JUN YAN UNIVERSITY OF MASSACHUSETTS AMHERST

SCIENCE OF TWO DIMENSIONAL MATERIALS

2015 SUMMER INSTITUE ON NANOSCIENCE

A reminder of oleic acid molecule

Water molecule (polar)

Water molecules in a tray.

Polar end of oleic acid molecule: hydrophilic

Non-polar end of oleic acid molecule: hydrophobic

1.97 nm

From nano to sub-nano

1.97 nm

From nano to sub-nano

Benzene molecule: a very thin and flat disk! The thickness is less than 1 nm – sub-nano!

120º

120º

120º

Graphene!

Graphene is a single atomic sheet of graphite

Layered structure of graphiteCarbon atomic layers slide with respect to each other under shear force during writing

Writing makes graphene: a single atomic layer of graphite!

0.335nm

How do we make graphene?

graphite

Silicon chip

Scotch tape

100μm

100μm

2010: Nobel award over flake of carbon

Andre Geim Konstantin Novoselov

How to make large size graphene?

Chemical vapor deposition: breaking the methane (CH4) apart at high temperature!

~1000 Cº Samsung, Korea

Graphene for flexible touch screenElectrical conductive and mechanically flexible and robust

Flexible touch screen

Tensile strain 18.7%

In salt water 3.5% NaCl

Corrosion resistant

Exercise: how much graphene do we need to cover the empire state building with graphene touch screen?

See graphene

By eye

100μm

100μm

By optical microscope

By atomic force microscope

How to see the carbon atoms in graphene?

Transmission electron microscope

TEM image of graphene

‘Seeing’ the carbon atoms of graphene

Scanning tunneling microscope STM images

Brian LeRoy U. Arizona

Joe StrocioNIST

Exercise: how much graphene do we need to cover the surface of the empire state building?

Exercise: how much graphene do we need to cover the surface of the empire state building?

1st task: find the density of carbon atoms, i.e. number of carbon atoms per unit area

Observation: periodicity! (property of a crystal)

Exercise: how much graphene do we need to cover the surface of the empire state building?

Let’s start from one hexagon:

How many carbon atoms are there in each hexagon?

6×13=2

What is the area of each hexagon?

6× √34×(0.14𝑛𝑚)2=0.05𝑛𝑚2

Next the empire state building:

Height: 381 m; length: 129.2 m; width: 57 m

2×129.2×381+2×57×381+1×129.2×57=149,248.8𝑚2≈1.5×105𝑚2

What is its surface area (excluding the bottom surface)?

How many carbon atoms do we need?

Consider carbon atoms with 6 protons and 6 neutrons

6×102 4  6×1023 ×12𝑔𝑟𝑎𝑚=120𝑔𝑟𝑎𝑚

The amount of graphene we need is:

=

6×1023 (1 mol) carbon atoms weigh 12 gram

Exercise: how much graphene do we need to cover the surface of the empire state building?

1𝑛𝑚2=10−18𝑚21𝑛𝑚=10− 9𝑚

2D materials beyond graphene:

Carbon atomBoron atom

Nitrogen atom

2D? yes yes

Conducts electricity? yes no

Graphene Boron nitride

2D materials beyond graphene:

Carbon atomBoron atom

Nitrogen atom

2D? yes yes

Conducts electricity? yes no

Very different properties!

Graphene Boron nitride

Another 2D materials: MoS2

Dry lubricant

Also a 2D material, each unit has three atomic layers, with molybdenum sandwiched by sulfur atoms.

Another 2D materials: MoS2

Occurs in nature

Single layer MoS2

Multi-layer MoS2

Si/SiO2 substrate

Sample produced by the ‘scotch tape method’

Electrical property?

Between graphene and boron nitride.

The 2D zooLasagna

The 2D zooAtomic lasagna

Having fun with 2D materials

Moire patterns as can be seen in STM measurements.

Electrical measurement of graphene on boron nitride.

B. Leroy, Arizona C. Dean, Columbia X. Duan, UCLA

Light emission diode made from MoS2-WSe2 atomic stacks.

Thank you!