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1. Electrically tunable total reflection of light by oblique helicoidal cholesteric

   https://doi.org/10.1557/s43577-024-00723-8  

   Iadlovska, Olena_S ; Thapa, Kamal ; Rajabi, Mojtaba ; Mrukiewicz, Mateusz ; Shiyanovskii, Sergij_V ; Lavrentovich, Oleg_D ( June 2024 , MRS Bulletin)

   An oblique helicoidal state of a cholesteric liquid crystal (Ch_OH) is capable of continuous change of the pitch$$P$$$P$in response to an applied electric field. Such a structure reflects 50% of the unpolarized light incident along the Ch_OHaxis in the electrically tunable band determined by$$P$$$P$/2. Here, we demonstrate that at an oblique incidence of light, Ch_OHreflects 100% of light of any polarization. This singlet band of total reflection is associated with the full pitch$$P$$$P$. We also describe the satellite$$P/2$$$P/2$,$$P/3$$$P/3$, and$$P/4$$$P/4$bands. The$$P/2$$$P/2$and$$P/4$$$P/4$bands are triplets, whereas$$P/3$$$P/3$band is a singlet caused by multiple scatterings at$$P$$$P$and$$P/2$$$P/2$. A single Ch_OHcell acted upon by an electric field tunes all these bands in a very broad spectral range, from ultraviolet to infrared and beyond, thus representing a structural color device with enormous potential for optical and photonic applications.

   Pigments, inks, and dyes produce colors by partially consuming the energy of light. In contrast, structural colors caused by interference and diffraction of light scattered at submicrometer length scales do not involve energy losses, which explains their widespread in Nature and the interest of researchers to develop mimicking materials. The grand challenge is to produce materials in which the structural colors could be dynamically tuned. Among the oldest known materials producing structural colors are cholesteric liquid crystals. Light causes coloration by selective Bragg reflection at the periodic helicoidal structure formed by cholesteric molecules. The cholesteric pitch and thus the color can be altered by chemical composition or by temperature, but, unfortunately, dynamic tuning by electromagnetic field has been elusive. Here, we demonstrate that a cholesteric material in a new oblique helicoidal Ch_OHstate could produce total reflection of an obliquely incident light of any polarization. The material reflects 100% of light within a band that is continuously tunable by the electric field through the entire visible spectrum while preserving its maximum efficiency. Broad electric tunability of total reflection makes the Ch_OHmaterial suitable for applications in energy-saving smart windows, transparent displays, communications, lasers, multispectral imaging, and virtual and augmented reality.

    

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2. Strain-switchable field-induced superconductivity

   https://doi.org/10.1126/sciadv.adj5200  

   Sanchez, Joshua J ; Fabbris, Gilberto ; Choi, Yongseong ; DeStefano, Jonathan M ; Rosenberg, Elliott ; Shi, Yue ; Malinowski, Paul ; Huang, Yina ; Mazin, Igor I ; Kim, Jong-Woo ; et al ( November 2023 , Science Advances)

   Field-induced superconductivity is a rare phenomenon where an applied magnetic field enhances or induces superconductivity. Here, we use applied stress as a control switch between a field-tunable superconducting state and a robust non–field-tunable state. This marks the first demonstration of a strain-tunable superconducting spin valve with infinite magnetoresistance. We combine tunable uniaxial stress and applied magnetic field on the ferromagnetic superconductor Eu(Fe_0.88Co_0.12)₂As₂to shift the field-induced zero-resistance temperature between 4 K and a record-high value of 10 K. We use x-ray diffraction and spectroscopy measurements under stress and field to reveal that strain tuning of the nematic order and field tuning of the ferromagnetism act as independent control parameters of the superconductivity. Combining comprehensive measurements with DFT calculations, we propose that field-induced superconductivity arises from a novel mechanism, namely, the uniquely dominant effect of the Eu dipolar field when the exchange field splitting is nearly zero.

