X-ray photoelectron spectroscopic investigations of Cu2O nanoparticles

Cuprous oxide nanoparticles of five different sizes were obtained by electrochemical as well as chemical routes. Various capping agents were used to passivate the nanoparticles. X-ray diffraction studies show formation of single phased, cubic Cu₂O nanoparticles. X-ray photoelectron spectroscopic studies indicate formation of CuO phase on the surface of Cu₂O nanoparticles for uncapped as well as for those, capped by tetraoctylammonium bromide. On the other hand polyacrylamide and polyvinyl pyrrolidone capped samples did not show presence of CuO. X-ray photoelectron spectroscopy also indicates formation of a Cu²⁺ complex with the capping material on the surface of Cu₂O nanoparticles. The results were discussed in terms of capability of passivation of various additives.     

X-ray photoelectron spectroscopic investigation of the durability of siloxane plasma polymer coatings in a steam atmosphere

Thin-film plasma polymer coatings were deposited on to titanium, stainless steel and 70/30 copper-nickel substrates from hexamethyldisiloxane (HMDSO) as potential permanent promoters of dropwise condensation of steam. Long-term durability condensation tests showed that HMDSO films on titanium exposed to low-velocity steam performed well with some lifetimes in excess of 12 000 h. X-ray photoelectron spectroscopy (XPS) was used to monitor the dependence of chemical composition of the films on the deposition conditions and it was shown that composition was not critically dependent on deposition conditions. Additionally, XPS was used to monitor chemical composition before and after exposure of specimens to steam in an attempt to identify the failure mechanisms for films which had ceased to sustain dropwise condensation over their entire surface. Furthermore, short tube sections were coated with plasma-polymerized HMDSO and exposed to steam at elevated velocities. In this case the durability was poor and this is attributed to water droplet impingement erosion on the tube surfaces. This was confirmed by a subsequent test where no water droplets were present in the steam flow and the coating lifetime was seen to increase.     

Pentafluorinated probes for the X-ray photoelectron spectroscopic study of immobilized bifunctional silanes

Bifunctional silanes constitute valuable linking agents for attachment of biomolecules at high levels of surface population density through the formation of thioether or disulfide bonds. Three such compounds, 1-((trifluoroacetyl)-thio)-11-(trichlorosilyl)undecane, 1-bromo-11-(trichlorosilyl)undecane, and 1-((bromoacetyl)oxy)-11-(trichlorosilyl)undecane, are discussed in terms of their surface chemistry on silicon wafers. To examine the electrophilic and nucleophilic generation of sulfur-containing linkages, three new probes, N'-(pentafluorophenyl)iodoacetohydrazide, N'-(pentafluorophenyl)-3-(2-pyridylthio)propriono-hydrazide, and N'-(pentafluorophenyl)mercaptoacetohydrazide, are introduced with respect to their reactions with silanized surfaces (studied by X-ray photoelectron spectroscopy). Thiol-functionalized surfaces obtained by silanization act as nucleophiles toward the probes. In air, low yields of conjugation are exhibited which are attributed to the unavailability of thiol groups because of intramolecular disulfide group formation instigated by oxygen or by disulfide exchange with the proprionyl probe. The behavior of electrophilic silanized surfaces toward the mercaptoacetyl-containing probe is governed by the nature of the leaving group and by steric factors.     

Hyrdogen bronzes from VMoO5.5 : An X-ray diffraction investigation

Hydrogen bronzes obtained by spillover of hydrogen onto Pt particles deposited on the surface of VMoO_5.5 have been examined by X-ray diffraction. The results show that H_3.4VMoO_5.5 is crystalline and that no intermediate crystalline phase is formed during the insertion of hydrogen in the host lattice. Oxidation of the bronze restores the initial oxide phase. Upon back-titration with H₂ at 60°C, the bronze phase reappears (indicating the reversible character of these bronzes) at a much higher rate than when the bronze is formed for the first time.     

