Oxidation reactions on semiconducting metal oxide (SMOs) surfaces have been extensively worked on in catalysis, fuel cells, and sensors. SMOs engage powerfully in energy-related applications such as batteries, supercapacitors, solid oxide fuel cells (SOFCs), and sensors. A deep understanding of SMO surface and oxygen interactions and defect engineering has become significant because all of the above-mentioned applications are based on the adsorption/absorption and consumption/transportation of adsorbed (physisorbed-chemisorbed) oxygen. More understanding of adsorbed oxygen and oxygen vacancies (${\mathrm{V}}_{\mathrm{O}}^{•},{\mathrm{V}}_{\mathrm{O}}^{••}$) is needed, as the former is the vital requirement for sensing chemical reactions, while the latter facilitates the replenishment of adsorbed oxygen ions on the surface. We determined the relation between sensor response (sensitivity) and the amounts of adsorbed oxygen ions (${\mathrm{O}}_{2\left(\mathrm{ads}\right)}^{-},{ \mathrm{O}}_{\left(\mathrm{ads}\right), }^{-}{\mathrm{O}}_{2\left(\mathrm{ads}\right)}^{2-},{ \mathrm{O}}_{\left(\mathrm{ads}\right)}^{2-}$), water/hydroxide groups (H₂O/${\mathrm{OH}}^{-}$), oxygen vacancies (${\mathrm{V}}_{\mathrm{O}}^{•},{ \mathrm{V}}_{\mathrm{O}}^{••}$), and ordinary lattice oxygen ions (${\mathrm{O}}_{\mathrm{lattice}}^{2-}$) as a function of temperature. During hydrogen (H₂) testing, the different oxidation states (W⁶⁺, W⁵⁺, and W⁴⁺) of WO₃ were quantified and correlated with oxygen vacancy formation (${\mathrm{V}}_{\mathrm{O}}^{•},{ \mathrm{V}}_{\mathrm{O}}^{••}$). We used a combined application of XPS, UPS, XPEEM-LEEM, and chemical, electrical, and sensory analysis for H₂ sensing. The sensor response was extraordinarily high: 424 against H₂ at a temperature of 250 °C was recorded and explained on the basis of defect engineering, including oxygen vacancies and chemisorbed oxygen ions and surface stoichiometry of WO₃. We established a correlation between the H₂ sensing mechanism of WO₃, sensor signal magnitude, the amount of adsorbed oxygen ions, and sensor testing temperature. This paper also provides a review of the detection, quantification, and identification of different adsorbed oxygen species. The different surface and bulk-sensitive characterization techniques relevant to analyzing the SMOs-based sensor are tabulated, providing the sensor designer with the chemical, physical, and electronic information extracted from each technique.

The most promising and utilized chemical sensing materials, WO₃ and SnO₂ were characterized by means advanced synchrotron based XPS, UPS, NAP-XPS techniques. The complementary electrical resistance and sensor testing experiments were also completed. A comparison and evaluation of some of the prominent and newly employed spectroscopic characterization techniques for chemical sensors were provided. The chemical nature and oxidation state of the WO₃ and SnO₂ thin films were explored at different depths from imminent surface to a maximum of 1.5 nm depth from the surface with non-destructive depth profiling. The adsorption and amount of chemisorbed oxygen species were precisely analyzed and quantified as a function of temperature between 25–400 °C under realistic operating conditions for chemical sensors employing 1–5 mbar pressures of oxygen (O₂) and carbon monoxide (CO). The effect of realistic CO and O₂ gas pressures on adsorbed water (H₂O), OH⁻ groups and chemisorbed oxygen species ( $O_{2\left(ads\right)}^{-}, O_{\left(ads\right), }^{-}{O}_{2\left(ads\right)}^{2-}$ ) and chemical stability of metal oxide surfaces were evaluated and quantified.

