Prof gehan presentation 15 nov 12-final
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Transcript of Prof gehan presentation 15 nov 12-final
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Being Ingenious at the Nanoscale
Gehan Amaratunga
Engineering Dept., Cambridge University
Sri Lanka Institute of Nanotechnology
Ray Wijewardane Memorial Lecture
15th November 2012
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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!
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The scale of the physical world
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Contact CE
NA
NO
NA
NO
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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
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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
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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
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Continuous shrinking of transistor sizes through ‘ingenious’ methods the source of shrinking electronic devices with increased functionality such as mobile phones
22nm
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Nanoscale effects in nature
http://www.youtube.com/watch?v=xdzS4-d31n8
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Engineered Lotus Leaf Effect
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Water drop from training slide http://youtu.be/ivcMUxCP0T0
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Light at the nanoscale
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Light at the nanoscale
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Iridescence – changing of colour with direction of observation- of the butterfly wing
Colours due to pigments do
not show angular variation
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The nanostructure of the butterfly wing
Constructive interference of reflected light at
400nm gives blue colour – structural light
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The colours of the peacock
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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)
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Engineering nanostructures to interact with light
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Photonic band gap defects in c-Si NW arrays for guiding light
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Light guiding in c-Si NW arrays
60 deg angle of incidence
H. Butt et al
Prog. Electromag. Res, (113), 2011
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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.
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Very tight control of diameter (catalyst size) and
height ( growth time)
400nm r=24.5nm r=40.5nm r=45nm
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Periodic and quasi periodic arrays of carbon nanotubes
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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
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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
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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
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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
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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