Browsing by Author "Allen, G. C."

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Open Access
Electron spectroscopic investigation of Sn coatings on glasses
(Springer, 1996) Süzer, Ş.; Voscoboinikov, T.; Hallam, K. R.; Allen, G. C.
Float glasses of different thicknesses and a conducting tin oxide glass have been investigated using Photo and Auger Electron Spectroscopy induced by AlKα X-rays. On the basis of measured chemical XPS shifts in the binding energies the chemical state of Sn (+2 or +4) incorporated on the float glasses could not be assigned. The use of the Auger parameter allows to separate relaxation and chemical contributions. The derived true chemical shifts of Sn on float-glasses are larger than those of SnO and/or SnO2 due to the larger ionic environment of the glass matrix. Ar+ or HF etching reveals that the concentration of Sn decreases exponentially as a function of depth from the surface. © Springer-Verlag 1996.
Open Access
A photoelectron spectroscopic investigation of conducting polypyrolle-polyamide composite film
(Elsevier, 1995-04) Süzer, Şefik; Toppare, L.; Allen, G. C.; Hallam, K. R.
X-ray photoelectron spectrum of the electrochemically prepared polypyrrole and polypyrrole-polyamide composite films exhibit an additional strong high binding energy peak at 402.0 eV corresponding to N+ moieties. Intensity of this peak is significantly reduced upon electrochemical reduction. Atomic concentrations derived from the observed N+ and F (stemming from the dopant BF4-) peaks reveal a slightly higher cation/anion ratio for this composite and suggest that the composite has a different chemical composition than the corresponding polymers. © 1995 Elsevier Science B.V.
Open Access
Surface spectroscopic studies of Cs+, and Ba2+ sorption on chlorite-illite mixed clay
(De Gruyter Oldenbourg, 2000) Shahwan, T.; Sayan, S.; Erten, H. N.; Black, L.; Hallam, K. R.; Allen, G. C.
The sorption behavior of Cs+, and Ba2+ on natural clay was investigated using ToF-SIMS, XPS, and XRD. The natural clay was composed mainly of chlorite and illite in addition to quartz and calcite. Depth profiling up to 70 Å was performed at 10 Å steps utilizing ToF-SIMS to study the amount of sorbed Cs+ and Ba2+ as a function of depth in the clay matrix. The results suggest that Cs+ and Ba2+ ions were sorbed primarily by ion exchange coupled with hydrolytic sorption. According to ToF-SIMS and XPS results, the total sorbed amount of Ba2+ was larger than that of Cs+. Quantitative determination of the primary cations within the analyzed clay before and after sorption indicated that for Ba2+ sorption, Ca2+, Mg2+ and for Cs+ sorption Ca2+, K+ were the major exchanging ions. The XRD spectra of Ba-sorbed clay contained new peaks that were identified as BaCO3.
Open Access
ToF-SIMS depth profiling analysis of the uptake of Ba2+ and Co2+ ions by natural kaolinite clay
(Academic Press, 2004) Shahwan, T.; Erten, H. N.; Black, L.; Allen, G. C.
The sorption behavior of Ba2+ and Co2+ ions on a natural clay sample rich in kaolinite was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling at 10-Å steps was performed up to a 70-Å matrix depth of the clay prior to and following sorption. The results showed that Co2+ is sorbed in slightly larger quantities than Ba2+, with significant numbers of ions fixed on the outermost surface of the clay. Depletion of the ions K+, Mg 2+, and Ca2+ from the clay lattice was observed to accompany enrichment with Co2+ and Ba2+ ions. The data obtained using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) indicated insignificant structural and morphological changes in the lattice of the clay upon sorption of both Ba2+ and Co2+ ions. Analysis using energy dispersive X-ray spectroscopy (EDS) showed that the average atomic percentage (±S.D.) of Ba and Co on kaolinite surface were 0.49±0.11 and 0.61±0.19, respectively, indicating a limited uptake capacity of natural kaolinite for both ions. © 2004 Elsevier Inc. All rights reserved.
Open Access
TOF-SIMS study of Cs+ sorption on natural kaolinite
(Elsevier, 1999) Shahwan, T.; Erten, H. N.; Black, L.; Allen, G. C.
The sorption of Cs+ on natural kaolinite has been studied using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Depth profiling up to 70 Å was performed to study the change in the amount of sorbed Cs+ as a function of depth in the kaolinite matrix. Quantitative determination of the amounts of primary cations in the kaolinite structure before and after sorption of Cs+ ions was carried out to identify which cations are possibly taking part in the sorption process. The experimental results showed that large amounts of Cs+ are sorbed onto the surface of kaolinite and that sorption decreases sharply over the first 10-Å depth. The fact that kaolinite surface was negatively charged under the operating pH indicates that physisorption has an important contribution to the sorption process. The results also showed that Na+, K+, Li+, Ca2+, Mg2+ and Fe3+ were involved in the sorption process with Cs+ and that the total decrease in the amounts of these cations is close to the amount of sorbed Cs+, suggesting that ion exchange is the dominant sorption mechanism. Copyright (C) 1999 Elsevier Science B.V. All rights reserved.
Open Access
X-ray photoelectron spectroscopic investigation of conducting polymer blends
(Springer, 1996) Süzer, Ş.; Toppare, L.; Hallam, K. R.; Allen, G. C.
Electrochemically prepared films of conducting polymers of polypyrrole and polythiophene and their blends with polyamide have been investigated by X-ray photoelectron spectroscopy. In the N1s region of the spectra of films containing polypyrrole the peak corresponding to N+ at 402.0 eV is separated from that of neutral N. The intensity of the N+ peak can be correlated with the electrical conductivity of the films and the spectroscopically derived ratio of F/N+ is close to 4 indicating that one BF4 - dopant ion is incorporated for every oxidized nitrogen center. In the spectra of films of polythiophene and its blends peaks corresponding to S and S+ can not be resolved but again the F/C ratio correlates with the electrical conductivity. © Springer-Verlag 1996.