Characterization of Metal Oxide-Based Gas Nanosensors and Microsensors Fabricated via Local Anodic Oxidation Using Atomic Force Microscopy

This work reports on nanoscale and microscale metal oxide gas sensors, consisting of metal-semiconductor-metal barriers designed via scanning probe microscopy. Two distinct metal oxides, molybdenum and titanium oxides, were tested at different temperatures using CO2 and H2 as test gases. Sensitivities down to ppm levels are demonstrated, and the influence of dry and humid working atmospheres on these metal oxide conductivities was studied. Furthermore, the activation energy was evaluated and analyzed within working sensor temperature range. Finally, full morphological, chemical, and structural analyses of the oxides composites are provided allowing their identification as MoO3 and Ti

Hardening of Al thin films by Ti–C doping

Amorphous aluminum alloys have been evaluated as suitable thin films for protective coatings. Magnetron sputtering deposition may provide the necessary conditions for preparing such alloys due to its far-from-equilibrium deposition conditions. In this work, Al-Ti-C nanocomposite films were deposited by magnetron sputtering technique using TiC and Al targets. The produced films are mainly composed of Al nanocrystallites embedded into an amorphous matrix. Films effective hardness varied in the 6.4–8.2 GPa range, while their elastic modulus ranged from 109 up to 134 GPa. The higher the TiC/Al target power ratio, the harder the film. Topographic atomic force microscopy (AFM) images showed that films are mainly constituted by unevenly dispersed grains. Also, the dark phase angle fraction calculation derived from the phase angle contrast AFM images could be correlated with the deposited Al–Ti–C films hardness measured by nanoindentation tests; the higher the surface dark phase angle fraction, the harder the Al–Ti–C films.Fil: Alencastro, Felipe S.. Universidade Federal do Rio de Janeiro; BrasilFil: Santos Jr., Emanuel. Universidade Federal do Rio de Janeiro; Brasil. Centro Universitário de Volta Redonda; BrasilFil: Mendoza, Martin E.. Escuela Superior Politécnica del Litoral.Facultad de Ingenieria Mecánica y Ciencias de la Producción; Ecuador. Instituto Nacional de Metrologia, Qualidade e Tecnologia; BrasilFil: Araújo, Joyce R.. Instituto Nacional de Metrologia, Qualidade e Tecnologia; BrasilFil: Suarez, Sergio Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Archanjo, Bráulio S.. Instituto Nacional de Metrologia, Qualidade e Tecnologia; BrasilFil: Simão, Renata A.. Universidade Federal do Rio de Janeiro; Brasi

Al-/Fe-(hydr)oxides–organic carbon associations in Oxisols — From ecosystems to submicron scales

Al-/Fe(hydr)oxides accumulation upon weathering favors soil organic carbon (SOC) protection into mineral-organic associations (MOAs). Paradoxically, tropical ecosystems on highly weathered soils are characterized by high turnover rates of SOC. Our objective was to propose an explanation for such apparent contradiction by inferring the chemical composition of MOAs in Oxisols. To this end, we compiled a large data set from 43 published articles providing chemical and physical properties of 179 Oxisols/Ferralsols and their SOC content in the A horizon. Thermal analysis (TA) coupled to evolved gas detection (EGD) was used to assess mineral dehydroxylation and SOC oxidation in two soils with contrasting SOC content. Scanning transmission electron microscopy (STEM) was used to probe MOAs within the soil fraction < 53 μm. At large scales, SOC content was strongly correlated to Al extractable by both ammonium oxalate (AO) (r = 0.71) and dithionite-citrate-bicarbonate (DCB) (r = 0.41). Weaker, but significant correlations occurred for SOC against Fe-AO and Fe-DCB (r = 0.38, and r = 014, respectively). At micro-scale, SOC also was found associated to Al-/Fe-(hydr)oxides, as inferred from the STEM imaging. TA-EGD indicated that with increasing SOC content, proportionally more organic matter was oxidized following the dehydroxylation of Al-/Fe-(hydr)oxides at temperatures < 400 °C. Within the first 20 cm of the topsoil of the Oxisols included in our data set, Al-AO explained 62% of the total variation in SOC. However, while SOC content varied from 0.8 up to 145.8 g kg− 1 soil, Al-AO varied between 0.2 and 15.3 g kg− 1 soil. From the perspective of mineral control on SOC retention, reactive species of Al-(hydr)oxides should interact with a disproportionally large amount of organic matter. Because mineral protection is seemingly reduced upon increasing C content in MOAs, SOC in Oxisols may be more vulnerable to environmental changes than currently recognized

Understanding growth mechanisms and tribocorrosion behaviour of porous TiO2 anodic films containing calcium, phosphorous and magnesium

International audienceThe growth of the dental implant market increases the concern regarding the quality, efficiency, and lifetime of dental implants. Titanium and its alloys are dominant materials in this field thanks to their high biocompatibility and corrosion resistance, but they possess a very low wear resistance. Besides problems related to osteointegration and bacterial infections, tribocorrosion phenomena being the simultaneous action between corrosion and wear, are likely to occur during the lifetime of the implant. Therefore, tribocorrosion resistant surfaces are needed to guarantee the preservation of dental implants.This work focused on the incorporation of magnesium, together with calcium and phosphorous, in the structure of titanium oxide films produced by micro-arc oxidation (MAO). The characterization of morphology, chemical composition, and crystalline structure of the surfaces provided important insights leading to (1) a better understanding of the oxide film growth mechanisms during the MAO treatment; and (2) a better awareness on the degradation process during tribocorrosion tests. The addition of magnesium was shown to support the formation of rutile which improves the tribocorrosion properties of the surfaces