By adapting the concept of epitaxy to two-dimensional space, we show the growth of a single-atomic-layer, in-plane heterostructure of a prototypical material system--graphene and hexagonal boron nitride (h-BN). Monolayer crystalline h-BN grew from fresh edges of monolayer graphene with atomic lattice coherence, forming an abrupt one-dimensional interface, or boundary. More important, the h-BN lattice orientation is solely determined by the graphene, forgoing configurations favored by the supporting copper substrate.

With the rise of graphene research since 2004, the past few years have witnessed rapid progreess in exploiting graphene as an electronic material that shows great promise for future nanoelectronic devices. [1][2][3] Particular interest in this regard stems from the remarkable electronic properties of graphene, ranging from the extremely high mobility to the tunable carrier type and density. [ 1 , 2 ] However, the fact that graphene is a zero-bandgap semimetal poses a major problem for its practical applications in making high-performance fi eld-effect transistors (FETs). [ 2 , 3 ] As to how an energy gap can be induced in graphene, a known paradigm is to fabricate 1D ultranarrow graphene nanoribbons (GNRs) in which the lateral confi nement of charge carriers creates an energy gap near the charge neutrality point. [3][4][5][6][7][8][9][10][11][12][13][14] Experimentally, ultranarrow GNRs were fi rst fabricated by standard electron beam lithography (EBL) patterning in combination with reactive O 2 plasma etching of graphene sheets; [ 5 , 6 ] however EBL is known to be limited by its serial processing nature, low throughput, and high cost. Later on, the chemically derived GNRs produced via a solution processing route were reported as an alternative, but the synthetic yield was quite low. [ 7 ] More recently, some other strategies, e.g., the longitudinal unzipping of carbon nanotubes, [8][9][10] the inorganic nanowire, [ 11 ] and diblock copolymer [12][13][14] templated etching of graphene sheets, have also been proposed and demonstrated. Despite these important advances, an increasing demand for rapid, massively parallel, high-throughput, and low-cost fabrication strategies for ultranarrow GNRs continues to motivate research.Here, we present an innovative approach for ultranarrow GNRs fabrication by utilizing nanosphere lithography (NSL) [ 15 ] in combination with low-power O 2 plasma etching. NSL, a technique that takes advantage of the self-assembled, ordered arrays of latex nanospheres as lithographic masks for deposition of various metal nanostructures, has long been known to be a inherently parallel, high-throughput, and low-cost nanofabrication strategy. [ 15 ] However, in general, a perceived limitation of a common NSL process has been that it can only produce a limited range of nanostructure shapes that are determined by the projection of the nanosphere mask interstices onto underlying substrates. [ 15 , 16 ] In this work, when applying NSL nanopatterning for the lithographic etching of graphene sheets, we surprisingly found that it was capable of fabricating a variety of interesting 1D-based nanoribbon structures. It is shown that the non-uniform and anisotropic distribution of plasma ion, as mediated by the NSL masks, provides a subtle reason for the etching formation of nanoribbons. By proper adjustment of the plasma process parameters, a precision control of the nanoribbon widths is achieved in a size regime comparable with the standard EBL approach. [ 5 , 6 ] Remarkably, due to its unusual simplic...

Two-dimensional interfaces between crystalline materials have been shown to generate unusual interfacial electronic states in complex oxides. Recently, a one-dimensional interface has been realized in hexagonal boron nitride and graphene planar heterostructures, where a polar-on-nonpolar one-dimensional boundary is expected to possess peculiar electronic states associated with edge states of graphene and the polarity of boron nitride. Here we present a combined scanning tunnelling microscopy and first-principles theory study of the graphene-boron nitride boundary to provide a first glimpse into the spatial and energetic distributions of the one-dimensional boundary states down to atomic resolution. The revealed boundary states are about 0.6 eV below or above the Fermi level depending on the termination of the boron nitride at the boundary, and are extended along but localized at the boundary. These results suggest that unconventional physical effects similar to those observed at two-dimensional interfaces can also exist in lower dimensions.

A suspended graphene oxide device is fabricated and investigated using a transmission electron microscope (TEM) scanning tunneling microscope (STM) setup. A detailed study of step-by-step reduction of an individual graphene oxide sheet under current flow and Joule heating in tandem with conductivity measurements, atomic structure imaging, chemical composition, and bonding alternations tracing is performed. As monitored by electron energy loss spectroscopy, the oxygen content is tuned from that peculiar to a pristine graphene oxide (i.e., 23.8 at %) to oxygen-free pure graphene. Six orders of magnitude conductance rise is observed during this process with the final conductivity reaching 1.5 × 10(5) S/m. Quantification of plasma energy losses of the starting graphene oxide shows that ∼40% of the oxygen atoms are in the form of epoxy, and ∼60% oxygen atoms are in the form of hydroxyl. The total portion of sp(3) bonds in pristine graphene oxide is estimated to be ∼45%. The epoxy groups show a larger influence on the conductivity of graphene oxide than hydroxyl ones. Through analyzing consecutive plasma-loss energy spectra under gradual graphene oxide to graphene transformation, it is found that the oxygen atoms in epoxy groups decompose prior to those in hydroxyl groups.