X-ray photoelectron spectroscopy (XPS) investigation of the surface film on magnesium powders

Magnesium (Mg) and its alloys are attractive for use in automotive and aerospace applications because of their low density and good mechanical properties. However, difficulty in forming magnesium and the limited number of available commercial alloys limit their use. Powder metallurgy may be a suitable solution for forming near-net-shape parts. However, sintering pure magnesium presents difficulties due to surface film that forms on the magnesium powder particles. The present work investigates the composition of the surface film that forms on the surface of pure magnesium powders exposed to atmospheric conditions and on pure magnesium powders after compaction under uniaxial pressing at a pressure of 500 MPa and sintering under argon at 600 °C for 40 minutes. Initially, focused ion beam microscopy was utilized to determine the thickness of the surface layer of the magnesium powder and found it to be ~10 nm. The X-ray photoelectron analysis of the green magnesium sample prior to sintering confirmed the presence of MgO, MgCO(3)·3H(2)O, and Mg(OH)(2) in the surface layer of the powder with a core of pure magnesium. The outer portion of the surface layer was found to contain MgCO(3)·3H(2)O and Mg(OH)(2), while the inner portion of the layer is primarily MgO. After sintering, the MgCO(3)·3H(2)O was found to be almost completely absent, and the amount of Mg(OH)(2) was also decreased significantly. This is postulated to occur by decomposition of the compounds to MgO and gases during the high temperature of sintering. An increase in the MgO content after sintering supports this theory.     

Evaluation of the depth resolutions of Auger electron spectroscopic, X-ray photoelectron spectroscopic and time-of-flight secondary-ion mass spectrometric sputter depth profiling techniques

Concentration-depth profiles of sputter-deposited Si/Al multilayered specimens were determined by model fitting to measured data obtained by depth profiling, using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectrometry (TOF-SIMS). The model used for calculation of the concentration-depth profile accounts for the broadening (“smearing”) upon experimental depth profiling owing to the effects of atomic mixing, preferential sputtering, surface roughness and information depth of either the Auger electrons (for AES depth profiling) or the photoelectrons (for XPS depth profiling) or the secondary ions (for SIMS depth profiling). The depth resolution for each technique was derived directly from the values determined for the fitting parameters in the model.     

An X-ray photoelectron spectroscopy study of the chemical changes in oxide and hydroxide surfaces induced by Ar+ ion bombardment

In the course of X-ray photoemission studies on the oxidation of metals and alloys and on bulk oxides, we found that in addition to physical sputtering Ar⁺ ion bombardment can in many cases reduce an oxide to a mixture of the original oxide, lower oxides and metal. The effect is even more pronounced in systems containing hydroxyl groups which are readily destroyed by the ion beam. Specific examples for oxidized cobalt, nickel and iron surfaces and their bulk oxides and hydroxides are given. The relative reduction rates of Co^II and Fe^III in CoFe₂O₄ are also examined. From these observations, it is clear that any depth compositional profiling using ion sputtering in conjunction with Auger or X-ray photoelectron spectroscopy should be treated with extreme caution. The mechanism for the chemical changes induced by ion bombardment is briefly discussed.     

Properties of SiO2 films formed by oxygen implantation into silicon

Oxygen ions with energies of 5–60 keV were implanted into Si at doses of 10¹⁵–10¹⁸ ions cm^?2 to form SiO₂ layers. Annealing was carried out in nitrogen at 500–1000 °C and in hydrogen at 450 °C. By monitoring the IR transmission spectra, the refractive index, the etching behaviour and the electrical characteristics, it was established that stoichiometric SiO₂ layers can be produced with doses of 10¹⁸ ions cm^?2 on annealing at 700–1000 °C. A voltage-dependent capacitance was obtained only for samples implanted with a dose of 10¹⁸ ions cm^?2 and annealed at 1000 °C in nitrogen and at 450 °C in hydrogen. In the interface state spectrum of such samples, maxima at 0.55 eV and at 0.80 eV below the conduction band were found.     

