IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, United States.
Nano Lett. 2012 Jul 11;12(7):3431-6. doi: 10.1021/nl300563h. Epub 2012 Jun 5.
Wrinkling is a ubiquitous phenomenon in two-dimensional membranes. In particular, in the large-scale growth of graphene on metallic substrates, high densities of wrinkles are commonly observed. Despite their prevalence and potential impact on large-scale graphene electronics, relatively little is known about their structural morphology and electronic properties. Surveying the graphene landscape using atomic force microscopy, we found that wrinkles reach a certain maximum height before folding over. Calculations of the energetics explain the morphological transition and indicate that the tall ripples are collapsed into narrow standing wrinkles by van der Waals forces, analogous to large-diameter nanotubes. Quantum transport calculations show that conductance through these "collapsed wrinkle" structures is limited mainly by a density-of-states bottleneck and by interlayer tunneling across the collapsed bilayer region. Also through systematic measurements across large numbers of devices with wide "folded wrinkles", we find a distinct anisotropy in their electrical resistivity, consistent with our transport simulations. These results highlight the coupling between morphology and electronic properties, which has important practical implications for large-scale high-speed graphene electronics.
褶皱是二维膜中普遍存在的现象。特别是在金属衬底上大规模生长石墨烯时，通常会观察到高密度的褶皱。尽管褶皱普遍存在且可能对大规模石墨烯电子学产生影响，但人们对其结构形态和电子特性的了解相对较少。通过原子力显微镜对石墨烯进行扫描，我们发现褶皱在折叠之前会达到一定的最大高度。通过对能量学的计算可以解释这种形态转变，并表明高波纹会因范德华力而坍塌成狭窄的立起褶皱，类似于大直径的纳米管。量子输运计算表明，通过这些“坍塌褶皱”结构的电导主要受到态密度瓶颈和跨坍塌双层区域的层间隧穿的限制。通过对大量具有宽“折叠褶皱”的器件进行系统测量，我们发现它们的电阻率存在明显的各向异性，这与我们的输运模拟结果一致。这些结果突出了形态和电子特性之间的耦合，这对大规模高速石墨烯电子学具有重要的实际意义。
