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Controlling Electronic and Geometrical Structure of Honeycomb-Lattice Materials Supported on Metal Substrates: Graphene and Hexagonal Boron Nitride
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis is focused on various methods of controlling electronic and geometrical structure of two-dimensional overlayers adsorbed on metal surfaces exemplified by graphene and hexagonal boron nitride (h-BN) grown on transition metal (TM) substrates. Combining synchrotron-radiation-based spectroscopic and various microscopic techniques with in situ sample preparation, we are able to trace the evolution of overlayer electronic and geometrical properties in overlayer/substrate systems, as well as changes of interfacial interaction in the latter.It is shown that hydrogen uptake by graphene/TM substrate strongly depends on the interfacial interaction between substrate and graphene, and on the geometrical structure of graphene. An energy gap opening in the electronic structure of graphene on TM substrates upon patterned adsorption of atomic species is demonstrated for the case of atomic oxygen adsorption on graphene/TM’s (≥0.35 eV for graphene/Ir(111)). A non-uniform character of adsorption in this case – patterned adsorption of atomic oxygen on graphene/Ir(111) due to the graphene height modulation is verified. A moderate oxidation of graphene/Ir(111) is found largely reversible. Contrary, oxidation of h-BN/Ir(111) results in replacing nitrogen atoms in the h-BN lattice with oxygen and irreversible formation of the B2O3 oxide-like structure.     

Pronounced hole doping (p-doping) of graphene upon intercalation with active agents – halogens or halides – is demonstrated, the level of the doping is dependent on the agent electronegativity. Hole concentration in graphene on Ir(111) intercalated with Cl and Br/AlBr3 is as high as ~2×1013 cm-2 and ~9×1012 cm-2, respectively.    

Unusual periodic wavy structures are reported for h-BN and graphene grown on Fe(110) surface. The h-BN monolayer on Fe(110) is periodically corrugated in a wavy fashion with an astonishing degree of long-range order, periodicity of 2.6 nm, and the corrugation amplitude of ~0.8 Å. The wavy pattern results from a strong chemical bonding between h-BN and Fe in combination with a lattice mismatch in either [11 ̅1] or [111 ̅] direction of the Fe(110) surface. Two primary orientations of h-BN on Fe(110) can be observed corresponding to the possible directions of lattice match between h-BN and Fe(110).    

Chemical vapor deposition (CVD) formation of graphene on iron is a formidable task because of high carbon solubility in iron and pronounced reactivity of the latter, favoring iron carbide formation. However, growth of graphene on epitaxial iron films can be realized by CVD at relatively low temperatures, and the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a periodically corrugated pattern on Fe(110): it is modulated in one dimension forming long waves with a period of ~4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The novel 1D templates based on h-BN and graphene adsorbed on iron can possibly find an application in 1D nanopatterning. The possibility for growing high-quality graphene on iron substrate can be useful for the low-cost industrial-scale graphene production.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 103 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1019
Keyword [en]
graphene, h-BN, electronic structure, adsorption, doping, nano-templates, PES, NEXAFS, LEEM, STM
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-194089ISBN: 978-91-554-8598-6 (print)OAI: oai:DiVA.org:uu-194089DiVA: diva2:606739
Public defence
2013-04-05, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2013-03-13 Created: 2013-02-08 Last updated: 2013-03-22Bibliographically approved
List of papers
1. Controlling hydrogenation of graphene on transition metals
Open this publication in new window or tab >>Controlling hydrogenation of graphene on transition metals
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2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 43, 18559-18565 p.Article in journal (Refereed) Published
Abstract [en]

A monatomic layer of graphite (MG or graphene) adsorbed on the (111) faces of transition metals Pt, Ir, and Ni, has been employed for controlling the atomic hydrogen adsorption site selectivity and the amount of hydrogen adsorbed upon saturation. The variations in the graphene-metal chemical bonding caused by hydrogenation and the values of saturated hydrogen coverage have been studied by X-ray photoemission and X-ray absorption spectroscopy. The hydrogenation of the graphene/metal systems has also been compared to the hydrogen adsorption on highly oriented pyrolytic graphite under the same experimental conditions. It has been found that graphene adsorption on the transition metal substrates can drastically enhance the hydrogen uptake values. The highest values have been observed for MG/Ir(111), less for MG/Pt(111), even less for MG/Ni and the least for the adsorption on bulk graphite. The high level of H coverage on MG/Ir and MG/Pt has been assigned to the preferential H adsorption on the more bonding patches (pores) of the MG/metal coincidence lattice. This adsorption creates unpaired electrons which contribute to a strengthening of the graphene-metal bonds. In this way, the densest possible graphane-like patches can be formed on MG/Pt and MG/Ir. On the MG/Ni interface the formation of graphane is obstructed by the strong interfacial bonding.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-130322 (URN)10.1021/jp106361y (DOI)000283519400037 ()
Available from: 2010-09-07 Created: 2010-09-06 Last updated: 2017-12-12Bibliographically approved
2. Impact of Atomic Oxygen on the Structure of Graphene Formed on Ir(111) and Pt(111)
Open this publication in new window or tab >>Impact of Atomic Oxygen on the Structure of Graphene Formed on Ir(111) and Pt(111)
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2011 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 19, 9568-9577 p.Article in journal (Refereed) Published
Abstract [en]

