Biological/Biomedical Accelerator Mass Spectrometry Targets. 2. Physical, Morphological, and Structural Characteristics

The number of biological/biomedical applications that require AMS to achieve their goals is increasing, and so is the need for a better understanding of the physical, morphological, and structural traits of high quality of AMS targets. The metrics of quality included color, hardness/texture, and appearance (photo and SEM), along with FT-IR, Raman, and powder X-ray diffraction spectra that correlate positively with reliable and intense ion currents and accuracy, precision, and sensitivity of fraction modern (Fm). Our previous method produced AMS targets of gray-colored iron−carbon materials (ICM) 20% of the time and of graphite-coated iron (GCI) 80% of the time. The ICM was hard, its FT-IR spectra lacked the sp2 bond, its Raman spectra had no detectable G′ band at 2700 cm−1, and it had more iron carbide (Fe3C) crystal than nanocrystalline graphite or graphitizable carbon (g-C). ICM produced low and variable ion current whereas the opposite was true for the graphitic GCI. Our optimized method produced AMS targets of graphite-coated iron powder (GCIP) 100% of the time. The GCIP shared some of the same properties as GCI in that both were black in color, both produced robust ion current consistently, their FT-IR spectra had the sp2 bond, their Raman spectra had matching D, G, G′, D+G, and D′′ bands, and their XRD spectra showed matching crystal size. GCIP was a powder that was easy to tamp into AMS target holders that also facilitated high throughput. We concluded that AMS targets of GCIP were a mix of graphitizable carbon and Fe3C crystal, because none of their spectra, FT-IR, Raman, or XRD, matched exactly those of the graphite standard. Nevertheless, AMS targets of GCIP consistently produced the strong, reliable, and reproducible ion currents for high-throughput AMS analysis (270 targets per skilled analyst/day) along with accurate and precise Fm values

TCO materials for gas sensors : stakes and challenges

International audienceThe range of major applications of transparent conducting oxides (TCOs) continues to expand, thus generating a growing demand for new materials with lower resistivity and higher transparency over extended wavelength ranges. In addition, p-type TCOs are opening new horizons for highperformance devices based on p-n junctions. Among the most commonly used TCO materials are tin oxide (SnO2), indium oxide (In2O3), indium tin oxide (ITO), zinc oxide (ZnO). But design and synthesis of improved TCO materials leading to a marked increase in conductivity and robustness remain highly desirable while a more detailed understanding of the conductivity mechanisms is critical to further improvement. This lecture will review new developments in TCO materials to be used in high-performance and cost-effective gas sensors. The stakes in the sensor market and the current scientific and technological challenges to be taken up will be discussed

Dual contribution of FTIR spectroscopy to nanoparticles characterization : surface chemistry and electrical properties

International audienceIn a combined approach toward the optimization of chemical gas sensors, Fourier transform infrared spectroscopy is used to investigate in situ the surface reactions taking place at the surface of semiconductor nanoparticles and to simultaneously monitor the variations of the free-carrier density. The correlation between the surface reactions and the changes in the infrared absorbance under gas adsorption/desorption cycles gives information on the chemical phenomena responsible for electrical conductivity variations and therefore for the gas detection. Interaction of CO and NOX with tin oxide nanoparticles is presented and discussed. While the chemical reactions leading to the increase of the electrical conductivity under CO adsorption are relatively straightforward, the adsorption of NOX is much more complex. It is demonstrated that, although generating a strong increase of the electrical conductivity, the NOX adsorption on a fresh tin oxide surface is not fully reversible and actually poisons the surface. Subsequent NOX adsorptions lead to reversible chemical reactions even though the electrical response of the sensor is weake

NOx detection by semiconductor Tin oxide nanoparticles : FTIR analysis of transducing mechanisms

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Chemical investigation of the NOx detection mechanisms by semiconductor metal oxide nanoparticles

International audienceThis work reports an FTIR study of the NOx adsorption/desorption cycles on tin oxide nanosized particles under the operating conditions of real sensors (150 degrees C, in presence of O-2). The chemical reactions are monitored in situ and correlated with the variations of the SnO2 electrical conductivity. On the basis of the FTIR spectra, two contributing mechanisms for the NOx detection are suggested. The first one presents the formation of bridged nitrate groups bound to the SnO2 surface via oxygen vacancies acting as electron donor sites. The second mechanism also involves surface oxygen vacancies in the coordination of NOx, but this time the formation of NOx- anionic species is considered. Both mechanisms lead to the decrease of the electrical conductivity under NOx adsorption. However, the bridged nitrate groups are not reversible under gas desorption and thus irreversibly contaminate the surface after the first NOx adsorption. On the contrary, the nitrosyl anionic species are reversible and, from the second NOx adsorption/desorption cycle, ensure the reproducibility of the sensor response

Ion projection direct-structuring for nanotechnology applications

Large-field ion-optics has been developed for reduction printing. Sub-100nm ion projection direct-structuring (IPDS) of patterned magnetic media discs has been demonstrated, extending over 17mm diameter exposure fields, in a single exposure. First results of IPDS patterning of nanocomposite resist material are presented. Information about a novel 200x reduction projection focused ion multi-beam (PROFIB) tool development is provided. Further IPDS nanotechnology applications are discussed