Electron Spectroscopy Methods Research Articles

Proton-impact ionization cross sections of adenine measured at 0.5 and 2.0 MeV by electron spectroscopy

Double-differential ionization cross sections (DDCSs) of vapor-phase adenine molecules (${\mathrm{C}}_{5}{\mathrm{H}}_{5}{\mathrm{N}}_{5}$) by 0.5- and 2.0-MeV proton impact have been measured by the electron spectroscopy method. Electrons ejected from adenine were analyzed by a 45${}^{\ensuremath{\circ}}$ parallel-plate electrostatic spectrometer over an energy range of 1.0--1000 eV at emission angles from 15${}^{\ensuremath{\circ}}$ to 165${}^{\ensuremath{\circ}}$. Single-differential cross sections (SDCSs) and total ionization cross sections (TICSs) were also deduced. It was found from the Platzman plot, defined as SDCSs divided by the classical Rutherford knock-on cross sections per target electron, that the SDCSs at higher electron energies are proportional to the total number of valence electrons (50) of adenine, while those at low-energy electrons are highly enhanced due to dipole and higher-order interactions. The present results of TICS are in fairly good agreement with recent classical trajectory Monte Carlo calculations, and moreover, a simple analytical formula gives nearly equivalent cross sections in magnitude at the incident proton energies investigated.

Bionano Donor–Acceptor Hybrids of Porphyrin, ssDNA, and Semiconductive Single-Wall Carbon Nanotubes for Electron Transfer via Porphyrin Excitation

Photoinduced electron transfer in self-assemblies of porphyrins ion-paired with ssDNA wrapped around single-wall carbon nanotubes (SWCNTs) has been reported. To accomplish the three-component hybrids, two kinds of diameter-sorted semiconducting SWCNT(n,m)s of different diameter ((n,m) = (6,5) and (7,6)) and free-base or zinc porphyrin bearing peripheral positive charges ((TMPyP(+))M (tetrakis(4-N-methylpyridyl)porphyrin); M = Zn and H(2)) serving as light-absorbing photoactive materials are utilized. The donor-acceptor hybrids are held by ion-pairing between the negatively charged phosphate groups of ssDNA on the surface of the SWCNT and the positively charged at the ring periphery porphyrin macrocycle. The newly assembled bionano donor-acceptor hybrids have been characterized by transmission electron microscopy (TEM) and spectroscopic methods. Photoinduced electron transfer from the excited singlet porphyrin to the SWCNTs directly and/or via ssDNA as an electron mediator has been established by performing systematic studies involving the steady-state and time-resolved emission as well as the transient absorption studies. Higher charge-separation efficiency has been successfully demonstrated by the selection of the appropriate semiconductive SWCNTs with the right band gap, in addition to the aid of ssDNA as the electron mediator.

Structural and electronic properties of the graphene/Al/Ni(111) intercalation system

Decoupling of the graphene layer from the ferromagnetic substrate via intercalation of sp metal has recently been proposed as an effective way to realize a single-layer graphene-based spin-filter. Here, the structural and electronic properties of the prototype system, graphene/Al/Ni(111), are investigated via a combination of electron diffraction and spectroscopic methods. These studies are accompanied by state-of-the-art electronic structure calculations. The properties of this prospective Al-intercalation-like system and its possible implementations in future graphene-based devices are discussed.

Influence of Pd‐Au/MWCNTs surface treatment on catalytic activity in the formic acid electrooxidation

AbstractInfluence of different treatments of Pd‐Au/MWCNTs prepared by a modified polyol microwave‐assisted method on the morphology and the catalytic activity in the formic acid electrooxidation was investigated. The following standard treatments were applied to purify the metal particles surface from the carbonaceous deposits formed from ethyl glycol adsorbed on the catalyst after the preparation: 1. annealing in air at 300 °C, 2. annealing in air at 300 °C and then reduction in 5%H2/Ar at 200 °C, 3. reduction in 5%H2/Ar at 200 °C. Surprisingly, the most catalytically active sample was that without additional purification treatments. The TEM, XRD and electron spectroscopy methods were applied to characterise the catalysts. Two Pdx Au1–x phases are present in all catalysts. The treatment number 1 and 2 caused: 1. partial removing of the carbonaceous deposits from the metal surface, 2. increases metal particle sizes, 3. decreases of Pd rich phase content, 4. increases ratio of Au to Pd in the catalyst surface layer. Treatment number 4 did not change significantly the sample morphology but decreased its catalytic activity in formic acid fuel cell. It can be due oligomerization of carbon deposits during thermal treatment in reducing (H2) atmosphere (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hybrid nickel oxide-carbon fiber composites obtained in the presence of surfactants

