Figure 1

(Color online) Constant current images for cleavage of ${\text{BaFe}}_{1.86}{\text{Co}}_{0.14}{\text{As}}_2$ at low temperature $\left(<80\text{K}\right)$. (a) and (b) are taken on the same cleave using a junction resistance $R_J=2.4\text{G}\Omega$, (c) and (d) on a different cleave $\left(R_J=0.65\text{G}\Omega \right)$. Inset of (b): Fourier transform of (b) highlighting the unit-cell spots (circles) and $2\times 1$ reconstruction spot (arrow). All topographic types shown have been observed on numerous cleaves. Line scans along the paths indicated are shown below each panel. The insets of (c) and (d) show enlargements of size $189\text{Å}$. Axes indicate the crystallographic orientation as determined from LEED.Reuse & Permissions

Figure 2

(Color online) Constant current images for various cleaves of ${\text{BaFe}}_{1.86}{\text{Co}}_{0.14}{\text{As}}_2$ at room temperature $\left(R_J\sim 0.75\text{G}\Omega \right)$. Line scans along the paths indicated are shown below each panel. The insets to (c) and (d) show enlargements of size $189\text{Å}$. Axes indicate the crystallographic orientation as determined from LEED.Reuse & Permissions

Figure 3

(Color online) Constant current images of ${\text{Fe}}_{1.07}{\text{Se}}_{0.45}{\text{Te}}_{0.55}$, $V_{\text{sample}}=20\text{mV}$, and $I_{\text{set}}=2\text{nA}$. (a) Large field of view with the inset showing the Fourier transform with spots corresponding to the atomic lattice vector (black arrow) and higher order spots (gray arrow). (b) Zoom of the box in panel (a) showing the atomic resolution, visible even on the bright blobs.Reuse & Permissions

Figure 4

(Color online) Low-energy electron diffraction, taken at 110 eV. (a) ${\text{BaFe}}_{1.86}{\text{Co}}_{0.14}{\text{As}}_2$ cleaved and measured at 17 K. The spots marked with a circle are the tetragonal $\left(\frac{1}{2},0\right)$ (white), $\left(\frac{1}{2},\frac{1}{2}\right)$ (gray), and $\left(\frac{1}{2},1\right)$ (black) reflections. (b) Same surface, but warmed up and measured at 200 K. (c) ${\text{Fe}}_y{\text{Se}}_{1-x}{\text{Te}}_x$, cleaved and measured at 17 K. (d) I(v) trace of the $\left(\frac{1}{2},\frac{1}{2}\right)$ spot. (e) Sketch of various possible Ba surface overlayer configurations. Large (small) circles indicate the presence (absence) of a Ba atom. The dotted atom (left top) indicates a missing atom resulting in a black spot in topography. Extra atoms can similarly lead to bright spots. Antiphase boundaries are shown running along two observed directions. Broader “backbones” in the ribcage structure are created by adding atoms at the phase-shift boundary.Reuse & Permissions