Xiao Wei Sun, Jianxiong Wang, Lionel Vayssieres and Yi Yang

Who are you?

Figure Yi Yang
Figure Lionel Vayssieres
Figure Jianxiong Wang
Figure Xiao Wei Sun

Xiao Wei Sun: I am Xiao Wei Sun, a Chair Professor in the Department of Electrical and Electronic Engineering, South University of Science and Technology in Shenzhen, P. R. China. I am presently on leave from the School of Electrical and Electronic Engineering, Nanyang Technological University. Jianxiong Wang was my post-doc, and Yi Yang was my PhD student. H Huang and Y C Lee were from the group of my colleague Professor Ooi Kiang Tan at Nanyang Technological University. Dr Lionel Vayssieres was working at NIMS, Japan and he was visiting us as we completed this research.

Jianxiong Wang: I am currently a research Fellow in School of Electrical and Electronic Engineering, Nanyang Technological University.

Lionel Vayssieres: I am a one-thousand talent scholar Professor and co-director of the newly established International Research Center for Renewable Energy at Xi'an Jiaotong University, P.R. China.

Yi Yang: I am currently a research scientist at Data Storage Institute, Singapore, specializing in material characterization and failure analysis using analytical transmission electron microscope and focused ion beam.

What prompted you into this field of research?

Xiao Wei Sun: At that time, we were interested in the thin film form of ZnO and then we discovered Charles Lieber's work on semiconducting nanowires and Peidong Yang's work on ZnO nanowire lasing. So we started working on ZnO nanowires/nanorods for device applications. Gas sensors are one of the applications we explored. In fact, other areas include nanolaser, nano-LED, field emitter, biosensor, flexible dye-sensitized solar cell, electronic paper, etc.

Jianxiong Wang: At that time, the application of the ZnO nanostructure focused on the lasing, transistor and the field emission. We wanted to extend their application to other fields. Traditionally, metal oxide film is broadly used for sensing applications. We wanted to know whether we could replace the film with the ZnO nanorods. We then successfully utilized a modified hydrothermal method to produce vertical aligned ZnO nanorods in large area, which provided a good platform to realize our target.

Lionel Vayssieres: I initiated the concept of purpose-built nanomaterials by developing low cost syntheses of metal oxide dots and rods onto various substrates. At the time, vertically oriented iron-based nanorods showed the greatest performance for photovoltaics. However, vertically oriented ZnO nanorods have been the most successful according to citation counts. Indeed, I had developed the synthesis back in 2001 consisting of heating up below 100°C an equimolar aqueous solution of zinc nitrate and HMT in the presence of a substrate to create crystalline and oriented microrods and microtubes of controlled length and diameter.

Can you briefly describe what your paper reports and the impact that it has had on the field?

Xiao Wei Sun: The papers published in my group on various ZnO nanodevices have earned more than 4000 external citations. The ZnO gas sensor paper we reported here is just one example of quite a few highly cited papers. It is really amazing that we can make ZnO in nanowire form and greatly enhance its sensitivity, as was shown in this paper.

Jianxiong Wang: We studied the gas sensing properties of the vertical aligned ZnO nanorods films to different flammable and toxic gas. The paper provides an example of a constructed gas sensor with improved performance using vertical aligned ZnO nanorods.

Lionel Vayssieres: It was an idea of the NTU group led by Professor X W Sun to design a ZnO gas sensor based on my vertically oriented nanorods. While ZnO was already known as a gas sensor (mostly in pressed powder form), the strategy of using aqueous-grown oriented nanorods was completely new for such an application. The results showed unprecedented response and sensitivity at room temperature of this nanodevice while most ceramic-based sensors operate at elevated temperature (ca. 200-400°C). Room temperature operated sensors are of crucial importance for several sensitive applications as well as to reduce the overall cost of devices.

Can you detail what direction your research went following on from this article and, if applicable, how the results reported in this article helped to influence this?

Xiao Wei Sun: Following the gas sensor research, we further explored ZnO nanowires for biosensor applications. We are the first to report ZnO nanowire biosensors, which was considered the pioneering work in this field. Our papers on ZnO gas sensors and biosensors have also influenced a lot of others coming into the field.

Jianxiong Wang: Following this study, we also studied the sensing properties based on vertical aligned nanostructures with different shape and composition. We further applied the hydrothermally grown nanorods array to different fields, including biosensors, dye-sensitized solar cells, and electronic paper.

Lionel Vayssieres: The success of this paper triggered a real interest in combining the output of fundamental academic research and engineering in joint collaborative work to create functioning nanodevices. It also truly established the nanorod-based device concept. I kept on working on dimensional control of oxides looking at size effects on interfacial chemistry and electronic structure as well as generating more advanced ones such as quantum-confined oxide heteronanostructures to develop nanodevices for various energy related applications such as solar water splitting.

Co-author on the paper:

Figure
Ooi Kiang Tan