importance of plasma conditions for vertically aligned carbon nanowalls synthesis_2005_07_09

Importance of plasma

conditions for vertically

aligned carbon nanowalls

synthesis

L. Bónová, J. Bohovičová, J. Halanda,

M. Muška and M. Meško

STU ATRI

SLOVAK UNIVERSITY OF

TECHNOLOGY

ADVANCED TECHNOLOGIES

RESEARCH INSTITUTE

Outline

Importance of plasma conditions for vertically aligned carbon nanowalls synthesis|

ISSP 2015| Kyoto|10.07.2015|Page 02

Carbon nanomaterials and their emerging applications

Plasma concept and fundamentals for nanofabrication

Plasma sheath relevant properties for nano-assembly

Plasma surface interactions at nanoscale

Plasma top-down, bottom-up and directed self-assembly synthesis approach

Combined thermal chemical vapor deposition reactor with direct

current discharge

Alignment mechanism of carbon nanotubes and nanowalls

Effect of bombarding ions

Effect of electric field

Direct and remote plasma graphite oxide reduction

STU ATRI

Motivation

Carbon nanomaterials | Plasma concept for nanofabrication | Experimental | CNTs and CNWs alignment mechanisms | GO reduction |

SWNTs

1 nm

Graphene

Graphite Oxide

nanosheets Carbon nanowalls

Carbon nanomaterials and their emerging applications

Carbon nanotubes: FETs transistors, emitting diodes OLEDs

Graphene: high frequency FET graphene transistors, transparent

conducting electrodes, flash memory cells

Graphite Oxide: drug delivery

Carbon nanowalls: batteries, supecapacitors


ISSP 2015| Kyoto|10.07.2015|Page 03 STU ATRI

Plasma sheath relevant properties for nano-assembly

Active discharge

e-

e-

e- e-

e-

- electron

e- - positive ion

- negative ion

- radical

H .

H+ H+

H+

H+

H .

H .

H .

H .

H . H .

H .

H

H . H . H .

H . H .

H+

H+

H- H-

- 1 kV

Remote

plasma

x

x

x

x

x

x

.




e-

Plasma

bulk

Presheath

Sheath

ne ni = n

ne ni

Vplasma

Po

ten

tial

den

sit

y

e-

e-

e- e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Vwall

or

Vbias

Acceleration

region

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

H+ 2

Plasma

density

(cm-3)

Debye

length

(µm)

Sheath

(µm)

109 230 1170

1010 70 370

1011 20 120

1012 7 40

1013 2 12

Sheath thickness 5D

Electron temperature

Te 1 eV

Ion energy Ei = e(Vplasma-Vbias)

Debye length

Plasma surface interactions at nanoscale

e-

Surface

diffusion

Main gas

flow region

Adsorption

from precursor

Radicals

Transport

to

surface

Desorption

Nucleation

and island

growth

Step growth

Ions

Desorption

of

volatile

products

Bulk

plasma

Alig

nm

en

t re

gio

n Plasma

sheath

Pre

sen

ce o

f

ele

ctr

ic f

ield

K Ostrikov et al „Plasma Nanoscience:

From Nature’s Mastery to Deterministic

Plasma-Aided Nanofabrication“(2007)

IEEE Trans. Plasma Sci., 35,127

Charged particles move along

electric field neutrals randomly




Top-down and bottom-up synthesis approaches

Top-down:

„classical approach of

miniaturization“(scaling down

from the macroscopic world)

Bottom-up:

„synthetical approach“ (scaling-up

from the atomic entities)

Example: conductive interconnectors

Copper via filling Vertically oriented carbon nanotube

P. Vašina et al „Reduction of transient regime in fast preionized high-power pulsed-magnetron

discharge“ (2005) Europhys. Lett,72, 390




Directed self-assembly for enhanced electron emission

Bottom-up

Self-assembling

material

Top-down

Lithographically

patterned substrate

Directed Self-

assembly

Limited emission

performance

No placement control

Enhanced emission

performance

Placement control

T Matsuda et al „Synthesis of vertically aligned carbon nanotubes on submicron-sized dot-catalyst array using

plasma CVD method“ (2008) Diamond Relat. Mater., 17, 772




CVD reactor with dc discharge




Electric furnace

(T＜950oC) Rotary pump

Pressure gauge

Substrate

Quartz tube

Mass

flow

controller C2H2

NH3

Vacuum

valve

Vbias

CNTs growth condition

NH3/C2H2：150/50sccm

Tsub ：700 oC

Pressure：5Torr

Tdep.：5 min

CNWs growth condition

Ar/H2/ethanol(bubbler)：500/10sccm

Tsub ：800 oC

Pressure：atmospheric 760Torr

Tdep.：5 min

25 20 15 10 5 0

100

200

300

400

500

600

700

800

900

sample position

furnance temperature 900 oC

tem

pera

ture

(oC

)

