CO Induced Single and Multiple Au Adatoms Trapped by Melem Self-Assembly
CO Induced Single and Multiple Au Adatoms Trapped by Melem Self-Assembly
复制标题
CO 诱导 Melem 自组装捕获的单个和多个 Au 吸附原子
DOI：
10.3866/pku.whxb201804191
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
SHAO Xiang
中科院分区：
文献类型：
--
作者：
HUANG Lili;SHAO Xiang
金属吸附原子的可控性一直受到越来越多的关注，因为金属物种，特别是单原子金属可以在各种表面过程中发挥重要作用，包括多相催化反应。另一方面，有机自组装薄膜被认为是一种高效且通用的自下而上制造表面纳米结构的方法，其功能和周期性可以高度设计。在这项工作中，我们开发了一种新颖的策略，通过将表面自组装与暴露于小无机气体分子相结合来引导金属吸附原子的产生和分布。更具体地说，我们在 Au(111) 表面上制备了基于结构良好的氢键网络的蜜勒姆（三氨基-s-庚嗪）蜂窝结构。所实现的蜜勒姆自组装体包含直径约 1 nm 的周期性六角形孔。更重要的是，纳米孔的外围装饰有杂环N原子，它们可能与金属物质形成强烈的相互作用。在室温下将蜜勒姆自组装体暴露于 CO 气氛中时，会产生相当数量的金吸附原子，并被捕获在被蜜勒姆分子包围的纳米孔内。高分辨率扫描隧道显微镜（STM）图像证实，单个或簇状的金空位同时形成，这些空位也被梅勒姆孔捕获并被周围分子稳定。两种类型的添加物质均与 CO 暴露呈正相关，并在 0.01 单层左右饱和。此外，由于孔径较大，以及纳米孔内存在多个对接位点，蜜勒姆纳米孔中可以驻留多个Au吸附原子；它们可以分布在双金（两个金吸附原子）和三金（三个金吸附原子）物种的各种配置中，其数量可以通过二氧化碳暴露来控制。此外，对照实验表明，这些 CO 诱导的 Au 物种（包括吸附原子和空位）可以在退火处理中幸存下来，直至蜜勒姆分子开始解吸的温度，这表明具有相当大的热稳定性。形成的金物质可能具有作为表面反应活性位点的巨大潜力。更有趣的是，双金和三金物种具有适中的金-金区间，并且可能对某些结构敏感的双分子反应具有潜在活性。考虑到所有这些方面，我们相信这项工作提出了一种利用有机自组装薄膜的新方法，并展示了一种在基材表面制备各种单原子金属物种的相当新颖的策略。
The controllability of metal adatoms has been attracting ever-growing attention because the metal species in particular single-atom metals can play an important role in various surface processes, including heterogeneous catalytic reactions. On the other hand, organic self-assembly films have been regarded as an efficient and versatile bottom-up method to fabricate surface nanostructures, whose functionality and periodicity can be highly designable. In this work, we have developed a novel strategy to steer the generation and distribution of metal adatoms by combining the surface self-assemblies with exposure to small inorganic gaseous molecules. More specifically, we have prepared a honeycomb structure of melem (triamino-s-heptazine) on the Au(111) surface based on a well-structured hydrogen bonding network. The achieved melem self-assembly contains periodic hexagonal pores having diameters as large as around 1 nm. More importantly, the peripheries of the nanopores are decorated with heterocyclic N atoms that can probably form strong interactions with the metal species. Upon exposing the melem self-assembly to a CO atmosphere at room temperature, a fair number of Au adatoms were produced and trapped inside the nanopores encircled by the melem molecules. Single or clustered Au vacancies were concomitantly formed that were also trapped by the melem pores and stabilized by the surrounding molecules, as confirmed by high-resolution scanning tunneling microscopy (STM) images. Both types of added species showed positive correlations with the CO exposure and saturated at around 0.01 monolayer. In addition, owing to the large pore size, as well as the presence of multiple docking sites inside the nanopores, more than one Au adatom can reside in a melem nanopore; they can be distributed in a variety of configurations for bi-Au (two Au adatoms) and tri-Au (three Au adatoms) species, whose population can be manipulated with the CO exposure. Moreover, control experiments demonstrated that these CO-induced Au species, including the adatoms and vacancies, can survive annealing treatments up to the temperature at which the melem molecules start to desorb, indicating a substantial thermal stability. The formed Au species may hold great potential for serving as active sites for surface reactions. More interestingly, the bi-Au and tri-Au species have moderate Au-Au intervals, and can be potentially active for certain structurally sensitive bimolecular reactions. Considering all these aspects, we believe that this work presents a fresh approach to utilizing organic self-assembly films and has demonstrated a rather novel strategy for preparing various single-atom metal species on substrate surfaces.