Quantitative analysis of trace levels of surface contamination by X‐ray photoelectron spectroscopy. Part II: Systematic uncertainties and absolute quantification

We discuss analyses of trace levels of surface contamination using X‐ray photoelectron spectroscopy (XPS). The problem of quantifying common sources of statistical and systematic uncertainties for these measurements is formulated in terms of the needs of extreme ultraviolet lithography, but the results and conclusions are applicable to a broad range of XPS applications. We quantify the systematic uncertainties introduced by particular cases of overlapping peaks on different substrate structures by simulating measured spectra with the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis (SESSA). One example demonstrates that the relative atomic concentrations of trace elements such as S, P, and halogens on a Ru surface could be dramatically overestimated if the fitting of the overlapping Ru 3d and C 1s peaks excludes the contribution from carbon. We also show how spectra generated by SESSA can be compared with measured spectra to determine absolute amounts of surface impurities on layered samples of the type used for extreme ultraviolet lithography. We provide estimates of the total uncertainty for such measurements by considering the systematic limitations of SESSA and the statistical uncertainties of the measurements. The same procedure can be employed for other multilayered materials. Finally, we describe two approaches for converting XPS detection limits for an elemental impurity in an elemental matrix to the corresponding detection limits for the impurity as a thin film on the surface of the matrix material.     

A potent antimalarial trichothecene from hyphomycete species

Antimalarial screening of diverse fungal samples resulted in the isolation and identification of a new sesquiterpene, trichothecinol D (1), which exhibited potent in vitro activity against Plasmodium falciparum with a 200-fold selectivity for parasite versus mammalian cytotoxicity. Trichothecinol D was obtained by bioassay-guided fractionation of two hyphomycete species. Its chemical characterization was performed by detailed NMR spectroscopy and high resolution mass spectrometry. The absolute configuration of trichothecinol D was determined by X-ray crystallography.     

Catalytic asymmetric alkylation in water in the presence of surfactants: influence of the nature of the nucleophile and the allylic acetate on the activity and enantioselectivity

Asymmetric palladium-catalyzed alkylation of 1,3-diphenyl-2-propenyl acetate with carbon and nitrogen nucleophiles occurs in water in the presence of a surfactant, a base, and Binap as the chiral ligand. Enantioselectivities up to 91% were obtained using carbon nucleophiles, and 93% using nitrogen nucleophiles, in the presence of CTHASO₄ as the surfactant. While the efficiency of the catalyst was higher in water in the presence of the surfactant in the case of carbon nucleophiles, no micellar effects were observed using the nitrogen nucleophiles. The alkylation was extended to other allylic acetates, but the efficiency as well the enantioselectivity of the coupling were lower.     

Free volume expansion and nanofoaming of supercritical carbon dioxide treated polystyrene

Free volume of polystyrene films treated with supercritical carbon dioxide (SCCO 2) were examined by positron annihilation lifetime spectroscopy. Variation of the free volume sizes after the SCCO 2 treatment due to the release of trapped CO 2 and structural relaxation of the polymer was observed. After 500 h from the depressurization, the free volume of the treated films free from CO 2 was approximately 0.306 nm in radius and much larger than that of the untreated films of approximately 0.295 nm in radius due to the freezing of the swollen structure caused by the large solubility of CO 2.     

Trachycladindoles A-G: cytotoxic heterocycles from an Australian marine sponge, Trachycladus laevispirulifer

A southern Australian marine sponge, Trachycladus laevispirulifer, yielded the cytotoxic agents trachycladindoles A-G (1-7) as a selection of novel indole-2-carboxylic acids bearing a 2-amino-4,5-dihydroimidazole moiety. The trachycladindoles displayed promising selective cytotoxicity against a panel of human cancer cell lines and their structures were assigned on the basis of detailed spectroscopic analysis. Preliminary structure activity relationship (SAR) investigations by co-metabolite defined structural features key to the trachycladindole pharmacophore, highlighting an unusual bioactive molecular motif deserving of future investigation.