Pressure/temperature phase diagrams and superlattices of organically functionalized metal nanocrystal monolayers: The influence of particle size, size distribution, and surface passivant
Pressure/temperature phase diagrams and superlattices of organically functionalized metal nanocrystal monolayers: The influence of particle size, size distribution, and surface passivant
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DOI：
10.1021/jp9611582
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发表时间：
1997-01-09
影响因子：
3.3
通讯作者：
Leff, DV
中科院分区：
文献类型：
--
作者：
Heath, JR;Knobler, CM;Leff, DV
通过Langmuir单层膜的表面等温线和Langmuir- blodgett （LB）薄膜的透射电子显微图，研究了有机钝化20-75埃直径Ag和Au纳米晶体的相行为。研究了温度、有机钝化剂链长、纳米晶尺寸和组成等因素的影响。观察到三种不同类型的相行为，并可以根据额外的（锥形）体积（V-e）来分类，因为烷基盖层基团从接近球形的金属芯延伸出来。对于V-e b> 350埃(3)，相图以扩展的低维结构为主，这些结构在高压下压缩成二维泡沫状相。这种行为被合理化为源于相邻粒子的配体壳的相互渗透。当V-e < 350埃(3)时，金属芯间的色散吸引主导了粒子的凝聚。在350埃(3)> V-e > 150埃(3)时，颗粒凝聚形成最紧密的排列结构，对于足够窄的粒径分布，其特征是结晶相。当V-e接近30埃(3)时，粒子不可逆地聚集成类似于扩散限制聚集（DLA）模型所期望的结构。报道了某些最致密相LB膜的光学性质。
The phase behavior of organically passivated 20-75 Angstrom diameter Ag and Au nanocrystals is investigated by examining surface-area isotherms of Langmuir monolayers and transmission electron micrographs of Langmuir-Blodgett (LB) films. The effects of temperature, organic passivant chain length, and nanocrystal size and composition are studied. Three distinct types of phase behavior are observed and may be classified in terms of the extra (conical) volume (V-e) available to the alkyl capping group as it extends from a nearly spherical metal core. For V-e > 350 Angstrom(3), the phase diagram is dominated by extended, low-dimensional structures that, at high pressures, compress into a two-dimensional foamlike phase. This behavior is rationalized as originating from the interpenetration of the ligand shells of adjacent particles. For V-e < 350 Angstrom(3), dispersion attractions between the metal cores dominate particle condensation. For 350 Angstrom(3) > V-e > 150 Angstrom(3), the particles condense to form closest packed structures, which, for sufficiently narrow particle size distributions, are characterized by crystalline phases. For V-e approximate to 30 Angstrom(3), the particles irreversibly aggregate into structures similar to those expected from a diffusion-limited-aggregation (DLA) model. Optical properties of certain LB films of the closest packed phases are reported.