Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics - Field-Coupled Nanocomputing: Paradigms, Progress, and Perspectives - page 50

contacts will be connected and active while a device is in the STM fabrication
and inspection tool allowing prototyping methods and device testing to advance
substantially over what has been available to date.
In parallel with the development of nano-lithographic methods, a multi-probe
STM has been developed to allow nano-scale electrical characterization that
has until now been out of reach. The instrument shown in Fig. 18 has three
independently scannable tips, watched over by a scanning electron microscope.
Each tip can be quickly redeployed as a scanned probe for imaging or touched
down as a current source or as a voltage probe. Initial applications have enabled
the first detection of a potential step on a crystalline silicon surface [ 30 ], the
absolute measurement of the Si(111)-7 × 7 surface conductivity [ 31 ], the absolute

value of the Si(111)-7 7 step resistivity [ 31 ] and the conductivity of a DB wire

on the H-Si(100) surface [ 32 ]. Various measurements related to and enabling of
atomic silicon surface electronic circuitry will follow.

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8 Quantum Silicon Incorporated and First Proto-Circuits

A spin-off company has been created to exploit the recently discovered DB/ASiQD
properties reviewed here. The goal is to undertake focused development of all the
many components needed to demonstrate working atom scale field controlled
computing elements. In so doing, fundamental components and methods will be
developed that also enable analog and quantum circuitry.
It has been 2 decades since Lyding, Tucker and associates first made DB wires
[ 33 ]. Though many subsequent studies explored other aspects of that system lim-
ited progress has been made in fabricating atomically precise patterns. Making
precise DB patterns is dicult with standard equipment. The first ASiQD paper
several years ago made the key step forward [ 14 ]. Despite years of work by many
researchers the evidence of coupling among DBs and their quantum dot charac-
ter was a surprising and disruptive event. It changed entirely what was known
to be possible with DBs.
There were numerous other diculties slowing the recognition of DBs as
circuit building blocks. Though dangling bond type defects were identified by
Bardeen in the 1940s only in the last several years has a robust theory describing
the properties of the DBs and importantly how those are manifest in STM images
been completed [ 12 , 15 , 34 - 36 ]. While clear indications that the DB can exhibit
a positive charged state were recorded by us one decade ago those results went
unreported for want of fuller theoretical or experimental verification. Additional
experimental proof has appeared just in the past year and been reported together
with the original observations [ 16 ].
While the above advances have established the value of DBs as circuit ele-
ments it has remained clear that wished-for ensembles of DBs would never be
studied or deployed until advances in fabrication were made. The 2006 ASiQD
paper reported on rare successful fabrication efforts. It was then impractical to
make even a 2 cell QCA structure [ 13 ].
Efforts to better understand and control STM scanning have led to some
improvements [ 37 , 38 ] but fell short of control necessary to fabricate atom scale