Synthesis of Oxide-Free InP Quantum Dots: Surface Control and H2-Assisted Growth
Synthesis of Oxide-Free InP Quantum Dots: Surface Control and H2-Assisted Growth
复制标题
DOI：
10.1021/acs.chemmater.7b04069
复制
发表时间：
2017-11-28
影响因子：
8.6
通讯作者：
Delpech, Fabien
中科院分区：
文献类型：
--
作者：
Baquero, Edwin A.;Virieux, Heloise;Delpech, Fabien
在纳米尺度上，颗粒表面对化学物质(溶解度、胶体稳定性、催化活性等)的作用占主导地位。和物理(光、磁、交通等)属性。因此，了解纳米颗粒的表面属性是控制其特征的关键。许多人已经对几种半导体纳米晶体(量子点、量子点)的表面进行了研究，从而产生了大量的知识和控制。1−4这为在许多科学领域取得重大成就打开了大门，例如使用这些材料作为生物标记、激光、发光二极管(LED)和太阳能电池。1−5然而，对于有毒的Cd和Pb基系统，大多数这样的进展已经实现，而其他系统，如III-V半导体(特别是InP)，6，7还没有得到充分的研究。事实上，In−P固体的共价性质及其对氧化的高度敏感性解释了控制InP表面化学以及对于核/壳系统的壳层界面的复杂性。我们和其他人已经证明了这些材料对溶液中存在的水的敏感性，无论是作为反应物杂质还是作为在目前报道的合成的高温条件下产生的副产品。8−12这会导致氧化物和氢氧化物物种的形成，从而显著且不可逆地改变表面。重要的是要注意，InP合成介质中的水的存在不是例外，而是一般情况。大多数程序的前提是在高温(>；188℃)下使用羧酸铟前体和/或其他含氧配体。羧酸是一种这样的稳定剂，在8，9的温度范围内，作为脱羧基偶联的副产物产生水，导致意想不到的和不想要的影响，8，9，11，12最显著的是抑制进一步的颗粒生长。这种现象对准确研究量子点生长机制是一个巨大的障碍，因为它使得对其他参数的独立分离和研究变得不可能。例如，当水的浓度同时变化时，酸浓度对颗粒生长的真实影响不能令人满意地描述。7此外，水的关键作用(有时是有害的)已被证明，即使在被认为具有很大阻力的材料的情况下也是如此。例如，在PbS量子点和CdSe纳米片系统中，水和氢氧化物配体改变了特定平面的表面能量。13、14同样，水被怀疑会导致PbSe和PbS量子点基薄膜的光学和电学性能的恶化。在这里，我们讨论了InP QD表面化学控制的问题，特别是防止表面氧化/羟化的问题，即使在含有O的配体和水存在的情况下也是如此。我们描述了基于一种新的铟前体：三(N，N‘-二异丙基乙酰胺)铟(III)的两种替代方法。有趣的是，虽然人们很早就知道了酰胺酸铟的络合物，但它们只是在最近才被用作铟基材料的CVD和ALD生长的试剂。在我们的胶体合成中使用这种特殊的胺化铟络合物可以产生完全不含氧化物的颗粒，使它们能够生长到更大的直径。描述了150℃(在Ar气氛下)和230℃(在氢气气氛下)的防氧化机理。在后一种情况下，用2H魔角自旋(MAS)…证明了量子点表面史无前例的氢键解离。普遍的共识是，NMR
At the nanoscale, the role of the particle surface is predominant for the chemical (solubility, colloidal stability, catalytic activity, etc.) and physical (optical, magnetic, transport, etc.) properties. Understanding the surface properties of nanoparticles is thus key to controlling their features. The surfaces of several semiconductor nanocrystals (quantum dots, QDs) have been investigated by many, leading to a substantial amount of knowledge and control. 1− 4 This has opened the door to great achievements in many scientific disciplines, as exemplified by the use of these materials as biolabels, lasers, light-emitting diodes (LEDs) and solar cells. 1− 5 However, most such advancements have been achieved for toxic Cd-and Pbbased systems, whereas others, such as III-V semiconductors (in particular InP), 6, 7 have not been as thoroughly studied. Indeed, the more covalent nature of the In− P solid and its high sensitivity toward oxidation account for the complexity of controlling both the InP surface chemistry and, in the case of core/shell systems, the shelling interface. 8, 9 We and others have demonstrated the sensitivity of these materials to the water present in solution either as a reactant impurity or as a byproduct generated under the high-temperature conditions of currently reported syntheses. 8− 12 This results in the formation of oxide and hydroxide species, which dramatically and irreversibly alter the surface. It is important to note that the presence of water in the InP synthesis medium is not an exception but rather the general case. Most procedures are predicated on the use of indium carboxylate precursors and/or other oxygen-containing ligands at high temperatures (> 188 C). Carboxylic acids, one such stabilizing agent, produce water as a coproduct of decarboxylative coupling in this temperature range, 8, 9 leading to unexpected and unwanted effects, 8, 9, 11, 12 most notably the inhibition of further particle growth. This phenomenon serves as an immense obstacle to the accurate study of QD growth mechanisms, as it renders impossible the independent isolation and investigation of other parameters. The true effect of acid concentration on particle growth, for example, cannot be satisfactorily described while the concentration of water varies simultaneously. 6, 7 Moreover, the pivotal (and sometimes detrimental) effect of water has been demonstrated even in the case of materials considered to be largely resistant. For instance, in both PbS QDs and CdSe nanoplatelet systems, water and hydroxide ligands alter the surface energy of specific planes. 13, 14 Likewise, water is suspected to engender deterioration of the optical and electrical properties of PbSe and PbS QDs-based films. 15, 16 Herein, we address the issue of InP QD surface chemistry control and, in particular, the prevention of surface oxidation/hydroxylation, even when in the presence of O-containing ligands and water. We describe two alternative approaches based on a novel indium precursor: tris (N, N′-diisopropylacetamidinato) indium (III). Interestingly, though indium amidinate complexes have been known for a long time, 17 they have only very recently been used as reagents for CVD and ALD growth of indium-based materials. 18, 19 The use of this particular indium amidinate complex in our colloidal synthesis produces particles completely devoid of oxides, allowing them to grow to larger diameters. The mechanism of protection from oxidation at 150 C (under argon) and at 230 C (under dihydrogen) are described. In the latter case, an unprecedented H2 bond dissociation at the QD surface is demonstrated by 2H magic angle spinning (MAS) NMR.The general consensus suggests that the …