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Emerging fields of quantum technologies and biomedical applications demand pure nanodiamonds (NDs) with well-defined surface chemistry. Therefore, an inexpensive, scalable and eco-friendly ND surface purification technology is required. In this study, we report our method, salt-coated air oxidation (SCAO) thermal annealing, to achieve uniform purification of a ND surface without the loss of diamond material. A photoluminescence (PL) spectroscopy quality control method is proposed to evaluate the degree of purification. The presence of an isoemission point in the set of nitrogen vacancy (NV) center PL spectra, obtained through the photochromic effect, is examined as a surface purity indicator. The ratio of the NV centers in NDs after the SCAO treatment was determined by decomposing the PL spectra using the non-negative matrix factorization technique. [ABSTRACT FROM AUTHOR]

Electron clouds hinder the operation of particle accelerators. In the Large Hadron Collider (LHC), the copper beam screens are located within close proximity to the beam path, resulting in beam-induced electron multipacting, which is the main source of electron cloud formation. Conditions for multipacting are encountered when such surfaces have a secondary electron yield (SEY) greater than unity. Roughening the surface through laser processing offers an effective solution for reducing secondary electrons. Laser ablation leaves behind a complex rough, multi-scale geometrical surface with an altered chemical composition. Current models often over-simplify the geometry, do not have sufficient experimental data to derive input parameters, and exclude SEY-reducing mechanisms such as the surface chemistry. Leading to electron-matter interactions which do not resemble that of a real surface. Here, this complex surface is studied on copper used in the LHC, and the influence of microgeometry, inhomogeneous nanostructure and complex surface chemistry on the SEY is investigated. A novel, improved model is proposed that characterises these sophisticated structures, enabling the efficient design of surfaces to reduce SEY. To validate the model, samples were made using a variety of laser parameters. Modelling insights revealed that secondary electron suppression is not only caused by the microgeometry but also the nanostructure and chemical modification play a role. Contrary to the conventional theory, high aspect ratio structures are not necessarily required for effective SEY reduction. Currently, the model is applicable to a variety of surface morphologies and could be employed for other materials. [ABSTRACT FROM AUTHOR]

In this perspective we discuss the progress made in the mechanistic studies of the surface chemistry associated with the atomic layer deposition (ALD) of metal films and the usefulness of that knowledge for the optimization of existing film growth processes and for the design of new ones. Our focus is on the deposition of late transition metals. We start by introducing some of the main surface-sensitive techniques and approaches used in this research. We comment on the general nature of the metallorganic complexes used as precursors for these depositions, and the uniqueness that solid surfaces and the absence of liquid solvents bring to the ALD chemistry and differentiate it from what is known from metalorganic chemistry in solution. We then delve into the adsorption and thermal chemistry of those precursors, highlighting the complex and stepwise nature of the decomposition of the organic ligands that usually ensued upon their thermal activation. We discuss the criteria relevant for the selection of co-reactants to be used on the second half of the ALD cycle, with emphasis on the redox chemistry often associated with the growth of metallic films starting from complexes with metal cations. Additional considerations include the nature of the substrate and the final structural and chemical properties of the growing films, which we indicate rarely retain the homogeneous 2D structure often aimed for. We end with some general conclusions and personal thoughts about the future of this field. [ABSTRACT FROM AUTHOR]

Ozone, O3, is a strong oxidizing agent often used for water purification. O3 is typically produced in dielectric barrier discharges (DBDs) by electron-impact dissociation of O2, followed by three-body association reactions between O and O2. Previous studies on O3 formation in low-temperature plasma DBDs have shown that O3 concentrations can drop to nearly zero after continued operation, termed the ozone-zero phenomenon (OZP). Including small (<4%) admixtures of N2 can suppress this phenomenon and increase the O3 production relative to using pure O2 in spite of power deposition being diverted from O2 to N2 and the production of nitrogen oxides, N x O y. The OZP is hypothesized to occur because O3 is destroyed on the surfaces in contact with the plasma. Including N2 in the gas mixture enables N atoms to occupy surface sites that would otherwise participate in O3 destruction. The effect of N2 in ozone-producing DBDs was computationally investigated using a global plasma chemistry model. A general surface reaction mechanism is proposed to explain the increase in O3 production with N2 admixtures. The mechanism includes O3 formation and destruction on the surfaces, adsorption and recombination of O and N, desorption of O2 and N2, and NO x reactions. Without these reactions on the surface, the density of O3 monotonically decreases with increasing N2 admixture due to power absorption by N2 leading to the formation of nitrogen oxides. With N-based surface chemistry, the concentrations of O3 are maximum with a few tenths of percent of N2 depending on the O3 destruction probability on the surface. The consequences of the surface chemistry on ozone production are less than the effect of gas temperature without surface processes. An increase in the O3 density with N-based surface chemistry occurs when the surface destruction probability of O3 or the surface roughness was decreased. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) has become an essential technology in many areas. To better develop and use this technology, it is of the pivot to understand the surface chemistry during the ALD film growth. The growth of an ALD oxide film may also induce an electric dipole at the interface, which may be further tuned to modulate the flat band voltage for electronic device applications. To understand the associated surface chemistry and interface dipole formation process, we herein employ an in situ x-ray photoelectron spectroscopy technique to study the ALD growth of Al2O3, from trimethylaluminum and H2O, on the SiO x /Si surface. We find that an electric dipole is formed at the Al2O3/SiO x interface immediately after the first Al2O3 layer is deposited. We also observe persistent surface methyl groups in the H2O half-cycle during ALD, and the amount of the persistent methyls is particularly higher during the initial Al2O3 ALD growth, which suggests the formation of Si−CH3 on the surface. These findings can provide useful routes and insights toward interface engineering by ALD. [ABSTRACT FROM AUTHOR]

The photocatalytic degradation of the wastewater dye pollutant methylene blue (MB) at ZnO nanostructured porous thin films, deposited by direct current reactive magnetron sputtering on Si substrates, was studied. It was observed that over 4 photocatalytic cycles (0.3 mg · l−1 MB solution, 540 minUV irradiation), the rate constant k of MB degradation decreased by ∼50%, varying in the range (1.54 ÷ 0.78) · 10–9 (mol·l−1·min−1). For a deeper analysis of the photodegradation mechanism, detailed information on the nanostructured ZnO surface morphology and local surface and subsurface chemistry (nonstoichiometry) were obtained by using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) as complementary analytical methods. The SEM studies revealed that at the surface of the nanostructured ZnO thin films a coral reef structure containing polycrystalline coral dendrites is present, and that, after the photocatalytic experiments, the sizes of individual crystallites increased, varying in the range 43 ÷ 76 nm for the longer axis, and in the range 28 ÷ 58 nm for the shorter axis. In turn, the XPS studies showed a slight non-stoichiometry, mainly defined by the relative [O]/[Zn] concentration of ca. 1.4, whereas [C]/[Zn] was ca. 1.2, both before and after the photocatalytic experiments. This phenomenon was directly related to the presence of superficial ZnO lattice oxygen atoms that can participate in the oxidation of the adsorbed MB molecules, as well as to the presence of surface hydroxyl groups acting as hole-acceptors to produce OH· radicals, which can be responsible for the generation of superoxide ions. In addition, after experiments, the XPS measurements revealed the presence of carboxyl and carbonyl functional groups, ascribable to the oxidation by-products formed during the photodegradation of MB. [ABSTRACT FROM AUTHOR]

