University of Groningen Tailoring molecular nano-architectures on metallic surfaces Solianyk, Leonid

University of Groningen

Tailoring molecular nano-architectures on metallic surfaces

Solianyk, Leonid

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Tailoring molecular nano-architectures

on metallic surfaces

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 and Thin Films of the Zernike Institute for Advanced Materials at the University of Groningen and financially supported by the European Research Concil (ERC).

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

Zernike Institute for Advanced Materials PhD-thesis series 2019-01 ISSN: 1570-1530

ISBN: 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

Supervisors

Assessment Committee

Prof. A.A. Khajetoorians Prof. R. Möller

To my beloved parents

and 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

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 molecular network pores...82

4.4 Conclusions...86

4.4 Experimental details...86

References... 87

Chapter 5 Terphenyl-dicarbonitrile molecule and Co adatoms on Au(111): A

combined 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 porous network... 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): A

combined 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 species within the molecules...106

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

6.5 Conclusions...114

6.6 Experimental details...114

References...115

Contents iii

Appendix A

...123

Appendix B

...133

Appendix C

... 137

Samenvatting

... 139

Curriculum Vitae

... 143

Acknowledgments

... 145

1

Introduction

Bottom” [1] predicted fabrication of ultimately small systems with dimensions on the

order of tens of nanometres. He anticipated that these small systems might revolutionize science and technology affecting our everyday lives. This talk is considered as the commencement of nanotechnology, which aims to fabricate systems with extraordinary functional properties at the ultimate length scale of atoms and molecules. In the following years, the top-down and bottom-up approaches of nanotechnology were developed [2]. The top-down approach starts from larger pieces of material and employs cutting or etching techniques to create smaller structures, while the bottom-up approach, in contrast, employs small building blocks such as molecules or even atoms for assembling nanoscale structures. One of the applications where both approaches can be utilized is electronics. In particular, the top-down approach has been successfully used for production of semiconductor electronic devices. In order to improve the performance of semiconductor devices, the comprising electronic components undergo constant miniaturization involving a higher level of structural complexity. Nowadays, the production of transistors, the fundamental building blocks of modern semiconductor devices, with characteristic feature sizes in the order of 10 nm became common [3]. However, it is clear that there is a limit for the scaling down process. By further reducing the size of transistors, the semiconductor technology will soon face fundamental limits which will adversely affect the performance of the fabricated devices [4,5]. One of the major fundamental limits is related to insufficient electrical insulation. For instance, shrinking the transistor gate insulation made of silicon oxide to five atomic layers will induce unwanted leakage currents driven by tunnelling effects [6,7]. In addition, the miniaturization of semiconductor devices will increase the number of defective transistors due to the implementation of the more complex fabrication technology. This number might play a critical role for the overall device performance. Therefore, it is important to explore new approaches for the fabrication of (nano)electronic devices. A promising alternative approach is to synthesize supramolecular architectures with desired functionality. This bottom-up approach is based on concepts of supramolecular chemistry [8] which aims to understand the structure, functions and properties of supermolecules. The central concept of supramolecular chemistry is

Introduction

2

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

Motivated by the prospects of molecular self-assembled structures in organic and molecular electronics, this thesis addresses two main topics. The first topic focuses on controlled fabrication of two-dimensional supramolecular structures on metallic surfaces. Special attention is paid to the topography of molecular arrangements and underlying interactions, including intermolecular and molecule-substrate interactions. The second topic is centred on understanding the local adsorption geometry, chemical and electronic environment of the created molecular overlayers. 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 intermolecular and molecule-substrate interactions, which govern molecular self-assembly on solid surfaces. Several examples of molecular self-assembled structures stabilized by different types of intermolecular interactions are given and the particularities of related self-assembly processes are emphasized.

Chapter 2 presents an overview of the experimental techniques and

instrumentation used in the studies of this thesis. Working principles of different surface-sensitive techniques such as scanning tunnelling microscopy (STM) and spectroscopy (STS), low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) as well as X-ray standing wave (XSW) and near-edge X-ray absorption fine structure (NEXAFS) measurements are described.

Chapter 3 reports on the self-assembly of pyridyl-functionalized molecule 1 on

Introduction

3 stabilized by different intermolecular interactions were achieved. Close attention is given to the structures stabilized by coordination of the molecules to the Au atoms originated from the underlying surface. We investigate what predetermines the formation of Au-coordinated molecular structures with a particular number of coordinated ligands as well as what makes some of these structures favourable on Au substrates. In addition, by means of XPS and NEXAFS we characterize the chemical environment and conformation of molecule 1 in the observed structures.

Chapter 4 focuses on the self-assembly of pyridyl-functionalized molecule 2 on

the Au(111) surface. We demonstrate that the formation of created Au-coordinated molecular networks can be steered by the substrate temperature. By comparing the observed self-assembly with the one of the similar molecule 1, we investigate the influence 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 the observed molecular networks. In addition, we find that one of the observed molecular networks formed by molecule 2 can confine the Au surface state electrons inside its pores, which makes this network a promising candidate for tuning the electronic properties of metals by molecular patterning.

Chapter 5 shows how the electronic properties of metallic surfaces can be tuned

by molecular pattering in a controllable manner. We created a long-range ordered porous metal-coordination network by depositing linear cyano-functionalized molecule and Co atoms on Au(111). This porous network confines the Au surface state electrons inside its cavities. Observed electron confinement leads to the formation of a new electronic band structure with band gaps at the boundaries of the network Brillouin zone, which is of particular interest for building organic based electronic devises.

Chapter 6 extends the knowledge about the porphyrin/metal interface. It gives

insight into the chemical environment and conformation of pyridyl-functionalized porphyrin molecule adsorbed on Ag(111). We characterized the binding energies and vertical adsorption heights of the chemically different atomic species within the molecules by means of XPS and XSW. The obtained results shed light onto the molecule-substrate interactions and pave the path towards employing porphyrin molecules with magnetic metal atoms as single-molecule magnets on non-magnetic metallic 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).