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Influence of precursor, solvent, and ambient on surface sol-gel process

Influence of precursor, solvent, and ambient on surface sol-gel process. Experiment. Surface sol-gel (ambient condition) Aggregated particles deposited. Experiment. Ellipsometric thickness measurement reliable over 2nm ex) surface sol-gel of silica, ZnO , ZnS. Experiment.

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Influence of precursor, solvent, and ambient on surface sol-gel process

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  1. Influence of precursor, solvent, and ambient on surface sol-gel process

  2. Experiment Surface sol-gel (ambient condition) Aggregated particles deposited

  3. Experiment • Ellipsometric thickness measurement • reliable over 2nm • ex) surface sol-gel of silica, ZnO, ZnS

  4. Experiment Ellipsometric thickness measurement Non-accurate thickness control (generally thicker than expected)

  5. Experiment SEM image of HfO2 film surface (moisture-controlled condition) - consists ~10nm size islands or particles (10-cycles)

  6. Surface sol-gel The large frequency change of ~272Hz = Oligomers formation in stock solution & adsorbed without disaggregation. Aluminum alkoxide usually tetrameric, in form of Al4(OR)12 Bridging can be prevented by steric hinderence

  7. Surface sol-gel Volatility: Monomer > Oligomer High volatility = Tendency to remain as monomer Volatile alkoxides: Large alkyl group Many alkyl group Smaller atomic radius of metal atom (Steric hinderence)

  8. Surface sol-gel Precursor: Hafnium n-butoxide Transition metals are generally more electropositive Highly susceptive to nucleophilic attack

  9. Surface sol-gel Hydrolysis of alkoxide precursor 1. Nucleophilichydroxyl anions attack the metal atom 2. Inversion of hafnium tetrahedron 3. Detachment of alcohol Hf Hf Hf Higher partial positive charge of metal atom = Higher hydrolysis rate

  10. Surface sol-gel Steric effects Increased length or branch of alkoxy groups → lowered hydrolysis rate OH- hard easy OH-

  11. Surface sol-gel Solvent (Ethanol:Toluene = 1:1) Polarity Determines solubility of alkoxide More polar solvents are used to solvate polar, tetrafunctionalalkoxide Less polar solvents are used in alkyl-substituted systems Hafnium butoxide: soluble in polar solvent

  12. Surface sol-gel Availability of labile protons Protic solvents hydrogen bond to hydroxyl ions or hydronium ions → Reduce the catalytic activity Hydrogen bonding may also influence the hydrolysis reaction or reverse reaction example) OH OH OH OH OH OH OH OH OH OH

  13. Surface sol-gel Adsorption step: Oligomers are hardly generated without hydrolysis Polymerization (product: dibutylether) Transesterification Surface reaction (product: butanol) OH OH OH OH OH OH OH OH OH OH

  14. Surface sol-gel Rinsing step: Possible reaction: transesterification & desorption Transesterification (butyl group ↔ ethyl group) OH OH OH OH OH OH OH OH

  15. Surface sol-gel Hydrolysis step: Possible reaction: hydrolysis & desorption Hydrolysis (product: butanol) OH OH OH OH OH OH OH OH

  16. Surface sol-gel Effect of water Alkoxides are hydrolized and readily form polymers Polymerization (product: water or butanol) Surface reaction (product: butanol) OH OH OH OH OH OH OH OH OH OH

  17. Surface sol-gel Surfactant micelle + TEOS Surface sol-gel process: 1. Forming TiO2 monolayer inside mesopore2. Attaching Au nanoparticles on

  18. Surface sol-gel Process environment Procedure Hafnium butoxide adsorption Methanol washing Water hydrolysis Solution & solvents are injected by syringe (Solvents are anhydrous) (Vacuum filtration) (Vacuum drying) (Vacuum drying) Reactor is flushed several time & sealed with rubber septum SBA-15 is loaded Solution is removed by vacuum filtration

  19. Surface sol-gel Pore size is decreased by SSG deposition Monolayer thickness ~1.3nm Au NP on ordered mesoporous silica Application: CO catalyst

  20. Surface sol-gel Accurate thickness control Using zinc acetate aqueous solution

  21. Surface sol-gel No ZnO deposition on hydroxyl surface (amine is stronger) ZnS: separated crystal nuclei ZnO: flat separated island (RMS~0.85nm) Possible explanations: strong bonding or lateral mobility of amine surface (Uncareful washing can peel off ZnO film) Imperfect coverage (70~80%)

  22. Surface sol-gel Polyelectrolyte-assisted adsorption: process is not sensitive to ambient titanium(IV) bis(ammonium lactato)dihydroxide Pores are generated during calcination (Organic burning) Residual carbon

  23. Surface sol-gel Titanium isopropoxide + toluene (AAO substrate) Performed under ambient conditions (Solution is freshed after every 10 cycles) Process is unstable, prolonged exposure has to be evaded

  24. Surface sol-gel High surface tension of water Water cannot penetrate all pore channels Ethanol:water (9:1) Decreased surface tension Uniform tube wall thickness

  25. Surface sol-gel Hybrid organic solar cell application Highest efficiency ~0.3% Low efficiency: Failed infiltration of P3HT Bilayer structure Organic-inorganic hybrid

  26. Future work Experimental condition: Glove box Anhydrous solvents (ehtanol, toluene) Material characterization: Ellipsometry QCM measurement Electrical analysis Surface characterization Device fabrication: Low-voltage driving Stability test Mobility comparison

  27. Future work Nanotube with uniform size AAO template: uniform size but, too large aspect ratio, limited production Virus template Precise size & shape control Mass production

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