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1. Synthetic versatility, reaction pathway, and thermal stability of tetrahedrite nanoparticles

   https://doi.org/10.1039/d0tc03599h  

   Fasana, Christine D. ; Jensen, Mitchel S. ; García Ponte, Graciela E. ; MacAlister, Tyler R. ; Kunkel, Grace E. ; Rogers, John P. ; Ochs, Andrew M. ; Stevens, Daniel L. ; Weller, Daniel P. ; Morelli, Donald T. ; et al ( October 2020 , Journal of Materials Chemistry C)

   null (Ed.)

   Copper-antimony-sulfide compounds have desirable earth-abundant compositions for application in renewable energy technologies, such as solar energy and waste heat recycling. These compounds can be synthesized by bottom-up, solution-phase techniques that are more energy and time efficient than conventional solid-state methods. Solution-phase methods typically produce nanostructured materials, which adds another dimension to control optical, electrical, and thermal material properties. This study focuses on a modified-polyol, solution-phase synthesis for tetrahedrite (Cu 12 Sb 4 S 13 ), a promising thermoelectric material with potential also for photovoltaic applications. To dope the tetrahedrite and tune material properties, the utility of the modified polyol synthetic approach has been demonstrated as a strategy to produce phase-pure tetrahedrite that incorporates transition metal (Fe, Co, Ni, Zn, Ag) dopants for Cu, Te dopant for Sb, and Se for S. Six of these reported tetrahedrite compounds have not previously been made by solution-phase methods. For the bottom-up formation of the tetrahedrite nanomaterials, the evolution of the chemical phases has been determined by an investigation of the reaction progress as a function of temperature and time. Digenite (Cu 1.8 S), covellite (CuS), and famatinite (Cu 3 SbS 4 ) are identified as key intermediates and are consistently observed for both undoped and doped tetrahedrites. The effect of nanostructuring and doping tetrahedrite on thermal properties has been investigated. It was found that nanostructured undoped tetrahedrite has reduced thermal stability relative to samples made by solid-state methods, while the addition of dopants for Cu increased the thermal stability of the material. Crystallinity, composition, and nanostructure of products and intermediates were characterized by powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and transmission electron microscopy. Thermal properties were investigated by differential scanning calorimetry and thermal gravimetric analysis. This synthetic study with thermal property analysis demonstrates the potential of the modified polyol method to produce tetrahedrite and other copper-antimony-sulfide compounds for thermoelectric and photovoltaic applications. 

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2. Visible-light induced degradation of diphenyl urea and polyethylene using polythiophene decorated CuFe2O4 nanohybrids

   https://doi.org/10.1038/s41598-023-30669-x  

   Riaz, Ufana ; Gaffar, Shayista ; Hauser, Kristen ; Yan, Fei ( December 2023 , Scientific Reports)

   Abstract The present work reports facile synthesis of CuFe 2 O 4 nanoparticles via co-precipitation method and formulation of its nanohybrids with polythiophene (PTh). The structural and morphological properties were investigated using fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectra (SEM-EDS) and UV–Vis spectroscopy. The band gap was found to decrease with increase in the loading of PTh and was found to be 2.52 eV for 1-PTh/CuFe 2 O 4 , 2.15 eV for 3-PTh/CuFe 2 O 4 and 1.89 eV for 5-PTh/CuFe 2 O 4 . The nanohybrids were utilized as photocatalysts for visible light induced degradation of diphenyl urea. Diphenyl urea showed 65% degradation using 150 mg catalyst within 120 min. Polyethylene (PE) was also degraded using these nanohybrids under visible light as well as microwave irradiation to compare its catalytic efficiency under both conditions. Almost 50% of PE was degraded under microwave and 22% under visible light irradiation using 5-PTh/CuFe 2 O 4 . The degraded diphenyl urea fragments were analyzed using LCMS and a tentative mechanism of degradation was proposed. 

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3. The Doping Dependence of the Thermal Conductivity of Bulk Gallium Nitride Substrates

   https://doi.org/10.1115/1.4047578  

   Song, Yiwen ; Lundh, James Spencer ; Wang, Weijie ; Leach, Jacob H. ; Eichfeld, Devon ; Krishnan, Anusha ; Perez, Carlos ; Ji, Dong ; Borman, Trent ; Ferri, Kevin ; et al ( December 2020 , Journal of Electronic Packaging)

   null (Ed.)

