Themis g2 300

The cross-sectional TEM specimen is prepared by the focused ion beam system (ThermoFisher Helios G4 UX). The HRTEM images, DF images, and SAED patterns are performed on FEI Tecnai F20 TEM operated at 200 kV. And the HAADF images and EDS mapping are acquired at a spherical aberration-corrected FEI electron microscope (Titan Cubed Themis G2 300) operated at 300 kV. The camera length in HAADF mode is set as 145 mm. The convergence semi-angle of HAADF is 30 mrad and the collection semi-angle of HAADF is 39–200 mrad.

Scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) were taken on a GeminiSEM 500 field emission scanning electron microscope operated at 5 kV with EDS detector. SEM, optical microscope (Nikon Eclipse LV150N), and atomic force microscopy (Cypher ES) were used to reveal the surface morphology of the films, and XPS (K-Alpha, Thermo Fisher) was performed to determine their chemical compositions. UV-visible absorption spectrum (MStarter ABS) was measured to estimate the band gap of single-layer hBN transferred to a quartz substrate. High-resolution transmission electron microscope (TEM) and selected area electron diffraction patterns were acquired on JEOL 2100 F at 300 kV from a flat area of the sample suspended on a Gold 300 mesh TEM grid (Quantifoil R1.2/1.3). The HAADF-STEM experiments were performed at 80 kV using FEI Titan Themis G2 300. Gases accumulated in the closed gas circulation system were analyzed by gas chromatography (GC 2010, Shimadzu Co., thermal conductivity detector, Ar carrier gas).

Scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) were taken on a GeminiSEM 500 field emission scanning electron microscope operated at 5 kV with EDS detector. SEM, optical microscope (Nikon Eclipse LV150N), and atomic force microscopy (Cypher ES) were used to reveal the surface morphology of the films, and XPS (K-Alpha, Thermo Fisher) was performed to determine their chemical compositions. UV-visible absorption spectrum (MStarter ABS) was measured to estimate the band gap of single-layer hBN transferred to a quartz substrate. High-resolution transmission electron microscope (TEM) and selected area electron diffraction patterns were acquired on JEOL 2100 F at 300 kV from a flat area of the sample suspended on a Gold 300 mesh TEM grid (Quantifoil R1.2/1.3). The HAADF-STEM experiments were performed at 80 kV using FEI Titan Themis G2 300. Gases accumulated in the closed gas circulation system were analyzed by gas chromatography (GC 2010, Shimadzu Co., thermal conductivity detector, Ar carrier gas).

The microstructure before tensile straining was then observed using the electron backscattered diffraction (EBSD) imaging in a ZEISS Gemini 300 scanning electron microscope with an EBSD detector. CMRO observations were conducted before and after tensile testing (thin foils were cut from the gauge section). All thin foils were mechanically polished to 50 μm thick, which then punched to discs of 3 mm in diameter for perforation using twin-jet electro-polishing. The observations were performed by the high-resolution transmission electron microscope (HR-TEM), along with an aberration-corrected high-angle annular dark-field (HAADF)-scanning transmission electron microscope (STEM) in an FEI Titan Cubed Themis G2 300 operated at 300 kV, equipped with a Super-X energy-dispersive X-ray spectroscopy (EDS) with four windowless silicon-drift detectors. The nano-beam diffraction was performed under the mode of TEM microprobe, with an electron beam spot diameter of 35 nm. The image was obtained by using the Flucam-Viewer with Sensitivity 6. The atomic-resolution EDS mapping was conducted at the count rate ranging from 180 to 500 cps and the dwell time was 5 μs per pixel with a map size of 512 × 512 pixels.

The nanostructures of the GNEC films were observed by transmission electron microscopy (FEI Titan Cubed Themis G2 300).