University of Groningen

Tailoring molecular nano-architectures on metallic surfacesSolianyk, Leonid

IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.

Document VersionPublisher's PDF, also known as Version of record

Publication date:2019

Link to publication in University of Groningen/UMCG research database

Citation for published version (APA):Solianyk, L. (2019). Tailoring molecular nano-architectures on metallic surfaces. [Groningen]: University ofGroningen.

CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).

Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.

Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.

Download date: 24-06-2020

Tailoring molecular nano-architectureson metallic surfaces

Leonid Solianyk

Tailoring molecular nano-architectures on metallic surfaces

Leonid Solianyk

PhD Thesis

University of Groningen

The work presented in this thesis was performed in the research group Surfaces andThin Films of the Zernike Institute for Advanced Materials at the University ofGroningen and financially supported by the European Research Concil (ERC).

Front cover, designed by Leonid Solianyk, shows a scanning tunnelling microscopyimage with the superimposed tentative structural model of a molecular nano-architecture created on Au(111).

Zernike Institute for Advanced Materials PhD-thesis series 2019-01ISSN: 1570-1530ISBN: 978-94-034-1201-6 (printed version)ISBN: 978-94-034-1200-9 (electronic version)Printed by: Gildeprint - Enschede

Tailoring molecular nano-architectures on metallic surfaces

PhD thesis

to obtain the degree of PhD at the University of Groningen on the authority of the

Rector Magnificus prof. E. Sterken and in accordance with

the decision by the College of Deans.

This thesis will be defended in public on

Monday 14 January 2019 at 9.00 hours

by

Leonid Solianyk

born on 29 April 1989 in Skvyra, Ukraine

Supervisors Prof. M.A. Stöhr Prof. P. Rudolf

Assessment Committee Prof. R.A. Hoekstra Prof. A.A. Khajetoorians Prof. R. Möller

To my beloved parentsand brother

i

Contents

Introduction.............................................................................................................. 1

References.................................................................................................................. 4

Chapter 1 Molecular self-assembly at the solid-vacuum interface: An overview.........................................................................................................................5

1.1 Introduction.....................................................................................................6

1.2 Assemblies based on hydrogen bonding.....................................................11

1.3 Assemblies based on metal-coordination................................................... 14

References................................................................................................................ 21

Chapter 2 Experimental techniques and setup................................................... 25

2.1 Scanning tunnelling microscopy and spectroscopy...................................26

2.2 Low-energy electron diffraction.................................................................. 30

2.3 X-ray photoelectron spectroscopy...............................................................32

2.4 X-ray standing wave technique....................................................................34

2.5 Near-edge X-ray absorption fine structure measurements.......................37

2.6 Experimental setup.......................................................................................41

References................................................................................................................ 44

Chapter 3 Pyridyl-functionalized molecule 1 on Au(111): Insight into Au-coordination.................................................................................................47

3.1 Introduction...................................................................................................48

3.2 STM characterization of the molecular networks...................................... 49

3.3 XPS study of the chemical environment before and after Au-coordination........................................................................................................................54

3.4 NEXAFS study of the molecular conformation before and after Au-coordination..................................................................................................63

3.5 Conclusions....................................................................................................68

3.6 Experimental details.....................................................................................68

References................................................................................................................ 70

Contents

ii

Chapter 4 Pyridyl-functionalized molecule 2 on Au(111): Insight into Au-coordination.................................................................................................75

4.1 Introduction...................................................................................................76

4.2 STM characterization of the molecular networks...................................... 77

4.3 STS study: Electron confinement observation inside the molecularnetwork pores...............................................................................................82

4.4 Conclusions....................................................................................................86

4.4 Experimental details.....................................................................................86

References................................................................................................................ 87

Chapter 5 Terphenyl-dicarbonitrile molecule and Co adatoms on Au(111): Acombined STM/STS and ARPES study.......................................................89

5.1 Introduction...................................................................................................90

5.2 STM characterization of the Co-coordinated porous network..................91

5.3 STS characterization of the surface electrons confined by the porousnetwork......................................................................................................... 93

5.4 ARPES results: Observation of a new electronic band structure.............. 96

5.5 Conclusions....................................................................................................98

5.6 Experimental details.....................................................................................98

References................................................................................................................ 99

Chapter 6 Metal-free pyridyl-functionalized porphyrins on Ag(111): Acombined XPS and NIXSW study..............................................................103

6.1 Introduction................................................................................................ 104

6.2 STM and LEED insight into the molecular arrangement......................... 104

6.3 XPS results: Differentiation of the chemically different atomic specieswithin the molecules..................................................................................106

6.4 NIXSW results: Determination of the vertical adsorption heights for theatomic species............................................................................................ 109

