A Comparison of Porous Silicon and Silicon Nanocrystallite Photoluminescence Quenching with Amines

We report here a comparison of the ability of the monodentate Lewis base n -propylamine and the bidentate molecule ethylenediamine to quench the photoluminescence of light-emitting silicon in three different structural environments. These include porous silicon fabricated from p-type substrates; porous silicon from n-type substrates, and Si nanocrystallites derived from porous silicon. Both types of porous Si substrates were characterized by conventional transmission electron microscopy, while the Si nanocrystallites were characterized by high-resolution transmission electron microscopy. The fractional changes in photoluminescence as a consequence of amine addition were measured and fitted to a static equilibrium model from which adduct formation constants were calculated. It is found that the Si lumophores embedded in the porous oxides on n- and p-type substrates interact similarly with n -propylamine and ethylenediamine; however, ultrasonic extraction of the nanocrystalline Si fragments from the porous oxide layers and subsequent exposure to these amines reveals a near order of magnitude difference between the equilibrium constants for n -propylamine (log K ∼ 4.9) and ethylenediamine (log K ∼ 5.8) addition.