Effects of organic monolayer formation on electrochemiluminescence behavior of porous silicon

The effects of various organic monolayers on the surface of porous silicon on the electrochemiluminescence (ECL, also referred to as electroluminescen ce in the literature) characteristics were investigated. Surfaces were term inated with alkyne, alkene, and alkyl functionalities through cathodic elec trografting (CEG), Lewis acid-mediated hydrosilylation (LA), and anodic ele ctrografting (AEG), respectively. ECL was induced through the known formic acid/sodium formate electron injection system. Alkyl-terminated surfaces pr oduced through AEG yielded the brightest emission of any of the functionali zed surfaces although ECL emission was about half as intense as that from t he underivatized Si-H-terminated surface. The lifetime, however, was extend ed by a factor of 2, and these surfaces demonstrate an unprecedented rechar ging phenomenon. When ECL ceases, a brief 10 s application of a cathodic bi as restores most of the ECL emission intensity. This process can be cycled about 10 times, and results in a substantially greater light output than th at from any of the surfaces examined here, including the Si-H-terminated su rface. Dodecenyl-terminated surfaces, produced through Lewis acid-mediated hydrosilylation of 1-dodecyne, show the greatest lifetimes, an order of mag nitude longer than that of an Si-H-terminated surface, but their emission i ntensity is unfortunately very low. The induction times for light emission to occur decreased for all the functionalized surfaces, as compared to the native Si-H surface. Explanations for the effects of organic monolayer form ation on ECL observed here are described.