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  • Scanning Tunneling Microscopy

    Studies of Organic Molecules

    on Metal Surfaces

    Michael Schunack Institute of Physics and Astronomy

    Center for Atomic-scale Materials Physics University of Aarhus, Denmark

    PhD thesis January 2002

  • ii

    This thesis is submitted to the Faculty of Science at the University of Aarhus, Denmark, in order to fulfill the requirements for obtaining the PhD degree in physics. The studies have been carried out under the su- pervision of Flemming Besenbacher in the scanning tunneling microscopy laboratory at the Institute of Physics and Astronomy from November 1998 to January 2002.

  • iii

    Contents

    List of Publications vii

    Abbreviations ix

    1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Other studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

    2 Experimental methods 9 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2 Scanning tunneling microscopy . . . . . . . . . . . . . . . . . . . . . 11

    2.2.1 Basic principles . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.2 Aarhus STM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2.3 Theory of STM . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2.4 Imaging of adsorbates . . . . . . . . . . . . . . . . . . . . . . 18 2.2.5 General remarks . . . . . . . . . . . . . . . . . . . . . . . . . 20

    2.3 Low- and variable-temperature STM . . . . . . . . . . . . . . . . . . 21 2.3.1 General set-up . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.3.2 Cryostat sample holder connection . . . . . . . . . . . . . . . 26 2.3.3 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

    2.4 Molecular evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.4.1 General design . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.4.2 Uniformity of the deposited layer . . . . . . . . . . . . . . . 37

    3 Bonding of molecules to surfaces 39 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2 A chemist’s view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.3 A physicist’s view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.4 van-der-Waals bonding . . . . . . . . . . . . . . . . . . . . . . . . . . 46

  • iv CONTENTS

    4 HtBDC on Cu(110) 49 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.2 HtBDC molecule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 4.3 Restructuring of the surface . . . . . . . . . . . . . . . . . . . . . . . 53

    4.3.1 Double row structure . . . . . . . . . . . . . . . . . . . . . . . 53 4.3.2 STM manipulation experiments . . . . . . . . . . . . . . . . 58 4.3.3 Driving force for the restructuring . . . . . . . . . . . . . . . 62

    4.4 Chirality of the restructuring . . . . . . . . . . . . . . . . . . . . . . 66 4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

    5 DC on Cu(110) 73 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 5.2 DC molecule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 5.3 Low coverages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 5.4 High coverages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

    6 Lander molecules on Cu(110) 83 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 6.2 Lander molecule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 6.3 Adsorption geometries . . . . . . . . . . . . . . . . . . . . . . . . . . 86 6.4 Restructuring processes . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

    7 Surface diffusion of large molecules 97 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 7.2 Data acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

    7.2.1 Tip influence . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 7.3 Theoretical background . . . . . . . . . . . . . . . . . . . . . . . . . 105

    7.3.1 General relations . . . . . . . . . . . . . . . . . . . . . . . . . 105 7.3.2 Rate theories and multiple jumps . . . . . . . . . . . . . . . . 107

    7.4 Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 7.4.1 Extraction of the hopping rate . . . . . . . . . . . . . . . . . 111 7.4.2 Kinetic Monte Carlo simulations . . . . . . . . . . . . . . . . 115

    7.5 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 121 7.5.1 Arrhenius parameters . . . . . . . . . . . . . . . . . . . . . . 122 7.5.2 RMS jump lengths . . . . . . . . . . . . . . . . . . . . . . . . 127

    7.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

    8 Summary 135

    A Stereochemical principles 139 A.1 General definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 A.2 Cahn-Ingold-Prelog convention . . . . . . . . . . . . . . . . . . . . . 140 A.3 Fischer convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

  • CONTENTS v

    B Random walk theory 143 B.1 Poisson process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 B.2 Displacement distributions . . . . . . . . . . . . . . . . . . . . . . . 144

    C Nucleation and growth of a new CAMP member 147

    Bibliography 151

    Acknowledgements 169

  • vi CONTENTS

  • vii

    List of Publications

    Publications related to thesis

    [I] A fast-scanning, low- and variable-temperature scanning tunneling micro- scope L. Petersen, M. Schunack, B. Schaefer, T. R. Linderoth, P. B. Rasmussen, P. T. Sprunger, E. Lægsgaard, I. Stensgaard, and F. Besenbacher, Rev. Sci. Instrum. 72, 1438–1444 (2001).

