Nano-Liquids, Nano-Particles, Nano-Wetting: X-ray Scattering Studies P.S. Pershan: Physics & DEAS, Harvard Univ. Physics of Confined Liquids with/without Nanoparticles: Confinement Phase transitions are suppressed and/or shifted. When do Liquids fill nano-pores? (i.e. wetting and capillary filling). Contact Angles vary with surface structure. (i.e. roughness & wetting) Attraction/repulsion between surfaces. (i.e. dispersions or aggregation) Important for formation of Nanoparticle arrays: (i.e. electronic/optical properties, potential use for sensors, catalysis, nanowires) How will these affect nano-scale liquid devices? How will these affect processes that are essential for nano-scale liquid technology? Co Workers Harvard Students and Post Docs K Alvine D. Pontoni O. Gang O. Shpykro M. Fukuto Y. Yano Graduate Student PhD March 06, Post Doc. Former Post Doc. Former Grad. Student & Post Doc. Former Grad. Student & Post Doc. Former Guest. Current: NIST Current: Brookhaven National Lab. Current: Argonne National Lab Current: Brookhaven National Lab Current: Gakushuin Univ., Japan Others B. Ocko D. Cookson A. Checco F. Stellacci K. Shin T. Russell C. Black Brookhaven National Lab. Argonne National Lab. Brookhaven National Lab. MIT U. Mass. Amherst U. Mass. Amherst I.B.M. Experiments: Thin to Thick Liquids Thin liquids adsorb on nano-structured surface Liquids fill nano-pores Thin liquids surround and solvate nano-particles Control of Liquid Thickness Outer cell: 0.03C Inner cell: 0.001C Wetting film on Si(100) at T = Trsv + DTm. Saturated vapor Nano Thin Films Bulk liquid reservoir: at T = Trsv. Vapor Pressure Thickness mP ~ DTm Van der Waals DTm ~ m ~ D 3 Van der Waals 1/3 Power Law r r r r 6 V ( r1 r2 ) ~ A r1 r2 Molecule-Molecule: r1 z r2 Molecule to Surface: V (z) ~ 3r d r2 A r r 6 r1 r2 ~ A z 3 X-Ray Reflectivity: Film Thickness Qz 4 sin 2 2 R(Qz ) RF (Qz ) (Qz ) exp Qz2 eff 2 (Qz ) ~ A 2 B 2 2AB cosQz D 2 exp[Qz2 eff ] Example of 1/3 Power Law Methyl cyclohexane (MC) on Si at 46 °C • Via temperature offset DmComparisons • Via gravity Thickness L [Å] For h < 100 mm, Dm < 105 J/cm3 L (2Weff /Dm)1/3 (DTm)1/3 L > ~500 Å small Dm, large L • Via pressure under-saturation For DP/Psat > 1%, DTm [K] Dm > 0.2 J/cm3 L < 20 Å large Dm, small L Dm [J/cm3] Capillary Filling of Nano-Pores (Alumina) Capillary Filling: Dmor DT Transition Energy Cost of Liquid Surface 2 R0 D Min: DR0 2 Volume Dm R02 R0 D Min: D0 Anodized Alumina (UMA) Top Fig. 1: AFM image (courtesy UMA) of anodized alumina sample. The ~15nm pores are arranged in a hcp array with inter-pore distance ~66nm ~90 microns thick ~ 15nm Side Fig 2: SEM (courtesy of UMA) showing hcp ordering of pores and cross-section showing large aspect ratio and very parallel pores. SAXS Data Pore fills with liquid Contrast Decreases Short Range Hexagonal Packing <10> ∆T decreasing Thin films <11> <20> Condensation Capillary filling—film thickness Wall film thickness [nm] Transition Liquid Layer ~ 1nm Pore Diameter~15nm What is the filling process? ~ 2/D Geometry: Theoretical Background C. Rascon and A. O. Parry, "Geometry-dominated fluid adsorption on sculpted solid substrates",Nature 407, 986 (2000). Liquid Filling of Troughs y L(x / x0 ) Parabolic Pits =2): Tom Russell (UMA) Diblock Copolymer in Solvent Self Alignment on Si PMMA removal by UV degradation & Chemical Rinse Reactive Ion Etching C. Black (IBM) ~40 nm Spacing ~20 nm Depth/Diameter Height ~ r 2 2 X-ray Grazing Incidence Diffraction (GID) ] In-plane surface structure Diffraction Pattern of Dry Pits Hexagonal Packing Liquid Fills Pore: Scattering Decreases: Thickness D~Dm Cross over to other filling! X-ray Measurement of Filling GID Reflectivity Filling Electron Density vs DT Filling Results for Sculpted Surface Sculpted is Thinner than Flat c ~ DT c Flat Sample R-P Prediction c~3.4 c Observed c Sculpted Crossover to Flat Gold Nanoparticles & Controlled Solvation Conventional Approach: Dry Bulk Solution Imaging of Dry Sample Controlled Wetting: Liftoff Area Dry Monolayer Adsorption (Wetting Liquid) Of Monolayer Formation Langmuir Isotherms Thiol Coated Au Particles TEM bi-modal distribution Size Segregation Stellacci et al OT: MPA (2:1) OT=CH3(CH2)7SH MPA=HOOC(CH2)2SH GID: X-ray vs Liquid Adsorption (small particles) Adsorption GID Return to Dry Qz Qxy Qxy Qxy Reversible Self Assembly: Annealing Bimodal/polydisperse Au nanocrystals in equilibrium with undersaturated vapor Poor vs Good Solvent Good Solvent (1) dry Reversible (2) ethanol DT ~ 1 K Aggregation in Poor Solvent (3) ethanol DT ~ 15 mK (4) QuickTime™ and a TIFF (LZW) decompressor dry are again (etOH extracted) needed to see this picture. (5) toluene DT = 15 K (6) toluene DT ~ 15 mK Dissolution in Good Solvent (7) toluene DT ~ 3 K Self Assembly NanoParticle SelfAssembly in Nanopores: Tubes Empty 50 nm SEM of empty pores, diameter~30nm Fill with Particles ~2nm dia. Filled TEM of nanoparticles in pores. SAXS Experimental Setup Brief experiment overview: •Study in-situ SAXS/WAXS of particle self assembly as function of added solvent. •Solvent added/removed in controlled way via thermal offset as in flat case. Scattered x-rays Incident x-ray's Alumina membrane With nano-particles Top z DT Qx Toluene Q Small Qx: Pore-Pore Distances Large Qx, Qy.Qz: Particle-Particle Distances x Qz Small Q peaks pore filling hysteresis Heating/Cooling, w/ nanoparticles With nanoparticles Thermal Cycling; Hysteresis <01> <11> <02> Volume (normalized) Hex. Packing 1.2 1 Heating Cooling 2 Cooling 1 0.8 0.6 0.4 0.2 0 -0.2 0 Note: Shift in Capillary Condensation • Decrease/Increase in contrast indicates pores filling/emptying. •Capillary transition shifts from for pores w/o nanoparticles to about ~8K w/ nanoparticles •Strong hysteresis ~2K T~ /R 4 8 12 16 20 24 28 32 DT (K) Below: w/o nanoparticles Summary of Au-Au Scattering(Drying) Images Slices Real space model Intensity Cylind. Shell q radial Intensity q radial Intensity Shell + Isotropic solution q radial Heating Shell + Isotropic clusters Summary • • • • Control Thickness: DT~Dm X-ray: Non-destructive probe Capillary Filling: pores & structures Thin Liquid Solvation