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Parametri chimici nel processo CVD Atmosfera di reazione Superficie di crescita

Parametri chimici nel processo CVD Atmosfera di reazione Superficie di crescita  Composti precursori Gas, liquidi o solidi. Composti inorganici SiH 4 , WF 6 , TiCl 4 , BaNO 3. Composti metallorganici o con leganti organici Ga(CH 3 ) 3 ,Ti(O t -Bu) 3 ,. Metal center. Ligand. CVD.

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Parametri chimici nel processo CVD Atmosfera di reazione Superficie di crescita

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  1. Parametri chimici nel processo CVD Atmosfera di reazione Superficie di crescita  Composti precursori Gas, liquidi o solidi Composti inorganici SiH4, WF6, TiCl4, BaNO3.. Composti metallorganici o con leganti organici Ga(CH3)3,Ti(Ot-Bu)3,...

  2. Metal center Ligand CVD Chemical Vapor Deposition y x v z w Substrate u Thermal-CVD Photo Assisted-CVD Plasma Enhanced-CVD uMain flow vDiffusion towards the surface wSurface reaction xByproducts desorption yByproductselimination zNucleation and growth R R R R R R R R

  3. Precursori MOCVD Composti metallorganici o con leganti organici REQUISITI Elevata volatilità Stabilità termica Alta purezza Facile preparazione Dissociazione metallo-legante pulita Decomposizione a temperature relativamente basse

  4. Precursori MOCVD “second generation” M(b-dichet)2.poliammine  M(b-chetoimminati)2 Metallo-carbossilati Vantaggi Sintesi “one-pot” Ottima volatilità e stabilità termica Sublimazione quantitativa

  5. Plasma-Enhanced ChemicalVaporDeposition (PE-CVD) and/or RF/Sputtering

  6. combined RF Sputtering CVD/ PE/CVD route Sol-Gel Step 2 Vapor deposition Step 1 Sol-gel matrix (xerogel) porous structure MOx(OH)y M’Oz(guest) MOx(OH)y (host) Outside / Inside nanoclusters Solid solutions Step 3 Thermal treatment tailored dispersion intermixing

  7. - activation of gas-phase species and growth surface - activated species - - infiltration power MOx(OH)ylayer - flexibility processing conditions coverage substrate Plasma processing of xerogel matrices

  8. semiconduttore fino a 400 K LaCoO3 metallo al di sopra di 1200K LaCoO3 (Perovskite) Co (III) Facile accessibilità degli stati di ossidazione II e III La (III) Catodo in SOFCs - stabilità chimica e strutturale - alta conducibilità elettronica - porosità

  9. Step 1: Deposizione sol-gel LaOx(OH)y La(OCH2CH2OCH3)3 + H2O - Struttura porosa - Soluzione etanolica microstruttura (Grazing Incidence-XRD) Composizione chimica (XPS) dip-coating (su SiO2)

  10. Co-O Co-O-La La-OH Step 2 Chemical Vapor deposition (CVD) Co(dpm)2 (dpmH: 2,2-6,6-tetrametil-3,5-eptandione) 110°C O2 350°C CVD flow rate = 150 sccm Ptot = 10 mbar

  11. XPS - profilo di profondità as-grown Co-La intermixing Co-rich La-rich 80 60 O 40 Percentuali atomiche (%) Si 20 La Co 0 0 50 100 150 200 Tempo di erosione (min)

  12. XPS - profilo di profondità 800°C-annealed sample (5h) Distribuzione più uniforme di cobalto e lantanio O La atomic concentration (%) Co Si etching time (min)

  13. GIXRD Jinc = 1.5° Annealing temperature and time influence… (I) (II) (III) (IV) • annealing @ 700°C, t≥8h LaCoO3 decomposition • 700°C, 2h LaCoO3 (I, II, III, IV) • T≥400°C  Co3O4(*) + LaOF(◊) 700°C,2h Intensity (a.u.) 600°C,8h ◊ ◊ 400°C,2h * ◊ ◊ as-grown 20 25 30 35 40 45 50 55 2J (degrees) Nanocrystallites Ø = 7÷17 nm

  14. XPS Intermixing La-Co as-grown 60 O F Si 40 atomic % La 20 Co 0 20 40 60 80 100 depth (nm)  Surface: %La >> %Co  Intermixing Co  La [La]/[Co]≈1 after annealing  no F signals SIMS Cs+, 14.5 keV 700°C, 2h O 60 O 105 Si 104 40 La Co 103 La atomic % Intensity (c/s) Si Co 20 102 F 101 0 100 20 40 60 80 100 120 20 40 60 80 100 120 depth (nm) depth (nm)

