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Covalent Graphene Functionalization for the Modification of Its Physical Properties
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. (Electron microscopy and Nanoengineering)ORCID iD: 0000-0003-1050-8441
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

Graphene, a two dimensional monolayer carbon sheet with the atoms tightly packed in a hexagonal lattice, has exhibited so many excellent properties, which enable graphene to break several material records with regard to carrier mobility, strength yield and thermal conductivity to name a few. Therefore, graphene has been placed as a potential candidate to allow truly next-generation material. Graphene is a zero band gap material, implying that an energy band gap around the Dirac point is supposed to be open to make graphene applicable as a semiconductor. Covalent bond graphene functionalization becomes an essential enabler to open the energy gap in graphene and extend graphene applications in electronics, while the densely packed hexagonal carbon atoms as well as the strong sp2 hybridization carbon-carbon bonds jointly result in a changeling topic of allowing graphene to be decorated with functional groups.

Here in this thesis, different routes to realize graphene functionalizations are implemented by using physical and chemical ways. The physical functionalization methods are the ion/electron beam induced graphene fluorination as well as local defect insertion and the chemical ways correspond to the photochemistry techniques to approach hydrogenation and hydroxypropylation of graphene. Furthermore, to incorporate graphene into devices, the tuning of mechanical properties of graphene is desired. Towards this aim, the structure modification of graphene is employed to investigate the nanometer size-effect of crystalline size of graphene on the mechanical properties, namely Young’s modulus and surface energy. In the process of the graphene hydrogenation project, we discovered a high yield way to synthesis high quality graphene nanoscroll (GNS). Interestingly, the GNS shows superadhesion property through our atomic force microscopy measurements. This superadhesion is around 6-order stronger than van der Waals interaction and even higher than the hydrogen bonding enhanced and solid/liquid interfaces.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 60
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1472
Keywords [en]
graphene; functionalization; nanomechanical property, graphene nanoscroll
National Category
Materials Engineering Physical Sciences Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-314176ISBN: 978-91-554-9807-8 (print)OAI: oai:DiVA.org:uu-314176DiVA, id: diva2:1069522
Public defence
2017-03-17, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 23:15 (English)
Opponent
Supervisors
Available from: 2017-02-24 Created: 2017-01-30 Last updated: 2017-02-24
List of papers
1. Fabrication of reproducible sub-5 nm nanogaps by a focused ion beam and observation of Fowler-Nordheim tunneling
Open this publication in new window or tab >>Fabrication of reproducible sub-5 nm nanogaps by a focused ion beam and observation of Fowler-Nordheim tunneling
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 10, article id 103108Article in journal (Refereed) Published
Abstract [en]

Creating a stable high resistance sub-5 nm nanogap in between conductive electrodes is one of the major challenges in the device fabrication of nano-objects. Gap-sizes of 20 nm and above can be fabricated reproducibly by the precise focusing of the ion beam and careful milling of the metallic lines. Here, by tuning ion dosages starting from 4.6 x 10(10) ions/cm and above, reproducible nanogaps with sub-5 nm sizes are milled with focused ion beam. The resistance as a function of gap dimension shows an exponential behavior, and Fowler-Nordheim tunneling effect was observed in nanoelectrodes with sub-5 nm nanogaps. The application of Simmon's model to the milled nanogaps and the electrical analysis indicates that the minimum nanogap size approaches to 2.3 nm.

National Category
Physical Sciences Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-264851 (URN)10.1063/1.4930821 (DOI)000361640200043 ()
Available from: 2015-10-19 Created: 2015-10-19 Last updated: 2018-04-12Bibliographically approved
2. Biomineralization on Single Crystalline Rutile: The Modulated Growth of Hydroxyapatite by Fibronectin in a Simulated Body Fluid
Open this publication in new window or tab >>Biomineralization on Single Crystalline Rutile: The Modulated Growth of Hydroxyapatite by Fibronectin in a Simulated Body Fluid
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2016 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, p. 35507-35516Article in journal (Refereed) Published
Abstract [en]

The aim of this study is to probe the complex interaction between surface bioactivity and protein adsorption on single crystalline rutile. Our previous studies have shown that single crystalline rutile possessed in vitro bioactivity and the crystalline faces affected the hydroxyapatite (HA) formation. However, upon implantation, a fast adsorption of proteins, from the biological fluids, is intermediated by a water layer towards the biomaterial interface. Thus the effect of protein on the bioactivity must be addressed. In this study, the HA growth dynamics on (001), (100) and (110) faces was investigated in a simulated body fluid with the presence of fibronectin (FN) by two different processes. The surface adhesion of each face before and after FN adsorption, as revealed by direct numerical values, was determined by atomic force microscopy (AFM) based peak force quantitative nanomechanical mapping (PF-QNM) for the first time. The findings suggest the surface energies of FN pre-adsorbed (001), (100) and (110) faces have been enhanced, leading to the subsequent accelerated HA formation. Furthermore, (001) and (100) faces were found to have larger coverage of HA crystals than (110) face at an early stage. In addition, various characterizations were performed to probe the chemical and crystal structures of as-grown biomimetic HA crystals, and in particular, the Ca/P ratio variations at different soaking time points.