6.5 Conclusions..................................................................................................114

6.6 Experimental details...................................................................................114

References..............................................................................................................115

Summary...............................................................................................................119

Contents

iii

Appendix A............................................................................................................123

Appendix B............................................................................................................133

Appendix C............................................................................................................ 137

Samenvatting....................................................................................................... 139

Curriculum Vitae.................................................................................................. 143

Acknowledgments................................................................................................ 145

1

Introduction

In 1959, Richard P. Feynman in his famous talk “There is Plenty of Room at theBottom” [1] predicted fabrication of ultimately small systems with dimensions on theorder of tens of nanometres. He anticipated that these small systems mightrevolutionize science and technology affecting our everyday lives. This talk isconsidered as the commencement of nanotechnology, which aims to fabricate systemswith extraordinary functional properties at the ultimate length scale of atoms andmolecules. In the following years, the top-down and bottom-up approaches ofnanotechnology were developed [2]. The top-down approach starts from larger piecesof material and employs cutting or etching techniques to create smaller structures,while the bottom-up approach, in contrast, employs small building blocks such asmolecules or even atoms for assembling nanoscale structures. One of the applicationswhere both approaches can be utilized is electronics. In particular, the top-downapproach has been successfully used for production of semiconductor electronicdevices. In order to improve the performance of semiconductor devices, thecomprising electronic components undergo constant miniaturization involving ahigher level of structural complexity. Nowadays, the production of transistors, thefundamental building blocks of modern semiconductor devices, with characteristicfeature sizes in the order of 10 nm became common [3]. However, it is clear that thereis a limit for the scaling down process. By further reducing the size of transistors, thesemiconductor technology will soon face fundamental limits which will adverselyaffect the performance of the fabricated devices [4,5]. One of the major fundamentallimits is related to insufficient electrical insulation. For instance, shrinking thetransistor gate insulation made of silicon oxide to five atomic layers will induceunwanted leakage currents driven by tunnelling effects [6,7]. In addition, theminiaturization of semiconductor devices will increase the number of defectivetransistors due to the implementation of the more complex fabrication technology.This number might play a critical role for the overall device performance. Therefore, itis important to explore new approaches for the fabrication of (nano)electronic devices.

A promising alternative approach is to synthesize supramolecular architectureswith desired functionality. This bottom-up approach is based on concepts ofsupramolecular chemistry [8] which aims to understand the structure, functions andproperties of supermolecules. The central concept of supramolecular chemistry is

Introduction

2

molecular self-assembly. In general, molecular self-assembly is defined as thespontaneous association of well-defined molecular building blocks into orderedstructures stabilized by non-covalent bonds. This concept is ubiquitous in biologicalsystems where vital processes such as enzyme action, molecular transport, processingof genetic information and protein assembly are fulfilled by complex and exquisitesupermolecules. By carefully designing molecular building blocks a diverse class ofcomplex organic supermolecules exhibiting versatile functional properties can beachieved. In recent years, research has been rapidly growing to produce moleculararchitectures with a wide range of potential applications in organic and molecularelectronics such as molecular sensors [9], nanoelectronics [10], optoelectronics[11,12], organic solar cells [13,14] and heterogeneous catalysis [15,16]. The conceptof molecular self-assembly was also applied to construct low-dimensional moleculararchitectures upon adsorption of organic molecules on solid surfaces [17,18]. Inparticular, molecular architectures assembled on well-defined metallic surfacesprovide versatile examples of how specific structural features such as shape,composition and adsorption geometry control extraordinary functional properties ofmolecular nano-architectures [19].

Motivated by the prospects of molecular self-assembled structures in organicand molecular electronics, this thesis addresses two main topics. The first topicfocuses on controlled fabrication of two-dimensional supramolecular structures onmetallic surfaces. Special attention is paid to the topography of moleculararrangements and underlying interactions, including intermolecular and molecule-substrate interactions. The second topic is centred on understanding the localadsorption geometry, chemical and electronic environment of the created molecularoverlayers. The present thesis is organized as follows:

Chapter 1 briefly reviews the up-to-date fundamental aspects of molecular self-assembly at the solid-vacuum interface. The chapter focuses on the intermolecularand molecule-substrate interactions, which govern molecular self-assembly on solidsurfaces. Several examples of molecular self-assembled structures stabilized bydifferent types of intermolecular interactions are given and the particularities ofrelated self-assembly processes are emphasized.

Chapter 2 presents an overview of the experimental techniques andinstrumentation used in the studies of this thesis. Working principles of differentsurface-sensitive techniques such as scanning tunnelling microscopy (STM) andspectroscopy (STS), low-energy electron diffraction (LEED) and X-ray photoelectronspectroscopy (XPS) as well as X-ray standing wave (XSW) and near-edge X-rayabsorption fine structure (NEXAFS) measurements are described.

