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The electronic structure of Os0.5Pt0.5 bimetallic nanoalloys is studied by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The electronic population on the atoms of these alloys is determined from the obtained experimental data. It is shown that the alloy formation is accompanied by electron transfer from Os atoms to Pt atoms, while the sign and magnitude of the chemical shift are largely determined by the Madelung potential. The shape of the XPS spectra of core lines and the valence band indicate that the local density of states increases on the Os atoms near the Fermi level. Prospects of using the nanoalloys in catalytic reactions are discussed by analyzing the valence d-band parameters. [ABSTRACT FROM AUTHOR]

Nowadays, Pt-Os binary systems are mainly considered as catalysts and electrocatalysts, but the role of Os in these processes is still poorly understood. The electronic structure of Pt-Os nanosystems remains a few studied as well. Using bimetallic (NH4)2[Pt0.5Os0.5Cl6] as a single-source precursor for preparing Pt-Os nanoalloy through the thermal decomposition in hydrogen and inert atmospheres, the relation of morphology, atomic ordering, and electronic structure of Pt-Os nanoalloy was examined by in situ Quick XAFS, XPS, PXRD, SEM, and HRTEM techniques. Being the only variable parameter, the decomposition atmosphere was found to govern the morphology of the Pt-Os nanoalloy and change the atomic ordering (alloying extent), which involves a change in the electronic structure. In a hydrogen atmosphere, the nanofibers (NFs) (ø ~ 5–6 nm) with the atomic ordering Oscore&Pt-richshell were observed to form; in a nitrogen atmosphere, thin nanoplates (NPLs) (~ 12 nm) with the atomic architecture Os-richcore&Pt-richshell were found out. The depletion in the Os 5d5/2 and Pt 5d5/2,3/2 states was revealed for Pt-Os nanoalloys. This unusual result disagrees with the known d-band theory and indicates that there is a gain of non-d conduction electron counts at one or both sites. Mixed conductivity may exist in such Pt-Os nanoalloy that may be responsible for a manifestation of new physical properties of this binary system. [ABSTRACT FROM AUTHOR]

Nowadays, Pt-Os binary systems are mainly considered as catalysts and electrocatalysts, but the role of Os in these processes is still poorly understood. The electronic structure of Pt-Os nanosystems remains a few studied as well. Using bimetallic (NH4)2[Pt0.5Os0.5Cl6] as a single-source precursor for preparing Pt-Os nanoalloy through the thermal decomposition in hydrogen and inert atmospheres, the relation of morphology, atomic ordering, and electronic structure of Pt-Os nanoalloy was examined by in situ Quick XAFS, XPS, PXRD, SEM, and HRTEM techniques. Being the only variable parameter, the decomposition atmosphere was found to govern the morphology of the Pt-Os nanoalloy and change the atomic ordering (alloying extent), which involves a change in the electronic structure. In a hydrogen atmosphere, the nanofibers (NFs) (ø ~ 5–6 nm) with the atomic ordering Oscore&Pt-richshell were observed to form; in a nitrogen atmosphere, thin nanoplates (NPLs) (~ 12 nm) with the atomic architecture Os-richcore&Pt-richshell were found out. The depletion in the Os 5d5/2 and Pt 5d5/2,3/2 states was revealed for Pt-Os nanoalloys. This unusual result disagrees with the known d-band theory and indicates that there is a gain of non-d conduction electron counts at one or both sites. Mixed conductivity may exist in such Pt-Os nanoalloy that may be responsible for a manifestation of new physical properties of this binary system. [ABSTRACT FROM AUTHOR]

The possibility to obtain novel data by standard electron spectroscopy and quantum chemical techniques is exemplified by C2FBr0.15 intercalate and silver foil. The features of extended X-ray photoelectron spectra are interpreted by electronic transitions in the valence band of similar unit cells. The analysis of experimental and calculated spectra reveals two states of intercalated Br2: molecular and chain-like. The interaction of Ag with NO2 at 300–520 K is limited by the formation of an oxidized state in the near-surface layer with a thickness of ∼6 A, with the metallic state of silver dominating in the Ag3d И Ag MNN spectra. Geometric parameters, states of atoms, and the character of bonds between them are consistent with the previously obtained results. [ABSTRACT FROM AUTHOR]