The composite material nickel hydroxide (oxide)/carbon fiber has been obtained by hydroxide deposition on the surface of the activated carbon fiber (ACF) via urea hydrolysis in the presence of a surfactant. The organomineral composite NiO/CHIT/carbon fiber has been obtained by electrochemical deposition of nickel hydroxide on the ACF surface in combination with chitosan as well as by cathode deposition on a carbon fiber electrode preliminarily modified by chitosan. The surface of the obtained hybrid materials has been investigated by means of the methods of X-ray photoelectron spectroscopy (XPS), atomic force and scanning electron spectroscopy (AFM and SEM), and cyclic voltamperometry. The composition and properties of the obtained composites have been discussed.

X-ray-electron and electron diffraction study of ordering alloys of the Ni – Mo system

Ni4Mo and Ni3Mo alloys subjected to different modes of heat treatment are studied by the methods of electron diffraction and x-ray electron spectroscopy. The temperature ranges of the occurrence of the processes of layering and ordering are determined. The structural states of the alloys undergoing ordering and layering are deciphered.

ChemInform Abstract: A Study of Iron Catalyst for Ammonia Synthesis by Electron Spectroscopy Methods

AbstractReview: 63 refs.

Interaction of dental and maxillofacial keradent-1 alloy with oral cavity electrolyte

The methods of potentiodynamic polarization curves and quantitative Auger electron spectroscopy are used to establish the formation of a protective multilayer film in the interaction of dental and maxillofacial Keradent-1 alloy with the oral cavity electrolyte (3% NaCl solution). It is shown that the first (inner) part of the protective film (30 nm thick) represents a solid solution of oxygen in the metals of the alloy and the outer part of the film consists of three layers: CoO oxide (5 nm thick) at the boundary with the solid solution of oxygen, a mixture of CrO and CoO oxides (3 nm thick) in the middle, and Cr2CoO4 spinel (2 nm thick) in the outer sublayer. The experiment and calculations using the Faraday law show the number of Cr3+, Co2+, and Ni2+ ions that pass into the solution during electrolysis. These numbers are almost one three-hundredth of the admissible concentrations of these metals in the oral cavity.

Pd/MWCNTs catalytic activity in the formic acid electrooxidation dependent on catalyst surface treatment

The catalytic activity in the formic acid (HCOOH) electrooxidation reaction of the Pd multiwall carbon nanotubes (MWCNTs) supported catalyst, prepared by a microwave-assisted polyol method, treated under different gas atmospheres, and temperatures (200 and 300 °C), was investigated. Their respective catalysts surface characterization proceeded in UHV using the electron spectroscopy methods. Content of constituents, i.e., Pd nanoparticles, C and O, was examined quantitatively. Content of Pd phases and chemical forms of C atoms was analyzed assuming respective binding energy (BE) values to Pd 3d and C 1s X-ray photoelectron spectra (XPS) spectra fitted to Gaussian–Lorentzian components. Surface structure was examined from the 3D nanostructure analysis by quantitative analysis of surfaces by electron spectroscopy (QUASES). Catalytic activity of Pd/MWCNTs after various surface treatments was attributed to different surface content and forms of Pd nanoparticles, and PdOx/C overlayer morphology, coverage, and thickness.