    [II] Anchoring of organic molecules to a metal surface: HtBDC on Cu(110) M. Schunack, L. Petersen, A. Kühnle, E. Lægsgaard, I. Stensgaard, I. Jo- hannsen, and F. Besenbacher, Phys. Rev. Lett. 86, 456–459 (2001).

    [III] A chiral metal surface M. Schunack, E. Lægsgaard, I. Stensgaard, I. Johannsen, and F. Besenbacher, Angew. Chem. 113, 2693–2696 (2001) Angew. Chem. Int. Ed. 40, 2623–2626 (2001).

    [IV] Long jumps in the surface diffusion of large molecules M. Schunack, T. R. Linderoth, F. Rosei, E. Lægsgaard, I. Stensgaard, and F. Besenbacher, submitted to Phys. Rev. Lett. .

    [V] Lander molecules acting as nanomolds on metal surfaces F. Rosei, M. Schunack, P. Jiang, A. Gourdon, E. Lægsgaard, I. Stensgaard, C. Joachim and F. Besenbacher, submitted to Science.

    [VI] Lander molecules on clean and oxygen covered Cu(110): a way of preparing ordered molecular domains Y. Naitoh, F. Rosei, M. Schunack, E. Lægsgaard, I. Stensgaard, and F. Besen- bacher, in preparation.

  • viii LIST OF PUBLICATIONS

    [VII] Bonding and mobility of related aromatic molecules on Cu(110) M. Schunack, T. R. Linderoth, E. Lægsgaard, I. Stensgaard, and F. Besen- bacher, to be published.

    Other publications

    [VIII] Chiral modifier: cinchona alkaloids on Pt(111) M. Schunack, E. Lægsgaard, I. Stensgaard, and F. Besenbacher, to be published.

    [IX] Cysteine on Au(111) M. Schunack, A. Kühnle, T. R. Linderoth, and F. Besenbacher, in preparation.

    [X] Nucleation and growth of a new German CAMP member J. Schunack, M. Schunack, and not F. Besenbacher, Single-paper handout publishing company Schunack LTD 1, 1 (2000).

  • ix

    Abbreviations

    AES Auger electron spectroscopy AFM atomic force microscopy CD compact disk CIP Cahn-Ingold-Prelog DC decacyclene DOS density of states EMT effective medium theory ESQC electron scattering quantum chemistry FCC face centered cubic FIM field ion microscopy GLE generalized Langevin equation GS ground state HOMO highest occupied molecular orbital HtBDC hexa-(tert-butyl)decacyclene IC integrated circuit KMC kinetic Monte Carlo LDOS local density of states LED light emitting diode LEED low energy electron diffraction LITD laser induced thermal desorption LUMO lowest unoccupied molecular orbital MD molecular dynamics ML monolayer MS mass spectrometry NN nearest neighbor NNN next-nearest neighbor OFHC oxygen-free high conductivity OMBD organic molecular beam deposition PC personal computer PID proportional integral differential

  • x ABBREVIATIONS

    PVBA 4-Trans-2-(pyridy-4-yl-vinyl)benzoic acid RMS root mean-squared ROM read only memory RT room temperature SPM scanning probe microscope STM scanning tunneling microscope TMR transfer and mobility of researchers TPD temperature programmed desorption TS transition state TST transition state theory UHV ultrahigh vacuum

  • 1

    CHAPTER 1

    Introduction

    1.1 Motivation

    Nanotechnology is the blanket term used to describe the precision manufacture of materials and structures where the characteristic dimensions are less than about 100 nm. [1]. The long-term goals of nanotechnology are to design materials with specific, advanced properties by controlling processes at the ultimate length scale of atoms and molecules [2]. In order to reach this goal, fundamental problems have to be tackled in areas as diverse as molecular biology, lithography, catalysis, and molecular-scale machines [3], as will be exemplified in the