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M. A. Vorotyntsev
1

1,2,3,

D. V. Konev3, M. Skompska

4

ICMUB-UMR 6302 CNRS, Universite de Bourgogne, Dijon, France 2 M. V. Lomonosov Moscow State University, Russia 3 Institute for Problems of Chemical Physics, Chernogolovka, Russia 4 University of Warsaw, Poland
mivo2010@yandex.com, mv@elch.chem.msu.ru, mv@u-bourgogne.fr


In situ measurements of specific conductivity of films on electrode surface Specific conductivity: function of potential Impedance problems: 1. Special equipment 2. Interpretation (electrode/film resistance!) 3. Non-uniform electric field distribution


Principal in situ method: microband electrodes
Various constructions (no commercial supply!): 2 metal plates separated by a thin insulating layer One can clean by polishing Lithographic metal layers:

Film above electrodes and gaps. Current between them via film Film resistance U / I = Rf Film conductivity: Rf = G /


Film resistance: U / I = Rf

Film conductivity: Rf = G /

Problem of two electrodes configuration: contribution of electrode/film resistance 4 microband electrodes: separation of Rf and Rm/f U.Lange, V.M.Mirsky, Analyt. Chim. Acta, 2011, 687,105 Another problem: Is the film uniform? Which thickness? Another opinion: G = Lg / Af One opinion: only Rf Gap width: 5-100 µm Film thickness? Microband height?


Our study: film growth on microband electrodes
Disk + single microband

Series of pot-static depositions: various PPy film thicknesses


Disk + single microband Large scale AFM device Contact mode

900 800 700 600 500 400 300 200 100 0 -4

Z, nm

20um A 50um B 100um B

Similar profiles near edges of microband and macrodisk Slightly different film thicknesses in central areas
4

-2

0 2 Distance, um


Single microband: film cross-section
2.5 2.0

Thickness

1.5

bare s3 s2 s1 s6 20um s6 100um s4
2

bare s3 s2 s1 s4 s6 100um

Spread

Z (um)

1.0

Z (um)

1

0.5

0
0.0

-7
-6 -4 -2 0 2 4 6
2.4

-6

-5

-4

4

5

6

7

X (um)
X (um)
Thickness = k*q, k=2.29nm*cm /mC Thickness, um Spread, um
2

Growth rates in normal and tangent directions are comparable

2.0 1.6 1.2 0.8 0.4 0.0 0 100 200 300
2

Distance, um

400

500

600

qdep, mC/cm


Disk: AFM images

Increase of film thickness: Greater elements Higher roughness Impossible to estimate G, i.e. film conductivity


Film conductivity: novel method
M. A. Vorotyntsev, D. V. Konev, Electrochim. Acta, 2011, 56, 9105

Standard 3-electrode cell with static disc electrode

Solution: 3D distribution. Thin film: 1D distribution


Film conductivity: novel method
Electrochim. Acta, 2011, 56, 9105

Potential step: non-stationary potential/current distributions Primary (short-time) potential/current distributions: 1) no concentration changes, 2) no changes at interfaces Only induced fluxes of mobile charges in solution & film = 0 at z > 0 (solution) i = - s at z > 0 (solution) iz f (V - o) / Lf (thin film) V: amplitude of potential step


Electrochim. Acta, 2011, 56, 9105

Total short-time resistance: Rtot = V/Io Nonadditive contributions of solution (Rs) and film (Rf) resistances Analytical formulas: Rtot(Rs, Rf) & Rf(Rs, Rtot) If Rtot is measured for a set of electrode potentials, Rtot(E), one can determine Rf(E) Specific conductivity of the film, f(E): Rf = Gf / f, Gf = Lf / Af , Af = ro2


Conclusions
· For the first time: study of polymer film growth on nonuniform surfaces (single- and double-bands) · Contrary to a widely-used hypothesis: no preferential film propagation along the surface · To measure the interband current, i.e. film resistance the film thickness should be about a half of the interband gap, i.e. micrometer range, while the local and global film morphologies become non-uniform Novel "potential-step method for disk electrode" to measure absolute values of in situ specific conductivity f(E) of film on electrode surface, i.e. in contact with solution under electrode potential control.


Advantages:
· Standard electrochemical cell, · Measuring device = potentiostat (short-time signals), · Normal-size (about mm) disk electrode, no need of micro/nanoelectrodes or larger-size (cm) electrodes, · Standard film deposition procedure, · Thin films (from a few tens of nm), · Electronic or ionic or mixed (electron-ion) conductivity, · Non-destructive type of measurement Limitations of potential step method: 1) Rf << Rs, 2) too low conductivity (displacement current) Combination of microband and potential step methods: matching dependences resistance vs potential. Another method to determine film conductivity, (E)