Aging In Ambient Air Research Articles

Luminescence and EPR studies of defects in Si-SiO2films

Co-sputtered Si-rich SiO 2 films annealed at 1150 °C are studied by photoluminescence and EPR methods. It is found that the emission spectrum of as-prepared samples contains one broad infrared band. It is shown that one-year aging in ambient air and low-temperature annealing in an oxygen atmosphere leads to an increase in the infrared band intensity and the appearance of additional bands with maxima at 1.7 eV, 2.06 eV and 2.3 eV while annealing in a hydrogen atmosphere results in the decrease of the 1.7 eV and 2.06 eV band intensities. A correlation between the 1.7-eV band intensity and the EPR signal from EX-centers is found to exist. The decrease of crystallite sizes results in a high-energy shift of the infrared band while the peak positions of the other ones (at 1.7 eV, 2.06 eV and 2.3 eV) do not change. The infrared band is ascribed to recombination in Si crystallites while the others are attributed to silicon oxide defects. the 1.7-eV and 2.06-eV bands being due to oxygen-excess defects such as EX-center and NBOHC.

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 °C) with alkenes (RCHCH2) 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 °C for 6 weeks, only a small increase in the PL intensity was observed. This severe treatment completely transformed H-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.