CVD Grown Tungsten Oxide for Low Temperature Hydrogen Sensing: Tuning Surface Characteristics via Materials Processing for Sensing Applications

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 19; no. 1; pp. e2204636 - n/a
• Main Authors: Wilken, Martin, Ciftyürek, Engin, Cwik, Stefan, Mai, Lukas, Mallick, Bert, Rogalla, Detlef, Schierbaum, Klaus, Devi, Anjana
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.01.2023
• Subjects: Chemical vapor deposition; Electrical properties; Emission microscopy; Gas sensors; Hydrogen; hydrogen sensing; Low temperature; Materials processing; metalorganic chemical vapor deposition (MOCVD); Microscopy; Morphology; Nanostructure; nanostructured layers; Nanotechnology; Oxidation; Photoelectrons; Sensors; Stoichiometry; surface characteristics; Surface properties; Synchrotrons; Thin films; Tungsten oxides; Valence; X ray photoelectron spectroscopy; hydrogen sensing; nanostructured layers; surface characteristics; metalorganic chemical vapor deposition (MOCVD); tungsten oxides
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202204636

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(NtBu)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 implementation of new volatile heteroleptic W‐complex [W(NtBu)2(NiPr2)2] as precursor in a chemical vapor deposition (CVD) process enabled the growth of highly pure and crystalline WO3. Advanced surface characterization demonstrates that WO3 thin film implementation in a custom‐built mobile sensor device shows outstanding sensing response at low temperature toward hydrogen.