Schottky Diode Based on a Single Carbon–Nanotube–ZnO Hybrid Tetrapod for Selective Sensing Applications

• Published in: Advanced materials interfaces Vol. 4; no. 19
• Main Authors: Postica, Vasile, Schütt, Fabian, Adelung, Rainer, Lupan, Oleg
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 09-10-2017
• Subjects: ammonia; Carbon nanotubes; Charge transfer; Detection; Gas sensors; Gases; hydrogen sensors; Nanotubes; Operating temperature; Schottky diodes; Selectivity; single tetrapod; Zinc oxide
• ISSN: 2196-7350; 2196-7350
• DOI: 10.1002/admi.201700507

In this work, a general strategy to change the selectivity of individual ZnO tetrapod (ZnO‐T)‐Schottky diode‐based devices by hybridization with carbon nanotubes (CNT) is presented. A microscale Schottky diode based on Pt‐nanocontacts to a single ZnO‐T covered/hybridized with CNT, designated as ZnO‐T−CNT, is fabricated and the temperature‐dependent UV and gas sensing properties are investigated. The gas sensing investigations indicate that due to the presence of CNTs on the surface of the ZnO‐T a higher NH3 response (factor of ≈90) at room temperature is observed, compared to H2 gas response (≈14). This effect is attributed to the excellent charge transfer between the CNTs and ZnO‐T as well as NH3 molecule adsorption on the surface of the CNTs, which can efficiently reduce the Schottky barrier height. By increasing the operating temperature up to 150 °C (starting from 50 °C) the NH3 response is considerably reduced, leading to an excellent H2 gas selectivity. In the case of H2 gas, an increase in temperature up to 150 °C shows a considerably increase in gas response of about 140 (≈10 times). Thus, this device offers the possibility to be used for selective detection of NH3 and H2 by only changing the operating temperature. Furthermore, by using the developed strategy/approach other materials can be used for the fabrication of gas sensors with selectivity to other gases.
A change in selectivity from NH3 to H2 gas by changing the operating temperature of a Schottky diode based on individual ZnO tetrapods covered with carbon nanotubes is reported. Thus, at room temperature the device has a higher response to NH3, while by increasing the temperature up to 150 °C the response to NH3 is considerably decreased while the response to H2 gas is gradually increasing.