Nowadays, there are many environmental concerns that require continuous improvements in the development of gas sensors. Gas sensors are useful in detecting toxic and flammable gases in the atmosphere such as hydrogen (H2), ammonia (NH3), carbon monoxide (CO) and many others. However, more emphasis has been placed on H2 detection due to its abundance and use as a renewable and clean energy source. Gas sensors derived from n-type metal oxide nanowires have been extensively researched, while p-type metal oxides are just getting started. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essayNiO is a p-type metal oxide semiconductor that has a cubic rock salt structure with a wide bandgap ranging from 3.6 eV to 4.0 eV. As for this research, N Kaur et al. studied NiO nanowires in the field of gas sensing applications. There are several ways to synthesize NiO nanowires, such as sol-gel method, electrospinning method, and for this research, vapor-liquid-solid method. The vapor-liquid-solid (VLS) method has many advantages over other methods such as: reduced reaction energy, no need for precursor, direct growth on an active substrate and only requires an oven and a pump. Using the VLS method to synthesize NiO nanowires also results in single-crystal nanowires with low defects that are preferable in many applications. The researcher of this academic journal presents the synthesis of NiO nanowires using the VLS method on an alumina substrate with different catalysts. The morphology of the synthesized product will be studied by scanning electron microscopy (SEM). As for structural characterization, GI-XRD (X-ray diffraction) and Raman spectroscopy were used. To test the gas sensing ability of NiO nanowires, conductometric sensing devices were prepared under different gases and working temperatures. To prepare the substrate, the alumina substrate was first ultrasonically cleaned in acetone and dried with synthetic air. Then, catalysts (platinum, palladium, and gold) were deposited on the substrate using a magnetron sputtering technique. The purpose of the catalyst in the substrate is to promote nucleation sites during the deposition and growth process of NiO nanowires. To synthesize NiO nanowires using VLS technique, NiO powder was used as the source material. The NiO powder and the substrate are placed in the oven; however, NiO is placed at a higher temperature and heated until evaporation. To transfer the NiO vapors to the alumina substrate deposited by the catalyst, argon gas was used as a carrier gas to transport the NiO vapors. Therefore, the higher temperature NiO will condense on the substrate because the substrate is at a lower temperature. To synthesize the gas sensing device, alumina substrates were used to prepare a conductometric sensing device. First, solder pads with a titanium-tungsten alloy as an adhesion layer were deposited on the substrates. Second, an interdigitated platinum contact was deposited to achieve higher electrical conductance. On the other side of the substrate, a heating element was deposited to study the response to different working temperatures. Finally, the device was attached to the TO packages using electrowelded gold wires.,.