Comparison of fullerene and large argon clusters for the molecular depth profiling of amino acid multilayers.

A major challenge regarding the characterization of multilayer films is to perform high-resolution molecular depth profiling of, in particular, organic materials. This experimental work compares the performance of C60(+) and Ar1700(+) for the depth profiling of model multilayer organic films. In particular, the conditions under which the original interface widths (depth resolution) were preserved were investigated as a function of the sputtering energy. The multilayer samples consisted of three thin δ-layers (~8 nm) of the amino acid tyrosine embedded between four thicker layers (~93 nm) of the amino acid phenylalanine, all evaporated on to a silicon substrate under high vacuum. When C60(+) was used for sputtering, the interface quality degraded with depth through an increase of the apparent width and a decay of the signal intensity. Due to the continuous sputtering yield decline with increasing the C60(+) dose, the second and third δ-layers were shifted with respect to the first one; this deterioration was more pronounced at 10 keV, when the third δ-layer, and a fortiori the silicon substrate, could not be reached even after prolonged sputtering. When large argon clusters, Ar1700(+), were used for sputtering, a stable molecular signal and constant sputtering yield were achieved throughout the erosion process. The depth resolution parameters calculated for all δ-layers were very similar irrespective of the impact energy. The experimental interface widths of approximately 10 nm were barely larger than the theoretical thickness of 8 nm for the evaporated δ-layers.

Molecular depth profiling of organic photovoltaic heterojunction layers by ToF-SIMS: comparative evaluation of three sputtering beams.

With the recent developments in secondary ion mass spectrometry (SIMS), it is now possible to obtain molecular depth profiles and 3D molecular images of organic thin films, i.e. SIMS depth profiles where the molecular information of the mass spectrum is retained through the sputtering of the sample. Several approaches have been proposed for "damageless" profiling, including the sputtering with SF5(+) and C60(+) clusters, low energy Cs(+) ions and, more recently, large noble gas clusters (Ar500-5000(+)). In this article, we evaluate the merits of these different approaches for the in depth analysis of organic photovoltaic heterojunctions involving poly(3-hexylthiophene) (P3HT) as the electron donor and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as the acceptor. It is demonstrated that the use of 30 keV C60(3+) and 500 eV Cs(+) (500 eV per atom) leads to strong artifacts for layers in which the fullerene derivative PCBM is involved, related to crosslinking and topography development. In comparison, the profiles obtained using 10 keV Ar1700(+) (∼6 eV per atom) do not indicate any sign of artifacts and reveal fine compositional details in the blends. However, increasing the energy of the Ar cluster beam beyond that value leads to irreversible damage and failure of the molecular depth profiling. The profile qualities, apparent interface widths and sputtering yields are analyzed in detail. On the grounds of these experiments and recent molecular dynamics simulations, the discussion addresses the issues of damage and crater formation induced by the sputtering and the analysis ions in such radiation-sensitive materials, and their effects on the profile quality and the depth resolution. Solutions are proposed to optimize the depth resolution using either large Ar clusters or low energy cesium projectiles for sputtering and/or analysis.

Exploring dysmenorrhoea and menstrual experiences among Lebanese female adolescents.

Data on menstrual experiences and their impact on quality of life among women in developing countries are scant. The aim of this study was to assess the prevalence of dysmenorrhoea among adolescent girls in Sidon city and suburbs, Lebanon, and to explore its possible relationship with menstrual experience. In a cross-sectional design, 389 post-menarcheal schoolgirls aged 13-19 years were selected using a cluster random sampling method. Of these 161 (41.4%) were regularly or sometimes absent from school due to menstrual problems and 289 (74.3%) experienced dysmenorrhoea. Nevertheless only 7.3% of the girls had consulted a physician about dysmenorrhoea. Three-quarters of these young women (75.2%) had scores indicating negative menstrual experience based on the Menstrual Experience and Behavior Questionnaire. Significant predictors of dysmenorrhoea were negative menstrual experience, younger age of girl, longer duration of bleeding and longer cycle length. Better reproductive health educational programmes focusing on menstruation are needed for female adolescents.

