Kind: captions
Language: en
I want to show you how to color a transparent
piece of plastic without adding anything to
it, no dyes, paint, nothing except holes.
But first we have to talk about light.
Most people know that it is a form of electromagnetic
radiation.
But have you ever stopped to think about how
strange that is?
I mean, light is a combination of electric
and magnetic fields.
Electric fields like the ones that make these
balloons repel and magnetic fields like the
ones that make these magnets attract.
But how can you strip off the electric field
from around charge and the magnetic field
from around a magnet and combine those fields
together so that they can propagate out through
space at the speed of light?
Well, the key is the electric and magnetic
fields need to be continuously changing and
this is usually accomplished by wiggling some
electrons.
That creates these oscillating electric and
magnetic fields that propagate out through
space as an electromagnetic wave.
So how big is a wavelength of visible light?
Well, take a ruler and have a look at a millimeter.
Imagine magnifying that millimeter so that
it is the size of a meter.
Now divide that millimeter into a thousand.
Or, in other words, take a millimeter of a
millimeter and then divide that in half and
that is the wavelength of green light.
Now, granted, that is tiny, but my point is,
it is not that tiny.
And nature has actually figured out a way
to take advantage of the size of light.
Have a look at this blue morpho butterfly.
>> What is really neat about the blue morpho
is, yeah, it has this really blue iridescent
shiny wings.
But nobody really actually knows why they
are this way.
>> You mean it is to attract a mate or something?
>> The leading theory that I have read is
actually to let predators know, like birds,
that, hey, you know me.
I am really fast.
I move really well through the jungle.
Don’t even bother.
>> That beautiful iridescent blue color isn’t
created by a pigment.
No, .the color of the blue morpho is created
by the structure of its scales.
If we were to zoom in on this butterfly we
would see all these little sort of gratings
and holes within these gratings that trap
the light and reflect out this blue.
And if we just kind of look at it, direct
into the light...
>> So we have taken away the light that was
bouncing off the front.
>> Yeah.
You can see that the blue goes away and all
you can see is really the back of it.
And, in fact, that is because the wings are
almost transparent.
Without that light being able to reflect off
of it, you don’t get any blue.
>> Scientists like Flint are trying to create
similar structures to be used as security
devices on bank notes, bank cards and tickets.
>> What you are looking at is the thin transparent
piece of plastic and we have punched little,
tiny holes.
The holes are about 100 nanometers deep and
about 100 nanometers in diameter.
Each little image that you use on there has
about 500 million holes punched into it.
And those holes create a three dimensional
kind of grating that allow for the light to
reflect and reflect out and create those brilliant
colors.
>> The color is created in a similar way to
the color of a soap film.
If you carefully study a soap bubble, our
will notice that you can’t see all the colors
of the rainbow in the soap film.
All you can really see is cyan, magenta and
yellow.
But the reason or that is what the soap film
is doing is it is actually removing colors
from the light.
So the full spectrum of visible light hits
the film, but depending on the thickness of
the soap layer, certain colors are removed.
And so what we see is the spectrum of visible
light minus a color that has been taken out.
So, for example, in order to see magenta,
what we need to do is remove the green light
from the spectrum.
The light that bounces off the front surface
will interfere with the light that bounces
off the back surface of that soap film.
So when it comes out, any light that is about
500 nanometers is removed from the light.
And what we see is a mixture of the rest of
the spectrum.
So longer wavelengths than green and shorter
wavelengths than green.
Together they make that beautiful magenta
color.
>> So what you want to look for is structures
that are similar but can be compatible with
manufacturing processes where, for example,
a printing press process where you have a
big roll of substrate.
It is going to come along and you have got
a big press that is just going to stamp down
and punch in those structures.
>> But how could you create like nano scale
structures and punch them into a material?
Isn’t that nearly impossible?>>
No, not at all.
>> But it sounds like you are going to manufacture
these tiny things and then they are not going
to break off when you stamp into it.
>> No and that is the only thing everybody
thinks is, you know, oh, they are small.
And small things are fragile.
That is just the case.
One of the reasons that our structure can
be strong is that it has a low aspect ratio,
which means that the height to width is low.
So a high aspect ratio, let’s say, might
be 10:1.
So it is long and skinny.
And that is a weak structure.
Ideally you want a structure that is 1:1 or
maybe 1:2.
And what we do is we create structures that
are 200 nanometers wide and, maybe, 300, 400
nanometers tall.
And we use that to punch in.
And those structures are really, really strong.
>> For the moment Australian bills are made
of plastic and they have this little transparent
window in them to stop counterfeiters.
But perhaps in the future they will have hundreds
of millions of tiny nano scale holes instead.
>> The Australians were the ones that, you
know, invented the polymer bank note.
>> So would you be looking to get your technology
in there?
Have you been in dialog with the Australians?>>
I cannot comment on that.