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Dynamic investigation of polymeric materials [Elektronische Ressource] : reproducible data acquisition and profound mechanical analysis / vorgelegt von: Alexander Michael Gigler

176 pages
DYNAMIC INVESTIGATION OF POLYMERIC MATERIALS- REPRODUCIBLE DATA ACQUISITIONAND PROFOUND MECHANICAL ANALYSISABTEILUNG EXPERIMENTELLE PHYSIKausUlmDoktoUniversit?tErlangungderDr.Naturwissenschaftenrechtingenzurdesvorgradesvon:rer.Michaelf?rrgelegtFAlexanderakult?tGiglerDissertationHerbder2006nat.IIAmtierender Dekan: Prof. Dr. Klaus Dieter Spindler1. Gutachter: Prof. Dr. Othmar Marti2. Gutachter: Prof. Dr. Paul ZiemannTag der mündlichen Prüfung: 05. Juli 2006AbstractThe investigation of the mechanical properties of surfaces has attracted increasing atten tion over the last decades. At the same time, miniaturization of mechanical devices suchas MEMS - micro electro mechanical systems - has reached nanoscale dimensions. Bymeans of the Atomic Force Microscope (AFM), the mechanical properties at these length scales can be accessed. Theories and simulations describing these nano mechanics, how ever, are not yet conclusive.The reliable and reproducible acquisition of AFM data has often been doubted, since thecalculated results of the measurements did not fully comply with the results from macro scopic experiments. The AFM, however, is able to determine the mechanical behavior ofsurfaces reproducibly if the apparatus is calibrated thoroughly before and after the mea surements are taken. With the Digital Pulsed Force Mode (DPFM) technique, it is possibleto access the entire spectrum of sample dynamics and indentation behavior.
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DYNAMIC INVESTIGATION OF POLYMERIC MATERIALS
- REPRODUCIBLE DATA ACQUISITION
AND PROFOUND MECHANICAL ANALYSIS
ABTEILUNG EXPERIMENTELLE PHYSIK
ausUlmDoktoUniversit?tErlangungderDr.Naturwissenschaftenrechtingenzurdesvorgradesvon:rer.Michaelf?rrgelegtFAlexanderakult?tGiglerDissertationHerbder2006nat.II
Amtierender Dekan: Prof. Dr. Klaus Dieter Spindler
1. Gutachter: Prof. Dr. Othmar Marti
2. Gutachter: Prof. Dr. Paul Ziemann
Tag der mündlichen Prüfung: 05. Juli 2006Abstract
The investigation of the mechanical properties of surfaces has attracted increasing atten
tion over the last decades. At the same time, miniaturization of mechanical devices such
as MEMS - micro electro mechanical systems - has reached nanoscale dimensions. By
means of the Atomic Force Microscope (AFM), the mechanical properties at these length
scales can be accessed. Theories and simulations describing these nano mechanics, how
ever, are not yet conclusive.
The reliable and reproducible acquisition of AFM data has often been doubted, since the
calculated results of the measurements did not fully comply with the results from macro
scopic experiments. The AFM, however, is able to determine the mechanical behavior of
surfaces reproducibly if the apparatus is calibrated thoroughly before and after the mea
surements are taken. With the Digital Pulsed Force Mode (DPFM) technique, it is possible
to access the entire spectrum of sample dynamics and indentation behavior. Using a com
mercial setup and AFM tips, the mechanical properties of a dewetting polymer mixture of
styrene butadiene rubber (SBR) and polymethylmethacrylate (PMMA) have been inves
tigated. From the experiments, a recipe for the reliable acquisition of AFM data has been
constructed. Furthermore, an algorithmic framework based on contact mechanical mod
els has been developed and implemented as evaluation software. This software allows the
quantitative evaluation of entire data sets acquired in DPFM experiments. This amount of
data has not been evaluated before, and thus adds an important statistical certainty to the
results obtained from the measurements. In addition to the polymer mixture, which is a
passive sample system, experiments have also been conducted on living cells. Operating
the DPFM in a physiologic buffer solution allowed acquisition of maps of the mechanical
response.
Another field that is accessible by the AFM techniques is the determination of the lateral
force between an indenter and a sample under an additional lateral relative movement.
This is known as Dynamic Friction Force Microscopy (DFFM). However, the relative
speeds between the tip and the sample are generally rather low and not comparable with
speeds that occur in macroscopic reality. To gain more information on the lateral forces
occurring at these velocities, a special add on system to the AFM has been devised, which
IIIIV Abstract
makes realistic velocities of several centimeters or even meters per second accessible. The
successful operation of the apparatus is shown by exemplary measurements.
