Leif Johansson

Leif Johansson
Linköping University | LiU · Department of Physics, Chemistry and Biology (IFM)

PhD

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212
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Publications

Publications (212)
Article
Full-text available
The calculated electronic band structure of graphene is relatively simple, with a Fermi surface consisting only of six Dirac cones in the first Brillouin zone—one at each K¯. In contrast, angle-resolved photoemission measurements of graphene grown on SiC(0001) often show six satellite Dirac cones surrounding each primary Dirac cone. Recent studies...
Article
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 intercalati...
Article
Full-text available
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...
Article
Full-text available
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...
Article
Full-text available
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 sp...
Article
Full-text available
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 °C initiates migration of Al throug...
Data
Influences on electronic structure induced by platinum (Pt) deposited on monolayer graphene grown on SiC(0001) are investigated by photoelectron spectroscopy (PES), selected area low energy electron diffraction (mu-LEED) and angle resolved photoelectron spectroscopy (ARPES) techniques at the MAX Laboratory. Stable monolayer graphene electronic prop...
Article
Full-text available
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...
Data
Full-text available
Scientific Reports 4, Article number: 4157 10.1038/srep04157 (2014); Published: February242014; Updated: July082014 The authors neglected to cite a related study that reports an ARPES experiment indicating the presence of multiple π bands in multilayer graphene on C-face SiC.1 This is given below as Reference 1. In the present Article, nano-ARPES...
Article
Full-text available
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...
Article
Full-text available
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...
Article
Influences on electronic structure induced by Platinum (Pt) deposited on monolayer graphene grown on SiC(0001) 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 prope...
Article
Full-text available
The rare-earth metal, ytterbium (Yb), was deposited on graphene grown on Si-face SiC, kept at room temperature. Yb was not found to intercalate, destroy or dope the graphene layer before subsequent heating, unlike alkali metals such as Li and Na. Our photoemission results reveal that heating to 300˚C promotes Yb intercalation into the graphene-subs...
Article
Full-text available
Studies of the effects induced on the electron band structure after Na deposition, and subsequent heating, on a C-face 2 MLs graphene sample will be presented. Na deposition shifts the Dirac point downwards from the Fermi level by about 0.5 eV due to electron doping. After heating at temperatures from around 120 to 300C, the π-band appears consider...
Article
Full-text available
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 diffe...
Article
Full-text available
The Si3N4/TiN Interface: 2. Si3N4/TiN(001) Grown with a −7 V Substrate Bias and Analyzed In situ using Angle-resolved X-ray Anomalous Rashba effect of bismuth(111) thin films studied by high-resolution spin-and angle-resolved photoemission spectroscopy J. Vac Synchrotron-based core level and angle resolved photoemission spectroscopy was used to stu...
Article
Full-text available
Graphene grown on C-face SiC substrates using two procedures, high and low growth temperature and different ambients, was investigated using Low Energy Electron Microscopy (LEEM), X-ray Photo Electron Electron Microscopy (XPEEM), selected area Low Energy Electron Diffraction (μ-LEED) and selected area Photo Electron Spectroscopy (μ-PES). Both types...
Article
Full-text available
Studies of the effects induced on the electron band structure after Na deposition, and subsequent heating, on a C-face 2 MLs graphene sample are reported. Na deposition shifts the Dirac point downwards from the Fermi level by about 0.5 eV due to electron doping. After heating at temperatures from around 120℃ to 300℃,thep-band appears considerably b...
Conference Paper
Full-text available
We report graphene thickness, uniformity and surface morphology dependence on the growth temperature and local variations in the off-cut of Si-face 4H-SiC on-axis substrates. The transformation of the buffer layer through hydrogen intercalation and the subsequent influence on the charge carrier mobility are also studied. A hot-wall CVD reactor was...
Article
Graphene samples were grown on the C-face of SiC, at high temperature in a furnace and an Ar ambient, and were investigated using LEEM, XPEEM, LEED, XPS and ARPES. Formation of fairly large grains (crystallographic domains) of graphene exhibiting sharp 1x1 patterns in m-LEED was revealed and that different grains showed different azimuthal orientat...
Article
Full-text available
Detailed studies of Li deposition on monolayer graphene grown on the Si-face SiC surface were performed using LEEM, mu-LEED, PES and ARPES. Li was found to intercalate directly after the deposition at room temperature. However, excess Li was also observed on the surface and found to form a compound with carbon atoms. This compound is suggested to g...
Article
Full-text available
The effects of Na deposited on monolayer graphene on SiC(001) were investigated by synchrotron-based photoelectron spectroscopy and angle resolved photoelectron spectroscopy. The experimental results show that Na prefers to adsorb on the graphene layer after deposition at room temperature. Nonetheless, part of the Na atoms are able to intercalate i...