The changes of the surface morphology and the surface chemistry of LSC thin films grown on different substrates were tracked for 100 hours under SOFC operation conditions. Atomic force microscopy was used to monitor the formation of particles at the LSC surface. Depending on the thin film structure (polycrystalline vs. epitaxial), different particle formation dynamics were observed. Electron microscopy was employed to investigate the chemistry of the segregated particles and revealed that the particles were Srand S-rich. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy measurements were performed on degraded LSC thin films, which also found significant amounts of sulfur on the LSC surface, despite no deliberate addition of sulfur compounds, as well as A-site cation enrichment. Impedance spectroscopy was used to track the polarization resistance of LSC grown on YSZ over the same degradation period and a strong increase inthe polarization resistance and in its activation energy was revealed (1.09 to 1.73 eV). The experimental results indicate that sulfur adsorption on LSC surfaces is omnipresent in the investigated conditions and even trace amounts of sulfur compounds present in nominally pure measurement gases account for particle formation and multiple degradation effects under operating conditions. [ABSTRACT FROM AUTHOR]

Silica shell-isolated Au nanoparticles are used as reporters for shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) measurements to track and map the coverage and state of surfactant additives during electrochemical deposition. The propensity of a sub-monolayer coverage of Au@SiO2−x nanoparticles to remain segregated on advancing surfaces during Cu Damascene electrodeposition is demonstrated including enrichment (dilution) on concave (convex) surface segments. The local coverage of sulfonate-terminated disulfide (SPS) and/or thiolate (MPS) accelerator and co-adsorbed chloride is mapped during superconformal deposition on SPS-derivatized trench patterned arrays. Comparison with Cu deposition on nanoparticle-free regions indicate that for sub-monolayer coverages the Au@SiO2−x nanoparticles do not hinder the essential SPS/MPS adsorbate and metal deposition dynamics responsible for trench superfilling. X-ray photoelectron spectroscopy (XPS) studies on nanoparticle-free specimens reveal similar quantitative trends in SPS/MPS adsorbate coverage during metal deposition congruent with the effect of area change as detailed by the curvature enhanced accelerator mechanism (CEAC). SHINERS provides a powerful means for investigating the molecular details of superfilling and, more generally, surfactant mediated growth. [ABSTRACT FROM AUTHOR]

With the ever-increasing detection of sulfur-bearing molecules and the high abundance and refractory nature of aluminum, the [Al, S, O2] isomers may play an important role in the gas-phase chemistry of circumstellar envelopes and the chemistry on the surface of dust grains. High-level theoretical exploration of the [Al, S, O2] molecular system yielded five isomers, and predictions of their rotational, vibrational, and electronic spectroscopic properties are provided to inform experimental and observational searches. Cis-AlOSO and diamond isomers are isoenergetic and connected via a very small (∼1 kcal molâˆ'1) transition-state barrier. These isomers may act as intermediates along the chemical pathway between Al + SO2 and AlO + SO. Other isomers OAlOS and SAlO2 are stable relative to their corresponding dissociation asymptotes. Large permanent dipole moments of 2.521 D (cis-AlOSO), 1.239 D (diamond), and 5.401 D (OAlOS) predict strong rotational transitions and indicate these molecules as prime candidates for experimental study. Due to the low transition-state barrier, mixing of the vibrational levels is anticipated, complicating the vibrational spectrum. Electronic spectroscopy may be used as a means to differentiate between the two isomers. Strong electronic transitions are predicted to occur in the 200â€"300 nm range for cis-AlOSO and diamond. Simulated electronic absorption spectra provide a starting point for experimental characterization and spectral deconvolution of these isomers. [ABSTRACT FROM AUTHOR]

In this study, we developed a green and easy to scale up approach for producing Au/g-C3N4 (Au/GCN) hybrid plasmonic photocatalyst without using the chemical reducing agents via the growing of Au nanoparticles (Au NPs) on the surface of GCN nanosheets under the photo-reduction of ultraviolet (UV)-radiation. Different characterization techniques were conducted for investigating the structure, morphology, surface chemistry and optical properties of the as-prepared catalysts. The scanning electron microscope image shows that the homogeneous Au NPs anchored on the surface of the GCN nanosheet increased with the UV illumination time. The x-ray photoelectron spectroscopy results prove the coexistence of GCN nanosheets with heptazine heterocyclic ring (C6N7) units and Au NPs in the Au/GCN. The photoluminescence intensity decreased sharply with the time of UV irradiation, indicating that the recombination rate of photogenerated electronâ€"hole recombination decreased. The photocatalytic activity of the hybrid catalysts was evaluated by degrading rhodamine B (RhB) under simulated sunlight irradiation. The results show that the Au/GCN photocatalyst exhibits superior sunlight photocatalytic activity than that of bare GCN. The 6 h irradiated fabricating sample exhibited the strongest photocatalytic activity, completely decomposing the 10 ppm RhB in 30 min of irradiation. This report can provide the design of a simple and green synthesis method for the highly active Au/GCN photocatalyst. [ABSTRACT FROM AUTHOR]

Plasmonic effects including near-field coupling, light scattering, guided mode through surface plasmon polaritons (SPPs), Förster resonant energy transfer (FRET), and thermoplasmonics are extensively used for harnessing inexhaustible solar energy for photovoltaics and photocatalysis. Recently, plasmonic hot carrier-driven photocatalysis has received additional attention thanks to its specific selectivity in the catalytic conversion of gas molecules and organic compounds, resulting from the direct injection of hot carriers into the lowest unoccupied molecular orbital of the adsorbate molecule. The excellent light trapping property and high efficiency of hot charge-carrier generation through electromagnetic surface plasmon decay have been identified as the dominant mechanisms that promote energy-intensive chemical reactions at room temperature and atmospheric pressure. However, understanding the electromagnetic effects of plasmonics and distinguishing them from chemical effects in photocatalysis is challenging. While there exist several reviews underlining the experimental observations of plasmonic effects, this critical review addresses the physical origin of the various plasmon-related phenomena and how they can promote photocatalysis. The conditions under which each plasmonic effect dominates and how to distinguish one from another is also discussed, together with the analysis of the photoconversion efficiency. Finally, future research directions are proposed with the aim to accelerate progress in this field at the interface between chemistry and physics. [ABSTRACT FROM AUTHOR]

