1 Reunion SOS nanotube12 13 octobre 2011 H. Okuno, J. Dijon, E. De Vito, E. Quesnel CEA Grenoble...

1Reunion SOS nanotube12 13 octobre 2011

H. Okuno, J. Dijon, E. De Vito, E. QuesnelCEA Grenoble Liten-DTNM

SOS nanotubes 12-13 octobre 2011


Outline

XPS results: role of the substrate and of the gas phase on the catalyst reduction

Cross section of Si/Fe sample before and after annealing

Dense Carpet of SW last results

Next steps


XPS analysis

Objective: determine the role of the substrate and gas phase on the oxidation state of the catalyst just before growth

Role of the substrate • Vacuum annealing

XPS

Plasma pretreatment

vacuum

transfer

( Before TT) ( After TT)


New preparation chamber

Role of the gas phase• Annealing under reactive atmosphere

XPS

Plasma pretreatment

vacuum

transfer

Process gas H2, He, C2H2

Gas lines installed H2, He operational

C2H2 we are waiting for the bottle

First experiments


Samples

Oxide substrate Metallic substrate

HF de-oxidation of Si or Al

1nm Fe by e beam or IBS

10, 20nm Al2O3 or SiO2

Si or AlSi

SiO2 or Al2O3


Summary of the results after plasma before TT

Oxide substrate Metallic substrate

SiO2 Si

Al2O3 Al

With plasma

FeIII FeII

Fe°

Fe°

w/o plasma


Summary

Before annealing

• Fe fully oxidized on Al2O3, SiO2

• Slightly reduced on Al

• Partially oxidized on Si

Si <Al< SiO2=Al2O3

Iron oxidation Initial state

Plasma pre treatment important on Fe°/Fe(II+III) content and CNT growth


Summary of the results after TT (600°C)

Oxidized substrate Metallic substrate

SiO2 Si

Al2O3 Al Fe°

Fe°

Low reduction

oxideAfter TT

before TT

Fe3+ Fe2+


Summary

After thermal annealing (600°C)

• Fe partly reduced (FeII+FeIII) on Al2O3, SiO2

• Mostly reduced on Si (Fe°+FeII)

• Totally reduced Fe° on Al

Fe reduction final state

Al2O3<SiO2<Si<Al

FexOy reduction in solid phase by Si and Al


Reduction of oxidized iron by silicon and aluminum is allowed by thermodynamic

Si+O2

Fe+O2

Higher stability

Al+O2

Better reduction with Al


Sample cross section before and after annealing


Our sample: 5nm Si, 2 nm Fe after Deposition Step 1 (Room temperature)

c_Si

a_Si

Fe (oxidized)

Protective layer SiO2


Sample cross section after annealing (Step 3) just before Growth (1)

0.8 nm

3.6 nm

8.1 nm

7.2 nm

0.8 nm

3.6 nm

8.1 nm

7.2 nm

0.8 nm

3.6 nm

8.1 nm

7.2 nmCatalyst nano particle


Fe+O

Sample cross section after annealing (Step 3) just before Growth (2)

Fe

Si

O

Fe+Si

Si+O

a_Si

Formation of an oxide layer below the iron layer Formation of a silicide layer below the oxide layer


Possible Mechanism

Initial system (room Temp)

Iron diffusion:

Silicide Medium T(300°C):

Diffusion of Fe in Si and silicide formation

Final T(600°C)

Reduction of Fe by Silicon formation of SiOx

SiOx formation

After plasma step some Metal is still detected by XPS at Room Temp

a-Si Si

Fe2O3

a-Si

silicide


2.2nm

2.6nm

SW + DW avec de petits diametres:

SW carpet Fe = 0.37 nm/Al2O3

Tube diameter is too large for chirality analysisBy Raman


SW carpet new process Fe = 0.37 nm/Al2O3

2.7 nm

Carpet of SW diametres: < 3 nm

Decrease the tube diameter…


SW carpet process Improvement Fe = 0.37 nm/Al2O3

OBJECTIVE for next step: -Increase the small tube content (~ 1 nm) -Chirality measurement / metallic composition (Samples available) -Control of metallic content should be input into the process (how?)

3.7 nm

1.1 nm

3.1 nm

1.2 nm

Dense SW avec 2 types de diametres: 3 – 4 nm ~ 1 nm


Conclusions

Substrate / Catalyst study

Reduction of Fe is important on Si and Al at high temperature. (completely reduced on Al) Metallic Fe is observed on Si after plasma treatment at room temperature. Diffusion of Fe through Si with a formation of silicide.

CNT growth control

Dense carpet consisting of only SWNTs is realized. Appearance of 1 nm diameter SWNTs is observed.

To realize a dense carpet with only 1 nm tubes…Fe-CoChirality analysis !!!!

Post-doc??

1 Reunion SOS nanotube12 13 octobre 2011 H. Okuno, J. Dijon, E. De Vito, E. Quesnel CEA Grenoble...

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