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

This paper describes the chemical modification of high surface area, photoluminescent porous silicon (PSi) by reaction at a moderately elevated temperature (< 115 degreesC) with alkenes (RCH=CH(2)) 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 reflectance infrared Fourier transform (DRIFT), transmission FTIR, Raman, X-ray photoelectron, and Auger spectroscopies. Auger depth profiling results are consistent with homogeneous incorporation of organic molecules on the internal surface of the PSi. The functionalized surfaces demonstrate high chemical stability in boiling aqueous and organic solvents and even in harsher environments such as aqueous HF or KOH. Aging in ambient air for several months has no effect on the PL intensity or energy. Notably, when the surfaces were treated at 100 percent humidity at 70 degreesC for 6 weeks, only a small increase in the PL intensity was observed. This severe treatment completely transformed R-terminated PSi into a transparent oxide layer. This result is consistent with the formation of organic films with a very low defect density at the interface. Thus, these organic monolayers have unprecedented stability and ideally passivate the PSi.