Department of Chemistry and ‡Department of Materials Science and Engineering, National Tsing Hua University , Hsinchu 30013, Taiwan.
J Am Chem Soc. 2015 Feb 18;137(6):2265-75. doi: 10.1021/ja509044q. Epub 2015 Feb 6.
Au-Pd core-shell nanocrystals with cubic, truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures have been employed to form micrometer-sized polyhedral supercrystals by both the droplet evaporation method and novel surfactant diffusion methods. Observation of cross-sectional samples indicates shape preservation of interior nanocrystals within a supercrystal. Low-angle X-ray diffraction techniques and electron microscopy have been used to confirm the presence of surfactant between contacting nanocrystals. By diluting the nanocrystal concentration or increasing the solution temperature, supercrystal size can be tuned gradually to well below 1 μm using the surfactant diffusion method. Rectangular supercrystal microbars were obtained by increasing the amounts of cubic nanocrystals and surfactant used. Au-Ag core-shell cubes and PbS cubes with sizes of 30-40 nm have also been fabricated into supercrystals, showing the generality of the surfactant diffusion approach to form supercrystals with diverse composition. Electrical conductivity measurements on single Au-Pd supercrystals reveal loss of metallic conductivity due to the presence of insulating surfactant. Cubic Au-Pd supercrystals show infrared absorption at 3.2 μm due to extensive plasmon coupling. Mie-type resonances centered at 9.8 μm for the Au-Pd supercrystals disappear once the Pd shells are converted into PdH after hydrogen absorption.
采用 Au-Pd 核壳纳米晶体的立方、截角立方、十二面体、截角八面体和八面体结构，通过液滴蒸发法和新型表面活性剂扩散法形成了微米级的多面超晶体。对截面样品的观察表明，超晶体内部纳米晶体的形状得以保留。采用低角度 X 射线衍射技术和电子显微镜证实了接触纳米晶体之间存在表面活性剂。通过稀释纳米晶体浓度或提高溶液温度，使用表面活性剂扩散法可以逐渐将超晶体尺寸调至远小于 1μm。通过增加立方纳米晶体和表面活性剂的用量，可以得到矩形超晶微棒。还制备了尺寸为 30-40nm 的 Au-Ag 核壳立方体和 PbS 立方体的超晶体，表明了该表面活性剂扩散方法在形成具有不同组成的超晶体方面具有通用性。对单个 Au-Pd 超晶体的电导率测量表明，由于存在绝缘表面活性剂，金属导电性丧失。立方 Au-Pd 超晶体在 3.2μm 处表现出强烈的等离子体耦合红外吸收。由于广泛的等离子体耦合，Au-Pd 超晶体的 Mie 型共振在 9.8μm 处消失，一旦 Pd 壳在吸收氢气后转化为 PdH。