An investigation into the structure of aqueous NaCl electrolyte solutions under magnetic fields

Molecular dynamics simulations are performed to investigate the effects of magnetic fields with intensities of 1–10 T on aqueous NaCl electrolyte solutions at 298 K. The simulations employ the F3C (flexible three centered) water model and investigate electrolyte solutions with both low (1 M) and high (5 M) NaCl concentrations. The results show that the self-diffusion coefficient of the water molecules decreases in a low-concentration solution as the magnetic field intensity is increased, but increases in a high-concentration solution. The magnetic field enhances the mobility of the Na⁺ and Cl⁻ ions in both low- and high-concentration solutions. The average number of hydrogen bonds increases when the magnetic field is applied to pure water or to a solution with a low NaCl concentration, but decreases in a solution with a high-concentration. The results show that the enhanced mobility of the ions under a magnetic field causes serious damage to the hydrogen bond network in the high-concentration solution. Conversely, in the low-concentration solution, the structural behavior is dominated by the properties of the water molecules, and hence the hydrogen bonding ability is enhanced as the magnetic field is increased.     

Lattices in citation networks: An investigation into the structure of citation graphs

The main purposes of this article are to uncover interesting features in real-world citationnetworks, and to highlight important substructures. In particular, it applies lattice theory tocitation analysis. On the applied side, it shows that lattice substructures exist in real-word citationnetworks. It is further shown that, through its relations with co-citations and bibliographiccoupling, the diamond (a four-element lattice) is a basic structural element in citation analysis.Finally, citation compactness is calculated for the four- and five element lattices.     

An X-ray photoelectron study of the interaction of uranyl group with sulfosuccinyl chitosan

Interaction of uranium with low-molecular-weight sulfosuccinyl chitosan (SSLMWC) from sulfate solutions was studied by X-ray photoelectron spectroscopy. The interaction involves formation of complexes with the uranyl group on the SSLMWC surface. The equatorial plane of these complexes can contain nitrogen atom of the amino group and oxygen atoms of the sulfato and sulfo groups SO₄²⁻ and -SO₃H, carboxy groups, and free hydroxy groups. On keeping the complex in a vacuum, two chemically nonequivalent states of U ions, U⁴⁺ and UO₂²⁺, are observed. The U⁴⁺ formation in solid U-containing samples of chitosan and SSLMWC is attributed to the radical reaction of the UO₂²⁺ reduction with the primary hydroxy group of chitosan in a vacuum of the spectrometer under the action of X-ray radiation.     

Effect of oxide dopant on the structure of fluorozirconate glasses studied by X-ray photoelectron spectroscopy

The effect of oxide dopant on the structure of 62ZrF₄-30BaF₂-8LaF₃ (mol%) glass by equimolar substitution of BaO for BaF₂ was studied by X-ray photoelectron spectroscopy (XPS). The XPS spectra of La 3d, Ba 3d, F 1s, O 1s and Zr 3d were measured. From the deconvoluted results for the XPS spectra of elements in the glass, it was proposed that the oxide ions added to the glass mainly bond to Zr⁴⁺ and replace the bridging fluoride ions resulting in the formation of the F-Zr-O bond. Further analyses indicated that the oxide ions mainly play a non-bridging role instead of a bridging role in the glass structure.     

X-ray photoelectron spectroscopic studies of evaporated V2O2and co-evaporated V2O5/B2O3 films

X-ray photoelectron spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been investigated. The photoelectron spectrum of a simple V₂O₅ film shows the splitting of the V 2p level in accordance with the spins. The values of binding energies corresponding to V 2p and O1s are comparable with those reported previously. For co-evaporated V₂O₅/B₂O₃ films a chemical shift in the O 1s level has been observed which has been attributed to the changed chemical environment of oxygen as a result of the presence of boron and vanadium atoms. The values of binding energies for V 2p_3/2 and O 1s corresponding to simple evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ show the presence of V₂O₄ species in the films.     

