XPS studies

High quahty SAMs of alkyltrichlorosilane derivatives are not simple to produce, mainly because of the need to carefully control the amount of water in solution (126,143,144). Whereas incomplete monolayers are formed in the absence of water (127,128), excess water results in facile polymerization in solution and polysiloxane deposition of the surface (133). Extraction of surface moisture, followed by OTS hydrolysis and subsequent surface adsorption, may be the mechanism of SAM formation (145). A moisture quantity of 0.15 mg/100 mL solvent has been suggested as the optimum condition for the formation of closely packed monolayers. X-ray photoelectron spectroscopy (xps) studies confirm the complete surface reaction of the —SiCl groups, upon the formation of a complete SAM (146). Infrared spectroscopy has been used to provide direct evidence for the hiU hydrolysis of methylchlorosilanes to methylsdanoles at the soHd/gas interface, by surface water on a hydrated siUca (147). 

Recent XPS studies of interfaces have been performed on U/Si(lll)-7 x 7 face... 

The effect of irradiation of samples in the absence of TAC on the contact angles is also reported in Table 7. Modification of the surface takes place, as is evident from the decrease in the contact angles of water and formamide. The change, which is maximum at an irradiation dose of 10 Mrad, is due to the generation of polar functionalities on the surface. This is also corroborated from the IR/XPS studies described later. The contact angles are lowered further when TAC is incorporated in the system (compare TO/5 with Tl/5, TO/15 with Tl/15, etc.)... 

The effect of Oj, SOj, NOj, HjS, CI2, CO and NH3 on Sn/50%Pb in atmospheres of different relative humidity were investigated but only SO2 and NO2 were active at low concentrations (<100 ppm). An XPS study of Sn/50 7oPb solder exposed to O2, HjO and NO2 was conducted to establish both the surface species formed and the ratio of the concentration of each metal in the surface. Previous XPS studies had only considered the interaction of tin/lead solder with the air . 

Treverton, J. A. and Davies N. C. XPS Studies of a Ferricyanide Accelerated chromate Paint PretreatmenI Film on an Aluminium Surface , Surf. Interfacial Ana ., 3, 194-200 (1981)... 

M. Ayyoob, and M.S. Hegde, An XPS study of the adsorption of oxygen on silver and platinum surfaces covered with potassium or cesium, Surf. Sci. 133, 516-532 (1983). 

X-ray photoelectron spectroscopic (XPS) studies of Ag63,64 and Pt6,56-62 films deposited on YSZ under positive current application conditions have confirmed the proposition2-4 that NEMCA with oxide ion conducting solid electrolytes is due to an electrochemically induced and controlled backspillover of oxide ions on the catalyst surface. 

A subsequent detailed XPS study of Pt films interfaced with YSZ6 (Figs 5.35 to 5.37) has shown that ... 

It should be clear that, as well known from the surface science literature (Chapter 2) and from the XPS studies of Lambert and coworkers with Pt/(3"-A1203 (section 5.8), the Na adatoms on the Pt surface have a strong cationic character, Nas+-5+, where 5+ is coverage dependent but can reach values up to unity. This is particularly true in presence of other coadsorbates, such as O, H20, C02 or NO, leading to formation of surface sodium oxides, hydroxides, carbonates or nitrates, which may form ordered adlattices as discussed in that section. What is important to remember is that the work function change induced by such adlayers is, regardless of the exact nature of the counter ion, dominated by the large ( 5D) dipole moment of the, predominantly cationic, Na adatom. 

Many thanks are also expressed to Professor Milan Jaksic who spent years in our lab and played a significant role in our first aqueous and Nafion NEMCA studies. And to Dr. P. Stonehart who from the USA kept sending valuable samples and advice over the years. Also to Professors S. Ladas and S. Kennou for their precious collaboration in the first XPS studies proving O2 backspillover as the origin of NEMCA. 

Weser U (1985) Redox Reactions of Sulphur-Containing Amino-Acid Residues in Proteins and Metalloproteins, an XPS Study. 61 145-160 Weser U (1973) Structural Aspects and Biochemical Function of Erythrocuprein. 17 1-65 Weser U, see Abolmaali B (1998) 91 91-190... 

Differences in behavior between polycrystalline and single-crystal CdSe electrodes in polysulfide PEC involving the short- and long-term changes in photovoltage and photocurrents have been discussed by Cahen et al. [88], on the basis of XPS studies, which verified the occurrence of S/Se substitution in these electrodes when immersed in polysulfide solution, especially under illumination. The presence of a thin (several nanometers) layer of CdS on top of the CdSe was shown to influence... 

Gonbeau D, Guimon C, Pfister-Guillouzo G, Levasseur A, Meunier G, Dormoy R (1991) XPS study of thin films of titanium oxysulfides. Surface Sci 254 81-89... 

This has been corroborated by the complementary XPS study in which the spectra were recorded without air contacting the reduced samples. As already discussed, the binding energies are referred to an internal standard, ie., the A1 2p line of AI2O3 (73 8 eV) or the Zr 3d line of ZrOj (182.2 eV). 

After the reaction for 5 h in a reactant stream of CH , O, and Hj (P(CHJ= 33.7, P(0,)= 8.4 and P(H2)= 50.7 kPa), the catalyst was analyzed by XRD, Mossbauer and XPS studies. As regarding the XRD and Mossbauer spectroscopic measurements, obvious changes were not observed before and after the reaction. On the other hand, a marked change was observed in the XPS spectrum of the catalyst after the reaction. As shown in Fig. 2, besides the peak at 57.7 eV, which was the only peak of Fe3p obtained for the sample before the reaction and was ascribed to Fe(III), a clear shoulder at 56.1 eV was observed after the reaction. This can be ascribed to the Fe(ll) on the catalyst surface. The same phenomenon has been reported for FeP04 catalyst [13]. Such observations suggest the occurrence of the redox of iron between Fe(Iil) and Fe(II) during the reaction. We believe that this redox plays a key role in the formation of a new active center and thus is important in the selective oxidation of CH4... 

Hamm UW, Kramer D, Zhai RS, Kolb DM. 1998. On the valence state of bismuth adsorbed on a Pt(lll) electrode—An electrochemistry, LEED and XPS study. Electrochim Acta 43 2969-2978. 

Zhou WP, Kibler LA, Kolb DM. 2004. XPS study of irreversibly adsorbed arsenic on a Pt(l 11) electrode. Electrochim Acta 49 5007-5012. 

Shukla A, Neergat M, Parthasarathi B, Jayaram V, Hegde MS. 2001. An XPS study on binary and ternary alloys of transition metals with platinized carbon and its bearing upon oxygen electroreduction in direct methanol fuel cells. J Electroanal Chem 504 111-119. 

In the following paragraphs, reports on XPS studies of a-C N H films are discussed. Most of the work that is discussed is not related to usual plasma deposition, but is related to ion-beam deposition, ion-beam assisted deposition, or other methods, because only a very few wide scope XPS studies on plasma-deposited a-C(N) H films were done up to this moment. Nevertheless, these results bring useful information on the role of hydrogen in the structure of a-C(N) H films. 

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