Indium oxide quasi-monodimensional low temperature gas sensor

https://doi.org/10.1016/j.snb.2006.04.023Get rights and content

Abstract

We have investigated the sensing properties of indium oxide nanostructures and tailored the deposition conditions in order to obtain nano-wires of indium oxide. We have comparatively tested the gas sensing properties of nano-wires with micrometric or even nanometric size. The micro-wires feature interesting gas sensitivity at room temperature, particularly in the case of nitrogen dioxide detection. The sensing performance is improved as the lateral dimension of the wire decreases.

Introduction

In the past few years, significant progress has been achieved in the synthesis, structural and physical characterization of nanostructures. Among existing materials, metal oxides are appealing due to their wide variability in electrical behavior, from metallic to semiconducting and even insulating.

A new generation of metal oxide semiconducting nanostructures, such as nano-wires and nano-belts, has recently attracted the interest of the research community, due to their potential applications in electronic, optical and sensor field. Because of their peculiar structural characteristics, the effects arising from size reduction result in novel physical properties for these materials, which are of great interest for both fundamental study and potential nanodevice applications. Newly developed metal oxide nano-belts and nano-rings [1] are potential candidates for fabrication of nanoscale devices. Their extraordinary sensing properties have been recently shown for ultra-sensitive gas [2] and DNA detection [3], [4].

In the field of chemical gas sensing, a huge effort was made worldwide to overcome the major drawbacks of metal oxide sensors, i.e. improving the well known “3S”: Sensitivity, Selectivity and Stability. In 1991 Yamazoe showed that reduction of crystallite size causes a huge improvement in sensor performance [5]. The basic problem is to prepare a sensing material with small crystallite size but stable when operated at high temperature for long periods.

An innovative approach to material synthesis consists in the preparation of stable single-crystal quasi-one-dimensional semiconducting oxides nanostructures (so called nano-belts, nano-wires or nano-ribbons) starting from evaporation of the metal oxide powders at high temperatures [6], [7].

The sensing mechanism of metal oxide gas sensors is the same as in thin or thick films, but their high degree of crystallinity assures stability and, at the same time, the nanosized lateral dimension foresees enhanced sensing properties. Furthermore number grain boundaries are less than in polycrystalline materials. The peculiar characteristics of nanowires make them to the building blocks of a third generation of metal oxide gas sensors.

Among the studies on one dimensional (1-D) nanostructures, several investigations have been devoted to tin, zinc and indium oxide nano-wires/nano-belts and different approaches to their synthesis have been developed [8], [9], [10], [11], [12], [13], [14]. Presently, growth from vapor phase seems to be the most promising one, due to its simplicity and low cost. Some works marked the difference between the basic vapor–solid (VS) and vapor–liquid–solid (VLS) processes. This latter mechanism may assist thermal evaporation; resulting in fast growth rates at temperatures below 1000 °C (crystal growth by thermal evaporation of SnO2 powders usually occurs at temperatures higher than 1300 °C).

In this work we focused our attention to preparation, morphological, structural and electrical characterization, with particular regard to gas sensing properties of indium oxide nanowires.

Section snippets

Experimental

The high evaporation temperature of indium oxides requires a tubular furnace with maximum heating temperatures higher than 1000 °C, together with alumina tube, and low vacuum pumping system. The experimental set-up was designed to allow a direct (from the source material to the substrates) or reversed (from the substrates to the source) flux of carrier gas. The direct flux was used during the deposition process while the reversed flux was used during the temperature transients in order to avoid

Results and discussion

The morphology and crystalline shape of the indium oxide structures turned out to depend on the deposition condition and particularly on the temperature, which the substrate was maintained at. By decreasing the temperature from 1100 to 800 °C, different crystalline structures were obtained, ranging from coarse and equiaxed grains to whisker like structures, nanowires and nano-belts. The SEM images in Fig. 1, Fig. 2 show the influence of substrate temperature on the shape of the crystalline

Conclusions

We have deposited indium oxide nanostructures by the vapor phase process and tailored the deposition conditions in order to obtain nanostructures with reduced dimensionality of In2O3 in the form of wires. We proposed the use of nano-wires of indium oxide for gas sensing and we proved their capability to detect of gases like CO and NO2 or ethanol vapors in the single and multiple wire configuration.

