Chemical vapor deposition growth of carbon...

Chemical vapor deposition growth

of carbon nanotubes:

characterization and applications

University of L’Aquila - Italy

Maurizio PassacantandoDipartimento di Fisica, Università degli Studi dell’Aquila

Structure of SWCNTs

Diameters: 0.6 - 2.0 nm

Length: 1 - 103 μm

Chiral Vector

Ch = nâ1 + mâ2

n2m

n3tan 1-

Chiral Angle

h

t

Cad

2

1

22 )nmn(m 3

CC-

Diameter

Electronic structure of SWCNTs

Energy dispersion relations for 2D graphite Wave vector k for 1D CNTs in 2D Brillouin

zone of graphite (hexagon) as bold lines for

(a) metallic and (b) semiconducting CNTs

CNTmetallic

semiconducting

n − m = 3q

n – m ≠ 3qq

Density of states of SWCNTs

dEEkE

dk

kdEN

TED

N

1

)()(

1

2)(

1D density of states in units of states/C-atom/eV

Quantization of the wave vector along the circumferential direction leads to a

density of states characterized by sharp van Hove singularities.

semiconductor side metal side

Structure of carbon nanotubes (CNTs)

Diameters: 0.6 - 2.0 nm

Length: 1 - 103 μm

Single-Wall Carbon Nanotubes (SWCNTs)

Multi-Wall Carbon Nanotubes (MWCNTs)

Diameters: 2.0 - 100 nm

Length: 1 - 103 μm

More complex is the behaviour for

multi-wall carbon nanotubes

(MWCNTs)

because of interactions

between adjacent layers

Sample Preparation:

Chemical Vapor Deposition (CVD)SubstratesCatalyst filmGrowth

Characterizations:

Scanning Electron Microscopy (SEM)X-ray Photoelectron Spectroscopy (XPS)Electron Energy Loss Spectroscopy (EELS)Raman Spectroscopy Transmission Electron Microscopy (TEM)

Applications:

NanolytographyNanomanipulationI-V measurementsGas SensingPhotoconductivityField Emission

Outline

Ni or

Sample Preparation:

• Catalyst particle in

molten state absorbs

carbon in vapor form

(a) to form an alloy (b).

• As the particle

becomes saturated

with carbon, a solid

CNT begins to extrude

from the particle.

• The final location of the

catalyst particle

defines tip grown (c) or

root grown (d) CNTs.

Stig Helveg et al.

Nature 427, 426 (2004)

Catalyst Film:

Ni or Fe

Substrate

Substrate:

Silicon, Glass, Aluminum, Copper, …

Clusterization of catalyst film:

Annealing in H2 or NH3

CNTs growth:

C2H2 : H2

C2H2 : NH3

Sample Preparation:

Vertical CVD

Pumping

System

Heater

Power Supply

HV Power

Supply

Vacuum

Gauge

C2H2 H NH3

V1

V2

V3

V4 V5V6

Mass

Flow

50 sccm

Temperature

Control

Mass

Flow

100 sccm

Mass

Flow

200 sccm

Sample Preparation:

Horizontal CVDSample Preparation:

DT

New CVD reactor

TOP

VIEW

Synthesis of CNTs:

Chemical Vapour Deposition (CVD)

T= 500 °C

T= 700 °CCharacterizations: SEM

XPS

1000 800 600 400 200 0

0

20000

40000

60000

80000

100000

120000

C (KVV)

O(1s)F(1s)

C(1s)

c/s

Energia di legame (eV)

0 10 20 30 40

0.00

0.02

0.04

0.06

0.08

0.10

0.8

1.0

HOPG

CNT old growth

CNT new growth

Inte

nsity (

arb

itra

ry u

nits)

Energy Loss (eV)

-plasmon

EELS

Ep=1000 eV

EELSRaman

1000 1200 1400 1600 1800

Inte

nsity (

arb

itra

ry u

nits)

Raman shift (cm-1)

D peak G peak

Characterizations:

TEM: Morphology

CNT growth at 500 °C

135 nm

• Elongated structures (l ~ 50 – 150 nm, d ~ 30 – 50 nm)

• The structure is more similar to a filled cylinder than to a tube

• At the edges round particles are visible with diameter 5 – 20 nm.

