High Performance MEMS of Pt Single Atoms Loaded on ALD ZnO Layer
Authors: Xu Jiaqiang , Hu Qingmin , Ma Zhiheng , Li Gaojie , Fan Yu 
Published: May 2020

Introduction
Single atom catalysts have draw increasing attention of enormous researchers due to its atomically disperation on supports, high efficiency and high catalytic performance. Despite those obvious advantages, there is still rare study about the single atom catalyst’s application in sensors. It was firstly reported the palladium single atoms on TiO2 used as a photocatalytic sensing platform to analyzed organophosphorus pesticide chlorpyrifos[1]. Catalyst-based sensing platform opens up a new pathway for exploring novel strategy of design sensors.
Micro-electro-mechanical system (MEMS) process have advantages such as, miniaturization, small size, mechanical parts high resonance frequency, and low power consumption. However, the MEMS prepared by traditional method possess poor stability. Here, we employed the atomic layer deposition to prepare ZnO layer on MEMS.
Atomic layer deposition (ALD) is a powerful technique for depositing nanoparticles or thin films and has outstanding advantages, including precise control of size and thickness and excellent uniformity[2], except that the substrate is exposed separately to each gaseous precursor and that the deposition is broken into cycles[3]. ALD functionalized method could gain high performance in thermal stability, mechanical and catalytic performance[4]. It was interesting to obtain single atom MEMS sensors via ALD.

Method

Prior to ALD, MEMS (Shanghai lingpan Electronic Technology Co., Ltd) were put into ethanol and cleaned by ultrasonic agitation for ten minutes. MEMS were put on quartz wafers and dried in air. ZnO films were deposited onto the MEMS by a hot-wall, closed-chamber ALD reactor. N2 (99.999%) was used as carrier gas. The precursors of ZnO were diethyl zinc and water (H2O). Water acts as an oxidant and enables growth over a wide temperature range. The deposition temperature was 150 °C, and the diethyl zinc was kept at room temperature. After the deposition of ZnO layers, Pt single atoms ALD was subsequently deposited with (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O3 as precursors at the same temperature as our precious work[2]. Ultimately, the MEMS sensors were tested.

Results and Conclusions

Fig.1 Response performance for ALD SnO2 layer on MEMS
It can be seen from the Fig.1 that sensor response increased with the concentration increase gradually. With the concentration increase for about 1 PPM, response value of sensors gradually reduced. It could also be seen that ALD ZnO sensor have a response time of 90 s and recovery time of 120 s. Baseline with drift less than 4 also demonstrated its good stability. It has little increase in response performance as the concentration increased to 80 PPM, it could be caused by the surface electron transfer arrived balance within high concentrations

References

[1] X. Ge, P. Zhou, Q. Zhang, Z. Xia, S. Chen, P. Gao, Z. Zhang, L. Gu, S. Guo, Palladium single atoms on TiO2 as a photocatalytic sensing platform for analyzing organophosphorus pesticide chlorpyrifos, Angew Chem Int Ed Engl, (2019).
[2] Q. Hu, S. Wang, Z. Gao, Y. Li, Q. Zhang, Q. Xiang, Y. Qin, The precise decoration of Pt nanoparticles with Fe oxide by atomic layer deposition for the selective hydrogenation of cinnamaldehyde, Applied Catalysis B: Environmental, 218 (2017) 591-599.
[3] Z. Gao, Y. Qin, Design and Properties of Confined Nanocatalysts by Atomic Layer Deposition, Acc Chem Res, 50 (2017) 2309-2316.
[4] M.M. Biener, J. Biener, A. Wichmann, A. Wittstock, T.F. Baumann, M. Baumer, A.V. Hamza, ALD functionalized nanoporous gold: thermal stability, mechanical properties, and catalytic activity, Nano Lett, 11 (2011) 3085-3090.

Figure 1