High surface area carbon powders are used in many electrochemical applications, e.g., fuel cells, supercapacitors, and batteries. However, despite their advantages, they are susceptible to oxidation and carbon corrosion when exposed to oxidizing potentials. Our goal has been to use diazonium chemistry to attach surface groups to block corrosion-susceptible sites and alter wettability. In prior work, mesoporous colloid imprinted carbons (CICs) with pores of 12-50 nm and still smaller pore necks hindered access of the diazonium precursors and limit mass transport in electrochemical applications. Here, CIC-85 powders (85 nm pores) were modified with -PhF5 or PhSO3H groups to engender hydrophobicity or hydrophilicity, respectively. Both groups decrease corrosion-induced surface roughening of the CIC-85 by ~50% in 0.5 M sulfuric acid. The -PhF5 group decreases irreversible oxidation of carbon to CO2 by a factor of ~9, while the -PhSO3H group protects the CIC-85 surface by ~4 times. An analogous free-standing, binder-free 85 nm pore size carbon sheet, exhibiting similar oxidation behavior, was examined by XPS, showing that surface functionalities are fully retained after corrosion. This work offers novel insights on the role, impact, and fate of diazoniumattached surface groups in protecting carbon surfaces during accelerated stress testing in sulfuric acid. [ABSTRACT FROM AUTHOR]

The toxicity towards viruses of silver nanoparticles (AgNPs) has been reported to be dependent on several factors such as particle concentration, size, and shape. Although these factors may indeed contribute to the toxicity of AgNPs, the results presented in this work demonstrate that surface chemistry and especially surface charge is a crucial factor governing their antiviral activity. Here, this work investigated the influence of capping agents representing various surface charges ranging from negative to positive. These AgNPs were capped with citrate, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP) mercaptoacetic acid (MAA) and (branched polyethyleneimine (BPEI). We show that AgNPs exhibited surface charge-dependent toxicity towards MS2 bacteriophages. Among the capping agents under investigation, BPEI capped AgNPs (Ag/BPEI) exhibited the highest reduction of MS2 resulting in ≥6 log10-units reductions, followed by 4–5 log10-units reductions with PVP and PEG capping's and 3–4 log10-units with MAA and citrate cappings. Bare nanoparticles reported a mere 1–2 log10-units reduction. Electrostatic interaction between the positively charged BPEI-coating and the negatively charged virus surface played a significant role in bringing the MS2 closer to toxic silver ions (Ag+). Further results obtained from TEM showed that Ag/BPEI nanoparticles could directly damage the structure of the MS2 bacteriophages. AgNPs and cationic capping agents' observed synergy can lead to much lower and much more efficient dosing of AgNPs for antiviral applications. [ABSTRACT FROM AUTHOR]

Core–shell structures with ZnO cores have been widely investigated due to their effectiveness in suppressing surface defects of ZnO nanostructures. As the surface defects are hugely dependent on the synthesis conditions, it is important to understand the interactions between shell material and ZnO with different surface chemistry. Here we produce well-aligned ZnO nanorods using two growth methods, leading to ZnO with different surface chemistries. A thin layer of TiO2 shell is applied via layer-by-layer adsorption method. The core–shell structure is confirmed via high-resolution transmission electron microscopy. The optical properties and chemical states of both bare nanorods and core–shell structures are investigated and compared using photoluminescence (PL) measurement and x-ray photoelectron spectroscopy (XPS). Both PL and XPS results suggest surface defects are passivated by TiO2 shell coating. The shell coating has a stronger effect on ZnO synthesized in OH− rich environment, due to excessive hydroxyl groups provided during synthesis, which remain even after annealing-induced crystallization. [ABSTRACT FROM AUTHOR]

The thermal oxidation of Ru(0001) has been extensively studied in the surface science community to determine the oxidation pathway towards ruthenium dioxide (RuO2(110)), improving the knowledge of Ru(0001) surface chemistry. Using time-lapsed ambient-pressure x-ray photoelectron spectroscopy (APXPS), we investigate the thermal oxidation of single-crystalline Ru(0001) films toward rutile RuO2(110) in situ. APXPS spectra were continuously collected while the Ru(0001) films were exposed to a fixed O2 partial pressure of 10−2 mbar and the sample temperature was increased stepwise from room temperature to 400 °C. We initially observe the removal of adventitious carbon and subsequent formation of a chemisorbed oxygen overlayer at 250 °C. Further annealing to 300 °C leads to an increase in thickness of the oxide layer and a shift in the Ru–O component of the Ru 3d spectra, indicating the presence of a metastable O–Ru–O trilayer structure. A rapid formation of the RuO2 rutile phase with an approximate thickness of at least 2.6 nm is formed about four minutes after stabilizing the temperature at 350 °C and subsequent annealing to 400 °C, signaled by a distinct binding energy shift in both the Ru 3d and O 1s spectra, as well as quantitative analysis of XPS intensities. This observed autocatalytic oxidation process agrees well with previous theoretical models and experimental studies, and the data provide the unambiguous spectral identification of one proposed metastable precursor required for full oxidation to rutile RuO2(110). Further ex situ characterization of the grown oxide with x-ray photoelectron diffraction confirms the presence of three rotated domains of rutile RuO2(110) and reveals their orientation relative to the substrate lattice. [ABSTRACT FROM AUTHOR]

Gallium phosphide (GaP) is a promising catalyst material used in the photo-electrochemical carbon dioxide (CO2) reduction reaction (CO2RR). However, experimental data needed to interpret the interactions between CO2 and GaP at their interfaces must be gathered in order to develop advanced GaP based catalysts for the CO2RR. Here we used ambient pressure x-ray photoelectron spectroscopy to characterize the surface chemistry at 298 K on the GaP surface exposed to CO2 alone and in the presence of H2O under both dark and illuminated conditions. We found that a carbonate-like configuration is stable on the GaP surface exposed solely to 0.35 Torr CO2. Shining solar light promoted the CO2 dissociation process on the surface while negligibly influencing the CO2 adsorption configuration on GaP. Based on the surface chemistry change under dark and illuminated conditions, we propose a CO2 dissociation pathway on GaP. We also found that linear physisorbed CO2 formed on the surface of GaP when 0.35 Torr CO2 is co-dosed with 0.35 Torr H2O. Co-dosing H2O with CO2 also created a surface dipole, which is further influenced by solar light illumination. This work provides a fundamental atomic level understanding of how CO2 adsorption and activation happened on the GaP surface and how it was further influenced by solar light. [ABSTRACT FROM AUTHOR]