Characterizations:

Unfiltered Energy filter Carbon edge Energy filter Nickel edge

The particles (d~20 nm) are made of Nickel and are located close the apex

of the structures.

TEM: Chemical Composition


Characterizations:

The external shells are not well graphitized

Catalyst grains

Around the grains there is a crystalline core

TEM: Crystalline Structure


Characterizations:

• Tubes with hollow interior (l ~ micron scale, dext ~ 10 – 30 nm).

• Several tubes look bended

• At the edges particles are visible with diameter 5 – 20 nm.

• Inclusions of particles are also present along the tubes.

TEM: Morphology


Characterizations:

Unfiltered Energy filter Carbon edge Energy filter Nickel edge



Characterizations:

Unfiltered Energy filter Nickel edge

Long Nickel inclusions (defects) are observed



Characterizations:

• Outer diameter: 15 – 25 nm

• Inner diameter: 5 – 10 nm

• Average # of tubes: 10 – 15

TEM: Crystalline Structure


Characterizations:

TEM: Tubes Capping


Characterizations:

In proximity of the catalyst the

carbon is highly graphitized Uncapped Tubes: cores

TEM: Particle Inclusion


Characterizations:

Self-patterned Growth: Black & White

BlackNi catalyst

Whiteno catalyst

Binding Energy (eV)

Inte

nsit

y (

arb

itra

ry u

nit

s)

Inte

nsit

y (

arb

itra

ry u

nit

s)

Energy Loss (eV)

Inte

nsit

y (

arb

itra

ry u

nit

s)

Raman Shift (cm-1)

Applications:

Nanolithography

&

design for the CNTs growth

GINT collaboration

Applications:

lift-off of Nichel film (3 nm)

Silicon

Silicon

GDSII mask design

Electron beam exposure

Silicon

After developing

Nichel film deposition

Silicon

Aceton bath

Applications:

GDSII mask design

Applications:

Applications:

CNTs

CNTs

CNTs

CNTsCNTs

CNTs

Selective Chemical Vapour

Deposition growth of carbon

nanotubes on submicrometric Ni

patterns fabricated with Scanning

Probe Nanolithography

Digital Instruments D5000 Microscope

(Nanoscope IV controller) using

commercial silicon tips (frequency

range 310-370 kHz) scanned by

means of a Veeco Nanoman closed

loop XY head.

Applications:

(a) 18.0 μm × 2.5 μm AFM micrograph of 13 nm PMMA

on SiO2 substrate after nanoindentation.

(b) AFM micrograph of the same area of panel (a) after

deposition of 3 nm of Ni and subsequent lift-off of

resist.

(c) Height profile of the written line on PMMA (see

panel (a)).

(d) Height profile of a Ni stripe, evidenced in panel (b).

(a-c) 5 μm × 3 μm AFM and SEM

(60000x) micrographs of three Ni

stripes before (a-b) and after (c)

growth of CNTs.

M. Passacantando et al., J. Appl. Phys. 101, 066101 (2007)

Applications:

Applications:

Manipulation and electrical characterization of

carbon nanotubes by using

nanomanipulators inside SEM

CNT metal contact

M M

CNT

SiO2

Silicon

Schematic picture of CNT distortion across metallic pads

... influence on the CNT intrinsic electronic transport properties

CNT structural distortions ...

CNT on surface/metallic pads:

It is therefore advantageous to performs electrical measurement on CNTs inthe free space, and it is also desirable to have the possibility to manipulate acharacterized carbon nanotubes into predetermined position for deviceconstruction.

CNT 3D manipulation in free space (!)‏

Applications:

• no structural distortions

• no post-processing process (lift off, metallization, etc...)‏

Nanomanipulation under Scanning Electron Microscopy:

+

nanomanipulator

SEMCNT manipulation@NIST

Applications:

CNT 3D manipulation in free space‏

• Viewing and placement of probe contacts at specified locations along a CNT.

• Three dimensional freedom=all the aspects of the investigated CNT can be explored.

• No ambiguities related to the interpretation of the results of electrical and mechanical experiments.

