Rational Synthesis and Optimization of Multifunctional Solid-State Gas Sensors
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Rational Synthesis and Optimization of Multifunctional Solid-State Gas Sensors Johannes Schwank and Ghenadii Korotcenkov1 Department of , University of Michigan, 3014 H.H. Dow Building, 2300 Hayward, Ann Arbor, MI 48109-2136 1 Laboratory of Microelectronics, Technical University of Moldova, Bld.Stefan cel Mare, 168 Chisinau, MD-2004, Moldova ABSTRACT A new approach is discussed for the rational synthesis and development of optimized multifunctional solid-state gas sensors. Multifunctionality—the incorporation of multiple types of reactivities into a material, such as acid and/or base functionalities, oxidation and/or reduction functionalities, etc.—is a requirement in many gas sensing applications. The front end of many gas sensors contains catalytic layers, so that optimization of catalysts and optimization of gas sensors can be carried out in a synergistic fashion. Multifunctionality presents unique challenges to rational catalyst and sensor systems development because the overall performance of the material is a convolution of the performance of the various subcomponents, and optimization of these individual subcomponents in isolation does not necessarily lead to optimal, or even acceptable, overall performance. A major obstacle to dealing with these difficulties is the inherent complexity of heterogeneous systems prepared by traditional approaches, which makes it difficult to unambiguously identify the compositions and morphologies of the local active sites and their interactions. Further complicating the problem is the requirement to function in environments that can vary on both short and long time scales. A key to understanding, controlling, and optimizing these materials is the ability to produce and study well-defined sensor materials with well-defined composition and morphology, with the flexibility to vary the composition easily without jeopardizing the structural uniformity. The development of new or improved materials for gas sensor applications requires a search for novel and innovative approaches to the nano-scale design of these materials. The use of the technology of surface modification by successive ionic layer deposition (SILD) method is such an innovative approach that will be discussed in this paper. INTRODUCTION The selection, synthesis, and optimization of front-end materials for gas sensors have traditionally relied on trial and error methods. Although in recent years, there has been increasing guidance provided by modeling of gas surface interactions, thanks to advances in methods such as density functional theory, empirical sensor screening methods are still widely used due to the inherent complexities of gas sensors. The primary front-end ingredient should be a material with high affinity and selectivity for the target gas molecule. In many cases, it is necessary to add structural promoters, stabilizers, and binders to maintain the mechanical and thermal stability of the sensor. The interactions between these ingredients and the morphological and surface compositional changes indu
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