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Johansson, Leif
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Publications (10 of 78) Show all publications
Xia, C., Tal, A., Johansson, L., Olovsson, W., Abrikosov, I. & Virojanadara, C. (2018). Effects of rhenium on graphene grown on SiC(0001). Journal of Electron Spectroscopy and Related Phenomena, 222, 117-121
Open this publication in new window or tab >>Effects of rhenium on graphene grown on SiC(0001)
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2018 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 222, p. 117-121Article in journal (Refereed) Published
Abstract [en]

We study the effects of Rhenium (Re) deposited on epitaxial monolayer graphene grown on SiC(0001) and after subsequent annealing at different temperatures, by performing high resolution photoelectron spectroscopy (PES) and angle resolved photoelectron spectroscopy (ARPES). The graphene-Re system is found to be thermally stable. While no intercalation or chemical reaction of the Re is detected after deposition and subsequent annealing up to 1200 degrees C, a gradual decrease in the binding energy of the Re 4f doublet is observed. We propose that a larger mobility of the Re atoms with increasing annealing temperature and hopping of Re atoms between different defective sites on the graphene sample could induce this decrease of Re 4f binding energy. This is corroborated by first principles density functional theory (DFT) calculations of the Re core-level binding energy shift. No change in the doping or splitting of the initial monolayer graphene electronic band structure is observed after Re deposition and annealing up to 1200 degrees C, only a broadening of the bands. (C) 2017 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Rhenium; Graphene; Photoelectron spectroscopy; Core-level shift; Ab initio density functional theory
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-145152 (URN)10.1016/j.elspec.2017.07.006 (DOI)000423638100016 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation [2012.0083]; Knut and Alice Wallenberg Foundation through CoTXS; Swedish Foundation or Strategic Research (SSF) program SRL Grant [10-0026]; Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [200900971]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Swedish Research Council [621-2011-4252]

Available from: 2018-02-13 Created: 2018-02-13 Last updated: 2018-03-19Bibliographically approved
Nuala, M., Johansson, L. I., Xia, C., Armiento, R., Abrikosov, I. & Jacobi, C. (2016). Structural and electronic properties of Li-intercalated graphene on SiC(0001). Physical Review B: covering condensed matter and materials physics, 93(19), 195421-1-195421-9
Open this publication in new window or tab >>Structural and electronic properties of Li-intercalated graphene on SiC(0001)
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2016 (English)In: Physical Review B: covering condensed matter and materials physics, ISSN 2469-9950, Vol. 93, no 19, p. 195421-1-195421-9Article in journal (Refereed) Published
Abstract [en]

We investigate the structural and electronic properties of Li-intercalated monolayer graphene on SiC(0001) using combined angle-resolved photoemission spectroscopy and first-principles density functional theory. Li intercalates at room temperature both at the interface between the buffer layer and SiC and between the two carbon layers. The graphene is strongly n-doped due to charge transfer from the Li atoms and two pi bands are visible at the (K) over bar point. After heating the sample to 300 degrees C, these pi bands become sharp and have a distinctly different dispersion to that of Bernal-stacked bilayer graphene. We suggest that the Li atoms intercalate between the two carbon layers with an ordered structure, similar to that of bulk LiC6. An AA stacking of these two layers becomes energetically favourable. The pi bands around the (K) over bar point closely resemble the calculated band structure of a C6LiC6 system, where the intercalated Li atoms impose a superpotential on the graphene electronic structure that opens gaps at the Dirac points of the two pi cones.

Place, publisher, year, edition, pages
American Physical Society, 2016
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-129161 (URN)10.1103/PhysRevB.93.195421 (DOI)000376248200006 ()
Note

Funding Agencies|Swedish Research Council (VR) [621-2011-4252, 621-2011-4426]; Swedish Foundation for Strategic Research (SSF) program [10-0026]; European Union Seventh Framework Programme, Graphene Flagship [604391]; Swedish Government Strategic Research Areas SeRC and in Materials Science on Functional Materials at Link oping University [2009 00971]; SRC VR Grant [621-2011-4249]; Linnaeus Environment at Linkoping on Nanoscale Functional Materials (LiLi-NFM) - VR; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D. I. Mendeleev Fund Program [8.1.18.2015]

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2016-07-11Bibliographically approved
Xia, C., Johansson, L. I., Niu, Y., Hultman, L. & Virojanadara, C. (2015). Effects of aluminum on epitaxial graphene grown on C-face SiC. Journal of Applied Physics, 117(19), 195306
Open this publication in new window or tab >>Effects of aluminum on epitaxial graphene grown on C-face SiC
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2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 19, p. 195306-Article in journal (Refereed) Published
Abstract [en]

