Session: 13-01-01: Design and Fabrication, Analysis, Processes, and Technology for Micro and Nano Devices and Systems

Paper Number: 95307

95307 - Improvement of the Sensitivity and Selectivity of Gas Molecules of Graphene-Base Gas Sensor With Carbon Nanotubes Under the Application of Strain 

In recent years, it has become essential to develop various environmental and health monitoring technologies for the future society with decreasing birthrate and aging population. Since human breath usually consists of about 870 different kinds of gas molecules with concentration ranging from 1 to 5000 parts per billion, some gas molecules are indicators of various diseases such as lung cancer, asthma and so on. The development of multifunctional next-generation gas sensors that are compact and can detect multiple gas molecules is, therefore, strongly demanded for early detection of those diseases without doctors’ medical examination. A biochemical sensor using graphene nanoribbons as a sensing element was developed for a new generation highly-sensitive and compact multi-gas sensor. Graphene is a monolayer material with a six-membered ring structure of carbon, and it can adsorb various molecules on its surface. It was reported that its electrical resistance changed under the adsorption of gas molecules. Even though the resistance changes of graphene appeared by adsorption of various gases, it was impossible to identify the gas molecules individually when plural kinds of gas molecules adsorbed on graphene at the same time. No selectivity was confirmed so far. To realize the selectivity, the authors found that the application of strain to graphene varied the adsorption energy of gas molecules on graphene, and adsorption-desorption behavior was controlled by the application of appropriate strain.

In this study, to improve the sensitivity and selectivity of graphene-base gas sensor, carbon nanotubes (CNTs) were directly synthesized on graphene nanoribbons for increasing the molecular adsorption surface. The synthesis of graphene was carried out inside a low-pressure chemical vapor deposition chamber on a copper catalyst substrate with very high purity. The carbon resource gas was supplied by using acetylene (C₂H₂) while hydrogen (H₂) was used to control the concentration of acetylene, in other words, growth rate. C₂H₂ was supplied at a flow rate of 0.4 sccm together with H₂ gas at a flow rate of 320 sccm at 1000^oC and 0.1 Torr pressure for 10 minutes. The synthesized graphene was transferred to a silicon substrate. A dumbbell-shape graphene nanoribbon (DS-GNR) structure was then, fabricated on this transferred graphene on a Si/SiO₂ substrate by using an electron beam lithography. A thermochemical vapor deposition method was also applied to the production of a CNT layer directly on the GNR sensor elements. Fine catalysts were grown on the GNR by using Fe and Al₂O₃. After the deposition of 5-nm-thick iron catalyst the DS-GNR by electron beam deposition, 3-nm-thick alumina catalyst was deposited on it. Then, annealing at 750°C for 3 minutes in an atmosphere of 125 sccm N₂ flow and 100 sccm H₂ flow made dense granules of iron catalyst. Next, 1-mm-long CNTs were successfully synthesized on the fine catalysts at 750°C for 10 min in acetylene atmosphere. The stable ohmic contact between the synthesized CNTs and the base graphene layer was confirmed.

The graphene-base gas sensor with a CNT layer showed drastic increase in the sensitivity of gas molecules comparing with a conventional single graphene-base sensor. This drastic increase was attributed to the increase in the adsorption surface area of the sensor devices. The reaction time of the sensor device was also improved significantly. These results clearly indicated the possibility of the development of a graphene-based multi-gas detecting sensor with high sensitivity and selectivity.

Presenting Author: Yuto Hirose Department of Finemechanics, Graduate School of Engineering, Tohoku University

Presenting Author Biography: Yuto Hirose is a student in the Department of Finemechanics at Tohoku University Graduate School. His research is related to the development of bio-chemical sensors using graphene. His hobby is traveling by motorcycle.

Authors:

Yuto Hirose Department of Finemechanics, Graduate School of Engineering, Tohoku University
Xiangyu Qiao Department of Finemechanics, Graduate School of Engineering, Tohoku University
Wangyang Fu School of Materials Science, Tsinghua University
Ken Suzuki Fracture and Reliability Research Institute, Graduate School of Engineering, Tohoku University
Hideo Miura Fracture and Reliability Research Institute, Graduate School of Engineering, Tohoku University