Structural, Topography, and Optical Properties of Ba‐Doped Mn₃O₄ Thin Films for Ammonia Gas Sensing Application

Abstract

The fabrication of reliable and cost‐effective gas sensor for low concentrations of toxic gases such as ammonia is still a challenging task, in this work the authors report structural, topography, and optical properties of pure and Ba‐doped Mn3O4 thin films prepared by chemical spray pyrolysis (CSP) as well as its gas sensing performance toward low concentrations of ammonia gas. XRD analyses prove the films have tetragonal spinel structure with a preferred orientation along the direction (103). AFM and SEM measurements show the films have homogeneous with rough surfaces and porous structures. EDS measurement confirms the presence of Mn, O, and Ba elements according to a doping concentration ratio. Optical measurements show the optical band gap redshifts and the bond length expands as Ba concentration increases. The optimal results are achieved in Mn3O4:Ba1% thin films where porous structure, rough surface, high crystallinity, and maximum response toward (20, 30, 40, and 50 ppm) of ammonia gas with great stability. Empirical equations are suggested to evaluate the sensitivity in terms of relative bond length and RMS roughness. These results show the films are good candidates in p‐type MOS gas sensors.

High Magnetic Coercivity in Nanostructured Mn3O4 Thin Films Obtained by Chemical Vapor Deposition

“…Such features were relatively similar to those previously reported for Mn 3 O 4 films obtained by PLD and chemical bath deposition . Conversely, spray-deposited Mn 3 O 4 films were composed by densely packed flakes or characterized by a poor morphology control . Mn 3 O 4 films obtained by SILAR, spray pyrolysis, soft templating with block copolymers, microwave calcination, or atomic layer deposition were characterized by the presence of interconnected nanosheets, by a granular morphology, ,,,,,,− or by interconnected spherical beads. , …”

“…52 Conversely, spraydeposited Mn 3 O 4 films were composed by densely packed flakes 13 or characterized by a poor morphology control. 19 Mn 3 O 4 films obtained by SILAR, spray pyrolysis, soft templating with block copolymers, microwave calcination, or atomic layer deposition were characterized by the presence of interconnected nanosheets, 49 by a granular morphology, 14,20,21,48,50,51,53−55 or by interconnected spherical beads. 56,57 An additional important insight into Mn 3 O 4 nanostructure was gained by TEM analyses on representative samples (Figures 2 and S3).…”

“…Nanostructured spinel oxides have been widely investigated over the last two decades for both fundamental studies and technological applications (such as energy, catalysis, biomedicine, sensing, and information storage) because of the large variety and tuneability of their chemico-physical properties. − Among the family members, α-Mn 3 O 4 ( haussmannite ), one of the most stable manganese oxides endowed with large natural abundance, cost-effectiveness, and environmental compatibility, − is an attractive multifunctional platform for various end-uses, including, among others, super/pseudo-capacitors, − electrodes for batteries, ,, gas sensors, − and heterogeneous catalysts. ,, Beside these applications, haussmannite has attracted attention because of its peculiar magnetic properties . In fact, bulk Mn 3 O 4 is magnetically ordered at 42 K to form a collinear ferrimagnetic array, , whereas at lower temperatures a canted spin array is produced. − Because the magnetic properties of nanomaterials are directly dependent on the aggregate size and shape, ,,, as well as on their structural features and the presence of defects, − nanostructured Mn 3 O 4 systems in the form of nanoparticles ,,,,− and nanorods/wires ,,,, fabricated by means of different synthesis techniques have been widely studied in recent years.…”

Conducting Polymer Based Ammonia and Hydrogen Sulfide Chemical Sensors and Their Suitability for Detecting Food Spoilage

“…There have been several promising NH 3 sensors reported based on inorganic and organic materials. [73][74][75][76][77][78] There are good room temperature Cu based NH 3 sensors where Mahnaz et al presented a sensor with responses of 11% at 50 ppm of NH 3 and 36.46% at 6 ppm of NO 2 . [79] Faegheh et al presented a sensor with responses of 4.34% at 99 ppm of NH 3 and 7.3% at 6 ppm of NO 2 .…”

“…[74,76] It has been reported that a 1% Ba doped Mn 3 O 4 thin film ammonia sensor shows a linear response from 20 to 50 ppm with high sensitivity at an optimum operating temperature of 400 °C. [76] Mn 3 O 4 functionalized with Fe 2 O 3 and ZnO sensors demonstrated detection limits of 2.3 and 2.0 ppm, respectively at an optimum operating temperature of 300 °C. [74] Indeed, this is one of the significant drawbacks of using metal oxide sensors for gas sensing that they need to be operated at high temperature to ensure good sensitivity.…”