Article
The effects of Li deposition on hydrogenated bilayer graphene on SiC(0001) samples, i.e. on quasi-freestanding bilayer graphene samples are studied using low energy electron microscopy, micro-low-energy electron diffraction and photoelectron spectroscopy. After deposition, some Li atoms form islands on the surface creating defects that are observed...
Article
Full-text available
A study of effects induced in the Be 1s core level spectrum and in the surface band structure after Si adsorption on Be(0001) is reported. The changes in the Be 1s spectrum are quite dramatic. The number of resolvable surface components and the magnitude of the shifts do decrease and the relative intensities of the shifted components are drasticall...
Article
The intercalation and deintercalation mechanisms of Si deposited on monolayer graphene grown on SiC(0001) substrates and after subsequent annealing steps are investigated using low-energy electron microscopy (LEEM), photoelectron spectroscopy (PES), and micro-low-energy electron diffraction (μ-LEED). After Si deposition on samples kept at room temp...
Article
Full-text available
Epitaxial graphene grown on the silicon-terminated SiC(0001) is doped by alkali metals deposited on the surface. The synchrotron radiation based photoelectron spectroscopy results presented reveal that Rb and Cs deposited on monolayer graphene samples, grown on the silicon-terminated SiC(0001), gives rise to n-type doping, i.e. electron transfer fr...
Article
An x-ray photoemission electron microscope (X-PEEM) equipped with a hemispherical energy analyzer is capable of fast acquisition of momentum-resolved photoelectron angular distribution patterns in a complete cone. We have applied this technique to observe the 3-D $(E, k_{x}, k_{y})$ electronic band structure of zero-, one-, and two-monolayer (ML) g...
Article
Graphene was grown on the C-face of nominally on-axis SiC substrates using high-temperature sublimation with Ar as the buffer inert gas. The results of studies of the morphology, thickness, and electronic structure of these samples using low-energy electron microscopy (LEEM), x-ray photoelectron emission microscopy, photoelectron spectroscopy, angl...
Article
The interactions of thin Ti layers deposited on the SiC(0001) √3 × √3 R30° surface at room temperature and after annealing at temperatures from 450 to 1200 °C was investigated using photoemission and LEED. Chemically shifted components were revealed in the Si 2p spectrum and found to be more intense and pronounced than the shifted component in the...
Article
The results of photoemission studies of SiO/SiC samples for the purpose of revealing presence of any carbon containing by-products at the interface are reported. Two components could be identified in recorded Si 2p and C 1s core level spectra. For Si 2p these were identified to originate from SiO and SiC while for C 1s they were interpreted to orig...
Article
Full-text available
The effects induced by the deposition of Li on 1 and 0 ML graphene grown on SiC(0001) and after subsequent heating were investigated using low-energy electron microscopy (LEEM) and x-ray photo-emission electron microscopy (XPEEM). For 1 ML samples, the collected photoelectron angular distribution patterns showed the presence of single π-cones at th...
Article
The influence of lithium (Li) exposures on monolayer graphene grown on the silicon-terminated SiC(0001) surface is investigated using low-energy electron microscopy, photoelectron spectroscopy, and micro-low-energy electron diffraction. After Li deposition, islands or Li droplets are observed on the surface, and are found to coalesce together with...
Article
In this paper we discuss and review results of recent studies of epitaxial growth of graphene on silicon carbide. The presentation is focused on high quality, large and uniform layer graphene growth on the SiC(0 0 0 1) surface and the results of using different growth techniques and parameters are compared. This is an important subject because acce...
Article
Full-text available
We are aiming at understanding the graphene formation mechanism on different SiC polytypes (6H, 4H and 3C) and orientations with the ultimate goal to fabricate large area graphene (up to 2 inch) with controlled number of monolayers and spatial uniformity. To reach the objectives we are using high-temperature atmospheric pressure sublimation process...
Article
The influence of hydrogen exposures on a high quality monolayer graphene grown on SiC(0001) is investigated using photoelectron spectroscopy (PES), low-energy electron microscopy (LEEM) and micro low energy electron diffraction (mu-LEED). We observe significant changes in the C1s core level, electron reflectivity curve, and electron diffraction aft...
Article
The influence of hydrogen exposures on monolayer graphene grown on the silicon terminated SiC(0001) surface is investigated using photoelectron spectroscopy (PES), low-energy electron microscopy (LEEM) and micro low-energy electron diffraction (μ-LEED). Exposures to ionized hydrogen are shown to have a pronounced effect on the carbon buffer (interf...
Article
The influence of substrate orientation on the morphology of graphene growth on 6H-SiC(0 0 0 1) was investigated using low-energy electron and scanning tunneling microscopy (LEEM and STM). Large area monolayer graphene was successfully furnace-grown on these substrates. Larger terrace widths and smaller step heights were obtained on substrates with...
