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1. Impact of direct exchange coupling via the insulator on the magnetic tunnel junction based molecular spintronics devices with competing molecule induced inter-electrode coupling

   https://doi.org/10.1063/9.0000225  

   Brown, Hayden; Grizzle, Andrew; D’Angelo, Christopher; Dahal, Bishnu_R; Tyagi, Pawan (January 2021, AIP Advances)

   The magnetic tunnel junction (MTJ) based molecular spintronics device (MTJMSD) approach is suitable for mass production. This approach provides solutions to fabrication difficulties related to reliably connecting molecular device elements to the ferromagnets (FMs). To producing MTJMSD, the molecular channels are bridged across the insulator of an MTJ testbed with exposed side edges. In an MTJMSD, two FMs are simultaneously connected by an insulator film and the molecular channels along the exposed sides. In our prior experimental studies, we observed that molecules could produce strong coupling between ferromagnets in the presence of the competing coupling via an insulator. In this paper, our Monte Carlo Simulation (MCS) was used to study the impact of coupling variation via insulator (a.k.a. Ji) on the magnetic properties of an MTJMSD. We studied the effect of Ji while varying the molecule induced antiferromagnetic exchange coupling. The ferromagnetic or antiferromagnetic nature and magnitude of Ji determined the resultant effect. Antiferromagnetic Ji enhanced the pre-existing antiferromagnetic molecular coupling effect. Ferromagnetic Ji competed with the opposite nature of antiferromagnetic molecular coupling. Our MCS may help to understand the impact of insulator thickness and defects on the molecular spintronics device performance and design process. 

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2. Realization of efficient 3D tapered waveguide-to-fiber couplers on a nanophotonic circuit

   https://doi.org/10.1364/OE.468738  

   Chang, Tzu-Han; Zhou, Xinchao; Tamura, Hikaru; Hung, Chen-Lung (August 2022, Optics Express)

   We report the realization of efficiently coupled 3D tapered waveguide-to-fiber couplers (TWCs) based on standard lithography techniques. The 3D TWC design is capable of achieving highly efficient flat-cleaved fiber to silicon nitride photonic waveguide coupling, withT ≈ 95 % polarization-insensitive coupling efficiency, wide bandwidth, and good misalignment tolerance. Our fabricated 3D TWCs on a functional nanophotonic circuit achieveT ≈ 85% coupling efficiency. Beyond applications in high-efficiency photon coupling, the demonstrated 3D lithography technique provides a complementary approach for mode field shaping and effective refractive index engineering, potentially useful for general applications in integrated photonic circuits. 

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3. Anisotropic leaky-like perturbation with subwavelength gratings enables zero crosstalk

   https://doi.org/10.1038/s41377-023-01184-5  

   Kabir, Md Faiyaz; Mia, Md Borhan; Ahmed, Ishtiaque; Jaidye, Nafiz; Ahmed, Syed Z.; Kim, Sangsik (June 2023, Light: Science & Applications)

   Abstract Electromagnetic coupling via an evanescent field or radiative wave is a primary characteristic of light, allowing optical signal/power transfer in a photonic circuit but limiting integration density. A leaky mode, which combines both evanescent field and radiative wave, causes stronger coupling and is thus considered not ideal for dense integration. Here we show that a leaky oscillation with anisotropic perturbation rather can achieve completely zero crosstalk realized by subwavelength grating (SWG) metamaterials. The oscillating fields in the SWGs enable coupling coefficients in each direction to counteract each other, resulting in completely zero crosstalk. We experimentally demonstrate such an extraordinarily low coupling between closely spaced identical leaky SWG waveguides, suppressing the crosstalk by ≈40 dB compared to conventional strip waveguides, corresponding to ≈100 times longer coupling length. This leaky-SWG suppresses the crosstalk of transverse–magnetic (TM) mode, which is challenging due to its low confinement, and marks a novel approach in electromagnetic coupling applicable to other spectral regimes and generic devices. 

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4. Edge‐Decorated Polycyclic Aromatic Hydrocarbons by an Oxidative Coupling Approach

   https://doi.org/10.1002/chem.202203405  

   Gilmartin, Philip; Vu, Cassandra; Rotella, Madeline; Kaur, Jasjit; Kozlowski, Marisa (December 2022, Chemistry – A European Journal)

   Abstract Oxidative phenol coupling reduces reliance on halo/metalated substrates used in conventional redox neutral couplings. A new strategy for constructing polycyclic aromatic hydrocarbons (PAHs) that incorporates oxidative phenol coupling is outlined in a three‐stage approach: oxidative fragment coupling, linking of the two resultant units, and oxidative cyclization. The protocol allows rapid assembly of both planar and helical systems with a high degree of edge functionalization. The incorporation of 12 alkoxy groups on systems with 12 rings gave rise to lower optical gaps compared to systems with a lesser degree of edge functionalization. 

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5. Four‐Selective Pyridine Alkylation via Wittig Olefination of Dearomatized Pyridylphosphonium Ylides

   https://doi.org/10.1002/anie.202109271  

   Fricke, Patrick_J; Dolewski, Ryan_D; McNally, Andrew (August 2021, Angewandte Chemie International Edition)

   Abstract Methods to synthesize alkylated pyridines are valuable because these structures are prevalent in pharmaceuticals and agrochemicals. We have developed a distinct approach to construct 4‐alkylpyridines using dearomatized pyridylphosphonium ylide intermediates in a Wittig olefination‐rearomatization sequence. PyridineN‐activation is key to this strategy, andN‐triazinylpyridinium salts enable coupling between a wide variety of substituted pyridines and aldehydes. The alkylation protocol is viable for late‐stage functionalization, including methylation of pyridine‐containing drugs. This approach represents an alternative to metal‐catalyzedsp²‐sp³cross‐coupling reactions and Minisci‐type processes. 

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