Materials Today: Proceedings
Ammonia sensing by silicon nanowires (SINWs) obtained through metal assisted electrochemical etching
Introduction
Silicon nanowires (SINWs) have become a dominant material in electronics and semiconducting devices due to their excellent electrical, optical, mechanical, thermal properties and environmental compatibility [1], [2], [3], [4], [5]. In last few years, SINWs are highly studied by the researchers to investigate their applicability in numerous fields. SINWs can be fabricated by both top down and bottom up approaches. Bottom up approach requires high vacuum, high temperature high power consumption, making the process more expensive. Top down approach, on the other hand, provides ordered SINWs with high homogeneity by considerably reducing some of the issues in the bottom up process. Metal assisted electrochemical etching is one of the most efficient top down approaches which can produce large number of SINWs at short interval of time. In the present work, SINWs are fabricated by metal assisted electrochemical etching. Metal assisted electrochemical etching method is a cost effective route which produces finely oriented silicon nanowires at one go with optimized electrolyte concentration. Ordered SINWs with large surface area shows immense potentiality in chemical/bio-sensors [6], [7], [8], [9], [10]. Chemical modification of SINWs surface highly effects on its electrical properties [11], [12], [13].
In the present article we report detection of ammonia through SINWs array. Ammonia is a toxic gas with pungent smell, released in industrial and natural processes [14]. Inhalation of ammonia is harmful to health, it can causedreadful diseases like lung damage, kidney failure etc. [15], [16]. Ammonia can be fatal at long exposure time or highconcentrations [17]. Therefore, ammonia detection is an utmost necessity to minimize its impact. There are many studies on ammonia detection.To cite a few, F. Winquist et al. developed modified palladium metal oxide semiconductor structures with increased ammonia gas sensitivity [18]. P. Nath et al. developed PANI passivated porous silicon for ammonia detection [19]. Mausumi Das et al. developed zinc oxide-polyaniline nanocomposite for fabrication of efficient room temperature ammonia gas sensor [20]. In respect of, sensor mechanism, SINWs based gas sensors are better understood compared to metal oxide and polymer nanowires [21], [22]. Present study shows ammonia detection by SINWs with fair response and recovery times at room temperature. The samples are characterized through FESEM measurements to correlate sensing mechanism with the morphology.
Section snippets
Experimental details
The p-type 〈1 0 0〉 Si wafers with resistivity of 1–10 Ω cm and thickness of 375 µm are used for SINWs fabrication. The wafers are cleaned with RCA technique to remove the native oxides prior to use. After RCA treatment the wafers are dipped in a mixture of 15% HF and 20 mM AgNO3 for Ag electroplating on Si wafer. For SINWs formation, electroplated Si wafers are loaded in an electrochemical cell with etchant solution a mixture of 15% HF and 2M H2O2, where Aluminum act as working electrode and
Morphological analysis
Morphological analysis of SINWs is studied through FESEM measurements which are shown in Fig. 1. Fig. 1(a)shows the planar view of SINWs surface, it is clearly visualized that the surface is full of finely distributed pores across the area. Inset shows the magnified image which asserts, pores are depth in nature. Fig. 1(b) shows the crosssectional view of SINWs, it is estimated the average length of SINWs is23 µm. Inset of Fig. 1(b) shows magnified cross sectional view, depicting vertically
Conclusion
SINWs are successfully fabricated by metal assisted electrochemical etching. FESEM shows fine alignment of SINWs of diameter in the range of 85-450 nm with porous structure. Gas sensing studies infer that SINWs shows fair response and recovery times with lower detection of 10 ppm. SINWs are seen to be highly selective towards ammonia compared to other gases with good response sensitivity. Overall, it can be concluded that SINWs could be a better ammonia sensor for practical applications.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
Authors are thankful to Department of Science and Technology (DST, India) and University Grants commission (UGC, India) for providing instrumental facility through various projects grants, DST/TSG/PT2009/96 and 40-438/2011 SR. Authors are grateful to CIF, Gauhati University for FESEM measurements.
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