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SOS nanotubes 12-13 octobre 2011. H. Okuno, J. Dijon, E. De Vito, E. Quesnel CEA Grenoble Liten-DTNM. 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
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SOS nanotubes 12-13 octobre 2011 H. Okuno, J. Dijon, E. De Vito, E. Quesnel CEA Grenoble Liten-DTNM 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 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 beforegrowth Role of the substrate Vacuum annealing vacuum Plasma pretreatment XPS transfer ( After TT) ( Before TT) Reunion SOS nanotube12 13 octobre 2011
New preparation chamber • Role of the gas phase • Annealing under reactive atmosphere Process gas H2, He, C2H2 vacuum Plasma pretreatment transfer XPS First experiments Gas lines installed H2, He operational C2H2 we are waiting for the bottle Reunion SOS nanotube12 13 octobre 2011
Samples Metallic substrate Oxide substrate Si or Al SiO2 or Al2O3 Si HF de-oxidation of Si or Al 10, 20nm Al2O3 or SiO2 1nm Fe by e beam or IBS Reunion SOS nanotube12 13 octobre 2011
Summary of the results after plasma before TT Oxide substrate Metallic substrate SiO2 Si Fe° With plasma w/o plasma FeIII FeII Al2O3 Al Fe° Reunion SOS nanotube12 13 octobre 2011
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 Reunion SOS nanotube12 13 octobre 2011
Summary of the results after TT (600°C) Oxidized substrate Metallic substrate SiO2 Si oxide After TT before TT Fe3+ Fe2+ Low reduction Fe° Al2O3 Al Fe° Reunion SOS nanotube12 13 octobre 2011
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 Al2O3<SiO2<Si<Al Fe reduction final state FexOy reduction in solid phase by Si and Al Reunion SOS nanotube12 13 octobre 2011
Reduction of oxidized iron by silicon and aluminum is allowed by thermodynamic Fe+O2 Si+O2 Al+O2 Higher stability Better reduction with Al Reunion SOS nanotube12 13 octobre 2011
Sample cross section before and after annealing 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 SiO2 Reunion SOS nanotube12 13 octobre 2011
Sample cross section after annealing (Step 3) just before Growth (1) Catalyst nano particle Reunion SOS nanotube12 13 octobre 2011
Sample cross section after annealing (Step 3) just before Growth (2) Fe a_Si Fe+Si Si Si+O O Fe+O Formation of an oxide layer below the iron layer Formation of a silicide layer below the oxide layer Reunion SOS nanotube12 13 octobre 2011
Possible Mechanism Initial system (room Temp) Fe2O3 Si a-Si After plasma step some Metal is still detected by XPS at Room Temp SiOx formation Iron diffusion: Silicide silicide a-Si Medium T(300°C): Diffusion of Fe in Si and silicide formation Final T(600°C) Reduction of Fe by Silicon formation of SiOx Reunion SOS nanotube12 13 octobre 2011
2.2nm 2.6nm SW carpet Fe = 0.37 nm/Al2O3 SW + DW avec de petits diametres: Tube diameter is too large for chirality analysis By Raman Reunion SOS nanotube12 13 octobre 2011
2.7 nm SW carpet new process Fe = 0.37 nm/Al2O3 Carpet of SW diametres: < 3 nm Decrease the tube diameter… Reunion SOS nanotube12 13 octobre 2011
1.1 nm 3.7 nm 1.2 nm 3.1 nm SW carpet process Improvement Fe = 0.37 nm/Al2O3 Dense SW avec 2 types de diametres: 3 – 4 nm ~ 1 nm 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?) 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?? Reunion SOS nanotube12 13 octobre 2011
