Novel low-temperature growth of SnO 2 nanowires and their gas-sensing properties R. Rakesh Kumar, a,⇑ Mitesh Parmar, a,b K. Narasimha Rao, a K. Rajanna a and A.R. Phani c a Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India b School of Mechanical Systems Engineering, Chonnam National University, Gwangju 500-757, Republic of Korea c Nano-Research for Advanced Materials and Technologies, Bangalore 560040, India Received 26 September 2012; revised 5 November 2012; accepted 7 November 2012 Available online 12 November 2012 A simple thermal evaporation method is presented for the growth of crystalline SnO 2 nanowires at a low substrate temperature of 450 °C via an gold-assisted vapor–liquid–solid mechanism. The as-grown nanowires were characterized by scanning electron micros- copy, transmission electron microscopy and X-ray diffraction, and were also tested for methanol vapor sensing. Transmission elec- tron microscopy studies revealed the single-crystalline nature of the each nanowire. The fabricated sensor shows good response to methanol vapor at an operating temperature of 450 °C. Ó 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Physical vapor deposition (PVD); Semiconductors; SnO 2 nanowires; Transmission electron microscopy (TEM); Sensors In recent years, one-dimensional metal oxide nanostructures such as nanowires, nanotubes and nano- belts have attracted much attention due to their practical applications in various fields [1,2]. Nanowires of semi- conducting oxides such as ZnO [3], SnO 2 [4], In 2 O 3 [5] and TiO 2 [6] grown by different methods have been used in a variety of applications. Among them, SnO 2 nano- wires are particularly important because of their applica- tions in a number of fields such as Li-ion batteries [7], gas sensors [8], UV detectors [9], field emitters [10] and super- hydrophobic surfaces [11]. Therefore, it is important to grow SnO 2 nanostructures. Techniques for growing SnO 2 nanowires include pulse laser deposition [12], hydrothermal growth [13], thermal evaporation [7] and chemical vapor deposition [11]. The most commonly used method for producing SnO 2 nanowires is tube fur- nace type thermal evaporation due to the simplicity and low cost of this approach. The main drawbacks of this method are the high temperatures involved (>600 °C for SnO 2 ) and the lack of exact control of parameters such as length of the nanowires and the diffi- culty of aligning nanowires on the substrate [7,8,10]. To overcome the above drawbacks we have adopted the vapor–liquid–solid (VLS) mechanism using gold as a cat- alyst in combination with thermal evaporation (not in a tube furnace) to avoid high temperature on the substrate side (Supporting information S1). The evaporation source is located 20 cm below the substrate holder in such a way that the substrates were at room temperature even though the evaporation boat was at a higher tem- perature. This method enabled better control over the deposition parameters such as substrate temperature and deposition rate (length of the nanowires). In this work, we report a low-temperature process for SnO 2 nanowire growth by thermal evaporation, as well as their methanol sensing properties. The experimental set-up consists of a thermal evapo- ration arrangement for the evaporation of tin by passing a current through evaporation boat and also has the facility to allow O 2 gas through a flow meter (Support- ing information S1). Initially, we have taken Si as well as SiO 2 (300 nm) grown on Si substrates (1 cm  1 cm). The substrates were first cleaned with acetone by ultra- sonication, followed by methanol, then DI water, and fi- nally dried in a N 2 stream. The cleaned substrates were immediately transferred to a sputter coater to deposit Au film 3 nm thick. Immediately after Au deposition, substrates were loaded into the deposition chamber. The deposition chamber was evacuated by a combination of a diffusion pump and a rotary pump with a liquid 1359-6462/$ - see front matter Ó 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.scriptamat.2012.11.002 ⇑ Corresponding author. Tel.: +91 (80) 22933190; fax: +91 (80) 23600135; e-mail: rakeshr@isu.iisc.ernet.in URL: http://isu.iisc.ernet.in/~rakeshr/. Available online at www.sciencedirect.com Scripta Materialia 68 (2013) 408–411 www.elsevier.com/locate/scriptamat