Thermal decomposition of ammonium hexachloroiridate(IV) in inert and reducing atmospheres are studied by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Particular attention is paid to the formation of metallic iridium particles. The processes of thermal decomposition proceed similarly in an inert atmosphere and in a vacuum as is evidenced by equal charge states of Ir, Cl, and N at different decomposition stages in these two cases. According to XPS data, the decomposition process can be described as consisting of three main stages. At the first stage, an intermediate product with atomic charge states corresponding to {Ir(NH3)xCl6−x}(x−3) (1 ≤ x ≤ 3) and metallic iridium are formed. At the second stage, atomic charge states indicate formation of {IrClx}3−x, NH4Cl. The metal nanoparticles appearing at these stages have different shapes: spherical, "flakes", dendritic networks. The final decomposition product (metallic iridium) is agglomerates of regularly shaped spherical nanoparticles of uniform sizes. The process of thermal decomposition in a reducing atmosphere leads to the formation of nanoporous metal crystallites with a shape similar to that of the initial complex salt. Such crystallites are formed as a result of complicated channels that are developed due to the release of gaseous products (N2 and HCl) and are directed from the bulk of the crystallite to its surface. The atomic charge states of the intermediate decomposition product correspond to {IrClx}3−x. [ABSTRACT FROM AUTHOR]

The products of mechanosynthesis in the systems "superstoichiometric fluorocarbon nanomaterial CF1.2-thermally expanded graphite" are studied using X-ray photoelectron spectroscopy and low-temperature nitrogen adsorption to identify texture characteristics. A correlation is revealed between the conductivity of the composites and functional composition of their surface layers. The obtained results are explained by the fact that mechanosynthesis products contain mesoporous carbon-fluorocarbon nanocomposites consisting of micro- and nanoparticles CF1+x coated by an outer nanolayer sp2-C-sp3-C-F. [ABSTRACT FROM AUTHOR]

The regularities of the electron energy dissipation found in the subsurface atomic layer are valid in the bulk of a solid, too. On the example of model graphite-based materials it is shown that energy losses in X-ray photoelectron spectra agree with the calculated valence electron excitation spectra in analogous unit cells. The control of conjugate electron transitions opens the way to gain new data on the geometry, character, and order of bonding between atoms in the sample by the conventional electron spectroscopy and quantum chemistry methods. [ABSTRACT FROM AUTHOR]

In the paper results of the investigation of the thermal decomposition process of double complex salt [Pt(NH)][OsCl] by x-ray absorption (XAFS) and photoelectron (XPS) spectroscopies have been presented. The data obtained allows a mechanism of the thermal decomposition to be refined. An influence of size effect and nanoalloy formation on chemical shift of Pt and Os is discussed. [ABSTRACT FROM AUTHOR]

Nanocomposites based on PtPd nanoparticles with chemical ordering like disordered solid solution on surface of multilayer graphene have been prepared through thermal shock of mechanically obtained mixture of double complex salt [Pd(NH)][PtCl] and different carbon materials-exfoliated graphite, graphite oxide and graphite fluoride. An effect of original carbon precursors on formation of PtPd bimetallic nanoparticles was studied using X-ray absorption spectroscopy (XAFS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was shown that the distribution of bimetallic nanoparticles over the multilayer graphene surface as well as the particles size distribution is controlled by the graphene precursors. For all nanocomposites, the surface of the nanoparticles was found to be Pd-enriched. In case when the thermal exfoliated graphite and graphite oxide were used as the graphene precursors a thin graphitized layer covered the nanoparticles surface. Such a graphitized layer was not observed in the nanocomposite, which used the fluorinated graphite as the precursor. [ABSTRACT FROM AUTHOR]

