High-Resolution X-ray Photoelectron Spectroscopic Studies of Alkylated Silicon(111) Surfaces

Hydrogen-terminated, chlorine-terminated, and alkyl-terminated crystalline Si(111) surfaces have been characterized using high-resolution, soft X-ray photoelectron spectroscopy from a synchrotron radiation source. The H-terminated Si(111) surface displayed a Si 2p_(3/2) peak at a binding energy 0.15 eV higher than the bulk Si 2p_(3/2) peak. The integrated area of this shifted peak corresponded to one equivalent monolayer, consistent with the assignment of this peak to surficial Si−H moieties. Chlorinated Si surfaces prepared by exposure of H-terminated Si to PCl_5 in chlorobenzene exhibited a Si 2p_(3/2) peak at a binding energy of 0.83 eV above the bulk Si peak. This higher-binding-energy peak was assigned to Si−Cl species and had an integrated area corresponding to 0.99 of an equivalent monolayer on the Si(111) surface. Little dichloride and no trichloride Si 2p signals were detected on these surfaces. Silicon(111) surfaces alkylated with C_nH_(2n+1)^− (n = 1 or 2) or C_6H_5CH_2^− groups were prepared by exposing the Cl-terminated Si surface to an alkylmagnesium halide reagent. Methyl-terminated Si(111) surfaces prepared in this fashion exhibited a Si 2p_(3/2) signal at a binding energy of 0.34 eV above the bulk Si 2p_(3/2) peak, with an area corresponding to 0.85 of a Si(111) monolayer. Ethyl- and C_6H_5CH_2-terminated Si(111) surfaces showed no evidence of either residual Cl or oxidized Si and exhibited a Si 2p_(3/2) peak ∼0.20 eV higher in energy than the bulk Si 2p_(3/2) peak. This feature had an integrated area of ∼1 monolayer. This positively shifted Si 2p_(3/2) peak is consistent with the presence of Si−C and Si−H surface functionalities on such surfaces. The SXPS data indicate that functionalization by the two-step chlorination/alkylation process proceeds cleanly to produce oxide-free Si surfaces terminated with the chosen alkyl group

High-Resolution Soft X-ray Photoelectron Spectroscopic Studies and Scanning Auger Microscopy Studies of the Air Oxidation of Alkylated Silicon(111) Surfaces

High-resolution soft X-ray photoelectron spectroscopy was used to investigate the oxidation of alkylated silicon(111) surfaces under ambient conditions. Silicon(111) surfaces were functionalized through a two-step route involving radical chlorination of the H-terminated surface followed by alkylation with alkylmagnesium halide reagents. After 24 h in air, surface species representing Si^+, Si^(2+), Si^(3+), and Si^(4+) were detected on the Cl-terminated surface, with the highest oxidation state (Si^(4+)) oxide signal appearing at +3.79 eV higher in energy than the bulk Si 2p_(3/2) peak. The growth of silicon oxide was accompanied by a reduction in the surface-bound Cl signal. After 48 h of exposure to air, the Cl-terminated Si(111) surface exhibited 3.63 equivalent monolyers (ML) of silicon oxides. In contrast, after exposure to air for 48 h, CH_3-, C_2H_5-, or C_6H_5CH_2-terminated Si surfaces displayed <0.4 ML of surface oxide, and in most cases only displayed ≈0.20 ML of oxide. This oxide was principally composed of Si+ and Si^(3+) species with peaks centered at +0.8 and +3.2 eV above the bulk Si 2p_(3/2) peak, respectively. The silicon 2p SXPS peaks that have previously been assigned to surface Si−C bonds did not change significantly, either in binding energy or in relative intensity, during such air exposure. Use of a high miscut-angle surface (7° vs ≤0.5° off of the (111) surface orientation) yielded no increase in the rate of oxidation nor change in binding energy of the resultant oxide that formed on the alkylated Si surfaces. Scanning Auger microscopy indicated that the alkylated surfaces formed oxide in isolated, inhomogeneous patches on the surface

IgG subclass response to Helicobacter pylori and CagA antigens in children

Specific serum IgG subclass antibodies against Helicobacter pylori antigens and recombinant CagA were analysed in 75 symptomatic children with histologically confirmed H. pylori infection. H. pylori stimulated an IgG1 predominant response, and IgG3 titres showed a positive association with peptic ulcer disease, chronicity of antral inflammation and density of H. pylori colonization. Two methods used for assessing serum IgG CagA antibody status, i.e. Western blotting and enzyme-linked immunosorbent assay (ELISA), were concordant. CagA stimulated an IgG1 and IgG3 predominant humoral response. Total CagA IgG titres were higher in children with active and more severe chronic antral inflammation. These findings suggest that in children the systemic humoral immune response to H. pylori infection may reflect gastroduodenal pathology