Br 3d Research Articles

Shell-dependent photofragmentation dynamics of a heavy-atom-containing bifunctional nitroimidazole radiosensitizer.

Radiation therapy uses ionizing radiation to break chemical bonds in cancer cells, thereby causing DNA damage and leading to cell death. The therapeutic effectiveness can be further increased by making the tumor cells more sensitive to radiation. Here, we investigate the role of the initial halogen atom core hole on the photofragmentation dynamics of 2-bromo-5-iodo-4-nitroimidazole, a potential bifunctional radiosensitizer. Bromine and iodine atoms were included in the molecule to increase the photoionization cross-section of the radiosensitizer at higher photon energies. The fragmentation dynamics of the molecule was studied experimentally in the gas phase using photoelectron-photoion-photoion coincidence spectroscopy and computationally using Born-Oppenheimer molecular dynamics. We observed significant changes between shallow core (I 4d, Br 3d) and deep core (I 3d) ionization in fragment formation and their kinetic energies. Despite the fact, that the ions ejected after deep core ionization have higher kinetic energies, we show that in a cellular environment, the ion spread is not much larger, keeping the damage well-localized.

Bromine Adsorption and Thermal Stability on Rh(111): A Combined XPS, LEED and DFT Study.

This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33-0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages.

Hydrogen migration in inner-shell ionized halogenated cyclic hydrocarbons

We have studied the fragmentation of the brominated cyclic hydrocarbons bromocyclo-propane, bromocyclo-butane, and bromocyclo-pentane upon Br(3d) and C(1s) inner-shell ionization using coincidence ion momentum imaging. We observe a substantial yield of CH3+ fragments, whose formation requires intramolecular hydrogen (or proton) migration, that increases with molecular size, which contrasts with prior observations of hydrogen migration in linear hydrocarbon molecules. Furthermore, by inspecting the fragment ion momentum correlations of three-body fragmentation channels, we conclude that CHx+ fragments (with x = 0, …, 3) with an increasing number of hydrogens are more likely to be produced via sequential fragmentation pathways. Overall trends in the molecular-size-dependence of the experimentally observed kinetic energy releases and fragment kinetic energies are explained with the help of classical Coulomb explosion simulations.

Constructing built-in electric field within CsPbBr3/sulfur doped graphitic carbon nitride ultra-thin nanosheet step-scheme heterojunction for carbon dioxide photoreduction.

Lead halide perovskites are promising for photocatalysis due to their excellent optoelectronic properties, high extinction coefficients, and long electron-hole diffusion lengths. However, severe recombination of photogenerated carriers limits their photocatalytic activity. Herein, we describe a perovskite-based step-scheme (S-scheme) heterojunction by interfacing CsPbBr3 perovskite nanocrystals with sulfur (S) doped graphitic carbon nitride (g-C3N4) ultrathin nanosheet. The formation of S-scheme heterojunction was substantiated by in-situ x-ray photoelectron spectra, showing a negative shift for Cs 1s, Pb 4f, and Br 3d binding energy in CsPbBr3, while a positive shift for C 1s, N 1s, and S 2p in S-doped g-C3N4 upon light irradiation. Moreover, alignment of Fermi levels in both semiconductors results in constructing a built-in electric field in the heterojunction, which enhances S-scheme electron transfer from g-C3N4 to CsPbBr3, favorable for electron (CsPbBr3) and hole (g-C3N4) separation for enhanced carbon dioxide (CO2) photoreduction. Indeed, compared with CsPbBr3, the developed CsPbBr3/S doped g-C3N4 composite showed a ∼16-fold improvement in the photocatalytic CO2 reduction rate (∼83.6μmolh-1 g-1), thus holding great potential for photocatalysis applications in environmental and energy fields.

Li7P2S8Br0.5I0.5 (LPSBI) solid state electrolyte by XPS

There have been increasing surface characterization studies of battery materials specifically in the context of before and after cell operation to determine any chemical changes. Therefore, providing reliable reference spectra of battery-related materials is important. In this paper, survey and high-energy resolution data are reported for the solid-state electrolyte Li7P2S8Br0.5I0.5, which has been synthesized and characterized at Pacific Northwest National Laboratory. The current data present narrow-scan regions of I 3d, I 4d, Br 3d, O 1s, P 2p, S 2p, and C 1s core-level spectra, as well as wide-scan survey data that were obtained using the Al Kα x-ray source with a Thermo Fisher Nexsa instrument.

