On-surface formation of polymers and molecular networks

Browning, Abigail S. (2019) On-surface formation of polymers and molecular networks. PhD thesis, University of Nottingham.

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Abstract

Self-assembly of ordered molecular structures on surfaces is of great interest in the formation of devices with novel properties. By utilising molecules that form ordered structures, structures can form spontaneously without the need for lithographic processes. The de-halogenation and polymerisation of 1,3,5-tris-(4-iodophenyl)benzene on the hBN surface was investigated with AFM, XPS and SIMS. The molecules were deposited both from solution and in vacuum in minor variations of the previously reported sine-wave structure. Above 100°C, polymerisation was observed with AFM and confirmed with SIMS, which revealed that, after polymerisation, additional iodine was still present suggesting that dehalogenation had not fully taken place prior to polymerisation occurring as suggested by the XPS results.

Using a vacuum deposition method, the structures formed by melamine on the hBN surface were investigated with AFM. Thick film triangular islands suggested an alignment of the molecular structure with the hBN substrate. Two main structures were seen: a rhombic lattice 0.87 ± 0.01 nm by 0.89 ± 0.01 nm and a square lattice 2.22 ± 0.03 nm by 2.10 ± 0.10 nm. An additional structure was seen on the top of the thick islands of 2.02 ± 0.06 nm by 0.77 ± 0.03 nm which was deemed to be a variant of the rhombic structure with out-of-plane rows due to the transition into the bulk structure. The rhombic structure was also deemed to be the structure forming an observed moiré pattern with a period of 3.19 ± 0.03 nm.

The polymerisation of porphyrin monomers with varying numbers of reactive ethynyl groups on Ag(111) was investigated in vacuum using a novel indirect deposition method and STM. The 2R porphyrin was found to form chains when annealed to 120°C for 15 min with an intra-chain porphyrin separation of 1.33 ± 0.05 nm and an inter-chain distance of 1.90 ± 0.10 nm. The 4R porphyrin was also observed to form a lattice of 1.53 ± 0.04 nm by 1.69 ± 0.02 nm which was rationalised to be partially reacted into chains containing Ag atoms in one direction after heating to 120°C for a 15 min. The 3R porphyrin was observed to form short chains without heating when imaged with a low temperature STM. The 4R porphyrin was also deposited onto HOPG using a solution deposition method and formed lines separated by 1.70 ± 0.20 nm.

Finally, mechanical transfer of hBN supported C60 islands was carried out. The C60 islands were found to be undamaged by soft deposit mechanical transfer process from a PPC/PDMS stamp. The transfer process using PPC/PDMS stamps was also used to form hBN/ C60 /hBN heterostructures and to transfer these to silicon nitride TEM grids for imaging although this step involved delaminating the PPC material at high temperature and subsequent cleaning.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Beton, Peter H.
Keywords: hBN, AFM, nanoscience, SPM, polymers
Subjects: Q Science > QC Physics > QC170 Atomic physics. Constitution and properties of matter
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 57293
Depositing User: Browning, Abigail
Date Deposited: 25 Nov 2021 09:08
Last Modified: 25 Nov 2021 13:54
URI: http://eprints.nottingham.ac.uk/id/eprint/57293

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