<s>
Molecular	B-Algorithm
scale	I-Algorithm
electronics	I-Algorithm
,	O
also	O
called	O
single-molecule	B-Algorithm
electronics	I-Algorithm
,	O
is	O
a	O
branch	O
of	O
nanotechnology	O
that	O
uses	O
single	O
molecules	O
,	O
or	O
nanoscale	O
collections	O
of	O
single	O
molecules	O
,	O
as	O
electronic	O
components	O
.	O
</s>
<s>
The	O
field	O
is	O
often	O
termed	O
simply	O
as	O
"	O
molecular	B-Algorithm
electronics	I-Algorithm
"	O
,	O
but	O
this	O
term	O
is	O
also	O
used	O
to	O
refer	O
to	O
the	O
distantly	O
related	O
field	O
of	O
conductive	B-Algorithm
polymers	I-Algorithm
and	O
organic	O
electronics	O
,	O
which	O
uses	O
the	O
properties	O
of	O
molecules	O
to	O
affect	O
the	O
bulk	O
properties	O
of	O
a	O
material	O
.	O
</s>
<s>
A	O
nomenclature	O
distinction	O
has	O
been	O
suggested	O
so	O
that	O
molecular	O
materials	O
for	O
electronics	O
refers	O
to	O
this	O
latter	O
field	O
of	O
bulk	O
applications	O
,	O
while	O
molecular	B-Algorithm
scale	I-Algorithm
electronics	I-Algorithm
refers	O
to	O
the	O
nanoscale	O
single-molecule	O
applications	O
treated	O
here	O
.	O
</s>
<s>
This	O
is	O
the	O
idea	O
behind	O
molecular	B-Algorithm
electronics	I-Algorithm
,	O
with	O
the	O
ultimate	O
miniaturization	O
being	O
components	O
contained	O
in	O
single	O
molecules	O
.	O
</s>
<s>
In	O
single-molecule	B-Algorithm
electronics	I-Algorithm
,	O
the	O
bulk	O
material	O
is	O
replaced	O
by	O
single	O
molecules	O
.	O
</s>
<s>
The	O
molecules	O
used	O
have	O
properties	O
that	O
resemble	O
traditional	O
electronic	O
components	O
such	O
as	O
a	O
wire	O
,	O
transistor	B-Application
or	O
rectifier	B-Algorithm
.	O
</s>
<s>
Single-molecule	B-Algorithm
electronics	I-Algorithm
is	O
an	O
emerging	O
field	O
,	O
and	O
entire	O
electronic	O
circuits	O
consisting	O
exclusively	O
of	O
molecular	O
sized	O
compounds	O
are	O
still	O
very	O
far	O
from	O
being	O
realized	O
.	O
</s>
<s>
Molecular	B-Algorithm
electronics	I-Algorithm
operates	O
in	O
the	O
quantum	O
realm	O
of	O
distances	O
less	O
than	O
100	O
nanometers	O
.	O
</s>
<s>
In	O
contrast	O
,	O
in	O
molecular	B-Algorithm
electronics	I-Algorithm
the	O
transfer	O
of	O
one	O
electron	O
alters	O
the	O
system	O
significantly	O
.	O
</s>
<s>
This	O
Meir-Wingreen	O
formulation	O
has	O
been	O
used	O
to	O
great	O
success	O
in	O
the	O
molecular	B-Algorithm
electronics	I-Algorithm
community	O
to	O
examine	O
the	O
more	O
difficult	O
and	O
interesting	O
cases	O
where	O
the	O
transient	O
electron	O
exchanges	O
energy	O
with	O
the	O
molecular	O
system	O
(	O
for	O
example	O
through	O
electron-phonon	O
coupling	O
or	O
electronic	O
excitations	O
)	O
.	O
</s>
<s>
Common	O
for	O
molecules	O
used	O
in	O
molecular	B-Algorithm
electronics	I-Algorithm
is	O
that	O
the	O
structures	O
contain	O
many	O
alternating	O
double	O
and	O
single	O
bonds	O
(	O
see	O
also	O
Conjugated	O
system	O
)	O
.	O
</s>
<s>
As	O
