An STM study of the localized atomic reaction of 1,2- and 1,4-dibromobenzene at Si(111)-7×7

Developing 1D nanostructure arrays for future nanophotonics

“…Figure 3 is the physisorption geometry of CH 3 Br(ad)/Si(111) 7 · 7 computed in the MP2 approximation. As expected the most-stable configuration is that with the Br-end of CH 3 Br pointing downward toward the Si surface. However, the C-Br bond is found to be at an angle of approximately 60°to the surface normal.…”

“…Figure 1d shows the effect of 193 nm radiation on CH 3 Br(ad) at the unchanged surface voltage of V s = 1.5 V; the bright physisorbed circles of CH 3 Br(ad) have disappeared leaving dark circles of Br-Si which, in Fig. 1e, 'light up' to give 12 bright BrSi at V s = 2.5 V. This is the well-known voltagedependence of Br-Si STM images [3]. Definitive proof that the physisorbed CH 3 Br(ad), only observable at the surface £50 K, had been converted to a chemisorbed species was to be found in the fact that the circular patterns of Fig.…”

“…However, the C-Br bond is found to be at an angle of approximately 60°to the surface normal. When, therefore, an electron is transferred to the CH 3 Br -anti-bonding orbital, causing the C-Br bond in CH 3 Br -to extend, the Br is expected to hit the surface at an angle to the surface-plane (cf. condition (a) of the previous discussion).…”

“…The proposed explanation [1] is that the Br -from CH 3 Br recoiling toward the surface (even though at a glancing angle of incidence) rides up a repulsive wall and spends~10…”

Mapping the site-specific potential energy landscape for chemisorbed and physisorbed aromatic molecules on the Si(1 1 1)-7 × 7 surface by time-lapse STM

“…77 K, where molecules can be trapped in the physisorbed state, they cannot be reliably captured via STM as they are still able to diffuse across the surface [23]. At room temperature the physisorbed state is too short lived to appear in an STM image; from [24] we estimate the life time for physisorbed benzene on Si(1 1 1)-7×7 to be ∼1 µs. Instead, we image here the outcome of a molecule leaving its chemisorbed state, transiting through the physisorbed state, and either finding a chemisorption site (creating a new black spot) or leaving the surface entirely.…”