Research ArticleMATERIALS SCIENCE

In situ manipulation and switching of dislocations in bilayer graphene

See allHide authors and affiliations

Science Advances  10 Aug 2018:
Vol. 4, no. 8, eaat4712
DOI: 10.1126/sciadv.aat4712
  • Fig. 1 Overview of the dislocation manipulation.

    (A) Artistic representation of the manipulation process. Dislocations in bilayer graphene, which relax into atomic-scale topographic ripples, can be controlled using a fine tip mounted on a piezo-driven micromanipulator. (B) Overview of the types of dislocations to be considered for this work: In-plane dislocations are mobile contrary to the sessile out-of-plane dislocations. In-plane dislocations are of the partial type and necessitate a stacking fault between them. (C) Schematic representation of the in situ setup in the SEM. A low-energy electron probe is scanned over a graphene flake on a TEM grid. The transmitted electrons carrying the crystallographic information are detected with a segmented detector, allowing bright-field and different DF imaging modes (see fig. S2 for details on contrast formation). Micromanipulators can be placed below and above the sample to allow access from both sides for manipulations and mechanical cleaning. (D to F) Exemplary in situ dislocation manipulation process: Three dislocations are visible at the upper part of the hole in the support film. Dislocations 1 and 2 (as well as 3 and 2) enclose a different stacking order of AC stacking, compared to the AB stacking elsewhere. (E) Using a micromanipulator, the dislocations can be extended to about three times their length, in turn also changing their character from dominantly screw type to edge type and vice versa. The interaction of the dislocations also results in a dislocation reaction, creating an intersection that includes the energetically unfavorable AA stacking [see fig. S6 for high-resolution TEM (HRTEM) of such an intersection]. (F) Releasing the micromanipulator leads to an almost complete reversal of the dislocation structure due to line tension.

  • Fig. 2 Switching reactions at a dislocation array pinned at out-of-plane dislocations.

    (A) Overview of the membrane containing an array: Pairs of in-plane partial dislocations are pinned at out-of-plane dislocations. Because those dislocations all lie on a line, there is a small-angle tilt grain boundary (ca. 0.2°) in the first layer. (B) The magnification of several dislocation lines shows the alternating screw and edge character of the defects. The contrast width in the tSEM images fits very well to the relation between Burgers vector and line direction (see also fig. S4). a.u., arbitrary units. (C) Proposed growth mechanism of the in-plane dislocations: A perfect out-of-plane dislocation is present in the first layer. Upon growth of the second layer, the dislocation line turns perpendicular to the original direction and follows the growth of the second layer. To minimize the energy of the system, the dislocation splits into two partial dislocations. (D to G) Frames from an in situ experiment with a fine tip (see movies S3 and S4), in which dislocation switching reactions were observed. For each image, a schematic representation including information about Burgers vectors, stacking orders, and dislocation labeling is shown. Because of the influence of the manipulator, the dislocations are forced to move, and different line segments and areas with the same stacking order recombine. Dislocation A, for instance, is attached to out-of-plane dislocation I at the beginning of the manipulation but changes its attachment step by step to be finally linked to out-of-plane dislocation III. During this process, the two green AC stacked areas also combine to form a larger area of this stacking, in turn dividing the area of AB stacking, meaning that it is possible to travel from one area to the other without crossing a topological defect.

  • Fig. 3 Schematic representation of a topological switch with potential functional properties and the switching process.

    (A) Perspective view of the switch in the “On” position. A defined dislocation configuration is contained in a ribbon of bilayer graphene contacted at two sides. Mechanical switching (B) can change the dislocation state from an open to a closed configuration (C), meaning that, traversing the membrane, a topological defect is encountered in one state, while none is encountered in the other state (30). (D) Graphene membrane with a real dislocation configuration similar to the proposed switch, which could be transformed into the element by lithographic means. (E) The detailed process of the switching reaction from On to Off: Extension of a partial dislocation in the direction of the second out-of-plane dislocation leads to a recombination of dislocation lines. Line tension then straightens the dislocations to a defined state of minimal energy, with two dislocation lines running parallel through the ribbon. The configuration can be switched back (F) by connecting the other partial to the second out-of-plane dislocation.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/8/eaat4712/DC1

    Fig. S1. Stacking orders in bilayer graphene.

    Fig. S2. Imaging modes in tSEM.

    Fig. S3. Manipulation of a dislocation without mechanical cleaning.

    Fig. S4. The relationship between dislocation type and line width.

    Fig. S5. Example demonstrating the interplay of membrane topography and dislocation line direction.

    Fig. S6. AA stacking in dislocation nodes.

    Fig. S7. Complete analysis of the Burgers vector of dislocations.

    Fig. S8. Dislocation interaction with free edges.

    Movie S1. Exemplary cleaning of bilayer graphene.

    Movie S2. Manipulation of three individual dislocations showing fundamental properties of dislocations.

    Movie S3. Manipulation of an array of dislocations pinned to threading dislocations.

    Movie S4. The whole, unabridged manipulation from movie S3.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Stacking orders in bilayer graphene.
    • Fig. S2. Imaging modes in tSEM.
    • Fig. S3. Manipulation of a dislocation without mechanical cleaning.
    • Fig. S4. The relationship between dislocation type and line width.
    • Fig. S5. Example demonstrating the interplay of membrane topography and dislocation line direction.
    • Fig. S6. AA stacking in dislocation nodes.
    • Fig. S7. Complete analysis of the Burgers vector of dislocations.
    • Fig. S8. Dislocation interaction with free edges.
    • Legends for movies S1 to S4

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Exemplary cleaning of bilayer graphene.
    • Movie S2 (.mp4 format). Manipulation of three individual dislocations showing fundamental properties of dislocations.
    • Movie S3 (.mp4 format). Manipulation of an array of dislocations pinned to threading dislocations.
    • Movie S4 (.mp4 format). The whole, unabridged manipulation from movie S3.

    Files in this Data Supplement:

Navigate This Article