New insights on surface‐enhanced Raman scattering based on controlled aggregation and spectroscopic studies, DFT calculations and symmetry analysis for 3,6‐bi‐2‐pyridyl‐1,2,4,5‐tetrazine adsorbed onto citrate‐stabilized gold nanoparticles

AbstractA systematic study on the surface‐enhanced Raman scattering (SERS) for 3,6‐bi‐2‐pyridyl‐1,2,4,5‐tetrazine (bptz) adsorbed onto citrate‐modified gold nanoparticles (cit‐AuNps) was carried out based on electronic and vibrational spectroscopy and density functional methods. The citrate/bptz exchange was carefully controlled by the stepwise addition of bptz to the cit‐AuNps, inducing flocculation and leading to the rise of a characteristic plasmon coupling band in the visible region. Such stepwise procedure led to a uniform decrease of the citrate SERS signals and to the rise of characteristic peaks of bptz, consistent with surface binding via the N heterocyclic atoms. In contrast, single addition of a large amount of bptz promoted complete aggregation of the nanoparticles, leading to a strong enhancement of the SERS signals. In this case, from the distinct Raman profiles involved, the formation of a new SERS environment became apparent, conjugating the influence of the local hot spots and charge‐transfer (CT) effects. The most strongly enhanced vibrations belong to a1 and b2 representations, and were interpreted in terms of the electromagnetic and the CT mechanisms: the latter involving significant contribution of vibronic coupling in the system. Copyright © 2010 John Wiley & Sons, Ltd.

In-situ optical spectroscopy and electronic properties of pyrrole sub-monolayers on Ga-rich GaAs(001)

We report on the characterization of sub-monolayers of pyrrole adsorbed on Ga-rich GaAs(001) surfaces. The interfaces were characterized by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and reflectance anisotropy spectroscopy (RAS) in a spectral range between 1.5 and 8 eV. The adsorption of pyrrole on Ga-rich GaAs(001) modifies the RAS spectrum of the clean GaAs surface significantly at the surface transitions at 2.2 and 3.5 eV indicating a chemisorption of the molecules. By the help of transients at these surface transitions during the adsorption process, we were able to prepare different molecular coverages from a sub-monolayer up to a complete molecular layer. The different coverages of pyrrole were imaged by STM and electronically characterized by STS. The measurements reveal that the adsorbed molecules electronically insulate the surface and indicate the formation of new interface states around −3.5 and +4.2 eV. The RAS measurements in the UV region show new anisotropies in the spectral range of the optical transitions of the adsorbed pyrrole molecules. Our measurements demonstrate the potential of optical and electronic spectroscopy methods for the characterization of atomically thin molecular layers on semiconductor surfaces allowing a direct access to the properties of single adsorbed molecules.

Defect structure in Zn+ implanted Si: HRXRD study

AbstractThe defect structure of the layer damaged by implantation with 64Zn+ ions and its evolution during subsequent annealing was studied by high‐resolution X‐ray diffraction combined with secondary ion mass spectrometry and Auger electron spectroscopy methods. The samples were pieces of n‐type Si(001) wafer cut from a Czohralski grown ingot. The samples were implanted with 64Zn+ ions at an energy of 100 keV and an ion dose of 2 × 1014 cm−2 with subsequent annealing at 400 °C for 60 min and 700 °C for 10 min. The strain and Debye–Waller depth profiles determined from the diffraction patterns were analyzed and compared to Zn profiles. Annealing leads to significant changes in the shape of the profiles. These changes can be caused by annihilation of Frenkel pair components, redistribution of both radiation‐induced point defects and the implanted impurity, and quasi‐chemical reactions between point defects and implanted impurity. Analysis of Si(‐2‐24) reciprocal space maps confirms that the damaged layer remains fully coherent to the Si matrix in as‐implanted state and after the heat treatments. The increase of X‐ray diffuse scattering intensity after annealing is caused by clustering of radiation‐induced point defects and implanted Zn atoms.

Electronic structure and magnetic properties of the graphene/Fe/Ni(111) intercalation-like system

The electronic structure and magnetic properties of the graphene/Fe/Ni(111) system were investigated via combination of the density functional theory calculations and electron-spectroscopy methods. This system was prepared via intercalation of thin Fe layers (1 ML) underneath graphene on Ni(111) and its inert properties were verified by means of photoelectron spectroscopy. Intercalation of iron in the space between graphene and Ni(111) changes drastically the magnetic response from the graphene layer that is explained by the formation of the highly spin-polarized 3d(z(2)) quantum-well state in the thin iron layer.

