I would like to wish you
all of a good afternoon and

thank you very much for coming.

Before I start this is the first
time that I'm presenting in front

of such a large audience in
such a large hall so one thing.

This place looks really
scary from down here and

it's not half as scary for mob which is
where I've spent most of my five years.

So not having said I like to share some of
the results that got recently published in

advance functional materials on
tunable crew salinity in politics and

typhoon and
how that impacts George transport.

Before I began I think it's very important
to put things in perspective and

show you where organic electronic
stands in the timeline for

the evolution of electronics so
electronics as we know it began with the.

I guess the fact that materials can
conduct charges across distances and

this was done by Stephen Grey and
seventeen twenty seven.

When he discovered that using
packing wire suspended on

threads that you can
get charges to conduct.

So the timeline for

electronics has been punctuated by
very important monumental events.

I like to point out nine hundred
forty seven which is when the point

contact understood was invented
by a body in Britain and shortly.

This is followed up very closely in nine
hundred seventy six by the discovery of

conduct of Indian polymers in polyethylene
again by three people he entered a cover.

At University of Pennsylvania.

And this marked a very monumental
achievement more so because of the fact

that up until nine hundred seventy
six polymers were known more for

their insulating properties and not
really for the conducting properties but

you fast forward into the present two
thousand level and you can see that

the achievements of nine hundred forty
seven and nine hundred seventy six.

They're ubiquitous especially the
achievements of nine hundred forty seven.

We're surrounded by products
microprocessors they drive our lives.

Organic electronics is not there yet but

it's getting that at breakneck speeds so
cannot cause plastics all ourselves.

Three dimensional organic light emitting
diode with displays these are all

shining examples of the success
stories of organic electronics info.

My phone.

This is a Samsung captivate a really
crappy phone but the display is amazing.

It's an organic light emitting diode
base display to really nice display.

These are all reasons why.

Organic electronics is here to stay.

So organic electronics is inevitably
going to draw comparisons with inorganic

electronics but

there are some distinct advantages that
are offered by a graphic electronics.

So one of the major selling points of
organic electronics is the fact that

you can literally make
conductive inks that you can

print onto larger circuits using loaded or
processing.

This enables a wide variety of
applications other ways not accessible

to conventional inorganic technology.

Stuff like flexible flexible
displays flexible circuitry the term

plastic electronics comes because you
can literally print these circuits onto

plastic substrates so all this is possible
because so the question to be answered.

Now is what is the science behind all
these materials that enables all these

wonderful applications so.

I'm going to start my talk by introducing
organic semiconductors one of

the science of organic semiconductors.

I'm going to use pallets we
have seen as a model material.

It has been the object of my affection for
the past three years and

I'm going to use that as a model system
to explain properties in general.

I'm going to follow that up with a very
brief introduction to the physics of

charge transport.

In organic semiconductors because I think
it's very important to understand how

judges move in these materials to
appreciate some of the results.

And I'm going to follow that up with
some of the pertinent results in

the paper where I'm going
to show you how we can

create ordered because using our
recent radiation of solutions.

So you have a wide variety of
organic semiconductors out there you

have molecular semiconductors small
molecules like fantasy in dependency and

you have conjugated
polymers like politics and.

If you notice all of them have one very
important quality one very important

thing in common which is
the presence of count.

And that is what is responsible for all
the interesting op electronic properties

that this class of materials
conjugated materials are displayed.

So what exactly is conjugation so
conjugation is nothing but

the presence of a network of carbon
atoms with alternating single and

double bonds across which the pilot
drawn can be localized and

it is this fundamental phenomenon that
is at the heart of all the optical and

electronic properties these
materials are displayed.

So I'm going to focus my attention
primarily on between H.T. The concepts.

Hopefully translate into
other materials as well.

So what exactly is.

So essentially what it is is it consists
of two very important but contrasting

components and I say that because you
have a bag one which I would label

the electronic component and that holds
the conjugated part of the molecule and

that is what is responsible for most of
the electronic an optical properties and

then you have these Alka side chains whose
sole purpose is to impart solid billeted

to the system because the main
chain by itself is intractable.

