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Electronic Structure and Film Morphology Studies of PTCDI on Metal/Semiconductor Surfaces
Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).ORCID-id: 0000-0003-1583-1731
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Organic semiconductors have received increasing attention over the last decades as potential alternatives for inorganic semiconductors. The properties of these films are highly dependent on their structural order. Of special interest is the interface between the film and its substrate, since the structure of the interface and the first few layers decide the growth of the rest of the film. The interface structure is determined by the substrate/molecule interactions, the intermolecular interactions and the growth conditions.

In this thesis, thin films of the organic semiconductor PTCDI have been studied using complementary microscopy and spectroscopy techniques on two metal-induced surface reconstructions, Ag/Si(111)-√3×√3 and Sn/Si(111)-2√3×2√3. These surfaces were chosen because they have different reactivities and surface periodicities. On the weakly interacting Ag-terminated surface, the film growth is mainly governed by the intermolecular interactions. This leads to well-ordered films that grow layer-by-layer. The interaction with the substrate is through electron charge transfer to the molecules from the substrate. This results in two different types of molecules with different electronic structure, which are identified using both STM images and PES spectra. On the more strongly interacting Sn-terminated surface the molecules adsorb in specific adsorption geometries and form 1D rows. At around 0.5 ML coverage the rows also interact with each other and form a 4√3×2√3 reconstruction and beyond one ML coverage the growth is characterized as island growth. The interaction with the substrate is mainly due to heavy electron charge transfer from the Sn atoms in the substrate to the C atoms in the imide group, but also the N atoms and the perylene core in PTCDI are involved. In these systems, the interactions with the surfaces result in new states inside the HOMO-LUMO gap, and the intermolecular interactions are dominated by O···H and O···H-N hydrogen bondings.

Abstract [en]

In our modern world we are surrounded by electronic devices that have become integral to how we live our lives. Central to most electrical devices are semiconductors such as silicon. The last decades a new type of materials, organic semiconductors, have received increasing attention. There exists a wide variety of these materials with a wide range of properties, so an organic molecule can be selected or even tailored for specific applications. Their tunable electronic properties have made it possible to use them in devices such as solar cells and light emitting diodes. Organic semiconductors have additional benefits, such as low weight and mechanical flexibility, which opens the horizon for new potential novel applications. A common device architecture involves layers of organic semiconductors sandwiched between metallic or semiconducting electrodes.

The thesis presents the use of complementary microscopy and spectroscopy methods to study thin films of the organic semiconductor PTCDI on two different semiconductor surfaces with different interaction strengths. The morphology of the film and its interface with the substrates are investigated. Additionally, the molecular interaction with these substrates are studied in detail.

Ort, förlag, år, upplaga, sidor
Karlstad: Karlstads universitet, 2018. , s. 55
Serie
Karlstad University Studies, ISSN 1403-8099 ; 2018:57
Nyckelord [en]
PTCDI, STM, LEED, XPS, UPS, NEXAFS, Organic Films, Semicondcutor Surfaces, Electronic Structure, Molecular Interactions, Film Morphology
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
URN: urn:nbn:se:kau:diva-70262ISBN: 978-91-7063-898-5 (tryckt)ISBN: 978-91-7063-993-7 (digital)OAI: oai:DiVA.org:kau-70262DiVA, id: diva2:1265196
Disputation
2019-01-25, Eva Eriksson-salen, 21A 342, 651 88 Karlstad, Karlstad, 13:15 (Engelska)
Opponent
Handledare
Anmärkning

Paper 4 published in the thesis as manuscript. Now published.

Tillgänglig från: 2018-12-20 Skapad: 2018-11-22 Senast uppdaterad: 2019-02-14Bibliografiskt granskad
Delarbeten
1. Scanning tunneling microscopy study of thin PTCDI films on Ag/Si(111)-root 3 x root 3
Öppna denna publikation i ny flik eller fönster >>Scanning tunneling microscopy study of thin PTCDI films on Ag/Si(111)-root 3 x root 3
2017 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 11, artikel-id 114702Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-root 3 x root 3 surface and studied by scanning tunneling microscopy/spectroscopy and low energy electron diffraction (LEED). The growth mode was characterized as layer-by-layer growth with a single molecular unit cell in a short range order. The growth of the first two monolayers involves a molecule/substrate superstructure and a molecule/molecule superstructure. At higher coverages, the molecules in each layer were found to align so that unit cells are on top of each other. The experimentally obtained LEED pattern is described as a combination of patterns from the molecular unit cell and the molecule/substrate superstructure. The electronic structure was found to be strongly dependent on the film thickness for the first few layers: Several extra states are found at low coverages compared to higher coverages resulting in a very small pseudo gap of 0.9 eV for the first layer, which widens up to 4.0 eV for thicker films.

Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2017
Nationell ämneskategori
Fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-65295 (URN)10.1063/1.4978470 (DOI)000397313600027 ()28330354 (PubMedID)
Tillgänglig från: 2017-11-30 Skapad: 2017-11-30 Senast uppdaterad: 2019-07-10Bibliografiskt granskad
2. Photoelectron spectroscopy studies of PTCDI on Ag/Si(111)-root 3 x root 3
Öppna denna publikation i ny flik eller fönster >>Photoelectron spectroscopy studies of PTCDI on Ag/Si(111)-root 3 x root 3
2018 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, nr 4, artikel-id 044702Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-root 3 x root 3 surface and studied using photoelectron spectroscopy and near edge X-ray absorption fine structure (NEXAFS). All core levels related to the imide group of the molecules showed a partial shift to lower binding energies at low coverages. In NEXAFS spectra, the first transitions to the unoccupied states were weaker at low coverages compared to thicker films. Also, extra states in the valence band between the regular highest occupied molecular orbital and the Fermi level were found at low coverages. These changes were explained by two types of molecules. Due to charge transfer from the surface, these two types have different interactions between the imide group and the substrate. As a result, one type has a partially filled lowest unoccupied molecular orbital while the other type does not. Published by AIP Publishing.

Ort, förlag, år, upplaga, sidor
American Institute of Physics (AIP), 2018
Nationell ämneskategori
Fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-69377 (URN)10.1063/1.5038721 (DOI)000440586200047 ()30068162 (PubMedID)
Tillgänglig från: 2018-09-21 Skapad: 2018-09-21 Senast uppdaterad: 2019-08-15Bibliografiskt granskad
3. Delicate Interactions of PTCDI molecules on Ag/Si(111)-√3×√3
Öppna denna publikation i ny flik eller fönster >>Delicate Interactions of PTCDI molecules on Ag/Si(111)-√3×√3
2018 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, nr 16, s. 164707-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

PTCDI molecules were evaporated onto a Ag/Si(111)√3×√3 surface and studied using scanning tun-resolution STM images are used to identify the delicate molecule/molecule and molecule/substrate interactions and the shapes of the molecular orbitals. The results show that the substrate/molecule interaction strongly modifies the electronic configuration of the molecules as their orbital shapes are quite different at 1 and 2 monolayer (ML) coverage. Simple models of molecular HOMO/LUMO levels and intermolecular hydrogen-bondings have been made for 1 and 2 ML PTCDI coverages to explain the STM images. Changes due to the interaction with the substrate are also found in ARUPS as extra states above the regular HOMO level at 1 ML PTCDI coverage. The ARUPS data also show that the electronic structure of the substrate remains unchanged after the deposition of molecules as the dispersion of the substrate related bands is unchanged. The changes in electronic structure ofthe molecules are discussed based on aHOMO/LUMO split.

Ort, förlag, år, upplaga, sidor
New York: American Institute of Physics (AIP), 2018
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-70246 (URN)10.1063/1.5053606 (DOI)000449103200074 ()
Projekt
Organic molecular layers for photovoltaic applications
Forskningsfinansiär
Vetenskapsrådet, 2013-5291
Tillgänglig från: 2018-11-22 Skapad: 2018-11-22 Senast uppdaterad: 2018-12-19Bibliografiskt granskad
4. Scanning tunneling microscopy study of PTCDI on Sn/Si(111)-2√3×2√3
Öppna denna publikation i ny flik eller fönster >>Scanning tunneling microscopy study of PTCDI on Sn/Si(111)-2√3×2√3
2019 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 4Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Perylene tetracarboxylic diimide molecules were evaporated onto a Sn/Si(111)-2 root 3 x 2 root 3 surface and studied using scanning tunneling microscopy (STM) and low energy electron diffraction. At low coverages, single molecules are locked into specific adsorption geometries, which are investigated in detail using high resolution STM. The electronic structure of these individual molecules was studied using bias dependent STM images. The molecules form 1D rows that become more common with increasing coverages. Possible intermolecular O center dot center dot center dot H interactions within the rows have been identified. At around half of a monolayer (ML), the rows of molecules interact with each other and form a commensurate 4 root 3 x 2 root 3 reconstruction. In a complete monolayer, several structures emerge as molecules fill in the space between the 4 root 3 x 2 root 3 stripes. Possible intermolecular interactions within the 1 ML structures have been discussed. At coverages above 1 ML, the growth is characterized by island growth, where the molecules are arranged according to the canted structure within the layers.

Ort, förlag, år, upplaga, sidor
New York: American Institute of Physics (AIP), 2019
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-70247 (URN)10.1063/1.5070120 (DOI)000457414600075 ()
Forskningsfinansiär
Vetenskapsrådet, 2013-5291
Anmärkning

Artikeln tidigare publicerad som manuskript i Emanuelssons (2018) doktorsavhandling Electronic Structure and Film Morphology Studies of PTCDI on Metal/Semiconductor Surfaces

Tillgänglig från: 2018-11-22 Skapad: 2018-11-22 Senast uppdaterad: 2019-07-11Bibliografiskt granskad
5. Photoelectron spectroscopy studies of PTCDI on Sn/Si(111)-2√3×2√3
Öppna denna publikation i ny flik eller fönster >>Photoelectron spectroscopy studies of PTCDI on Sn/Si(111)-2√3×2√3
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-70261 (URN)
Forskningsfinansiär
Vetenskapsrådet, 2013-5291
Tillgänglig från: 2018-11-22 Skapad: 2018-11-22 Senast uppdaterad: 2019-04-25Bibliografiskt granskad

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