An investigation into the structure and reactivity of calcium-zinc-silicate ionomer glasses using MAS-NMR spectroscopy

The suitability of Glass Polyalkenoate Cements (GPCs) for orthopaedic applications is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium-free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. However there is no data available on the structure of these glasses. ²⁹Si MAS-NMR, differential thermal analysis (DTA), X-ray diffraction (XRD), and network crosslink density (CLD) calculations were used to characterize the structure of five calcium zinc silicate glasses and relate glass structure to reactivity. The results indicate that glasses capable of forming Zn-GPCs are predominantly Q₂/Q₃ in structure with corresponding network crosslink densities greater than 2. The correlation of CLD and MAS-NMR results indicate the primary role of zinc in these simple glass networks is as a network modifier and not an intermediate oxide; this fact will allow for more refined glass compositions, with less reactive structures, to be formulated in the future.     

Interactions of thin films of Pd and Pd/Si on GaAs: an X-ray photoelectron spectroscopic study combined with a thermodynamic analysis

Interfacial reactions of Pd and Pd/Si films on [0 0 1]-oriented GaAs substrates have been studied by X-ray photoelectron spectroscopy. In the as-deposited Pd/GaAs system, Pd interacts with Ga and the As is isolated. A Pd–Ga–As compound is observed to form under the Pd–Ga and As layers. Annealing the Pd/GaAs system at 450°C leads to the formation of islands composed of Pd–Ga and Pd–As, amongst which a Pd–Ga–As compound forms. In the Pd/Si/GaAs system, Pd diffuses in to the GaAs substrate, the Pd–Ga and Pd–Ga–As compounds are formed. In the 450°C-annealed Pd/Si/GaAs system, little interfacial reaction at the GaAs substrate occurs. Possible interfacial reactions in the Pd/GaAs and Pd/Si/GaAs systems, including the previously investigated Pt/GaAs, Pt/Si/GaAs, Ni/GaAs and Ni/Si/GaAs systems are considered by calculation of the change in enthalpy of the reactions. The thermodynamic analyses agree with the experimental results.     

Raman spectroscopic investigation of the structure and crystallization of binary alkali germanate glasses

Raman spectra have been measured on bulk GeO₂ glass and the alkali germanate glasses of composition M₂OxGeO₂ where M=K, Na, Li, and x varies from 19 to 1, as well as on crystallized glasses. The low alkali content glasses (x3) retain a completely polymerized structure of germania polyhedra. Addition of small amounts of alkali oxide to GeO₂ glass does not break the Ge-O-Ge bridging bonds and creates higher co-ordination of germanium atoms. Further addition of alkali oxide eventually breaks up some of the Ge-O-Ge bonds to create Ge-O^– non-bridging oxygens. In the K- and Na-glasses a small number of non-bridging oxygens already exist at x=4.5, while in the Li-glasses they do not exist even at x=4. The structures of the low alkali content glasses start to disappear at x between 4 and 3 and they disappear almost completely at x=2. At x between 2 and 1, glass structures become analogous to the silicate glass structures. At x=2, the glass consists of disordered (Ge₂O₅) _n sheet-like structures and at x=1 disordered (GeO₃) _n chain structures.     

Raman spectroscopic investigation of the woodceramics derived from carbonized tobacco stems/phenolic resin composite

Woodceramics samples derived from carbonized tobacco stems and different contents of phenolic resin, using different carbonization temperatures have been investigated by Raman spectroscopy. It was found that the full width at half maximum (FWHM) and the R-value decreased with an increase of the carbonization temperature and the content of phenolic resin. And the crystallite size L_a of these samples show low microcrystalline size, i.e. L_a varying between 1.85 and 5.40 nm. The results obtained indicate that 973 K is the turning point temperature for the preparation of woodceramics. The results of Raman spectra were confirmed by SEM results of the woodceramics.     

An X-ray technique for investigation of the explosive-emission cathode surface

We present the results of pulsed X-ray radiography of an electron beam spot on the anode of a diode employing an explosive-emission cathode. It is demonstrated that this technique can provide objective information on the character of emissive centers on the cathode surface and can be used for preliminary evaluation of the possibility of using a particular explosive-emission cathode type for the formation of desired electron beams in a given diode.