   Abstract Gallium nitride (GaN) has emerged as one of the most attractive base materials for next-generation high-power and high-frequency electronic devices. Recent efforts have focused on realizing vertical power device structures such as in situ oxide, GaN interlayer based vertical trench metal–oxide–semiconductor field-effect transistors (OG-FETs). Unfortunately, the higher-power density of GaN electronics inevitably leads to considerable device self-heating which impacts device performance and reliability. Halide vapor-phase epitaxy (HVPE) is currently the most common approach for manufacturing commercial GaN substrates used to build vertical GaN transistors. Vertical device structures consist of GaN layers of diverse doping levels. Hence, it is of crucial importance to measure and understand how the dopant type (Si, Fe, and Mg), doping level, and crystal quality alter the thermal conductivity of HVPE-grown bulk GaN. In this work, a steady-state thermoreflectance (SSTR) technique was used to measure the thermal conductivity of HVPE-grown GaN substrates employing different doping schemes and levels. Structural and electrical characterization methods including X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS), Raman spectroscopy, and Hall-effect measurements were used to determine and compare the GaN crystal quality, dislocation density, doping level, and carrier concentration. Using this comprehensive suite of characterization methods, the interrelation among structural/electrical parameters and the thermal conductivity of bulk GaN substrates was investigated. While doping is evidenced to reduce the GaN thermal conductivity, the highest thermal conductivity (201 W/mK) is observed in a heavily Si-doped (1–5.00 × 1018 cm−3) substrate with the highest crystalline quality. This suggests that phonon-dislocation scattering dominates over phonon-impurity scattering in the tested HVPE-grown bulk GaN substrates. The results provide useful information for designing thermal management solutions for vertical GaN power electronic devices. 

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4. Stable Carbon Dots from Microwave-Heated Carbon Nanoparticles Generating Organic Radicals for In Situ Additions

   https://doi.org/10.3390/c9010005  

   Liang, Weixiong ; Singh, Buta ; Cao, Elton Y. ; Bunker, Christopher E. ; Cannon, William ; Petta, Lauren ; Wang, Ping ; Yang, Liju ; Cao, Li ; Scorzari, Annalise ; et al ( March 2023 , C)

   Carbon dots (CDots) are small carbon nanoparticles with effective surface passivation by organic functionalization. In the reported work, the surface functionalization of preexisting small carbon nanoparticles with N-ethylcarbazole (NEC) was achieved by the NEC radical addition. Due to the major difference in microwave absorption between the carbon nanoparticles and organic species such as NEC, the nanoparticles could be selectively heated via microwave irradiation to enable the hydrogen abstraction in NEC to generate NEC radicals, followed by in situ additions of the radicals to the nanoparticles. The resulting NEC-CDots were characterized by microscopy and spectroscopy techniques including quantitative proton and 13C NMR methods. The optical spectroscopic properties of the dot sample were found to be largely the same as those of CDots from other organic functionalization schemes. The high structural stability of NEC-CDots benefiting from the radical addition functionalization is highlighted and discussed. 

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5. Optical and spectroscopic characterization of crystalline structures in cannabis extracts

   https://doi.org/10.1111/1556-4029.14940  

   Abraham, Otyllia R. ; Waddell Smith, Ruth ( November 2021 , Journal of Forensic Sciences)

   Marijuana and hemp represent two broad classes ofCannabis sativaplants that are distinguished based on the concentration of the psychoactive cannabinoid delta‐9‐tetrahydrocannabinol (Δ⁹‐THC). In this work, solvent extracts derived from marijuana and hemp were characterized using optical and spectroscopic techniques. The crystalline components of the solvent extracts were first analyzed using polarized light microscopy to determine optical properties, namely, crystal system, optical sign, and principle refractive indices. Crystals from the marijuana‐derived extracts exhibited an orthorhombic crystal system and were optically negative, with n_βbetween 1.6320 and 1.6330 ± 0.0002. In contrast, crystals from hemp‐derived extracts exhibited a monoclinic crystal system and were optically positive, with n_βbetween 1.600 and 1.6040 ± 0.0002. Crystals were further distinguished through infrared spectroscopy, which highlighted structural differences between the two sample types, primarily based on differences in O‐H stretching. Finally, single‐crystal X‐ray diffraction was used to definitively identify the crystalline components, confirming the presence of tetrahydrocannabinolic acid in marijuana‐derived extracts and cannabidiol in hemp‐derived extracts. Given the differences in crystal structure identified between marijuana‐derived and hemp‐derived solvent extracts, optical characterization provides a screening method to differentiate visually similar samples prior to confirmatory analysis.

    

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