the	O
assembly	O
of	O
these	O
and	O
their	O
connection	O
to	O
a	O
macroscopic	O
circuit	O
is	O
still	O
not	O
mastered	O
,	O
the	O
focus	O
of	O
research	O
in	O
single-molecule	B-Algorithm
electronics	I-Algorithm
is	O
primarily	O
on	O
the	O
functionalized	O
molecules	O
:	O
molecular	O
wires	O
are	O
characterized	O
by	O
containing	O
no	O
functional	O
groups	O
and	O
are	O
hence	O
composed	O
of	O
plain	O
repetitions	O
of	O
a	O
conjugated	O
building	O
block	O
.	O
</s>
<s>
Single-molecule	O
transistors	B-Application
are	O
fundamentally	O
different	O
from	O
the	O
ones	O
known	O
from	O
bulk	O
electronics	O
.	O
</s>
<s>
The	O
gate	O
in	O
a	O
conventional	O
(	O
field-effect	O
)	O
transistor	B-Application
determines	O
the	O
conductance	O
between	O
the	O
source	O
and	O
drain	O
electrode	O
by	O
controlling	O
the	O
density	O
of	O
charge	O
carriers	O
between	O
them	O
,	O
whereas	O
the	O
gate	O
in	O
a	O
single-molecule	O
transistor	B-Application
controls	O
the	O
possibility	O
of	O
a	O
single	O
electron	O
to	O
jump	O
on	O
and	O
off	O
the	O
molecule	O
by	O
modifying	O
the	O
energy	O
of	O
the	O
molecular	O
orbitals	O
.	O
</s>
<s>
One	O
of	O
the	O
effects	O
of	O
this	O
difference	O
is	O
that	O
the	O
single-molecule	O
transistor	B-Application
is	O
almost	O
binary	O
:	O
it	O
is	O
either	O
on	O
or	O
off	O
.	O
</s>
<s>
Because	O
of	O
the	O
size	O
of	O
a	O
single	O
molecule	O
,	O
the	O
charging	O
due	O
to	O
a	O
single	O
electron	O
is	O
significant	O
and	O
provides	O
means	O
to	O
turn	O
a	O
transistor	B-Application
on	O
or	O
off	O
(	O
see	O
Coulomb	O
blockade	O
)	O
.	O
</s>
<s>
For	O
this	O
to	O
work	O
,	O
the	O
electronic	O
orbitals	O
on	O
the	O
transistor	B-Application
molecule	O
cannot	O
be	O
too	O
well	O
integrated	O
with	O
the	O
orbitals	O
on	O
the	O
electrodes	O
.	O
</s>
<s>
A	O
popular	O
group	O
of	O
molecules	O
,	O
that	O
can	O
work	O
as	O
the	O
semiconducting	O
channel	O
material	O
in	O
a	O
molecular	O
transistor	B-Application
,	O
is	O
the	O
oligopolyphenylenevinylenes	O
(	O
OPVs	O
)	O
that	O
works	O
by	O
the	O
Coulomb	O
blockade	O
mechanism	O
when	O
placed	O
between	O
the	O
source	O
and	O
drain	O
electrode	O
in	O
an	O
appropriate	O
way	O
.	O
</s>
<s>
Thus	O
,	O
it	O
is	O
being	O
researched	O
if	O
the	O
quantum	O
mechanical	O
properties	O
can	O
be	O
used	O
for	O
more	O
advanced	O
purposes	O
than	O
simple	O
transistors	B-Application
(	O
e.g.	O
</s>
<s>
Physicists	O
at	O
the	O
University	O
of	O
Arizona	O
,	O
in	O
collaboration	O
with	O
chemists	O
from	O
the	O
University	O
of	O
Madrid	O
,	O
have	O
designed	O
a	O
single-molecule	O
transistor	B-Application
using	O
a	O
ring-shaped	O
molecule	O
similar	O
to	O
benzene	O
.	O
</s>
<s>
Physicists	O
at	O
Canada	O
's	O
National	O
Institute	O
for	O
Nanotechnology	O
have	O
designed	O
a	O
single-molecule	O
transistor	B-Application
using	O
styrene	O
.	O
</s>
<s>
Molecular	O
