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This guide deals with methods to control surface charging during XPS analysis of insulating samples and approaches to extracting useful binding energy information. The guide summarizes the causes of surface charging, how to recognize when it occurs, approaches to minimize charge buildup, and methods used to adjust or correct XPS photoelectron binding energies when charge control systems are used. There are multiple ways to control surface charge buildup during XPS measurements, and examples of systems on advanced XPS instruments are described. There is no single, simple, and foolproof way to extract binding energies on insulating material, but advantages and limitations of several approaches are described. Because of the variety of approaches and limitations of each, it is critical for researchers to accurately describe the procedures that have been applied in research reports and publications., Funding Agencies|Swedish Research Council VRSwedish Research Council [2018-03957]; Carl Tryggers Stiftelse Contract [CTS 17:166]; DOE Office of Biological and Environmental ResearchUnited States Department of Energy (DOE)

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.

Coupling TiO2 with WO3 to develop photocatalytic heterojunctions is one of the most widely used strategies to realize their superior photoactivity. However, the interfacial charge transfer in these heterojunctions is not efficient to achieve an optimized activity. For the first time, the present study reports a facile hydrolysis-hydrothermal approach, whereby ultradispersed TiO2 nanocrystals and WO3 nanorods are concurrently anchored onto reduced graphene oxide (rGO) and formed a novel Z-scheme heterojunction photocatalyst TiO2/rGO/WO3 (TRW). Transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoluminescence spectra (PL) are employed to characterize TRW. Control experiments indicate that, in the synthesis process, glucose and the by-product sodium chloride from the hydrolysis reactions are critical for forming highly dispersed and uniform-sized TiO2 nanocrystals and WO3 nanorods. Compared with TiO2/WO3 nanocomposites, TRW shows enhanced activity for bacterial inactivation under simulated solar light. As confirmed by electrochemical characterizations and the reactive oxygen species, rGO in TRW suppresses the recombination of electron-hole pairs and boosts the O2 reduction reactions during photocatalytic process. Z-scheme electron transfer in TRW is proposed based on surface redox reactions and XPS analysis after light irradiation. This study could provide a new clue for designing graphene-based heterojunction photocatalysts for environmental applications.

The scalable synthesis of highly transparent and robust sub-monolayers of Co₃O₄ nano-islands, which efficiently catalyze water oxidation, is reported. Rapid aerosol deposition of Co₃O₄ nanoparticles and thermally induced self-organization lead to an ultra-fine nano-island morphology with more than 94% light transmission at a wavelength of 500 nm. These transparent sub-monolayers demonstrate a remarkable mass-weighted water oxidation activity of 2070–2350 A gCo₃O₄ ⁻¹ and per-metal turnover frequency of 0.38–0.62 s⁻¹ at an overpotential of 400 mV in 1 m NaOH aqueous solution. This mixed valent cobalt oxide structure exhibits excellent long-term electrochemical and mechanical stability preserving the initial catalytic activity over more than 12 h of constant current electrolysis and 1000 consecutive voltammetric cycles. The potential of the Co₃O₄ nano-islands for photoelectrochemical water splitting has been demonstrated by incorporation of co-catalysts in GaN nanowire photoanodes. The Co₃O₄-GaN photoanodes reveal significantly reduced onset overpotentials, improved photoresponse and photostability compared to the bare GaN ones. These findings provide a highly performing catalyst structure and a scalable synthesis method for the engineering of efficient photoanodes for integrated solar water-splitting cells.

