monitoring organic thin film growth and its water...
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Monitoring Organic Thin Film Growth and its Water Content With Combined Quartz Crystal Microbalance and Ellipsometry
A. Sarkar1 , A. Kjerstad1, T. Hofmann1, B. Laderian1,T. Viitala3, T. E.Tiwald2, J. A. Woollam2, and M. Schubert1*
*[email protected] http://ellipsometry.unl.edu
1Department of Electrical Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, U.S.A.2J.A.Woollam Co., Lincoln, NE,USA 3 KSV Instruments Ltd., Helsinki, Finland
Special acknowledgement: Mark Solinski Proctor & Gamble, Cincinnati, USA
• Simultaneous measurement of organic thin fimusing Quartz Crystal Microbalance (QCM) and
Our message Studying water rich organic thin films
How does the water content evolveEllipsometer is sensitive only to polymer mass
ltWater Synperonic
(polymer)Spectroscopic Ellipsometry (SE).
• Synperonic in aqueous phase deposited onoctadecane thiol coated gold surface is used as amodel system.
• QCM is measures total mass including waterentrapped in the thin organic film whereas SEexcludes water in the measurement. Thecombination of the two instruments allows one todetermine the porosity and thereby find the watercontent.
Methods to investigate this phenomena are:• Optical • Mechanical• Combination of optical and •mechanical methods
during organic thin film formation in an aqueous environment?
Porosity holds the key!
Substrate
y p ypolymerwater
Quartz Crystal Microbalance is sensitiveto total mass (polymer + water)
Comparison provides the porosity (fv) ,fraction of polymer in the film
Schematic diagram of film on QCM wafer
(polymer)
SAM
Auelectrode
Quartz (piezoelectric)
Description of System Studied
Instrumentation Synperonic
Liquid cellQuartz Crystal
g Q
QCM-SE liquid cell• Specially designed cell allows for simultaneous measurement of mass uptake by SE and QCM.•QCM and SE readings taken from sample surface.
•A self-assembled monolayer (SAM) composed of octadecanethiol was first assembled on to the gold surface. This was done to make the surface hydrophobic.
•Synperonic, a well studied polymer, was introduced to form a thin organic film on the SAM.
Molecular structure of Synperonic PE/F68
Combined stage for QCM and SE
Liquid cellQuartz Crystal Microbalance unit
Measurement of Film Thickness and Determining the Porosity
QCM and SE Determination of Porosity, fv
film on the SAM.
0.9
1.0
6
8
film thickness by QCM, dQCM
-50
Hz)
QCM
N
Determines dQCM
18 21 240.5
0.6
0.7
0.8
poro
sity
, fv
SE time (min)
0
2
4
6
film thickness by SE,dSE
dSE
, d
QC
M (n
m)
film thickness by QCM, dQCM
void fraction, fv-45
-40
-35
Δf/N
(H
3579
11
90
93 549.9 nm
degr
ees)
SE 135
899.62 nm
The formula for porosity (fv) relates the thicknessdetermined from SE (dSE) & QCM (dQCM) and
densities of water and polymer respectively. Monitoring the evolution of fv gives an idea of whether the film:
1 forms and swells by imbibing water
5th Workshop Ellipsometry, Zweibrücken, March 2-4, 2009
Top panel (QCM): Frequency shift normalized by harmonic number. The graphs do not overlap indicating formation of a viscoelastic film.
Bottom panel (SE): Δ at selected wavelengths from in-situ scanning ellipsometry (SE) measurements.
The graph above displays the variation of thickness of synperonic film over time as calculated from QCM (dQCM) and SE data (dSE). Also shown is the evolution of porosity (fv) over time. In this case, the film entraps water as it is formed.
Determines dSE
SE time (min)
10 20 3087
Δ (d
391.96 nm
Time (minutes)
1321.forms and swells by imbibing water.2.forms from an initial water rich state to a final
denser state by releasing water.