The effect of atomic oxygen adsorption on the structure and electronic properties of monolayer graphite (MG or graphene) grown on Pt(111) and Ir(111) has been studied using X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and scanning tunneling microscopy. For comparison, the adsorption of atomic oxygen on highly oriented pyrolytic graphite has been studied under the same conditions. Graphene oxidation predominantly occurs through the formation of epoxy groups and causes atomic-scale buckling of the graphene lattice, as evidenced by an sp(2)-to-sp(3) bonding transformation. The different parts of the graphene/metal moire superstructure show different oxidation dynamics, with the initial formation of epoxy groups in the more bonding "pores". Upon 0 adsorption, the nearest C neighbors of epoxy groups get engaged in a stronger bonding with the substrate. As a result, the pores of the graphene mesh become attracted and effectively pinned to the substrate by the 0 atoms. A limited intercalation of oxygen under graphene is also probable. Annealing of the samples after oxygen exposure only partially recovers the original graphene structure and results in the formation of a dense pattern of quasi-periodic, nanometer-sized holes. Both the selective oxidization and the hole formation can be exploited for selective functionalization or tuning of the electronic properties.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-154296 (URN)10.1021/jp111962k (DOI)000290427400033 ()
Available from: 2011-05-30 Created: 2011-05-30 Last updated: 2017-12-11Bibliographically approved
3. Bandgap formation in graphene on Ir(1 1 1) through oxidation
Open this publication in new window or tab >>Bandgap formation in graphene on Ir(1 1 1) through oxidation
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2013 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 267, 74-76 p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

A graphene monolayer on single crystal Ir(111) has been studied using angle-resolved photoemission spectroscopy (ARPES) before and after exposure to atomic oxygen. With increasing oxygen coverage the Dirac cone, centered on the K-point of the Brillouin zone, broadens and finally transforms to a parabolic rather than linear feature, introducing a pronounced energy bandgap at the Fermi level. The opening of a bandgap of at least 0.35 eV was observed at the oxygen exposure close to the saturation coverage.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
graphene, oxidation, band gap, adsorbates
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-194077 (URN)10.1016/j.apsusc.2012.07.122 (DOI)000314881900018 ()
Conference
11th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures, October 3-7, 2011 St. Petersburg, Russia
Available from: 2013-02-08 Created: 2013-02-08 Last updated: 2017-12-06Bibliographically approved
4. Controllable oxidation of h-BN monolayer on Ir(111) studied by core-level spectroscopies
Open this publication in new window or tab >>Controllable oxidation of h-BN monolayer on Ir(111) studied by core-level spectroscopies
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2012 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 606, no 3-4, 564-570 p.Article in journal (Refereed) Published
Abstract [en]

The effect of atomic oxygen adsorption on the structure and electronic properties of monolayer hexagonal boron nitride (h-BN) grown on Ir(111) has been studied using near edge X-ray absorption fine structure spectroscopy (NEXAFS), photoelectron spectroscopy (PES), and low-energy electron diffraction (LEED). It has been shown that the oxidation of the h-BN monolayer occurs through a gradual substitution of N by O in the h-BN lattice. This process leads to the formation of defect sites corresponding to three different types of the B atom environment (BN3-xOx with x=1,2,3). The oxidation of the h-BN monolayer is very different from the case of graphene on Ir(111), where adsorption of atomic oxygen results mainly in the formation of epoxy groups [J. Phys. Chem. C. 115, 9568 (2011)]. A post-annealing of the h-BN monolayer after oxygen exposure results in further destruction of the B N bonds and formation of a B2O3-like structure.

