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FIB fabrication of CNT devices
Lee Chow
Department of Physics
University of Central Florida
4/11/2011 1Lecture #9
Lecture 9
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Outline
Basic properties of CNT
Unique features of our F-CNT
FIB fabrication of CNT devices
Lecture #9 3
Physics
C60, C70, C80, Carbon Nanotube
Diamond fcc lattice
Graphite, HOPG
Graphene
4/11/2011 Lecture #9 4
Physics
History of Fullerenes and Carbon Nanotubes
In 1985 Kroto, Smalley, and colleagues discovered Fullerenes in a supersonic molecular beam. Nobel Prize in Chemistry 1996.
Kratschmer, Huffman et al in 1990 developed carbon arc method to mass produce Fullerenes.
In 1991, Ijima discovered carbon nanotubes in the cathode deposit of the carbon arc apparatus
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In 2004, Geim and Novoselov obtained graphene by mechanical exfoliation of graphite. Nobel prize in physics 2010.
Lecture #9 5
Fullerene & Carbon Nanotube
Physics
4/11/2011 Lecture #9 6
Synthesis of Carbon Nanotubes
• Carbon Arc Synthesis
• Laser‐Oven Synthesis
• Catalytic Chemical Vapor Deposition
• Electrochemical Deposition
Physics
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Carbon Arc MethodKratschmer, Huffman et al, Iijima, Ebbesen&Ajayan, Bethune et al
Synthesis Conditions
• 100 ~ 500 torr of He pressure
• 1/4” graphite rod
• 50 Amp of current
• Catalytic particles mixed
Physics
Lecture #9 8
Carbon Arc Technique
• Iijima discovered carbon nanotubes in the cathode deposits inside the carbon arc chamber.
• Nature, 354, 56 (1991).
Physics
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Laser‐Oven Synthesis (Smalley’s Group)
Physics
Lecture #9 10
Laser‐Oven Synthesis (Smalley’s Group)
Physics
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Lecture #9 11
Catalytic Chemical Vapor deposition
Apparatus
Physics
CH4/Ar/H2
T = 850° ‐ 1100° C
P = 10 ‐ 800 torr
Baker, Amelinckx, and, others
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Catalytic Chemical Vapor deposition
Deposition Conditions
• 10 ~ 800 torr of pressure
• 600° ~ 1100° C of temperature
• Hydrocarbon gases mixed with He/Ar and H2
• Nanosize catalytic particles deposited on substrates
Physics
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Lecture #9 13
Catalytic Chemical Vapor deposition
Physics
Catalytic nanoparticles
50 nm
10μm
Carbon nanotubes
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Physics
Electrochemical Deposition
• The potential supply ~ 1000 V
• Si substrate coated with Fe/Ni nanoparticles
• Electrolyte: a mixture of methanol and benzyl alcohol
• Deposition time ~ 24 hours
• Deposition temperature ~ 20°C
• Current density ~ 12 mA/cm2
Zhou and Chow at UCF (US patent 6,758,957 B1)
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Lecture #9 15
Electrochemical Deposition
Bundles of carbon nanofilaments with a uniform distribution on the Si substrate
Physics
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Electrochemical Deposition
Physics
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Lecture #9 17
Electrochemical Deposition
Physics
Internal structure of the electrochemically deposited carbon nanotubes
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Synthesis of all‐carbon nanoprobes
We developed a multi‐step processing method to fabricate all‐carbon nanoprobes consisting of carbon nanotube as the core of carbon fiber.
Physics
Kleckley, Chai, Zhou, and Chow (US Patent 6,582,673)
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Lecture #9 19
Synthesis of all‐carbon nanoprobes
Physics
Kleckley, Chai, Zhou, and Chow
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At UCF we acquired an FEI’s FIB instrument and set up Materials Characterization Facility (MCF) with funding from Lucent Technologies.
Lecture #9 21
Physics
Focused Ion Beam fabrication of CNT Electron
Source
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Physics
W tip
small slot
Intermediate Fiber
small slot
We first etch a 100μm W wire to a sharp tip, then use FIB to fabricate a small slot. Use a micro‐manipulator to pick up an intermediate carbon fiber.
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Lecture #9 23
Physics
Pick up an intermediate fiber
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Physics
Pick up a fiber that contains CNT at the end of the fiber
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Lecture #9 25
Physics
Attaching Carbon fiber to the W‐tip.
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Physics
Individual CNT tip on W tip
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Lecture #9 27
Physics
FIB fabricated CNT on a commercial electron source for electron microscope
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It took us almost ten years to finally get the USPTO to approve our patent application.
Lecture #9 29
Physics
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As you can see, focused ion beam is pretty destructive to the target. So how come we will able to fabricate devices that is functional?
