Binding of styrene on silicon (111)-7 × 7 surfaces as a model molecular electronics system
(Color online) Schematic representation and optimized model structure of the [4 + 2] cycloaddition [(a) and (c)] and [2 + 2] cycloaddition [(b) and (d)] binding modes of styrene on Si (111)-7 × 7.
(Color online) UPS spectra of bare silicon surfaces prepared by etch and anneal and direct flash and anneal (a). Features S1 and S2 represent the adatom and rest-atom dangling bond states respectively, indicating the presence of the 7 × 7 reconstruction. STM surface produced by flash anneal (b).
(Color online) Experimental STM images showing the Si (111)-7 × 7 surface after exposure to 0.1L of styrene at room temperature. Example molecular features are circled. The images were acquired with a tunneling current of 50 pA and sample biases of −2.0 V (a) and +2.0 V (b). Scans are 16 × 16 nm2.
(Color online) Simulated STM images of the [4 + 2] binding mode [(a) and (c)] and the [2 + 2] binding mode [(b) and (d)] at biases of +0.3 V (empty states) and −0.5 V (filled states). The simulations were done with a tunneling current of 30 pA. Images are plan view; the oval shows the location of the styrene molecule and the other two features represent silicon adatoms. The scale bar is 8.1 Å.
On-specular [(a) and (c)] and off-specular [(b) and (d)] HREELS of 0.5 L styrene exposed to Si(111) 7 × 7 at 300 K [(a) and (b)] and 105 K [(c) and (d)].
C 1s region XPS spectrum of 120 L styrene dosed on Si(111)-7 × 7 at room temperature.
UPS valence band region of Si (111)-7 × 7 dosed with 200 L styrene at room temperature, compared with a clean Si surface.
Comparison of apparent height of styrene features in Å.
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