EAGER: Interfacing Nanotubes and Graphene into Ordered Crystallographic Orientations Through Substrate-Induced Strain

Material interfaces are critically important in modern electronics, yet their precise crystallographic orientation does not typically play a significant role in conventional devices. In contrast to these conventional electronics, it is expected that for future devices, with overall sizes reduced to nanometer scales, the precise orientation of the interfaces will play a critical role in determining how current travels between the material components. In particular, ‘lego-snapped’ interfaces that consist of lattice-matched nanomaterials should lead to the transport being dominated by quantum, rather than diffusive, phenomena which could transform nanoscale devices. Moreover, there has been tremendous interest in the growing class of atomically-thin materials (such as MoS2, carbon nanotubes (CNTs), and graphene) for use in nanoscale electronics due to their extremely reduced dimensions. Thus, the ability to lego-snap the interfaces of these materials with mass-scale reproducibility and specificity is of great importance to future nanoelectronics. Achieving this goal, however, requires a fundamental understanding of the relevant interactions at the interfaces of these atomically-thin nanomaterials. As an important step in our long-term goal of understanding and controlling the relevant interactions of legosnapped atomically-thin materials, we will investigate the crystallographic alignment of CNTs and graphene through a systematic tuning of the competing interaction-scales. That such interfaces are of fundamental scientific importance is based on theoretical work indicating that graphitic interfaces (like those between CNTs and graphene) depend sensitively on their relative lattice orientation, and can become ballistic when legosnapped over extremely short (~ 10 nm) lengths due to coherent quantum effects.1-4 The work proposed here is based on our groundbreaking discovery that CNTs can be grown crystallographically-aligned to the three ‘armchair’ axes of graphene5 – the first demonstration that such lego-snapped interfaces can be formed on a mass scale (Fig. 1). Moreover, we have recently discovered that CNTs can be integrated into snapped crystallographic-orientations with graphene nanoribbons and etch tracks6 in device-like geometries -- making the synthesis relevant to future integrated sub-10 nm scale electronics. While my group and our collaborators have made the groundbreaking discoveries of crystallographicallyaligned CNTs,5,7 etch tracks,8,9 and their integration,6 these alignments generally occur along all three equivalent ‘armchair’ directions of the underlying graphene lattice. Potential applications of these nanoscale interfaces would greatly benefit from large-scale lego snapping along one specific armchair direction. To achieve such large-scale single-axis alignment requires an understanding of the fundamental competing interactions that control lego-snapping of atomically-thin materials. This understanding will be obtained through the following two aims using external competing interactions of an underlying crystal substrate having a grooved surface (Fig. 2),10 thereby introducing the necessary anisotropy. (1) The lego-snapping between CNTs and graphene will be determined as function of the relative crystal orientation of the graphene and the underlying crystal grooves; providing a direct indication of their relative alignment strengths. (2) The lego-snapping between CNTs and graphene will be examined as a function of the graphene layer number; determining the persistence of alignment mechanisms upon the film becoming structurally rigid as its thickness increases. Broader Impacts: The interfaces that will be achievable upon completion of the proposed work could have broad uses in future ultra-fast electronics (such as amplifiers, switches, and mixers) or for quantum computing where phase-coherent ballistic transport is critical. In addition, the low contact resistance expected for the lego-snapped interfaces could help achieve high-efficiency electronics that minimize deleterious heat dissipation – one of the major issues facing future electronics.11 The resulting insight into the mechanisms that dictate lego snapping of atomically-thin materials will also make the work broadly relevant to the science of this important class of nanomaterials. For example, the strained puckered regions that likely play a role in the alignment of CNTs to graphene are also thought to have a significant impact on frictional dissipation mechanisms, which are important due to the ubiquitous use of atomically-thin materials (like graphene and MoS2) as dry lubricants for minimizing one of the world’s greatest mechanical energy losses. Finally, the proposed work should povide critical information regarding the mechanisms for locally-forming to lego-snapped regions between a variety of atomically-thin materials, which has recently garnered significant attention for achieving behaviors beyond those of the bare constituents.