So the sort ability is
demonstrated in this picture here.

This is a solution of P three H.T.
in chloroform that I prepared in my lab.

It shows that it's perfectly
homogeneous not solid military issues.

This is also one of
the major driving forces and

one of the major selling points of organic
electronics because you can you can make

conductive inks that I was telling
you about in the very first slide and

this is what is used for
literally printing your circuits.

So the key question now is

if you want to understand charge
transport at the microscopic level.

You have to understand how these
molecules back at the microscopic level.

So if I make a film of them or
do you make it using spin coating but

you have a variety of other
methods that can be used.

What is the film look
like in the solid state.

So people have done actually
diffraction studies of P.T.S.D.

and they've sort of come to
the conclusion that between the facts and

what is known as known as
a level of fashion and

what that means is you have stacking
of the polymer genes along one axis and

you have laminar stacking between
the sides and along the other axis.

This is very important.

Microscopic droughts transport because if
you take a look at movement of charges

at the molecular level.

They can either move along the backbone
and they can move between the backbone and

that's the so-called by stacking direction
or they can move between the side chains.

Not for the purposes of this presentation.

We're going to ignore the movement
of carriers along the side James and

it's not it's not an outrageous
claim because that insulating So

it's highly unlikely that that's
going to dominate John's transport.

So looking at the remaining
two modes of transport.

So you have to transport
along a single column a chain

which is the in truck chain.

Transport or

you have transport between polymer
genes which is into chain transport.

But if you take a look at the molecular
dimensions you and I'm I'm going

to focus mainly on microscopic transport
because the devices that I primarily used

to characterize the firms are organic
feel effect on distance and

I require charges to move across distances
that are several tens of microns.

So given that and

comparing that with more likely
dimensions of a single problem a chain.

It is highly unlikely that interchange or

transport although it's
important if you want to.

It's not going to dominate
microscopic judge transport so

that like that that basically leaves us
with movement of Guardians between polymer

chains or interchange transport and that's
what I'm going to focus my attention on.

But before I move on.

I'd like to introduce
the concept of mobility.

So when I when I'm actually testing a
transistor the values that I actually get

out of it is the field effect mobility and
all that is that it's giving me an idea of

how easily the ideas are actually moving
across a certain distance in my phone.

So now that I'm fully giving
you an introduction to

the materials involved
in organic electronics.

What is it that dictates the mobility.

So for that to explain that I'm going to
invoke democracy electron transfer theory

because at the microscopic level.

The movement of charges is nothing but
a full on assisted hop and

this hopping transport is very analogous

to self exchange redux reaction
that model that was originally my.

Really.
Marcus and

who came up with the Marcus equation.

So if you take a look
at the Marcus equation.

There are two very important parameters
that dictate the hopping rate and

hopping it's going to
determine the mobility.

Firstly it's longer a longer
the organization energy.

And I'm not really going to go
into details of what lambda is but

it will suffice to say at this point there
is a measure of the extent of interest

in ordering the can to the configurational
character of a single problem.

What I'm going to focus my
attention on right now is we re

is the interchange transfer or
transfer integral and

what we tell you is for example when
you have just transferred taking place

from one conjugated segment which
is to another conjugated segment.

The the probability of
the drawn dition depends

upon the electronic overlap between
those two states and we basically

quantifies what that transition
probability is it's the transfer integral.

But very importantly from the point of
view of the stock we is very intricately

linked with the crystal quality of my film
the microstructure which is why I and

a lot of other people have focused on
understanding what exactly is that all of

micro structure in charge transport
because it controls we the people

of done a wide variety of studies
identifying different parameters in P.

three H.T. that can control
the microstructure for example people have

explored the role of visual regularity how
you attach the sightings to the backbone.

Polamalu it can make a big difference to
the microstructure and just transfer and

thus charge transport.

We ourselves have done quite a bit
of work especially Dr Morman.

Where we explored not only the final
microstructure of the films and

how it impacts microstructure and
transport.

But how does microstructure
evolve in the first place.

So all these studies.

Have have have have you learned
a lot of useful information but

a couple of key questions
still remain unanswered.

