Detection of CO and O₂ Using Tin Oxide Nanowire Sensors

Abstract

na powder (P172SB, PØchiney) with a specific area of 10.2 m 2 g ±1 , a refractive index of 1.70, and a mean diameter of 0.5 lm. A dispersant (phosphoric ester) is also used to decrease the viscosity and to increase the stability of the suspension. The final mixture is prepared with 80 wt.-% (50 vol.-%) of alumina, dispersant (1.5 wt.-% with respect to alumina) and photoinitiator (5.56 wt.-% with respect to the monomer) mixed in a ball mill for 20 min at 350 rpm.The scraper is based on a 10 mm long scalpel. It is moved at a speed of 1.2 mm s ±1, which corresponds to a shear rate varying from 60 to 24 s ±1 , depending on the layer thickness (from 20 to 50 lm, respectively).The debinding step consists of several heating steps. First, the sample is heated to 120 C (degradation temperature of the polymer) at 60 C h ±1. A slower second temperature gradient of 6 C h ±1 is applied up to 500 C and the temperature is maintained for 30 min. The quick heating of the sintering step is applied by increasing the temperature at 900 C h ±1 to 1550 C. The object to be sintered is kept at this temperature for 5 h, and is then cooled to ambient temperature. Detection of CO and O 2 Using Tin Oxide Nanowire Sensors** By Andrei Kolmakov, Youxiang Zhang, Guosheng Cheng, and Martin Moskovits* Solid-state gas sensors play a major role in semiconductor processing, medical diagnosis, environmental sensing, personal safety, and national security, with economic impact in agriculture, medicine, and in the automotive and aerospace industries.[1±3] Most sensors operate on the basis of the modification of the electrical properties of an active element, normally a metal oxide film, brought about by the adsorption of an analyte on the surface of the sensor. A current major goal in gas sensing is massive parallelism, wherein many sensors, each with its unique chemical properties, are operated together and their outputs processed simultaneously, perhaps using learning strategies like neural networks, so that the overall device operates ªintelligentlyº, mimicking, for example, the complex operation of a mammalian nose and its corresponding brain function. [4] This task implies the need for further miniaturization of the active elements with the simultaneous sensitivity increase to compensate for surface area loss. Here, conventional thin film technology faces its fundamental limits. Promising strategies for achieving the above goal of using many sensing elements restricted to a small volume will likely come out of nanoscience and technology and, specifically, out of a subset of technologies amenable to parallelism and array fabrication that do not sacrifice sensitivity and selectivity. This challenge necessitates several design features to be achieved simultaneously, including the development of new materials, innovation in structure and architecture, and the development of highly sensitive, responsive, and selective, yet ultra-small active elements arranged so as to minimize inter-element cross-talk. [5,6] The high surface-to-volume ratio of nano...

Room temperature gas sensing properties of SnO2/multiwall-carbon-nanotube composite nanofibers

“…11 The complexity and cost of fabrication as well as power consumption may hinder their applications. Komalkov et al 7 reported the O 2 and CO sensing properties based on an individual SnO 2 nanowire and a detection limit of a few 100 ppm for CO in dry air at 300°C was measured. Ultraviolet illumination was used to improve the sensitivity at room temperature.…”

“…Upon exposure to reductive gas species such as CO, the arrested electrons are released by the reactions between the reductive gas and the negatively charged ions: CO + O − → CO 2 + e − , reducing the steady-state surface oxygen concentration and donating a few electrons back to the bulk resulting in an increased conductivity. 7 Of these negatively charged ions, O − appears on tin oxide surface at a high temperature of about 150°C. 8 Most tin oxide gas sensors are effective only at temperatures above 200°C.…”

“…7 Among these methods, electrospinning is relatively simple and cost effective to produce nanofibers from a wide variety of polymer solutions. Sb-doped SnO 2 nanofibers were prepared by electrospinning a solution containing poly͑vinyl pyrrolidone͒ ͑binder͒, tin and antimony ͑III͒ alkoxides, acetic acid and organic solvents.…”

Scattering attributes of one-dimensional semiconducting oxide nanomaterials individually probed for varying light-matter interaction angles

“…The insight gained from this study can advance our fundamental understanding of the optical behaviors of the technologically useful nanomaterials and, at the same time, promote the development of highly miniaturized, photonic and bio-optical devices utilizing the spatially controllable, optical responses of the individual semiconducting oxide NRs. [16][17][18][19][20][21][22][23][24] In many of these technologically important applications, the fundamental optical properties of 1D SO nanomaterials govern their functional outcomes. Light can produce various optical and optoelectronic responses from the materials and, therefore, light-matter interactions can be engineered to produce desirable optical properties such as spontaneous and stimulated emission, 1,25-29 waveguiding, 1-3 and evanescence field enhancement.…”

“…One-dimensional (1D) nanomaterials based on semiconducting oxides (SOs) have demonstrated their useful properties in numerous applications of photonics, 1-4 electronics, [5][6][7][8] optoelectronics, 9,10 photovoltaics, [11][12][13][14][15] and chemical/biological sensing. [16][17][18][19][20][21][22][23][24] In many of these technologically important applications, the fundamental optical properties of 1D SO nanomaterials govern their functional outcomes. Light can produce various optical and optoelectronic responses from the materials and, therefore, light-matter interactions can be engineered to produce desirable optical properties such as spontaneous and stimulated emission, 1,25-29 waveguiding, 1-3 and evanescence field enhancement.…”