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(Subtitle on screen: Professor Geoffrey S.D. Beach, Materials Science and Engineering)
The Materials Research Laboratory at MIT
is home to the MIT Materials Research,
Science and Engineering Center (MRSEC) –
a National Science Foundation supported program
that enables interdisciplinary research,
education and outreach efforts.
The MRL MRSEC oversees a suite of Shared Experimental Facilities
with cutting-edge tools that enable materials research
and enable us to train the next generation of materials scientists and engineers.
These facilities support over
a thousand users per year
both internally at MIT and externally across the nation.
The properties of a material depend on its structure
and the structure of material depends on how that material is processed.
In order to understand these relations,
we require the tools
that allow us to see structure at the atomic scale
to understand how a material behaves.
The X-ray Shared Experimental Facility at MIT allows us to do just that.
We can see the structural material down to its atomic scale
to figure out how that material works and why.
to the MIT Materials Research Laboratory X-ray facility.
I'm Charles Settens, and I overlook the X-Ray facility.
We have a variety of pieces of equipment
in order to perform X-ray diffraction analyses
of anything from a powder sample
to a thin film
to an epitaxial thin film.
We are studying functional oxides of perovskite type largely and to some extent also
simpler binary oxides, and in these materials the properties can be
significantly dependent on the type and concentration of different imperfections
that we call point defects. This could be atoms missing from their lattice sites
or excess atoms where they normally are not.
Each of these different defect types
have a different lattice signature that we can detect by characterizing these
thin films using X-ray diffraction.
A primary use of the materials research
laboratory X-ray facility is powder diffraction.
To prepare a powder sample
we have to put it into a cavity
and make sure that the sample is
as flat as possible.
Polycrystals are ubiquitous within our world.
It turns out we're standing on polycrystalline material.
Most minerals are made of
polycrystalline material.
This lab analyzes polycrystalline materials
in order to find out the atomic composition.
I also teach practical research skills for X-ray crystallography
so that you can learn about the structure of materials at the atomic scale.
X-ray diffraction is a very powerful technique to reveal the microstructure of the system.
We study the electrical properties of different lithium-based materials.
This thin film that has been grown by pulsed laser deposition
on top of metallic electrode, we investigate a possible memory effect on this thin film.
It could be a new class of memristors.
It could be used as an advanced
computing element or information storage.
In the sample holder which is sealed,
we can perform the X-ray measurement without degradation of the film.
X-ray characterization is really pretty basic
to understand the relation between the
electrical properties of the system,
with the crystalline structure and microstructure.
Whereas most of the equipment in the facility is targeting hard materials,
small angle X-ray scattering (SAXS) equipment
characterizes soft materials.
You can learn about the structure of a material
not on the angstrom scale, but on the hundreds of nanometers scale.
The beam stop that looks like a clock hand
rotates into position
in order to block the main X-ray beam
and allows us to see the scattering very close to the main beam.
Students in Robert Macfarlane's research group,
in the Department of Materials Science and Engineering,
use the small angle scattering system
in order to take measurements of samples
that are nanoparticles
that are arranged in a crystalline lattice.
So instead of atoms sitting at the positions of a
body centered cubic cell, instead it's nanoparticles
that are functionalized with DNA.
In the Macfarlane group at MIT, we work on self-assembling nanoparticles.
We take nanoparticles, and we functionalize them
with some kind of a chemical component.
At the very tip of the chemical component,
we have a special molecule
that we call a sticky group.
When we are doing this, we'll have two different types of nanoparticles
each with a complementary sticky group to one another.
Then when we mix the two particles together,
the sticky groups can recognize each other and then they'll self-assemble.
I wrote a program that will heat the particles to different temperatures, and I will use
the SAXS to monitor the crystallinity in situ.
This will let me make insights
into the molecular behavior of the system as it crystallizes.
What's special about the sticky groups is we can heat them up above a certain temperature
and the bonds that are holding together the two nanoparticles will start to weaken
and they'll be able to break and re-form.
Some groups take measurements at higher temperatures
such as room temperature to 1,200 degrees Celsius using a
high temperature stage. This is important for groups that want to monitor their
synthesis process as a function of temperature.
A particular crystal structure that is analyzed often
using a powder diffractometer is a perovskite structure.
So the system we're working on is perovskite thin film oxides.
The reason we choose this system (is) because previous research has shown
that under certain conditions, these perovskite thin films could generate stable nanoparticles on the top
of the surface which is very crucial for catalysts and also energy conversion devices.
We want to use strain to enhance its capability.
Imagine you have a rubber ball
and when you squeeze and stretch it, you are changing its shape.
The shape is changing because you have strain in your materials,
but for real materials we're working on, thin films, when you squeeze and stretch it,
you can change its energetics. That's where you can change
the property of this material.
The most important thing is to measure
the atomic distance between every atom.
So a very perfect strategy is using X-ray diffraction.
The facility here allows us to quantify, characterize,
the structure of our thin films,
as well as identify the defect states,
because these different point defects
have different signatures in the crystalline lattice
that we can detect by measuring their lattice parameters
using X-Ray diffraction equipment in this laboratory.
Thank you for watching, and we look forward
to working with you in the Materials Research Laboratory X-Ray facility.