Article
The influence of substrate orientation on the morphology of graphene growth on 6H-SiC(0001) was investigated using low-energy electron and scanning tunneling microscopy (LEEM and STM). Large area monolayer graphene was successfully furnace-grown on these substrates. Larger terrace widths and smaller step heights were obtained on substrates with a s...
Article
Large area graphene growth on commercial Si-face on-axis 6H-SiC(0001) is demonstrated in this work. Samples were produced in a prototype of an inductively heated furnace. The growth was carried out in strongly isothermal conditions at a temperature of 2000 C and at an ambient argon pressure of 1 atm. The quality and thickness of the graphene layers...
Article
The atomic and electronic structure of 4H-SiC(1 1̄ 02) surfaces were investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) and photoemission (PES). Two well ordered phases existing on this surface, i.e. (2×1) and c(2×2) are discussed. The (2×1) phase consists of a Si adlayer which is topped by an array of or...
Article
Homogeneous large-area graphene monolayers were successfully prepared ex situ on 6H-SiC(0001). The samples have been studied systematically and the results are compared with those from a sample cut from the same wafer and prepared by in situ heating. The formation of smaller graphene flakes was found on the in situ prepared sample, which is in line...
Article
The electronic and atomic structure of the 4H-SiC(1 (1) over bar 02) - (2 x 1) surface was investigated. Photoemission data indicate that the surface contains about 2 Si layers on top of the bulk layers. Scanning tunneling microscopy images show that these adlayers are terminated by an ordered array of adatom chains separated by the unit cell size....
Article
The electronic and atomic structure of the 4H-SiC(11¯02)-(2×1) surface was investigated. Photoemission data indicate that the surface contains about 2 Si layers on top of the bulk layers. Scanning tunneling microscopy images show that these adlayers are terminated by an ordered array of adatom chains separated by the unit cell size. An electronic s...
Article
The (11¯02) orientated plane of hexagonal silicon carbide of the 4H polytype consists of a periodic arrangement of stripes with alternating bond configuration on a nanometer scale. The two stripe configurations of the bulk truncated surface have an atomic structure very close to the carbon-face SiC basal plane and the cubic SiC(1 0 0) surface, resp...
Article
Low energy electron diffraction, grazing incidence X-ray diffraction and photoemission were used to decipher the detailed structural arrangement and chemical composition of the surface region of a transition metal carbide, VC0.8(1 1 0). In agreement with previous scanning tunneling microscopy (STM) studies, we find that the surface reconstructs wit...
Article
The growth and thermal stability of ultrathin ZrO2 films on the Si-rich SiC(0 0 0 1)-(3 × 3) surface have been explored using photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The films were grown in situ by chemical vapor deposition using the zirconium tetra tert-butoxide (ZTB) precursor. The O 1s XAS results show that grow...
Article
Full-text available
The ESCA technique has been used to determine the energy difference between the top of the valence band and the outermost core levels in LiF, LiCl and LiBr. The energy differences obtained between the top of the valence band and the Li 1s line in LiF, LiCl and LiBr were respectively 49.8 eV, 53.2 eV and 54.1 eV. These results agree rather well with...
Article
Synchrotron radiation excited photoelectron spectra of the 4f emission region for all lanthanide metals Ce58 to Lu71 (except Pm61) have been recorded. Photon energies ranging from 30 eV to 200 eV have been used to excite the 4f electrons with maximum surface sensitivity. The 4f emission spectra of all metals studied, with the exception of Ce, show...
Article
An angle-resolved photoemission study of a ZrN0.93 (110) single crystal is reported. Off-normal spectra recorded using unpolarized Ne I and He I resonance radiation are presented and the determined experimental peak dispersion are compraed with possible direct transitions calculated for ZrN1.0. The results show that dominant emission peaks at these...
Article
Photoelectron spectra of the Hf 4f core levels from a HfN(100) single crystal and a polycrystalline HfC sample have been measured and analysed. Surface-shifted 4f levels could be identified for both compounds, at a smaller binding energy than the bulk 4f levels in HfN and at a larger binding energy in HfC. The surface core level shifts were extract...
Article
Full-text available
Photoemission studies using synchrotron radiation have been performed on epitaxial Ti3SiC2(0001) and compound nanocrystalline (nc-)TiC/amorphous (a-)SiC thin films deposited by magnetron sputtering. As-introduced samples were found to be covered by surface oxides, SiOx and TiOx. These oxides could be removed by in-situ annealing to ∼1000 °C. For as...