The effects of Al layers deposited on graphene grown on C-face SiC substrates are investigated before and after subsequent annealing using low energy electron diffraction (LEED), photoelectron spectroscopy, and angle resolved photoemission. As-deposited layers appear inert. Annealing at a temperature of about 400 degrees C initiates migration of Al through the graphene into the graphene/SiC interface. Further annealing at temperatures from 500 degrees C to 700 degrees C induces formation of an ordered compound, producing a two domain root 7 x root 7R19 degrees LEED pattern and significant changes in the core level spectra that suggest formation of an Al-Si-C compound. Decomposition of this compound starts after annealing at 800 degrees C, and at 1000 degrees C, Al is no longer possible to detect at the surface. On Si-face graphene, deposited Al layers did not form such an Al-Si-C compound, and Al was still detectable after annealing above 1000 degrees C.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-119250 (URN)10.1063/1.4921462 (DOI)000355005600036 ()
Note

Funding Agencies|Swedish Research Council [621-2011-4252]; Linnaeus Grant

Available from: 2015-06-12 Created: 2015-06-12 Last updated: 2017-12-04
Johansson, L. I., Xia, C. & Jacobi, C. (2015). Li induced effects in the core level and pi-band electronic structure of graphene grown on C-face SiC. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, 33(6), Article ID 061405.
Open this publication in new window or tab >>Li induced effects in the core level and pi-band electronic structure of graphene grown on C-face SiC
2015 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 33, no 6, article id 061405Article in journal (Refereed) Published
Abstract [en]

Studies of the effects induced in the electronic structure after Li deposition, and subsequent heating, on graphene samples prepared on C-face SiC are reported. The as prepared graphene samples are essentially undoped, but after Li deposition, the Dirac point shifts down to 1.2 eV below the Fermi level due to electron doping. The shape of the C 1s level also indicates a doping concentration of around 10(14) cm(-2) after Li deposition, when compared with recent calculated results of core level spectra of graphene. The C 1s, Si 2p, and Li 1s core level results show little intercalation directly after deposition but that most of the Li has intercalated after heating at 280 degrees C. Heating at higher temperatures leads to desorption of Li from the sample, and at 1030 degrees C, Li can no longer be detected on the sample. The single pi-band observable from multilayer C-face graphene samples in conventional angle resolved photoelectron spectroscopy is reasonably sharp both on the initially prepared sample and after Li deposition. After heating at 280 degrees C, the p-band appears more diffuse and possibly split. The Dirac point becomes located at 0.4 eV below the Fermi level, which indicates occurrence of a significant reduction in the electron doping concentration. Constant energy photoelectron distribution patterns extracted from the as prepared graphene C-face sample and also after Li deposition and heating at 280 degrees C look very similar to earlier calculated distribution patterns for monolayer graphene. (C) 2015 Author(s).

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-123832 (URN)10.1116/1.4927856 (DOI)000365503800032 ()
Note

Funding Agencies|Swedish Natural Research Council [621-2011-4252]; Swedish Natural Research Council (Linnaeus Grant)

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-12-01Bibliographically approved
Watcharinyanon, S., Xia, C., Niu, Y., Zakharov, A. A., Johansson, L. I., Yakimova, R. & Virojanadara, C. (2015). Soft X-ray Exposure Promotes Na Intercalation in Graphene Grown on Si-Face SiC. Materials, 8(8), 4768-4777
Open this publication in new window or tab >>Soft X-ray Exposure Promotes Na Intercalation in Graphene Grown on Si-Face SiC
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2015 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 8, no 8, p. 4768-4777Article in journal (Refereed) Published
Abstract [en]

An investigation of how electron/photon beam exposures affect the intercalation rate of Na deposited on graphene prepared on Si-face SiC is presented. Focused radiation from a storage ring is used for soft X-ray exposures while the electron beam in a low energy electron microscope is utilized for electron exposures. The microscopy and core level spectroscopy data presented clearly show that the effect of soft X-ray exposure is significantly greater than of electron exposure, i.e., it produces a greater increase in the intercalation rate of Na. Heat transfer from the photoelectrons generated during soft X-ray exposure and by the electrons penetrating the sample during electron beam exposure is suggested to increase the local surface temperature and thus the intercalation rate. The estimated electron flux density is 50 times greater for soft X-ray exposure compared to electron exposure, which explains the larger increase in the intercalation rate from soft X-ray exposure. Effects occurring with time only at room temperature are found to be fairly slow, but detectable. The graphene quality, i.e., domain/grain size and homogeneity, was also observed to be an important factor since exposure-induced effects occurred more rapidly on a graphene sample prepared in situ compared to on a furnace grown sample.