rectifiers	B-Algorithm
are	O
mimics	O
of	O
their	O
bulk	O
counterparts	O
and	O
have	O
an	O
asymmetric	O
construction	O
so	O
that	O
the	O
molecule	O
can	O
accept	O
electrons	O
in	O
one	O
end	O
but	O
not	O
the	O
other	O
.	O
</s>
<s>
Because	O
the	O
current	O
photolithographic	B-Algorithm
technology	O
is	O
unable	O
to	O
produce	O
electrode	O
gaps	O
small	O
enough	O
to	O
contact	O
both	O
ends	O
of	O
the	O
molecules	O
tested	O
(	O
on	O
the	O
order	O
of	O
nanometers	O
)	O
,	O
alternative	O
strategies	O
are	O
applied	O
.	O
</s>
<s>
Further	O
,	O
the	O
reach	O
of	O
conventional	O
photolithography	B-Algorithm
can	O
be	O
enhanced	O
by	O
chemically	O
etching	O
or	O
depositing	O
metal	O
on	O
the	O
electrodes	O
.	O
</s>
<s>
In	O
polymers	B-Language
,	O
classical	O
organic	O
molecules	O
are	O
composed	O
of	O
both	O
carbon	O
and	O
hydrogen	O
(	O
and	O
sometimes	O
additional	O
compounds	O
such	O
as	O
nitrogen	O
,	O
chlorine	O
or	O
sulphur	O
)	O
.	O
</s>
<s>
However	O
,	O
naturally	O
occurring	O
carbon	O
is	O
conducting	O
,	O
especially	O
graphite	B-Application
recovered	O
from	O
coal	O
or	O
encountered	O
otherwise	O
.	O
</s>
<s>
From	O
a	O
theoretical	O
viewpoint	O
,	O
graphite	B-Application
is	O
a	O
semi-metal	O
,	O
a	O
category	O
in	O
between	O
metals	O
and	O
semi-conductors	O
.	O
</s>
<s>
Tailoring	O
the	O
graphite	B-Application
sheet	O
to	O
obtain	O
well	O
defined	O
nanometer-sized	O
objects	O
remains	O
a	O
challenge	O
.	O
</s>
<s>
After	O
studying	O
the	O
interstellar	O
conditions	O
under	O
which	O
carbon	O
is	O
known	O
to	O
form	O
clusters	O
,	O
Richard	O
Smalley	O
's	O
group	O
(	O
Rice	O
University	O
,	O
Texas	O
)	O
set	O
up	O
an	O
experiment	O
in	O
which	O
graphite	B-Application
was	O
vaporized	O
via	O
laser	O
irradiation	O
.	O
</s>
<s>
Coined	O
buckminsterfullerenes	O
,	O
buckyballs	O
,	O
or	O
C60	O
,	O
the	O
clusters	O
retained	O
some	O
properties	O
of	O
graphite	B-Application
,	O
such	O
as	O
conductivity	O
.	O
</s>
<s>
These	O
objects	O
were	O
rapidly	O
envisioned	O
as	O
possible	O
building	O
blocks	O
for	O
molecular	B-Algorithm
electronics	I-Algorithm
.	O
</s>
<s>
A	O
metallic	O
grain	O
between	O
the	O
electrodes	O
can	O
act	O
as	O
a	O
single	O
electron	O
transistor	B-Application
by	O
the	O
mechanism	O
described	O
above	O
,	O
thus	O
resembling	O
the	O
traits	O
of	O
a	O
molecular	O
transistor	B-Application
.	O
</s>
<s>
One	O
of	O
the	O
biggest	O
hindrances	O
for	O
single-molecule	B-Algorithm
electronics	I-Algorithm
to	O
be	O
commercially	O
exploited	O
is	O
the	O
lack	O
of	O
methods	O
to	O
connect	O
a	O
molecular	O
sized	O
circuit	O
to	O
bulk	O
electrodes	O
in	O
a	O
way	O
that	O
gives	O
reproducible	O
results	O
.	O
</s>
<s>
Likewise	O
,	O
a	O
1974	O
paper	O
from	O
Mark	O
Ratner	O
and	O
Ari	O
Aviram	O
illustrated	O
a	O
theoretical	O
molecular	O
rectifier	B-Algorithm
.	O
</s>
<s>
In	O
1988	O
,	O
Aviram	O
