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The development of atomically precise metals on the surface of graphene has led to superior electrocatalytic properties for the clean oxygen production. In this study, Cu single-atom and NiCu dual-atom catalysts supported on different graphene variants were effectively developed as electrocatalysts for the production of clean oxygen. Various techniques, including XRD, SEM, Raman, HR-TEM, EXAFS and XPS, were used to characterize these synthesized electrocatalysts. The extent of reduction in graphene oxide (GO) support was confirmed using Raman analysis which demonstrated a greater I D /I G -apparent intensity ratio, indicating that the GO (I D /I G =0.9) has more sp 3 -hybridized carbon with respect to the rGO (I D /I G = 0.6). The HR-TEM analysis with EDX and STEM data confirmed the dispersion of Cu and NiCu dimer over the surface of graphene variants. XPS and EXAFS studies revealed predominant metallic nature of Cu and NiCu dimer with the synergistic interplay between the constituent atoms. Copper-nickel dimer catalyst supported on reduced graphene oxide (CuNi/rGO) demonstrated the best electrocatalytic performance, where a lower overpotential of 320 mV was observed to reach a current density of 10 mA cm−2 with lowest Tafel slope of 110 mV/dec for oxygen evolution reaction. Good stability was observed after 1000 CV cycles and 50 h of electrolysis in 1.0 M KOH electrolytic solution at an oxidation potential of 1.62 V (vs RHE). Control experiments were also performed using borosilicate pyrex glass and Teflon made electrochemical cells in order to over rule the probable involvement of leached out impurities in OER reaction under extreme alkaline conditions. The calculations obtained from Density Functional Theory (DFT) suggest that the dual-atom catalysts have lower overpotential (0.33 V at Cu-site) with respect to the single-atom catalysts, which agreed well with the experimental results. Also, the Cu-site OER was found to have lower overpotential (0.33 V) than the Ni-site (0.47 V). Thus, this study can provide valuable insights into developing low-cost dual-atom electrocatalysts, where the synergism between constituent elements in the dimer and their stabilization by graphene matrix can be exploited for various electrochemical reactions. [Display omitted] • Dual Atom (Cu-Ni) successfully grown on Graphene oxide variants. • Comprehensive characterization proved formation of dimers. • Dual Atom Dimers showed interesting Oxygen generation. • Computational results supported experimental Data. [ABSTRACT FROM AUTHOR]

• We synthesized and investigated gold nanoparticle (NP) contrast in spectral CT. • New contrast-detail phantom to measure contrast Limit Of Detectability (LOD). • The LOD of gold NP are 10 and 5 mg/ml for 1 and 2 mm lesions, respectively. • Phantom modular design and can be adapted for other imaging modalities. • Measurement methods of contrast LOD is required before clinical studies. This study involves the synthesis, characterization, and spectral photon counting CT (SPCCT) imaging of gold nanoparticles tailored for enhancing the contrast of small cancer lesions. We used the modified Turkevich method to produce thiol-capped gold nanoparticles (AuNPs) at different concentrations (20, 15, 10, 5, 2.5, 1.25, 0.6 mg/ml). We thoroughly characterized the AuNPs using Transmission Electron Microscopy (TEM), X-ray diffraction spectroscopy (XRD), Dynamic Light Scattering (DLS), and UV–visible absorption spectroscopy. To assess the AuNPs contrast enhancing performance, we designed and built a new material contrast detail phantom for CT imaging and determined the minimum detectable concentrations of AuNPs in simulated lesions of small diameters (1, 2, 3, and 5 mm). The synthesized AuNPs are spherical with an average size of approximately 20 ± 4 nm, with maximum UV absorption occurring at 527 nm wavelength, and exhibit a face-centered cubic structure of gold according to XRD analysis. The synthesized gold nanoparticles demonstrated high contrast in SPCCT, suggesting their potential as contrast agents for imaging cancer tissues. The AuNPs image contrast was directly proportional to the AuNPs concentration. We are the first to determine that the lowest visually distinguishable contrast was achieved at a gold concentration of 5 mg/ml for a 2 mm simulated lesion. For 1 mm size lesion the smallest visible concentration was 10 mg/ml. This newly developed phantom can be used for determining the minimal concentration required for various high-Z nanoparticles to produce detectable contrast in X-ray imaging for small-size simulated lesions. [ABSTRACT FROM AUTHOR]

