Surface Chemical Distribution Research Articles

Insights into surface chemistry down to nanoscale: An accessible colour hyperspectral imaging approach for scanning electron microscopy

Chemical imaging (CI) is the spatial identification of molecular chemical composition and is critical to characterising the (in-) homogeneity of functional material surfaces. Nanoscale CI on bulk functional material surfaces is a longstanding challenge in materials science and is addressed here.We demonstrate the feasibility of surface sensitive CI in the scanning electron microscope (SEM) using colour enriched secondary electron hyperspectral imaging (CSEHI). CSEHI is a new concept in the SEM, where secondary electron emissions in up to three energy ranges are assigned to RGB (red, green, blue) image colour channels. The energy ranges are applied to a hyperspectral image volume which is collected in as little as 50 s. The energy ranges can be defined manually or automatically.Manual application requires additional information from the user as first explained and demonstrated for a lithium metal anode (LMA) material, followed by manual CSEHI for a range of materials from art history to zoology.We introduce automated CSEHI, eliminating the need for additional user information, by finding energy ranges using a non-negative matrix factorization (NNMF) based method. Automated CSEHI is evaluated threefold: (1) benchmarking to manual CSEHI on LMA; (2) tracking controlled changes to LMA surfaces; (3) comparing automated CSEHI and manual CI results published in the past to reveal nanostructures in peacock feather and spider silk. Based on the evaluation, CSEHI is well placed to differentiate/track several lithium compounds formed through a solution reaction mechanism on a LMA surface (eg. lithium carbonate, lithium hydroxide and lithium nitride). CSEHI was used to provide insights into the surface chemical distribution on the surface of samples from art history (mineral phases) to zoology (di-sulphide bridge localisation) that are hidden from existing surface analysis techniques. Hence, the CSEHI approach has the potential to impact the way materials are analysed for scientific and industrial purposes.

Surface chemical heterogeneous distribution in over-lithiated Li1+xCoO2 electrodes

In commercial Li-ion batteries, the internal short circuits or over-lithiation often cause structural transformation in electrodes and may lead to safety risks. Herein, we investigate the over-discharged mechanism of LiCoO2/graphite pouch cells, especially spatially resolving the morphological, surface phase, and local electronic structure of LiCoO2 electrode. With synchrotron-based X-ray techniques and Raman mapping, together with spectroscopy simulations, we demonstrate that over-lithiation reaction is a surface effect, accompanied by Co reduction and surface structure transformation to Li2CoO2/Co3O4/CoO/Li2O-like phases. This surface chemical distribution variation is relevant to the depth and exposed crystalline planes of LiCoO2 particles, and the distribution of binder/conductive additives. Theoretical calculations confirm that Li2CoO2-phase has lower electronic/ionic conductivity than LiCoO2-phase, further revealing the critical effect of distribution of conductive additives on the surface chemical heterogeneity evolution. Our findings on such surface phenomena are non-trivial and highlight the capability of synchrotron-based X-ray techniques for studying the spatial chemical phase heterogeneity.

The magnetic field of the chemically peculiar star V352 Peg

ABSTRACTWe present a spectropolarimetric analysis of the hot star V352 Peg. We have acquired 18 spectropolarimetric observations of the star with ESPaDOnS at the CFHT between 2018 and 2019 and completed our data set with one archival ESPaDOnS measurement obtained in 2011. Our analysis of the spectra shows that the star is on the main sequence and chemically peculiar, i.e. it is a Bp star, with overabundances of iron peak elements (Ti, Cr, and Fe) and underabundance of He and O. Through a Least-Square Deconvolution of each spectrum, we extracted the mean Zeeman signature and mean line profile of thousands of spectral lines and detected a magnetic field in V352 Peg. By modelling the Stokes I and V profiles and using the Oblique Rotator Model, we determined the geometrical configuration of V352 Peg. We also performed Zeeman–Doppler Imaging (ZDI) to provide a more detailed characterization of the magnetic field of V352 Peg and its surface chemical distributions. We find a magnetic field that is mainly dipolar, dominantly poloidal, and largely non-axisymmetric with a dipole field strength of ∼9 kG and a magnetic axis almost perpendicular to the rotation axis. The strong variability of Stokes I profiles also suggests the presence of chemical spots at the stellar surface.

