Improving the CO and CH4 Gas Sensor Response at Room Temperature of α-Fe2O3(0001) Epitaxial Thin Films Grown on SrTiO3(111) Incorporating Au(111) Islands

In this work, the functional character of complex alpha-Fe2O3(0001)/SrTiO3(111) and Au(111) islands/alpha-Fe2O3(0001)/SrTiO3(111) heterostructures has been proven as gas sensors at room temperature. Epitaxial Au islands and alpha-Fe2O3 thin film are grown by pulsed laser deposition on SrTiO3(111) substrates. Intrinsic parameters such as the composition, particle size and epitaxial character are investigated for their influence on the gas sensing response. Both Au and alpha-Fe2O3 layer show an island-type growth with an average particle size of 40 and 62 nm, respectively. The epitaxial and incommensurate growth is evidenced, confirming a rotation of 30 degrees between the in-plane crystallographic axes of alpha-Fe2O3(0001) structure and those of SrTiO3(111) substrate and between the in-plane crystallographic axes of Au(111) and those of alpha-Fe2O3(0001) structure. alpha-Fe2O3 is the only phase of iron oxide identified before and after its functionalization with Au nanoparticles. In addition, its structural characteristics are also preserved after Au deposition, with minor changes at short-range order. Conductance measurements of Au(111)/alpha-Fe2O3(0001)/SrTiO3(111) system show that the incorporation of epitaxial Au islands on top of the alpha-Fe2O3(0001) layer induces an enhancement of the gas-sensing activity of around 25% under CO and 35% under CH4 gas exposure, in comparison to a bare alpha-Fe2O3(0001) layer grown on SrTiO3(111) substrates. In addition, the response of the heterostructures to CO gas exposure is around 5-10% higher than to CH4 gas in each case.

Automated summary

This work demonstrates the functional character of complex alpha-Fe2O3(0001)/SrTiO3(111) and Au(111) islands/alpha-Fe2O3(0001)/SrTiO3(111) heterostructures as gas sensors at room temperature. The epitaxial growth of Au islands and alpha-Fe2O3 thin film on SrTiO3(111) substrates is investigated for their gas-sensing response. The incorporation of epitaxial Au islands on top of the alpha-Fe2O3(0001) layer enhances gas-sensing activity under CO and CH4 gas exposure, with the response to CO gas being higher than to CH4 gas.