Chirality Transfer from Chiral Mesoporous Silica to Perovskite CsPbBr 3 Nanocrystals: The Role of Chiral Confinement

Chirality Transfer from Chiral Mesoporous Silica to Perovskite CsPbBr ₃ Nanocrystals: The Role of Chiral Confinement

Impact of Tetrabutylammonium on the Oxidation of Bromide by Ozone.

The reaction of ozone with sea-salt derived bromide is relevant for marine boundary layer atmospheric chemistry. The oxidation of bromide by ozone is enhanced at aqueous interfaces. Ocean surface water and sea spray aerosol are enriched in organic compounds, which may also have a significant effect on this reaction at the interface. Here, we assess the surface propensity of cationic tetrabutylammonium at the aqueous liquid–vapor interface by liquid microjet X-ray photoelectron spectroscopy (XPS) and the effect of this surfactant on ozone uptake to aqueous bromide solutions. The results clearly indicate that the positively charged nitrogen group in tetrabutylammonium (TBA), along with its surface activity, leads to an enhanced interfacial concentration of both bromide and the bromide ozonide reaction intermediate. In parallel, off-line kinetic experiments for the same system demonstrate a strongly enhanced ozone loss rate in the presence of TBA, which is attributed to an enhanced surface reaction rate. We used liquid jet XPS to obtain detailed chemical composition information from the aqueous-solution–vapor interface of mixed aqueous solutions containing bromide or bromide and chloride with and without TBA surfactant. Core level spectra of Br 3d, C 1s, Cl 2p, N 1s, and O 1s were used for this comparison. A model was developed to account for the attenuation of photoelectrons by the carbon-rich layer established by the TBA surfactant. We observed that the interfacial density of bromide is increased by an order of magnitude in solutions with TBA. The salting-out of TBA in the presence of 0.55 M sodium chloride is apparent. The increased interfacial bromide density can be rationalized by the association constants for bromide and chloride to form ion-pairs with TBA. Still, the interfacial reactivity is not increasing simply proportionally with the increasing interfacial bromide concentration in response to the presence of TBA. The steady state concentration of the bromide ozonide intermediate increases by a smaller degree, and the lifetime of the intermediate is 1 order of magnitude longer in the presence of TBA. Thus, the influence of cationic surfactants on the reactivity of bromide depends on the details of the complex environment at the interface.

Surface Chemistry of Gold Nanoparticles Produced by Laser Ablation in Pure and Saline Water.

Pulsed laser ablation in liquid (PLAL) is a powerful method for producing nanoparticle colloids with a long-term stability despite the absence of stabilizing organic agents. The colloid stability involves different reactivities and chemical equilibria with complex ionic-specific effects at the nanoparticle/solvent interface which must be strongly influenced by their chemical composition. In this work, the surface composition of PLAL-produced gold nanoparticles in alkaline and saline (NaBr) water is investigated by X-ray photoelectron spectroscopy on free-flying nanoparticles, exempt from any substrate or radiation damage artifact. The Au 4f photoelectron spectra with a depth profiling investigation are used to evaluate the degree of nanoparticle surface oxidation. In alkaline water, the results preclude any surface oxidation contrary to the case of nanoparticles produced in NaBr solution. In addition, the analysis of Br 3d core-level photoelectron spectra agrees with a clear signature of Br on the nanoparticle surface, which is confirmed by a specific valence band feature. This experimental study is supported by DFT calculations, evaluating the energy balance of halide adsorption on different configurations of gold surfaces including oxidation or adsorbed salts.

1-Bromonaphthalene, by near-ambient pressure XPS

Near ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 5000 Pa. With NAP-XPS, liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly can be studied. In this submission, we show survey, C 1s, Br 3p, and Br 3d NAP-XPS spectra of 1-bromonaphthalene. Small O 1s and N 1s signals from background gas (N2 and air) are also observed.