Structural investigation of the Plasma Transferred Arc hardfaced glass mold after operation

The paper presents the results of research aimed at detecting the causes of premature wear of molds for glass shaping, manifesting the formation of pits in the Plasma Transferred Arc pad-welds in which the working surface of the mold was shaped. The weld microstructure was tested, the chemical composition was determined in the pad-weld’s cross-section, linear and surface chemical distributions were made in the pad-weld’s cross-section, the surface morphology in damaged areas, and the chemical composition of surface inclusions were examined. The too high temperature of formed glass associated with wettability of the glass of the mold was indicated as the primary cause of premature mold wear.

An aggregated understanding of physicochemical properties and surface functionalities of wheat straw node and internode

The variation of physicochemical characteristics across wheat straw node and internode with their surface functionalities was investigated. Node yielded slightly higher klason lignin, extractives and ash content than internode, which could be related to their morphology; specifically the higher ash and extractives content in the node are explained by thicker epidermis tissue. These properties make nodes defects in composite and bio-energy production, while internodes could be more favourable for aerobic digestion for biogas production. Surface chemical distribution examinations revealed, higher intensities of the hydrophobic aliphatic fraction of waxes on the outer surface, whereas the hydrophilic tendency of inner surface was reflected by the broad and more intense band in the 3200–3600cm−1 region, due to OH stretching vibration of hydroxyl groups. This could translate into better interface when water-based resins are used for wheat straw composites. An environmentally friendly pre-treatment was employed to further investigate the effects on the physicochemical properties. The results showed: i) the reduction of waxes from the outer surface, ii) significantly lower (P<0.05) extractives, along with iii) significant dissolution of Si (weight%) on the outer surface of both node and internode. These results could be beneficiary for composite production or for pulp and paper manufacturers.

Facile fabrication of superhydrophobic polyimide/polytetrafluoroethylene composite coatings with high water adhesion

ABSTRACTA facile casting method was used to fabricate superhydrophobic polyimide/polytetrafluoroethylene composite coatings with high water adhesion. The water contact angles of the composite coatings were larger than 150 °, expressing superhydrophobic property. But water droplets pinned tightly on the composite coating, even if it was upside down. The X‐ray photoelectron spectrum analysis indicated that polyimide and polytetrafluoroethylene coexisted in the resulting coating. The observation with scanning electron microscopy showed that the composite coating formed lotus‐like structure with many spherical polyimide papillae randomly bonding on the surface. But the tops of the polyimide papillae were not covered by lance‐shaped Teflon fibres, forming an inhomogenous and discontinuous surface structure. This special surface chemical distribution and lotus‐like structure combined to contribute to the high adhesive superhydrophobicity. This simple method may greatly extend the application range of high adhesive superhydrophobic surfaces in microcontrollable and microfluidic application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42810.

Scanning Photoemission Spectromicroscopic Study of 4-nm Ultrathin SiO3.4 Protrusions Probe-Induced on the Native SiO2 Layer

Atomic force microscopy probe-induced large-area ultrathin SiO(x) (x ≡ O/Si content ratio and x > 2) protrusions only a few nanometers high on a SiO(2) layer were characterized by scanning photoemission microscopy (SPEM) and X-ray photoemission spectroscopy (XPS). SPEM images of the large-area ultrathin SiO(x) protrusions directly showed the surface chemical distribution and chemical state specifications. The peak intensity ratios of the XPS spectra of the large-area ultrathin SiO(x) protrusions provided the elemental quantification of the Si 2p core levels and Si oxidation states (such as the Si(4+), Si(3+), Si(2+), and Si(1+) species). The O/Si content ratio (x) was evidently determined by the height of the large-area ultrathin SiO(x) protrusions.