Water-in-salt electrolytes (WiSEs) are a class of super-concentrated electrolytes that have shown much promise in replacing organic electrolytes in lithium-ion batteries. At the extremely high salt concentrations of WiSEs, ionic association is more complicated than the simple ion pair description. In fact, large branched clusters can be present in WiSEs, and past a critical salt concentration, an infinite percolating ionic network can form spontaneously. In this work, we simplify our recently developed thermodynamic model of reversible ionic aggregation and gelation, tailoring it specifically for WiSEs. Our simplified theory only has a handful of parameters, all of which can be readily determined from simulations. Our model is able to quantitatively reproduce the populations of ionic clusters of different sizes as a function of salt concentration, the critical salt concentration for ionic gelation, and the fraction of ions incorporated into the ionic gel, as observed from molecular simulations of three different lithiumbased WiSEs. The extent of ionic association and gelation greatly affects the effective ionic strength of solution, the coordination environment of active cations that is known to govern the chemistry of the solid-electrolyte interface, and the thermodynamic activity of all species in the electrolyte. [ABSTRACT FROM AUTHOR]

Plasma catalysis, the combination of plasma and catalysis, is used to achieve efficient molecule conversion, supporting the flexibility of operating parameters and feed gases. By combining plasmas with conventional thermal catalysis, the temperature windows may be changed and the process may be made insensitive to catalyst poisoning. However, understanding plasma catalysis mechanisms is extremely difficult, due to the strong coupling between plasma, gas-phase chemistry and surface. A multitude of reaction pathways may be enhanced or reduced by the presence of a plasma that provides excited species as reaction partners. We developed a robust setup to analyse those processes, based on a parallel-plate atmospheric-pressure plasma jet that allows a plug flow design. The plasma chemistry is analysed by Fourier transform infrared absorption spectroscopy and mass spectrometry. The electrodes in contact with the plasma are temperature controlled and can easily be replaced to apply a catalyst on top of them. The basic characteristics of the setup are discussed and three examples for its application are given: (a) the analysis of methane oxidation using the plug flow scheme; (b) the plasma catalytic conversion of CO2, and (c) the plasma catalytic conversion of methane in methane–oxygen mixtures. [ABSTRACT FROM AUTHOR]

Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZTO) ferroelectric ceramic loaded with Ag nanoparticles (NPs) was explored for its photo/piezocatalytic performance. The presence of Ag loading on BCZTO ceramic was confirmed using electron microscopes. X-ray photoelectron spectroscopy revealed the metallic chemical state of Ag NPs loaded on the surface of BCZTO ceramic. The absorbance spectrum of the Ag-loaded BCZTO sample showed a visible light absorption hump due to the phenomenon of surface plasmonic resonance. During the photocatalysis process, the 99% of rhodamine B (RB) dye was degraded in aqueous solution using the Ag-loaded BCZTO sample, showing its promising photocatalysis activity. During the piezocatalysis process, the 95% of RB dye was degraded using the Ag-loaded BCZTO sample, showing its promising piezocatalytic activity. The ·OH radical species were found responsible for the photocatalytic and piezocatalytic performance. The photo/piezocatalytic performance was found to be consistent over five cycles, indicating promising reusability of the Ag-loaded BCZTO sample. [ABSTRACT FROM AUTHOR]

Cell patterning holds significant implications for cell-based analysis and high-throughput screening. The challenge and key factor for formation of cell patterns is to precisely modulate the interaction between cells and substrate surfaces. Many nanosubstrates have been developed to control cell adhesion and patterning, however, requirements of complicated fabrication procedures, harsh reaction conditions, and delicate manipulation are not routinely feasible. Here, we developed a hierarchical polydimethylsiloxane nanosubstrate (HPNS) coated with mussel-inspired polydopamine (PDA) micropatterns for effective cell patterning, depending on both surface topography and chemistry. HPNSs obtained by facile template-assisted replication brought enhanced topographic interaction between cells and substrates, but they were innately hydrophobic and cell-repellent. The hydrophobic nanosubstrates were converted to be hydrophilic after PDA coatings formed via spontaneous self-polymerization, which greatly facilitated cell adhesion. As such, without resorting to any external forces or physical constraints, cells selectively adhered and spread on spatially defined PDA regions with high efficiency, and well-defined cell microarrays could be formed within 20 min. Therefore, this easy-to-fabricate nanosubstrate with no complex chemical modification will afford a facile yet effective platform for rapid cell patterning. [ABSTRACT FROM AUTHOR]

Li–O2 batteries (LOB) are considered as one of the most promising energy storage devices using renewable electricity to power electric vehicles because of its exceptionally high energy density. Carbon materials have been widely employed in LOB for its light weight and facile availability. In particular, graphene is a suitable candidate due to its unique two-dimensional structure, high conductivities, large specific surface areas, and good stability at high charge potential. However, the intrinsic catalytic activity of graphene is insufficient for the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in LOB. Therefore, various surface functionalization schemes for graphene have been developed to tailor the surface chemistry of graphene. In this review, the properties and performances of functionalized graphene cathodes are discussed from theoretical and experimental aspects, including heteroatomic doping, oxygen functional group modifications, and catalyst decoration. Heteroatomic doping breaks electric neutrality of sp2 carbon of graphene, which forms electron-deficient or electron-rich sites. Oxygen functional groups mainly create defective edges on graphene oxides with C−O, C=O, and −COO−. Catalyst decoration is widely attempted by various transition and precious metal and metal oxides. These induced reactive sites usually improve the ORR and/or OER in LOB by manipulating the adsorption energies of O2, LiO2, Li2O2, and promoting electron transportation of cathode. In addition, functionalized graphene is used in anode and separators to prevent shuttle effect of redox mediators and suppress growth of Li dendrite. [ABSTRACT FROM AUTHOR]

The detection of phosphorous-bearing molecules in interstellar environments constitutes a fundamental task for understanding the formation of prebiotic molecules, but it is also a challenge. In cold interstellar environments, where rich chemistry is expected to happen, only PN and PO have been detected. Phosphine (PH3) must also play an essential role in these regions, since P is expected to deplete onto dust grains significantly, and hydrogenation reactions are dominant in such environments. Surface chemistry on dust grains shows a particular idiosyncrasy where an equilibrium between competitive reactions, photoconversion processes, and desorption are in continuous interplay, modifying both the dust composition and the gas composition. In this study, we theoretically study in detail the interconversion of P to PH3 via subsequent additions of H on cold dust grain analogs. For all reactions, we provide the binding energy of the adsorbates, reaction energies, and, when present, activation barriers and tunneling-corrected rate constants. We also present an estimate of the desorption temperature of these species based on transition state theory. Using recently available experimental results on PH3 desorption via chemical reactions, we conclude that all of the intermediate products of the hydrogenation sequence to phosphine may be released to the gas phase. [ABSTRACT FROM AUTHOR]

