The Role of ALD-ZnO Seed Layers in the Growth of ZnO Nanorods for Hydrogen Sensing

Abstract

Hydrogen is one of the most important clean energy sources of the future. Because of its flammability, explosiveness, and flammability, it is important to develop a highly sensitive hydrogen sensor. Among many gas sensing materials, zinc oxide has excellent sensing properties and is therefore attracting attention. Effectively reducing the resistance of sensing materials and increasing the surface area of materials is an important issue to increase the sensitivity of gas sensing. Zinc oxide seed layers were prepared by atomic layer deposition (ALD) to facilitate the subsequent hydrothermal growth of ZnO nanorods. The nanorods are used as highly sensitive materials for sensing hydrogen due to their inherent properties as oxide semiconductors and their very high surface areas. The low resistance value of ALD-ZnO helps to transport electrons when sensing hydrogen gas and improves the sensitivity of hydrogen sensors. The large surface area of ZnO nanorods also provides lots of sites of gas adsorption which also increases the sensitivity of the hydrogen sensor. Our experimental results show that perfect crystallinity helped to reduce the electrical resistance of ALD-ZnO films. High areal nucleation density and sufficient inter-rod space were determining factors for efficient hydrogen sensing. The sensitivity increased with increasing hydrogen temperature, from 1.03 at 225 °C, to 1.32 at 380 °C after sensing 100 s in 10,000 ppm of hydrogen. We discuss in detail the properties of electrical conductivity, point defects, and crystal quality of ALD-ZnO films and their probable effects on the sensitivity of hydrogen sensing.

Atomic Layer Deposition of ZnO for Modulation of Electrical Properties in n-GaN Schottky Contacts

“…25 Lu et al observed lower GPC values for higher Ar flow rates during the purge. 26 Based on these results, we suspect that partial loss of surface hydroxyl groups would occur more significantly during long H 2 O purges, resulting in the lower GPC value. The thickness of the ZnO films was determined by using an FS-1 multiwavelength ellipsometer.…”

Recent Advances in Zinc Oxide Nanostructures with Antimicrobial Activities

“…As it is known, atomic layer deposition (ALD) and chemical vapor deposition (CVD) are widely used for a large-scale production of thin films for electronic and optoelectronic device applications. In particular, ALD has been employed for forming a large range of metal oxide films including ZnO [198][199][200]. In the process, chemical precursor reactants (e.g., diethylzinc and water vapor) are alternatively introduced into the growth chamber, and react sequentially on desired substrate surfaces to form nano-ZnO films of uniform and reproducible thickness, even at low deposition temperatures of 25-300 • C [199,200].…”

“…In particular, ALD has been employed for forming a large range of metal oxide films including ZnO [198][199][200]. In the process, chemical precursor reactants (e.g., diethylzinc and water vapor) are alternatively introduced into the growth chamber, and react sequentially on desired substrate surfaces to form nano-ZnO films of uniform and reproducible thickness, even at low deposition temperatures of 25-300 • C [199,200]. Recently, 1D-ZnO nanostructures have received considerable attention because of their potential applications in advanced optoelectronic devices.…”

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphologies

“…In optoelectronics, various ZnO nanostructures are used for producing e.g., refractive index sensors [ 123 ], surface-enhanced Raman scattering (SERS) sensors [ 124 ], lasers, UV detectors, and UV diodes [ 74 , 125 , 126 , 127 , 128 ]. ZnO nanostructures may serve for producing sensors of gases [ 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 , 151 , 152 ] such as steam (humidity, H 2 O) [ 133 ], ammonia (NH 3 ) [ 129 , 130 , 131 , 143 ], nitrogen (N 2 ) [ 131 ], nitrogen monoxide (NO) [ 129 , 130 , 139 ], nitrogen dioxide (NO 2 ) [ 129 , 131 , 134 , 135 , 136 ,…”