Article
A study of surface and interface properties of reconstructed Au–SiC(0001) surfaces is reported. Two reconstructions were prepared on SiC(0001), a √3×√3R30° and a Si-rich 3×3, before Au deposition and subsequent annealing at different temperatures. For the Si-rich 3×3 surface the existence of three stable reconstructions 2√3×2√3R30°, 3×3 and 5×5 are...
Article
A study of surface and interface properties of thin Au layers deposited on SiC(0001¯) surfaces is reported. Two reconstructions were prepared, a Si-rich 2 × 2 and a C-rich 3 × 3 surface, before Au deposition and subsequent annealing at different temperatures. For the Si-rich 2 × 2 surface a stable &surd;7 × &surd;7 R19° reconstruction is obtained a...
Article
Photoemission studies of Si-rich polar and nonpolar 4H-SiC surfaces before and after oxygen exposures are reported. For the clean Si-rich (0001)-3×3 surface, three prominent surface-shifted components are revealed in the Si 2p spectrum. This observation agrees well with the structural model suggested for this surface but disagrees with earlier resu...
Article
The effects of Au overlayers prepared on the SiC(000-1) surface have been investigated. A 2x2 reconstructed surface was prepared by Si deposition at substrate a temperature of 800^oC. A 3x3 reconstructed surface was prepared by in situ heating to ca 1050^ oC. By utilizing high resolution photoemission and synchrotron radiation together with low ene...
Article
Full-text available
A photoemission study of Si-rich polar and nonpolar 4H-SiC surfaces before and after initial oxidation are presented. Core level and valence band data recorded using synchrotron radiation are utilized to explore the properties of these surfaces and of the interfaces. The Si-rich surfaces showed three prominent surface Si 2p components. These compon...
Article
Two questions thought to have a significant effect on SiC-MOS device characteristics are treated. The existence of carbon clusters or carbon containing by-products and the existence of sub-oxides at the SiO2/SiC interface. Results of photoemission studies using synchrotron radiation of the interface of the Si-terminated surface of n-type SiC(0001)...
Article
Detailed studies of the effects induced on the R 30° 4H-SiC(0001) surface after different NO exposures, at a substrate temperature of 800 °C, have been made. Photoemission experiments using synchrotron radiation were performed in order to study the properties of the interface formed after gas exposures. Recorded Si 2p spectra show three shifted com...
Article
Photoemission studies and layer resolved Korringa-Kohn-Rostoker (KKR) multiple scattering calculations are used to find the assignment of the surface core-level shifts to the top layers of the Be(101[over ¯]0) surface. Striking similarities between experimental and calculated data make it possible to assign the largest shift to layer two, the secon...
Article
Full-text available
Oxidation of hexagonal SiC surfaces and SiO2/SiC interfaces were analyzed using photoemission and synchrotron radiation. The existence of carbon clusters or carbon-containing by-products and the existence of sub-oxides at the SiO2/SiC interface had a significant effect on MOS device characteristic. Si-terminated surfaces of hexagonal n-type SiC(000...
Article
Photoemission studies of oxidized SiC samples grown ex situ in N2O, at a temperature of 900 °C, on the (0001), (0001̄), (112̄0) and (101̄0) surfaces are reported. Angle resolved data from the Si 1s and Si 2p core levels and the Si KL2,3L2,3 Auger transitions are analyzed and compared to data from a sample grown in O2 on the (0001) surface. The resu...
Article
Full-text available
The results of a photoemission study of clean and oxidized non-polar (101̄0) and (112̄0) surfaces of 4H-SiC crystals are reported. The effects induced in the core levels and valence bands upon initial oxidation were investigated. The surfaces were oxidized gradually from 1 L to 106 L while keeping the substrate at a temperature of 800°C. Recorded S...
Article
Full-text available
Angle resolved photoemission studies of SiO2/SiC samples grown ex situ in N2O on polar and non-polar 4H-SiC surfaces are reported. Data from the Si Is and Si 2p core levels and the Si KL2,3L 2,3 Auger transitions are analyzed and compared to data from a sample grown in O2 on the (0001) surface. The results show oxide growth without nitride or oxyni...
Article
The results of a photoemission study of clean and oxidized nonpolar (101¯0) and (112¯0) surfaces of 4H-SiC crystals are reported. For the clean surfaces prominent surface shifted components are revealed in the C1s spectra, although with different relative strengths for the two surfaces. In the Si2p spectra only one weak surface related feature is o...
Article
Effects induced by nitrogenmonoxide (NO) exposures on the √3×√3 R30° reconstructed 4H–SiC(0 0 0 1) surface are reported. NO exposures from 0.3 to 1 × 106 L at a substrate temperature of 800 °C are investigated. Recorded Si 2p spectra show three shifted components, besides the bulk SiC peak. These are assigned to originate from SiO2, N–Si–O and Si3N...