as we've done in a couple of other
videos sean we're going to talk about
those links between physics and
computing
and again we're back to the ultimate
limits of computation and the book i
have in front of me is a book that has
caused a massive amount of consternation
over the last few decades it's by a guy
called k eric drexler now the reason
it's perhaps of interest to a computer
file audience is 1992 most outstanding
computer science book
well what drexler is talking about in
drexel is a very polarizing figure is
can we do computing with individual
atoms can we think of instead of
compiling code
could we compile matter or to put it in
another way though drexler didn't put it
in these terms
but could we do 3d printing with
individual atoms
could we use those as our very you know
very smallest building block
and if we could that's a remarkable
technology that means we
you know because
as some of the more extreme proponents
of drexler's
vision had in mind
we could for example envision some
technology which is effectively looks
like a microwave we'd go outside
we'd get some grass
we'd come we'd put it into our thing
that looks like a microwave oven we
press a button and the ding 30 seconds
later i pops a stick this is like
replicators and stuff it's exactly like
star trek replicators one pan-fried
catfish
we talked about this on one of previous
videos that you guys have manipulated
atoms and made a switch with atoms yes
these sorts of basic building blocks are
being pushed around at the minute they
are and
but drexler's vision is much much
grander than that drexler claims that we
should be able to take any
lump of matter and convert it not quite
into any other lump of matter but
certainly to break those chemical bonds
down and form a structure to a
predefined blueprint importantly he's
not saying that we have to you know that
we're going to disobey the laws of
physics it's not saying that we're
operating in some strains parallel
universe where the normal laws of
physics don't work but he is for example
talking about systems like diamond he
spends a lot of time with diamond
which is a strongly bonded substance you
know diamond is fairly hard tight
covalent bonds holding the atoms in
place and he makes the argument that we
should be able to
um under those circumstances if we can
control the bonding on a single chemical
bond by single chemical bond basis the
atoms will stay in place and we should
be able to build up different structures
so he focused a lot of his time on on
diamond um i can show you a short video
sean okay so we have this microwave
object
and on the side here with these
canisters what we have a very simple
food stock so very simple stock that's
that's put in so simple molecules like
co2 water co methane perhaps molecules
that can be broken down into component
atoms and then built up into something
bigger and just how much bigger we'll
see in a second and cooling etc quite
how it all works we don't know this is
science fiction
but like the best science fiction it
makes you think is this possible could
we manipulate matter like this out there
on computer phylum think about this does
this disobey any of the laws of physics
and you know drex has been widely
castigated perhaps unfairly i think
certainly unfairly in some cases because
these are these are grand ideas grand
visions that are worth worth exploring
are we anywhere near this no we're
nowhere near this but you can see what's
happening as we're zooming in and now
we're down to the 10 nanometer level so
just to give you an idea an atom's a few
there's a fraction of a nanometer across
8.3 of nanometers so once we're 10
nanometers we're talking about say 300
atoms something like that across so
here's these molecules streaming in so
in this case it's c2h2
and what's happening is they're being
fed through
moving across it looks very much like
the type of machinery work on mills
and factories we're used to in the
macroscopic world except it's all shrunk
down each one of these single spheres is
a single atom
and what's happening is you're getting
atom atom transfer you're breaking these
molecules down you can see what's
happening now transferring them across
to these tips these probes this is where
scanning pro microscopes get like myself
get very very interested in that we have
a sharp probe we bring it in close to a
surface move it back and forth this
probe is atomically sharp so it allows
us to see single atoms and single
molecules and manipulate single atoms
and single molecules so some scanning
probe microscopes at least look at this
and think well parts of that we can do
the problem is very very small parts of
it we can do moving the video on let's
scroll through various different
elements what happens later on is we
have
different blocks that are transferred
across
different elements quite how any of this
works we don't know where does it get
its energy source we don't know and out
at the end pops a laptop the argument
being that what's happened is that those
very simple molecules at the start by
building them up manipulating the very
individual atoms we've compiled matter
into this final final form
so this video that you said this is
science fiction this isn't science
fiction as far as whoever you've written
this is drexler drexler believes this is
this is something that that would be
possible in the future um
many of us have many issues surfaces in
particular are a particular issue in
terms of it looks very simple like we'll
just get some blocks and we'll snap them
together
in reality surface physics is incredible
