Optimizing of Gold Nanoparticles on Porous Silicon Morphologies for a Sensitive Carbon Monoxide Gas Sensor Device Amer B. Dheyab 1 & Alwan M. Alwan 2 & Mehdi Q. Zayer 2 Received: 22 June 2018 /Accepted: 8 August 2018 # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract A set of carbon monoxide (CO) gas sensors based on porous silicon (PSi)/gold nanoparticle (AuNP) hetro structures were fabricated. Different forms of PSi surface morphologies were studied as a substrate for growth of AuNPs. Simple dipping process of PSi in hydrogen tetrachloroaurate (III) solution (HAuCl 4 ) at fixed concentrations of 10 -2 M/3.5 HF was used to synthesize AuNPs. The n-type PSi was equipped through photo-electrochemical etching process at current density value of 10 mA/cm 2 under illumination condition of 530-nm wavelength and laser illumination intensity of 20 to 80 mW/cm 2 . Three different forms of PSi morphology, meso, macro, and double layers with pore shapes and sizes, were prepared. The structural and surface morphology properties of PSi-based substrate before and after deposition of AuNPs were investigated through studying of scanning electron microscopy (SEM), photoluminescence (PL), and X-ray diffraction (XRD). The electrical property (J-V) was carried out in primary vacuum and CO at low pressure. The results show that PSi surface morphologies strongly influenced the AuNP sizes and hence the sensor performance. It was found that decrease the AuNP sizes could be occasioned in high and fast current response. Keywords PSi . SEM . Response . Recovery . AuNP hetro structures . Gas sensing Introduction Porous silicon (PSi) has attracted much attention as a promising electronic material since as a result of its outstanding mechan- ical and thermal features and its low charge [1–3]. The high surface area inside a slight volume, its well-regulated morphol- ogies, and its high chemical activity make it to be remarkable candidate for gas sensing applications [4, 5]. Gas sensors on the market today have many limitations that prevent real-world applications. The largest issues with current sensors are that the sensors cannot differentiate between gasses and also strug- gle to detect gasses at low concentrations. PSi is optimal for gas sensing because it operates at room temperature, has a large surface area, can be created with a hybrid micro/nanostructure for sensitivity, and can be produced using well-known etching techniques. The surface morphology of the silicon skeleton, the pore shape, and the density of the dangling bonds can be influ- enced by many etching parameters especially the etching cur- rent density and laser illumination power densities [6, 7]. Modifying the surface morphologies of porous layer by incor- porating metallic nanoparticles represents as procedures for im- proving the performance of gas sensors owing to its catalytic property [8–11]. In this work, Al/PSi/AuNP n-Si/Al hetro struc- ture has been fabricated and tested as carbon monoxide gas sensors operated at room temperature. The role of porous sili- con morphologies on growth and morphology of gold nanopar- ticle (AuNP) that improves the performance of the hetro sensors has been examined. The surface morphologies of PSi layer before and after incorporation of AuNPs were studied by SEM, EDS, J-V, and XRD analysis. Experimental Details PSi substrates were fabricate via photo-electrochemical etch- ing of (100) n-type silicon wafer of resistivity 100 Ω cm in a * Amer B. Dheyab amer.aljoburi@yahoo.com 1 Ministry of Science and Technology, Baghdad, Iraq 2 School of Applied Science, University of Technology, Baghdad, Iraq Plasmonics https://doi.org/10.1007/s11468-018-0828-x