Nitrogen-doped and pure carbon nanotube (CNT) based composites were fabricated for investigating their dielectric properties in static regime as well as electromagnetic response properties in microwave frequency range (Ka-band). Two classes of host matrix-polystyrene and phosphate unfired ceramics-have been used for composites fabrication. The study reveals miscellaneous effect of nitrogen doping on the dielectric permittivity, dc conductivity and electromagnetic interference shielding efficiency of CNT-based composites, produced with both polymer and ceramic matrices. The high-frequency polarizability, estimated for different-length CNTs, and static polarizability, calculated for nitrogen-containing CNT models using a quantum-chemical approach, show that this effect results from a decrease of the nanotube defect-free-length and deterioration of the polarizability with incorporation of nitrogen in pyridinic form. [ABSTRACT FROM AUTHOR]

The electronic structure and functional composition of products of the graphite oxide (GO) interaction with concentrated sulfuric acid (HSO) are studied, depending on the oxygen content in the precursor and the treatment temperature. X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) measured at the CK edge, and infrared spectroscopy are used to show the recovery of the π electron system of graphene planes at a temperature of 200 °C. Aggregation of functional groups in GO containing more than 40% of oxygen causes the formation of vacancy defects in the planes with treatment. When the GO treatment temperature rises to 280 °C, the oxidation of the basal plane π-regions occurs. The results can underlie the control of the functional composition, vacancy number, and size in graphite materials. [ABSTRACT FROM AUTHOR]

The element composition and chemical bonds of nanocomposite films of hydrogenated silicon oxycarbonitride fabricated through high-frequency plasma-chemical deposition from initial gas mixtures of 1,1,3,3-tetramethyldisilazane with nitrogen and oxygen in the temperature range 373-973 K depending on the synthesis conditions is studied. The effect of changes in the temperature and chemical composition of the initial gas mixtures on the element composition and types of chemical bonds in SiCNO:H films is investigated. [ABSTRACT FROM AUTHOR]

Few-layer graphene samples have been obtained by a thermal expansion of bromine-intercalated fluorinated graphite with a ∼C2F matrix composition at 600, 700, and 800 °C. X-ray photoelectron spectroscopy detected that the products contained almost the same quantities of foreign atoms independently on the exfoliation temperature. However, the Raman spectra showed a progressive increase in the relative intensity of the D mode with the temperature growth. This was attributed to more edge states developed in graphene planes at the higher temperature. Thin films from obtained samples were tested as sensors using 1000 ppm nitrogen dioxide (NO2) in argon. The film from few-layer graphene produced at 800 °C had the largest relative response, while its recovery was quite low at room temperature. The sensor performances were related with the structural characteristics of the exfoliated graphenes. Left: Relative response of gas sensors based on few-layer graphene products of an expansion of fluorinated graphite at 600, 700, and 800 °C toward 1000 ppm NO2. Right: Proposed structures of the products. [ABSTRACT FROM AUTHOR]

Nitrogen-containing carbon (CNx) nanotubes have been grown vertically on silicon substrates by decomposition of a ferrocene/acetonitrile aerosol at temperatures 750, 800, 850, and 900 °С. A CNx nanotube array, produced at 850 °С, had the greatest height ∼220 μm and the smallest nitrogen content ∼3.8 at%. The content of graphitic nitrogen form, referred to a nitrogen atom with three carbon neighbors in a hexagonal lattice, increased gradually with the synthesis temperature. Field electron emission measurements showed that the CNx nanotube arrays have better characteristics than aligned non-doped carbon nanotubes. To reveal effect of nitrogen on the filed threshold, we calculated current-voltage dependencies for CNx nanotube models containing different amount of graphitic and pyridinic nitrogen species. Influence of the synthesis temperature on the height and total nitrogen content in CNx nanotube array and relation of these parameters with the threshold of field emission appearance. [ABSTRACT FROM AUTHOR]

