Cover Page
The following handle holds various files of this Leiden University dissertation:
http://hdl.handle.net/1887/58611
Author: Tewari, S.
Title: Molecular electronics: controlled manipulation, noise and graphene architecture
Issue Date: 2018-03-27
Molecular Electronics
Controlled manipulation, Noise and Graphene
architecture
Molecular Electronics
Controlled manipulation, Noise and Graphene architecture
Proefschrift
ter verkrijging van
de graad van Doctor aan de Universiteit Leiden, op gezag van Rector Magnificus prof. mr. C.J.J.M. Stolker
volgens besluit van het College voor Promoties te verdedigen op dinsdag 27 maart 2018
klokke 15:00 uur
door
Sumit Tewari
geboren te Nainital, India
in 1985
Promotor: Prof. dr. J.M. van Ruitenbeek (Universiteit Leiden, The Netherlands)
Promotiecommissie: Prof. dr. E.R. Eliel (Universiteit Leiden, The Netherlands) Prof. dr. ir. T.H. Oosterkamp (Universiteit Leiden, The Netherlands) Prof. dr. E. Scheer (Universität Konstanz, Germany) Dr. M.P. Allan (Universiteit Leiden, The Netherlands)
Dr. M. Kumar (École Normale Supérieure de Paris,
France)
ISBN: 978-90-8593-336-6
Casimir PhD series, Delft-Leiden 2018-04
Cover photo (Front): Courtesy Matt Crux @PhoenixLove.net
Cover photo (Back) is prepared using our low temperature scanning tunneling mi- croscope © Sumit Tewari
Cover design: Sumit Tewari Copyright © 2018 Sumit Tewari
Contents
1 Introduction . . . 1
1.1 The concept of the atom 2 1.2 From macro to nano 3 1.3 Molecular electronics 5 1.4 Experimental techniques 6 1.4.1 Mechanically controllable break junctions . . . 6
1.4.2 Electromigration break junctions . . . 8
1.4.3 Methods based on scanning probe microscopy . . . 10
1.4.4 Data analysis and conductance histograms . . . 11
1.5 The notorious lot 12 1.5.1 Benzenedithiol . . . 13
1.5.2 Alkane dithiols . . . 15
1.6 Shot noise 20 1.7 Two-level fluctuations 21 1.8 Organization of the thesis 22
I Part One: Atomic and Molecular Manipulation 2 Human-machine augmented system to control single atoms . . . 26
2.1 Introduction 28 2.2 Experimental setup 29 2.3 Real-time molecular dynamic simulation 30 2.3.1 Implementation . . . 32
2.3.2 Speed-up techniques . . . 34
2.4 Experimental measurements 36 2.4.1 Obtaining the positions of the background substrate atoms . . . 37
2.4.2 Point contact pushing . . . 38
2.4.3 Lifting of gold atomic chain . . . 40
2.4.4 Parity oscillations . . . 42
2.4.5 Lifting of a gold atomic chain along a step edge . . . 44
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CONTENTS
2.5 Discussion 45
2.6 Conclusion and outlook 46
3 Single molecule STM control: GPU implementation . . . 48
3.1 Introduction 50
3.2 Single-shot measurements - Overview 51
3.3 Molecular dynamics 53
3.3.1 Challenges in making real-time MD simulations . . . 54
3.4 Molecular dynamics - GPU implementation 55
3.4.1 Gold-gold forces . . . 56 3.4.2 Forces on molecule atoms . . . 59
3.5 Results and discussion 62
3.6 Conclusion and outlook 66
II Part Two: Shot Noise
4 Shot noise measurements in the MHz regime . . . 68
4.1 Introduction 70
4.2 Principles of the method 73
4.3 Description of the instrument 75
4.3.1 Mechanical design . . . 75 4.3.2 Analog electronics . . . 77 4.3.3 Digital electronics and data manipulation. . . 80
4.4 Testing, calibration, and accuracy 84
4.5 Measurements on Au and Pt atomic contacts 85
4.6 Conclusions 89
5 Anomalous non-linear shot noise at high voltage bias . . . 90
5.1 Introduction 92
5.2 Measurement setup 93
5.3 Shot-noise measurements 93
5.4 Quantum interference model 96
5.4.1 Extraction of the voltage and energy dependent transmission 101 5.4.2 Analysis of the experimental data . . . 101 5.5 More general energy and voltage dependent transmission functions 103
5.6 Discussion 105
5.7 Conclusion and outlook 106
vi
CONTENTS
6 Two-level fluctuations in molecular junctions . . . 108
6.1 Introduction 110
6.2 Literature review 110
6.3 Experimental setup 114
6.4 Measurements on a D2 molecule 114
6.4.1 Step down in junction conductance . . . 115 6.4.2 Inelastic electron noise spectroscopy (IENS) . . . 117 6.5 Inelastic tunneling versus two-level fluctuations? 118 6.5.1 Step-up in junction conductance close to 1 G0 . . . 119
6.6 Conclusion 121
III Part Three: Graphene Architecture
7 Graphene based circuit . . . 124
7.1 Introduction 126
7.2 Graphene vs metallic electrodes 127
7.3 Electromigration, electroburning vs direct cutting methods 128 7.3.1 Estimation of nanogap size . . . 131 7.3.2 Direct cutting methods . . . 131
7.4 Our approach 132
7.4.1 Helium-ion milling . . . 132 7.4.2 Scanning probe microscopy based cutting . . . 135
7.5 Conclusion 140
Appendix A. Atomic manipulation . . . 143
A.1 Force derivation 143
A.2 Lifting of gold atomic chain 146
A.3 Point-contact push manipulation technique 147
Appendix B. Molecular manipulation . . . 149
B.1 GPU programming 149
B.1.1 Programming in the CUDA framework . . . 150
B.2 Intramolecular forces 154
B.3 Gold-molecule force calculations 155
B.3.1 Morse potential: Au-N bond . . . 155 B.3.2 Lennard-Jones (LJ) potential . . . 156
Appendix C. Shot noise . . . 159
C.1 Excess Noise derivation 159
C.2 Two channel fit 160
vii
CONTENTS
Appendix D. Robust procedure for creating and characterizing the atomic
structure of scanning tunneling microscope tips . . . 163
Appendix E. Inhomogeneous broadening of the conductance histograms for molecular junctions . . . 169
Summary . . . 173
Samenvatting . . . 177
Acknowledgement . . . 181
Curriculum vitae . . . 183
Publications . . . 185
Index . . . 187
viii
An expert is a person who has made all the mistakes that can be made in a very narrow field.
-Niels Bohr
