b.sc. and m.sc. - · pdf file b.sc. and m.sc. submitted in fulfilment of the requirements for...

MOLECULAR REACTIONS ON SURFACES: TOWARDS THE GROWTH OF SURFACE-

CONFINED POLYMERS

Maryam Abyazisani

B.Sc. and M.Sc.

Submitted in fulfilment of the requirements for the degree of

Doctor of Philosophy

School of Chemistry, Physics and Mechanical Engineering

Science and Engineering Faculty

Queensland University of Technology

2019

To love of my life

Molecular reactions on surfaces: towards the growth of surface-confined polymers i

Abstract

The development of surface-confined nanostructures is a promising approach

towards developing new electronic and optoelectronic devices. Molecular assembly

under ultra-high vacuum (UHV) conditions offers precise control over the reaction

conditions. Despite all the control provided by the UHV, achieving high quality and

well-ordered nanostructures in both one and two dimensions is still a challenging

problem. A detailed understanding of the reaction of a range of molecules on surfaces

will be the key to developing targeted strategies for on-surface synthesis.

In this regard, the Ullmann reaction is very well-studied and constitutes an aryl-

aryl coupling of halogenated moieties. This reaction produces chemisorbed metal

halides as a byproduct and has consequently been a hotly-debated issue owing to the

presumed detrimental effects on the quality of the products. To find a solution for this

challenge, this thesis aims to contribute to the understanding of the absence of metal

halide byproducts in two ways. Firstly, employing the decarboxylative coupling

known as a “clean” reaction which produces volatile byproducts, and secondly in

removing the metal halide byproducts resultant from the Ullman reaction by using

hydrogen etching following the polymerisation step.

To investigate the decarboxylative reaction, the adsorption and reaction of 3,5-

pyridinedicarboxylic acid (PDC) and isophthalic acid (IPA) have been studied using

photoemission spectroscopy (PES) and near edge x-ray absorption fine structure

(NEXAFS) at the Australian Synchrotron facility. PE spectra of PDC reveal the

presence of nitrogen on the central group of the precursor result in different adsorption

configurations of the molecule on the surface: (a) via the nitrogen, and (b) via the

deprotonated carboxyl group. The result from NEXAFS supports that molecules are

adsorbed tilted with respect to the surface. The extracted activation energy for PDC

decarboxylation is (1.93 ± 0.17) eV which is large compared to the activation energy

for decarboxylation of a planar aromatic molecule, suggesting the tilted adsorption

configuration may change the activation energy. These results reveal a competition

between decarboxylation and molecular fragmentation at temperatures near

decarboxylation temperature.

ii Molecular reactions on surfaces: towards the growth of surface-confined polymers

Photoemission spectra of IPA reveal that the molecule partially deprotonated

upon adsorption on Cu(111). In addition, the beam energy dependence and angular

dependence spectroscopy of the IPA illustrates the relative geometry of the carboxyl

group, deprotonated carboxyl group and phenyl ring. The deprotonated carboxyl group

is buried beneath the phenyl ring, suggesting the molecule is anchored to the surface

via the deprotonated carboxyl group, and the NEXAFS data support the PES result.

Furthermore, STM illustrates that decarboxylative coupling of IPA successfully

proceeds on Cu(111). The IPA and PDC studies represent a step forward in

understanding the decarboxylation reaction and highlight the importance of the

chemistry of the building block in the adsorption geometry of the molecule and

therefore in the polymerization reaction.

To study the removal of by-product halogens from the surface, 1,4

dibromobenzene was deposited on Cu(111) and Cu(110). Atomic hydrogen was dosed

to the surface after the polymerization reaction completed. STM and XPS data

confirmed that halogens have been removed from the surface. This characteristic opens

up the possibility of employing the Ullmann reaction while a flux of atomic hydrogen

may offer effective way for removing unwanted halide by-products and a possibility

for improving the network qualities as well as polymer’s coverage on the surface.

Molecular reactions on surfaces: towards the growth of surface-confined polymers iii

Table of Contents

Abstract ..................................................................................................................................... i

Table of Contents .................................................................................................................... iii

List of Publication .....................................................................................................................v

List of Figures ....................................................................................................................... viii

List of Tables ..........................................................................................................................xv

List of Abbreviations ............................................................................................................ xvi

Statement of Original Authorship ........................................................................................ xvii

Acknowledgements ............................................................................................................. xviii

Chapter 1: Introduction ...................................................................................... 1

1.1 Background .....................................................................................................................1

1.2 Context ............................................................................................................................2

1.3 Purposes ..........................................................................................................................3

1.4 Thesis Outline .................................................................................................................4

1.5 References ......................................................................................................................5

Chapter 2: Literature Review ............................................................................. 7

2.1 Historical Background ....................................................................................................7

2.2 Ullmann Reaction ...........................................................................................................9

2.3 Decarboxylation Reaction ............................................................................................23

2.4 Pyridine-Based Polymer ...............................................................................................25

2.5 Summary and Implications ...........................................................................................29

2.6 References ....................................................................................................................32

Chapter 3: Research Design .............................................................................. 39

3.1 Important Parameters In Surface-Confined Reactions .................................................39

3.2 Surface Sensitive Analysis Techniques ........................................................................45

3.3 References ....................................................................................................................52

Chapter 4: Adsorption and Reactivity of Pyridine Dicarboxylic Acid on Cu(111) .......................................................................................................... 55

4.1 Abstract .........................................................................................................................57

4.2 Introduction ..................................................................................................................58

4.3 Experimental Methods ..................................................................................................59

4.4 Results ..........................................................................................................................62

4.5 Discussion .....................................................................................................................73

4.6 Conclusions ..................................................................................................................75

4.7 References ....................................................................................................................77

iv Molecular reactions on surfaces: towards the growth of surface-confined polymers

4.8 Supporting Information ................................................................................................ 82

Chapter 5: Adsorption, deprotonation and decarboxylation of isophthalic

acid on Cu(111) ............