Fabrication of size-selected bimetallic nanoclusters using magnetron sputtering
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Hussain Alawadhi Department of Applied Physics, University of Sharjah, United Arab Emirates (Received 11 March 2012; accepted 31 May 2012)
Copper–tin (CuxSn1x) nanocluster is a promising system for gas sensing applications, mainly because of its sensitivity and selectivity for H2S. In this work, pure Sn and Cu as well as composite CuxSn1x nanoclusters were synthesized using the dc magnetron sputtering gas condensation technique. Nanoclusters with different Sn to Cu ratios were produced by changing the ratio of Sn and Cu in the target. The dependence of Sn, Cu, and CuxSn1x nanoclusters’ size distribution on various source parameters, such as the inert gas flow rate and aggregation length, has been investigated in detail. The results show that as the inert gas flow rate increases, the mean nanocluster size increases for Sn, decreases for Cu, while increases and then decreases for CuxSn1x. The results could be understood in terms of the contribution percentage of the nanocluster formation mechanism. Furthermore, this work demonstrates the ability of tuning the CuxSn1x nanoclusters’ size and composition by a proper optimization of the source operation conditions. I. INTRODUCTION
Metal nanoclusters are the subject of numerous studies for applications in several fields, and the attention dedicated to this topic is witnessed by the increasing number of related contributions within the material science community. These nanoclusters exhibit striking optical properties1–3 and superparamagnetism with enhanced coercivity and a shift of their hysteresis loop.4,5 Tin (Sn) has been used since early 1960s as a solid-state gas sensor, and it became the main material commercially available in sensors for detecting fuel gas, carbon monoxide, general purpose combustible gases, ammonia, water vapor, etc. A considerable enhancement in the sensitivity was reported for Sn alloyed with noble metals.6,7 Furthermore, alloying Sn thin films with copper (Cu) nanoclusters was found to enhance their sensing characteristics for gases such as H2S considerably.8–14 This makes such material particularly useful in industries where, e.g., leak detection and process control are significant issues. Therefore, in addition to the large surface area of Sn nanoclusters, alloying them with Cu is expected to further improve their sensing properties. However, to use those nanoclusters for applications, precise control of their size, yield, alloying concentration, and of size distribution is needed. The present investigation focuses on the synthesis of pure Cu, pure Sn, and composite Cu–Sn nanoclusters using a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.205 J. Mater. Res., Vol. 27, No. 18, Sep 28, 2012
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the magnetron sputtering technique inside an ultra-high vacuum (UHV) compatible system. This method of preparing composite Cu–Sn nanoclusters has many advantages: (i) nanoclusters are produced with a narrow size distribution; (ii) the average nanocluster siz
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