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

2 Reunion SOS nanotube12 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

3 Reunion SOS nanotube12 13 octobre 2011 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)

4 Reunion SOS nanotube12 13 octobre 2011 New preparation chamber  Role of the gas phase Annealing under reactive atmosphere XPS Plasma pretreatment vacuum transfer Process gas H 2, He, C 2 H 2 Gas lines installed H 2, He operational C 2 H 2 we are waiting for the bottle First experiments

5 Reunion SOS nanotube12 13 octobre 2011 Samples Oxide substrate Metallic substrate HF de-oxidation of Si or Al 1nm Fe by e beam or IBS 10, 20nm Al 2 O 3 or SiO 2 Si or Al Si SiO 2 or Al 2 O 3

6 Reunion SOS nanotube12 13 octobre 2011 Summary of the results after plasma before TT Oxide substrate Metallic substrate SiO 2 Si Al 2 O 3 Al With plasma FeIII FeII Fe° w/o plasma

7 Reunion SOS nanotube12 13 octobre 2011 Summary  Before annealing Fe fully oxidized on Al 2 O 3, SiO 2 Slightly reduced on Al Partially oxidized on Si Si <Al< SiO 2 =Al 2 O 3 Iron oxidation Initial state Plasma pre treatment important on Fe°/Fe(II+III) content and CNT growth

8 Reunion SOS nanotube12 13 octobre 2011 Summary of the results after TT (600°C) Oxidized substrate Metallic substrate SiO 2 Si Al 2 O 3 Al Fe° Low reduction oxide After TT before TT Fe3+Fe2+

9 Reunion SOS nanotube12 13 octobre 2011 Summary  After thermal annealing (600°C) Fe partly reduced (FeII+FeIII) on Al 2 O 3, SiO 2 Mostly reduced on Si (Fe°+FeII) Totally reduced Fe° on Al Fe reduction final state Al 2 O 3 <SiO 2 <Si<Al Fe x O y reduction in solid phase by Si and Al

10 Reunion SOS nanotube12 13 octobre 2011 Reduction of oxidized iron by silicon and aluminum is allowed by thermodynamic Si+O2 Fe+O2 Higher stability Al+O2 Better reduction with Al

11 Reunion SOS nanotube12 13 octobre 2011 Sample cross section before and after annealing

12 Reunion SOS nanotube12 13 octobre 2011 Our sample: 5nm Si, 2 nm Fe after Deposition Step 1 (Room temperature) c_Si a_Si Fe (oxidized) Protective layer SiO 2

13 Reunion SOS nanotube12 13 octobre 2011 Sample cross section after annealing (Step 3) just before Growth (1) Catalyst nano particle

14 Reunion SOS nanotube12 13 octobre 2011 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

15 Reunion SOS nanotube12 13 octobre 2011 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 Fe 2 O 3 a-Si silicide

16 Reunion SOS nanotube12 13 octobre nm 2.6nm SW + DW avec de petits diametres: SW carpet   Fe = 0.37 nm/Al2O3 Tube diameter is too large for chirality analysis By Raman

17 Reunion SOS nanotube12 13 octobre 2011 SW carpet new process  Fe = 0.37 nm/Al2O3 2.7 nm Carpet of SW diametres: < 3 nm Decrease the tube diameter…

18 Reunion SOS nanotube12 13 octobre 2011 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

19 Reunion SOS nanotube12 13 octobre 2011 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-Co Chirality analysis !!!! Post-doc??