Scanning tunneling microscopy study of single molecule motion on the Si(100)- surface
Synthesis procedure for 5-vinyl-2,3-dihydrobenzofuran.
(a) Schematic of cycloaddition of a 4-methoxystyrene molecule on a dimer on the clean Si(100) surface. The methoxy group is expected to have the rotational degree of freedom indicated in the figure; (b) UHV STM image of 4-methoxystyrene molecules on the clean Si(100) surface following a dose of 0.7 L. Several of the molecules (indicated by white arrows) exhibit multiple switching events. Imaging conditions are sample bias of and tunneling current of 0.1 nA.
Tunneling current vs time plot obtained by holding the STM tip stationary over an individual 4-methoxystyrene molecule. The sample bias was held constant at .
UHV STM images of a single 4-methoxystyrene molecule showing net displacement along a dimer row over the course of four successive scans shown in (a)–(d). All images were obtained at a sample bias of and a tunneling current of 0.1 nA. During the course of each image, a molecule may move back and forth about its chemisorbed location [(a) and (c)] or move to a new dimer location [(b)]. The last figure in the panel [(d)] shows the net displacement of the molecule from its original position as indicated by the white dotted arrow.
(a) Schematic of a 4-methoxystyrene molecule chemisorbed in a cross-dimer (CD) configuration; (b) schematic of a 4-methoxystyrene molecule alternately switching between a dimer (D) and a cross-dimer (CD) configuration; (c)–(f) two pairs of UHV STM images showing a 4-methoxystyrene molecule switching between a dimer binding (indicated by D) and a cross-dimer binding configuration (indicated by CD). The white lines have been drawn to indicate the dimer rows and the black dotted circles indicate the spatial extent of the molecules in their bistable configurations. In both cases, the imaging conditions were sample bias of and tunneling current of 0.1 nA.
(a) Schematic of chemisorption of a styrene molecule to a Si(100) dimer; (b) UHV STM image of styrene molecules on clean Si(100) following a dose of 0.2 L. In contrast to 4-methoxystyrene, no switching events are observed in this case. Imaging conditions are sample bias of and tunneling current of 0.1 nA.
(a) Schematic of a 5-vinyl-2,3-dihydrobenzofuran bound to Si(100). This molecule is analogous to 4-methoxystyrene except that its methoxy group is covalently linked to the aromatic ring in order to inhibit its rotational degree of freedom; (b) UHV STM image of a submonolayer coverage of 5-vinyl-2,3-dihydrobenzofuran on the clean Si(100) surface following a dose of 0.4 L. No switching events are observed in this case. Imaging conditions are sample bias of and tunneling current of 0.1 nA.
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