Switching the photoinduced processes in host–guest complexes of β-cyclodextrin-substituted silicon(iv) phthalocyanines and a tetrasulfonated porphyrin

Porphyrins and phthalocyanines are two attractive classes of functional dyes for the construction of artificial light harvesting and charge separation molecular systems. The assembly of these components by supramolecular approach is of particular interest as this provides a facile route to build multi-chromophoric arrays with various architectures and tuneable photophysical properties. We report herein a series of host-guest complexes formed between a tetrasulfonated porphyrin and several silicon(IV) phthalocyanines substituted axially with two permethylated β-cyclodextrin units via different spacers. As shown by electronic absorption and fluorescence spectroscopic methods, the two components bind spontaneously in a 1:1 manner in water with large binding constants in the range of 1.1 × 10(7) to 3.5 × 10(8) M(-1). The photophysical properties of the resulting supramolecular complexes have also been studied in detail using steady-state and time-resolved optical spectroscopic methods. It has been found that two major photoinduced processes, namely fluorescence resonance energy transfer and charge transfer are involved which are controlled by the spacer between the β-cyclodextrin units and the silicon centre of phthalocyanine. Despite the fact that charge transfer is a thermodynamically favourable process for all the complexes, only the ones with a tetraethylene glycol or oxo linker exhibit an efficient charge transfer from the excited phthalocyanine to the porphyrin entity. The lifetimes of the corresponding charge-separated states have been determined to be 200 and 70 ps by picosecond pump-probe experiments.

New organic ligands of the terpyridine series: modification of gold nanoparticles, preparation of coordination compounds with Cu(I), catalysis of oxidation reactions

Organic ligands containing terpyridine and disulfide groupings linked between one another by a bonding –O(CH2)n- (n = 6, 12) fragment have been synthesized. Gold nanoparticles of mean size 1.8 nm modified with the indicated ligand were obtained by the method of Brust. By methods of electron spectroscopy and cyclic voltamperometry, the possibility of forming of coordinated compounds on the surface of gold nanoparticles modified by a terpyridine ligand, on interaction with Cu(MeCN)4ClO4 has been shown. The obtained nanoparticles catalyze the oxidation of 2,4-di-tert-butylphenol into 3,3',5,5'-tetra(tert-butyl)biphenyl-2,2'-diol.

Chemical effect of inert argon beam on nitride nanolayer formed by ion implantation into GaAs surface

The composition of a nitride nanolayer formed on a GaAs(100) surface by the implantation of ions with an energy of E i = 2.5 keV and the chemical state of nitrogen in this layer have been studied by the method of Auger electron spectroscopy. It is established that, in addition to GaN, a GaAsN solid solution phase is formed in the ion-implanted layer. The energies of N KVV Auger electron transitions in these phases are determined as E A (GaN) = 379.8 ± 0.2 eV and E A (GaAsN) = 382.8 ± 0.2 eV (relative to the Fermi level), which allowed the distribution of nitrogen between these phases to be evaluated as [N(GaN)] = 70% and [N(GaAsN)] = 30%. It is established that an argon ion beam produces a chemical effect on the nitride layer, which is related to a cascade mixing of the material. Under the action of the argon ion bombardment, the distribution of nitrogen in the indicated phases changes to opposite. As a result a nitride nanolayer is formed in which the narrow-bandgap semiconductor (GaAsN) predominates rather than the wide-bandgap component (GaN).