XPS spectra as a tool for studying photochemical and thermal degradation in APbX3 hybrid halide perovskites

Abstract This article features the potential and examples of the comprehensive use of X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) to analyze the degradation processes in APbX3 hybrid halide perovskites, where the X-site anion is I– and Br– and the A-site cation is represented by CH3NH3, CH(NH2)2, and Cs. The whole set of XPS options is used, including the measurements of survey, core levels (C 1s, N 1s, Pb 4f, I 3d and Br 3d), and valence bands spectra, which provides a complementary understanding of the electronic structure and chemical bonding of perovskites while excluding the random errors. It is found that stability of APbX3 perovskites with respect to light soaking and heat stress is connected with the formation of PbX2 degradation product, which can be monitored by high-energy resolved XPS Pb 4f, I 3d-spectra and valence band spectra. The obtained results are confirmed by DFT calculations of the formation energies of intrinsic PbX2-defects. Furthermore, our results show that the resistance of hybrid lead halide perovskites to stress factors (light or heat) is gradually increased while substituting the A-site cation going from CH3NH3+ to CH(NH2)2+ and then to Cs+.

XPS of the surface chemical environment of CsMAFAPbBrI trication-mixed halide perovskite film

Perovskite-based materials have been considered as the most promising materials in several solar-driven processes, especially photovoltaics. Some features such as high sunlight harvesting and improved carrier transport have been highlighted to have an impact on the efficiency of the above topics, but limited studies have pointed out their surface composition, which mainly influence the above abilities. As a starting point to recognize the surface environment and chemical states of these materials, x-ray photoelectron spectroscopy measurements were performed. Trication-mixed halide perovskite films based on Cs0.08MA0.18FA0.78PbBr0.42I2.58 were prepared by a one step process and deposited on an indium tin oxide substrate by spin-coating. Survey spectra, Pb 4f, I 3d, Br 3d, Cs 3d, C 1s, N 1s, Pb 4d, and Pb 5d core levels, and valence band spectra were measured for the semiconductor sample. Results exhibit symmetrical peaks, indicating that a homogenous solid solution was achieved. Main chemical states of this kind of perovskites such as Cs-Br and Pb-I species are also shown. We deduced that the later signals are associated with the [PbI6]4− octahedra existing in the perovskite lattice, while the former one is related to Cs+ bounded to [PbBr6]4− units on the perovskite surface. Interestingly, the NR4+ signal was also identified, associated with the presence of methylammonium and formamidinium cations.

Tuning the Cation-Anion Interactions by Methylation of the Pyridinium Cation: An X-ray Photoelectron Spectroscopy Study of Picolinium Ionic Liquids.

X-ray photoelectron spectroscopy is used to investigate the impact of methylation on the electronic environment of pyridinium cations. Because of the electron-donating effect of the methyl group, there is a significant increase in electron density on the cationic nitrogen. The shift of the N 1s binding energy is inversely proportional to the anion basicity. The methylation position on the electronic environment of the cationic nitrogen is investigated. The N 1s binding energy follows the trend: 1-octylpyridinium > 1-octyl-3-picolinium > 1-octyl-4-picolinium > 1-octyl-2-picolinium, which is in good agreement with the cation acidity. The increase in the inductive effect subsequently weakens the cation-anion interactions through charge transfer from the anion to the cation, causing a subtle change in the electronic environment of the anion. Such an effect is noticeably reflected in the Br 3d binding energy. It shows that the Br 3d5/2 binding energy of 1-octyl-2-picolinium bromide is 0.2 eV lower than that of 1-octylpyridinium bromide.

Perovskite Nanocrystal Fluorescence-Linked Immunosorbent Assay Methodology for Sensitive Point-of-Care Biological Test

Summary Quantitative fluorescence immunoassay is a vital and convenient method in point-of-care (POC) testing for food safety and clinical healthcare. However, current marking materials, from organic luciferin to quantum dots, still lack the requirement of increasing need for multiple targets of interest because of their too broad emission. Here, a new label material, perovskite nanocrystals (Pe-NCs), with a narrower photoluminescence spectrum is reported, and a sensitive and quantitative immunoassay method named the perovskite nanocrystal fluorescence-linked immunosorbent assay is preliminarily demonstrated. The key point of realizing water-dispersed and stable Pe-NCs was addressed by functionalizing with hydroxyl groups. The fluorescent probes (perovskite antibody) were constructed via electrostatic adsorption with narrow full-width at half-maximum (∼18 nm), laying the foundation for future study of multi-target detection. Both indirect competitive immunity and sandwich immunoassay were successfully demonstrated. This work provides a possible label material for POC tests and may open up a promising avenue of next-generation immunoassay.