Abstract Group-III nitride nano-dimensional materials with noncentrosymmetric crystal structure offer an exciting area of piezotronics for energy conversion applications. We experimentally report the piezotronic and piezo-phototronic effects of n -InGaN nanowires (NWs) having an emission wavelength in the visible region (≈510 nm). The n -type InGaN NWs, exhibiting high structural and optical quality, were grown by plasma-assisted molecular beam epitaxy (PAMBE) on Ti/TaN/Si substrates to facilitate the direct bottom electrical contact to the NWs. Further, we use Pt/Ir conductive atomic force microscopy (c-AFM) tip as a top electrical contact to the NW. Applying compressive strain on the NWs using a c-AFM tip, the Schottky barrier height (SBH) formed at the metal-semiconductor NW interface was tuned by means of strain induced piezo-potential. Thus, we study the two-way coupling of mechanical and electrical energy results in piezotronics of n -InGaN NWs. Such measurements were further carried out under optical excitation with 405 nm laser to understand its effect on change in SBH. Thereby, we demonstrate the three-way coupling of the piezo-phototronics of n -InGaN NWs by exploiting their excellent visible optoelectronic properties. The photogenerated carriers reduce the SBH while they play a lesser role at higher tip deflection force on NWs. This revealed that at the higher strain on NW, the piezo fields screen the photoexcited carriers hence resulting in a negligible change in I-V characteristics for ≥ 6 nN tip force with and without illumination. Thus, the investigation of nanoscale piezotronic and piezo-phototronic effects of n -InGaN NWs provides an opportunity to enable piezoelectric functional devices to be used as strain-tunable, self-powered electronics and optoelectronics applications. Graphical abstract The two-way coupling of mechanical and electrical energy is examined by applying external compressive strain on the n-InGaN nanowires (NWs), using a c-AFM Pt/Ir conductive tip, which induced a piezoelectric potential in the NW. Furthermore, the piezo-phototronic effect associated with the three-way coupling of n -InGaN NWs is demonstrated by exploiting their excellent visible optoelectronic properties. Under optical excitation, the photogenerated carriers reduce the strain induced SBH. At higher compressive strain, no change in the I-V characteristics was observed which reveals the dominant role of strain induced piezo fields. fx1 Highlights • We report the first systematic study on the piezotronic and piezo-phototronic effects in n-type InGaN nanowires (NWs) with the well-revealed mechanism. • The two-way coupling of mechanical and electrical energy is verified by applying external compressive strain on the NWs using a c-AFM Pt/Ir conductive tip. • The piezo-phototronics effect using the three-way coupling of n -InGaN NWs is demonstrated by exploiting their excellent visible optoelectronic properties. Under optical excitation, the photogenerated carriers reduce the strain induced SBH. • The change in SBH with and without illumination exhibited a linear relationship with the external compressive strain. • At higher compressive strain, the piezo fields have a dominant role over the optical excitation induced fields. [ABSTRACT FROM AUTHOR]

We report a phosphine (PH 3 ) plasma activation strategy for significantly boosting the electrochemical performance of supercapacitor electrodes. Using Fe 2 O 3 as a demonstration, we show that the plasma activation simultaneously improves the conductivity, creates atomic-scale vacancies (defects), as well as increases active surface area, and thus leading to a greatly enhanced performance with a high areal capacitance of 340 mF cm −2 at 1 mA cm −2 , compared to 66 mF cm −2 of pristine Fe 2 O 3 . Moreover, the asymmetric supercapacitor devices based on plasma-activated Fe 2 O 3 anodes and electrodeposited MnO 2 cathodes can achieve a high stack energy density of 0.42 mW h cm −3 at a stack power density of 10.3 mW cm −3 along with good stability (88% capacitance retention after 9000 cycles at 10 mA cm −2 ). Our work provides a simple yet effective strategy to greatly enhance the electrochemical performance of Fe 2 O 3 anodes and to further promote their application in asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