The release of gases through electrolyte decomposition is a problem of prominent concern in the Li-ion battery industry, due to the negative impact of gassing on cell safety and performance. The development of new electrolytes and additives is essential in enabling low-gassing batteries. Organosilicon (OS) molecules, which merge a silane with a Li+ coordinating functionality, have been developed by Silatronix® as additions to conventional carbonate electrolytes, demonstrating critical high thermal and voltage stability to enable next-generation Li-ion batteries. In this study we report performance testing and fundamental mechanistic studies to investigate gassing phenomena in advanced Li-ion chemistries under storage test conditions. Novel organosilicon nitriles developed by Silatronix® as well as common gas reducing additives (i.e. 1,3-propanesultone, succinonitrile) were evaluated in a 4.35 V Graphite/NMC622 (LiNi0.6Mn0.2Co0.2O2) multi-layer pouch cell. Potential synergies between OS materials and these additives were investigated. The dependence of gassing on electrolyte composition and test conditions was investigated, and connections between gassing behavior and electrode surface chemistry are also reported. Key experimental results show that all OS concentrations reduce gas generation during 60 °C storage, and higher OS content provides greater benefit. Overall, we show that organosilicon additives substantially reduce gassing from carbonate-based electrolytes while maintaining cell performance. [ABSTRACT FROM AUTHOR]

Operation of a magnetron sputtering gas aggregation cluster source in a plasma jet regime is presented. In specific experimental conditions, the plasma extends from the inside of the cluster source in the deposition chamber as a plasma jet, transporting also the nanoparticles (NPs) produced in the cluster source. The chemistry of the NP surface is modified in-flight by injecting a chemical precursor in the plasma jet, resulting in core–shell NPs. Also, the plasma jet presents a low gas temperature, safely interacting with materials sensitive to thermal degradation (like polymers). These findings prove the potential of the presented plasma jet for applications in nanotechnology. [ABSTRACT FROM AUTHOR]

This paper reports an unpredictable insulation surface flashover phenomenon triggered by surface charge clusters under DC electric field, which is experimentally revealed by a donut-shaped dust cluster figure, presenting the outline of these surface charge clusters and showing a hollow donut-shaped structure interestingly. The charge cluster is randomly formed when ions originating from local micro-protrusions accumulate on the insulation surface, the edge of which produces a strong electrical field to induce local streamers. These local streamers provide an inducing factor, unpredictably triggering surface flashover. An in-depth illustration of how the dust phase transition depicts surface charge cluster evolution is proposed. This uncovered phenomenon has significant physical implications in revealing unpredictable insulation surface flashover and has great significance in further developing of HVDC gas insulated power transmission systems and other fields, such as microelectronics and space aircrafts. [ABSTRACT FROM AUTHOR]

This paper reports an unpredictable insulation surface flashover phenomenon triggered by surface charge clusters under DC electric field, which is experimentally revealed by a donut-shaped dust cluster figure, presenting the outline of these surface charge clusters and showing a hollow donut-shaped structure interestingly. The charge cluster is randomly formed when ions originating from local micro-protrusions accumulate on the insulation surface, the edge of which produces a strong electrical field to induce local streamers. These local streamers provide an inducing factor, unpredictably triggering surface flashover. An in-depth illustration of how the dust phase transition depicts surface charge cluster evolution is proposed. This uncovered phenomenon has significant physical implications in revealing unpredictable insulation surface flashover and has great significance in further developing of HVDC gas insulated power transmission systems and other fields, such as microelectronics and space aircrafts. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) is exceedingly apposite for liquid-based sensor applications because of their high internal piezoelectric polarization, chemical and high temperature stability. In this work, the interaction between GaN and H2O has been investigated using a novel methodology. We report the fabrication of single crystal GaN lamella with thickness of few hundreds of nanometer using focused ion-beam milling technique, for sensing applications. Results signify that the device resistivity increases with time at room temperature during the GaN-H2O interaction. Such a change in electrical resistivity is explained based on the electron transfer and electrochemical reactions at the surface of GaN. Study of the surface chemistry transformation of the tested GaN lamella is conducted using high-angle annular dark-field scanning transmission electron microscopy coupled with electron energy loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (EDS) techniques. EDS and EELS results signify the presence of a region containing Ga and O at the interface of the H2O/GaN which is a result due to the adsorption of molecular H2O and its dissociation products implying the occurrence of GaN-water reaction. [ABSTRACT FROM AUTHOR]

The ability of hydroxyapatite (HA) to convert readily into an electret under low polarizing fields (⩽1 kV cm−1) makes it as an excellent substitute for electro-active prosthetic implants. In the present study, compacts of electrovector HA and ferroelectric Na0.5K0.5NbO3 (NKN) were developed via the spark plasma sintering route. The compacts were then polarized at various polarizing fields of 30, 50, and 90 kV cm−1, respectively, at 150 °C, for 1 h. Thereafter, samples were depolarized at heating rates of 1, 5, and 10 °C min−1, respectively. The thermally stimulated depolarization current (TSDC) measurement reveals that the charge density in HA increases from ∼0.2 nC cm−2 to ∼2 µC cm−2 with an increase in the polarizing field from 30 to 90 kV cm−1. The dielectric (ϵ), as well as the ac conductivity behaviour of unpolarized and polarized (90 kV cm−1) HA, are compared. The activation energy is measured to be in the range of 0.6–0.7 eV, which is mainly associated with proton (H+) migration. For NKN, TSDC spectra reveal a slight shift in the phase transition temperatures (TO−T, TC) towards higher temperatures, with an increase in the polarizing field (30–90 kV cm−1) as well as the heating rate. The dielectric and ac conductivity measurements suggest that the polarization of NKN slightly decreases TO−T and TC, as compared to its unpolarized counterpart. The conductivity in NKN is mainly attributed to the migration of oxygen vacancies and n-type charge carriers. Furthermore, x-ray photoelectron spectroscopy analyses suggest that the polarization of HA at such a high field (90 kV cm−1) does not alter its surface chemistry. [ABSTRACT FROM AUTHOR]

Long-term electrochemical performance of polymeric precursor-derived films of LaCoO3 doped with Ca2+ (LCC), instead of the larger Sr2+ which segregates at the electrode surface forming oxides/hydroxides, was investigated in the present study. It was determined that pre-calcination at 800 °C (LCC02-800) resulted in a higher electrochemical performance but a poorer long-term stability than those pre-calcined at 700 °C (LCC02-700) or 900 °C (LCC02-900). Increasing Ca2+ content (LCC04-800) enhanced the initial electrochemical performance slightly, while causing a much poorer long-term stability. Microstructural evolution analyses revealed that, although it had some impact on the initial and long-term performance of LCC electrodes, it was not the strongest influence. It was determined via XPS analyses that formation of CaO and CaO + La2O3 layers at the LCC02-800 and LCC04-800 surfaces, respectively, accompanied by a decrease in the relative amounts of adsorbed oxygen species (corresponding to surface oxygen vacancies) caused a faster performance degradation in these samples than those pre-calcined at 700 or 900 °C. Eventually, only the surface cation ratio of LCC02-700 became close to the theoretical one after long-term operation. [ABSTRACT FROM AUTHOR]

