Supporting Information. Anisotropic Etching of Hexagonal Boron Nitride and. Graphene: Question of Edge Terminations.

Transcription

1 Supporting Information Anisotropic Etching of Hexagonal Boron Nitride and Graphene: Question of Edge Terminations. Yijing Y. Stehle *, Xiahan Sang, Raymond R. Unocic, Dmitry Voylov, Roderick K. Jackson, Sergei Smirnov* and Ivan Vlassiouk* Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States University of Tennessee, Knoxville, Tennessee 37996, United States National Renewable Energy Laboratory, Golden, Colorado 80401, United States Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88011, United States 1

2 Figure S1. a. Typical EBSD maps of NiCu catalyst foil used for hbn and graphene growth. Mixed orientations are observed on the foil. EBSD patterns were acquired using a JEOL 6500 SEM, which was equipped with an EDAX EBSD System. b. Typical XRD of CuNi foil. XRD was measured using PANalytical Empyrean XRD using Cu K alpha X-ray source. 2

3 Figure S2. Additional images of etched complete hbn monolayer (similar to fig. 1b of the main text). Sample was heated on a hot plate after synthesis and etching step. Etched holes have yellow/red color due to oxidized CuNi catalyst surface. All etched triangular holes point to the same direction suggesting epitaxial growth on the CuNi catalyst. 3

4 Figure S3. hbn growth on the NiCu foils. SEM image (left) and EBSD map (right) of the same region. Over 85% of the observed hbn triangular crystals point in the same direction on individual domains suggesting that hbn crystals have preferable orientation on NiCu substrate (epitaxial growth). hbn crystal orientations are highlighted by lines having the same color as corresponding copper domain in EBSD map on the right. Circles highlights hbn crystals which are not oriented in the same direction with majority of the hbn crystals. 4

5 Figure S4. SEM images similar to Figure 2a showing hbn triangular crystals grown on the CuNi substrate after etching procedure. Crystals with triangular etched holes (highlighted by blue circles), as well hbn multilayers in the crystals center, are clearly seen. Percentage of hbn crystals with additional hbn layers in the center depend on the growth conditions including precursor (borazane) loading and the temperature for its sublimation, buffer gas flow through the tube and the growth temperature. These parameters can be optimized to yield almost exclusively single layer hbn crystals. [12] 5

6 Figure S5. Optical microscope image of hbn etched sample using argon as a buffer gas (bottom) on oxidized CuNi substrate and SEM image of a sample with transferred etched hbn triangular crystals onto SiO2/Si wafer (top). Fraction of etched holes varied from sample to sample reaching >80% as for the shown examples. 6

7 Figure S6. Additional optical images of etched graphene crystals on oxidized CuNi substrate (similar to figure 4b of the main text). a,b 10 min. etching; c,d 15 min. etching ; e 20 min. etching; f - 15 min. etching, lower magnification. 7

8 Figure S7. Additional examples of etched inversed triangles in hbn under nitrogen atmosphere: SEM image (top) and optical image (bottom). Inversed holes are highlighted by white dashed circles. 8

9 Figure S8. Additional examples of etched regular triangles (top) as well as hexagons and inversed triangles etched under nitrogen atmosphere in hbn (bottom). 9