Nguyen Hao A, Hammel Benjamin F, Sharp David, Kline Jessica, Schwartz Griffin, Harvey Samantha, Nishiwaki Emily, Sandeno Soren F, Ginger David S, Majumdar Arka, Yazdi Sadegh, Dukovic Gordana, Cossairt Brandi M
Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
Materials Science and Engineering, University of Colorado, Boulder, Colorado 80309-0215, United States.
ACS Nano. 2024 Jul 26. doi: 10.1021/acsnano.4c06961.
Single-photon sources are essential for advancing quantum technologies with scalable integration being a crucial requirement. To date, deterministic positioning of single-photon sources in large-scale photonic structures remains a challenge. In this context, colloidal quantum dots (QDs), particularly core/shell configurations, are attractive due to their solution processability. However, traditional QDs are typically small, about 3 to 6 nm, which restricts their deterministic placement and utility in large-scale photonic devices, particularly within optical cavities. The largest existing core/shell QDs are a family of giant CdSe/CdS QDs, with total diameters ranging from about 20 to 50 nm. Pushing beyond this size limit, we introduce a synthesis strategy for colossal CdSe/CdS QDs, with sizes ranging from 30 to 100 nm, using a stepwise high-temperature continuous injection method. Electron microscopy reveals a consistent hexagonal diamond morphology composed of 12 semipolar {101̅1} facets and one polar (0001) facet. We also identify conditions where shell growth is disrupted, leading to defects, islands, and mechanical instability, which suggest synthetic requirements for growing crystalline particles beyond 100 nm. The stepwise growth of thick CdS shells on CdSe cores enables the synthesis of emissive QDs with long photoluminescence lifetimes of a few microseconds and suppressed blinking at room temperature. Notably, QDs with 80 and 100 CdS monolayers exhibit high single-photon emission purity with second-order photon correlation (0) values below 0.2.
单光子源对于推动量子技术发展至关重要，可扩展集成是一项关键要求。迄今为止，在大规模光子结构中确定性地定位单光子源仍然是一项挑战。在这种背景下，胶体量子点（QDs），特别是核/壳结构，因其溶液可加工性而具有吸引力。然而，传统量子点通常很小，约为3至6纳米，这限制了它们在大规模光子器件中的确定性放置和应用，特别是在光学腔内。现有的最大核/壳量子点是一类巨型CdSe/CdS量子点，总直径约为20至50纳米。突破这一尺寸限制，我们采用逐步高温连续注入法，引入了一种合成尺寸范围为30至100纳米的巨大CdSe/CdS量子点的策略。电子显微镜显示出由12个半极性{101̅1}面和一个极性（0001）面组成的一致的六方菱形形态。我们还确定了壳生长受到干扰的条件，这会导致缺陷、岛状物和机械不稳定性，这表明了生长超过100纳米的晶体颗粒的合成要求。在CdSe核上逐步生长厚CdS壳能够合成具有几微秒长光致发光寿命且在室温下抑制闪烁的发光量子点。值得注意的是，具有80和100个CdS单层的量子点表现出高单光子发射纯度，二阶光子关联（g(2)）值低于0.2。
