CO₂ gas sensor based on macro porous silicon modified with trimetallic nanoparticles

Two kinds of modified macro porous silicon (maPsi) layer with trimetallic nanoparticles surface alloying and core–shell forms CO₂ gas sensors were fabricated and tested successfully. Trimetallic Au–Ag–Pd nanoparticles were prepared by an ion reduction process of different metallic salts on maPsi layer by a simple immersion process. As-formed maPsi layer was fabricated by a laser assisted etching (LAE) process with laser power density illumination, current density and etching time of about: 25 mW/cm², 20 mA/cm² and 20 min, respectively. Immersion process with different immersion times were carried out at a fixed concentration 1 mM of HAuCl_4, AgNO₃ and PdCl₂ to synthesize Au–Ag–PdNPs/maPsi hybrid structures. Trimetallic core–shell nanoparticles form was prepared at (6, 8) min immersion times, while for surface alloying nanoparticles form was prepared at (2, 4) min immersion times in a mixed solution with a fixed ratio 1:1:1 at room temperature. The structural aspects of the as-formed maPsi layer and trimetallic Au–Ag–Pd nanoparticles were demonstrated by field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS). The electrical properties of the modified maPsi layers with trimetallic nanoparticles with and without CO₂ gas sensor were found at room temperature. A specific enhancement in gas sensitivity for trimetallic surface alloying nanoparticles form compared with that of the core–shell nanoparticles form was obtained due to the higher specific area to volume ratio.