surface chemistry is incredibly credibly
challenging to um surmount but the again
the ideas here are fascinating it it
really is
could we could we do this even at the
level of you know how would we get a
power source here for that little sorter
for the molecules forget about a whole
laptop let's let's reduce this all the
way down can we do information
processing with single atoms of single
molecules
or groups of atoms or groups of
molecules can we translate all that
complexity down and think can we on the
basis of individual atoms and molecules
do information processing and yes we've
done that the nano science community has
done that i suspect not many computer
file land are familiar with this it's a
beautiful beautiful piece of work and
stunningly elegant piece of work
from uh don eigler's group so don's
retired now but his group at ibm almaden
was was sir slabs was responsible for a
lot of the pioneering um work in
nanoscience indeed iglor's group is
responsible for manipulating atoms for
the very first time and what they spelt
out was the ibm logo this is beyond
elegant they've done computing
information processing they've set up
logic gates with
molecules and they've done it in a
really fascinating way because they've
effectively used a domino effect in
terms of how molecules interact with
each other
to transfer information from inputs to
output and
they've done on the basis of co carbon
monoxide very very small quantities you
don't have to worry about any poisoning
or anything like that also in an ultra
high vacuum also at very very low
temperatures four degrees above absolute
zero so it's not toxic at all but they
put them down on a copper surface and
when the seal molecules go down on the
copper surface they absorb in a number
of different states they absorb like
this where it forms this little dark
patch the red dot represents a co
molecule or it forms this type of
structure where the two molecules are
beside each other which is a dimer two
co molecules together or it forms this
structure which is a trimer three
molecules together how do they image
this how do they see the individual
molecules well it comes back to that
scanning probe technology sharp probe
closer surface move back and forth and
if the probe is atomically sharp you can
see individual atoms and molecules so
what they do is they manipulate the co
molecules here's a co molecule so you
can operate in a mode where you scan or
you operate something very
straightforward you push the probe
towards the surface
and you do that
and you move it across the surface so
you can manipulate an image just by
moving the height of the the probe above
the surface so what they do is they set
up these arrangements they set up dimers
dimer dimer dimer diver dimer then what
they do is they bring in another
molecule this one with the green arrow
bring it close and what that does is it
triggers see the red dots or the
positions in co it triggers this cascade
process whereby they all rearrange just
like a set of dominoes they're not
falling the molecules are rearranging
themselves it's not like they're falling
over but they're rearranging themselves
now that's clever enough that's really
clever and although this is uh 2002
although it's 16 years ago it's still
like an incredible phenomenal paper is
that a reversible process that no
because dominoes aren't easy reversible
no so what what we're not talking about
is so this is this is the difference
between fundamental science and
technological application
first of all you know if we were to take
this type of approach
i think we're gonna be hard-pressed to
sell it to anyone because most people
are not gonna want to top the computer
up with liquid helium that's the first
thing
pretty pretty complicated and irritating
to keep an ultra high vacuum going
moreover the bandwidth is about
0.1 or maybe 0.01 of a hertz
because you have to set this entire
system up
and then
set it off it's not reversible there are
other systems for which it is reversible
but not this but this is
this is exploring the limits what they
do here is they develop different gates
by setting up different arrangements of
molecules so here's one example of an
and gate whereby you've got input x
and input y
here
and so by by bringing in molecules
either by causing a cascade here or
causing a cascade here or causing a
cascade at both points then the output
here will change so basically here if we
bring
a molecule in here to set a one here but
there's a zero here there's no molecule
here then what happens is there's no
change the output remains however
and similarly the opposite way however
in this case
if you bring in a tripping molecule here
and a tripping molecule here or control
molecule here then what happens is there
is a big change and you can read that as
a change in the output
so what we have is a logic gate made out
of molecules which is is and made out of
this molecular cascade okay it operates
incredibly slowly okay it's under
extreme conditions but as a piece of
elegant science it's phenomenal why do
they need these incredibly low
temperatures why do they need to be at
four degrees above absolute zero the
problem is with this system with
molecules on metal surfaces what happens
is if you warm the temperature up even
slightly by 10 20 30 degrees something
like that then thermal motion kicks in
and the molecule starts to wander across
the surface so these beautifully
engineered structures you've made will
fall apart just due to diffusion
effectively brownian motion it's not
quite pretty in motion but the same type