In this report, we show that oxide battery anodes can be grown on two-dimensional titanium carbide sheets (MXenes) by atomic layer deposition. Using this approach, we have fabricated a composite SnO 2 /MXene anode for Li-ion battery applications. The SnO 2 /MXene anode exploits the high Li-ion capacity offered by SnO 2 , while maintaining the structural and mechanical integrity of the conductive MXene platform. The atomic layer deposition (ALD) conditions used to deposit SnO 2 on MXene terminated with oxygen, fluorine, and hydroxyl-groups were found to be critical for preventing MXene degradation during ALD. We demonstrate that SnO 2 /MXene electrodes exhibit excellent electrochemical performance as Li-ion battery anodes, where conductive MXene sheets act to buffer the volume changes associated with lithiation and delithiation of SnO 2 . The cyclic performance of the anodes is further improved by depositing a very thin passivation layer of HfO 2 , in the same ALD reactor, on the SnO 2 /MXene anode. This is shown by high-resolution transmission electron microscopy to also improve the structural integrity of the SnO 2 /MXene anode during cycling. The HfO 2 coated SnO 2 /MXene electrodes demonstrate a stable specific capacity of 843 mAh/g when used as Li-ion battery anodes. [ABSTRACT FROM AUTHOR]

Solution-manufacturing of organic solar cells with best-in-class power conversion efficiency (PCE) will require all layers to be solution-coated without compromising solar cell performance. To date, the hole transporting layer (HTL) deposited on top of the organic bulk heterojunction layer in the inverted architecture is most commonly an ultrathin (<10 nm) metal oxide layer prepared by vacuum-deposition. Here, we show that an alcohol-based nanocrystalline MoO x suspension with carefully controlled nanocrystal (NC) size can yield state of the art reflective and semitransparent solar cells. Using NCs smaller than the target HTL thickness (∼10 nm) can yield compact, pinhole-free films which result in highly efficient polymer:fullerene bulk heterojunction (BHJ) solar cells with PCE=9.5%. The solution processed HTL is shown to achieve performance parity with vacuum-evaporated HTLs for several polymer:fullerene combinations and is even shown to work as hole injection layer in polymer light emitting diodes (PLED). We also demonstrate that larger MoO x NCs (30–50 nm) successfully composite MoO x with Ag nanowires (NW) to form a highly conducting, transparent top anode with exceptional contact properties. This yields state-of-the-art semitransparent polymer: fullerene solar cells with PCE of 6.5% and overall transmission >30%. The remarkable performance of reflective and semitransparent OPVs is due to the uncommonly high fill factors achieved using a carefully designed strategy for implementation of MoO x nanocrystals as HTL materials. [ABSTRACT FROM AUTHOR]

Ultrafine TaO x nanoparticles were electrodeposited on carbon black (CB) powder in a nonaqueous Ta complex solution at room temperature, and the resultant TaO x /CB catalysts were assessed as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte fuel cell (PEFC) cathodes. The Ta electrodeposition process was scaled up using a newly designed working electrode containing a CB dense layer, without introducing any binder such as the ionomer Nafion in the electrode for electrodeposition. The electrodeposited TaO x /CB powders were removed from the deposition electrode and subsequent H 2 treatment at varying temperatures between 523 and 1073 K was attempted to increase the ORR performance. The TaO x /CB samples were characterized by SEM, STEM, XPS, and EELS measurements. XPS and EELS results indicated the reduced nature of the Ta species caused by the high-temperature treatment in H 2 , while STEM images clearly revealed that the TaO x particles aggregated as the treatment temperature increased. When the TaO x /CB catalyst, which was treated at 873 K for 2 h, was deposited on a glassy carbon substrate with Nafion ionomer, it resulted in the highest activity among the samples investigated, giving an onset potential of 0.95 V RHE at -2 μA cm −2 in a 0.1 M H 2 SO 4 solution. Moreover, the long-term stability test with 10,000 cycles of the voltammetry only led to a 6% loss in the ORR currents, demonstrating the high stability of the TaO x /CB catalysts. Kinetic analysis by R(R)DE indicated that the four-electron transfer pathway in the ORR process was dominant for this TaO x /CB catalyst, and Tafel plots showed a slope corresponding to a one-electron reaction for the rate-determining step. [ABSTRACT FROM AUTHOR]

