Figure 1

Overview of a large area $(2\mu \mathrm{m}\times 2\mu \mathrm{m})$ of the KBr(001) surface covered with 0.3 molecular layers of PTCDA. PTCDA islands are marked by arrows. The circles highlight rectangular pits and protrusions of the bare KBr. The image has been acquired using $\Delta f=-3\mathrm{Hz}$ or $\gamma =k{A}^{3∕2}\Delta f∕f_0=-1.3{\mathrm{fNm}}^{1∕2}$, the height range is about $10\mathrm{nm}$.Reuse & Permissions

Figure 2

Part of an individual PTCDA crystallite showing molecular resolution on the flat top as well as on two of the three observed facets. The image of $80\mathrm{nm}\times 60\mathrm{nm}$ has been acquired using $\Delta f=-3\mathrm{Hz}$ $(\gamma =-1.3{\mathrm{fNm}}^{1∕2})$.Reuse & Permissions

Figure 3

(a) Molecular resolution of PTCDA obtained on the top of a crystallite. The set point for the frequency shift has been increased to $\Delta f=-10\mathrm{Hz}$ $(\gamma =-4.4{\mathrm{fNm}}^{1∕2})$ compared to Figs. 1, 2. The displayed area is approximately $10\mathrm{nm}\times 10\mathrm{nm}$. The upper left corner shows the Fourier transform of the image. Neither the topographic image nor the Fourier transform have been corrected for thermal drift. In both images the primitive unit cell of the structures is shown. (b) Simulated hypersurface for $\gamma =-5{\mathrm{fNm}}^{1∕2}$ based on a simple force field calculation. The displayed area amounts to $5\times 5{\mathrm{nm}}^2$. The height varies between 0.49 and $0.54\mathrm{nm}$ referring to the distance between the center of the outermost atom of the tip and the center plane of the molecules. To indicate the position of the molecules, they have been sketched for one unit cell. (c) Molecular resolution image on the top layer of a different PTCDA crystallite on KBr showing a localized defect in the lower right corner. The scan area is approximately $10\times 10{\mathrm{nm}}^2$. This image has been acquired using $\Delta f=-11.8\mathrm{Hz}$ $(\gamma =-5.2{\mathrm{fNm}}^{1∕2})$.Reuse & Permissions