Tribromide Ionic Liquids: Probing the Charge Distribution of the Anion by XPS

We investigate a typical trihalide ionic liquid, 1-octyl-3-methylimidazolium tribromide, using X‑ray photoelectron spectroscopy. The electronic environment of the anion is analyzed in detail. The Br 3d binding energies of the two components are both higher than that measured for 1-octyl-3-methylimidazolium bromide, due to the delocalization of the negative charge spreading over three atoms within the anion. The basicity of [Br3]– is estimated based upon N 1s binding energy. It is found similar to that of [BF4]–.

Effect of ultrasound pretreatment on bromination of double-walled carbon nanotubes

Bromination of double-walled carbon nanotubes (DWCNTs) was carried out using a saturated vapor of Br2 at room temperature with or without a pretreatment in bromine water. X-ray photoelectron spectroscopy revealed that ultrasound pretreatment modified the chemical state of bromine in the product. The binding energies of the Br 3d electrons in the pre-sonicated DWCNT sample were between those characteristic of the covalent C–Br bonds and the negatively charged Br2 molecules, observed when the pretreatment was not performed. Raman spectroscopy, however, clearly evidenced Br–Br vibrations in both brominated samples. Calculations of CNT–Br2 models within density functional theory were used to propose that the electronic state of a Br2 molecule depends on the adsorption site. The bromine molecules prefer to be located near edge hydroxyl groups, which acept the electron density from Br2. This increases the binding energy of Br 3d levels as compared to that for Br2 molecules in other adsorption sites.

Characterization of Fe2+ Aqueous Solutions with Liquid Jet X-ray Photoelectron Spectroscopy: Chloride Depletion at the Liquid/Vapor Interface Due to Complexation with Fe2.

Liquid jet X-ray photoelectron spectroscopy is used under near ambient pressure conditions to characterize Fe2+ aqueous solutions. Counter ions, such as Cl- and Br- ions, added to the solution lead to changes in the first solvation sphere of the Fe-aqua complex in solution. Binding energy shifts of 0.4 eV to lower binding energy are observed in the Cl 2p spectra, 2 eV to higher binding energy in the Fe 2p spectra and no shifts are observed in the Br 3d spectra. Depletion of the Cl- species is observed at the interface, caused by coordination with Fe2+. Depletion of Cl- at the liquid/vapor interface may have significant impacts on oxidative chemistry at the interface of atmospheric aerosols that contain both chloride and iron. The Cl- complexation with the Fe2+ ions will also affect the Fenton chemistry that is dependent on this metal ion.

Probing ultrafast C-Br bond fission in the UV photochemistry of bromoform with core-to-valence transient absorption spectroscopy.

UV pump–extreme UV (XUV) probe femtosecond transient absorption spectroscopy is used to study the 268 nm induced photodissociation dynamics of bromoform (CHBr3). Core-to-valence transitions at the Br(3d) absorption edge (∼70 eV) provide an atomic scale perspective of the reaction, sensitive to changes in the local valence electronic structure, with ultrafast time resolution. The XUV spectra track how the singly occupied molecular orbitals of transient electronic states develop throughout the C–Br bond fission, eventually forming radical Br and CHBr2 products. Complementary ab initio calculations of XUV spectral fingerprints are performed for transient atomic arrangements obtained from sampling excited-state molecular dynamics simulations. C–Br fission along an approximately symmetrical reaction pathway leads to a continuous change of electronic orbital characters and atomic arrangements. Two timescales dominate changes in the transient absorption spectra, reflecting the different characteristic motions of the light C and H atoms and the heavy Br atoms. Within the first 40 fs, distortion from symmetry to form a quasiplanar CHBr2 by the displacement of the (light) CH moiety causes significant changes to the valence electronic structure. Displacement of the (heavy) Br atoms is delayed and requires up to ∼300 fs to form separate Br + CHBr2 products. We demonstrate that transitions between the valence-excited (initial) and valence + core-excited (final) state electronic configurations produced by XUV absorption are sensitive to the localization of valence orbitals during bond fission. The change in valence electron-core hole interaction provides a physical explanation for spectral shifts during the process of bond cleavage.