  15. AFM globular grains • homogeneopus surface • Ø = f(temperature,time) 50-180 nm 700°C, 2h 700°C, 2h TEM • double-layer structure • morphology EDS: [La]/[Co] ≈ 1 LaCoO3 SiO2

  16. Case studies Guest phase Side-view few nm Host matrix RF sputtering t = 10’, T=60°C Arplasma, 10 sccm; 0.080 -0.380 mbar, 5 – 35 W Au Au/TiO2 CeO2/ZrO2 LaCoO3 CeO2 PE-CVD from Ce(dpm)4 T = 200°C, t = 10’, 30’, 60’ ((Ar/O2) = 20/5 sccm; 40 W; 1.5 mbar LaOx CVD from La(hfa)3.diglyme T = 200°C, t = 50’ Φ(O2+H2O)/Φ(N2)=3 Ti(iPrO)4+ HAcac in EtOH TiOx(OA)y Sol-gel ZrOx(OA)y sol-gel Zr(OBut)4 in EtOH CoOx(OA)y sol-gel Co(CH3COO)2·4H2O in MeOH

  17. Au/TiO2 - Catalysis and photocatalysis Grätzel cells - Non-linear optics Guest phase (Au) Side-view few nm Host matrix (TiO2) Size effects Interfacial phenomena Soft preparative strategies Nanocomposites with tailored properties Metal particle dispersion Metal-oxide interactions Au-based nanosystems

  18. as-grown Au TiO2 GIXRD SiO2 Jinc = 1.5° set 1 set 2 set 3 annealing in air 0.380 mbar 5 W, 20’ 0.080 mbar 5 W, 10’ 0.380 mbar 25 W, 10’ T (°C) 200 400 600 set 3 Au (111) set 1 600°C 14 set 2 Au (200) 12 set 3 TiO2 (101) TiO2 (200) 10 d (nm) 8 6 4 as-grown 100 200 300 400 500 600 20 25 30 35 40 45 50 2J (°) T (°C) -250 -305 -550 Vbias (V)

  19. 600°C set 3 as-grown 40 lp 630 nm 600°C 600°C Absorbance (a.u.) as-grown 30 % Au 20 as-grown 10 450 500 550 600 650 700 750 800 l (nm) 0 0 10 20 30 40 depth (nm) Au penetration

  20. set 2 Au 0.080 mbar 5 W, 10’ TiO2 TEM SiO2 TiO2anatase multi-domain particles annealing at 600°C

  21. Why CeO2/ZrO2 Nanocomposite systems ? Interest Solid oxide fuel cells (SOFCs) automotive three-way catalysts (TWCs) Rh NOx N2 Pt, Pd CO, HC CO2 + H2O • higher thermal stability • improved redox properties Ceria OSC (Oxygen Storage Capacity) Ce(IV)  Ce(III) Al2O3 / CexZr1-xO2/ NM (Pt, Pd, Rh) • free noble metal processing • defective nanocomposites

  22. CeO2(PE-CVD)/ZrO2(SG) annealing in air t = 30’ t = 60’ T (°C) 600 900 q ZrO2 q 8 q CeO2 8 8 8 q q 8 8 q q 8 900°C 600°C as-grown 25 30 35 40 45 50 55 J 2 (°) peak shift (≈ 0.2 ) with respect to ZrO2 positions ....solid solution? • Zirconia crystallization above 600°C • Nanocomposite systems 5÷13 nm

  23. TEM SAED t = 60’ 900°C Formation of a Ce-Zr-O ternary phase Grain coarsening t = 60’ 600°C Co-presence of CeO2 e ZrO2 Uniform dispersion of CeO2 on ZrO2

  24. CeO2(PE-CVD)/ZrO2(SG) XPS 40 as-grown Ce 30 Zr Si 20 atomic percentage (%) 10 0 30 0 40 80 120 900°C Zr sputtering time (min) Si 20 atomic percentage (%) Ce 10 0 0 40 80 120 160 sputtering time (min) t = 60’ • In-depth Ce penetration already at 200°C! porous matrix, plasma action • More homogeneous distribution • Similar Ce andZrprofiles ….Ce0.3Zr0.7O2 ?

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