The intrinsic properties of semiconducting oxides having nanostructured morphology are highly appealing for gas sensing. In this study, the fabrication of nanostructured WO₃ thin films with promising surface characteristics for hydrogen (H₂) gas sensing applications is accomplished. This is enabled by developing a chemical vapor deposition (CVD) process employing a new and volatile tungsten precursor bis(diisopropylamido)‐bis(tert‐butylimido)‐tungsten(VI), [W(N^tBu)₂(NⁱPr₂)₂]. The as‐grown nanostructured WO₃ layers are thoroughly analyzed. Particular attention is paid to stoichiometry, surface characteristics, and morphology, all of which strongly influence the gas‐sensing potential of WO₃. Synchrotron‐based ultraviolet photoelectron spectroscopy (UPS), X‐ray photoelectron spectroscopy (XPS), X‐ray photoelectron emission microscopy (XPEEM), low‐energy electron microscopy (LEEM) and 4‐point van der Pauw (vdP) technique made it possible to analyze the surface chemistry and structural uniformity with a spatially resolved insight into the chemical, electronic and electrical properties. The WO₃ layer is employed as a hydrogen (H₂) sensor within interdigitated mini‐mobile sensor architecture capable of working using a standard computer's 5 V 1‐wirebus connection. The sensor shows remarkable sensitivity toward H₂. The high, robust, and repeatable sensor response (S) is attributed to the homogenous distribution of the W⁵⁺ oxidation state and associated oxygen vacancies, as shown by synchrotron‐based UPS, XPS, and XPEEM analysis.

The identification of bis‐3‐( N,N ‐dimethylamino)propyl zinc ([Zn(DMP) ₂ ], BDMPZ) as a safe and potential alternative to the highly pyrophoric diethyl zinc (DEZ) as atomic layer deposition (ALD) precursor for ZnO thin films is reported. Owing to the intramolecular stabilization, BDMPZ is a thermally stable, volatile, nonpyrophoric solid compound, however, it possesses a high reactivity due to the presence of Zn‐C and Zn‐N bonds in this complex. Employing this precursor, a new oxygen plasma enhanced (PE)ALD process in the deposition temperature range of 60 and 160 °C is developed. The resulting ZnO thin films are uniform, smooth, stoichiometric, and highly transparent. The deposition on polyethylene terephthalate (PET) at 60 °C results in dense and compact ZnO layers for a thickness as low as 7.5 nm with encouraging oxygen transmission rates (OTR) compared to the bare PET substrates. As a representative application of the ZnO layers, the gas sensing properties are investigated. A high response toward NO ₂ is observed without cross‐sensitivities against NH ₃ and CO. Thus, the new PEALD process employing BDMPZ has the potential to be a safe substitute to the commonly used DEZ processes.

Oxidation reactions on semiconducting metal oxides (SMOs) surfaces have been extensively worked on in catalysis, fuel cells, and sensors. SMOs engaged powerfully in energy-related applications such as batteries, supercapacitors, solid oxide fuel cells (SOFCs), and chemical gas sensors. The deep understanding of SMO surface and oxygen interactions and defect engineering has become significant because all those mentioned applications are based on the adsorption/absorption and consumption/transportation of adsorbed (physisorbed-chemisorbed) oxygen. More understanding of adsorbed oxygen and oxygen vacancies (〖V_O^•,V〗_O^(••)) is needed, as the former is the vital requirement for sensing chemical reactions, while the latter facilitates the replenishment of adsorbed oxygen ions on the surface. We determined the relation between sensor response (sensitivity) and the amounts of adsorbed oxygen ions (O_(2(ads))^-,O_((ads),)^- O_2(ads)^(2-),O_((ads))^(2-)), water/hydroxide groups (H2O/OH^-), oxygen vacancies (〖V_O^•,V〗_O^(••)), and ordinary lattice oxygen ions (O_lattice^(2-)) as a function of temperature. During hydrogen (H2) testing, the different oxidation states (W6+, W5+, and W4+) of WO3 were quantified and correlated with oxygen vacancy formation (〖V_O^•,V〗_O^(••)). We used a combined application of XPS, UPS, XPEEM-LEEM, and chemical, electrical and sensory analysis for H2 sensing. We established a correlation between the H2 sensing mechanism of WO3, sensor signal magnitude, the amount of adsorbed oxygen ions, and sensor testing temperature. This paper also provides a review of the detection, quantification, and identification of different adsorbed oxygen species. The different surface and bulk-sensitive characterization techniques relevant to analyzing the SMOs-based sensor are tabulated, providing the sensor designer with the chemical, physical, and electronic information extracted from each technique.

Crystalline MoS ₂ thin films are deposited via MOCVD using a new molybdenum precursor, 1,4-di- tert -butyl-1,4-diazabutadienyl-bis( tert -butylimido)molybdenum( vi ) [Mo(N ^t Bu) ₂ ( ^t Bu ₂ DAD)], and elemental sulfur.