A Variable Response Phosphine Sensing Matrix Based on Nanostructure Treated p and n-Type Porous Silicon Interfaces

We study the dynamic interplay as PH₃ interacts at room temperature to contribute electrons to nanostructure modified p and n-type porous silicon (PS) interfaces. A nanopore coated microporous interface is treated to form TiO₂, SnO_x, Cu_xO, and Au_xO (x ≫ 1) nanostructured centers deposited in fractional coverage on the PS interface. Relative sensitivities of the surface sites are measured under 2-5 and 10 ppm PH₃ exposure. The interaction with two p-type nanostructure decorated boron-doped interfaces demonstrates enhancement of sensitivity relative to undecorated PS. The results are explained using the inverse hard/soft acid/base (IHSAB) principle, combining the tenants of acid/base chemistry and semiconductor physics. Analyte coupling to the majority charge carriers of the extrinsic semiconductor determines the nature of directed electron transduction as it induces a change in conductance. As applied, the nanostructured metal oxides serve as gateways, forcing a dominant electron transduction (versus chemisorption) at the decorated extrinsic semiconductor interface. A study of gold clustered oxide depositions on p-type (1-3 Q-cm) PS demonstrates that an optimal fractional deposition can be attained and should not be exceeded to avoid crosstalk between the deposited nanoparticles. It appears that phosphine can be converted on interaction with phosphorous doped n-type PS. A reversal of the response signal observed with increased PH₃ concentration, considered within the IHSAB model, suggests that the conductance might be associated with the formation of the electron withdrawing PH₂ radical.