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
ilh.upb.de
1
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
ilh.upb.de
2
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
ilh.upb.de
3
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
ilh.upb.de
4
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
ilh.upb.de
5
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
ilh.upb.de
In foil
6
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
ilh.upb.de






Type of background
Lineshape (Gauss, Lorentz)
FWHM
Peak position
Parameter constrains
…
7
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. ???
ilh.upb.de
8
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
ilh.upb.de
2µm
9
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
10
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
11
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
14
Prof. Dr. –Ing Guido Grundmeier
Technical and Macromolecular Chemistry
Thank you for your attention
ilh.upb.de
15

Download Report