Synthetic scheme for high-quality InAs nanocrystals based on self-focusing and one-pot synthesis of InAs-based core-shell nanocrystals
Synthetic scheme for high-quality InAs nanocrystals based on self-focusing and one-pot synthesis of InAs-based core-shell nanocrystals
复制标题
DOI：
10.1002/anie.200802867
复制
发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Peng, Xiaogang
中科院分区：
文献类型：
--
作者：
Xie, Renguo;Peng, Xiaogang
胶体半导体纳米晶体（量子点）的合成化学近年来引起了人们的极大兴趣。在研究高质量CdSe量子点的生长时，发现了形成几乎单分散纳米晶体的关键概念，即尺寸分布的聚焦[1]。这一概念意味着，如果所有的核在开始时形成并迅速停止生长，如单体浓度降低或较低的反应温度所触发的，随后的生长过程将集中于纳米晶体的尺寸分布。这是因为如果单体浓度高于溶液中所有纳米晶体的溶解度，则较小的纳米晶体应通过消耗残留的溶解单体而生长得更快。该方法的关键特征是在颗粒生长期间恒定的颗粒浓度。计算机模拟显示，纳米晶体的尺寸分布也可以通过奥斯特瓦尔德熟化集中，但最终的尺寸分布仍然相当宽。[2]在这里，我们证明，InAs纳米晶体的尺寸和尺寸分布控制良好，可以形成一个特殊的成熟过程，称为自聚焦的尺寸分布（简称自聚焦）。[3，4]与传统的尺寸分布聚焦不同，颗粒浓度在生长过程中急剧下降，并且由于相邻纳米颗粒之间的溶解度梯度，单体通过颗粒间扩散从小纳米晶体驱动到较大的纳米晶体。[3]另一个特征是自聚焦的温度比成核温度高得多。据我们所知，这是第一次，粒子间扩散和自聚焦已被有目的地用于纳米晶体的控制合成。在II-VI，III-V和IV-VI半导体纳米晶体中，如果排除A类元素，如Cd，Hg和Pb，高质量的InAs纳米晶体可能是近红外（NIR）窗口（700- 1400 nm）量子点发射器的最佳候选者[5]。NIR发射器对于体内生物医学成像[5-11]和电信都很重要。[12]由于InAs纳米晶体对空气氧化的极端敏感性和大的激子尺寸，这种NIR发射器应该外延地涂覆有其他类型的宽带隙半导体。考虑到InAs的窄体带隙（约. 0.4 eV），用于构建在NIR范围内发射的核-壳纳米晶体的该材料的核纳米晶体应小于大约3 nm。实验细节作为支持性信息提供;简要程序如下。将硬脂酸铟（0.4mm）、三辛基膦（0.5mL）和十八烯（ODE，3.5mL）的混合物在氩气流下加热至150 ℃。在手套箱中制备的As（Si（CH 3）3）3溶液（约0.1向反应溶液中引入0.01mmol），并将反应在150 ℃下保持几分钟以将所有砷前体转化为InAs纳米团簇。随后，将反应溶液加热至所需温度（高达300 ℃），以生长具有不同尺寸的InAs纳米晶体。III-V族量子点的合成一直是一项具有挑战性的任务，[1，5，12，13-21]并且它们的开发大大落后于它们的II-VI和IV-VI类似物。[22]上述合成程序是在我们将最近开发的InP纳米晶体[23]合成方案扩展到InAs失败后开发的。将InAs量子点与InP制成的量子点进行比较，最初的努力表明，反应性更强的前体（As（Si（CH 3）3）3与P（Si-（CH 3）3）3）总是产生小的纳米团簇（小于1 nm），使用相同的光谱。
Synthetic chemistry of colloidal semiconductor nanocrystals (quantum dots) has attracted substantial interest in recent years. A key concept for formation of nearly monodisperse nanocrystals, namely focusing of size distribution,[1] was discovered upon studying the growth of high-quality CdSe quantum dots. This concept implies that if all nuclei are formed in the beginning and stop growing promptly, as triggered by a decrease in monomer concentration or lower reaction temperature, the subsequent growth process will focus the size distribution of the nanocrystals. This is so because the smaller nanocrystals should grow faster by consuming the residual dissolved monomer if the monomer concentration is higher than the solubility of all nanocrystals in the solution. The key feature of this method is the constant particle concentration during particle growth. Computer simulations revealed that the size distribution of nanocrystals could also be focused through Ostwald ripening, but the final size distribution would still be quite broad.[2] Herein, we demonstrate that InAs nanocrystals with well-controlled size and size distribution can be formed by a special ripening process, called self-focusing of size distribution (in short, selffocusing).[3, 4] Different from traditional focusing of size distribution, the particle concentration decreases drastically in the growth process, and the monomers are driven from small nanocrystals to larger ones by interparticle diffusion, owing to solubility gradients between neighboring nanoparticles.[3] An additional feature is that the temperature for self-focusing is much higher than the nucleation temperature. To our knowledge, this is the first time that interparticle diffusion and self-focusing have been purposely employed for the controlled synthesis of nanocrystals. High-quality InAs nanocrystals are likely the best candidates for quantum-dot emitters in the near infrared (NIR) window (700–1400nm) among II–VI, III–V, and IV–VI semiconductor nanocrystals [5] if Class A elements, such as Cd, Hg, and Pb, are excluded. NIR emitters are important for both in vivo biomedical imaging [5–11] and telecommunications.[12] Because of the extreme sensitivity of InAs nanocrystals to air oxidation and the large exciton size, such NIR emitters should be epitaxially coated with other types of wideband-gap semiconductors. Given the narrow bulk band gap of InAs (ca. 0.4 eV), core nanocrystals of this material for building core–shell nanocrystals that emit in NIR range should be smaller than roughly 3 nm. Experimental details are provided as Supporting Information; a brief procedure is as follows. A mixture of indium stearate (0.4 mm), trioctylphosphine (0.5 mL), and octadecene (ODE, 3.5 mL) was heated to 1508C under an argon flow. As (Si (CH3) 3) 3 solution made in the glove box (ca. 0.1 mmol) was introduced into the reaction solution, and the reaction was held at 1508C for a couple of minutes to convert all arsenic precursors to InAs nanoclusters. Subsequently, the reaction solution was heated to a desired temperature (up to 3008C) for the growth of InAs nanocrystals with different sizes.Synthesis of III–V quantum dots has been a challenging task,[1, 5, 12, 13–21] and their development lags substantially behind that of their II–VI and IV–VI analogues.[22] The synthetic procedure described above was developed after our failed efforts to extend the recently developed synthetic scheme for InP nanocrystals [23] to InAs. Comparing InAs quantum dots with those made of InP, initial efforts revealed that the more reactive precursor (As (Si (CH3) 3) 3 vs. P (Si-(CH3) 3) 3) always generated small nanoclusters (less than 1 nm) with a fixed spectrum using the same …