Effect of pH on Phase, Morphology and Photocatalytic Properties of BiOBr Synthesized by Hydrothermal Method

Effect of pH on crystalline structure, morphology and visible-light-driven photocatalysis of BiOBr samples hydrothermally synthesized in solutions with the pH of 2–10 was investigated. The as-synthesized BiOBr samples investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. In this research, the as-synthesized samples are pure tetragonal BiOBr phase at the pH of 2–10, and were composed of microplates, nanoplates and hierarchical micro-flowers controlled by the solution pH. The as-synthesized sample at the pH 8 was revealed the presence of Bi 4f, O 1s and Br 3d. Visible-light-driven photocatalytic properties of the BiOBr photocatalyst with different morphologies were investigated through the photodegradation of rhodamine B (RhB). The BiOBr hierarchical micro-flowers synthesized in the solution with the pH 8 show the best photocatalytic activity for wastewater treatment and the ·O2− radicals were attributed to be the primary active species for photodegradation of RhB under visible light irradiation.

The Role of Kinetics versus Thermodynamics in Surface-Assisted Ullmann Coupling on Gold and Silver Surfaces.

Surface-assisted Ullmann coupling is the workhorse of on-surface synthesis. Despite its obvious relevance, many fundamental and mechanistic aspects remain elusive. To shed light on individual reaction steps and their progression with temperature, temperature-programmed X-ray photoelectron spectroscopy (TP-XPS) experiments are performed for a prototypical model system. The activation of the coupling by initial dehalogenation is tracked by monitoring Br 3d core levels, whereas the C 1s signature is used to follow the emergence of metastable organometallic intermediates and their conversion to the final covalent products upon heating in real time. The employed 1,3,5-tris(4-bromophenyl)benzene precursor is comparatively studied on Ag(111) versus Au(111), whereby intermolecular bonds and network topologies are additionally characterized by scanning tunneling microscopy (STM). Besides the well-comprehended differences in activation temperatures for debromination, the thermal progression shows marked differences between the two surfaces. Debromination proceeds rapidly on Ag(111), but is relatively gradual on Au(111). While on Ag(111) debromination is well explained by first-order reaction kinetics, thermodynamics prevail on Au(111), underpinned by a close agreement between experimentally deduced and density functional theory (DFT) calculated reaction enthalpies. Thermodynamically controlled debromination on Au(111) over a large temperature range implies an unexpectedly long lifetime of surface-stabilized radicals prior to covalent coupling, as corroborated by TP-XPS of C 1s core levels. These insights are anticipated to play an important role regarding our ability to rationally synthesize atomically precise low-dimensional covalent nanostructures on surfaces.

Surface Mediated Synthesis of 2D Covalent Organic Networks: 1,3,5‐Tris(4‐bromophenyl)benzene on Au(111)

Covalent organic networks derived from surface‐mediated self‐assembly of 1,3,5‐tris(4‐bromophenyl)benzene into two‐dimensional networks on Au(111) have been studied by scanning tunneling microscopy (STM) and by X‐ray spectroscopic methods. High resolution soft X‐ray photoemission spectroscopy (SXPS) using synchrotron radiation have been used to study the formation of the 1,3,5‐tris(4‐bromophenyl)benzene‐derived 2D networks by observing temperature‐dependent C 1s and Br 3d core level XPS spectra. X‐ray absorption (XA) measurements of the formation of these 2D networks have been obtained at the C K‐edge where their temperature and angular dependence are examined. The results of these XPS and XA spectroscopic measurements are compared to detailed ab initio electronic structure calculations of 1,3,5‐tris(4‐bromophenyl)benzene molecules to aid the interpretation of the features of these spectra.