Together, the reproducibility of indentation measurements and the measurement of lat
eral forces under realistic shear conditions might add a new quality to the experiments
conducted on the nanoscale using Atomic Force Microscopy.Contents
Abstract III
Contents V
List of Figures IX
List of Tables XIII
List of Abbreviations XV
1 Introduction 1
1.1 Scanning Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Modes of SPM Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1 Static Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.2 Dynamic Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Theoretical Contact Mechanics 11
2.1 Hertzian Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Sneddon’s Extensions to the Hertzian Model . . . . . . . . . . . . . . . . 15
2.3 Models Incorporating Adhesion . . . . . . . . . . . . . . . . . . . . . . 18
3 Experimental Setup for Indentation Experiments 23
3.1 a SNOM in AFM Operation . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Digital Pulsed Force Mode Implementation . . . . . . . . . . . . . . . . 25
3.2.1 Technical Implementation of Pulsed Force Mode . . . . . . . . . 28
3.2.2 Analogies and Differences of PFM, JM & Force Volume Mode . 29
3.2.3 Extended DPFM - Digital CODYMode . . . . . . . . . . . . . . 29
4 Measurements and Calibration Techniques for Digital Pulsed Force Mode 31
4.1 Force Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2 Calibration for Force Measurements . . . . . . . . . . . . . . . . . . . . 34
4.3 Dewetting Polymer Mixtures . . . . . . . . . . . . . . . . . . . . . . . . 36
VVI Contents
4.4 DPFM on Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.4.1 Results from Individual DPFM Force Curves . . . . . . . . . . . 40
4.4.2 Mapping Physical Quantities to the Topographical Features . . . . 43
4.4.3 Reproducibility Experiments . . . . . . . . . . . . . . . . . . . . 67
4.5 Recipe for Acquisition of Quantitative AFM Data . . . . . . . . . . . . . 77
4.6 DPFM on Living Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5 DPFM Data Handling 81
5.1 Data Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.2 Calibration of the DPFM Apparatus . . . . . . . . . . . . . . . . . . . . 84
5.3 Data Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.3.1 Data Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.3.2 Forces versus Indentation Depth . . . . . . . . . . . . . . . . . . 85
5.3.3 Zero Assumption Data Conversion . . . . . . . . . . . . . . . . 88
6 Lateral Forces Measured by AFM 91
6.1 High Speed Friction Implementation . . . . . . . . . . . . . . . . . . . . 92
6.1.1 High Bandwidth Photodetector . . . . . . . . . . . . . . . . . . 92
6.1.2 Vibrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.1.3 Lock In Technique . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.1.4 Acousto Optical Modulator . . . . . . . . . . . . . . . . . . . . 94
6.1.5 The Actual Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7 Approaches for Calibration and Evaluation of Lateral Force Experiments 97
7.1 Empirical Model for Dynamic Friction . . . . . . . . . . . . . . . . . . . 98
7.1.1 Modeling Sticking Friction . . . . . . . . . . . . . . . . . . . . . 99
7.1.2 Kinetic . . . . . . . . . . . . . . . . . . . . . 99
8 Experiments Using the Novel Setup 103
8.1 Results on Polymer Blends . . . . . . . . . . . . . . . . . . . . . . . . . 103
8.2 Optimized Samples by Microcontact Printing . . . . . . . . . . . . . . . 108
8.3 Results on Oligomeric SAMs . . . . . . . . . . . . . . . . . . . . . . . . 111
9 Conclusions 115
10 Zusammenfassung 119
References 123
A Automated DPFM Data Evaluation 133Contents VII
B Composition of Inks and Etchants 137
C Recipe for m CP 139
D m CP of Fischer Projection Patterns 141
E Lateral Force Calibration 143
E.1 Friction on Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
E.2 on Flat Planes . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Acknowledgements 151
Issue of Statement 153
Curriculum Vitae 155
Posters - Paper - Presentations 157VIII ContentsList of Figures
1.1 Components of an AFM setup . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Schematics of the AFM detection and feedback system . . . . . . . . . . . 3
1.3 Amplitude of a damped and driven harmonic oscillator. . . . . . . . . . . 4
1.4 Phase of a damped and driven harmonic oscillator. . . . . . . . . . . . . 5
2.1 Impact of two elastic spheres . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Indentation of a sphere into an elastic half space . . . . . . . . . . . . . 14
2.3 Normalized plot of contact mechanical models . . . . . . . . . . . . . . . 22
3.1 Schematic drawing of the a SNOM. . . . . . . . . . . . . . . . . . . . . 24