Or at least they're not
fully answered yet.

So one is what is the exact role of
microstructure What is the exact

dependence of microstructure of Judge
transport on microstructure is.

A one to one correspondence.

We don't know yet.

But in order to answer the first question
another question must be answered.

How do you do in the microstructure
because if you're not able

to radio microstructure How
do you draw correlations.

This is when we chanced upon a very
interesting phenomenon in our lab and

this is purely purely accidental but

it is a good accident because it
gave me the paper on the award.

So.

That's nice.

But what I basically noticed was
you take a solution of P.T.S.D.

employer reform and I figured that I
wanted to make a homogeneous solution.

And I routinely.

During my master's work at routinely used
or Sonic Youth radiation to disperse

carbon nanotubes and solvent so I thought
why not use the same technique here.

But when I actually applied that
technique the solutions of between H.T.

which are orange the pristine
solution the orange and color.

It started changing color
within five minutes.

And I was really surprised by this because
I wasn't expecting this color change but

more importantly from the point of view
of organic electronics what I noticed was

when I made transistors from
these two different solutions

the the mobility of the transistor of the
of the transistor made from this solution

was routinely hundred forty higher
than the mobility of the transistor or

pain from the or in solution without or
sonic radiation.

So this basically piqued my interest so

a couple of very important
questions popped into my head one.

Why is that a color change.

So in order to investigate
the color change.

We're talking about color and

conjugated materials you want to start
with spectroscopy which is what I did so

I have I have you have the solution state
as well as a solid state of spectra of.

Solutions and phones before and
after our sonic radiation and

I want to draw your attention to two very
particular features in the solution state.

So the development of these vibrant excite
bands as a result of the recent occasion

is what I believe is causing
the color change but more importantly

from the point of view of solid state
structure the order in charge transport.

If you look at corresponding features
in the solid state you lot is that one

the absorption maximum of the Solid State
of the film obtained from the radio.

Good solutions is better
quickly shifted and

that tells me that I have mentioned
clean radiation and the mentioned clean

resolution and done is is resulting in
increased molecular order as is evident by

the zero zero Browning transition which is
more intense in the film which has been

trying to get it would have been
obtained from Sun a good solution.

So to cut the story short what absorption
spectra is telling me is arsenic in

radiation is indeed creating ordered
because in the solution state would

survive the casting process and a manifest
in the final film and this could possibly

contain evidence as to why I am seeing
the mobility increase in the first place.

But before I explain
the defect in charge transport

I did raise the concept of to an ability.

So let's explore that a little bit more.

So when I will actually repeat
the same experiment but

this time I started reading
these on occasion time.

What I found as the vibrant features
don't actually increase abruptly.

But it's more like an evolution these
features evolve as a function of

radiation time and this is also mirrored
in the development of the zero zero peak

intensities in the solid state all this is
telling me is increased on occasion time

results in increased formation of
molecular aggregates and solution and

increase molecule in order in
the solid state cause and effect.

Now all this is well and
fine you know I'm claiming that through

absorption spectroscopy we are seeing
increased molecular order but

this remains indirect evidence which is
when I decided to take it one step further

and see what happens in my F.M. scans.

So when I ran F.M.
atomic force microscope in these out

of phase images stopping would
face images I saw that for

the films of pain from pristine solutions
and thirty seconds on a good solutions.

They are pretty much featureless which is
sort of expected because chloroform is

a highly volatile solvent.

But if you look at
the the film from one minute

onwards you start seeing the development
of these crystal lights.

I'm going to put Crystal Light on court
I'll come back to that but you can clearly

see the effect of sanitation as you
increase on occasion time it's lead.

Two more and more.

None of crystal or none of the below
structures being incorporated

in the other ways amorphous filled
with increased concentration.

So so far everything everything
seems to be agreeing with

the evolution of ironic features
in absorption spectra but

I have no evidence that these none of the
below structures are actually chrysolite

So this is what I decided to run X.
ray diffraction and X. ray diffraction

basically showed me a remarkable almost
a one to one correspondence between

the between the development of these
Not a fabulous Crystal Light and

the evolution of the one zero zero peak
intensity inexorably which basically

told me that indeed the molecular order
in the film is increasing as a result of

increasing competition of these not
a fiber in an otherwise amorphous firm so

combining the results of X. R.T.F.M. and
absorption spectra we have a nice picture

forming that of as I mentioned earlier
ordered precursors in the solution state

which are getting transferred in the solid
state so now I have reason to believe.

