Kinetic and Strain-Induced Self-Organization of SiGe ...

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32 CHAPTER 3. METHODS OF INVESTIGATION less than a few ˚Angstroms above the sample surface, and the van der Waals force between tip and sample is repulsive. In non-contact mode the tip is held tens or hundreds of ˚Angstroms from the surface, and therefore the intermittent force is attractive due to long-range van der Waals interactions. [74] 3.3.1 Scanning Modes Contact Mode In this repulsive mode the AFM tip makes soft ”physical contact” with the sample. The tip is attached to the cantilever with a low spring constant, and therefore the contact force causes the cantilever to bend and accommodate the changes in topography, as the scanner traces the tip across the sample (or the sample under the tip). Usually, the position of the cantilever (degree of deflection) is detected with optical tech- niques. A laser beam is reflected from the back of the cantilever onto a position-sensitive photodetector (PSPD). A change in the bending of the cantilever results in a shift of the laser beam on the detector. This system is suited to resolve the vertical movement of the cantilever tip with sub-˚Angstrom resolution. The AFM can be operated either in constant-height or constant-force mode. In constant- height mode the height of the tip is fixed, and the spatial change in cantilever deflection is Figure 3.1: Dependence of interatomic force on tip-to-sample separation [74]. � Source: AFM van-der-Waals.jpg
3.3. ATOMIC FORCE MICROSCOPY (AFM) 33 used to generate the topographic data. In constant-force mode a feed-back loop moves the scanner up and down in z-direction, responding to the local topography, and thereby keeping the force and thus the deflection of the cantilever constant. In this case the topographic map can be directly drawn using the z-motion of the scanner as height-information. Due to the ”hard contact” between tip and sample, soft surfaces may be deformed, tips may collect dirt or are rubbed off and become blunt. Non-contact Mode In NC-mode, the system vibrates a stiff cantilever with an amplitude of a few tens to hundreds of ˚Angstroms near its resonant frequency (several 100 kHz). Using a sensitive AC detection scheme, the changes in resonant frequency of the cantilever are measured. Since the resonant frequency is a measure of the force gradient (i.e. derivative of the force versus distance curve), the force gradient reflects the tip-to-sample spacing [74, 79, 80]. Comparable with the constant-force mode in contact regime, a feed-back system moves the scanner up and down in order to keep the resonant frequency or amplitude constant. Again this corresponds to a fixed tip-to-sample distance, and the motion of the scanner is used to generate the topographic data set (see Fig. 3.2 [81]). NC-AFM does not suffer from tip or sample degradation effects and is suited to scan even soft samples and to keep the tips sharp. Intermittent-contact Mode IC-AFM is similar to NC-AFM, except that in this mode the vibrating cantilever tip is brought closer to the sample, so that it barely hits (”taps”) the surface. The changes in cantilever oscillation amplitude responding to the tip-to-sample separation are monitored to obtain the surface topography. This mode is usually preferred as it combines the high resolution of contact mode, and the low wear and tear of the tip in NC-mode. [74] 3.3.2 AFM-Probes The AFM-tips are the crucial point in AFM as they are in contact with the surface and probe the sample. The sharpest tips that are commercially available have a tip radius as small as 50 ˚A. Due to the fact, that the interaction area of tip and sample is just a fraction of the tip radius, these tips would result in a lateral resolution of at least 20 ˚A. In this case the
Page 1: J O H A N N E S K E P L E R U N I V
Page 4 and 5: ii PREFACE Kurzfassung Eine kinetis
Page 6 and 7: iv PREFACE
Page 8 and 9: vi CONTENTS 2.1.3 Growth-Modes . .
Page 10 and 11: viii CONTENTS B General Physical Da
Page 13 and 14: Chapter 1 Silicon-Germanium Materia
Page 15 and 16: 1.1. STRUCTURAL PROPERTIES 5 Figure
Page 17 and 18: 1.2. VICINAL SI(001) 7 Vicinal subs
Page 19 and 20: 1.3. ELECTRONIC PROPERTIES 9 Monoat
Page 21 and 22: 1.3. ELECTRONIC PROPERTIES 11 Silic
Page 23 and 24: 1.4. SILICON GERMANIUM ALLOYS (SI1
Page 25 and 26: Chapter 2 Molecular Beam Epitaxy (M
Page 27 and 28: 2.1. MBE-GROWTH 17 hit the substrat
Page 29 and 30: 2.1. MBE-GROWTH 19 Figure 2.3: The
Page 31 and 32: 2.2. CLEANING PROCEDURE 21 rameter
Page 33 and 34: 2.2. CLEANING PROCEDURE 23 H2SO4 :
Page 35 and 36: 2.3. MBE-SYSTEM 25 Figure 2.7: All-
Page 37 and 38: 2.3. MBE-SYSTEM 27 Figure 2.9: Sche
Page 39 and 40: Chapter 3 Methods of Investigation
Page 41: 3.2. SCANNING ELECTRON MICROSCOPY (
Page 45 and 46: 3.3. ATOMIC FORCE MICROSCOPY (AFM)
Page 51: Part II Main Research 41
Page 54 and 55: 44 CHAPTER 4. SELF-ORGANIZED GROWTH
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82 CHAPTER 5. SELF-ORGANIZED GROWTH
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84 CHAPTER 5. SELF-ORGANIZED GROWTH
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86 CHAPTER 6. P-MODULATION DOPING A
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100 CHAPTER 6. P-MODULATION DOPING
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Chapter 7 Transient-Enhanced Si Dif
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7.3. EXPERIMENTAL RESULTS 117 > 100
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7.3. EXPERIMENTAL RESULTS 119 Figur
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7.4. DETAILED CHARACTERIZATION AND
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7.4. DETAILED CHARACTERIZATION AND
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Chapter 8 Germanium Source Reconstr
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Figure 8.2: Elevated front-view of
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water lines. Figure 8.4: Photograph
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Figure 8.7: Part 2 of final constru
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Appendix A Calibration and Characte
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A.1. CALIBRATIONS 135 Figure A.1: X
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A.1. CALIBRATIONS 137 Figure A.3: N
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A.2. PHOTOLUMINESCENCE 139 Sample 1
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A.2. PHOTOLUMINESCENCE 141 Figure A
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A.2. PHOTOLUMINESCENCE 143 Figure A
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Appendix B General Physical Data B.
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Bibliography [1] Herbert Lichtenber
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BIBLIOGRAPHY 149 [42] M. B. Prince,
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BIBLIOGRAPHY 151 [85] J. Zhu, K. Br
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BIBLIOGRAPHY 153 [130] C. S. Peng,
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BIBLIOGRAPHY 155 [174] G. Medeiros-
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BIBLIOGRAPHY 157 [214] G. Bastard,
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Postface Curriculum Vitae ⋄ ∗ 1
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POSTFACE 161 � D. Gruber, D. Pach
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POSTFACE 163 Abbreviations AFM Atom
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