Abstract: A multi-element diffusion flame burner (MEDB) is useful in the study of flame synthesis of nanomaterials. Here, the growth of pure anatase and carbon-coated titanium dioxide (TiO2) using an MEDB is demonstrated. Hydrogen (H2), oxygen (O2), and argon (Ar) are utilized to establish the flame, whereas titanium tetraisopropoxide is used as the precursor for TiO2. The nanoparticles are characterized using high-resolution transmission electron microscopy, with elemental mapping (of C, O, and Ti), X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The growth of pure anatase TiO2 nanoparticles occurs when Ar and H2 are used as the precursor carrier gas, while the growth of carbon-coated nanoparticles ensues when Ar and ethylene (C2H4) are used as the precursor carrier gas. A uniform coating of 3–5nm of carbon is observed around TiO2 particles. The growth of highly crystalline TiO2 nanoparticles is dependent on the gas flow rate of the precursor carrier and amorphous particles are observed at high flow rates. Carbon coating occurs only on crystalline nanoparticles, suggesting a possible growth mechanism of carbon-coated TiO2 nanoparticles. [Copyright &y& Elsevier]

• A novel method for diesel fuel formulation is studied through aromatics oxygenation. • Diesel surrogate is modified by replacing a portion of aromatics with oxygenated ones. • A reduction in threshold soot index with negligible effect on cetane number is observed. • Soot is collected from flames of diesel surrogate and fuels with benzyl alcohol and anisole. • Soots from oxygenated fuels exhibited lower crystallite lengths and higher reactivity. To address the rising demand for cost-effective and eco-friendly transportation fuels, the blending of fossil fuels with oxygenated biofuels presents a promising solution to reduce our dependence on fossil fuels as well the emission of pollutants such as CO, soot, and NOx. However, biofuels have limited availability and are generally expensive to produce. To achieve low pollutant emissions due to the existence of fuel-bound oxygen, in this study, a portion of sooting aromatics existing in diesel is replaced with oxygenated-aromatics to validate if a clean fuel formulation strategy, where a hydrocarbon stream in a refinery rich in aromatics is catalytically oxygenated to obtain oxygenated aromatics before blending it with other hydrocarbons to produce diesel, could be beneficial. For reproducibility, a diesel surrogate fuel containing n -decane, n -hexadecane, and toluene was formulated that had properties such as molecular weight, density, threshold sooting index, and cetane index similar to that of commercial diesel. In line with the above fuel formulation strategy, a portion of aromatics (toluene) in diesel surrogate fuel is changed with oxygenated aromatics, benzyl alcohol and anisole that have structural similarity with toluene. The threshold sooting indices of the diesel surrogate and the oxygenated fuel blends indicate reduced sooting propensity of the latter in comparison to the former fuel. The characterization of soot particles, produced from the combustion of diesel surrogate and oxygenated blends, using TGA, XRD, HRTEM, and EDS elemental analysis indicates higher soot reactivity with smaller particle and crystallite sizes with oxygenated blends. Thus, the fuel formulation strategy discussed in this study can decrease diesel soot emission by hampering soot growth and accelerating oxidation and can enhance soot reactivity to diminish its lifespan in the environment. [ABSTRACT FROM AUTHOR]

