Local Chemistry Research Articles

Investigation of crystallographic changes across the Cr/a-Si interface by X-ray absorption spectroscopy

X-ray Absorption Fine Structure spectroscopy (XAFS) has been employed to investigate the crystallographic changes that evolved across the Cr/a-Si interface as a function of annealing temperature. A stack of 400nm a-Si and50nm metallic Cr film is deposited onto a fused silica substrate by electron beam evaporation. Thesestacks are subjected to annealing temperature from 200°C to 700°C in nitrogen-rich atmosphere to facilitate the metal diffusion and subsequent phase formation across the interface. XAFS investigations were carried out in twoconfigurations to study the change in local chemistry of Cr indepth andtop layers of the stack simultaneously. XAFS analysis confirmed thatthe FSC stack annealed at 200°C has a dominant metallic Cr concentration along with a minority content of Cr2O3 andCr3Si. On increasing the annealing temperature, metallic Cr converted into Cr2O3 andCr3Si up to an intermediate temperature of 500°C and finally at 700°C it transformed to CrSi2. It is also confirmed from total reflection XAFSthatCr diffusion intoa-Si is the preferred phenomenon that takes place acrossthe Cr/a-Si interface. The diffusion of Cr and subsequent thermodynamic conditions required for the formation of different Cr phases are discussed to understand the factors that affect the Schottky properties of the Cr/a-Si interface.

Characterization of chemical and physical changes in atmospheric aerosols during fog processing at Baengnyeong Island, South Korea

In situ interactions between aerosols and atmospheric fog droplets were explored using aerosol physical and chemical measurements and fog samples taken at the Baengnyeong Island Intensive Air Quality Monitoring Station, South Korea during June 16th to July 21st, 2014. To investigate wet scavenging by fog, aerosols were characterized by aerosol mass spectrometer before, during, and after five fog events. Total non-refractory PM1 mass decreased by an average of 22.8% with the onset of fog. The scavenging efficiency (η) of organics was 7–34%, where lower η was associated with lower organic oxidation and hygroscopicity. The η was 16–68% for NH4+, -1–35% for SO4, and 17–86% for NO3−, consistent with previous studies and the relatively high NO3− hygroscopicity. The variation in scavenging was size dependent for both organics and NO3−. Particles with lower NO3−η on 7/18 were smaller (mode = 346 nm), while those with higher NO3−η were larger (593 nm). Differences in mass were also explored before and after fog events. Three episodes showed overall decreases in all the components after the fog event, while two episodes showed overall increases, most notably in organics. Both organic mass and SO2+/H2SO4+ ratio were used to indicate the prevalence of hydroxymethanesulfonate (HMS), an aqueous secondary organic aerosol (aqSOA) formation marker, which increased after the 7/18 fog episode. The aerosol carbon oxidation state decreased toward the end of all fog episodes suggesting possible molecular fragmentation and loss of highly oxidized functional groups. On 7/18, the organic content developed lower O:C and higher H:C moving “up” a slope of −1 in a van Krevelen diagram over the course of the fog episode, indicating carboxylic acid or hydroxycarbonyl loss. This study explores relatively rare time-resolved aerosol fog processing measurements. The results confirm previously established relationships between scavenging and particle size, demonstrate overall increases and decreases in particle mass after fog processing based on dominant local chemistry and wet deposition, and show predominant decreases in organic oxidation after fog processing, thereby, contributing to our understanding of particle processing and organic cycling in the atmosphere.

Creating Hybrid Coordination Environment in Fe-Based Single Atom Catalyst for Efficient Oxygen Reduction.