    

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3. Wide Dynamic Range in Tunable Electrochromic Bragg Stacks from Doped Semiconductor Nanocrystals

   https://doi.org/10.1002/adfm.201904555  

   Heo, Sungyeon ; Agrawal, Ankit ; Milliron, Delia J. ( July 2019 , Advanced Functional Materials)

   Electrochromic properties can be enhanced by constructing photonic architectures, in which the reflectance contributes to optical modulation along with the intrinsic dynamic absorptivity of the material. However, optimization of reflectance is challenging without a rational design approach. Here, electrochemically tunable Bragg reflectors are demonstrated that are tuned to be highly transparent in the “off” state, achieving synergistic dynamic optical modulation of absorption and reflection in the visible and near‐infrared range. These Bragg stacks are composed of alternating doped semiconductor nanocrystal (NC) layers of 5 nm sized oxygen vacancy‐doped WO_3−xand 15 nm sized 0.4 at% Sn:In₂O₃NCs. Combining judicious NC selection and processing optimization with guidance from optical simulations, optimized Bragg stacks are implemented for electrochromic window applications. NCs with high absorption coefficients are essential for strong transmission modulation, though this characteristic limits the dynamic range of the Bragg reflectance. Optimal reflectance modulation including a highly transparent “off” state is confirmed with in situ reflectance and transmittance measurement. More broadly, ligand‐stripped NCs can enable fabrication of complex device architectures on low‐cost flexible substrates. These results guide the design rules for accessing different types of doped semiconductor NC‐based tunable Bragg stacks, an exemplary photonic structure, over a broad wavelength range.

    

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4. The atmospheric oxidation of hydroxyacetone: Chemistry of activated and stabilized CH 3 C(O)CH(OH)OO• radicals between 252 and 298 K

   https://doi.org/10.1002/kin.21346  

   Orlando, John J. ; Tyndall, Geoffrey S. ( February 2020 , International Journal of Chemical Kinetics)

   The products of the Cl‐atom‐initiated oxidation of hydroxyacetone (HYAC, CH₃C(O)CH₂OH) have been examined under conditions relevant to the earth's lower atmosphere. Over the range of temperatures studied (252‐298 K), in the absence of NO_x, methylglyoxal (CH₃C(=O)CH=O, MGLY) was formed with a primary yield >84% (96 ± 9% at 298 K), while in the presence of elevated NO_x, MGLY and formic acid were both formed as major primary products. In contrast to a previous study, acetic acid was not identified as a major primary product under the conditions studied. The results are quantitatively interpreted from a consideration of the formation of a stabilized CH₃C(O)CH(OH)OO• radical, either in a ≈50% yield from the addition of O₂to CH₃C(O)CH•(OH) or in 100% yield from the addition of HO₂to MGLY. At high temperature and low NO_x, decomposition of the stabilized CH₃C(O)CH(OH)OO• radical to MGLY is favored, while lower temperatures and conditions of high NO_xfavor bimolecular reactions of the stabilized radical, with subsequent production of formic acid. Analysis of the data allows for a semiquantitative determination ofK₃ = (2.9 ± 0.4) × 10⁻¹⁶cm³molecule⁻¹, for the HO₂+ MGLY ↔ CH₃C(O)CH(OH)OO• equilibrium process at 298 K and a roughly order of magnitude increase inK₃at 252 K.

    

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5. Ultrasmall Cu Nanoparticles Supported on Crystalline, Mesoporous ZnO for Selective CO 2 Hydrogenation

   https://doi.org/10.1002/cctc.202301077  

   Hu, Mingzhen ; Lu, Xingxu ; Zhu, Chunxiang ; Yang, Tiangang ; Tan, Haiyan ; Jin, Lei ; Kerns, Peter ; Meng, Michael ; Suib, Steven L. ; Gao, Puxian ; et al ( December 2023 , ChemCatChem)

   Converting CO₂to value‐added chemicals,e. g., CH₃OH, is highly desirable in terms of the carbon cycling while reducing CO₂emission from fossil fuel combustion. Cu‐based nanocatalysts are among the most efficient for selective CO₂‐to‐CH₃OH transformation; this conversion, however, suffers from low reactivity especially in the thermodynamically favored low temperature range. We herein report ultrasmall copper (Cu) nanocatalysts supported on crystalline, mesoporous zinc oxide nanoplate (Cu@mZnO) with notable activity and selectivity of CO₂‐to‐CH₃OH in the low temperature range of 200–250 °C. Cu@mZnO nanoplates are prepared based on the crystal‐crystal transition of mixed Cu and Zn basic carbonates to mesoporous metal oxides and subsequent hydrogen reduction. Under the nanoconfinement of mesopores in crystalline ZnO frameworks, ultrasmall Cu nanoparticles with an average diameter of 2.5 nm are produced. Cu@mZnO catalysts have a peak CH₃OH formation rate of 1.13 mol h⁻¹per 1 kg under ambient pressure at 246 °C, about 25 °C lower as compared to that of the benchmark catalyst of Cu−Zn−Al oxides. Our new synthetic strategy sheds some valuable insights into the design of porous catalysts for the important conversion of CO₂‐to‐CH₃OH.

    

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