Place, publisher, year, edition, pages
MDPI AG, 2015
Keywords
graphene on Si-face SiC; intercalation of Na; soft X-ray exposure; electron exposure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-121762 (URN)10.3390/ma8084768 (DOI)000360643900010 ()
Note

Funding Agencies|Swedish Research Council [621-2011-4252]

Available from: 2015-10-06 Created: 2015-10-05 Last updated: 2017-12-01
Xia, C., Johansson, L. I., Zakharov, A. A., Hultman, L. & Virojanadara, C. (2014). Effects of Al on epitaxial graphene grown on 6H-SiC(0001). Materials Research Express, 1(1), 1-13, Article ID 015606.
Open this publication in new window or tab >>Effects of Al on epitaxial graphene grown on 6H-SiC(0001)
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2014 (English)In: Materials Research Express, ISSN 2053-1591, Vol. 1, no 1, p. 1-13, article id 015606Article in journal (Refereed) Published
Abstract [en]

Aluminum was deposited on epitaxial monolayer-grown graphene on SiC(0001). The effects of annealing up to 1200 °C on the surface and interface morphology, chemical composition, and electron band structure were analyzed in situ by synchrotron-based techniques at the MAX Laboratory. After heating at around 400 °C, Al islands or droplets are observed on the surface and the collected Si 2p, Al 2p, and C 1s core levels spectra indicate Al intercalation at the graphene SiC interface. Also, the original single π -band splits into two, indicating decoupling of the carbon buffer layer and the formation of a quasi-free-standing bilayer-like electronic structure. Further heating at higher temperatures from 700 to 900 °C yields additional chemical reactions. Broader core level spectra are then observed and clear changes in the π -bands near the Dirac point are detected. More electron doping was detected at this stage since one of the π -bands has shifted to about 1.1 eV below the Fermi level. Different ordered phases of (7x7), (4x4), (1x1)Al , and (1x1)G were also observed on the surface in this temperature range. The original single π π-band was restored after heating at ~1200°C, although an Al signal was still able to be detected.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-120851 (URN)10.1088/2053-1591/1/1/015606 (DOI)
Available from: 2015-08-28 Created: 2015-08-28 Last updated: 2016-08-31Bibliographically approved
Xia, C., Johansson, L. I., Niu, Y., Zakharov, A. A., Janzén, E. & Virojanadara, C. (2014). High thermal stability quasi-free-standing bilayer graphene formed on 4H-SiC(0 0 0 1) via platinum intercalation. Carbon, 79, 631-635
Open this publication in new window or tab >>High thermal stability quasi-free-standing bilayer graphene formed on 4H-SiC(0 0 0 1) via platinum intercalation
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2014 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 79, p. 631-635Article in journal (Refereed) Published
Abstract [en]

Influences on electronic structure induced by platinum (Pt) deposited on monolayer graphene grown on SiC(0 0 0 1) are investigated by photoelectron spectroscopy (PES), selected area low energy electron diffraction (μ-LEED) and angle resolved photoelectron spectroscopy (ARPES) techniques at the MAX Laboratory. Stable monolayer graphene electronic properties are observed after Pt deposition and after annealing at temperatures below 600 °C. At ⩾600 °C platinum silicide forms at the graphene/SiC interface. Annealing at 900 °C results in an efficient decoupling of the carbon buffer layer from the SiC substrate and transformation into a second graphene layer. At this stage a quasi-free standing bi-layer graphene sample is obtained. The new superstructure spots then appearing in μ-LEED pattern suggest formation of an ordered platinum silicide at the interface. This silicide is found to be stable even after annealing at temperature up to 1200 °C.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-111494 (URN)10.1016/j.carbon.2014.08.027 (DOI)
Available from: 2014-10-20 Created: 2014-10-20 Last updated: 2017-12-05Bibliographically approved
Johansson, L. I., Armiento, R., Avila, J., Xia, C., Lorcy, S., Igor A., A., . . . Virojanadara, C. (2014). Multiple π-bands and Bernal stacking of multilayer graphene on C-face SiC, revealed by nano-Angle Resolved Photoemission. Scientific Reports, 4(4157)
Open this publication in new window or tab >>Multiple π-bands and Bernal stacking of multilayer graphene on C-face SiC, revealed by nano-Angle Resolved Photoemission
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2014 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, no 4157Article in journal (Refereed) Published
Abstract [en]

