Phosphorus K-edge Research Articles

Studies on ZDDP Anti-Wear Films Formed Under Different Conditions by XANES Spectroscopy, Atomic Force Microscopy and 31P NMR

Antiwear (AW) films, generated from a mineral base oil containing a zinc dialkyl dithiophosphate (ZDDP) additive, were studied as a function of formation temperature, load and rubbing time. The surface morphology of these films was investigated using atomic force microscopy (AFM), and surface roughness calculated for the observed differing surface morphologies. The morphology of the films is heterogeneous for all the tested conditions, but the surface roughness is dependent on the rubbing condition. X-ray absorption near edge structure (XANES) spectroscopy has been used to characterize the chemistry of these films, and the intensity of the phosphorus K-edge was also used to monitor their thickness. The thickness of these films is in the range of 10–90 nm depending on the running conditions. Phosphorus L-edge spectra show that these films have a similar chemical nature with variable polyphosphate chain-lengths. 31P NMR was used to study the decomposition of ZDDP in the residual oils. The spectra show that the primary and secondary ZDDP react differently under the various conditions. The tribological characteristics of these AW films were probed by measuring the coefficients of friction (μ) and the wear scar width (WSW) of the counter faces. μ is highly related to the applied load and the results of WSW measurements show that the wear performance is related to all the tested parameters, temperature, load and rubbing time.

Phosphorus Speciation in Manure and Manure-Amended Soils Using XANES Spectroscopy

Previous studies suggested an increase in the proportion of calcium phosphates (CaP) of the total phosphorus (P) pool in soils with a long-term poultry manure application history versus those with no or limited application histories. To understand and predict long-term P accumulation and release dynamics in these highly amended soils, it is important to understand what specific P species are being formed. We assessed forms of CaP formed in poultry manure and originally acidic soil in response to different lengths of mostly poultry manure applications using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Phosphorus K-edge XANES spectra of poultry manure showed no evidences of crystalline P minerals but dominance of soluble CaP species and free and weakly bound phosphates (aqueous phosphate and phosphate adsorbed on soil minerals). Phosphate in an unamended neighboring forest soil (pH 4.3) was mainly associated with iron (Fe) compounds such as strengite and Fe-oxides. Soils with a short-term manure history contained both Fe-associated phosphates and soluble CaP species such as dibasic calcium phosphate (DCP) and amorphous calcium phosphate (ACP). Long-term manure application resulted in a dominance of CaP forms confirming our earlier results obtained with sequential extractions, and a transformation from soluble to more stable CaP species such as beta-tricalcium calcium phosphate (TCP). Even after long-term manure application (> 25 yr and total P in soil up to 13,307 mg kg(-1)), however, none of the manure-amended soils showed the presence of crystalline CaP. With a reduction or elimination of poultry manure application to naturally acidic soils, the pH of the soil is likely to decrease, thereby increasing the solubility of Ca-bonded inorganic P minerals. Maintaining a high pH is therefore an important strategy to minimize P leaching in these soils.

Application of X-ray standing wave (XSW) technique for studies of Zn incorporation in InP epilayers

We present a new approach to determine the site incorporation of p-type impurities in the doped layers of microelectronic device structures based on X-ray standing wave (XSW) technique. Activation behavior of Zn in InP epitaxial layers grown by metal organic vapor phase epitaxy (MOVPE) on InP(1 0 0) substrates has been studied. The XSW experiments were performed at the A2 beamline of the Cornell high-energy synchrotron source (CHESS). Angular dependences of the Zn–K fluorescence intensity excited by the XSW field inside the InP layer for symmetrical (4 0 0) reflection have been measured along with the Indium L-edge and phosphorus K-edge fluorescence and X-ray reflectivity. Analysis of the XSW data based on the dynamical diffraction theory in layered crystal structures allowed us to determine the fractions of both Zn atoms incorporated into crystal lattice and interstitial Zn. In our example, a 1 μm thick MOCVD-grown InP layer with the nominal concentration of Zn atoms of (2.4 ± 0.2) × 10 18 cm −3 has the fraction of the substitutional Zn of (65 ± 5)%. This result is in a good agreement with electrical activation of Zn measured with a combination of SIMS and CV profilometry. The accurate knowledge of the interstitial-to-substitutional ratio as a function of growth conditions is required to optimize electrical activation of Zn and to control its diffusion in the device structures.

Structural instability and electronic localization in the 2:1 salts: The case of the Fabre and the (DMtTTF)2CIO4salts

The charge ordering observed in the (TMTTF) 2 X family has been studied by X-ray absorption spectroscopy. XANES measurements at the Sulfur K-edge show no evidence of charge disproportionation larger than 0.5 e, and EXAFS at the Phosphorus K-edge indicate no displacements of the PF 6 anion larger than 0.05 A. The difficulty to observe a structural signature of this charge ordering is due to the triclinic symmetry of these salts. By contrast, in the monoclinic charge transfer salt (DMtTTF) 2 ClO 4 , a screw axis symmetry constrains the molecular stacks to be uniform. In this real 1/4-filled system, charge localization is observed at about 150 K. We show that around this temperature an incommensurate modulation of reduced wave vector (0.58,0,-0.275) is stabilized. The transition is strongly hysteretic, but no long range order is established. We suggest that this modulation, which has the 4kF periodicity in the chain direction, stabilizes a local antiferroelectric state similar to the one previously observed in (TMTTF) 2 SCN.