Tailoring the local chemistry environment to optimize the geometric and electronic properties of single atom catalysts has received much attention recently. Yet, most efforts have been devoted to establishing the preferable binding between the solid support and the single metal atom. In this work, a hybrid coordination environment was created for Fe‐based single atom catalysts, comprising inorganic anchoring site from the support and organic ligands from the precursor. Using N,S co‐doped graphene oxide as the support, Fe phthalocyanine was selectively anchored by the N/S sites, creating the unique N/S−Fe−N4 active sites as evidenced by extended X‐ray absorption fine structure and Mössbauer spectrometry. Compared with other analogues with different metal centers or support, N/S−Fe−N4 showed much improved activity in oxygen reduction reaction, delivering onset and half‐wave potentials of 1.02 and 0.94 V. This was superior over the state‐of‐the‐art 20 wt % Pt/C and the classic Fe−N4 carbon catalysts. Density functional theory calculations revealed that the interaction between phthalocyanine ligands and heteroatom dopant from the support pushed electrons of Fe site to para‐position, facilitating O2 adsorption and activation. This work shows the exciting opportunities of creating a hybrid coordination environment in single atom catalysts and paves a new avenue of improving their catalytic performance.

Water masses and their associated temperature and cross-domain biotic factors co-shape upwelling microbial communities

Disentangling the drivers and mechanisms that shape microbial communities in a river-influenced coastal upwelling system requires considering a hydrologic dimension that can drive both deterministic and stochastic community assembly by generating hydrological heterogeneity and dispersal events. Additionally, ubiquitous and complex microbial interactions can play a significant role in community structuring. However, how the hydrology, biotic, and abiotic factors collectively shape microbial distribution in the hydrologically complicated river plume-upwelling coupling system remains unknown. Through underway sampling and daily observations, we employed 16S and 18S ribosomal RNA sequencing to disentangle drivers and mechanisms shaping the protist-bacteria microbiota in a river-influenced coastal upwelling system. Our findings indicate that the composition of microbial communities was water mass specific. Collectively, water mass, local water chemistry (mostly temperature) and biotic interaction (mostly cross-domain biotic interaction) shaped the protistan-bacterial communities. In comparison to protists, bacteria were more influenced by abiotic factors such as temperature than by cross-domain biotic factors, implying a stronger coupling of geochemical cycles. Both deterministic and stochastic processes had an effect on the distribution of microbial communities, but deterministic processes were more important for bacteria and were especially pronounced for upwelling communities. The co-occurrence network revealed strong associations between the protistan assemblages Orchrophyta and Ciliophora and the bacterial assemblages Alphaproteobacteria, Deltaproteobacteria, and Bacteroidetes, which may reflect predation and mutualism interactions. Overall, this study emphasizes the importance of taking water masses, temperature and domains of life into account when seeking to understand the drivers and assemblies of protist-bacteria microbiome dynamics in coastal upwelling systems, which is especially true given the complex and dynamic nature of the coastal ecosystem.

From Doping to Dilution: Local Chemistry and Collective Interactions of La in HfO2

Lanthanum (La) doping is considered as a promising route to overcome reliability issues of switchable ferroelectric HfO2‐based devices. This study links the local chemistry at the La lattice sites with local and collective electronic properties of the La:HfO2matrix using hard X‐ray photoelectron spectroscopy. The satellite structure of the La 3dcore level, the plasmonic excitation energies, and core‐level rigid binding energy shifts are investigated for La:HfO2samples with a wide range of La doping, ranging from 3.5% to 33%, i.e., from the doping to dilution level. The emerging chemical phases and electronic properties are discussed as a function of La content. From the evolution of the plasmon excitation energies and rigid binding energy shifts, it is concluded that electronic charge compensation by oxygen vacancies occurs for increasing La content.

Experimental Investigation on Corrosion Behavior of X80 Pipeline Steel under Carbon Dioxide Aqueous Conditions.

