Figure 1

(a) Constant-current STM image ($120\AA \times 57\AA$) of a single Cu (left) and a Co adatom (right) on Cu(111); panels (b) to (e) show images ($30\AA \times 15\AA$) of a pure ${\mathrm{Cu}}_5$ chain (b) and five-atomic Co-Cu chains [(c)–(e)] of various composition as indicated, together with the corresponding height profiles measured along the chain axis (f). All images taken at 0.1 nA, 0.1 V, and 7 K.Reuse & Permissions

Figure 2

$dI/dV$ spectra of Co-Cu chains comprised of $N=3$ [(a),(b)] and $N=5$ atoms [(c)–(f)] indicated by black curves; sphere models show the chain structure with Co (Cu) atoms in black (white) and the tip position during $dI/dV$ detection. Systematic downward shifts $\Delta E$ in binding energy are observed for the ground state ($n=1$) and the first excited state resonance ($n=2$) relative to the simultaneously measured resonances of pure ${\mathrm{Cu}}_N$ reference chains (gray curves). Panel (g) shows the resonance peak shifts $\Delta E$ observed for various Co-Cu chains (black symbols) compared to tight-binding-calculated values (open symbols). Set point current and bias: 0.1 nA, 0.1 V; tip retraction prior to bias ramping at constant tip height: 0.4 Å [(c),(d)], and 1.3 Å [(a),(b),(e),(f)]; lock-in modulation amplitude and frequency: 25 mV and 670 Hz.Reuse & Permissions

Figure 3

Constant-current images ($37\AA \times 18\AA$, 0.1 nA, 0.1 V) of a ${\mathrm{Cu}}_8$ (a) and a ${\mathrm{Cu}}_3{\mathrm{CoCu}}_4$ chain (b) along with the corresponding height profiles (c). $dI/dV$ maps ($37\AA \times 18\AA$) of the ground state (d) and the first (e) and second excited state (f) of the ${\mathrm{Cu}}_3{\mathrm{CoCu}}_4$ chain; basic features of the corresponding LDOS profiles measured along the chain axis (h) are qualitatively reproduced by the tight-binding-calculated state density profiles (g). Set point current and bias prior to $dI/dV$ mapping at constant tip height: 0.1 nA, 0.2 V.Reuse & Permissions