Keyword
Photoelectron spectroscopy, Near-edge X-ray absorption fine structure, h-BN monolayer, Graphene, Oxidation
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-171678 (URN)10.1016/j.susc.2011.11.031 (DOI)000300458600072 ()
Available from: 2012-03-26 Created: 2012-03-25 Last updated: 2017-12-07Bibliographically approved
5. Controllable p-doping of graphene on Ir(111) by chlorination with FeCl3
Open this publication in new window or tab >>Controllable p-doping of graphene on Ir(111) by chlorination with FeCl3
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2012 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 31, 314202- p.Article in journal (Refereed) Published
Abstract [en]

The in situ chlorination of graphene on Ir(111) has been achieved by depositing FeCl3 followed by its thermal decomposition on the surface into FeCl2 and Cl. This process is accompanied by an intercalation of Cl under graphene and formation of an epitaxial FeCl2 film on top, which can be removed upon further annealing. A pronounced hole doping of graphene has been observed as a consequence of the annealing-assisted intercalation of Cl. This effect has been studied by a combination of core-level and angle-resolved photoelectron spectroscopies (CL PES and ARPES, respectively), near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and low-energy electron diffraction (LEED). The ease of preparation, the remarkable reproducibility of the doping level and the reversibility of the doping upon annealing are the key factors making chlorination with FeCl3 a promising route for tuning the electronic properties in graphene.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-179902 (URN)10.1088/0953-8984/24/31/314202 (DOI)000306686800007 ()
Available from: 2012-08-28 Created: 2012-08-27 Last updated: 2017-12-07Bibliographically approved
6. Hole doping of graphene supported on Ir(111) by AlBr3
Open this publication in new window or tab >>Hole doping of graphene supported on Ir(111) by AlBr3
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2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 6, 061601- p.Article in journal (Refereed) Published
Abstract [en]

In this Letter we report an easy and tenable way to tune the type of charge carriers in graphene, using a buried layer of AlBr3 and its derivatives on the graphene/Ir(111) interface. Upon the deposition of AlBr3 on graphene/Ir(111) and subsequent temperature-assisted intercalation of graphene/Ir(111) with atomic Br and AlBr3, pronounced hole doping of graphene is observed. The evolution of the graphene/Br-AlBr3/Ir(111) system at different stages of intercalation has been investigated by means of microbeam low-energy electron microscopy/electron diffraction, core-level photoelectron spectroscopy and angle-resolved photoelectron spectroscopy.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
Keyword
graphene, hole doping, adsorption, intercalation, charge carriers
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-194084 (URN)10.1063/1.4790579 (DOI)000315053300016 ()
Available from: 2013-02-25 Created: 2013-02-08 Last updated: 2017-12-06Bibliographically approved
7. One-Dimensional Corrugation of the h-BN Monolayer on Fe(110)
Open this publication in new window or tab >>One-Dimensional Corrugation of the h-BN Monolayer on Fe(110)
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2012 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 3, 1775-1781 p.Article in journal (Refereed) Published
Abstract [en]

We report on a new nanopatterned structure represented by a single atomic layer of hexagonal boron nitride (h-BN) forming long periodic waves on the Fe(110) surface. The growth process and the structure of this system are characterized by X-ray absorption (XAS), core-level photo-emission spectroscopy (CL PES), low-energy electron microscopy (LEEM), microbeam low-energy electron diffraction (mu LEED), and scanning tunneling microscopy (STM). The h-BN monolayer on Fe(110) is periodically corrugated in a wavy fashion with an astonishing degree of long-range order, periodicity of 2.6 nm, and the corrugation amplitude of A. The wavy pattern results from a strong chemical bonding between h-BN and Fe in combination with a lattice mismatch in either [(1) over bar 11] or [1 (1) over bar1] direction of the Fe(110) surface. Two primary orientations of h-BN on Fe(110) can be observed corresponding to the possible directions of lattice match between h-BN and Fe(110), with approximately equal area of the boron nitride domains of each orientation.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-169107 (URN)10.1021/la2035642 (DOI)000299366500016 ()
Available from: 2012-02-27 Created: 2012-02-23 Last updated: 2017-12-07Bibliographically approved
8. Formation and Structure of Graphene Waves on Fe(110)
Open this publication in new window or tab >>Formation and Structure of Graphene Waves on Fe(110)
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2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 2, 026101- p.Article in journal (Refereed) Published
Abstract [en]

A very rich Fe-C phase diagram makes the formation of graphene on iron surfaces a challenging task. Here we demonstrate that the growth of graphene on epitaxial iron films can be realized by chemical vapor deposition at relatively low temperatures, and that the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a novel periodically corrugated pattern on Fe(110). Using low-energy electron microscopy and scanning tunneling microscopy, we show that it is modulated in one dimension forming long waves with a period of similar to 4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The observed topography of the graphene/Fe superstructure is well reproduced by density functional theory calculations, and found to result from a unique combination of the lattice mismatch and strong interfacial interaction, as probed by core-level photoemission and x-ray absorption spectroscopy.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-179022 (URN)10.1103/PhysRevLett.109.026101 (DOI)000306324100012 ()
Funder
Swedish Research CouncilEU, European Research Council
Available from: 2012-08-06 Created: 2012-08-06 Last updated: 2017-12-07Bibliographically approved

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