A combined steady-state and transient approach is employed to investigate the corrosion behavior of X80 pipeline steel in carbon dioxide-saturated brines. Continuous bubbling of carbon dioxide into a test vessel with 1 liter capacity is performed to simulate the flowing condition. The measurement of time-dependent open-circuit potential, polarization resistance, and electrochemical impedance spectroscopy (EIS) is conducted to interpret the evolution of dissolution processes at the corroding interface. Three distinguishing stages are observed at a temperature of 60 °C during a whole exposure of 144 h. Analyses mainly based on the consecutive mechanism show that after the first stage of the active-adsorption state, the anodic reaction is significantly retarded by the accumulation of (FeOH)ads on the iron surface, causing a sharp increase in the polarization resistance and the open-circuit potential, as well as the disappearance of the inductive loop in EIS. At the third stage, the formation of the corrosion product layer similarly reduces both the anodic and cathodic reactions, which arouses a linear increase in the polarization resistance with time and a capacitive loop in EIS but changes the open-circuit potential slightly. An increase in salinity in this study reduces the polarization resistance and enhances iron dissolution by promoting the formation and relaxation of (FeOH)ads; however, it brings little change to the developing time of the three stages obviously. At a low temperature of 20 °C, a protective product layer is not observed in carbon dioxide-saturated brine, and the dissolution of iron is mainly under activation control during the whole exposure. A notable enlarged polarization resistance and different interfacial processes are observed in an alkaline solution compared with those in acidic environments, which is deduced to be resulted from an impedance in the relaxation of (FeOH)ads by increasing pH. The observations in this study support well that the iron dissolution reaction at the initial stage exposed in carbon dioxide aqueous environments is dominant by water adsorption on the iron surface, and further investigation should be performed on the role that carbon dioxide plays in the evolution of corrosion products and the formation of a protective film on the steel surface by taking into account local water chemistry.

In-depth understanding of local soil chemistry reveals that addition of Ca may counteract the mobilisation of 226Ra and other pollutants before wetland creation on the Grote Nete river banks

The “Sigma plan” https://www.sigmaplan.be/en/ aims to create in Belgium inundation zones along the Grote Nete river to prevent Antwerp from flooding in extreme weather conditions. The riverbanks of the Grote Nete are at some hotspots historically contaminated by the phosphate industry resulting in Naturally Occurring Radionuclides (NOR) legacy. 226Ra is from a radiation protection point of view one of the most important radionuclides present at the hot spot under study, with a local soil activity concentration higher than 3000 Bq/kg 226Ra. In this paper, we identify the most relevant mechanisms governing the mobility of 226Ra. We selected for this study the role of CaSO4.2H2O, clay minerals and humic acids as the main contributors determining the speciation of Ra, due to their presence at the hot spot, their cation exchange capacity and their functional group density, respectively. Various novel analytical chemistry approaches were developed to study the prevailing reaction mechanisms that impact the solid-liquid distribution of 226Ra. We show that 226Ra coprecipitates in a (Ca,Ra)SO4 solid solution due to the high Ca2+ and SO42− concentrations in the local hot spot. If CaSO4.2H2O is not saturated in the soil solution, 226Ra adsorption to clay minerals counteracts the tendency of 226Ra partitioning to the liquid phase by interactions with humic and fulvic acids. Interactions between different soil compounds may further alter the partitioning of Ra. As, Cd, Pb and Zn in the hot spot are significantly above background values in Flemish sediments. Pb may be coprecipitated as sulphate salts, whereas Cd and Zn are most probably partially present as arsenate salts. The excess of Zn may interact with humic acids. The observed reaction mechanisms suggest that Ca2+ might play a key role in the immobilisation of Ra. The role of Ca2+ as immobilisation agent of the other contaminants is discussed.

3D direct writing of bandgap tunable nanocrystals in transparent material

Ultrafast-laser direct lithography strategy engineers local chemistry at the nanoscale in glass, to achieve 3D direct writing of nanocrystals with a widely tunable bandgap. Feng Chen provides a commentary on the reported technique and its potential for nanocrystal-based device fabrication.