Solid-state nanopores (SSNs) are single-molecule resolution sensors with a growing footprint in real-time bio-polymer profiling—most prominently, but far from exclusively, DNA sequencing. SSNs accessibility has increased with the advent of controlled dielectric breakdown (CDB), but severe fundamental challenges remain: drifts in open-pore current and (irreversible) analyte sticking. These behaviors impede basic research and device development for commercial applications and can be dramatically exacerbated by the chemical complexity and physical property diversity of different analytes. We demonstrate a SSN fabrication approach attentive to nanopore surface chemistry during pore formation, and thus create nanopores in silicon nitride (SiNx) capable of sensing a wide analyte scope—nucleic acid (double-stranded DNA), protein (holo-human serum transferrin) and glycan (maltodextrin). In contrast to SiNx pores fabricated without this comprehensive approach, the pores are Ohmic in electrolyte, have extremely stable open-pore current during analyte translocation (>1 h) over a broad range of pore diameters (3— ∼30 nm) with spontaneous current correction (if current deviation occurs), and higher responsiveness (i.e. inter-event frequency) to negatively charged analytes (∼6.5 × in case of DNA). These pores were fabricated by modifying CDB with a chemical additive—sodium hypochlorite—that resulted in dramatically different nanopore surface chemistry including ∼3 orders of magnitude weaker Ka (acid dissociation constant of the surface chargeable head-groups) compared to CDB pores which is inextricably linked with significant improvements in nanopore performance with respect to CDB pores. [ABSTRACT FROM AUTHOR]

The design of smart and functional nanocarriers for drug delivery systems that use a variety of organic and inorganic materials has led to the development of nanomedicines with improved therapeutic efficiency and reduced side effects. In this study, a pH- and temperature-responsive, controlled-release system with a high capacity for drug loading was developed based on radially porous silica nanoparticles composed of functionalized ligands and polymer encapsulation. This drug delivery system uses radially oriented mesoporous silica nanoparticles as the drug carrier, and control of the surface chemistry of those nanocarriers allows high-capacity loading efficiency of target drugs and stimuli-responsive release kinetics governed by pH and temperature. The delivery of ibuprofen was chosen to test this system, and a maximum loading efficiency of ca. 270 wt% was established, which was 3 times greater than that in previous studies for silica nanoparticles such as SBA-15, MCA-41, and MCM-48. In addition, the pH- and temperature-responsive release of ibuprofen was achieved when the surface of the nanocarriers was treated by pH-responsive amine functionalization and a temperature-responsive surface coating of agarose gel. Finally, cytotoxicity testing using the fibroblast cells showed that the developed silica nanocarriers have no toxicity on the cells, which should allow these nanocarriers to be applied as a nanomedicine in drug delivery systems. [ABSTRACT FROM AUTHOR]

In this work, we present the results of simulations carried out for N2–H2 capacitively coupled radio-frequency discharges, running at low pressure (0.3–0.9 mbar), low power (5–20 W), and for amounts of H2 up to 5%. Simulations are performed using a hybrid code that couples a two-dimensional time-dependent fluid module, describing the dynamics of the charged particles in the discharge, to a zero-dimensional kinetic module, that solves the Boltzmann equation and describes the production and destruction of neutral species. The model accounts for the production of several vibrationally and electronic excited states, and contains a detailed surface chemistry that includes recombination processes and the production of NHx molecules. The results obtained highlight the relevance of the interactions between plasma and surface, given the role of the secondary electron emission in the electrical parameters of the discharge and the critical importance of the surface production of ammonia to the neutral and ionic chemistry of the discharge. [ABSTRACT FROM AUTHOR]

In this work, comparative studies of the surface morphology and surface chemistry of SnO2 nanolayers prepared by spin coating with subsequent thermal oxidation (SCTO) in the temperature range of 400–700 °C using scanning electron microscopy (SEM), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) methods, are presented. The SEM images show that SCTO SnO2 nanolayers contain partly connected irregular structures strongly dependent on the final oxidation temperature, with interconnected single grains of longitudinal shape and size, resulting in a flatter surface morphology with respect to the commonly used three-dimensional (3D) SnO2 thin films. In turn, AFM studies additionally confirm that SCTO SnO2 nanolayers after post-oxidation annealing at higher temperatures contain isolated grains of average lateral dimensions in the range of 20–50 nm having a rather flat surface morphology of average surface roughness defined by the root mean square factor at the level of ∼2 nm. From the XPS experimental research it can be concluded that, for our SCTO SnO2 samples, a slight surface nonstoichiometry defined by the relative [O]/[Sn] concentration at the level of 1.8–1.9 is observed, also depending on the final post-oxidation temperature, being an evident contradiction to recently published literature using x-ray diffraction data. Moreover, XPS experiments show that there is also a permanent small amount of carbon contamination present at the surface of internal grains of our SCTO SnO2 nanolayers, creating an undesired potential barrier for interactions with gaseous species when they are used as the active materials for gas sensing devices. [ABSTRACT FROM AUTHOR]

We report the results from a comprehensive study of the effect that annealing FeSe0.35Te0.65 single crystals in different atmospheres has on the surface chemistry, the superconducting transition temperature, Tc, and the critical current density, Jc. A review of the literature and our data shows that annealing in oxygen, nitrogen, air or vacuum atmosphere leads to a universal superconducting phase diagram that is independent of the variance in the as-grown properties. We show that atmospheres with an oxygen partial pressure of p > 10−3 hPa during annealing are necessary to improve the superconducting properties in this compound. This is demonstrated by Raman and magnetisation measurements on air, nitrogen, or low vacuum annealed FeSe0.35Te0.65 samples, which show that the improvement in the superconducting properties is strongly correlated to the formation of a thin iron oxide surface layer. However, annealing under high vacuum does not lead to the formation of an iron oxide layer and no improvement in the superconducting properties is observed. Our findings show that the previously reported improvements in the superconducting properties after annealing under vacuum or in nitrogen are thus likely to have been caused by residual oxygen. Furthermore, we propose a diffusion model for the formation of the iron oxide layer as the driving force for the reduction of interstitial excess iron that suppresses superconductivity in this compound. Overall, our results show that the presence of an iron reactant, such as oxygen, during annealing is necessary to improve the superconducting properties of FeSe1−xTex. [ABSTRACT FROM AUTHOR]

