Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics - Field-Coupled Nanocomputing: Paradigms, Progress, and Perspectives - page 38

(a) (b)

Fig. 5. (a) Various processes in a chain reaction resulting in the growth of lines a
special class of molecules (e.g. styrene) on a H-Si(100) surface. R here denotes various
possible radicals. (b) A line of about 20 styrene molecules grown in this fashion and
imaged at different STM setpoints. The charge on the terminal DB at the top of the
line depends on the STM setpoint and therefore causes (or not) a Stark shift in the
molecular line.

radical C abstracts an H atom from an adjacent surface site to create a stably
attached molecule, and a regenerated DB positioned one lattice step removed
from the original DB position. The process repeats and repeats to create a multi-
molecular line that gains a degree of order from the crystalline substrate.
Figure 5 b shows an approximately 20 molecule long line of styrene grown in
this way. The bright feature at the end of the line is a DB. It has been shown that
under conditions where the terminal DB is negatively charged that charge acts
to gate (Stark shift) the molecular energy levels causing conduction through the
molecule where ordinarily it would not occur [ 19 ]. In other words the ensemble
forms single-electron gated, one-molecule field effect transistor. The point of
this discussion is to show there is precedent for microscopic observation of DBs
at different charge-states, and to point out that a structure like the molecule
transistor arrangement could be a useful detector of DB charge state [ 20 ].

4 Dangling Bonds Are Atomic Silicon Quantum Dots

The atoms in a silicon crystal enter into bonding and anti-bonding relationships
with neighbouring and distant silicon atoms to form bands that span the crys-
tal. In doing so the atoms give up their zero dimensional electronic character. Si