Department of Mechanical Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States.
Department of Materials Science and Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States.
Nano Lett. 2017 Jan 11;17(1):220-227. doi: 10.1021/acs.nanolett.6b03894. Epub 2016 Dec 8.
The effect of the local molecular environment on thermal transport through organic-inorganic heterojunctions is investigated using binary self-assembled monolayer (SAM) junctions built from a mixture of alkanethiol and alkanedithiol species sandwiched between gold leads. Thermoreflectance measurements and molecular dynamics simulations demonstrate that the thermal conductances of the binary SAM junctions vary with molecular composition and are greater than predictions of a parallel resistance model. The enhancement results from increased thermal transport through the alkanethiols, whose terminal methyl groups are confined by the anchored alkanedithiols. This confinement effect extends over length scales that are more than twice the range of the van der Waals interactions between molecules and are commensurate to the sizes of experimentally observed molecular domains. Conversely, for a partially packed (i.e., submonolayer) alkanedithiol unary SAM, increasing the molecular packing density decreases the per molecule thermal conductance. This finding indicates that thermal transport measurements of SAMs cannot be used to predict the thermal transport properties of single molecules.
采用由金电极夹在中间的混合烷硫醇和烷二硫醇自组装单分子层（SAM）结，研究了局部分子环境对有机-无机杂化结中热输运的影响。热反射测量和分子动力学模拟表明，二元 SAM 结的热导与分子组成有关，并且大于平行电阻模型的预测。这种增强是由于通过烷硫醇的热传输增加，其末端甲基被锚定的烷二硫醇限制。这种限制效应的延伸超过了分子间范德华相互作用的范围的两倍以上，与实验观察到的分子域的大小相当。相反，对于部分填充（即亚单层）的烷二硫醇单分子层，增加分子堆积密度会降低每个分子的热导率。这一发现表明，SAM 的热传输测量不能用于预测单个分子的热传输性质。