Study of cluster ions produced from ToF-SIMS analysis of a U-6%Nb target

Cluster ions have been previously observed during time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of metals and metal oxides. Here, we have used ToF-SIMS to investigate cluster ions formed from the hydrocarbon-containing overlayer, the mixed U and Nb surface oxide, and underlying metal of a U-6 %Nb (U6Nb) target. In the overlayer, we observe UxOy+ oxides and U-species likely containing hydrocarbons. In the surface oxide, we observe UO2+, U2O2+, U3O5+, and U4O6+ as the most intense ions for each family of oxide ions containing x U atoms. Nb oxides for NbO1-2- were only observed in negative polarity. In contrast to the oxide, analysis of the underlying U6Nb alloy resulted in repeating units of Un+, Un(Nb)+, and Un(Nb2) + ions for n = 3–11 as the highest intensity ions for each family of ions containing n U atoms. Nbn+ clusters were not observed. Un+, Un(Nb)+, and Un(Nb2)+ clusters containing C- and O-species were observed and were likely produced from soluble C or O species or precipitates known to be present in U6Nb.Cleaning of the surface oxide with varying ion current density of 25 keV 69Ga+ to perturb local chemistry did not influence ion distributions and suggests that observed high intensity ions are stable lattice fragments ejected from the surface oxide. Cleaning of the underlying alloy with varying ion current density increased the content of Un+, Un(Nb)+, or Un(Nb2)+ clusters in comparison to the C and O-containing species. These results suggest a different mechanism of cluster ion formation than what was observed in the metal oxide. Preferential sputtering of U from the surface or low local Nb content may also contribute to the enrichment of U in observed clusters. We conclude that cluster ions may be of great value in studying local chemistry, contaminants, and impurities in oxides and alloys.

Introducing NICE guidelines for intravenous fluid therapy into a district general hospital

BackgroundNational Institute for Health and Care Excellence (NICE) guidelines on intravenous fluid prescribing for adults in hospital, issued in 2013, advised less use of 0.9% sodium chloride than current practice,...

He-enhanced heterogeneity of radiation-induced segregation in FeNiCoCr high-entropy alloy

• Atom probe tomography reveals radiation-induced segregation around He bubbles • Electron energy-loss spectroscopy measures He density and pressure inside bubbles • The inverse Kirkendall effect dominates RIS around over-pressurized He bubbles • He atoms retard Co diffusion via the vacancy mechanism and enhance Co segregation • Local chemical order of medium-/high-entropy alloys can be tailored via He bubbles Radiation-induced segregation (RIS) is a typical non-equilibrium process that can dramatically alter the behavior of defect sinks and material properties under irradiation. However, RIS mechanisms have been rarely studied around small He bubbles owing to the technical challenges involved in direct measurements of local chemistry. Here, using state-of-the-art atom probe tomography, we report the RIS behavior near He bubbles in the FeNiCoCr high-entropy alloy that indicates Co segregates most strongly, followed by weaker Ni segregation, whereas Fe and Cr are depleted almost to the same degree. Exceptionally, the magnitude of Co segregation around He bubbles is higher than previously measured values at voids and dislocation loops. Electron energy-loss spectroscopy was used to measure the He density and pressure inside individual bubbles. We demonstrate that He bubbles are over-pressurized at the irradiation temperature that could result in the vacancy bias and the subsequent vacancy-dominated RIS mechanism. First-principles calculations further reveal that there are repulsive interactions between He and Co atoms that may reduce the frequency of Co-vacancy exchange. As a result, He atoms likely retard Co diffusion via the vacancy mechanism and enhance the heterogeneity of RIS in Co-containing multicomponent alloys. These insights could provide the basis for understanding He effects in nuclear materials and open an avenue for tailoring the local chemical order of medium-and high-entropy alloys.

Mechanistic Advantages of Organotin Molecular EUV Photoresists.

Extreme ultraviolet (EUV)-induced radiation exposure chemistry in organotin-oxo systems, represented by the archetypal [(R-Sn)12O14(OH)6](A)2 cage, has been investigated with density functional theory. Upholding existing experimental evidence of Sn-C cleavage-dominant chemistry, computations have revealed that either electron attachment or ionization can single-handedly trigger tin-carbon bond cleavage, partially explaining the current EUV sensitivity advantage of metal oxide systems. We have revealed that tin atoms at different parts of the molecule react differently to ionization and electron attachment and have identified such selectivity as a result of local coordination chemistry instead of the macro geometry of the molecule. An ionization-deprotonation pathway has also been identified to explain the observed evolution of an anion conjugate acid upon exposure and anion mass dependence in resist sensitivity.

