Ideal passivation of luminescent porous silicon by thermal, noncatalytic reaction with alkenes and aldehydes

This paper describes the chemical modification of high surface area, photol uminescent porous silicon (PSi) by reaction at a moderately elevated temper ature (< 115 degreesC) with alkenes (RCH=CH2) and aldehydes (RCHO) to give organic monolayers covalently bonded to the surface through Si-C and Si-O-C linkages, respectively. The monolayers are characterized using diffuse ref lectance infrared Fourier transform (DRIFT), transmission FTIR, Raman, X-ra y photoelectron, and Auger spectroscopies. Auger depth profiling results ar e consistent with homogeneous incorporation of organic molecules on the int ernal surface of the PSi. The functionalized surfaces demonstrate high chem ical stability in boiling aqueous and organic solvents and even in harsher environments such as aqueous HF or KOH. Aging in ambient air for several mo nths has no effect on the PL intensity or energy. Notably, when the surface s were treated at 100 percent humidity at 70 degreesC for 6 weeks, only a s mall increase in the PL intensity was observed. This severe treatment compl etely transformed R-terminated PSi into a transparent oxide layer. This res ult is consistent with the formation of organic films with a very low defec t density at the interface. Thus, these organic monolayers have unprecedent ed stability and ideally passivate the PSi.