Figure 1

(a) STM topography image ($V_s=+2\mathrm{V}$, $I_t=150\mathrm{pA}$) of the deactivated Si(111)-B surface obtained at 77 K. Surface is hexagonal with lattice parameter $a=6.65\pm 0.05\AA$. Bright features correspond to Si dangling bonds with the absence of underlying boron atoms. An individual adatom vacancy can also be observed. (b) STM topography image ($V_s=+2\mathrm{V}$, $I_t=35\mathrm{pA}$) of ZnPc on deactivated Si(111)-B obtained at 77 K. Unit cell of the molecular overlayer given by: $b_1=12.3\pm 0.1\AA$, $b_2=6.7\pm 0.1\AA$, and $\beta =92\pm 1°$. Green lines mark bright fringes of the moiré pattern. The periodicity of the pattern is $8.3\pm 0.2\mathrm{nm}$ along the $⟨11\overline{2}⟩$ direction of the Si substrate and $5.0\pm 0.2\mathrm{nm}$ along the moiré direction with angle of $104\pm 2°$ between the two, highlighted by black arrows. The gray scale bars are 6 nm (inset: atomic model of the ZnPc molecule).Reuse & Permissions

Figure 2

(a) Normalized STS spectra taken on the deactivated Si adatom sites (red) and ZnPc molecules (blue) over the same area as shown in (b). The peak in the ZnPc spectra near $+2.5\mathrm{V}$ was used for the simultaneous imaging of topology and differential conductance map in (b). (b) Left: Partial image showing both the ZnPc overlayer and the Si surface ($I_t=50\mathrm{pA}$, 77 K). $\theta$ represents the angle between $a_1$ and $b_1$, defining the azimuthal relation between the molecular overlayer and the substrate. Right: Differential conductance map taken simultaneously at the same imaging conditions. Black lines represent individual molecules with edge-to-edge distance between the 2 benzene rings measured to be $13.0\pm 0.2\AA$. Inset: atomic model of a ZnPc dimer in observed tilted orientation and LUMO of free ZnPc molecules calculated using density functional theory and the Perdew-Wang generalized gradient approximation. Gray scale bars are 3 nm.Reuse & Permissions

Figure 3

(a) Results of a geometric analysis as the molecular overlayer is rotated azimuthally on the Si substrate. First minimum in $V/V_0(=0.7)$ occurs at $28\pm 0.5°$ with other minima spaced in increments of 60° due to the substrate $C3$ symmetry. (b) Simulated overlayer-substrate geometry at an azimuthal rotation angle of 28°. Red circles outlined in blue represent Si adatoms. Black dots represent the ZnPc overlayer lattice. Green lines mark the bright fringes of the moiré pattern. The periodicity of the pattern is $8.5\pm 0.1\mathrm{nm}$ along the $⟨11\overline{2}⟩$ direction of the Si substrate and $4.8\pm 0.1\mathrm{nm}$ along the moiré direction with angle of $104\pm 1°$ between the two, highlighted by white arrows for comparison with Fig. 1b. Gray scale bar is 8 nm.Reuse & Permissions

Figure 4

(a) STM topography image ($V_s=+2\mathrm{V}$, $I_t=30\mathrm{pA}$) showing the initial step flow growth of ZnPc on Si(111)-B. Two parallel molecular stripes (arrows) originating from the same Si step are observed. Gray scale bar is 8 nm. (b) Tapping mode AFM topography image (with AC240TM cantilevers from Asylum Research, $k=2\mathrm{N}/\mathrm{m}$, $f_0=70\mathrm{kHz}$) of ZnPc thin film growth on Si(111)-B surface with a complete first monolayer and partial second and third layer coverage. Anisotropic step flow growth is observed for both the second and third monolayers with a dominant orientation with respect to the Si steps. The gray scale bar is 500 nm.Reuse & Permissions