Molecular bandgap engineering of bottom-up synthesized graphene nanoribbon heterojunctions
Molecular bandgap engineering of bottom-up synthesized graphene nanoribbon heterojunctions
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DOI：
10.1038/nnano.2014.307
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发表时间：
2015-02-01
影响因子：
38.3
通讯作者：
Crommie, Michael F.
中科院分区：
文献类型：
--
作者：
Chen, Yen-Chia;Cao, Ting;Crommie, Michael F.
带隙工程用于制造半导体异质结构器件，这些器件可进行诸如共振隧穿（1,2）和太阳能转换（3,4）等过程。然而，此类器件的性能会随着其尺寸减小而降低（5,6）。基于石墨烯的分子电子学已成为在单分子尺度上实现高性能的一个候选方案（7 - 17）。例如，石墨烯纳米带的宽度可小于2纳米，并且其带隙可通过宽度和对称性进行调节（6,18,19）。据预测，通过改变纳米带内共价键合片段的宽度，可在单个石墨烯纳米带内实现带隙工程（20 - 22）。在此，我们展示了这种宽度调制的扶手椅型石墨烯纳米带异质结构的自下而上合成，它是通过融合由两种不同分子构建单元制成的片段而获得的。我们利用扫描隧道显微镜和光谱学在亚纳米长度尺度上研究这些异质结，并确定了它们空间调制的电子结构，展示了分子尺度的带隙工程，包括I型异质结行为。第一性原理计算支持这些发现，并为带隙工程化的石墨烯纳米带异质结的微观电子结构提供了深入见解。
Bandgap engineering is used to create semiconductor hetero-structure devices that perform processes such as resonant tunnelling(1,2) and solar energy conversion(3,4). However, the performance of such devices degrades as their size is reduced(5,6). Graphene-based molecular electronics has emerged as a candidate to enable high performance down to the single-molecule scale(7-17). Graphene nanoribbons, for example, can have widths of less than 2 nm and bandgaps that are tunable via their width and symmetry(6,18,19). It has been predicted that bandgap engineering within a single graphene nanoribbon may be achieved by varying the width of covalently bonded segments within the nanoribbon(20-22). Here, we demonstrate the bottom-up synthesis of such width-modulated armchair graphene nanoribbon heterostructures, obtained by fusing segments made from two different molecular building blocks. We study these heterojunctions at subnanometre length scales with scanning tunnelling microscopy and spectroscopy, and identify their spatially modulated electronic structure, demonstrating molecular-scale bandgap engineering, including type I heterojunction behaviour. First-principles calculations support these findings and provide insight into the microscopic electronic structure of bandgap-engineered graphene nanoribbon heterojunctions.