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FIB fabrication of CNT devices

Lee Chow

Department of Physics

University of Central Florida

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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

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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

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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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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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Lecture #9 41

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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Lecture #9 45

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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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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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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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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