The Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, California 94720, United States.
J Am Chem Soc. 2014 May 14;136(19):7110-6. doi: 10.1021/ja502541z. Epub 2014 Apr 30.
Doped metal oxide nanocrystals represent an exciting frontier for colloidal synthesis of plasmonic materials, displaying unique optoelectronic properties and showing promise for a variety of applications. However, fundamental questions about the nature of doping in these materials remain. In this article, the strong influence of radial dopant distribution on the optoelectronic properties of colloidal indium tin oxide nanocrystals is reported. Comparing elemental depth-profiling by X-ray photoelectron spectroscopy (XPS) with detailed modeling and simulation of the optical extinction of these nanocrystals using the Drude model for free electrons, a correlation between surface segregation of tin ions and the average activation of dopants is observed. A strong influence of surface segregation of tin on the line shape of the localized surface plasmon resonance (LSPR) is also reported. Samples with tin segregated near the surface show a symmetric line shape that suggests weak or no damping of the plasmon by ionized impurities. It is suggested that segregation of tin near the surface facilitates compensation of the dopant ions by electronic defects and oxygen interstitials, thus reducing activation. A core-shell model is proposed to explain the observed differences in line shape. These results demonstrate the nuanced role of dopant distribution in determining the optoelectronic properties of semiconductor nanocrystals and suggest that more detailed study of the distribution and structure of defects in plasmonic colloidal nanocrystals is warranted.
掺杂金属氧化物纳米晶体代表了胶体合成等离子体材料的一个令人兴奋的前沿领域，具有独特的光电性能，并有望在各种应用中得到应用。然而，关于这些材料中掺杂的本质的基本问题仍然存在。本文报道了径向掺杂分布对胶体氧化铟锡纳米晶体光电性能的强烈影响。通过 X 射线光电子能谱（XPS）对元素深度分布进行比较，以及使用自由电子的 Drude 模型对这些纳米晶体的光吸收进行详细建模和模拟，观察到锡离子表面偏析与掺杂剂平均激活之间的相关性。还报道了锡的表面偏析对局域表面等离子体共振（LSPR）线形状的强烈影响。表面附近有锡偏析的样品显示出对称的线形状，表明等离子体由离化杂质引起的阻尼较弱或没有。据认为，表面附近的锡偏析有助于电子缺陷和氧间隙对掺杂离子的补偿，从而降低激活。提出了一种核壳模型来解释观察到的线形状差异。这些结果表明，掺杂分布在确定半导体纳米晶体的光电性能方面起着细微的作用，并表明有必要更详细地研究等离子体胶体纳米晶体中缺陷的分布和结构。
