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From single pulse to double pulse ns laser ablation of silicon in water: photoluminescence enhancement of silicon nanocrystals

In this paper we introduce a comparative approach for studying the emission properties of silicon nanocrystal (Si-nc) colloids prepared by single pulse and double pulse laser ablation processes of a silicon wafer in distilled water. Experiments were conducted to investigate the luminescence properties of the colloids considering the size distributions and surface characteristics of the synthesized Si-ncs. The results indicated that single pulse and double pulse laser ablation processes under similar experimental conditions can lead to the preparation of Si-nc colloids with almost the same size distributions and different surface chemistry. The results show that double pulse laser processing with an inter-pulse delay time of ~5 ns can produce Si-nc colloids with a much greater emission intensity (about fivefold to tenfold) in the orange–red region (550–700 nm) of the visible spectrum. Based on the detailed analysis of the Si-nc size distribution and surface characteristics, the observed prominent orange–red emission is possibly due to a different type of Si–OH surface termination that protects the nanocrystal core upon inward oxidation.