FIG. 1: (a) 3.5 nm × 3.5 nm STM images and (b) line profiles along unit vector a 1 , a 2 , and a 3 . I$_{ai}$ is the amplitude of the line profiles along a i . Sample A was cleaved in 10 $_{−}$8 Torr at 77 K and measured in situ at a sample bias voltage of V$_{s}$ =150 mV and a initial tunnelling current of I$_{t}$=0.3 nA at T=84 K. (c) FFT image of sample A and (d) line profiles along q 1 , q 2 , q 3 wave vector. I$_{qi}$ is the intensity of the line profiles along q i . FFT was performed over the entire field of view (25 nm × 25 nm) of STM image. 9