• PDF / 1,362,107 Bytes
• 7 Pages / 612 x 792 pts (letter) Page_size
• 64 Downloads / 291 Views

DOWNLOAD

REPORT

---

0951-E08-03

Gas Sensor Based on the Network of SnO2 Semiconducting Nanowires Young-Jin Choi1, In-Sung Hwang1, Kyoung-Jin Choi1, Jae-Hwan Park2, and Jae-Gwan Park1 1

Materials Science and Technology Division, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, 130-650, Korea, Republic of 2

Department of Electronic Engineering, Chungju National University, Chungju, 380-702, Korea, Republic of ABSTRACT A simple and efficient way of preparing highly sensitive SnO2 nanowire-based gas sensors without an arduous lithography process was studied. The network of SnO2 nanowires could be suspended upon the Si substrate by separating the Au catalyst layer from the substrate. As the electric current is transported along the networks of the nanowires, not along the bottom layer on the substrate, the sensitivity to gases was maximized in the suspended and networked structures. The sensitivities were 18 and 180 when the NO2 concentrations were 0.5 and 5 ppm. The response time was typically 20-50 s.

INTRODUCTION SnO2, an n-type semiconductor with a large band gap (Eg = 3.6 eV at 300K) have been studied for applications such as transparent conducting electrodes [1], varistors [2], gas sensors [3], and lithium ion batteries [4]. Particularly, SnO2 exhibits considerably selective sensitivities to the detection of CO and NOx gases, and therefore, numerous studies on SnO2-based gas sensors were conducted. The types of the SnO2 gas sensors used were typically thick films or porous bulk materials. Meanwhile, recently, one-dimensional semiconducting nanomaterials have attracted considerable interest for their potential as the building blocks for fabricating various nanodevices [5,6]. Among them, the SnO2 nanostructures including nanowires, nanorods, nanobelts, and nanotubes were synthesized and their electrochemical properties were evaluated [7-10]. As the nanowires could exhibit better crystallinity and electrical properties combined with much higher specific surface areas when compared to thick-films or bulk materials, SnO2 nanowire-based gas sensors demonstrated far better gas sensing properties. In the SnO2 nanowire or nanobelt gas sensors, almost all of the adsorbed species are active in producing a

surface depletion region along the longitudinal direction. The size of the depletion layer in SnO2 under typical ionosorption is ca. 50~100 nm [11,12]. Therefore, nanowires or nanobelts are largely depleted of carriers. SnO2 nanostructured gas sensors could detect 3 ppm NO2 at room temperature [13], and in one study [14], the sensing limit of 0.5 ppm NO2 was achieved. Although semiconducting nanowires have received considerable attention to date, their commercialization and mass production is still questionable especially due to the difficulties in the alignment and assembly of the building blocks. Individual e-beam or photolithographic processes for each nanowires are quite unacceptable in terms of mass production of devices. Though exhibiting fascinating gas sensing characteristics, SnO2 nanowires and nanobel