Seedless Hydrothermal Growth of ZnO Nanorods as a Promising Route for Flexible Tactile Sensors

Abstract

Hydrothermal growth of ZnO nanorods has been widely used for the development of tactile sensors, with the aid of ZnO seed layers, favoring the growth of dense and vertically aligned nanorods. However, seed layers represent an additional fabrication step in the sensor design. In this study, a seedless hydrothermal growth of ZnO nanorods was carried out on Au-coated Si and polyimide substrates. The effects of both the Au morphology and the growth temperature on the characteristics of the nanorods were investigated, finding that smaller Au grains produced tilted rods, while larger grains provided vertical rods. Highly dense and high-aspect-ratio nanorods with hexagonal prismatic shape were obtained at 75 °C and 85 °C, while pyramid-like rods were grown when the temperature was set to 95 °C. Finite-element simulations demonstrated that prismatic rods produce higher voltage responses than the pyramid-shaped ones. A tactile sensor, with an active area of 1 cm2, was fabricated on flexible polyimide substrate and embedding the nanorods forest in a polydimethylsiloxane matrix as a separation layer between the bottom and the top Au electrodes. The prototype showed clear responses upon applied loads of 2–4 N and vibrations over frequencies in the range of 20–800 Hz.

Simulation study of ZnO nanorod geometry for the development of high-performance tactile sensors and energy harvesting devices

“…Often chemical growth process of ZnO NRs leads to the growth of pyramid-like hexagonal structures in which the lower end of the NR is much wider relative to the top end [28,29]. Hence simulations on pyramid-like hexagonal structures are carried out.…”

Sensitivity enhancement of the tactile sensor based on hydrothermally grown ZnO nanorods modified by catalytic Au nanoparticles

“…The ensemble information from these receptors is subsequently interpreted by the human brain as body positions, object sizes, shapes, texture, etc [2]. Flexible tactile sensors can mimic the sensing capabilities of human skin, and obtain the corresponding information from the external stimuli by interacting with the surrounding environment or objects [3,4]. In recent years, flexible tactile sensors have attracted tremendous attention due to their superior perception ability to human skin in spatial resolution, response time, detection limit, etc [5][6][7], and their significant importance in various applications such as intelligent prosthesis, touch panels, artificial skins, human-machine interfaces, and wearable medical devices.…”

Rhodamine B Doped ZnO Monodisperse Microcapsules: Droplet-Based Synthesis, Dynamics and Self-Organization of ZnO Nanoparticles and Dye Molecules

“…Various synthetic approaches using different chemical and physical methods [15], such as electro-deposition [16][17][18], sol-gel [19], and hydrothermal [14,20,21] have been employed to fabricate several types of ZnO nano-and microstructures including nanorods [16,22,23], nanowires [20,24], and micro- [14,21,25] and nano-spheres [26]. Nevertheless, the fabrication of well-defined micrometer-sized particles is still challenging.…”