of thing
so what you need to do is find systems
whereby this type of diffusion doesn't
kick in
and actually drexler had it right
so what you need to think about is
covalently bonded systems where the
bonds are stronger instead of weak bonds
between the molecules and the surface
which is actually quite good because it
allows you to do this with ease to slide
things around with these
but the problem is
then in terms of trying to exploit that
in any type of realizable technology
it's really difficult so you need
something where the bonds are quite
strong and where you can raise the
temperature without things hopping
around
and
there's been major efforts over the last
few years
to do this with um silicon
and in fact we're now at the point where
this is michelle simmons group in
university of new south wales there are
a number of groups working on this
michelle's group in university new south
wales bob walker's group in um
university of alberta there's christians
you actually
sorry christian
you know i always get the pronunciation
wrong um uh cnrs who's later toulouse
who's led a big effort in this there's
steven schofield's group in university
college london we've dabbled a bit as
well not quite at the level of those
other groups where we've dabbled a
little bit in this in terms of really
manipulating at the single bond level
michelle's group however has
made that important leap whereby they've
taken
this type of atomic scale engineering
and they made a transistor out of it
this this paper really nails its colors
to the mast a single atom transistor and
what they do is they pattern a silicon
surface so we did a video for 60 symbols
a number of years ago
which describes just how this works but
basically you take a silicon surface you
crack it open
and you form two surfaces the atoms here
and the atoms here
are really uncomfortable they're no
longer in the nice environment where
they were bonded to the neighbors atoms
are very gregarious they like to bond so
when you split them open when you split
that crystal open expose the surfaces
it's a very high energy state the atoms
don't like to be in that state so what
you can do is you can passivate that
surface so you can make it less reactive
by adding other atoms to it so the bonds
are tied up and a really good one is
hydrogen so you for silicon
so you take the silicon crystal in
vacuum
the surface and you bombard it with
hydrogen and what you can do is you can
sit above an individual hydrogen atom
bombard it with electrons and remove one
single hydrogen atom so you've got one
chemical bond
and again to be fair to draxler this is
the type of thing he was talking about
quite some time ago
then what you can do and this is what
michelle's group has done is that that
one dangling bond now you've got that
one bond and it's literally called
dangling bond that's what we we call it
so you've got this inert surface with
this one dangling bond then what happens
if you put all the molecules down in
this case they've put a phosphorous
containing compound down is that it
would bond just at that point
and that means you can put down a single
phosphorus atom at that point and that's
what they've done and phosphorus is
what's called a dopant in silicon but
basically you add impurities to control
the electronic properties of silicon and
that's how pricked every single
electronic device and every single
semiconductor device relies on the
properties of doping in this case we're
down to the limit of doping with a
single atom and that's what they've
based this this single atom transistor
on is they've managed to
access and address that single atom to
form a single atom transistor so that
that's really quite phenomenal
interesting the one thing we were
missing okay you could create this this
dangling bond but really you need to be
able to correct it and to reverse it and
to be able to error correct for one
thing it's taken a long time to go it
was like 90s when it was shown that you
could
do you
remove the hydrogen it's taken a long
time to get enough control over the
probe to be able to just connect the
probe or push the probe into the surface
and transfer that single hydrogen atom
to heal out that defect so here's the
defect that one single bond and as you
can see hits functionalized tip then
they bring it in and they connect with
directly that that dangling bond so tip
comes in dangling bone tip
and at the end of the tip there's a
single hydrogen atom and it transfers
and you heal it up
so we're now at the point where we can
make these structures make these
dangling bond
features but also repair them which
means that when it comes to generating
logic gates
in terms of making structures whereby we
can have a rays of these dangling bond
features that communicate with each
other not in the same not quite the same
as the molecular cascades but the same
idea where perhaps we transfer instead
of a physical transfer of molecules we
have a transfer of electrons
then we really are processing at the
atomic limit we've got a long way to go
before we get back to draxler's nano
systems a long long way to go but then
the next idea is well can we actually
we've got information processing at the
single atom limit we're processing
matter at the single atom limit how far
can we push this
one three two one three there we are
back up nice
five
one
three
time because by narrowing down that time
we broaden out the energy associated
with the with the operation which sets a
fundamental limit because the narrower
and narrower narrower we get that the
broader