Determination of zeta potential by means of a rotating disk: planar, particulate, and porous samples! Paul J Sides! Zetametrix Inc! 5821 Kentucky Avenue! Pittsburgh, PA 15232! 1!
ZetaSpin: universal tool for determining zeta potential?! particles?! many applications! porous samples?! filters! "pcmp brushes! "CMP pads! fibrous samples! planar samples! (classic ZetaSpin)! 2!
What is zeta potential?! Diffuse Layer! Bulk Solution! Potential! 0! IHP! - - - - + + + Plane of shear! OHP! + + + + - - + + + - + + - - + + + + Debye length! - + + - - Distance! Zeta potential: electric potential at the plane of shear! 3!
Zeta potential: a message from the nano-world at the interface! Macroscopic data (streaming potential/current)! Surface Charge: Dissociation, Adsorption, Valence!!" 4!
Zeta potential and surface charge density! For a 1:1 electrolyte! q =!2!RT F" sinh " F # % $ ' # 2RT &!! zeta potential, volts (usually quoted on mv)! q!surface excess charge density (coul/m 2 ) in the diffuse layer! #!Debye length, m! $!permittivity of the liquid 78.3 x 8.8542 x 10-12 coul/v!m! F!Faraday's constant, 96487 coul/equivalent! 5!
Consequences of zeta potential/charge at the interface! Electrostatic repulsion between particles in a dispersion! If! > kt e If! < kt e (Stability of dispersions such as paints, pigments, )! 6!
Consequences of zeta potential/charge at the interface! Electrostatic repulsion or attraction between a particle and the surface of another material depends on the zeta potential! If! > kt/e! Opposite charge leads to adsorption/ deposition! If! < kt/e! (irreversible adsorption of colloids and bioparticles on membranes, filtration )! 7!
Use of shear flow to measure zeta! #! -! Streaming potential! voltmeter! Liquid velocity! + Conducted bulk charge! Convected diffuse layer charge! # % 10 nm for a 1 mm of 1:1 salt in water! 8!
ZetaSpin: A rotating disk generates streaming potential! z! r! a! 9!
Streaming potential, surface current, and bulk current! Transition from surface current to bulk current Surface current!" # r$ " # 0.51023 $3 % Bulk current, at the surface 2"# $ 10!
The electric circuit near a rotating disk! surface current! return current (ohmic)! 11!
Uniform accessibility of the rotating disk! For electrokinetics:! i =1.020!3! "# For mass transfer:! N A = 0.620D A! 1/2! 1/2 Sc1/3 C A," Uniform accessibility in both cases!! flux of neutral species or ions 12!
Streaming potential and return current near the disk! equipotentials! electric field! 13!
ZetaSpin: apparatus and theory for flat samples! 2a! z! 1. Sensors! 2. Sample & support! 3. Liquid! 4. Motor! f ( z ) =! = f ( z ) 1.96!! s a! 1+ z 2!! 3 1" 2z 1+ z 2 + 2z 2 where z # & = conductivity! ' = kinematic viscosity! a = radius! $ = permittivity! z a 14!
Apparatus! 15!
Acquisition of streaming potential! -0.0015! -0.002! Rotation: on! off! Streaming Potential (V)! -0.0025! -0.003! -0.0035! -0.004! Drift! -0.0045! 0! 10! 20! 30! 40! 50! Time(s)! Streaming potential! 16!
Sample types! 1. Originally developed for planar surfaces! 2. Can be used for studying particles and particle deposition! 3. Can be used for porous materials with open structures.! 17!
Zeta potential of a mineral: e.g. mica, silica, alumina! Scales et. al. data Nishimura et.al. data ZetaSpin; [KCl]=1mM 0! -20! Zeta Potential (mv) -40! -60! -80! -100! -120! -140! -160! [KCl] =1mM 2! 3! 4! 5! 6! 7! 8! 9! 10! ph 18!
Zeta potential of metals: gold, platinum, stainless steels! Potassium nitrate solution, approx. 1 mm! 19!
Zeta potential of CMP pads! Zeta Potential (mv)! 160! 120! 80! 40! 0! -40! -80! -120! -160! -200! -240! Flat Black Pad! Note values more negative than flat version of same material! Grooved Soft Black Pad (not subjeced to CMP)! Hard Grooved Pad P24!!"#$ % &'()*+,-. 2! 3! 4! 5! 6! 7! 8! 9! 10! ph! 20!
ZetaSpin: all purpose tool for determining zeta potential?! ZetaSpin works for planar surfaces.!! Can it make measurement on particles?!! Yes.! 21!
Adsorption/desorption of alumina nanoparticles on mica! 22!
Alumina nanoparticles on mica, effect of concentration! 23!
Adsorption of nanoparticles, effect of rotation rate: none?! 100! 60! #-potential (mv)! 20! -20! -60! -100! -140! 1000 rpm! 2000 rpm! 3000 rpm! 4000 rpm! -180! 0:00:00! 0:04:19! 0:08:38! 0:12:58! 0:17:17! 0:21:36! 0:25:55! 0:30:14! Time (h:m:s)! 24!
Initial adsorption, effect of rotation rate: 4000 rpm! just after! just before! 25!
Initial adsorption: 1000 rpm! 26!
Effect of rotation rate on initial measurements! 4000 rpm! 1000 rpm! 27!
AFM image of particles! Forward scan! Reverse scan! 28!
