Fig. 2. Low-energy electronic structure at the terminations of the Fe, Mn, and Co chains.

a Constant-current scanning tunneling microscope (STM) image of the end of a Fe₂₀ chain. b Differential tunneling conductance along the Fe₂₀ chain aligned with the topography shown in (a). c dI/dV spectra of the Fe₂₀ chain and substrate taken at the positions marked by crosses in (a) (V_stab = 1 mV, I_stab = 0.2 nA, and V_mod = 20 µV). d dI/dV spectrum on the chain’s end from (c) normalized by subtraction of a spectrum averaged along the chain’s interior. e Constant-current STM image of the end of a Mn₁₀₁ chain. f Differential tunneling conductance along the Mn₁₀₁ chain. g dI/dV spectra of the Mn₁₀₁ chain and substrate taken at the positions marked by crosses in (e) (V_stab = 1 mV, I_stab = 0.5 nA, and V_mod = 40 µV). h dI/dV spectrum on the chain’s end from (g) normalized by subtraction of a spectrum averaged along the chain’s interior. i Constant-current STM image of the end of a Co₈₄ chain. j Differential tunneling conductance along the Co₈₄ chain. k dI/dV spectra of the Co₈₄ chain and substrate taken at the positions marked by crosses in (i) (V_stab = 1 mV, I_stab = 0.5 nA, and V_mod = 40 µV). l dI/dV spectrum on the chain’s end from (k) normalized by subtraction of a spectrum averaged along the chain’s interior. All data (a, e, i) are recorded with V = 6 mV, I = 0.2 nA. Arrows in (b, c, f, g): see text.