described	O
in	O
detail	O
a	O
theoretical	O
single-molecule	O
field-effect	O
transistor	B-Application
.	O
</s>
<s>
The	O
concept	O
of	O
molecular	B-Algorithm
electronics	I-Algorithm
was	O
published	O
in	O
1974	O
when	O
Aviram	O
and	O
Ratner	O
suggested	O
an	O
organic	O
molecule	O
that	O
could	O
work	O
as	O
a	O
rectifier	B-Algorithm
.	O
</s>
<s>
Having	O
both	O
huge	O
commercial	O
and	O
fundamental	O
interest	O
,	O
much	O
effort	O
was	O
put	O
into	O
proving	O
its	O
feasibility	O
,	O
and	O
16	O
years	O
later	O
in	O
1990	O
,	O
the	O
first	O
demonstration	O
of	O
an	O
intrinsic	O
molecular	O
rectifier	B-Algorithm
was	O
realized	O
by	O
Ashwell	O
and	O
coworkers	O
for	O
a	O
thin	O
film	O
of	O
molecules	O
.	O
</s>
<s>
Recent	O
progress	O
in	O
nanotechnology	O
and	O
nanoscience	O
has	O
facilitated	O
both	O
experimental	O
and	O
theoretical	O
study	O
of	O
molecular	B-Algorithm
electronics	I-Algorithm
.	O
</s>
<s>
Development	O
of	O
the	O
scanning	O
tunneling	O
microscope	O
(	O
STM	O
)	O
and	O
later	O
the	O
atomic	O
force	O
microscope	O
(	O
AFM	O
)	O
have	O
greatly	O
facilitated	O
manipulating	O
single-molecule	B-Algorithm
electronics	I-Algorithm
.	O
</s>
<s>
Also	O
,	O
theoretical	O
advances	O
in	O
molecular	B-Algorithm
electronics	I-Algorithm
have	O
facilitated	O
further	O
understanding	O
of	O
non-adiabatic	O
charge	O
transfer	O
events	O
at	O
electrode-electrolyte	O
interfaces	O
.	O
</s>
<s>
A	O
collaboration	O
of	O
researchers	O
at	O
Hewlett-Packard	O
(	O
HP	O
)	O
and	O
University	O
of	O
California	O
,	O
Los	O
Angeles	O
(	O
UCLA	O
)	O
,	O
led	O
by	O
James	O
Heath	O
,	O
Fraser	O
Stoddart	O
,	O
R	O
.	O
Stanley	O
Williams	O
,	O
and	O
Philip	O
Kuekes	O
,	O
has	O
developed	O
molecular	B-Algorithm
electronics	I-Algorithm
based	O
on	O
rotaxanes	B-Algorithm
and	O
catenanes	O
.	O
</s>
<s>
Work	O
is	O
also	O
occurring	O
on	O
the	O
use	O
of	O
single-wall	O
carbon	O
nanotubes	O
as	O
field-effect	O
transistors	B-Application
.	O
</s>
<s>
Some	O
specific	O
reports	O
of	O
a	O
field-effect	O
transistor	B-Application
based	O
on	O
molecular	O
self-assembled	O
monolayers	O
were	O
shown	O
to	O
be	O
fraudulent	O
in	O
2002	O
as	O
part	O
of	O
the	O
Schön	O
scandal	O
.	O
</s>
<s>
Until	O
recently	O
entirely	O
theoretical	O
,	O
the	O
Aviram-Ratner	O
model	O
for	O
a	O
unimolecular	B-Algorithm
rectifier	I-Algorithm
has	O
been	O
confirmed	O
unambiguously	O
in	O
experiments	O
by	O
a	O
group	O
led	O
by	O
Geoffrey	O
J	O
.	O
Ashwell	O
at	O
Bangor	O
University	O
,	O
UK	O
.	O
</s>
<s>
Supramolecular	B-Algorithm
electronics	I-Algorithm
is	O
a	O
new	O
field	O
involving	O
electronics	O
at	O
a	O
supramolecular	O
level	O
.	O
</s>
<s>
An	O
important	O
issue	O
in	O
molecular	B-Algorithm
electronics	I-Algorithm
is	O
the	O
determination	O
of	O
the	O
resistance	O
of	O
a	O
single	O
molecule	O
(	O
both	O
theoretical	O
and	O
experimental	O
)	O
.	O
</s>