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Lecture #9 31
Fiber-protected carbon nanotube (F-CNT)
Physics
10μm
(US Patent #6,582,673, 2003)
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Physics
CNT loop 1
Loop radius:
R=300nm
Electron emission from the side‐wall of CNT
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Lecture #9 33
Physics
45 60 75 900
40
80
120
Em
issi
on
cu
rren
t (n
A)
Applied Vlotage (V)
before cleaning after cleaning after cleaning
12 15 18 21 24-34
-32
-30
-28
-26
-24Linear Fit
y=-13.5-1.06x y=-12.5-0.855x y=-12.0-0.898x
Ln
(I/V
2 )
1000/V
Field emission results from CNT loop 1
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Physics
35 40 45 500
40
80
120
Em
issi
on
cu
rren
t (n
A)
Applied Voltage (V)
before cleaning after cleaning after cleaning
20 22 24 26 28 30
-33
-30
-27
-24
Ln
(I/V
2 )1000/V
Linear Fit y=-0.78-1.16x y=-5.0-0.892x y=-3.8-0.949x
Field emission results after I = 1A burn
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Lecture #9 35
Physics
SEM image of the same CNT tip
At the top it formed a smaller loop with R = 36 nm.
The CNT was straighten by the field applied.
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Physics
Focused Ion Beam fabrication of CNT Atomic Force Microscope tip.
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Lecture #9 37
Physics
Conventional AFM cantilever Tip
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Physics
Adhering individual CNT on AFM tip
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Lecture #9 39
Physics
AFM cantilever with CNT tip
The zoom‐out SEM image The zoom‐in SEM image
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Physics
AFM images of CNT & conventional tip
CNT tip Conventional tip
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Physics
AFM Image of gradings Using carbon Nanotube tip
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Physics
CNT tip Si3N4 tip
Before scan Before scan
After two hour scan After one hour scan
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Lecture #9 43
Physics
FIB fabrication of Channeling device
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Physics
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Channeling & critical angle
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Physics
Using carbon nanotube as a channeling devices is a very interesting concept. It is not difficult to do simulation, but experimentally it is very challenging.
Two major difficulties:
1. The size of carbon nanotube
2. The damage caused by ion beam
We are in a unique situation that we may be able to overcome the above difficulties with our fiber‐protected carbon nanotube.
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Lecture #9 47
Physics
Fabrication of a 500 nm nanotube channeling device
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Physics
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Lecture #9 49
Physics
550 nm CNT channel device
Overview Close‐up and aligned
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Physics
Images of the channel when it is tilted.
5° tilt of the sample 10° tilt of the sample
From TEM tilted images we estimate the length of the channel to be 560 nm.
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Lecture #9 51
Physics
Line scan of the intensity
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Physics
Fabrication of a long nanotube channeling device
Deposit Pt coating Dig trenches on sides of CNT
Pick up CNT column
Put on Cu grid
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Lecture #9 53
Physics
Channeling results from a 3 μm nanotube device
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Physics
Electron Intensity calibration
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Lecture #9 55
Physics
Electron intensity comparison
A focusing effect due to carbon nanotube??
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Physics
To demonstrate channeling effect convincingly, it is important to carry out rocking curve measurement. We tilt the nanotube +1° and ‐1°.
Tilt +1° angle Tilt ‐1° angle
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Physics
FIB fabrication of nanopores
Current research
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Physics
Protein Nanopore Solid State nanopore
Si3N4
3 nm
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Lecture #9 59
Physics
TEM image of a CNT nanopore
Diameter of the hole ~ 12 nm
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Physics
Alternative method to prepare CNT‐based nanopores
Sun and Crooks, J. Am. Chem. Soc., 2000, 122, 12340‐12345
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Lecture #9 61
Physics
A schematic diagram of a CNT‐based Coulter counter.
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Physics
This is how the current signal looks
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Lecture #9 63
Physics
Protein nanopores Si3N4/SiO2
nanoporesCNT nanopores
Advantages:
Can be chemically engineered.
Well-studied.
Disadvantage:
DNA translocation is too fast, and can not be used for sequencing DNA.
Advantages:
Materials are well-developed.
Disadvantage:
Pore size is difficult to control using electron beams
Advantages:
Well defined pore size.
No charging problem.
Nanopores size from 1.2 nm (SWNT) to 10 nm (MWNT) is possible.
Comparison of different types of nanopores
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Conclusions
• Focused ion beam is a very useful technique in the fabrication of nano‐devices and nano‐structures.
• The Fiber‐protected configuration of F‐CNT has potential to be developed into various CNT devices.
• Three basic CNT devices have been demonstrated: (a) Electron emission source, (b) AFM tips, (c) CNT channel.
• But FIB has its limitations:
• (1) Sequential process
• (2) Create defects and damages during the process
Physics
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