Figure 1

(Color online) [(a) and (b)] Adsorption geometry of a ${\text{C}}_{60}$ molecule on a (relaxed and unreconstructed) Cu(111) surface, in (a) side and (b) top views; only atoms in one $\left(4\times 4\right)$ unit cell and 4 resp. 1 layers are shown. (c) Atomic-projected DOS from SIESTA self-consistent results, compared with corresponding PDOS obtained by fitting EHT parameters to the SIESTA results. The labels refer to atomic layers and groups marked in panel (a); group Cu-1a is shown in yellow (light gray), while group Cu-1 is shown in red (dark gray).Reuse & Permissions

Figure 2

(Color online) Simulated normalized $I\text{−}V$ curves of ${\text{C}}_{60}$ on Cu(111) with various W tips and several tip-to-${\text{C}}_{60}$ positions [positions 1, 2, 3, and 4 as shown in panel (f)]. Side views of the tip geometries are shown in each panel; in panels (a), (b), (d), and (e), the tips are pyramids, the apex atom being mostly responsible for the tunneling; in (c) the apex atom has been removed and the tunneling involves mainly four atoms; in (d) and (e) the apex atom has been replaced by an O and a Cu atom, respectively. Panels [(a)–(c)] show that NDR occurs prominently with various W tips; panels (d) and (e) show that NDR is weakened with oxidized and Cu-terminated W tips. (f) Empty local-density-of-states image for the adsorption geometry shown in Fig. 1b. The gray hexagon indicates the top hexagonal ring of C atoms while numbers denote several lateral tip positions: position 1 places the center of the tip above one C atom, position 2 is over the center of a C-C bridge site, position 3 is over the center of the hexagonal ring, and position 4 is over the brightest point in the image (i.e., over an adjacent pentagonal ring).Reuse & Permissions

Figure 3

(Color online) Simulated normalized $I\text{−}V$ curves of ${\text{C}}_{60}$ on Cu(111) for a Pt(100) tip (left) and an Ir(111) tip (right) for various tip positions, as labeled in Fig. 2f.Reuse & Permissions

Figure 4

(Color online) The total tunneling current decomposed according to the atomic orbitals of the tip apex atom (left) and the molecular orbitals of ${\text{C}}_{60}$ (right); the corresponding molecular-orbital wave functions are also shown.Reuse & Permissions

Figure 5

(Color online) [(a) and (b)] PDOS of the tip apex AOs and the ${\text{C}}_{60}$ MOs, respectively, that significantly contribute to the current (the small $p_z$ PDOS values are magnified in the inset); the Fermi energy is set to zero; [(c) and (d)] evolution of tip $d_{z^2}$ and $p_z$ orbitals, respectively, relative to the ${\text{C}}_{60}$ LUMOs, with increasing sample biases of 1.3 and 1.8 V. ${\text{C}}_{60}$-sum denotes LUMOa and LUMOb combined.Reuse & Permissions

Figure 6

(Color online) (a) The upshift of the W(111) tip $p_z$ states and (b) the Ir tip $d_{z^2}$ states relative to the ${\text{C}}_{60}$ LUMOs with increasing bias voltages. See Fig. 5 for more details.Reuse & Permissions