The interactions of Iridium (Ir) noble metal atoms/clusters (Ir NMAs/NMCs) with graphene are investigated due to their remarkable catalytic performance, resulting from the use of 100 % metal atoms compared to nanoparticle counterparts. Using scanning transmission electron microscopy (STEM), various forms of Ir dispersed on graphene were observed, including single atoms, dimers, and trimers clusters. The STEM data further revealed inter-atomic distances of 2.83 Å and 2.96 Å for dimers and trimers which were 20 % and 17 % larger than the numbers found through density functional theory (DFT) calculations. The DFT calculations further showed that the Dirac-cone of graphene at Ir NMAs/NMCs locations changes to metallic form due to the emergence of energy states at the Fermi level. This effect results in non-zero effective masses of charge carriers but enhances their density of states (DOS) by 2-fold which is believed to increase the energy absorption efficiency of graphene in the infra-red range of radiation. [Display omitted] • Understanding Ir NMCs' interactions with graphene through theory and experiment. • Reporting of a change in the local density of states of graphene in the presence of Ir NMCs. • Measuring interatomic distances between Ir metal dimers and trimer through experiment and their comparison with theory. [ABSTRACT FROM AUTHOR]

• We study the effect of Si/Al ratio in Zeolite-Y on heptane hydrocracking • The effect of bi-metallicity (Ni-W) was also examined. • Bimetallicity resulted in enhanced metal dispersion and larger BET surface area. • Ni-W/Zeolite-Y catalysts were more catalytically active than Ni/Zeolite-Y. • Hydrocracking over Zeolites with high Si/Al ratio was more stable with time. This study investigated the effect of the SiO 2 /Al 2 O 3 ratio in the range of 5-80 in zeolite Y (ZY) as a support for the bi-functional reaction of heptane hydrocracking. Bi-metallicity impact, through the addition of W on Ni in the supported metal catalysts was also examined. The catalytic activity was assessed at 350°C and 400°C in order to deduce an optimized composition of the catalyst in terms of metal composition and Si/Al ratio. The results were correlated to the catalysts' surface and bulk properties, the latter after employing a number of material characterization techniques. It was shown that Ni-W bimetallic catalysts demonstrated better catalytic activity (conversion, 78% to 91%) than Ni-based monometallic counterpart catalysts (conversion, 74.2% to 82.7%), with NiO-WO 3 -ZY30 (SiO 2 /Al 2 O 3 ratio equal to 30) exhibiting the highest conversion. This was attributed to the bimetallic's enhanced metal dispersion and smaller particle size, evaluated using temperature-programmed desorption (TPD) of H 2 and high-resolution transmission electron microscopy (HR-TEM) imaging. The stronger acidity, as quantified by total acidity calculations, of zeolite Y having higher Si/Al ratio, and their balanced ratio of micro- and meso-porosity played a vital role in their catalytic performance. This study provides useful design guidelines on how to adjust both the Si/Al ratio in the zeolite Y support and the catalyst's bimetallicity for enhanced hydrocracking performance. [Display omitted] [ABSTRACT FROM AUTHOR]

• Co 3 O 4 /phosphorus-doped g-C 3 N 4 /α-Fe 2 O 3 ternary composite derived using MOF precursors. • Ternary composite exhibits dual Z-scheme photocatalytic degradation mechanism. • Ternary composite shows higher degradation efficiency of 99.3 %. • Ternary composite possesses high structural stability and reusability. In this study, a Co 3 O 4 /phosphorus-doped g-C 3 N 4 /α-Fe 2 O 3 (Co 3 O 4 @P-CN/α-Fe 2 O 3) composite was synthesized by a two-step method using respective MOF precursors. Initially, amine-functionalized Fe-MOF (Fe-MIL-88b) was co-condensed with phosphonitrilic trimer and melamine in the presence of triethylamine, resulting in a crosslinked polymer of phosphazene-coated Fe-MIL88b (Pz/Fe-MIL-88b). Subsequent Pz/Fe-MIL-88b calcination at 550 °C yielded a P-doped g-carbon nitride (P-CN)/α-Fe 2 O 3 composite. Furthermore, ZIF-67 was co-doped with the P-CN/α-Fe 2 O 3 composite through ultrasonic dispersion, followed by thermal calcination at 350 °C, yielding Co 3 O 4 @P-CN/α-Fe 2 O 3. However, the hybrid ternary composite exhibited a dual Z-scheme heterojunction in persulfate (PS)-mediated bisphenol-A (BPA) degradation under visible light. Co 3 O 4 @P-CN/α-Fe 2 O 3 demonstrated superior degradation efficiency (99.3 %) with rapid photocatalytic kinetics (0.0663 min−1) for BPA degradation compared to the binary composite and P-CN. The magnetic Co 3 O 4 @P-CN/α-Fe 2 O 3 composite exhibited high structural stability and reusability, achieving over 95 % BPA degradation after five cycles under visible light. [Display omitted] [ABSTRACT FROM AUTHOR]