Fluorinated graphite intercalation compounds (FGICs) with acetonitrile C2F x · yCH3CN ( x = 0.92, 0.69, and 0.49) have been synthesized using a gaseous mixture of BrF3 and Br2 at room temperature and subsequent replacement of the reaction medium components on acetonitrile by isopiestic method. The change in functional composition and electronic structure of FGICs under annealing at 250-260 °C was studied by infrared, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) methods. Analysis of the data revealed interaction of acetonitrile with a C2F x matrix. The X-ray spectra detected formation of new nitrogen species attributed to two-coordinated and mono hydrogenated three-coordinated atoms. Mechanism of nitrogen incorporation in the fluorinated graphene layers was proposed. Schematic structure of graphite fluoride C2F x intercalated with acetonitrile and NEXAFS N K-edge spectrum of C2F0.69 · 0.137CH3CN before and after annealing at 250 °C. [ABSTRACT FROM AUTHOR]

Effect of corrugation of hexagonal carbon network on the collective electron excitations has been studied using optical absorption and X-ray photoelectron spectroscopy in conjunction with density functional theory calculations. Onion-like carbon (OLC) was taken as a material, where graphitic mantle enveloping agglomerates of multi-shell fullerenes is strongly curved. Experiments showed that positions of π and π + σ plasmon modes as well as π → π* absorption peak are substantially redshifted for OLC as compared with those of highly ordered pyrolytic graphite and thermally exfoliated graphite consisted of planar sheets. This effect was reproduced in behavior of dielectric functions of rippled graphite models calculated within the random phase approximation. We conclude that the energy of electron excitations in graphitic materials could be precisely tuned by a simple bending of hexagonal network without change of topology. Moreover, our investigation suggests that in such materials optical exciton can transfer energy to plasmon non-radiatively. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) demonstrate unique luminescence properties due to conjugated π domains of the sp2/sp3 hybridized carbon core, quantum-size effects, and passivation of CD surfaces by functional groups. In this work we present hydrothermal synthesis of nitrogen-doped and boron-doped CDs, their morphological, structural, optical characteristics, and luminescent properties. The CDs are first synthesized from trans-aconitic acid. X-ray photoelectron and infrared spectroscopy data indicate that prepared CDs contain nitrogen and boron atoms. The photoluminescence quantum yield of N-doped and B-doped CDs is 26% and 9%, respectively. [ABSTRACT FROM AUTHOR]

Solid solutions Mo1-xNbxS2 (x = 0, 0.05, 0.10, and 0.15) crystallizing in the hexagonal structure 2H-MoS2 are synthesized. The samples are characterized by powder X-ray diffraction (XRD) and Raman spectroscopies, X-ray photoelectron spectroscopy (XPS), and quantum chemical calculations (DFT). The changes occurring in the electronic properties of high-resistivity semiconductor MoS2 and indicating metallic behavior of obtained solid solutions Mo1-xNbxS2 are not accompanied by substantial changes in the atomic photoelectron spectra. [ABSTRACT FROM AUTHOR]

[M(NH3)5Cl][IrCl6], M = Co, Cr, Ru, Rh, and Ir, were proposed as single-source precursors for bimetallic alloys. Their thermal decomposition in inert and reductive atmospheres below 700 °C results in the formation of nanostructured porous Ir0.5M0.5 alloys. Salts decompose with a significant exothermal effect during the first stage of their thermal breakdown in an inert atmosphere above 200 °C. The exothermal effect gradually decreases in the series: [Co(NH3)5Cl][IrCl6] (1) ＞ [Cr(NH3)5Cl][IrCl6] (2) ＞ [Ru(NH3)5Cl][IrCl6] (3) ＞ [Rh(NH3)5Cl][IrCl6] (4); [Ir(NH3)5Cl][IrCl6] (5) does not exhibit any thermal effects and decomposes at much higher temperatures. To shed light on their thermal decomposition and the nature of the exothermal effect, DSC–EGA, in situ and ex situ IR, Raman, XPS and XAFS studies were performed. A combination of complementary techniques suggests a simultaneous ligand exchange and a reduction of central atoms as key processes. In [Co(NH3)5Cl][IrCl6], Co(iii) and Ir(iv) simultaneously oxidise coordinated ammonia, which can be detected due to a significant exothermal effect and the presence of Co(ii) and Ir(iii) in the intermediate product. The appearance of Ir–N frequencies demonstrates a ligand exchange between cations and the [IrCl6]2− anion. Salts with Cr(iii), Ru(iii), and Rh(iii) show a much lower exothermal effect due to the stability of their oxidation states. Salts with Rh(iii) and Ir(iii) demonstrate a high thermal stability and a low tendency for ligand exchange as well as decomposition with exothermal effects. [ABSTRACT FROM AUTHOR]

