热处理增强Au纳米颗粒超薄膜光电子发射的研究

Annealing-enhanced photoelectron emission from ultra-thin Au nanoparticle film

本文制备了平均直径为1.4 nm的11-巯基十一烷酸(Mercaptoundecanoic acid,MUA)修饰的金纳米颗粒,随后通过硅晶片上壳聚糖薄涂层静电吸附制备了厚度约为10 nm的超薄膜,原子力显微镜(Atomic Force Microscopy,AFM)和扫描电子显微镜(Scanning Electron Microscopy,SEM)表明金纳米颗粒在薄膜中分布较为均匀且薄膜较平整。进一步采用紫外光电子能谱(Ultraviolet Photoelectron Spectroscopy,UPS)研究了不同热处理温度对超薄膜的二次电子发射能力的影响。结果表明,适度的热处理有助于超薄膜二次电子发射强度的提高,尤其是经150°C热处理的薄膜二次电子发射峰强是未处理样品的4倍,更高的热处理温度造成二次电子发射峰强度急剧下降。本文结果有助于推动有机配体金纳米颗粒超薄膜在光电子发射材料方面的应用。

Background： Ligated Au nanoparticle （Au NP） thin films show enhanced photoemission due to the fact that Au-S chemical bonding significantly improves the Au NP-ligand interface transmission probability. Purpose： This study aims to investigate how annealing influences the secondary electron photoemission from ultra-thin ligated Au NP films. Methods： Transmission electron microscopy （TEM）, atomic force microscopy （AFM）, scanning electron microscopy （SEM）, synchrotron-based grazing incidence X-ray diffraction （GIXRD）, and ultraviolet photoelectron spectroscopy （UPS） were employed to study size distribution of ligated Au NP, surface morphology, elemental compositions, microstructure of the film, and photoelectron emission from the film, respectively. Results： Mercaptoundecanoic acid （MUA） ligated Au NP with an average diameter of -1.4 nm was used to fabricate ultrathin film with a thickness of 10 nm. AFM and SEM results showed that Au NP was distributed well and the film was quite smooth. Using SEM, it was found that S composition became less with increasing annealing temperature. UPS spectra revealed that the secondary electron photoemission peak from Au NP film after annealing at 150 ℃ was about 4 times larger than that of thin film without annealing. However, annealing at an even higher temperature caused a dramatic decrease of secondary electron photoemission. Conelusion： The present study demonstrated that an annealing at a proper elevated temperature enhanced the secondary electron photoemission from ultrathin MUA ligated Au NP films, which would promote applications of the ligated Au NP films as promising photoelectron-emission materials for photoelectron devices.