Transcript The Science of Two Dimensional Materials

JUN YAN
UNIVERSITY OF MASSACHUSETTS AMHERST
2015 SUMMER INSTITUE ON NANOSCIENCE
A reminder of oleic acid molecule
Non-polar end of oleic acid
molecule: hydrophobic
1.97 nm
Polar end of oleic acid
molecule: hydrophilic
Water molecules in a tray.
Water molecule (polar)
From nano to sub-nano
1.97 nm
From nano to sub-nano
120º
120º
120º
Benzene molecule: a very thin and flat disk! The
thickness is less than 1 nm – sub-nano!
Graphene is a single atomic sheet of graphite
Layered structure of graphite
Carbon atomic layers slide with respect to
each other under shear force during writing
0.335nm
Writing makes graphene: a single atomic layer of graphite!
How do we make graphene?
graphite
Scotch tape
100μm
Silicon chip
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 screen
Electrical conductive
and mechanically
flexible and robust
Corrosion resistant
Tensile strain 18.7%
In salt water 3.5% NaCl
Flexible touch screen
Exercise: how much graphene do we need to
cover the empire state building with graphene
touch screen?
See graphene
By optical
microscope
By eye
100μm
100μm
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 Strocio
NIST
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×
1
=2
3
What is the area of each hexagon?
6×
3
× (0.14𝑛𝑚)2 = 0.05𝑛𝑚2
4
Next the empire state building:
Height: 381 m; length: 129.2 m; width: 57 m
What is its surface area (excluding the bottom surface)?
2 × 129.2 × 381 + 2 × 57 × 381 + 1 × 129.2 × 57 = 149,248.8𝑚2 ≈ 1.5 × 105 𝑚2
Exercise: how much graphene do we need to
cover the surface of the empire state building?
How many carbon atoms do we need?
2
1.5×105 𝑚2
× 0.05𝑛𝑚2
= 2×
1 𝑛𝑚 = 10−9 𝑚
1.5×105 𝑚2
=
0.05×10−18 𝑚2
6 × 1024
1 𝑛𝑚2 = 10−18 𝑚2
Consider carbon atoms with 6 protons and 6 neutrons
6 × 1023 (1 mol) carbon atoms weigh 12 gram
The amount of graphene we need is:
6 × 1024
× 12 𝑔𝑟𝑎𝑚 = 120 𝑔𝑟𝑎𝑚
6 × 1023
2D materials beyond graphene:
Graphene
Boron nitride
Boron atom
Carbon atom
2D?
Conducts electricity?
Nitrogen atom
yes
yes
yes
no
2D materials beyond graphene:
Graphene
Boron nitride
Boron atom
Carbon atom
2D?
Conducts electricity?
Nitrogen atom
yes
yes
yes
no
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
Sample produced by the
‘scotch tape method’
Electrical property?
Single layer MoS2
Multi-layer
MoS2
Si/SiO2
substrate
Between graphene and
boron nitride.
The 2D zoo
Lasagna
The 2D zoo
Atomic lasagna
Having fun with 2D materials
Moire patterns as
can be seen in STM
measurements.
B. Leroy, Arizona
Electrical measurement
of graphene on boron
nitride.
C. Dean, Columbia
Light emission diode
made from MoS2-WSe2
atomic stacks.
X. Duan, UCLA
Thank you!