Vertically aligned multi-walled carbon nanotubes (MWNTs) were grown on the surface of electroconductive silicon substrate by catalytic chemical vapor deposition (CCVD) of a mixture of toluene and ferrocene vapors at 800°С. The anisotropic structure of the array that is due to the mutual orientation of MWNTs makes such materials attractive for use as supercapacitor electrodes. The effect of iron nanoparticles encapsulated in MWNTs as a result of synthesis on the electrochemical capacity of the sample in a 1 М HSO solution was studied. Iron was removed during the thermal treatment of the MWNT array in a 20% HSO solution under the normal or hydrothermal conditions. The contribution of redox processes involving iron was shown to be comparable to the contribution of the double-layer capacity of MWNTs. The hydrothermal treatment allows easy separation of the array from the silicon substrate without any loss of electric coupling of MWNTs. [ABSTRACT FROM AUTHOR]

Two few-layer graphene materials, strongly distinguished in structure, were compared as electrode materials for supercapacitor. The stacks of flat sheets with basal size of a few microns have been obtained as the result of ultrasonication of bromine intercalated graphite dispersion. The highly crumpled large-size layers have been produced by rapid heating of bromine intercalated graphite fluoride. The average number of layers and in-plane crystalline size in the materials were evaluated from Raman spectroscopy. The functional composition was studied using X-ray photoelectron and Infrared spectroscopy. Electrochemical testing of the graphene materials detected re-stacking of thin crumpled layers during the electrode preparation. Furthermore, graphene material produced from the fluorinated graphite showed poor wettability. The mild oxidation of the material in a mixture of sulfuric and nitric acids allowed increasing the capacitance in several times. [ABSTRACT FROM AUTHOR]

The heating of graphite oxide in concentrated sulfuric acid results in partial removal of oxygen and formation of holes with a size of ∼2 nm. The Raman scattering shows that the distance between the holes decreases with the time of processing while the temperature of the acid has no crucial effect on the defectiveness of a graphene layer. The functional composition of the reduced graphite oxide samples is studied by IR and X-ray photoelectron spectroscopy. From the spectral analyses the longer the treatment, the larger the amount of oxygen removed from the graphite oxide. It is found that the edges of the holes are decorated with hydroxyl, carbonyl, and carboxyl groups and hydrogen. An increase in the temperature promotes formation of carboxyl groups. The influence of oxygenated groups and holes on the supercapacitor performance of reduced graphite oxide samples is checked using cyclic voltammetry measurements in an acidic electrolyte. Specific capacitance of samples depending on temperature and time of graphite oxide treatment by concentrated H2SO4. The scan rate of the potential was 5 mV s−1. [ABSTRACT FROM AUTHOR]

Perforation of graphite is carried out by treating the graphite oxide with a boiling mineral acid H2SO4 or H3PO4. High-resolution transmission electron microscopy shows formation of a large number of vacancy defects (holes) in the graphene sheets, which are caused more likely by the CO2 liberation during the reduction process. The characteristic size of the holes is about 2 nm. The obtained materials are comparatively examined by X-ray diffraction, Raman and IR-absorption spectroscopy, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. It is found that the products obtained using a strong acid H2SO4 and a weak acid H3PO4 are different in the concentration and electronic state of oxygen and the mean distance between defects. [ABSTRACT FROM AUTHOR]