Silica on sapphire! Zeta Potential(mV)! 30! 20! 10! 0! -10! -20! -30! -40! -50! Silica (80nm) on sapphire!! 4000 RPM! [KNO 3 ]=0.25mM! ph ~ 3.65!!! 0! 100! 200! 300! 400! 500! Time(minutes)! 29!
TiO 2 on ITO for dye sensitized solar cells! ITO! TiO 2 particles! Zeta potential, mv! Panella et al. Rapid Deposition of Titania Nanoparticles for Dye Solar Cells! ph! 30!
Titration of ITO with and without adsorbed TiO 2! Zeta potential, mv! ITO! TiO 2 on ITO*! Panella, Ydstie, Prieve, Rapid Deposition of Titania Nanoparticles for Dye Solar Cells! ph! *adsorbed at ph = 5, then titrated!! 31!
Porous samples! Recently developed theory for measurements on porous samples.! 32!
Brushes for post cmp cleaning of wafers!? 33!
the Velcro experiment! (.!""#$%&'%()&%#(*+%&',#-(./01( /+((. /0(((. /0+((. /*(((. /*+((. (. ()+. 0. 0)+. 2345 6 7(./81( 34!
Theory for rotated porous samples! Inside the porous layer: v r (r)! Outside porous layer: v r (r,z)! 35!
Joseph model of flow into a rotating porous matrix! Darcy equation + rotational forces*! v =! k ( µ "p! F ) where ( )!F = 2!! # v +!! #! # r and! $!e z, r = re r + ze z v r =! k #"p µ "r! 2! v & % "#!! r# 2 ( $ ' v " =! k µ Rev r v z =! k "p µ "z Re! 2k! " ( ) p(z) = z z + 2h!" 2 1+ Re +!"µp 0 2 ( ) * Coriolis and central force arising from rotation about an axis! D. D. Joseph, Q. J. Mech. Appl. Math. 18 325 (1965).! z! r! 36!
Theoretical results! Equation for streaming potential! (Based on flow theory)!! s = a"#h $% & 2 1+ 4k 2 & 2 % 2 1 = "# 1! s! a$% h & + 4k2 " 2 a$% h# "#$! 2 slope = 4k 2!! 2 + "# " s "a!"h!"#! a!"h slope intercept intercept linear with inverse square of rotation "slope gives! h! intercept gives k! emphasizes! h! linear with square of rotation! slope gives k! "intercept gives! h! emphasizes higher rotation rates! 37!
Experimental verification:! Test sample: quartz frits!! Porosity:!50%! Pore size:!90 150 µm!!!150-200 µm!!!200-300 µm! Diameter:!25 mm! Thickness:!" 4 mm! 38!
Analysis for!h! Slope = 1! Log(-( 1 )! 4 different pore diameters! 1 = "# 1! s! a$% h & + 4k2 " 2 a$% h# "#$ slope intercept Log() -2 )! 39!
Experimental data: zeta potential of quartz (too low)! 0!! = -21 mv (low)! -0.5! -1! -1.5! y = -6956.2x - 0.0444! R$ = 0.99997! 1 1/phi!! s -2! -2.5! -3! -3.5! -4! -4.5! 0.E+00! 1.E-04! 2.E-04! 3.E-04! 4.E-04! 5.E-04! 6.E-04! 1/! 2 1/omega^2! 0.3 mm KCl! ph = 5.6! 25 mm diam! 5.34 mm thick! 51% porous! 200 300 µm pores!! 40!
Analysis for the Darcy coefficient, reasonable values! fine frit k = 0.2!10-9 m 2!! 2 " coarse frit k = 1.2!10-9 m 2!! 2 41!
Missing effect for zeta: conductivity of porous layer! drain! current! source! current! leak current! 42!
Missing effect: result! Correction for sample conductivity 1.000 0.800 0.600 0.400 0.200 0.000 0.000 0.200 0.400 0.600 0.800 1.000 sigma*! * "! h p! e a! s = a!"h!" # 2 1+ 4k 2! 2 " 2 g( z,! *) g( 0,! *) porosity = 50%! h = 5.3 mm! a = 12.5 mm! Quartz samples: g(z/a, "*) = 0.681! # = -30 mv! 43!
After analysis! Sample!!zeta, mv!k, m 2!!pore size, µm!! Quartz 00!!-24 ± 5!!12 10-10!200-300! Quartz 0S!!-28 ± 5!!9.1 10-10!150-200! Quartz 01!!-30 ± 5!!4.5 10-10!90-150! Quartz 02!!-29 ± 5!3.8 10-10!40-90! Literature values for quartz 30 40 mv! One obtains the zeta potential and the Darcy coefficient of the as-is sample.! 44!
Test brushes for post cmp cleaning of wafers?! Singh et al., Entegris: Levitronix Conference, Feb. 10-11, 2009, Santa Clara! 45!
Brush data, treated and untreated brushes! Zeta potential, normalized to Planarcore! at ph = 11! 0! -0.5! -1! -1.5! -2! -2.5! Lines are meant to guide the eye, only.! NZP Singh et al.! Untreated Planarcore AMAT Singh et al.! NZP ZetaSpin! Untreated Planarcore AMAT ZetaSpin! 2! 3! 4! 5! 6! 7! 8! 9! 10! 11! 12! ph! 46!
Summary! 1. The ZetaSpin can be used to determine the zeta potential of planar samples.! 2. The Zeta Spin can be used to determine the zeta potential of particles.!! 3. Adsorption of nanoparticles can be detected in real time.! 4. The Zeta Spin can be used to study the zeta potential of porous samples.!! 47!