CNT manipulation under SEMApplications:

•MWCNT manipulations under SEM

• MWCNT as grown on Ni wire by CVD

• I-V characterization of MWCNT

• I-V characterization of CNT/CNT

junction

“Nanowelding”via

Electron Beam Induced

Deposition

Applications:

Experimental

• MM3A-nanoprobe system (Kleindeik Company)‏

• Scanning Electron Microscopy (ZEISS, LEO 1430)

• The manipulators are coupled with a Keithley-236 electrometer to

perform electrical current-voltage (I-V) measurements.

Approaching CNT...

A

Ni wire

VW tip

Schematic of the I-V apparatus

Applications:

Experimental

MWCNT grown on Ni template:

low contact barrier at the Ni/CNT interface

‏the‏improving‏in‏irradiation‏Beam‏Electron‏the‏of‏effect‏The‏…W/CNT contact has been investigated …

Applications:

I-V vs Electron Irradiation

1) Approaching CNT protruding from the Ni tip

2) I-V acquisition

3) Electron beam irradiation of the contact area (10 keV, 10 min)‏

4) I-V acquisition after each irradiation cycle

Approaching CNT Electron beam irradiation of the W/CNT contact area

Irradiated area

Applications:

Ni tipW tip

Applications:

Applications:

Applications:

CNT W Tip CNT W Tip

Contact resistance

I-V vs Electron Irradiation: RESULTS

• Resistance at W/CNT junction:

• Contact area

• nature of metal electrode

• CNT/metal distance

Non linear (linear) dependence of the current in the high voltage (low

voltage) range observed is perfectly consistent with the presence of a

tunnel barrier in correspondence of the metallic CNT/movable junction

Applications:

Electron beam Induced deposition

CNT e- beam damaging ?

• Exposing medium regionof‏a‏suspended‏CNT…

• I-V before (a) and after (b) the exposure…

• No variations observed (c).

No damaging effecton the CNT structure

(10 keV, 1 hour exposure)‏

Applications:

-1.0 -0.5 0.0 0.5 1.0

-8.0x10-6

-6.0x10-6

-4.0x10-6

-2.0x10-6

0.0

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

0min

5min

10min

15min

20min

Curr

ent

(A)

Voltage (V)

Rsat=120 kW >12.9 kW

Welding of CNTse- beam exposed area

• After the welding, single nanotube can be pulled out from the Ni surface ...

• ... contacting another CNT ...

• a stable CNT/CNT omhicjunction can be produced by EB nanowelding.

Applications:

M. Passacantando et al. Phys. Rev. B 76, 125415 (2007)

Applications:

CNT welded on AFM tip

I-V measure on CNTsMicromanipulator Kleindiek

Applications:

MWCNT/Sapphire

Sample A: TG=500 °C

Sample B: TG=750 °C

Applications:

Photoconductivity in defective carbon nanotubes sheets

under UV-Vis-NIR radiationPassacantando et al. Appl. Phys. Lett. 93, 051911 (2008)

Applications: PhotoconductivityPassacantando et al. Appl. Phys. Lett. 93, 051911 (2008)

Photocurrent (Iph=Ilight-Idark)

White Light illumination

Relatively large area samples show,

under white light illumination, a

wide-range linear behavior of the

photocurrent as a function of bias

voltage and optical power density

Applications: PhotoconductivityPassacantando et al. Appl. Phys. Lett. 93, 051911 (2008)

The spectral photoresponse has beendetermined in terms of thephotoconductance (G ) normalized to theincident photon flux, nph=λF/hc, as givenby:

G=Iph/(SVpolnph)

where c is the speed of light, h is thePlanck constant, and S is the illuminatedarea.

The spectral photoresponse of

all the samples increases with

increasing photon energy and is

strongly correlated to the

absorbance.

Field emission from a selectedmultiwall carbon nanotube

Applications:

We have shown that the emission phenomenon is very well described by a

series resistance modified Fowler–Nordheim model.

M. Passacantando et al., Nanotechnology 19 (2008) 395701

M. Passacantando et al., Carbon 45 (2007) 2957

Applications:

This is an original method to limit or

suppress the field emission current from a

single nanotube through the controlled and

selective deposition of carbonaceous

species on its apical region.

This result opens several perspectives for

the study of the field emission properties of

carbon nanotube arrays, enabling the

switching of selected single emitters, as

well as for technological applications in

which tunable nanosized emitters might be

needed.