Colistin is often the only effective antibiotic against the respiratory infections caused by multidrug-resistant Gram-negative bacteria. However, colistin-resistant multidrug-resistant isolates have been increasingly reported and combination therapy is preferred to combat resistance. In this study, five combination formulations containing colistin (COL) and rifampicin (RIF) were prepared by spray drying. The lowest minimum inhibitory concentration (MIC) value against Pseudomonas aeruginosa PAO1 was measured for the formulation of COL/RIF = 4:1 with relatively high emitted doses (over 80%) and satisfactory fine particle fractions (over 60%). Data from X-ray photoelectron spectroscopy (XPS) and nano-time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed the surfaces of particles were mainly covered by rifampicin even for the formulation with a mass ratio of COL/RIF = 4:1. Because colistin is hygroscopic and rifampicin is hydrophobic, moisture absorption of combination formulations was significantly lower than the pure colistin formulation in the dynamic vapour sorption results. To investigate the dissolution characteristics, four dissolution test methods (diffusion Franz cell, modified Franz cell, flow-through and beaker methods) were employed and compared. The modified Franz cell method was selected to test the dissolution behaviour of aerosolised powder formulations to eliminate the effect of membrane on dissolution. The results showed that surface enrichment of hydrophobic rifampicin neither affected aerosolisation nor retarded dissolution rate of colistin in the combination formulations. For the first time, advanced surface characterisation techniques of XPS and ToF-SIMS have shown their capability to understand the effect of surface composition on the aerosolisation and dissolution of combination powders., Colistin is often the only effective antibiotic against the respiratory infections caused by multidrug-resistant Gram-negative bacteria. However, colistin-resistant multidrug-resistant isolates have been increasingly reported and combination therapy is preferred to combat resistance. In this study, five combination formulations containing colistin (COL) and rifampicin (RIF) were prepared by spray drying. The lowest minimum inhibitory concentration (MIC) value against Pseudomonas aeruginosa PAO1 was measured for the formulation of COL/RIF = 4:1 with relatively high emitted doses (over 80%) and satisfactory fine particle fractions (over 60%). Data from X-ray photoelectron spectroscopy (XPS) and nano-time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed the surfaces of particles were mainly covered by rifampicin even for the formulation with a mass ratio of COL/RIF = 4:1. Because colistin is hygroscopic and rifampicin is hydrophobic, moisture absorption of combination formulations was significantly lower than the pure colistin formulation in the dynamic vapour sorption results. To investigate the dissolution characteristics, four dissolution test methods (diffusion Franz cell, modified Franz cell, flow-through and beaker methods) were employed and compared. The modified Franz cell method was selected to test the dissolution behaviour of aerosolised powder formulations to eliminate the effect of membrane on dissolution. The results showed that surface enrichment of hydrophobic rifampicin neither affected aerosolisation nor retarded dissolution rate of colistin in the combination formulations. For the first time, advanced surface characterisation techniques of XPS and ToF-SIMS have shown their capability to understand the effect of surface composition on the aerosolisation and dissolution of combination powders.

A facile, two-step method for chemically attaching single-stranded DNA to graphitic surfaces, represented here by carbon nanotubes, is reported. In the first step, an azide-containing compound, N-5-azido-nitrobenzoyloxy succinimide (ANB-NOS), is used to form photo-adducts on the graphitic surfaces in a solid-state photochemical reaction, resulting in active ester groups being oriented for the subsequent reactions. In the second step, pre-synthesized DNA strands bearing a terminal amine group are coupled in an aqueous solution with the active esters on the photo-adducts. The versatility of the method is demonstrated by attaching pre-synthesized DNA to surfaces of carbon nanotubes in two platforms—as vertically-aligned multi-walled carbon nanotubes on a solid support and as tangled single-walled carbon nanotubes in mats. The reaction products at various stages were characterized by x-ray photoelectron spectroscopy. Two different assays were used to check that the DNA strands attached to the carbon nanotubes were able to bind their partner strands with complementary base sequences. The first assay, using partner DNA strands tethered to gold nanoparticles, enabled the sites of DNA attachment to the carbon nanotubes to be identified in TEM images. The second assay, using radioactively labelled partner DNA strands, quantified the density of functional DNA strands attached to the carbon nanotubes. The diversity of potential applications for these DNA-modified carbon-nanotube platforms is exemplified here by the successful use of a DNA-modified single-walled carbon-nanotube mat as an electrode for the specific detection of metal ions.