Cover Page The handle http://hdl.handle.net/1887/20925 holds various files of this Leiden University dissertation. Author: Tabak, F.C. Title: Towards high-speed scanning tunneling microscopy Issue Date: 2013-06-05
Towards high-speed scanning tunneling microscopy
Towards high-speed scanning tunneling microscopy 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 woensdag 5 juni klokke 13:45 uur door Femke Chantal Tabak geboren te Hilversum in 1984
Promotiecommissie Promotor: Co-promotor: Overige leden: Prof. dr. J. W. M. Frenken Dr. ir. W.M. van Spengen (Technische Universiteit Delft) Prof. dr. E. R. Eliel Prof. dr. U. Staufer (Technische Universiteit Delft) Prof. dr. P. Rudolf (Rijksuniversiteit Groningen) Prof. dr. ir. T. H. Oosterkamp Prof. dr. J. Aarts Dr. F. Galli Prof. dr. ing. A. J. H. M. Rijnders (Universiteit Twente) Casimir PhD series, Delft-Leiden 2013-19 ISBN 978-90-8593-160-7 An electronic version of this thesis can be found at https://openaccess.leidenuniv.nl and at http://www.interfacephysics.nl. The work described in this thesis was performed at the Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden University, The Netherlands and the Department of Precision - and Microsystems Engineering, Delft University of Technology, The Netherlands. It was financially supported by a Netherlands SmartMix grant and the nimic partner organisations.
Contents 1 STM and the need for faster scanners 1 1.1 STM principle............................ 1 1.2 Need for Speed: the importance of fast scanners......... 3 1.3 Current state-of-the-art fast scanners............... 5 1.4 Summary.............................. 9 1.5 Target................................ 10 2 MEMS-based STM scanners 11 2.1 MEMS introduction........................ 11 2.1.1 Working principle..................... 11 2.1.2 Failure modes of MEMS devices............. 13 2.1.3 Fabrication......................... 14 2.2 Introduction to MEMS STM scanners.............. 16 2.3 Advantages of MEMS in STM systems.............. 20 2.3.1 Resonance frequencies................... 20 2.3.2 MEMS-piezo hybrid scanning system........... 22 2.4 State-of-the-art high-speed MEMS SPM............. 27 3 Implementation of MEMS STM scanners 31 3.1 Design criteria of MEMS scanners................ 31 3.2 Finite-element based MEMS scanner design........... 33 3.3 MEMS actuation tested by AFM and white-light interferometry 33 3.4 Tip growth on MEMS....................... 41 3.4.1 Tip requirements...................... 41 3.4.2 Deposition techniques................... 42 3.4.3 Platinum STM tips by EBID............... 43 3.4.4 Conductance measurements of EBID tips........ 47 3.4.5 Towards atomic resolution................. 51 3.5 High-speed MEMS scanner actuation and capacitive coupling. 52 3.6 Mechanical integration of a MEMS scanner........... 54 3.7 Summary.............................. 55 v
Contents 4 Design of a high-speed STM with exchangeable scanning element 59 4.1 Design considerations....................... 59 4.2 Scanner design........................... 60 4.2.1 The scanner body and approach mechanism....... 61 4.2.2 Sample holder....................... 63 4.2.3 High-speed scan configurations.............. 66 4.3 UHV system and eddy current damping............. 67 4.4 Summary.............................. 69 5 MEMS STM experiments 73 5.1 First tunneling experiments.................... 73 5.2 MEMS-based STM on Au(111).................. 75 5.3 Conclusions on MEMS STM scanners.............. 78 5.4 Recommendations......................... 80 5.4.1 Tip deposition....................... 80 5.4.2 Incorporation in an STM................. 82 6 Compensation of force and torque in piezo-based STM scanners 83 6.1 Z-direction: force compensation.................. 83 6.1.1 Electronic testing of the z-direction piezo elements... 85 6.1.2 Mechanical characterisiation................ 89 6.2 Out-of-plane force balancing: conclusion............. 91 6.3 In-plane actuation: force or torque?............... 92 6.3.1 Electronic characterisation................ 93 6.3.2 Mechanical characterisation................ 94 6.4 Force and torque compensation: conclusion........... 101 7 Image distortions in high-speed imaging 105 7.1 Introduction............................. 105 7.2 Scanner characterisation with STM data............. 105 7.2.1 Fourier analysis....................... 106 7.3 The role of the actuation signal shape.............. 111 7.3.1 Appearance of higher harmonics in the linescan signal. 112 7.3.2 Image linearization after sinusoidal scanning....... 113 7.3.3 Frequency modulation during sinusoidal scanning.... 114 7.3.4 Influence of signal shape on image quality........ 115 7.4 Pro s and Con s of a compensating piezo element........ 118 7.4.1 Response to actuation of the compensating x piezo element............................. 118 vi
Contents 7.4.2 Response to actuation of the compensating y piezo element............................. 122 7.4.3 Compensation: conclusion................. 132 7.5 High-speed scanning........................ 136 7.6 Conclusions............................. 139 A Two- and three-dimensional MEMS scanners 143 Bibliography 145 Summary 157 Samenvatting 161 Curriculum Vitae 165 List of Publications 167 vii