XPS Data (xp + data)

Distribution by Scientific Domains

Selected Abstracts

Anisotropic surface chemistry of aspirin crystals

Jerry Y.Y. Heng
Abstract The wettability of the (001), (100), and (011) crystallographic facets of macroscopic aspirin crystals has been experimentally investigated using a sessile drop contact angle (,) method. , for a nonpolar liquid was very similar for all three facets, though significant , differences were observed for three polar probe liquids. The observed hydrophobicity of the (001) and (100) facets is ascribed to a reduced hydrogen bonding potential at these surfaces, whilst the observed hydrophilicity of facet (011) may be attributed to presence of surface carboxylic functionalities as confirmed by X-ray photoelectron spectroscopy (XPS). The dispersive component of the surface free energy (,) was similar for all three facets (35,,2 mJ/m2). The total surface energy, ,s varied between 46 and 60 mJ/m2 due to significant variations in the polar/acid,base components of , for all facets. Surface polarity as determined by , measurements and XPS data were in good agreement, linking the variations in wettability to the concentration of oxygen containing surface functional groups. In conclusion, the wettability and the surface energy of a crystalline organic solid, such as aspirin, was found to be anisotropic and facet dependant, and in this case, related to the presence of surface carboxylic functionalities. 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:2134,2144, 2007 [source]

Bis(salicyladiminato)Ni(II) Schiff base complexes, grafted on H-terminated Si(100) surfaces, observed by Scanning Near-field Optical/Atomic Force Microscopy (SNOM/AFM)

A. Ustione
Abstract This paper reports the synthesis and structure of a dipolar nonlinear optical bis(salicyladiminato)Ni(II) derived Schiff base complex, chemisorbed on H-terminated Si(100) surfaces. The existence of a monolayer of the derived complex, chemisorbed on the Si(100) surface is unambiguously confirmed by high resolution core-level XPS and AFM/SNOM analyses. The comparison between the optical SNOM images highlights the contribution of the monolayer to the local reflectivity of the sample. Angle-resolved XPS data indicate the presence of chlorine head-atoms on the monolayer surface. Altogether, XPS and AFM/SNOM data suggest the formation of a homogeneous, complete, and ordered monolayer self-assembled on the Si(100) surface. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

X-Ray Photoelectron Spectroscopy and Reactivity Studies of a Series of Ruthenium Catalysts

CHEMCATCHEM, Issue 1 2009
Katarzyna Jarzembska
Abstract X-Ray photoelectron spectroscopy (XPS) was applied to six selected ruthenium precatalysts. The XPS data obtained were compared against reactivity and structural results. The XPS data confirmed some dependencies such as the electron-donor properties of the substituents at the ruthenium center. Additionally, the data combined with structural and reactivity results explain the differences between the character of Grubbs and Hoveyda catalysts. It was found that changing the PCy3 ligand to OiPr (PCy3=tricyclohexylphosphane, OiPr=isopropoxy) has a major influence on relative electron-donating properties of the N-heterocyclic carbene ligand (NHC) and PCy3 groups, which was supported by the relative charges on the Ru center for the examined compounds. Moreover, the turnover frequency (TOF) of a selected example reaction decreased when introducing a NHC group in the case of Grubbs catalysts, but increased in the case of Hoveyda-type catalysts. The XPS data also explained the relative activity values of some catalysts (higher reactivity of nitro-Hoveyda than Hoveyda second-generation catalysts). However, the binding energies do not predict TOFs. Sole examination of the XPS data does not provide a base for reaching unambiguous and binding conclusions as to the relative reactivity of all the investigated systems. [source]

Effect of Substrate Temperature on the Plasma Polymerization of Poly(methyl methacrylate),

B. Casserly
Abstract Low-power, plasma-enhanced (PE)CVD together with polymerization of methyl methacrylate (MMA) can be used to deposit thin films of poly(methyl methacrylate) (PMMA) with,minimal loss of functional groups, as shown by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectrometry (RS). Retention of functional groups decreases with increased substrate temperature, corresponding to decreased deposition rates. From XPS data, the calculated percentage loss of functional groups ranges from 0.9,% to 43.4,%, changing as a function of deposition conditions. RS confirms the presence of C=C bonds in the polymer backbone as a result of scission of the ester group from MMA. The thermal properties of PECVD-produced films from MMA can be tailored by varying the substrate temperature. Onset of thermal decomposition increases with increased substrate temperature by eliminating thermally labile peroxide linkages in the polymer backbone, and by crosslinking that occurs at radical sites generated via scission of functional group bonds. The post-anneal thicknesses of the remaining polymer is of the order of 4,nm or less, indicating that low-power PECVD of PMMA is a viable candidate to act as a sacrificial material for air-gap fabrication. [source]