Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Nanoscale. 2018 Jan 18;10(3):1297-1307. doi: 10.1039/c7nr06771b.
In this work we report the influence of methane/hydrogen on the nucleation and formation of MgTi bimetallic nanoparticles (NPs) prepared by gas phase synthesis. We show that a diverse variety of structural motifs can be obtained from MgTi alloy, TiC/Mg/MgO, TiC/MgO and TiH/MgO core/shell NPs via synthesis using CH/H as a trace gas, and with good control of the final NP morphology and size distribution. Moreover, depending on the concentration of Ti and type of employed trace gas, the as prepared MgTi NPs can be tuned from truncated hexagonal pyramid to triangular and hexagonal platelet shapes. The shape of MgTi NPs is identified using detailed analysis from selected area electron diffraction (SAED) patterns and tomography (3D reconstruction based on a tilt series of Bright-Field transmission electron microscopy (TEM) micrographs). We observe the truncated hexagonal pyramid as a shape of MgTi alloy NPs in contrast to Mg NPs that show a hexagonal prismatic shape. Moreover, based on our experimental observations and generic geometrical model analysis, we also prove that the formation of the various structural motifs is based on a sequential growth mechanism instead of phase separation. One of the prime reasons for such mechanism is based on the inadequacy of Mg to nucleate without template in the synthesis condition. In addition, the shape of the TiC/TiH core, and the concentration of Mg have strong influence on the shape evolution of TiC/MgO and TiH/MgO NPs compared to TiC/Mg/MgO NPs, where the thermodynamics and growth rates of the Mg crystal planes dominate the final shape. Finally, it is demonstrated that the core shape of TiC and TiH is affected by the Mg/Ti target ratio (affecting the composition in the plasma), and the type of the trace gas employed. In the case of CH the TiC core forms a triangular platelet, while in the case of H the TiH core transforms into a hexagonal platelet. We elucidate the reason for the TiC/TiH core shape based on the presence of (i) defects, and (ii) hydrogen and carbon adsorption on {111} planes that alter the growth rates and surface facet stabilization.
在这项工作中，我们报告了甲烷/氢气对气相合成制备的 MgTi 双金属纳米粒子（NPs）成核和形成的影响。我们表明，通过使用 CH/H 作为痕量气体进行合成，可以从 MgTi 合金、TiC/Mg/MgO、TiC/MgO 和 TiH/MgO 核/壳 NPs 获得多种结构基元，并且可以很好地控制最终 NPs 的形态和尺寸分布。此外，根据 Ti 的浓度和所使用的痕量气体的类型，可以将制备的 MgTi NPs 调制成从截角六边形金字塔到三角形和六边形片状物的形状。通过详细的选区电子衍射（SAED）图谱和断层扫描（基于亮场透射电子显微镜（TEM）微图倾斜系列的 3D 重建）分析来确定 MgTi NPs 的形状。我们观察到截角六边形金字塔是 MgTi 合金 NPs 的形状，而 Mg NPs 则显示出六方棱柱形状。此外，根据我们的实验观察和通用几何模型分析，我们还证明了各种结构基元的形成是基于顺序生长机制而不是相分离。这种机制的一个主要原因是在合成条件下，Mg 没有模板就无法成核。此外，与 TiC/Mg/MgO NPs 相比，TiC/TiH 核的形状和 Mg 的浓度对 TiC/MgO 和 TiH/MgO NPs 的形状演化有很强的影响，其中 Mg 晶体面的热力学和生长速率主导最终形状。最后，证明了 TiC 和 TiH 的核形状受 Mg/Ti 靶比（影响等离子体中的组成）和所使用的痕量气体类型的影响。在 CH 的情况下，TiC 核形成三角形片状物，而在 H 的情况下，TiH 核转变为六边形片状物。我们根据（i）缺陷的存在以及（ii）氢和碳在 {111} 面上的吸附，解释了 TiC/TiH 核形状的原因，这改变了生长速率和表面面稳定。
