Growth and low-concentration gas monitoring with highly reproducible ultra-thin (<80 nm) SnO2 multiple nano structured layers.

Exploring the morphogical and structural properties along with gas sensing applications both pure and Ti-doped SnO2 ultra-thin films, were meticulously crafted on micromachined silicon substrate heater devices using a combination of classical soft chemical processes and hydrothermal techniques (SCPHTP). The fabrication process involved a two-step approach: initially, a 20nm layer of tin oxide was hydrothermally deposited onto the substrates, followed by annealing in wet air at 600∘C for 5h using a standardized temperature variation protocol. Subsequently, secondary layers with thicknesses of 20, 40 and 60nm were sequentially deposited onto the tin dioxide devices and oxidized in wet air at 550∘C and 600∘C for 20h each, using the same temperature modulation scheme. Throughout this process, the hydrothermal deposition temperature remained constant at 180∘C for both the initial and secondary layers of tin dioxide deposition. Additionally, Ti layers with thicknesses of 4 and 8nm were deposited onto the 20nm + 40nm system, subjected to annealing at 550∘C for 20h, followed by 1-min annealing in dry O2 at 700∘C and 800∘C, respectively, using a Rapid Thermal Annealing (RTA) system. Characterization of the crystalline and surface structures of the devices revealed a transformation of the soft chemical tin dioxide solution into the cassiterite structure of SnO2, resulting in uniform large surface areas for the sensor devices. Moreover, Ti metal layers of 4 and 8nm thicknesses were fully converted into TiO2 on the surface of the devices. Subsequent testing showcased higher current values in sandwich systems of 20nm + 60nm and 20nm + 40nm compared to the 20nm + 20nm configuration. Sensitivity and stability assessments for various volatile organic compounds (VOCs) and CO gases at a constant DC temperature of 400∘C indicated excellent performance, with sensitivity to CO gas being contingent on relative humidity (RH). Notably, RTA-annealed and Ti-8 nm-doped sensor devices exhibited superior sensitivity and reproducibility, particularly when treated at 800∘C in dry O2 for 1min. This heightened performance can be attributed to the occupation of chloride ions in the oxygen sites of the as-synthesized SnO2, resulting in enhanced sensing capabilities for VOC gases. [ABSTRACT FROM AUTHOR]