Surface Characterization of PZN Ceramics Prepared by a Columbite B-Site Precursor

Pyrochlore-type PZN ceramics have been obtained from a two-stage process with columbite B-site precursor. In order to determine the chemical composition of these samples, a combination between X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques has been performed. XRD analysis revealed the coexistence of unreacted PbO starting precursor and major phase of the pyrochlore-type PZN phase as average composition from the bulk volume. While different binding energies (multicomponents) of each chemical element e.g. Pb, Zn, Nb and O from the surface of PZN ceramics were identified by XPS, indicating inhomogeneous surface chemical distribution within these columbite-route samples.

Time-of-flight secondary-ion mass spectrometry for the surface characterization of solid-state pharmaceuticals

Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) is a highly surface sensitive analytical method for surface chemical identification and surface chemical distribution analysis (mapping). Here we have explored the application of ToF-SIMS for the characterization of solid-state pharmaceuticals and highlight specific case studies concerning the distribution and stability of pharmaceutical actives within solid matrices (pellets and polymeric carriers) and the face-specific properties of pharmaceutical crystals.

Loading and release of a model protein from porous silicon powders

AbstractPorous silicon (p‐Si) has been investigated as a novel delivery system for protein therapeutics. The loading of a model hydrophilic protein, Papain into anodised and stain etched p‐Si powders has been investigated using X‐ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR) and correlations made with the release kinetics. Variation in specific Papain (Amide I/II) and p‐Si (Si–Hx ) functional group absorbances with Papain loading level was characterised using FTIR, while the surface chemical distribution was assessed using XPS. A combination of burst release and sustained release of Papain was observed from p‐Si powders; this was dependent on p‐Si type and the Papain loading level. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Nickel on silica systems. Surface features and their relationship with support, preparation procedure and nickel content

The characteristics and structure of several silica-supported nickel systems, prepared by impregnation and precipitation-deposition and in a wide range of nickel contents (from 0.58 up to 69 wt% Ni), have been studied. Using mainly conventional sorption techniques the textural properties - BET surface area, pore volume, average pore radius, pore size distribution - and surface chemical distribution - nickel surface area, reduction degree, dispersion, crystallite particle diameter - of the samples have been determined. All these characteristics have been related to each other and globally analyzed to advance in the understanding of the final structure of the catalysts and its relationship with support structure, preparation procedure and nickel content.

Effect of thermal treatments on surface chemical distribution and catalyst activity in nickel on silica systems

The reducibility of several nickel on silica systems prepared by incipient wetness impregnation and precipitation-deposition has been studied using TPR and TG. The analysis of the results has allowed us to determine the minimum drying and reduction temperatures for both impregnation and precipitation catalysts. From an analysis of the obtained results, together with X-ray diffraction and the study of the reduction degree, dispersion and nickel particle size of catalysts activated at different reduction temperatures, conclusions on the nickel surface chemical distribution have been derived. An optimal reduction temperature for the catalysts has been determined from activity considerations in the hydrogenation of sunflower seed oil.

A seasonal three‐dimensional ecosystem model of nitrogen cycling in the North Atlantic Euphotic Zone

A seven‐component upper ocean ecosystem model of nitrogen cycling calibrated with observations at Bermuda Station “S” has been coupled to a three‐dimensional seasonal general circulation model (GCM) of the North Atlantic ocean. The aim of this project is to improve our understanding of the role of upper ocean biological processes in controlling surface chemical distributions, and to develop approaches for assimilating large data sets relevant to this problem. A comparison of model predicted chlorophyll with satellite coastal zone color scanner observations shows that the ecosystem model is capable of responding realistically to a variety of physical forcing environments. Most of the discrepancies identified are due to problems with the GCM model. The new production predicted by the model is equivalent to 2 to 2.8 mol m−2 yr−1 of carbon uptake, or 8 to 12 GtC/yr on a global scale. The southern half of the subtropical gyre is the only major region of the model with almost complete surface nitrate removal (nitrate&lt;0.1 mmol m−3). Despite this, almost the entire model is nitrate limited in the sense that any addition of nitrate supply would go predominantly into photosynthesis. The only exceptions are some coastal upwelling regions and the high latitudes during winter, where nitrate goes as high as ∼10 mmol m−3.