Yb-1 MCs consist of a Tb/YbGa 4 core with four [Ga III –N–O] repeating units forming a non-planar ring that coordinates the central Ln III through the oxygen atoms of the four shi 3− groups. Two H 2 shi − groups bridge the Ln III to the Ga III ring ions. The Yb III in Yb-1 is eight-coordinated while the ligation of the nine-coordinated Tb III in Tb-1 is completed by one chelating nitrate ion. Ln-1 complexes in the solid state showed characteristic sharp f–f transitions in the visible (Tb, Dy) and near-infrared (Dy, Ho, Er, Yb) spectral ranges upon excitation into the ligand-centered electronic levels at 350 nm. Observed luminescence lifetimes and absolute quantum yields were collected and discussed. For Yb-1 , luminescence data were also acquired in CH 3 OH and CD 3 OD solutions and a more extensive analysis of photophysical properties was performed. This work demonstrates that while obtaining highly luminescent lanthanide( iii ) MCs via a direct synthesis is feasible, many factors such as molar absorptivities, triplet state energies, non-radiative deactivations through vibronic coupling with overtones of O–H, N–H, and C–H oscillators and crystal packing will strongly contribute to the luminescent properties and should be carefully considered. 

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