We report the results from a comprehensive study of the effect that annealing FeSe0.35Te0.65 single crystals in different atmospheres has on the surface chemistry, the superconducting transition temperature, Tc, and the critical current density, Jc. A review of the literature and our data shows that annealing in oxygen, nitrogen, air or vacuum atmosphere leads to a universal superconducting phase diagram that is independent of the variance in the as-grown properties. We show that atmospheres with an oxygen partial pressure of p > 10−3 hPa during annealing are necessary to improve the superconducting properties in this compound. This is demonstrated by Raman and magnetisation measurements on air, nitrogen, or low vacuum annealed FeSe0.35Te0.65 samples, which show that the improvement in the superconducting properties is strongly correlated to the formation of a thin iron oxide surface layer. However, annealing under high vacuum does not lead to the formation of an iron oxide layer and no improvement in the superconducting properties is observed. Our findings show that the previously reported improvements in the superconducting properties after annealing under vacuum or in nitrogen are thus likely to have been caused by residual oxygen. Furthermore, we propose a diffusion model for the formation of the iron oxide layer as the driving force for the reduction of interstitial excess iron that suppresses superconductivity in this compound. Overall, our results show that the presence of an iron reactant, such as oxygen, during annealing is necessary to improve the superconducting properties of FeSe1−xTex. [ABSTRACT FROM AUTHOR]

Aseries of electrolytes based on ionic liquid (IL) N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl) amide (DEMETFSI) and individual or binary co-solvent(s) consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and/or 1,3-dioxolane (DOL) were investigated. The alterative solvent composition results in very different electrolyte properties (conductivity/viscosity, polysulfide solubility and film formation ability) and Li-S cell performances (specific capacity, cycle stability and rate capability). The hybrid system of DEMETFSI/TTE/DOL provides better overall performances compared to the IL with nonor single co-solvent, which is mainly profited from the synergistic function of TTE and DOL, together favorable for the improvement of ionic conduction of the electrolyte and Li surface chemistry. It is further emphasized that the construction of a rational counterbalance between polysulfide dissolution and shuttle suppression is more significant for the advanced Li-S batteries. [ABSTRACT FROM AUTHOR]

This study explores the surface chemistry of Inconel 625 samples exposed to molten LiCl-Li2O-Li solutions at 650°C for 500 and 1000hr and aims to understand the effect of solvated Li on corrosion behavior in molten LiCl-Li2O-Li. The surfaces of Inconel 625 samples were analyzed using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The oxide films formed on the surface of the samples in the absence of Li is composed of LiCrO2, with small contributions of Li2CrO4 and NiFexCr2-xO4. The presence of Li was observed to destabilize these compounds, resulting in a primarily metallic surface with trace amounts of oxidized Cr, Mo, and Nb present depending on the concentration of Li in solution. [ABSTRACT FROM AUTHOR]

Electrodeposition of Cu-SiO2 composite coatings from an alkaline non-cyanide electrolyte containing glutamate as complexing agent was studied. Silica mesoporous particles were synthesized using a modified Stöbermethodology, and later their surface chemistry was changed by functionalizing them with 3-aminopropyltriethoxysilane. Particles microstructure and morphology were characterized (SEM, TEM, XRD) and their charging behavior in several electrolytes was studied through ζ -potential measurements. Galvanostatic deposition was performed in electrolytes containing both as-prepared and functionalized SiO2 at various current densities, and the influence of ultrasonic irradiation (37 Hz) was evaluated. For some experiments, 1.5 g L- of Polyquaternium 7 were added to the solution. SEM and XRD were used to characterized coatings morphology and microstructure, whereas EDS was used to estimate SiO2 wt%. The results showed that the effect of ultrasound on the codeposition process depends on current density and particle surface chemistry. All the trends observed in this study could be explained taking into account ζ -potential values recorded and previously reported theories. Adjusting the experimental conditions, it was possible to obtain deposits with SiO2 contents of ≈5 wt%. Finally, it was found that both ultrasonic irradiation and Polyquaternium 7 affect the morphology and crystal orientation of the deposits. [ABSTRACT FROM AUTHOR]

Surface chemistry modification of positive electrodes has been used widely to decrease capacity loss during Li-ion battery cycling. Recent work shows that coupled LiPF6 decomposition and carbonate dehydrogenation is enhanced by increased metal-oxygen covalency associated with increasingNi and/or lithium de-intercalation inmetal oxide electrode, which can be responsible for capacity fading of Ni-rich oxide electrodes. Here we examined the reactivity of lithium nickel, manganese, cobalt oxide (LiNi0.6Mn0.2Co0.2O2, NMC622) modified by coating of Al2O3, Nb2O5 and TiO2 with a 1 M LiPF6 carbonate-based electrolyte. Cycling measurements revealed that Al2O3-coated NMC622 showed the least capacity loss during cycling to 4.6 VLi compared to Nb2O5-, TiO2-coated and uncoated NMC622, which was in agreement with smallest electrode impedance growth during cycling from electrochemical impedance spectroscopy (EIS). Ex-situ infrared spectroscopy of charged Nb2O5- and TiO2-coated NMC622 pellets (without carbon nor binder) revealed blue peak shifts of 10 cm-1, indicative of dehydrogenation of ethylene carbonate (EC), but not for Al2O3-coated NMC622. X-ray Photoelectron Spectroscopy (XPS) of charged TiO2-coated NMC622 electrodes (carbon-free and binder-free) showed greater salt decomposition with the formation of lithium-nickel-titanium oxyfluoride species, which was in agreement with ex-situ infrared spectroscopy showing greater blue shifts of P-F peaks with increased charged voltages, indicative of species with less F-coordination than salt PF6-anion on the electrode surface. Greater salt decomposition was coupled with the increasing dehydrogenation of EC with higher coating content on the surface. This work shows that Al2O3 coating on NMC622 is the most effective in reducing carbonate dehydrogenation and accompanied salt decomposition and rendering minimum capacity loss relative to TiO2 and Nb2O5 coating. [ABSTRACT FROM AUTHOR]

Roughening of metal electrodes in batteries is detrimental as it can lead to metal dendrites. Such dendrites can cause short circuits when they grow from the metal electrode to the other one, as can happen during battery operation when metal is plated onto the surface of an electrode. It has been suggested that solid electrolytes of sufficient elastic stiffness can suppress electrode surface roughening and dendriting, although experimental evidence is now emerging that this possibility is not valid. To investigate whether metal electrode surfaces will roughen during battery charging we carry out a linear perturbation analysis. Our calculations explore whether an electrode surface with one-dimensional sinusoidal roughness will experience growth of its amplitude. We assess a linear elastic electrolyte that is a single ion conductor bonded to a metal electrode being plated by a cathodic ionic current. We find that long wavelength perturbations will always increase in roughness. High current densities during battery charging are found to permit growth of the amplitude of small wavelength roughness. The stiffness of the solid electrolyte is found to play a role in limiting the growth of roughness, but its effect can always be overcome at high current densities and for long wavelength protrusions. © 2019 The Electrochemical Society. [ABSTRACT FROM AUTHOR]