position from the middle of furnance (cm)

temperature measured by thermocouple

10 mm

ground - 1kV

pin-plane geometry

2 mm

rod-plane geometry

- 3kV - +3kV ground

5 mm

Carbon nanotubes synthesis

2 mm

Carbon nanowalls synthesis

Alignment mechanism of carbon nanotubes

Si Temperature

700oC

Bulk plasma

Plasma sheath

Vertically aligned

CNTs

Ni

nanoparticle

CnHm C+H2

Alig

nm

en

t re

gio

n

Ele

ctr

ic f

ield




Dot size：100nm

Dot interval：5µm

Typical diameter：80~100nm

CNT length：3µm

Alignment mechanism of carbon nanowalls

Ni Temperature

800oC

Alig

nm

en

t re

gio

n

Vertically aligned

CNWs

CnHm C+H2

Ele

ctr

ic f

ield

Bulk plasma

Plasma sheath

1 µm



ISSP 2015| Kyoto|10.07.2015| STU ATRI

Vertically aligned carbon nanowalls

synthesis on catalytically active

surfaces

Effect of bombarding ions




Randomly grown Vertically aligned

Substrate bias：+3kV

(plasma present) Substrate bias：-3kV

(plasma present)

Negative bias in plasma environment is necessary for realization of

vertically aligned carbon nanotubes growth

T. Matsuda et al “Role of Negative Electric Field Biasing on Growth of Vertically Aligned Carbon

Nanotubes Using Chemical Vapor Deposition“(2008) Jpn. J. Appl. Phys.,47, 7436

Effect of electric field

3 µm 5 µm

1250 1500 1750 2000 2250 2500 2750

400

600

800

1000

1200

1400

1600

2D

D'

Raman shift (cm-1)

D

G

1000 1500 2000 2500 30000

50

100

150

200

250

2D

G

D

Inte

ns

ity

(a

.u.)

Raman shift (cm-1)




CVD

(plasma off) PECVD

(plasma on)

Graphite

sheets

parallel to

the

substrate

Graphite

sheets

perpendicular

to the

substrate

M.Mesko et al, Carbon nanowalls synthesis by means of atmospheric dcPECVD method, (2012) Phys. Status Solidi B,

249, 2625

Direct and remote plasma GO reduction

GO in active discharge

GO in remote plasma

Electrodes GO prepared by Hummers method,

foil thickness 30 µm, initial resistance

Oxygen functional groups are removed

by atomic hydrogen, as plasma can

create large amount of hydrogen atoms,

reduction process with plasma

assistance can be then effective at low

temperatures.

0,0

0,5

1,0

1,5

2,0

( cm

)

Themal and plasma GO reduction at 250 o

C

Th

erm

al

red

ucti

on

on

ly

Rem

ote

pla

sm

a

Acti

ve p

lasm

a



ISSP 2015| Kyoto|10.07.2015|

GO reduction conditions

Ar/H2：100/10sccm

Tsub ：250oC

Pressure：1.5 mbar

Time：30 min

STU ATRI

Conclusions

Effects of the bombarding ions and electric field have been revealed as

an aligned mechanism in the growth of carbon nanotubes and nanowalls.

Merging of top-down and bottom-up processes have been demonstrated

for vertically aligned CNTs with enhanced emission performance.

Active discharge can be use to reduce thick GO foils without significant

damage induced by bombarding ions

Relevant components and contributions of plasma discharges have been

recognized for plasma assisted nano-processing.



Acknowledgements

This work was funded by the ERDF – Research and Development Operational Programme under the project “University Scientific Park Campus MTF STU – CAMBO” ITMS: 2622022079 and by Slovak grant agency VEGA, project no. 1/0503/15.



Prof. Masaaki Nagatsu

Graduate School of Science

and Technology,

Shizuoka University, Japan

E-mail:

[email protected]

Prof. Viera Skakalova

Physics of Nanostructured

Materials

University of Vienna, Austria

E-Mail:

[email protected]

DanubiaNanoTech, s.r.o. Research in science and technology

Ilkovičova 3 841 04 Bratislava

Slovak Republic

http://www.danubiananotech.com

Thank you for your attention!

importance of plasma conditions for vertically aligned carbon nanowalls synthesis_2005_07_09

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