Enhancement of the Sensing Performance of Devices based on Multistimuli-Responsive Hybrid Materials.

Capturing environmental stimuli is an essential aspect of electronic skin applications in robotics and prosthetics. Sensors made of temperature- and humidity-responsive hydrogel and piezoelectric zinc oxide (ZnO) core-shell nanorods have shown the necessary sensitivity. This is achieved by using highly conformal and substrate independent deposition methods for the ZnO and the hydrogel, i.e., plasma enhanced atomic layer deposition (PEALD) and initiated chemical vapor deposition (iCVD). In this work, we demonstrate that the use of a multichamber reactor enables performing PEALD and iCVD, sequentially, without breaking the vacuum. The sequential deposition of uniform as well as conformal thin films responsive to force, temperature, and humidity improved the deposition time and quality significantly. Proper interlayer adhesion could be achieved via in situ interface activation, a procedure easily realizable in this unique multichamber reactor. Beyond the fabrication method, also the mechanical properties of the template used to embed the core-shell nanorods and the cross-linker density in the hydrogel were optimized following the results of finite element models. Finally, galvanostatic electrochemical impedance spectroscopy measurements showed how temperature and humidity stimuli have different effects on the device impedance and phase, and these differences can be the basis for stimuli recognition.

Tuning the Porosity of Piezoelectric Zinc Oxide Thin Films Obtained from Molecular Layer-Deposited "Zincones".

Porous zinc oxide (ZnO) thin films were synthesized via the calcination of molecular layer-deposited (MLD) "zincone" layers. The effect of the MLD process temperature (110 °C, 125 °C) and of the calcination temperature (340 °C, 400 °C, 500 °C) on the chemical, morphological, and crystallographic properties of the resulting ZnO was thoroughly investigated. Spectroscopic ellipsometry reveals that the thickness of the calcinated layers depends on the MLD temperature, resulting in 38-43% and 52-56% of remaining thickness for the 110 °C and 125 °C samples, respectively. Ellipsometric porosimetry shows that the open porosity of the ZnO thin films depends on the calcination temperature as well as on the MLD process temperature. The maximum open porosity of ZnO derived from zincone deposited at 110 °C ranges from 14.5% to 24%, rising with increasing calcination temperature. Compared with the 110 °C samples, the ZnO obtained from 125 °C zincone yields a higher porosity for low calcination temperatures, namely 18% for calcination at 340 °C; and up to 24% for calcination at 500 °C. Additionally, the porous ZnO thin films were subjected to piezoelectric measurements. The piezoelectric coefficient, d33, was determined to be 2.8 pC/N, demonstrating the potential of the porous ZnO as an, e.g., piezoelectric sensor or energy harvester.