Herein, 3D flower-like δ-MnO 2 , MXene and δ-MnO 2 /MXene in-situ hybrid (IH) composites were prepared (via hydrothermal and solution treatment methods) for the effective removal of Cr (VI) from the contaminated water. The effect of various experimental parameters including contact time, pH levels and initial Cr (VI) ions concentration was determined and compared under static conditions. The kinetics of Cr (VI) adsorption onto δ-MnO 2 , MXene, and IH confirmed the existence of a pseudo-second-order model. The obtained results reveal that the removal of Cr (VI) largely depends on the pH of the solution. The adsorption isotherm data fits best for Freundlich model, illustrating a multi-site adsorption mechanism of Cr (VI) ion on these adsorbents. The maximum Cr (VI) adsorption capacities onto δ-MnO 2 , MXene and IH are 235.65 mg g−1, 273.1 mg g−1 and 353.87 mg g−1, respectively. The study reveals that hetero-engineered approach of synthesizing transition metal oxides with MXenes provides abundant opportunities to remove contaminants from water with better efficiency due to reduction and electrostatic interaction. [ABSTRACT FROM AUTHOR]

The cost-efficient Ce-La-Cu-O based catalysts were fabricated under two different microwave conditions for efficient glycerol steam reforming to produce higher yield of hydrogen. [Display omitted] • Ce-La-xCu-O catalysts were fabricated through conventional (MW) and air cooling-assisted (AC) microwave methods. • Synthesis methods (MW & AC) influence the degree of Cu incorporation into catalysts. • Ceria doping tunes the chemisorption of glycerol; strength and distance from surface. • MW catalysts exhibit H 2 yield in the range of 3.8–5.0 mol/mole of glycerol. • AC catalyst displayed higher catalytic performance and stability than MW catalyst. In this study, Ce-La-xCu-O catalysts with distinct Cu contents were fabricated through two different microwave methods; conventional microwave (MW) method and enhanced microwave method, where air cooling (AC) during heating was applied and studied for glycerol steam reforming. The characterization of catalysts reveals that the synthesis methods (MW and AC) influence mainly on the degree of Cu incorporation into the Ce-La-O fluorite lattice, thus leading to one or two phases system. In glycerol steam reforming, MW catalysts showed improvement in glycerol conversion (X) and glycerol conversion to gaseous products (X gas) with an increase of temperature from 400 to 750 °C; a higher tradeoff between total conversion X (93–94%) and X gas (89–93%) was attained at 750 °C. The H 2 yield over MW catalysts was attained in the range of 3.8–5.0 mol/mole of glycerol. Interestingly, Ce-La-10Cu-O (AC) catalyst exhibits higher glycerol conversion, conversion to gaseous products and higher yield of H 2 (5.3 mol/mole of glycerol) as compared to MW catalyst. Moreover, the Ce-La-10Cu-O (AC) catalyst exhibited high stability and deactivated at slower rate. The improved performance of AC catalyst can correlate to a more homogeneous Cu incorporation into Ce-La-O mixed oxide thus forming more accessible active sites to reactants which overall impact on the catalytic performance. DFT calculations showed that doping ceria (1 1 1) surface greatly facilitates the adsorption of glycerol compared to the undoped ceria surface by tuning the adsorption energy and the surface-glycerol distance, to −1.42 eV and 1.09 Å, respectively, and by shifting the Fermi level into the valence band (p-type doping), enhancing with the latter the glycerol chemisorption. [ABSTRACT FROM AUTHOR]

