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(Color online) (a,b) Chemical structures of QTF8 (a) and FG1 (b). (c,d) Molecular mechanics simulations of QTF8 (c) and FG1 (d) edge-on stacks (side views). The lattice periodicity is highlighted for both molecular assemblies. Note that the plane of the conjugated systems is perpendicular to the substrate. For more details (including top views of the nanowires stacks) see Refs. 16 and 17.
(Color online) (a)–(c) Topographic (left panels), damping (middle panels), and CPD (right panels) images (600 nm × 600 nm, 512 × 512 pixels) of a FG1 stack on HOPG recorded with Avib = 55.7 nm and Δf = −4 Hz (a), Δf = −8 Hz (b), and Δf = −12 Hz (c). Color scales are given for the CPD levels only (right panels). (d) CPD difference between the stack and the substrate (ΔCPD = CPDFG1 − CPDHOPG) as a function of the frequency shift, at constant vibration amplitude, Avib = 55.7 nm. Inset: same parameter plotted as a function of the vibration amplitude, at constant normalized frequency shift γ = (Δf × k × Avib 3/2)/f0 = −3.7 fN m1/2.
(Color online) (a)–(c) Topographic (left panels), damping (middle panels), and CPD (right panels) high magnification images (100 nm × 100 nm, 400 × 400 pixels) of the FG1 stack recorded with Avib = 55 nm and Δf = −4 Hz (a), Δf = −6 Hz (b), and Δf = −11 Hz (c). At −6 Hz, a lateral resolution of a few nanometers is achieved in CPD images, as highlighted by the black arrow which pinpoints a defect at the edge of the molecular stack in (b) (right panel). CPD modulations correlated with the molecular lattice appear for Δf ≤ Δfsat, as shown by the data in (c).
(Color online) (a)–(c) Topographic (a), damping (b), and CPD (c) images (200 nm × 156 nm, pitch = 0.33 nm) of a QTF8 stack on HOPG recorded with Avib = 35 nm and Δf = −20 Hz. (d) Section (simulation from molecular mechanics) of an edge-on stack. Arrows pointing up and down highlight the locations corresponding to the two different molecular orientations. (e) CPD curves (averaged from several data) as a function of the tip-surface separation (Δf = −25 Hz, Avib = 41 nm), recorded over the two different molecular orientations within a QTF8 stack, as highlighted by the arrows in (d). Inset: damping curves recorded simultaneously with the CPD data.
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