Exploring dysmenorrhoea and menstrual experiences among Lebanese female adolescents

Data on menstrual experiences and their impact on quality of life among women in developing countries are scant. The aim of this study was to assess the prevalence of dysmenorrhoea among adolescent girls in Sidon city and suburbs, Lebanon, and to explore its possible relationship with menstrual experience. In a cross-sectional design, 389 post-menarcheal schoolgirls aged 13-19 years were selected using a cluster random sampling method. Of these 161 [41.4%] were regularly or sometimes absent from school due to menstrual problems and 289 [74.3%] experienced dysmenorrhoea. Nevertheless only 7.3% of the girls had consulted a physician about dysmenorrhoea. Three-quarters of these young women [75.2%] had scores indicating negative menstrual experience based on the Menstrual Experience and Behavior Questionnaire. Significant predictors of dysmenorrhoea were negative menstrual experience, younger age of girl, longer duration of bleeding and longer cycle length. Better reproductive health educational programmes focusing on menstruation are needed for female adolescents

Exploring dysmenorrhoea and menstrual experiences among Lebanese female adolescents

Data on menstrual experiences and their impact on quality of life among women in developing countries are scant. The aim of this study was to assess the prevalence of dysmenorrhoea among adolescent girls in Sidon city and suburbs, Lebanon, and to explore its possible relationship with menstrual experience. In a cross-sectional design, 389 post-menarcheal schoolgirls aged 13-19 years were selected using a cluster random sampling method. Of these 161 [41.4%] were regularly or sometimes absent from school due to menstrual problems and 289 [74.3%] experienced dysmenorrhoea. Nevertheless only 7.3% of the girls had consulted a physician about dysmenorrhoea. Three-quarters of these young women [75.2%] had scores indicating negative menstrual experience based on the Menstrual Experience and Behavior Questionnaire. Significant predictors of dysmenorrhoea were negative menstrual experience, younger age of girl, longer duration of bleeding and longer cycle length. Better reproductive health educational programmes focusing on menstruation are needed for female adolescents

Metal-assisted secondary ion mass spectrometry using atomic (Ga+, In+) and fullerene projectiles.

The advantages and drawbacks of using either monatomic or buckminsterfullerene primary ions for metal-assisted secondary ion mass spectrometry (MetA-SIMS) are investigated using a series of organic samples including additive molecules, polyolefins, and small peptides. Gold deposition is mostly performed by sputter-coating, and in some cases, the results are compared to those of thermal evaporation (already used in a previous article: Delcorte, A.; Médard, N.; Bertrand, P. Anal. Chem. 2002, 74, 4955). The microstructure of the gold-covered sample surfaces is assessed by scanning and transmission electron microscopies. The merits of the different sets of experimental conditions are established via the analysis of fragment and parent-like ion yields. For most of the analyzed samples, the highest yields of fragment and parent-like ions are already reached with the sole use of C60+ projectiles. Metallization of the sample does not lead to a significant additional enhancement. For polyethylene and polypropylene, however, gold metallization associated with Ga+/In+ projectiles appears to be the only way to observe large cationized, sample-specific chain segments (m/z approximately 1000-2000). A detailed study of the polypropylene mass spectra as a function of gold coverage shows that the dynamics of yield enhancement by metal nanoparticles is strongly dependent on the choice of the projectile, e.g., a pronounced increase with Ga+ and a slow decay with C60+. The cases of Irganox 1010, a polymer antioxidant, and leucine enkephalin, a small peptide, allow us to investigate the specific influence of the experimental conditions on the emission of parent(like) ions such as M+, (M + Na)+, and (M + Au)+. The results show a dependence on both the type of sample and the considered secondary ion. Using theoretical and experimental arguments, the discussion identifies some of the mechanisms underlying the general trends observed in the results. Guidelines concerning the choice of the experimental conditions for MetA-SIMS are provided.

Assessment of the plasma desorption time-of-flight mass spectrometry technique for pesticide adsorption and degradation on 'as-received' treated soil samples.

The assessment of the plasma desorption time-of-flight mass spectrometry (PD-TOFMS) technique as a tool for direct characterization of pesticides adsorbed on agricultural soil is made for the first time in this study. Pellets of soils impregnated by solutions of three pesticides, namely norflurazon, malathion and oxyfluorfen, as well as deposits of these solutions onto aluminum surfaces, were investigated to this end. The yield values of the most characteristic peaks of the negative ion mass spectra were used to determine both the lowest concentrations detected on soils and limits of detection from thin films. The lowest values on soils are for malathion (1000 ppm range), and the largest for norflurazon (20,000 ppm), which is close to the limit of detection (LOD) found for the pesticide on the aluminum substrate (approximately 0.2 microg . cm(-2)). Different behaviors were observed as a function of time of storage in the ambient atmosphere or under vacuum; norflurazon adsorbed on soil exhibited high stability for a long period of time, and a rapid degradation of malathion with the elapsed time was clearly observed. The behavior of oxyfluorfen was also investigated but segregation processes seem to occur after several days. Although by far less sensitive than conventional methods based on extraction processes and used for real-world analytical applications, this technique is well suited to the study of the transformations occurring at the sample surface. A discussion is presented of the future prospects of such experiments in degradation studies.