Chaki Nirmalya Kumar, Vijayamohanan Kunjukrishna Pillai
Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411 008, India.
J Phys Chem B. 2005 Feb 24;109(7):2552-8. doi: 10.1021/jp045709x.
Superlattices of monolayer protected metallic and semiconducting nanoclusters have attracted significant attention due to their promising applications in nanotechnology. In this paper, we investigate the effect of temperature on the ordered superlattice structure of relatively larger sized Au nanoclusters passivated with dodecanethiol [ca. Au1415(RS)328] with the help of in situ temperature controlled X-ray diffraction (XRD) and infrared spectroscopy (IR) in conjunction with thermogravimetric (TG) and differential scanning calorimetric (DSC) analysis. In brief, monolayer protected Au nanoclusters (AuMPC) were prepared by a modified Brust synthesis technique, where dodecanethiol itself acts as both phase transfer and simultaneous capping agent during the reduction process, generating an average particle size of 3.72 +/- 0.4 nm after repeated solvent extraction and careful fractionation experiments. These particles are characterized with the help of UV-vis, transmission electron microscopic (TEM), IR, and NMR techniques, where effective capping as well as the superlattice formation on the TEM grid is evident from the combined analysis of these results. In situ low-angle XRD analysis shows that the particles undergo an irreversible phase transition in the temperature range of 100-115 degrees C, which is also reflected in the data from in situ IR analysis. However, the DSC analysis does not account for this phase transition, although the reversible phase transition due to the alkyl chain dynamics is in good agreement with the previously reported results. These results indicate the formation of temperature-induced, diffusion-limited phase transition involving nonequilibrium fractal structures, which is in good agreement with the previous available theoretical studies. The determination of the temperature window for the stability of these ordered assemblies would be used to understand the effect of thermal stress for device applications.
单层保护的金属和半导体纳米团簇超晶格因其在纳米技术中的应用前景而备受关注。在本文中，我们借助原位温度控制X射线衍射（XRD）和红外光谱（IR），结合热重分析（TG）和差示扫描量热分析（DSC），研究了温度对用十二烷硫醇钝化的相对较大尺寸金纳米团簇[约Au1415(RS)328]有序超晶格结构的影响。简而言之，通过改进的Brust合成技术制备单层保护金纳米团簇（AuMPC），在还原过程中十二烷硫醇本身既是相转移剂又是同时的封端剂，经过反复溶剂萃取和仔细分级实验后产生的平均粒径为3.72±0.4 nm。这些颗粒借助紫外可见光谱、透射电子显微镜（TEM）、红外光谱和核磁共振技术进行表征，从这些结果的综合分析中可以明显看出在TEM网格上有效的封端以及超晶格的形成。原位低角度XRD分析表明，颗粒在100 - 115℃的温度范围内经历不可逆的相变，这也反映在原位红外分析的数据中。然而，DSC分析并未显示出这种相变，尽管由于烷基链动力学导致的可逆相变与先前报道的结果吻合良好。这些结果表明形成了涉及非平衡分形结构的温度诱导的、扩散受限的相变，这与先前可用的理论研究结果吻合良好。确定这些有序组装体稳定性的温度窗口将用于理解热应力对器件应用的影响。