How to Use Localized Surface Plasmon for Monitoring the Adsorption of Thiol Molecules on Gold Nanoparticles?

The functionalization of spherical gold nanoparticles (AuNPs) in solution with thiol molecules is essential for further developing their applications. AuNPs exhibit a clear localized surface plasmon resonance (LSPR) at 520 nm in water for 20 nm size nanoparticles, which is extremely sensitive to the local surface chemistry. In this study, we revisit the use of UV-visible spectroscopy for monitoring the LSPR peak and investigate the progressive reaction of thiol molecules on 22 nm gold nanoparticles. FTIR spectroscopy and TEM are used for confirming the nature of ligands and the nanoparticle diameter. Two thiols are studied: 11-mercaptoundecanoic acid (MUDA) and 16-mercaptohexadecanoic acid (MHDA). Surface saturation is detected after adding 20 nmol of thiols into 1.3 × 10−3 nmol of AuNPs, corresponding approximately to 15,000 molecules per AuNPs (which is equivalent to 10.0 molecules per nm2). Saturation corresponds to an LSPR shift of 2.7 nm and 3.9 nm for MUDA and MHDA, respectively. This LSPR shift is analyzed with an easy-to-use analytical model that accurately predicts the wavelength shift. The case of dodecanehtiol (DDT) where the LSPR shift is 15.6 nm is also quickly commented. An insight into the kinetics of the functionalization is obtained by monitoring the reaction for a low thiol concentration, and the reaction appears to be completed in less than one hour.

Ribosome exit tunnel electrostatics.

The impact of ribosome exit tunnel electrostatics on the protein elongation rate or on forces acting upon the nascent polypeptide chain are currently not fully elucidated. In the past, researchers have measured the electrostatic potential inside the ribosome polypeptide exit tunnel at a limited number of spatial points, at least in rabbit reticulocytes. Here we present a basic electrostatic model of the exit tunnel of the ribosome, providing a quantitative physical description of the tunnel interaction with the nascent proteins at all centro-axial points inside the tunnel. We show that a strong electrostatic screening is due to water molecules (not mobile ions) attracted to the ribosomal nucleic acid phosphate moieties buried in the immediate vicinity of the tunnel wall. We also show how the tunnel wall components and local ribosomal protein protrusions impact on the electrostatic potential profile and impede charged amino acid residues from progressing through the tunnel, affecting the elongation rate in a range of -40% to +85% when compared to the average elongation rate. The time spent by the ribosome to decode the genetic encrypted message is constrained accordingly. We quantitatively derive, at single-residue resolution, the axial forces acting on the nascent peptide from its particular sequence embedded in the tunnel. The model sheds light on how the experimental data point measurements of the potential are linked to the local structural chemistry of the inner wall, shape, and size of the tunnel. The model consistently connects experimental observations coming from different fields in molecular biology, x-ray crystallography, physical chemistry, biomechanics, and synthetic and multiomics biology. Our model should be a valuable tool to gain insight into protein synthesis dynamics, translational control, and the role of the ribosome's mechanochemistry in the cotranslational protein folding.

Regulating local chemistry in ZrCo-based orthorhombic hydrides via increasing atomic interference for ultra-stable hydrogen isotopes storage

