Figure shows a typical low-magnification annular dark field scanning TEM (ADF-STEM) image of the exfoliated hBN, showing a random stacking of micrometer-sized hBN layers. A high-magnification ADF-STEM image of nontwisted hBN layers are given in Fig. , illustrating 2D honeycomb structures of BN. Each single hexagonal ring consists of three boron and three nitrogen atoms, which can be distinguished by their intensity based on the Z-(atomic number) contrast principle (see the line profile in Fig. ). An HRTEM image shown in Fig. demonstrates that the resulting layers have a clean and adsorbates-free area extending tens of nanometers (see also Fig. ). The corresponding fast Fourier transform (FFT) image yields six spots of 0.21, 0.12 and 0.11 nm spacings attributed, respectively, to 100, 110 and 200 Bragg peaks (inset of Fig. ). Figure shows the edge area with four BN layers (see also the line profile in Fig. ). Any moiré patterns and the related rotational stacking faults are not present at the edge, indicating that the edges are not folded back bur rather exhibit the smallest possible scroll, as often observed in the edge structures of highquality free-standing graphene layers. Figure is the PPA strain mapping obtained for the HRTEM image shown in Fig. . As shown in Fig. , the stain tensor is estimated to be as low as 1 % over the entire region of interest (see Fig. for more details of the PPA analysis). All the above results demonstrate that as far as the non-twisted hBN layers are concerned, atomically clean, flat and strain-free samples can be obtained by the present exfoliation procedure.