Chapter 3 reports on the self-assembly of pyridyl-functionalized molecule 1 onthe Au(111) surface. By varying the substrate temperature, molecular structures

Introduction

3

stabilized by different intermolecular interactions were achieved. Close attention isgiven to the structures stabilized by coordination of the molecules to the Au atomsoriginated from the underlying surface. We investigate what predetermines theformation of Au-coordinated molecular structures with a particular number ofcoordinated ligands as well as what makes some of these structures favourable on Ausubstrates. In addition, by means of XPS and NEXAFS we characterize the chemicalenvironment and conformation of molecule 1 in the observed structures.

Chapter 4 focuses on the self-assembly of pyridyl-functionalized molecule 2 onthe Au(111) surface. We demonstrate that the formation of created Au-coordinatedmolecular networks can be steered by the substrate temperature. By comparing theobserved self-assembly with the one of the similar molecule 1, we investigate theinfluence of the structural differences between molecules 1 and 2 on their self-assembly behaviour as well as what leads to the different thermal stability of theobserved molecular networks. In addition, we find that one of the observed molecularnetworks formed by molecule 2 can confine the Au surface state electrons inside itspores, which makes this network a promising candidate for tuning the electronicproperties of metals by molecular patterning.

Chapter 5 shows how the electronic properties of metallic surfaces can be tunedby molecular pattering in a controllable manner. We created a long-range orderedporous metal-coordination network by depositing linear cyano-functionalizedmolecule and Co atoms on Au(111). This porous network confines the Au surface stateelectrons inside its cavities. Observed electron confinement leads to the formation of anew electronic band structure with band gaps at the boundaries of the networkBrillouin zone, which is of particular interest for building organic based electronicdevises.

Chapter 6 extends the knowledge about the porphyrin/metal interface. It givesinsight into the chemical environment and conformation of pyridyl-functionalizedporphyrin molecule adsorbed on Ag(111). We characterized the binding energies andvertical adsorption heights of the chemically different atomic species within themolecules by means of XPS and XSW. The obtained results shed light onto themolecule-substrate interactions and pave the path towards employing porphyrinmolecules with magnetic metal atoms as single-molecule magnets on non-magneticmetallic surfaces.

Introduction

4

References

[1] Feynman R. P. Eng. Sci. 23, 22–36 (1960).[2] Gates B. D., Xu Q., Stewart M., Ryan D., Willson C. G. and Whitesides G. M. Chem. Rev. 105,

1171–1196 (2005).[3] International Roadmap for Devices and Systems (IRDS) 2017 Edition, available on

https://irds.ieee.org/.[4] Ito T. and Okazaki S. Nature 406, 1027-1031 (2000).[5] Bohr, M. T. IEEE Trans. Nanotechnol. 1, 56–62 (2002).[6] Schulz M. Nature 399, 729-730 (1999).[7] Muller D., Sorsch T., Moccio S., Baumann F. H., Evans-Lutterodt K. and Timp G. Nature 399,

758-761 (1999).[8] Lehn J. M., Supramolecular Chemistry: Concepts and Perspectives, VCH, Weinheim (1995).[9] Anslyn E. V. J. Org. Chem. 72, 687–699 (2007).[10] Joachim C., Gimzewski J. and Aviram A. Nature 408, 541–548 (2000).[11] Forrest S. R. Chem. Rev. 97, 1793–1896 (1997).[12] Zhao Y. S., Fu H., Peng A., Ma Y., Xiao D., Yao J., Adv. Mater. 20, 2859 (2008).[13] Imahori H., Kimurac M., Hosomizua K. and Fukuzumi S., Journal. of Photochemistry and

Photobiology A: Chemistry 166, 57–62 (2004).[14] Li L.-L. and Diau E. W.-G. Chem. Soc. Rev. 42, 291–304 (2013).[15] Coperet C., Chabanas M., Petroff Saint-Arroman R. and Basset J.-M. Angew. Chem. Int. Ed. 42,

156–181 (2003).[16] Avenier P., Taoufik M., Lesage A., Solans-Monfort X., Baudouin A., de Mallmann A., Veyre L.,

Basset J.-M., Eisenstein O., Emsley L. and Quadrelli E. A. Science 317, 1056–1060 (2007).[17] Otero R., Gallego J. M., de Parga A. L. V., Martín N. and Miranda R. Adv. Mater. 23,

5148−5176 (2011).[18] Elemans J. A. A. W., Lei S. And De Feyter S. Angew. Chem. Int. Ed. 48, 7298-7332 (2009).[19] Barth J. V. Annu. Rev. Phys. Chem. 58, 375–407 (2007).