A method to obtain previously unknown layered structure composed of stacks of perforated graphene sheets is developed. The method consists in the thermal decomposition of graphite oxide in the concentrated HSO and HPO medium. In order to confirm the presence of holes in graphene layers, a large set of chemical and physicochemical analysis methods are applied. Based on a new matrix, treated thermally and chemically, layered compounds are obtained: oxide, fluoride, and fluoroxide of two types. The obtained compounds are analyzed by transmission electron microscopy, infrared absorption spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. [ABSTRACT FROM AUTHOR]

Electronic structure of the chlorinated fullerene D-CCl has been studied using X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), and quantum chemical B3LYP calculations. The calculated shift of the core C 1s lines corresponding to the chlorinated carbon atoms and bare carbon atoms was shown to well agree with the experimental value obtained from the XPS data. This shift was taken into account in the construction of the theoretical XANES spectra near the C K-edge of the molecule. Ground-state calculation of D-CCl and calculations of CNCl and CClAr ions simulating the excited states of the chlorinated fullerene ( Z + 1 approximation) were used for modeling of C K-edge and Cl L-edge XANES data. A satisfactory agreement between experiment and theory was obtained in the case of Z + 1 approximation. Distinctions between the structure of the lowest unoccupied levels in the ground state and the C 1s excited state of D-CCl have been revealed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

CNx nanotubes have been prepared by acetonitrile decomposition over Ni, Co and Ni/Co catalysts. X-ray photoelectron spectroscopy study on the samples revealed a change of nitrogen concentration and shape of N 1s line with variation of the catalyst used. Quantum-chemical calculations on tube fragments showed the energy of N 1s level depends on the atomic structure of carbon tube and kind of incorporated nitrogen. The largest binding energies were found to be characteristic of three-coordinated nitrogen atoms doping the zigzag and chiral carbon nanotubes. [ABSTRACT FROM AUTHOR]

The electrochemical reactions of natural n-type PbS in nitric and perchloric acid solutions have been studied using cyclic voltammetry, SEM and XPS. Several oxidation stages, which differ in their electrode kinetics, surface topography and sulfide phase composition, particularly Pb/S ratios and the state of sulfur, were demonstrated. The quantities of surface sulfate and thiosulfate were rather low at PbS oxidized in HNO3 solutions, even at high potentials. The magnitude of the reoxidation peaks of cathodically formed products, primarily Pb0, was found to increase as the electrodissolution of PbS on the preliminary positive-going sweep was hindered. It is proposed that the predominant donor-like defects in the disordered reaction layers limit the concentration and mobility of holes, thus inhibiting PbS oxidation and promoting metallic lead deposition in the course of potential cycling. The model developed as an alternative to the traditional explanations uses the concept of negative correlation energy centres resembling those in non-crystalline chalcogenide semiconductors. [ABSTRACT FROM AUTHOR]

Development of graphene spintronic devices relies on transforming it into a material with a spin order. Attempts to make graphene magnetic by introducing zigzag edge states have failed due to energetically unstable structure of torn zigzag edges. Here, we report on the formation of nanoridges, i.e., stable crystallographically oriented fluorine monoatomic chains, and provide experimental evidence for strongly coupled magnetic states at the graphene-fluorographene interfaces. From the first principle calculations, the spins at the localized edge states are ferromagnetically ordered within each of the zigzag interface whereas the spin interaction across a nanoridge is antiferromagnetic. Magnetic susceptibility data agree with this physical picture and exhibit behaviour typical of quantum spin-ladder system with ferromagnetic legs and antiferromagnetic rungs. The exchange coupling constant along the rungs is measured to be 450 K. The coupling is strong enough to consider graphene with fluorine nanoridges as a candidate for a room temperature spintronics material. [ABSTRACT FROM AUTHOR]

Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT-ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT-ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT-ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis. [ABSTRACT FROM AUTHOR]