Fundamental understanding of the reactivity between electrode and electrolyte is key to design the safety and life of Li-ion batteries. Herein X-ray photoelectron spectroscopy was used to examine the electrode/electrolyte interface (EEI) on carbon-free, binder-free LiCoO2 powder and thin-film electrodes in LP57 electrolyte as function of potential. Upon charging of LiCoO2 a marked growth of oxygenated and carbonated species was observed on the surface, consistent with electrolyte oxidation at high potentials. We also demonstrated that LiCoO2 oxide surface was prone to decompose the salt starting at 4.1 VLi, as evidenced by the increase of LiF and LixPFyOz species upon charging. By DFT calculations we proposed a correlation between the interface composition and the thermodynamic tendency of the EC solvent for dissociative adsorption on the LixCoO2 surface, through the generation of reactive acidic OH groups on the oxide surface, which can have a role in the observed salt decomposition. This is consistent with the evidence of HF and PF2O2 - species at 4.6 VLi observed by solution 19F-NMR measurements. Finally we compared EEI composition between composite and model electrodes and discussed the changes and mechanisms induced by the electrode composition or the use of electrolyte additives.We showed that the addition of diphenyl carbonate (DPC) in the electrolyte has a strong impact on the formation of solvent and salt decomposition products at the EEI layer. [ABSTRACT FROM AUTHOR]

In this work, passivation behavior and surface chemistry of 2507 super duplex stainless steel (SDSS) in acidified artificial seawater (ASW) containing different concentrations of thiosulfate are investigated using electrochemical techniques, X-ray photoelectron spectroscopy and the Point Defect Model. The 2507 SDSS is resistant to thiosulfate-induced pitting corrosion in the acidified ASW with a {[Cl-] + [SO4 2-]}: [S2O3 2-] ratio ranging from 59 to 5900, while the film dissolution rate is enhanced, resulting in a higher passive current density and lower polarization resistance. The passive film exhibits n-type semiconductivity in the acidified ASW and is independent of the thiosulfate levels. The donor density shows little change while the point defect diffusivity increases with increasing thiosulfate concentration. No elemental sulfur and sulfur-containing compounds can be detected on the well-passivated surface of 2507 SDSS, but increasing thiosulfate concentration results in the depletion of Cr2O3, enrichment of oxidized Fe, and thinning of the passive film. The influence of thiosulfate on the film composition depends on the passive states. Thiosulfate promotes the formation of Fe(II) in the prepassive region and accelerates the transformation of Cr(III) to Cr(VI) in the transpassive region. [ABSTRACT FROM AUTHOR]

Galvanic processes on silicon surfaces in alkaline fluoride-free solutions containing Cu(II) ions were investigated in this work. Deposition of copper (I) oxide (Cu2O) and copper metal at pH 14 onto silicon surfaces at room or elevated temperatures has been demonstrated. This deposition does not require the presence of a reducing agent in the solution. The results clearly show that Cu(II) ions can be reduced to Cu(I) or Cu(0) by silicon and, as a consequence, Cu2O or copper metal can be deposited at the surface of the substrate. [ABSTRACT FROM AUTHOR]

The diffusion and adsorption properties of an electrolyte additive polyethylenimine (PEI), employed during zinc (Zn) electrodeposition, are characterized via additive injection experiments implemented on a rotating disc electrode (RDE). Under galvanostatic Zn electrodeposition on a RDE, the transient response of the electrode potential upon PEI injection into the electrolyte is measured. The electrode potential response is indicative of the gradual adsorption of PEI on the electrode surface and thus provides an adsorption time constant. The measured adsorption time constant is analyzed using a transient diffusion-adsorption model, which leads to the determination of the PEI diffusion coefficient (DPEI) and its surface-limited adsorption rate constant (kads). Analysis confirms that PEI adsorption during Zn electrodeposition is limited by its slow diffusion and not by the fast kinetics of surface adsorption. The additive injection method implemented herein provides a convenient metrology for characterizing the diffusion and adsorption properties of polymeric additives used in numerous electrodeposition systems, while providing insights into the rate-limiting processes that govern additive adsorption during electrodeposition. [ABSTRACT FROM AUTHOR]

With the great progress being made in the development of cathodes in advanced lithium-sulfur (Li-S) batteries, the cycling stability of Li-metal anode has become an extremely urgent challenge presently. Herein, we report a new sulfonimide salt, namely lithium (trifluoromethanesulfonyl)(n-nonafluorobutanesulfonyl)imide (LiTNFSI), which can not only afford the excellent cycling and C-rate performances in Li-S batteries, but also deliver the superior cycling stability and comparable cycling efficiency for Li-metal anode, compared with conventional used LiTFSI (Li[(CF3SO2)2N]). It is demonstrated that the solid-electrolyte-interphase (SEI) films formed on the Li-metal anode in the LiTNFSI-based electrolyte are more stable than those formed in the LiTFSI-based one, due to the different surface chemistry developed on the Li-metal anode, essentially originated from the different anionic structures of Li salts (i.e., TNFSI- vs. TFSI-). [ABSTRACT FROM AUTHOR]

Nanoscale Au electrocatalysts demonstrate the extraordinary ability to reduce CO2 at low overpotentials with high selectivity to CO. Here, we investigate the role of surface chemistry on CO2 reduction behavior using AU25 and 5 nm Au nanoparticles. Onset potentials for CO2 reduction at AU25 nanoparticles in Nafion binders are shifted anodically by 190 mV while the hydrogen evolution reaction is shifted cathodically by 300 mV relative to Au foil. The net effect of this beneficial separation in onset potentials is relatively high Faradayic efficiencies for CO (90% at 0.8 V versus RHE) at high current densities. Experimental results show Faradayic efficiencies for CO are greatest using electrodes made with Nafion-immobilized Au25 nanoparticles. Likewise, CO2 reduction onset potential shifts are greater for smaller nanoparticles and when Nafion binders are used instead of (sulfonate-free) polyvinylidene fluoride. X-ray photoelectron spectroscopy analysis reveals Au nanoparticles may react with the sulfonates of Nafion binders. The results suggest sulfonate interfaces may alter the binding energies of key species or lead to favorable reconstructions, either of which ultimately results in remarkable improvements in Faradayic efficiencies relative to Au foil electrodes. [ABSTRACT FROM AUTHOR]

In this study, we proposed an electrolyte-insulator-semiconductor (EIS) device fabricating from Tb2O3 and Tb2Ti2O7 sensing films deposited on Si substrates through reactive sputtering. The effect of different annealing temperatures (600, 700, 800, and 900°C) on the structural and surface properties of the Tb2O3 and Tb2Ti2O7 sensing films was investigated. The performance of the Tb2O3 and Tb2Ti2O7 sensing films as pH sensors was evaluated and correlated with the observed material properties. Compared with the Tb2O3 sensing film, the EIS sensor using the Tb2Ti2O7 sensing film that had been annealed at 900°C exhibited better pH sensing performances, including a higher sensitivity (69.21 mV/pH), a smaller hysteresis voltage (4 mV), and a lower drift rate (0.113 mV/h) presumably the incorporation of Ti into the Tb2O3 to form a well-crystallized Tb2Ti2O7 structure. [ABSTRACT FROM AUTHOR]