Using localized surface plasmon resonance (LSPR) as an optical probe we demonstrate the presence of free carriers in phosphorus doped silicon nanocrystals (SiNCs) embedded in a silica matrix. In small SiNCs, with radius ranging from 2.6 to 5.5 nm, the infrared spectroscopy study coupled to numerical simulations allows us to determine the number of electrically active phosphorus atoms with a precision of a few atoms. We demonstrate that LSP resonances can be supported with only about 10 free electrons per nanocrystal, confirming theoretical predictions and probing the limit of the collective nature of plasmons. We reveal the appearance of an avoided crossing behavior linked to the hybridization between the localized surface plasmon in the doped nanocrystals and the silica matrix phonon modes. Finally, a careful analysis of the scattering time dependence versus carrier density in the small size regime allows us to detect the appearance of a new scattering process at high dopant concentration, which can be explained by P clustering inside the SiNCs.

中文翻译：

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少电子状态下超掺杂嵌入硅纳米晶体的红外纳米等离子体特性

使用局部表面等离子体共振 (LSPR) 作为光学探针，我们证明了嵌入二氧化硅基质中的磷掺杂硅纳米晶体 (SiNC) 中存在自由载流子。在半径范围为 2.6 至 5.5 nm 的小型 SiNC 中，红外光谱研究与数值模拟相结合，使我们能够以几个原子的精度确定电活性磷原子的数量。我们证明 LSP 共振可以支持每个纳米晶体仅约 10 个自由电子，证实了理论预测并探索了等离子体的集体性质的限制。我们揭示了与掺杂纳米晶体中的局部表面等离子体与二氧化硅基质声子模式之间的杂交相关的避免交叉行为的出现。最后，