SEM image of the field emission geometry

after a prolonged electron beam exposure

of the tip region.

Passacantando et al. Nanotechnology 19 (2008) 395701

Low (T=400 °C) temperature Growth

CNT / CopperCNT / Glass

Structural analysis: Raman Spectroscopy

Catania, 6th October 2010

G-band: crystallographic graphitic order

~ 1582 cm-1

D-band: structural defects ~ 1350 cm-1

RBM: radial breathing mode ~ 230 cm-1

D

G

D

G

λ=633 nm

750°C 750°C


λ=633 nm

Si-c

300 cm-1

277 cm-1

258 cm-1

247 cm-1

190 cm-1

RBM

Structural analysis: Raman Spectroscopy

Synthesis of graphene:

Chemical Vapour Deposition (CVD)

AcknowledgementsThe research staff of L’Aquila:

Prof. Sandro Santucci

Dr. Luca Lozzi

Dr. Fabio Bussolotti (Japan Advanced Institute of Science and Technology, Ishikawa)

Dr. Valentina Grossi (Post Doc position)

Collaborations:

Dr. Michelangelo Ambrosio – University of Napoli

Prof. Pasqualino Maddalena and his group – University of Napoli

Dr. Emanuela Esposito - CNR-ICIB – Napoli

Prof. Antonio Di Bartolomeo – University of Salerno

Prof. Maurizio De Crescenzi – University of Roma “Tor Vergata”

Prof. Gilles Martel – Université de Rouen – France

Financial support:

European Collaborative Project “S-five”.

GINT (Gruppo INFN per le Nano Tecnologie) program, funded by INFN.

SinPhoNIA program, funded by INFN.

Thanks!

Photosensor made of MWCNTs:

details of device fabrication

The devicePt electrodes

MWCNT film

Au strips

Multipin

sample holder

Rome, 17th September 2010

Photoelectric measurements

The sample holder has been connected

to external circuit for electrical measurements

(Keithley-236 electrometer controlled by LabView software)

Standard optical fiber:

light spot of ~0,8 mm2

Support for

external electrical contact

and horizontal movement

(step 0,625 mm)


Photoconductivity of MWCNT by white light

Pt

Si (100) n-type

Si3N4

Si3N4

Pt

V

A

+

-

-

+

I

V

I

V

Contacts: Ohmic – Schottky

ID: dark currentIL: current generated by a white light by a LED


Photoconductivity of MWCNT by white light

Vbias= -4 V

The photoconductivity measurements show that only the more defective

MWCNTs grown at 500 °C have a noticeable photosensitivity



Photoconductivity of MWCNT by LED light


IPh= IL - ID

The Iph has been normalized to the incident photon flux (nph):

Photoconductivity of MWCNT by LED light

where

The spectral photoresponse has been determined in terms of

the photoconductance (G) normalized

to the incident photon flux:

Photoconductance of MWCNT by LED light


phpol

ph

nSV

IG


Photoconductance of MWCNT by LED light

phpol

ph

nSV

IG

Application:

Photosensor made of MWCNTs


Standard optical fiber:

light spot of ~0,8 mm2

Support for

external electrical contact

and horizontal movement

(step 0,625 mm)

T= 500 °C and T= 750 °C

MWCNT

cross viewPt

Si (100) n-type

Si3N4

Si3N4

Pt

V

A


Application:

Photosensor made of MWCNTsID: dark currentIL: current generated by a white light by a LED

0 240 480 720 960 1200 1440

Time [min]

138

140

142

144

146

148

(a

) R

esis

tan

ce

[O

hm

]

Operating Temperature 165 °C

200

300

400

500

600

700

800

900

1000

(b)

Re

sis

tan

ce

[O

hm

]

(a)

(b)

10 25 50 75 100

ppb NO2

Appl. Phys. Lett., Vol. 82, 961 (2003)

First thermal

treatment

Second thermal

treatment

Resis

tance (W

)

Resis

tance (W

)

Time (min)

Growth over a Pt/Si3N4 Gas sensor deviceApplications:

Back Heater

Pt electrodes50 nm+10 nm Ta

Si3N4

Si3N4

30 m

Si

3 mm

5 mm

7,8 mm

Chemical vapor deposition growth of carbon...

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