Unusual Oxygen Partial Pressure Dependence of Electrical Transport of Single-Crystalline Metal Oxide Nanowires Grown by the Vapor–Liquid–Solid Process

Abstract

In general, the electrical conductivities of n-type semiconducting metal oxide nanostructures increase with the decrease in the oxygen partial pressure during crystal growth owing to the increased number of crystal imperfections including oxygen vacancies. In this paper, we report an unusual oxygen partial pressure dependence of the electrical conductivity of single-crystalline SnO 2 nanowires grown by a vapor−liquid−solid (VLS) process. The electrical conductivity of a single SnO 2 nanowire, measured using the four-probe method, substantially decreases by 2 orders of magnitude when the oxygen partial pressure for the crystal growth is reduced from 10 −3 to 10 −4 Pa. This contradicts the conventional trend of n-type SnO 2 semiconductors. Spatially resolved single-nanowire electrical transport measurements, microstructure analysis, plane-view electron energy-loss spectroscopy, and molecular dynamics simulations reveal that the observed unusual oxygen partial pressure dependence of the electrical transport is attributed to the intrinsic differences between the two crystal growth interfaces (LS and VS interfaces) in the critical nucleation of the crystal growth and impurity incorporation probability as a function of the oxygen partial pressure. The impurity incorporation probability at the LS interface is always lower than that at the VS interface, even under reduced oxygen partial pressures.

Face-selective tungstate ions drive zinc oxide nanowire growth direction and dopant incorporation

“…To confirm the hypothesis as to the face-selective dopant incorporation, we directly identify the dopant distribution in an individual ZnO nanowire. It should be described that the dopant distribution in hydrothermal ZnO nanowire has not been discussed before unlike that in VLS nanowire [16][17][18]25 . This might be due to that the impinging rate of impurity metal ions on each crystal plane of nanowire is equal in hydrothermal synthesis, but those on liquid-solid interface and vapor-solid interface in VLS synthesis are supposed to be different.…”

“…ydrothermal synthesis of inorganic nanomaterials [1][2][3][4] offers wide range of applications [5][6][7][8][9][10][11] due to the scalability and the compatibility with various substrates and material processes [12][13][14] originating from its low process temperature which is not available by vapor-phase synthesis [15][16][17][18] . The functions of inorganic nanomaterials strongly depend on their geometry.…”

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

“…Therefore, atmospheric electrical stability of ZnO nanowire devices is an essential subject for a long-term big data correction achieved by utilizing chemical sensors, UV detectors, force/pressure sensors, and energy-harvesting generators . ZnO nanostructures are relatively reactive to both acids and bases, and during their preservation in air, oxygen and water have been considered to have the most effect on their physical properties due to their chemical reactivity. − In addition, oxygen vacancies in the crystal, which react with oxygen and water in air, are widely recognized as electron donors in binary metal oxides such as ZnO, SnO 2 , and others; the formation/compensation of oxygen vacancies generates/eliminates mobile electrons. − Other species in air are relatively inactive or low in content and have been considered to interact with metal oxide surfaces only under more reactive conditions such as high temperatures. , Since the electrical properties of nanostructures are inherently affected by many factors, including their interfaces and surfaces, achieving the atmospheric electrical stability of single-crystalline ZnO nanowires remains a challenging issue for their device application to interactive electronics in air.…”