National Category
Engineering and Technology Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-277120 (URN)10.1039/C6RA04303H (DOI)000374349600042 ()
Available from: 2016-02-17 Created: 2016-02-17 Last updated: 2018-02-08Bibliographically approved
3. Site-selective local fluorination of graphene induced by focused ion beam irradiation
Open this publication in new window or tab >>Site-selective local fluorination of graphene induced by focused ion beam irradiation
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 19719Article in journal (Refereed) Published
Abstract [en]

The functionalization of graphene remains an important challenge for numerous applications expected by this fascinating material. To keep advantageous properties of graphene after modification or functionalization of its structure, local approaches are a promising road. A novel technique is reported here that allows precise site-selective fluorination of graphene. The basic idea of this approach consists in the local radicalization of graphene by focused ion beam (FIB) irradiation and simultaneous introduction of XeF2 gas. A systematic series of experiments were carried out to outline the relation between inserted defect creation and the fluorination process. Based on a subsequent X-ray photoelectron spectroscopy (XPS) analysis, a 6-fold increase of the fluorine concentration on graphene under simultaneous irradiation was observed when compared to fluorination under normal conditions. The fluorine atoms are predominately localized at the defects as indicated from scanning tunneling microscopy (STM). The experimental findings are confirmed by density functional theory which predicts a strong increase of the binding energy of fluorine atoms when bound to the defect sites. The developed technique allows for local fluorination of graphene without using resists and has potential to be a general enabler of site-selective functionalization of graphene using a wide range of gases.

Keywords
graphene, site-selective, fluorination, focused ion beam
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-268033 (URN)10.1038/srep19719 (DOI)000368926300001 ()26822900 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation
Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2017-12-01Bibliographically approved
4. Reversible Fluorination of Graphene Induced by Electron Beam Irradiation: Towards the Band Gap Manipulation
Open this publication in new window or tab >>Reversible Fluorination of Graphene Induced by Electron Beam Irradiation: Towards the Band Gap Manipulation
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences Materials Engineering
Identifiers
urn:nbn:se:uu:diva-314170 (URN)
Available from: 2017-01-29 Created: 2017-01-29 Last updated: 2017-01-29
5. Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene
Open this publication in new window or tab >>Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene
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2016 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723Article in journal (Refereed) Published
Abstract [en]

The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S0), becomes exergonic in the first triplet state (T1). This is in line with Baird’s rule, which tells that benzene is antiaromatic and destabilized in its T1 state and also in its first singlet excited state (S1), opposite to S0, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro)silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T1-state benzene is excellent at H-atom abstraction, while COT, aromatic in the T1 and S1 states according to Baird’s rule, is unreactive. Remarkably, also CVD-graphene on SiO2 is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions.

National Category
Chemical Sciences Chemical Engineering
Identifiers
urn:nbn:se:uu:diva-303639 (URN)10.1038/ncomms12962 (DOI)000385553900001 ()27708336 (PubMedID)
Funder
Wenner-Gren FoundationsSwedish Research CouncilKnut and Alice Wallenberg FoundationÅForsk (Ångpanneföreningen's Foundation for Research and Development)Magnus Bergvall Foundation
Available from: 2016-09-21 Created: 2016-09-21 Last updated: 2018-04-23Bibliographically approved
6. White-light photoassisted covalent functionalization of graphene using 2-propanol
Open this publication in new window or tab >>White-light photoassisted covalent functionalization of graphene using 2-propanol
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2017 (English)In: Small Methods, ISSN 2366-9608, Vol. 1, no 11, article id 1700214Article in journal (Refereed) Published
Abstract [en]

Herein, a photochemical method for functionalization of graphene using 2-propanol is reported. The functionalization method which is catalyst-free operates at ambient temperature in neat 2-propanol under an inert atmosphere of argon. The equipment requirement is a white-light source for the irradiation. The same methodology when applied to kish graphite results in a novel material, exhibiting significantly higher wettability than the starting material according to water contact angle measurements. Furthermore, the materials generated from both graphene and kish graphite exhibit increased adhesion energy, attributed to the fixation of isopropyl alcohol fragments onto graphene and graphite, respectively. The presence of hydroxyl groups and the possibility for further reactions on the functionalized graphene material are demonstrated through a substitution reaction with thionyl chloride, where the hydroxyl groups are replaced with chlorides, as confirmed through X-ray photoelectron spectroscopy analysis.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
National Category
Materials Engineering Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-314171 (URN)10.1002/smtd.201700214 (DOI)000417488900006 ()
Funder
Wenner-Gren FoundationsSwedish Research CouncilKnut and Alice Wallenberg FoundationÅForsk (Ångpanneföreningen's Foundation for Research and Development)Magnus Bergvall Foundation
Available from: 2017-01-29 Created: 2017-01-29 Last updated: 2018-03-09Bibliographically approved
7. Nanometer Size Effect of Mechanical Properties of Graphene
Open this publication in new window or tab >>Nanometer Size Effect of Mechanical Properties of Graphene
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences Materials Engineering
Identifiers
urn:nbn:se:uu:diva-314173 (URN)
Available from: 2017-01-29 Created: 2017-01-29 Last updated: 2017-02-05
8. Superadhesion of Graphene Nanoscrolls
Open this publication in new window or tab >>Superadhesion of Graphene Nanoscrolls
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2017 (English)In: Article in journal (Refereed) Submitted
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-314174 (URN)
Available from: 2017-01-29 Created: 2017-01-29 Last updated: 2017-12-28

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