Why I am getting the increase in mobility.

But I was more excited by the fact that
going by simply by the intensity that

I'm getting after ten
minutes the radiation.

I was expecting the abilities that are
going to be through the roof I was really

excited by this because you can imagine
that this is a very simple technique for

increasing mobility in organic
semiconductors which remains the top of

interest but when I actually measured the
mobility as using field effect on this.

I was in for a little bit of
a disappointment because if you notice

the initial period of Sonic a should
I do see the hundred fold increase in

the feel effect mobility as expected but
beyond about one to three minutes.

There's an apparent saturation of the
mobility which wasn't expected especially

given the fact that the way Browning
features the features in the F.M.

the features in X. are to continue to
evolve beyond one to three minutes.

So this to me contains enough evidence
that you're seeing a population type drugs

transport now percolation type drugs
transport is very common in composites in

fact when I used to make composites and
B.M.'s populations are very common.

Things like you do you increase
your loading concentration and

beyond a certain point you see a sharp
jump in the conduct of a day and

beyond that there's absolutely
no change very similar behavior.

Only this time I'm talking
about fuel effect mobility.

So let's take a look as to why
why the system behaving this way.

This is when I decided to explore the
fears images that I've got a little bit in

more deeper fashion when I notice that the
films actually consist of a multi-phase

morphology and I'm specifically
talking about a disordered phase

because I ordered phase and ordered phase
and my definitions of these different

phases the based on what is the polymer
Gene conformation within these phases.

So for example in a disordered phase you
want to have a significant amount of twist

between the Typhon units and
that's what the straps conjugation and

that in turn disrupts
into molecule packing.

So basically what F.M. is telling me is

you have a significant portion of the
disordered and the cause I ordered phases.

Even when you're developing.

Even when you develop a significant amount
of chrysolite you still have a very large

fraction the matrix is still mostly
amorphous of course I ordered and

what we proposed in the paper
was as long as you have

this distribution of ordered and
disordered phases.

You're always going to see
a scenario where no matter how much

you increase your crystal limited by it is
going to become independent at a certain

point because you're charged transport to
your disordered segment is what is going

to dominate microscopic transport.

So I like to conclude my talk by raising
some of the highlights of this work

primarily hopefully I've demonstrated that
are just sound is a very facile method of

incorporating order in the film but more
importantly from a scientific point of

view it represents a very simple technique
to study charge transport microstructure

correlations because you can literally do
in the microstructure and have many more

data points to actually draw correlations
with looking at the big picture.

I think there's a whole new area within
organic electronics that has not been

explored extensively understanding polymer
interactions with the solvent environment.

Instead of actually trying to alter
the microstructure after the film's

been formed.

What about inducing ordered
structures in the solutions

state before the films forming.

So this is something that needs to be
worked on taking advantage of polymer

processing and seeing how that
affects the structure of the film.

And the corresponding properties.

And if you want to extend if you want to
sort of get a holistic understanding of

this complex correlation between
microstructure and George transport.

I feel that we need to conduct
experiments at all and

scales starting from the nano scale
understanding how the charges

move in the molecule while and expand and
combining that with experiments that allow

the domination of charge
transport in the middle scale and

the macro scale which is what I'm doing
and it's only by a combination of all

these three experiments that we can
fully understand this correlation.

With that I'd like to acknowledge though
all my co-authors especially my advisor.

Dr college from chemistry they
have been absolutely fantastic.

I'd also like to thank the Ziegler family
and the Department for the absolute on.

And for the support that they've given me
over the years and for the fellowship and

the various funding agencies for
the money.

I'd like to thank you very much for

your attention I'd be more than happy
to answer any questions you have.

Yeah.

So this is a question that I get asked
often whenever I present as well.

So I guess what we have.

