JUN YAN UNIVERSITY OF MASSACHUSETTS AMHERST 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

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 Writing makes graphene: a single atomic layer of graphite! 0.335nm

How do we make graphene? graphite Silicon chip Scotch tape 100μm

2010: Nobel award over flake of carbon Andre GeimKonstantin Novoselov

How to make large size graphene? Chemical vapor deposition: breaking the methane (CH 4 ) apart at high temperature! ~1000 Cº Samsung, Korea

Graphene for flexible touch screen Electrical 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 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 Strocio NIST

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

1 st 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? What is the area of each hexagon? Next the empire state building: Height: 381 m; length: m; width: 57 m 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 The amount of graphene we need is: (1 mol) carbon atoms weigh 12 gram Exercise: how much graphene do we need to cover the surface of the empire state building?

2D materials beyond graphene: Carbon atom Boron atom Nitrogen atom 2D? yes Conducts electricity? yes no Graphene Boron nitride

2D materials beyond graphene: Carbon atom Boron atom Nitrogen atom 2D? yes Conducts electricity? yes no Graphene Boron nitride

Another 2D materials: MoS 2 Dry lubricant Also a 2D material, each unit has three atomic layers, with molybdenum sandwiched by sulfur atoms.

Another 2D materials: MoS 2 Occurs in nature Single layer MoS 2 Multi-layer MoS 2 Si/SiO 2 substrate Sample produced by the ‘scotch tape method’ Electrical property? 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. Electrical measurement of graphene on boron nitride. B. Leroy, Arizona C. Dean, ColumbiaX. Duan, UCLA Light emission diode made from MoS 2 -WSe 2 atomic stacks.

Thank you!