you've got physics-y things in front of
you i've got physically things in front
of me i've got also got a paper i'm
hugely hugely excited about um
unfortunately not from our group i
really wish i could say it was from our
group we've been interested in this type
of thing for for many years so as you
can see it's this autonomous scanning
probe microscopy in-situ tip
conditioning through machine learning
and this is from bob walker's group uh
in the university of alberta
and it's a phenomenal piece of work um
why i think it might be of interest to
computer file audience it could also be
of interest to 60 symbols audience but
for this in particular it's they're
basically controlling the atomic
structure of matter through machine
learning so it's really the interface
between physics and computer science
first of all it's all about scanning
probe microscopy now i think we've
talked a little bit about scanning for
microscopy but in essence what we have
is a sharp tip preferably atomically
sharp with one atom sticking out the end
and that sounds really difficult to do
but in practice not that difficult to do
what is difficult to control is just how
many atoms stick out the end and the
arrangement of the atoms at the end and
that is really the bane of any scanning
probe microscopic's life but let's say
we've managed to create this we've got
one atom sticking at the end here's our
surface here's our sample you bring it
in
and you move it so you're almost at the
touching point sometimes even at the
contact point whereby you have a very
small separation between the the tip and
the sample so what we have is our sharp
tip we bring it in really close to the
surface and we do that using
piezoelectric crystals actually those
barbecue lighter things that you use
where you click at the end pitot
electric crystals in those so you bring
it in really close within an atomic
diameter or so and then you move it
across the surface and what you're
picking up on is the interaction of that
atom right at the end of the tip with
the atoms at the surface so you move
back and forth back and forth and build
up an image that way it's a slow process
but it's a process that is incredibly
precise and we sacrifice speed for that
precision and the other great thing is
because it's a probe as well as imaging
what you can do is you can deliberately
try to manipulate the surface so you can
bring the tip in bond and try to pluck
atoms out for example or if they're
atoms absorbed in the surface you can
try and slide them move them across and
we're now at the point where in many
cases we can slide atoms of will across
the surface to spell out different
patterns
but
but and there's a big but as i said the
key thing here with scanning for
microscopy is controlling the structure
at the end of the probe and so we'll
start off we will
take our tip and the way we create our
tip the first stage in creating the tip
is we put it into a solution solution of
sodium hydroxide i know this is
chemistry of the computer file audience
bear with me you etch it down to a sharp
point but that's not good enough
generally it's not good enough
then you put it in your vacuum system
you move it in you'd like to be able to
see atoms but most the time you don't
see atoms so what do you do well you
apply a little voltage pulse to try and
jiggle the atoms around at the end of
the probe or you apply an increase in
the current and that can lead to effects
which will move the atoms around at the
end of the probe that doesn't work you
crush it gently in that doesn't work you
crush it a little bit further in that
doesn't work you drive it in half a
millimeter or so and push it around and
try to try to jiggle it around how do
you know if it's worked
very very good question you go
does this image look good
really yeah
what we really want to have is as an
image whereby
what we're seeing is the structure of
the surface and that this has as little
influence as possible so what we really
want to do is have a sharper probe as
possible because for example if we have
a probe that looks like this
where we've got a flat plane where each
one of these atoms will could
potentially contribute to the image that
can lead to very confusing images
because you've got multiple different
imaging centers let's say we have
something like this so it comes in like
this to the surface where you've got an
atom here and an atom here
and both of those can contribute to the
image and sometimes it'll be tilted
slightly and this one can contribute
more because it's closer to the surface
but this one can still contribute it's
reasonably close to the surface so those
are double tip images they're the bane
of the scanning pro microscope is life
because really what you want to do is to
get right down to that atomic level at
the moment what happens is students post
docs researchers
sit in the lab
and they they literally just trial and
error
push the tip into the surface apply
voltage pulses try and coerce it into
the state they want and it's a massive
bottleneck massive massive bottleneck
when in fact what we'd want is a sort of
auto tune or an autofocus button where
you get to the end of the day if you've
experienced your experiments might have
worked okay but perhaps your tip is not
in a good state and you want to press a
button which is optimized probe
and go home and then come in the morning
and do your proper experiments instead
of driving yourself to distraction just
pushing the tip into the surface to try
and change the structure of the tip
and that's been a long time coming
scanning for microscopy has been around
since the early 80s and we're still at
that level many and nottingham's no
different many many groups are still at
that level where it's a you know a phd
student in their second year literally
banging my head against the table going
please work
that's why this paper is so important
and it's it's really nice so what
they've done they've trained a
convolutional neural net and there are
many many good videos about neural nets
and convolutional neural nets and
computer file mike pound has done a
number of really good videos i
thoroughly recommend them that's what
they've used they've managed to train it
to distinguish between when it's got a
double tip and when it's got a proper
single atom tip and they've gone that
extra step and they've modified the
probe so that it will recover the
structure you need to get a good single
atom image as it were this is a really
big leap forward and for me it's it's
really exciting i'm slightly
disappointed that we didn't get that
we've been working on this type of
problem for for a number of years
actually another good reason why um it's
good to do computerified video and
there's actually with computer
scientists here in nottingham
and a number of years back we tried to
employ what are called
evolutionary algorithms or genetic
algorithms to try to tune the probe that
way it worked okay it didn't work
particularly well all the time and the
way to go obviously the next step the
next evolutionary stage in that was to
go to the machine learning side of
things and i actually had a summer
intern working on this last year but we
just as i said we were beaten to pip to
the post the great thing is is where it
can go because
they've controlled the probe and they've
been going for a particular atomic
resolution but actually sometimes
particularly if you want to do chemistry
let's use this one actually sometimes
that atom sticking out the end is what
you need but sometimes what you might
actually need just in terms of the
chemistry in the arrangement of the
electrons if you really want to
manipulate atoms if you want to do
chemistry computer controlled chemistry
you might actually need a structure a
bit more like this in terms of hybrid
bonds and how it interacts with the
surface the next step in this is to
not just give us a good tip give us a
tip with our particular structure give
us a tip with a particular state and
then we are really not just controlling
matter at the atomic level we're
controlling it right down to the single
chemical bond level and in fact we're
controlling the right the quantum
mechanical structure of the tip when we
go a little bit further along these
lines you know
can we actually just tell it we wanted
to build something like that
we just wanted you know can we get the
the computer to to as long as that's
within the laws of physics that's our
blueprint
you know and that might be a chunk of
silicon
can we actually get it to build that if
you're calibrating a camera there are
various test images that you can use to
to calibrate it from be it white balance
or focus or whatever
is there an equivalence in this that's
effectively what they do when they talk
about a single tip versus a double tip
this is a probe this is a sample so what
we would like is that the radius of
curvature the sharpness of this is
smaller than the object we're actually
imaging at the surface so if we do that
as we trace it across we'll map out
an image of what's happening at the
surface however that's just by symmetry
exactly equivalent to that so if you
have a relatively blunt tip like a
double tip or like a triple tip or a
quadruple tip or a cluster and you've
got something sharp at the surface like
a single atom or a single bond that
sticks out of the surface then what will
happen is that this will image this so
this is our test structure to come into
to to
map it across to the video uh process
this is our test structure this is
allowing us to see what's happening at
the end of the probe and that's exactly
what they're doing in this they have
single bonds which are sticking out the
surface when they see these sort of
ghost-like images it's telling us about
the structure the tip rather than the
structure of the surface and then they
control it accordingly so this is our
control it's built into the experiment
and you expose the plastic at the
surface in particular regions according
to the pattern and the important thing
is when the this particular polymer is
exposed to light it becomes soluble
the region