Developing a universal and reliable strategy for the modulation of composition and structure of energy storage materials with stable cycling performance is vital for hydrogen and its isotopes storage advanced system, yet still challenging. Herein, an ultra-stable lattice structure is designed and verified to increase atomic chaos and interference for effectively inhibiting disproportionation reaction and improving cycling stability in ZrCo-based hydrogen isotopes storage alloy. After screening in terms of configuration entropy calculation, we construct Zr1−xNbxCo1−2xCuxNix (x = 0.15, 0.2, 0.25) alloys with increased atomic chaos, and successfully achieve stable isostructural de-/hydrogenation during 100 cycles, whose cycling capacity retentions are above 99%, much higher than 22.4% of pristine ZrCo alloy. Both theoretical analysis and experimental evidences indicate the high thermo-stability of orthorhombic lattice in Zr0.8Nb0.2Co0.6Cu0.2Ni0.2 alloy. Notably, the increased atomic chaos and interference in Zr0.8Nb0.2Co0.6Cu0.2Ni0.2 alloy causes regulation in hydrogen local chemical neighborhood, thereby confusing the hydrogen release order, which effectively eliminates lattice distortion and unlocks an ultra-stable lattice structure. This study provides a new and comprehensive inspiration for hydrogen atoms transport behaviors and intrinsic reason of stable orthorhombic transformation, which can contribute to paving the way for other energy storage materials modulation.

Growth and structural transitions of core-shell nanorods in nanocrystalline Al-Ni-Y

Unique nanorod precipitates with a core-shell structure are found to nucleate from the grain boundaries of a bulk nanocrystalline Al-Ni-Y alloy fabricated via powder consolidation, contributing significantly to stabilization and strengthening. The local structure, chemistry, and evolution of these features during annealing are reported here. In the as-consolidated state, the nanorods can be either structurally ordered or disordered, yet a consistent chemical patterning is found where the core is primarily Al plus C while the shell is enriched with Y. As annealing time increases, more nanorods transform to an ordered structure as they coarsen while the core composition remains unchanged. In contrast, the shell chemistry transitions from Y-rich to Ni-rich with longer annealing treatments, most likely due to the different diffusivities of Y and Ni in Al. Moreover, a spatial and chemical correlation between the nanorods and amorphous complexions is observed, suggesting that these complexions serve as preferential nucleation sites.

Coatings Functionalization via Laser versus Other Deposition Techniques for Medical Applications: A Comparative Review

The development of new biological devices in response to market demands requires continuous efforts for the improvement of products’ functionalization based upon expansion of the materials used and their fabrication techniques. One viable solution consists of a functionalization substrate covered by layers via an appropriate deposition technique. Laser techniques ensure an enhanced coating’s adherence to the substrate and improved biological characteristics, not compromising the mechanical properties of the functionalized medical device. This is a review of the main laser techniques involved. We mainly refer to pulse laser deposition, matrix-assisted, and laser simple and double writing versus some other well-known deposition methods as magnetron sputtering, 3D bioprinting, inkjet printing, extrusion, solenoid, fuse-deposition modeling, plasma spray (PS), and dip coating. All these techniques can be extended to functionalize surface fabrication to change local morphology, chemistry, and crystal structure, which affect the biomaterial behavior following the chosen application. Surface functionalization laser techniques are strictly controlled within a confined area to deliver a large amount of energy concisely. The laser deposit performances are presented compared to reported data obtained by other techniques.

On Correlations between Local Chemistry, Distortions and Kinetics in High Entropy Nitrides: An Ab Initio Study

On Correlations between Local Chemistry, Distortions and Kinetics in High Entropy Nitrides: An Ab Initio Study

Coupling the chemistry and topography of block copolymer films patterned by soft lithography for nanoparticle organization.

Soft lithography techniques have become leading mesoscale approaches for replicating topographic features in polymer films. So far, modified polymer films formed by soft lithography only featured topographic heterogeneity. Here we demonstrate the application of soft lithography techniques to block copolymer films, and show that the preferential affinity of one of the blocks to the stamping material leads to chemical heterogeneity that corresponds to the topographic features. Detailed surface and structural characterization of the patterned films provided information on its three-dimensional structure, revealing insights on the domain reorganization that takes place in the block copolymer film concomitantly with topography formation. The formed structures were utilized for the selective assembly of gold nanoparticles into hierarchical structures. The versatility of this combined nanofabrication/self-assembly approach was demonstrated by the assembly of two types of metallic nanoparticles into two different arrangements with full control over the location of each type of nanoparticles.

Nano carbon materials synthesized by local probe chemistry

Nano carbon materials synthesized by local probe chemistry