We have also focused our attention on the influence of the deposition conditions (pressure,

Acknowledgement

This work has been founded by the European Strep project “Nano-structured solid-state gas sensors with superior performance” (NANOS4) no.: 001528.

S. Bianchi has received the MS degree in electronic engineering at Brescia University in 2005 with a thesis entitled “Growth and characterization of innovative In2O3 nanostructures”. Since November 2005 he is PhD student at the Sensor Lab at the University of Brescia. He is studying the growth of nanowires of different MOX and their application.

References (14)

  • N. Yamazoe

    Sens. Actuators B, Chem.

    (1991)
  • Y. Chen et al.

    Chem. Phys. Lett.

    (2003)
  • X.Y. Kong et al.

    Science

    (2004)
  • E. Comini et al.

    Appl. Phys. Lett.

    (2002)
  • Jong-in Hahm et al.

    NanoLetters

    (2004)
  • Z. Li et al.

    NanoLetters

    (2004)
  • Z.W. Pan et al.

    Science

    (2001)
There are more references available in the full text version of this article.

Cited by (0)

S. Bianchi has received the MS degree in electronic engineering at Brescia University in 2005 with a thesis entitled “Growth and characterization of innovative In2O3 nanostructures”. Since November 2005 he is PhD student at the Sensor Lab at the University of Brescia. He is studying the growth of nanowires of different MOX and their application.

E. Comini was born on 21 November 1972 and she received her degree in physics at Pisa University in 1996. She is presently working on chemical sensors. She received her PhD in material science at the University of Brescia. She is now a assistant professor at the University of Brescia.

M. Ferroni received his PhD degree in physics at the University of Ferrara in 1998, and became researcher at the Department of Chemistry and Physics of the University of Brescia in 2004. His mean research activity concerns the characterization of nanostructured metal oxides by means of transmission and scanning electron microscopy. Presently, Matteo Ferroni is in charge of the high-resolution scanning electron microscopy facility at the SENSOR CNR-INFM regional laboratory in Brescia.

G. Faglia received an MS degree from the Polytechnic of Milan in 1991 with a thesis on gas sensors. In 1992, he has been appointed as a Researcher by the Thin Film Lab at the University of Brescia. He is involved in the study of the interactions between gases and semiconductor surfaces and in gas sensors electrical characterization. In 1996, he has received the PhD degree by discussing a thesis on semiconductor gas sensors. In 2000, he has been appointed associate professor in experimental physics at University of Brescia. During his career Guido Faglia has published more than 50 articles on International Journals with referee.

A. Vomiero received his degree in physics at the University of Padova in 1999, and his PhD in electronic engineering at the University of Trento in 2003. His main activities deal with the synthesis of thin films by the means of PVD techniques and the application of low energy nuclear techniques to materials science. Actually he has a non-permanent post PhD position at the CNR-INFM SENSOR Lab, Brescia.

G. Sberveglieri was born on 17 July 1947, and received his degree in physics from the University Parma, where, starting in 1971, his research activities on the preparation of semiconducting thin film solar cells was conducted. He has been appointed associate professor at the University of Brescia in 1987. In the following year, he established the Thin Film Laboratory afterwards called Gas Sensor Laboratory, which is mainly devoted to the preparation and characterization of thin film chemical sensors. He has been the director of the GSL since 1988. In 1994, he was appointed full professor in physics, first at the Faculty of Engineering of University of Ferrara and then in 1996, at the Faculty of Engineering of University of Brescia. He is a referee of the journals Thin Solid Films, Sensors and Actuators, Sensors and Materials, etc., and is a member of the Scientific Committee of Conferences on Sensor and Materials Science. During his 25 years of scientific activities, Giorgio Sberveglieri has published more than 140 papers on international reviews; he has presented more than 50 Oral Communications to international congresses and numerous oral communications to national congresses.

View full text