Only a single linearly dispersing π-band cone, characteristic of monolayer graphene, has so far been observed in Angle Resolved Photoemission (ARPES) experiments on multilayer graphene grown on C-face SiC. A rotational disorder that effectively decouples adjacent layers has been suggested to explain this. However, the coexistence of μm-sized grains of single and multilayer graphene with different azimuthal orientations and no rotational disorder within the grains was recently revealed for C-face graphene, but conventional ARPES still resolved only a single π-band. Here we report detailed nano-ARPES band mappings of individual graphene grains that unambiguously show that multilayer C-face graphene exhibits multiple π-bands. The band dispersions obtained close to the K-point moreover clearly indicate, when compared to theoretical band dispersion calculated in the framework of the density functional method, Bernal (AB) stacking within the grains. Thus, contrary to earlier claims, our findings imply a similar interaction between graphene layers on C-face and Si-face SiC.

Place, publisher, year, edition, pages
Nature Publishing Group, 2014
Keywords
Electronic properties and materials, Graphene, Stacking
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-105279 (URN)10.1038/srep04157 (DOI)000331885900004 ()
Funder
Swedish Research Council, 621-2011-4252Swedish Research Council, 621-2011-4249Swedish Foundation for Strategic Research , 10-0026
Available from: 2014-03-14 Created: 2014-03-14 Last updated: 2017-12-05Bibliographically approved
Johansson, L. I. & Virojanadara, C. (2014). Properties of epitaxial graphene grown on C-face SiC compared to Si-face. Journal of Materials Research, 29(3), 426-438
Open this publication in new window or tab >>Properties of epitaxial graphene grown on C-face SiC compared to Si-face
2014 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 29, no 3, p. 426-438Article in journal (Refereed) Published
Abstract [en]

Epitaxial graphene of uniform thickness prepared on SiC is of great interest for various applications. On the Si-face, large area uniformity has been achieved, and there is a general consensus about the graphene properties. A similar uniformity has yet not been demonstrated on the C-face where the graphene has been claimed to be fundamentally different. A rotational disorder between adjacent graphene layers has been reported and suggested to explain why multilayer C-face graphene show the pi-band characteristic of monolayer graphene. Utilizing low energy electron microscopy, x-ray photoelectron electron microscopy, low energy electron diffraction, and photoelectron spectroscopy, we investigated the properties of C-face graphene prepared by sublimation growth. We observe the formation of micrometer-sized crystallographic grains of multilayer graphene and no rotational disorder between adjacent layers within a grain. Adjacent grains are in general found to have different azimuthal orientations. Effects on C-face graphene by hydrogen treatment and Na exposure were also investigated and are reported. Why multilayer C-face graphene exhibits single layer electronic properties is still a puzzle, however.

Place, publisher, year, edition, pages
Cambridge University Press (CUP), 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-105902 (URN)10.1557/jmr.2013.261 (DOI)000331962700013 ()
Available from: 2014-04-14 Created: 2014-04-12 Last updated: 2017-12-05
Xia, C., Watcharinyanon, S., Zakharov, A. A., Johansson, L. I., Yakimova, R. & Virojanadara, C. (2013). Detailed studies of Na intercalation on furnace-grown graphene on 6H-SiC(0001). Surface Science, 613, 88-94
Open this publication in new window or tab >>Detailed studies of Na intercalation on furnace-grown graphene on 6H-SiC(0001)
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2013 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 613, p. 88-94Article in journal (Refereed) Published
Abstract [en]

The effects induced by Na deposited on furnace grown graphene on SiC(0001) and after subsequent annealing are investigated using LEEM, mu-LEED, mu-PES and XPEEM. Intercalation in between carbon layers and at the interface is observed to occur both on the 1 ML and 2 ML areas directly after Na deposition. Annealing at a temperature around 100 degrees C is found to strongly promote Na intercalation. Exposure to the electron beam or the focused synchrotron radiation in the LEEM/XPEEM is also found to promote the intercalation, which is confirmed to begin at domain boundaries between the 1 ML and 2 ML areas, and also as stripe/streak-like features on the 1 ML areas. The XPEEM data show Na adsorption on the surface and intercalation at the interface to be quite non-uniform. When annealing at higher temperatures Na starts to de-intercalate and leave the sample, but Na is still detectable on the sample after annealing at 240 degrees C.

Place, publisher, year, edition, pages
Elsevier, 2013
Keywords
Epitaxial graphene on SiC, Sodium intercalation, LEEM, XPEEM, mu-LEED, mu-PES
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94593 (URN)10.1016/j.susc.2013.03.011 (DOI)000319180600014 ()
Note

Funding Agencies|Swedish Research Council|621-2011-4252|ESF||EU||

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2017-12-06
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