Redox-Inactive CO₂ Determines Atmospheric Stability of Electrical Properties of ZnO Nanowire Devices through a Room-Temperature Surface Reaction

Abstract

Emerging interactive electronics for the Internet of Things era inherently require the long-term stability of semiconductor devices exposed to air. Nanostructured metal oxides are promising options for such atmospherically stable semiconductor devices owing to their inherent stability in air. Among various oxide nanostructures, ZnO nanowires have been the most intensively studied for electrical and optical device applications. Here, we demonstrate a strategy for achieving the atmospheric electrical stability of ZnO nanowire devices. Although the chemically active oxygen and water in air are strong candidates for affecting the electrical stability of nanoscale metal oxides, we found that the ppm-level redox-inactive CO2 in air critically determines the atmospheric electrical stability of hydrothermally grown single-crystalline ZnO nanowires. A series of analyses using atmosphere-controlled electrical characterization of single nanowire devices, Fourier transform infrared spectroscopy, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy consistently revealed that atmospheric CO2 reacts substantially with the ZnO nanowire surfaces, even at room temperature, to form an electrically insulative zinc carbonate thin layer. The formation of this layer essentially limits the atmospheric electrical stability of the ZnO nanowire devices. Based on this surface carbonation mechanism, we propose a strategy to suppress the detrimental surface reaction, which is based on (1) reducing the density of surface hydroxyl groups and (2) improving the nanowire crystallinity by thermal pretreatment. This approach improves the atmospheric electrical stability to at least 40 days in air.

Surface Dissociation Effect on Phosphonic Acid Self-Assembled Monolayer Formation on ZnO Nanowires

“…Then the ZnO nanowires were annealed for 1 h at 600 °C in atmospheric air to prevent surface degradation. 47 …”

“…After growth, the samples were rinsed with DI water and IPA. Then the ZnO nanowires were annealed for 1 h at 600 °C in atmospheric air to prevent surface degradation …”

“…Then the ZnO nanowires were annealed for 1 h at 600 °C in atmospheric air to prevent surface degradation. 47 Modification of Octadecylphosphonic Acid SAMs on ZnO Nanowires. Modification solutions (0.1 mM) were prepared by dissolving octadecylphosphonic acid (ODPA) in methanol or toluene.…”

Moderate molecular recognitions on ZnO m-plane and their selective capture/release of bio-related phosphoric acids

“…For example, thermal annealing treatment is effective for increasing the crystallization and improving the stability of ZnO nanowires. 70,71 Then, we compared the stabilities of the annealed nanowires (350 C, 1 h) and as-grown nanowires in phosphate buffer. The stability of the annealed nanowires was clearly improved and the morphology is maintained aer immersing into phosphate buffer for 5 hours, even though the as-grown nanowires gradually change their morphology and dissolve completely aer 5 hours (Fig.…”

Robust and Electrically Conductive ZnO Thin Films and Nanostructures: Their Applications in Thermally and Chemically Harsh Environments

“…The intrinsic stability of electronic materials under harsh conditions is difficult to secure in harsh electronics because conventional encapsulation packaging cannot be used in bio- and chemical sensors, which must be exposed to the surroundings. − The thermal stability of the electrical properties is one of the most important requirements for materials used in harsh electronics because chemical sensor, chemical industry, and aerospace applications are typically operated at temperatures exceeding 200 °C. − Wide bandgap semiconductors are suitable for electron devices operated at high temperatures because the intrinsic carrier density increases significantly with temperature in conventional narrow bandgap semiconductors (Si, III–V). Morphological changes such as crystallization and phase transition can cause the electrical degradation of electronic materials at high temperatures. , Furthermore, in open-top applications such as chemical sensors, chemical reactions with chemically active species in atmospheric air (e.g., O 2 , H 2 O, and CO 2 ) must be suppressed at high operating temperatures. − Chemical stability is another essential challenge for materials used in harsh electronics. Biosensors and photoelectrochemical devices (e.g., water splitting and CO 2 reduction) require stable electronic materials under a wide pH range from acidic to basic conditions. − …”