Surface termination of BaTiO 3 (001) single crystals: A combined electron spectroscopic and theoretical study

The surface termination of oxide surfaces is of crucial importance for the growth of a second material like metals or other oxides. In this study we have investigated the surface of a BaTiO 3 (001) single crystal during sample preparation by various electron spectroscopic methods. It is shown by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and metastable induced electron spectroscopy (MIES) that during sputtering a Ba rich overlayer is formed, in which the Ba 2+ ions are under coordinated. Below this layer, an oxygen deficient BaTiO 3 layer is found. During annealing, we observe the reformation of the crystalline structure. UP and MIE spectra provide clear evidence of a BaO terminated surface. X-ray photoelectron diffraction studies support this result, comparing recorded polar angle scans with calculated intensity modulations using multiple scattering cluster models.

Adsorption of nitrogen oxide molecules to the surface of nanosized nickel clusters formed on the (111) surface of a magnesium oxide film

The properties of the systems formed on deposition of Ni atoms on the (111) surface of a MgO film of thickness equal to six monomolecular layers grown on a Mo(110) crystal face and the adsorption of NO nitrogen oxide molecules to the system surface have been studied by methods of electron spectroscopy (AES, XPES, LEED, LEIBSS) and reflective infrared absorption spectroscopy. On deposition of Ni atoms on the surface of MgO at a substrate temperature of 600 K, three-dimensional islands of Ni are formed. The subsequent adsorption of NO results in molecule dissociation even at 110 K. The efficiency of this process depends on the morphology of the Ni layer.

Study of Pd–Au/MWCNTs formic acid electrooxidation catalysts

AbstractThe Pd–Au multiwall carbon nanotubes (MWCNTs) supported catalyst exhibits higher power density in direct formic acid fuel cell (DFAFC) than similar Pd/MWCNTs catalyst. The Pd–Au/MWCNTs catalyst also exhibits higher activity and is more stable in electrooxidation reaction of formic acid during cyclic voltammetry (CV) measurements. After preparation by polyol method, the catalyst was subjected to two type of treatments: (I) annealing at 250 °C in 100% of Ar, (II) reducing in 5% of H2 in Ar atmosphere at 200 °C. It was observed that the catalyst after treatment I was completely inactive, whereas after treatment II exhibited high activity.In order to explain this effect the catalysts were characterized by electron spectroscopy methods. The higher initial catalytic activity of Pd–Au/MWCNTs catalyst than Pd/MWCNTs catalyst in reaction of formic acid electrooxidation was attributed to electronic effect of gold in Pd–Au solution, and larger content of small Au nanoparticles of 1 nm size. The catalytic inactivity of Pd–Au/MWCNTs catalysts annealed in argon is attributed to carbon amorphous overlayer covering of Pd oxide shell on the metallic nanoparticles.

Nickel extraction from sulfate media with Cyanex 301 in the presence of electron donor additives

Data is presented on the nickel(II) extraction from sulfate solutions with bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HR) (Cyanex 301) diluted with nonane in the presence of electron donor additives (L). Well-known extractants and modifiers, widely used in industry, trioctyl amine (TOA), trialkyl amine (TAA), trioctyl phosphine oxide (TOPO), trialkyl phosphine oxide (TAPO), tributyl phosphate (TBP), and n-octanol, were used as additives. The interaction between nickel-loaded extracts in nonane (NiR 2) and various electron donor additives was studied using an electronic spectroscopy method. It is shown that n-octanol and TBP do not interact with NiR 2 in the organic phase, as a result of no change in the square planar configuration of the initial nickel complex, while TOPO, TOA, and TAA form mixed complexes with nickel dithiophosphinate. For the NiR 2 and organic amine mixtures, the composition of the ternary complex having an octahedral configuration was found to be [NiR 2•2TOA] or [NiR 2•2TAA]. The introduction of additives into the organic phase results in a decrease in nickel extraction. The degree of extraction decreases in the series TAA > TOPO, TAPO >> TBP >> n-octanol. A decrease in the extractant activity resulting from the interaction between HR and L is the determinant factor during nickel extraction with bis(2,4,4-trimethylpentyl)dithiophosphinic acid in the presence of additives despite the formation of mixed nickel complexes in the HR and TOPO (TAPO) and TAA (TOA) mixtures in the organic phase. The most effective system, based on a mixture of Cyanex 301 and TAA, was proposed for nickel extraction from sulfate media, including leach liquors of oxidized nickel ores.