Surface Functionalization of Ceramic Nanoparticles: Application to Ion-Sensing and Gas-Sensing Devices
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Surface Functionalization of Ceramic Nanoparticles: Application to Ion-Sensing and Gas-Sensing Devices Marie-Isabelle Baraton, UMR 6638 CNRS, University of Limoges F-87060 Limoges, France [email protected] ABSTRACT The consequences of surface functionalization by grafting molecules like hydroxysilane, chlorosilane, and hexamethyldisilazane (HMDS) are reviewed for different types of nanoparticles including Si3N4, TiO2, and SnO2. Fourier transform infrared spectrometry is used as primary investigation tool. In terms of physical properties, these surface chemical modifications lead to improvements of the ion-sensitive FET and gas sensors characteristics. The beneficial effect of hydroxy- and chlorosilane grafted on Si3N4 used as ion sensitive membranes will be demonstrated. Then, the reduction of humidity effects on HMDS-grafted TiO2 and SnO2 nanosized powders used for screen-printed CO sensors will be reported. INTRODUCTION Tailoring the surface properties of nanosized ceramic particles is a challenging problem faced by scientists working in the fields of hybrid organic-inorganic nanocomposites (dispersion problems) and ceramic-based electronic transducers (selectivity and stability problems). For example, chemical grafting is a promising way to increase and tailor the selectivity of chemical sensors. Indeed, while protons can be easily detected using untreated silicon oxide, the detection of other ions requires the surface chemical affinity to be modified. As another example, the sensitivity to humidity of semiconductor-based gas sensors is an important drawback which could be minimized by appropriate surface chemical modifications. However, when working at the nanometer scale, modification of the surface properties by any means implies changes in the overall properties due to the major contribution of the surface in comparison with the bulk. This is particularly critical for semiconducting nanosized particles and nanoscale films for which changes in the chemical composition of the surface may affect the overall electrical properties. Because the surface of any material continuously evolves in order to be in equilibrium with the environment, intrinsic properties can hardly be defined for such nanomaterials. As a result, any tailoring of the surface properties must be carefully controlled at every stage of the process and its consequences on the overall properties clearly evaluated. SURFACE FUNCTIONALIZATION AND CONTROL The functionalization of surfaces is now considered as a necessary step in many fields of technology. The self-assembly of chemical monolayers, known for years, is a perfect example illustrating the importance of surface modification and control. One can also cite the assembly of organic molecules onto semiconductor surfaces to fabricate hybrid organic-semiconductor devices. As another example, the importance of the surface is critical in the lithographically induced self-assembly (LISA) process [1] because the patterned substrate (template) induces and guides the self-formation of pillars. Y6.1.1
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