Being Ingenious at the Nanoscale

Gehan Amaratunga

Engineering Dept., Cambridge University

Sri Lanka Institute of Nanotechnology

Ray Wijewardane Memorial Lecture

15th November 2012

Ingenieur Engineer

• Creator of things Ingenious is an Ingenieur (Engineer)

• Ray Wijewardane is a Sri Lankan Ingenieur par excellence

Ingenious – hand held tractor

Holistic – sustainable agriculture

Socially engaged – academia, government, commerce

• Cambridge Engineering Dept. almunus!

The scale of the physical world

Contact CE

NA

NO

NA

NO

Materials when taken down to the < 50nm scale can exhibit physical and chemical

properties not seen in bulk phases:

The Carbon Nanotube is a good example of

this

Carbon forms tubes when sheet structure in graphite goes to nanometer scale in one dimension

• Depends on the angle of rolling and diameter as to whether metallic or semiconducting

What does the 50 nm node in electronic devices mean?

• Man made electronic structures are smaller than the size of biological organisms

Transistor for 90 nm node (Source: Intel) Influenza virus (Source: CDC)

2012: 30nm node with

22nm gate length

Continuous shrinking of transistor sizes through ‘ingenious’ methods the source of shrinking electronic devices with increased functionality such as mobile phones

22nm

Nanoscale effects in nature

http://www.youtube.com/watch?v=xdzS4-d31n8

Engineered Lotus Leaf Effect

Water drop from training slide http://youtu.be/ivcMUxCP0T0

Light at the nanoscale

Light at the nanoscale

Iridescence – changing of colour with direction of observation- of the butterfly wing

Colours due to pigments do

not show angular variation

The nanostructure of the butterfly wing

Constructive interference of reflected light at

400nm gives blue colour – structural light

The colours of the peacock

Peacock feathers have

within them structures (50

-100 nm) which are

smaller than the blue

wavelength of light

(400nm).

They interact to

preferentially reflect blue

light in ‘blue’ feathers.

This is a photonic band

gap effect which was

understood in detail only

in1992 (Yabalanovich)

Engineering nanostructures to interact with light

Photonic band gap defects in c-Si NW arrays for guiding light

Light guiding in c-Si NW arrays

60 deg angle of incidence

H. Butt et al

Prog. Electromag. Res, (113), 2011

Precisely engineered carbon nanotube arrays through catalytic synthesis

• Step 1: At 700°C (growth temp), Ni catalyst agglomerates into catalyst clusters.

• Step 2: PECVD - C2H2 is the growth gas for CNTs, NH3 is the etching gas for unwanted a-C.

Very tight control of diameter (catalyst size) and

height ( growth time)

400nm r=24.5nm r=40.5nm r=45nm

Periodic and quasi periodic arrays of carbon nanotubes

Optical image of an engineered carbon

nanotube butterfly wing with an ‘ingenious’

feature

White light on rotating CNT array-2 http://youtu.be/4gitbgUIkFg

Red laser on Cambridge crest http://youtu.be/W8VDXMYatGU

Green laser on Cambridge crest-1 http://youtu.be/05mibZ4j-mg

In addition to normal iridescence the engineered butterfly wing has a holgram embedded within it. It can be seen at a specific wavelength of light ( green in this case) in the far field when a screen is placed: CNT holography

Metallic MWCNT arrays can be exploited for Plasmonic Photonic Band Gaps (P-PBG)

Extremely low frequency plasmons in metallic mesostructures – Pendry et al, PRL, 1996

r

a

Metamaterial design with heavy plasmons

E

H

Metamaterials being designed for invisibility cloaks

Object being

made invisible

Metamaterial cloak – it guides light around the object and reforms the

light waves without any reflection or absorption

Possible by engineering the optical characteristics of the cloak precisely

with spatial variation in the nanometer scale

End note

• Nanotechnology is the exploration of a new frontier, that of the ultra-small, in our continuous quest to be ‘ingenious’

Dedicated to Ray Wijewardane

In memorium