Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
PiKo-Workshop
Study of water adsorption and capillary bridge formation for SiO2
nanoparticle layers by means of a combined in-situ FT-IR
reflection spectroscopy – QCM-D set-up
Boray Torun, Christian Kunze, Guido Grundmeier
Magdeburg, April 3rd, 2014
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Table of Contents
 Introduction & Motivation
 Characterization of nanoparticles


Scanning electron microscope charaterization
X-Ray photoelectron spectroscopy
 Combined in-situ QCM-FTIR water adsorption studies


Basics of FT-IR and QCM
Results
 Conclusions and outlook
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
SEM Characterization
TiO2 primary particles
TiO2 sintered particles
Sample preparation:


400nm
glass-particles
„Sticky“ carbon pad
Deposition on metal
substrate (e.g. Au)
400nm
SiO2 Stöber particles
SEM gives insight on:



10µm
Morphology
Disperse properties
Composition (EDX)
400nm
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
SEM Characterization
400 nm
2 µm
Common problems:


Charging
 Sputtercoating helps with charging problems but alters interface
 Detection of backscattered instead of secondary electrons
 Usage of lower acceleration voltages
Small primary particles tent to form homogeneous film with no contrast
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
The Principle of X-Ray Photoelectron Spectroscopy
XPS requires:
kinetic-filter Ekin
detector



Ultra high vacuum conditions  p ≈ 10-10 to 10-9 mbar
Good sample preparation: sensitive to the top 5-10 nm
Set of sensitivity-factors for quantitative analysis
Main components:



X-Ray-source
 Typically Al or Mg with defined EX-Ray
Kinetic filter
 Analyzes electrons based on their speed
 Ramping the passing Ekin generates the spectrum
Detector
 Counts electrons at each given Ekin
XPS gives primary insights on:

0
Ebond = EX-Ray - Ekin
Ebond
ee-
e-
e-
e-

Advanced XPS techniques:




07.04.2014
Elemental composition
 Ebond is characteristic for each element
Chemical state
 Chemical shift of Ebond due to oxidation state
Determination of layer thickness
Measurement of valence band structure
Depth profiling of samples
Mapping of local elemental composition
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Experimental Setup for XPS-Analysis
Main components:
5
2
4
1.
2.
3.
4.
5.
X-Ray source
Monochromator
Sample chamber
Kinetic filter
Detector
Pumping system:
ee- ee- e-




3
Roughening pumps
Turbo pumps
Ion-getter pumps
Ti-sublimation pumps
Common problems:
1
pressure





Tricky sample preparation
Contamination of surfaces
Highly complex setup
Not all materials appropriate for
UHV conditions
Complex data evaluation
In foil
In foil
Al foil
07.04.2014
Al foil
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In foil
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Si 2s
Si 2p
Ca 2p
Mg KLL
C 1s
Na KLL
In 3d
O KLL
Na 1s
O 1s
How Does an XPS Spectrum Look Like
Peak fitting is very easy…..
…but doing it in a way that makes
sense is very complex!
Parameters to play with:



Peak width typically ≈3eV
Spectrum width typically 1200eV
 Most of the XPS-Peaks are isolated
 Elemental composition can easily be determined
Charging has to be compensated by electron shower
07.04.2014
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




Type of background
Lineshape (Gauss, Lorentz)
FWHM
Peak position
Parameter constrains
…
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Example: XPS data interpretation
Question:
1.
2.
Is the surface hydroxide terminated?
What is the OH- surface density
Peakshape: GL(30)
Peakshape: GL(50)
Atom %
Atom %
O2-
87
O2-
52
OH-
13
OH-
48
Answer:
1. YES! (easy)
2. ???
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
In-situ QCM-FTIR
 Water uptake studies by combined
in-situ QCM and FTIR spectroscopy
 Monolayers and multilayers of particles adsorbed on an
Au-coated quartz crystal
 Simultaneous collection of spectroscopic information
(FTIR) and measurement of mass change and energy
dissipation (QCM)
QCM–FTIR in-situ cell
 Why SiO2 Nanoparticles?


Well studied reference system
Commercially available in good quality:
 Monodisperse
 High purity
 Various sizes ranging from few nm to µm
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2µm
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
In-situ Quartz Crystal Micro Balance (QCM) and FTIR
 Fourier Transform Infrared Spectroscopy:


Absorbed light with energy in the regime of molecular vibrations
Information on surface composition and bonding types
r.H., T, V
quartz
IR detector
Information on surface composition and
bonding types (liquid vs. ice-like water)
QCM
Measurement of water uptake and
changes of mechanical properties
 QCM measurements:



Piezoelectric material  applied voltage results in physical deformation
Change of resonance frequency can be detected with high precision (Δ f noise << 1Hz)
Resonance frequency depends on the mass
𝑛𝑔
𝑛𝑔
∆𝑓[𝑠 −1 ]
∆𝑚
= 17.7
𝑐𝑚2
𝑐𝑚2 ∙ 𝑠 −1
𝑛
Phys. Chem. Chem. Phys., 2014,16, 7377-7384
ilh.upb.de
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Sample preparation / preliminary measurements
Au
quartz
Au
cleaning
Au
quartz
Au
reference for IR
 WCA  typically ≈ 110°
 AFM  no micelles
PE-CVD
SiO2
Au
quartz
Au
particles
particle sample
 SEM  typically 1 to 2 monolayers
 XPS  no adsorbates affecting

adsorption
 WCA  water spreads
Au
quartz
Au
ODT
SiO2
Au
quartz
Au
reference for QCM
 AFM  very smooth, RMS ≈1.7 nm
 XPS  no C, closed film
 WCA  typically ≈ 40°
Phys. Chem. Chem. Phys., 2014,16, 7377-7384
ilh.upb.de
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Results: QCM Data of SiO2 Particle Sample
QCM gives Δm per cm²  surface
increase λ has to be considered
𝜆 =1+
2𝜋
3
∙𝛼∙𝛽
Ratio of perfect sphere and
actual particle surface area
 BET
Monolayer count  SEM
Surface increase due to layer of
spheres
Uncovered substrate area assumed to be
a smooth plane  AFM / XPS
Layer of SiO2 nanoparticles
Significant higher shifts are observed than
the increase of surface would contribute.
 Additional water in capillaries
Phys. Chem. Chem. Phys., 2014,16, 7377-7384
ilh.upb.de
12
Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Results: QCM Data of SiO2 Particle Sample
Isotherm can be divided into three segments:
Dissipation indicates change in contact mechanics
1.
2.
3.

0% - 20% r.h. : rapid increase  favorable adsorption
20% - 80% r.h. : surface almost saturated
80% - 95% r.h.: multilayer formation and water film formation

Peak around 60% to 80% indicates transition from strongly
attached (Sauerbrey mass) to elastic behavior
Sauerbrey does not apply  no quantification
Phys. Chem. Chem. Phys., 2014,16, 7377-7384
ilh.upb.de
13
Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Results: FT-IR Data of SiO2 Particle Sample
Peak-Fitting with different OH-species depending
on the binding state
FT-IR data of particle sample vs. ODT reference
Isotherm is in good agreement with QCM data:


Low r.h. regime: strongly „ice-like“ bound water
High r.h. regime: „liquid like“ water  water film formation
Phys. Chem. Chem. Phys., 2014,16, 7377-7384
ilh.upb.de
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Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Thank you for your attention
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