Correlations between heterocycle ring size and x-ray spectra

X-ray absorption spectra are reported for two classes of ring systems, cyclic polymethylene sulfides and organochromium ring compounds with phosphorus-complexing bidentate ligands. For the cyclic polymethylene sulfides, spectra were acquired in the region of the sulfur K-edge. For the organochromium complexes, spectra were acquired at both the chromium K-edge and at the phosphorus K-edge. These systems allow one to interrogate how the spectra evolve as the bond angle about the absorbing atom is varied. Systematic trends are observed as a function of ring size/bond angle. For the cyclic sulfides, the peaks in the continuum above the sulfur K-edge shift to higher energy and broaden with increasing ring size. These continuum features are assigned to shape resonances. In the chromium K-edge measurements, changes in the P–Cr–C bond angle do not influence the spectra appreciably, indicating that the four carbonyl groups dominate the photoelectron scattering processes. However, the phosphorus K-edge spectra are sensitive to changes in the endocyclic Cr–P–C bond angle. The trends observed in the phosphorus K-edge region for the organometallic continuum features are consistent with those observed for the cyclic polymethylene sulfides.

Extended X-ray absorption fine structure analysis of Ni-P and Fe-P amorphous alloys at the phosphorus K-edge

Extended X-ray absorption fine structure analysis of Ni-P and Fe-P amorphous alloys at the phosphorus K-edge

Reparability of lethal lesions produced by phosphorus photoabsorption in yeast cells.

The characteristics of DNA lesions produced by the photoabsorption of phosphorus in yeast cells were studied using monochromatized soft X-rays tuned to the absorption peak of the phosphorus K-edge (2153 eV) and below the peak energy (2147 eV). The repaired fractions of DNA double-strand breaks (dsb) were measured relatively by using both a mutant, rad 54-3, which shows the temperature-sensitive dsb repair-deficient phenotype, and a wild-type strain. The repaired fraction of lesion in rad 54-3, which corresponds to the relative yield of dsb reparable by the RAD 54 pathway, was not affected by the phosphorus photoabsorption. Repair of the produced lesions in the wild-type cells was also measured by comparing the surviving fraction of the immediately plated cells to that of those cells plated after holding in a non-nutrient medium for 80 hrs. The recovery of the surviving fraction after the holding treatment was dependent upon the irradiated X-ray energy. These results suggest that irreparable lesions are produced by the inner-shell photoabsorption of phosphorus in DNA, although its yield is small.

X-ray absorption near-edge spectroscopy (XANES) at the phosphorus K-edge of triorganophosphinechalcogenides

In this paper, we present X-ray absorption near-edge structure (XANES) measurements of triorganophosphinechalcogenides at the phosphorus K-edge. Using the XANES spectra as fingerprints, we can analyse the influence of the local environment of the absorbing atom on the shape of the absorption spectra and the energy positions of the resonances. Effects caused by the first and by higher coordination shells can be distinguished by systematic variations of the type of atoms surrounding the phosphorus atom. The effect of the first coordination shell is to reflect the electronegativity of the nearest neighbours and the valency of the excited atom: the white line shifts to higher energies with increasing electronegativity of the neighbouring atoms and valency of the absorbing atom. Furthermore, we show that an aromatic substituent in the higher coordination shells causes a splitting of the first strong resonance. This can be traced back to the formation of a delocalised π-electron system which shortens the P–C aryl bond length because of its positive mesomeric effect. MS Xα calculations verify this assumption and indicate that the double-resonance structure can be interpreted by transitions of a 1s electron into the various unoccupied p-orbitals. These orbitals are mainly formed by phosphorus and carbon in the case of the low-energy resonance and by phosphorus and the chalcogene in the case of the high-energy resonance of the splitted white line. If an aliphatic ligand is bound to the excited atom there is no observable splitting in the spectra.

Investigation of P4O6, P4O10and P4O6S by X-Ray Absorption Spectroscopy at the Phosphorus K-Edge

Abstract X-ray photoabsorption spectra at the phosphorus K-edge are reported for P4O6, P4O10 and P4,O6S molecules in the gas phase. The XANES region is shown to be very sensitive to the valency of the excited phosphorus atom and to the electronegativity of its nearest neighbour-atoms. By considering P4O6 and (C6H5O)3PS as reference models corresponding to the various chemical environments of phosphorus in the P4O6S-molecule, its XANES-spectrum can be represented as an additive superpositon of the P4O6- and the (C6O)3PS-spectra. This indicates a localization of the different molecular orbitals in the corresponding parts of the molecule.