3.2 Force distance curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3 Force vs. time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1 Oliver Pharr data analysis method . . . . . . . . . . . . . . . . . . . . . 33
4.2 Reference curve on a hard substrate . . . . . . . . . . . . . . . . . . . . 35
4.3 Transformed reference curve without phase correction . . . . . . . . . . 35
–4.4 Phase correction 25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
–4.5 Phase correction 18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.6 Best fit of the reference data . . . . . . . . . . . . . . . . . . . . . . . . 35
4.7 A zoomed view of the best fit . . . . . . . . . . . . . . . . . . . . . . . . 35
4.8 Surface morphology of dewetting polymer mixtures. . . . . . . . . . . . . 37
4.9 Stepwise analysis of PFM curves . . . . . . . . . . . . . . . . . . . . . . 39
4.10 Closeup of the force traces of PMMA and Si. . . . . . . . . . . . . . . . . 40
4.11 Results from PFM data analysis . . . . . . . . . . . . . . . . . . . . . . 42
4.12 Masks used for data evaluation. . . . . . . . . . . . . . . . . . . . . . . 43
4.13 Relative error of the maximum force. . . . . . . . . . . . . . . . . . . . . 44
4.14 Topography at maximum force. . . . . . . . . . . . . . . . . . . . . . . . 45
4.15 Cross section of the topography at maximum force. . . . . . . . . . . . . 46
4.16 Indentation depth required to reach F . . . . . . . . . . . . . . . . . . 47max
4.17 Cross section of the indentation depth. . . . . . . . . . . . . . . . . . . . 47
4.18 Map of the real topography. . . . . . . . . . . . . . . . . . . . . . . . . . 48
IXX List of Figures
4.19 Cross section of the real topography. . . . . . . . . . . . . . . . . . . . . 48
4.20 Dimensionless deformation factor x . . . . . . . . . . . . . . . . . . . . . 49
4.21 Cross section of the map of x . . . . . . . . . . . . . . . . . . . . . . . . 50
4.22 Sample compliance calculated by flat punch. . . . . . . . . . . . . . . . . 50
4.23 Histogram of the flat punch map. . . . . . . . . . . . . . . . . . . . . . . 51
4.24 Sample compliance calculated by a JKR like model. . . . . . . . . . . . . 52
4.25 2D Histograms of effective modulus versus x . . . . . . . . . . . . . . . . 53
4.26 Stress strain curves of PMMA. . . . . . . . . . . . . . . . . . . . . . . . 53
4.27 Stress strain curves of rubber samples. . . . . . . . . . . . . . . . . . . . 54
4.28 Sample compliance calculated by a cone model. . . . . . . . . . . . . . . 56
4.29 Maximum indentation depth and post flow distance. . . . . . . . . . . . . 57
4.30 Post flow due to creep. . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.31 Cross section of post flow map.. . . . . . . . . . . . . . . . . . . . . . . 58
4.32 Energy needed to indent. . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.33 Energy lost during one cycle. . . . . . . . . . . . . . . . . . . . . . . . . 60
4.34 Remanent depth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.35 depth of an indentation. . . . . . . . . . . . . . . . . . . . . . 62
4.36 Map of the local adhesion of the dewetting polymers SBR and PMMA on
silicon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.37 Detachment position. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.38 Histogram of the detachment distance. . . . . . . . . . . . . . . . . . . . 65
4.39 Energy needed for detachment. . . . . . . . . . . . . . . . . . . . . . . . 65
4.40 Map of the energy of detachment. . . . . . . . . . . . . . . . . . . . . . . 66
4.41 A tip before use in DPFM. . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.42 The same tip after use. . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.43 The tip of the cantilever. . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.44 Sample reproducibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.45 Reproducibility of the indentation depth. . . . . . . . . . . . . . . . . . . 70
4.46 Repr of x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.47 Reproducibility of the flat punch compliance. . . . . . . . . . . . . . . . 71
4.48 Repr of the effective modulus. . . . . . . . . . . . . . . . . . . 72
4.49 Reproducibility of K versus x . . . . . . . . . . . . . . . . . . . . . . . . 72
4.50 Repr of the Young’s modulus. . . . . . . . . . . . . . . . . . . 73
4.51 Reproducibility of the hysteretic losses. . . . . . . . . . . . . . . . . . . . 74
4.52 Repr of the dissipation ratio. . . . . . . . . . . . . . . . . . . 74
4.53 Reproducibility of the detachment force. . . . . . . . . . . . . . . . . . . 75
4.54 Repr of the post flow. . . . . . . . . . . . . . . . . . . . . . . 76
4.55 DPFM on Living Cells. . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

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