Conduction mechanisms in one dimensional core-shell nanostructures for gas sensing: A review

Metal oxide based core-shell (C-S) nanostructures have been studied for gas sensing applications to mitigate poor selectivity. When designing core-shell nanostructures with n-n, p-n and n-p junctions, an equalization of the Fermi level induces the formation of accumulation and depletion layers at the interface through charge, modifying the conduction channel. Mechanisms such as potential barrier carrier transport and surface depletion layer formation play important roles in enhancing the gas sensing performance of C-S nanostructures. Synthesis of C-S nanostructures is a multi-step process involving fabrication of core and shell layers. Selection of the core and the shell material is important as it would affect the properties of the heterojunction interface. Parameters such as the thickness of the shell layer, type of sensing material and working temperature have been studied for C-S nanostructure based gas sensors. However, less attention has been given to factors affecting the conduction mechanisms in C-S nanostructures. This review deals with understanding conduction mechanisms in one dimensional C-S nanostructures used for gas sensing applications, studying them based on synthesis methods used for fabrication and selection of materials used for core and shell layers.