I went to some papers on understanding.

One of the effects of our
resigning creation and

one of the papers I came across was.

Aggregation of proteins using I
just want to get radiation and

I think very similar again in the
mechanisms might be at play here as well.

So what I believe is happening is you
can speak of addition process that.

That is actually happening in the solution
when you apply Alderson to get radiation

and apply the show to the bottom of genes.

It causes the bottom of
genes to open up and

then that's what I feel is going on
in the system as well but having said

that I think Elsa presented this work
at Air Force Research Labs and one of

the people there they proposed something
very interesting that maybe the pressure

that is there in the system when you have
acoustic of EDITION that's that's causing

the problem of genes to sort of collapse
into each other and that might also be

a reason why you see this by stacking
because of our recent to get radiation.

Yes been quoting here.

Why.

I'm going to say nor because in
all the films that I've measured

like in some cases when
I've done the F.M..

If you if you if you and
I certain sections of the film.

It's very easy to imagine that there's
some alignment but I think the process

itself is isotropic So I would say that I
don't think there's any alignment in any

one direction you're talking about
alignment of the Nano fibers themselves.

No I don't think I've seen that.

No no no I'm actually
sonic eating the solution.

And it's been coding.

Yeah.

Or that's a good question.

So I've done this experiment with with
with Jeff and silent and all three

of them basically they show a more rapid
response to sonic ation than chloroform.

So I believe what's going on in terms
of the McCann ism is it's a it depends

in a very complex manner on the solid
validity of the polymer in the given.

And so if it's for example if I'm
using fat as I lean or D.H. or which

are relatively poor solvent compared to
chloroform for P three H.T. It accelerates

the aggregation process in fact when
I did the experiment with Xylene.

It formed a gel within two minutes
completely press of a data.

At the same time and I used other
solvents like a lot of benzene.

Benzene I see absolutely no
effect of this phenomenon.

So I'm guessing there's some complex
interplay between Soul ability and

this custody of the solvent as well.

What assumption.

When I mean I guess the effects of
moisture and oxygen on Georgetown's not

trying to transport but on the performance
but amateurs of organic feel effect on

the sort of very commonly studied we
still don't understand what exactly is

happening in terms of the mechanics them
how exactly oxygen is participating.

But these experiments
were conducted in error.

And I've done the same experiments
in a glove box without any oxygen or

moisture the mobility is unchanged but
there's another but

I'm going to call the threshold age
which tells you what world age.

What the blade get wordage your
device is actually turning on

that is dramatically shifted.

If you do it in ambient atmosphere.

But I don't think
the mobility is affected.

Sure.

Sure.

Actually all these all these results
that have shown your the universal and

the heat sort of accident opposite manner
compared to are just on a good idea.

In fact I've done some experiments but

I've taken a solution of chloroform and
the water bought in the sanitation tool.

I heated that up.

So if ice.
Sonic it using a heart that

I would not see an effect of all
this on occasion that tells me that

thermal energy is acting against so
on occasion for some reason.

But all these processes the development
of the why running features

Crystal in a dream ability to
completely reversible if I heat them.

I can recover all the original properties.

Well I mean Petri actually.

I would say that the sort of it's
not the state of the art anymore.

So people have come up with more
improved designs and I guess the limit

that I've seen for Paul a medic materials
right now as of two thousand and eleven.

It's almost hit the one.

It's about once I mean a scrap of
world second so I would say even for

sonic it would be three H.D. for this
particular P three H.D. it's still like

an order to two orders of magnitude lower
than what the current state of the art is

but I've used a different variety of
the three H.D. with a with a higher.

And I've managed to hit point one
which is the highest I've seen.

I'm pretty sure it does but
I'm using a bench top and

I don't have the flexibility to change the
frequency on the power but I'm pretty sure

that the frequency and the intensity
would definitely impact the acoustic of

addition process which is what I
believe is the heart of everything but.

I would imagine if I did take a guess
that changing the frequency or

changing the intensity would accelerate or
decelerate the process but

I don't think it will change
the phenomenon as such

it is definitely possible yes that's
definitely worth looking into.

That's a great point.

Thank you.