• The determination of the presence of naturally occurring surfactants in the crude-oil. • Droplet size determination if emulsified water at nanoscale in the crude-oil. • Imaging of naturally surfactant made bilayer around the emulsified water in the crude-oil. • Determination of fraction of emulsified water at nanoscale in the crude-oil. The removal of the micro droplets of emulsified water from crude oil causes high cost and energy. In this paper we show that cryo electron microscopy (cryo-EM) imaging of micro and nano emulsions prepared from United Arab Emirate based crude oil provides critical information on their stability. Specifically, the cryoSEM imaging analysis applied to emulsion of murban-2019 , and upper zakum-2019 crude-oils allowed determining naturally occurring surfactants in these crude-oils. Moreover, the applied method also turned out to be an efficient way to qualitatively investigate the effect of synthetic surfactant on the stability of the emulsions. The high resolution cryoTEM imaging analysis of emulsions from upper zakum-2019 sample enabled visualizing "bilayer" of naturally occurring surfactants, presumably the asphaltene. The cryoTEM analysis further allowed estimating the volume-fraction of emulsified water in the crude-oil at nanoscales and turned out to be about 1% for the upper zakum-2019 samples. [ABSTRACT FROM AUTHOR]

• As-prepared GeTe films deposited at 25 °C were amorphous. • The degree of crystallinity of GeTe films increased when annealing time increased. • The average grain size increased by 60% upon doubling the annealing time. • Upon crystallization, Te-rich tetrahedra formation is favored over Ge-rich tetrahedra. This study investigates the effects of vacuum annealing on the structural and electrical properties of germanium telluride thin films. To this end, GeTe thin films were prepared via DC magnetron sputtering in three sets—as-prepared at 25 °C, as-prepared at 300 °C, and deposited and annealed at 300 °C for different time intervals. Post fabrication, the films were characterized using grazing-incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and four-point probe measurements. The as-prepared films deposited at 25 °C were amorphous, while the remaining film types exhibited crystalline conductivity and comparable sheet-resistance values. However, the observations of this study reveal a gradual increase in the degree of crystallinity and average grain size of the annealed films. The Raman spectroscopy results reveal the increase in film crystallinity to be due to an increase in the concentration of Te-rich tetrahedra at the expense of their Ge-rich equivalents. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, the photostability of gold nanoparticles (AuNPs) with different functional molecular coatings was investigated. Gold/water nanofluids were prepared using citrate (CIT) reduction, then coated with polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), or bovine serum albumin (BSA) by physical/chemical ligand adsorption. All nanofluids retained their monodispersity and extinction efficiency after ambient storage for three years. These long-term aged nanofluids were then subjected to accelerated indoor tests that mimic the prolonged and cyclic exposure to both full-spectrum and specific-band radiation. This included continuous exposure to broadband solar radiation at various intensities and focused near-ultraviolet (NUV) radiation for different durations, as well as cyclic exposure (in irradiation/darkening periods) to both solar and NUV radiation. Assessment of post-test stability has been realized using complementary characterization techniques. Results showed that stability was variable to the coating type, radiation exposure mode, and radiation spectrum. Subtle physicochemical transitions in the polymeric coatings, even in the absence of ligand desorption and particle clustering, were shown to alter the optical properties and wettability of the nanofluids. While the gold cores remained intact, some photoinduced instabilities occurred in the adsorbed polymeric coatings, including chain scission of PEG, conformational collapse of PVP, and partial denaturation of BSA. Largely attributed to the strong polymer-Au interactions and high surface grafting densities, and despite their coating transformations, AuNPs maintained a high level of photostability. This work marks important progress towards realizing photothermally superior, yet colloidally stable, solar nanofluids compatible with a wide range of direct-absorption photothermal applications in the water and energy sectors. [Display omitted] • Plasmonic gold nanoparticles stabilized using different polymeric coatings. • Accelerated radiation stability tests mimicking continuous/cyclic solar/UV exposure. • Insight gained into photoinduced physiochemical transitions in cores and coatings. • Stability variable to coating type, radiation exposure mode, and radiation spectrum. • Photostability limitations elucidated for photothermal conversion applications. [ABSTRACT FROM AUTHOR]