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  • 51.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Photoemission study of Si-rich 4H-SiC surfaces and initial SiO2 SiC interface formation2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, nr 19Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 results where only two surface-shifted Si 2p components were identified. Also for the other three Si-rich surfaces investigated three similar surface components are revealed although with different relative strengths. The C 1s spectrum exhibits only one sharp bulk peak for the clean Si-rich surfaces. This is different compared to earlier results from the same surfaces prepared by in situ heating only. The effects induced upon initial oxidation of these Si-rich surfaces are investigated. Recorded Si 2p spectra show only one suboxide, Si+1 and Si+2, for the polar (0001) and (000 1¯) surfaces, respectively, besides the fully developed Si+4 oxide (Si O2). For the nonpolar surfaces two suboxide, Si+1 and Si+2, are observed. Similarities and differences compared to earlier findings are discussed. Valence band spectra collected from clean surfaces, before Si deposition, are presented for the nonpolar surfaces. The presence of a sharp structure at binding energies of about 2.0 and 2.7 eV for the (10 1¯ 0) and the (11 2¯ 0) surfaces, respectively, is observed. This structure shows no dispersion with photon energy and is very sensitive to oxygen exposures and is therefore tentatively suggested to be a surface resonance state. © 2005 The American Physical Society.

  • 52.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Studies of NO on 4H-SiC (0001) using Synchrotron Radiation2004Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER,  ISSN (0953-8984): Volume: 16   Issue: 33   Special Issue: SI, Institute of Physics Publishing (IOPP), 2004, s. S3435-S3439Konferensbidrag (Refereegranskat)
    Abstract [en]

    Detailed studies of the effects induced on the root3 x root3 R30degrees 4H-SiC(0001) surface after different NO exposures, at a substrate temperature of 800degreesC, 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 components, besides the bulk SiC peak. These are assigned as originating from Si(3)N(4) or Si(1+) sub-oxide, N-Si-O and SiO(2). It was concluded that SiO(2) does grow on top of N-Si-O and that Si(3)N(4)/Si(1+) is located at the interface. Two N 1s components are observed after NO exposures. The main one, located at around 398.05 eV, is assigned as originating from Si(3)N(4) and the weaker one is suggested to correspond to N-Si-O bonding. The assignments are made with the aid of Si 2p and N 1s spectra collected after NH(3) and O(2) exposures under similar conditions. No graphite-like carbon or carbon by-product at the interface can be detected after large NO or O(2) exposures.

  • 53.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Studies of NO on 4H-SiC(0001) using synchrotron radiation2004Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, nr 33, s. S3435-S3439Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detailed studies of the effects induced on the root3 x root3 R30degrees 4H-SiC(0001) surface after different NO exposures, at a substrate temperature of 800degreesC, 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 components, besides the bulk SiC peak. These are assigned as originating from Si3N4 or Si1+ sub-oxide, N-Si-O and SiO2. It was concluded that SiO2 does grow on top of N-Si-O and that Si3N4/Si1+ is located at the interface. Two N 1s components are observed after NO exposures. The main one, located at around 398.05 eV, is assigned as originating from Si3N4 and the weaker one is suggested to correspond to N-Si-O bonding. The assignments are made with the aid of Si 2p and N 1s spectra collected after NH3 and O-2 exposures under similar conditions. No graphite-like carbon or carbon by-product at the interface can be detected after large NO or O-2 exposures.

  • 54.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Studies of oxidized hexagonal SiC surfaces and the SiC/SiO2 interface using photoemission and synchrotron radiation2004Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, nr 17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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(0001) crystals were considered since they were found to be efficient for device applications. The results show that no carbon clusters or carbon-containing by-product could be detected at the interface of in situ or ex situ grown samples with an oxide layer thickness larger than 10 Å.

  • 55.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Surface and Interface Studies of Si-rich 4H-SiC and SiO22005Ingår i: Materials Science Forum Vols. 483-485, Trans Tech Publications Inc., 2005, s. 581-584Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A photoemission study of Si-rich polar and nonpolar 4H-SiC surfaces before andafter initial oxidation are presented. Core level and valence band data recorded usingsynchrotron radiation are utilized to explore the properties of these surfaces and of theinterfaces.The Si-rich surfaces showed three prominent surface Si 2p components. These componentsare strongly attenuated upon oxygen exposures and can not be detected after an exposure of3000 L. After exposures of ≥200 L the number of oxidation states, i.e. Si+1, Si+2 and Si+4oxidation states, and also their shifts are found to be the same as after initial oxidation of thesame surfaces prepared by in situ heating.Only one sharp C 1s core level is observed on the Si-rich surfaces. This is quite differentcompared to earlier findings on the same surfaces prepared by in situ heating whereprominent surface shifted C 1s components are found. After oxygen exposure of ~ 200 L theC 1s peak is broadened and an asymmetry is observed on the high binding energy side. Thistogether with the Si 2p results show that oxygen exposures of ~200 L affect not only the Sioverlayers. Layers in the SiC substrate are also affected since the C 1s peak is broadened andthe Si 2p spectrum show the same oxidation states as after large exposures and after oxidationof these surfaces prepared without Si overlayers.

  • 56.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Zakharov, A A
    Lund University.
    Balasubramanian , T
    Lund University.
    Homogeneous large-area graphene layer growth on 6H-SiC(0001)2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, nr 24, s. 245403-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 with earlier observations. Distinctly different results are observed from the ex situ graphene layers of different thicknesses, which are proposed as a guideline for determining graphene growth. Recorded C 1s spectra consisted of three components: bulk SiC, graphene (G), and interface (I), the latter being a 6 root 3 layer. Extracted intensity ratios of G/I were found to give a good estimate of the thickness of graphene. Differences are also revealed in micro low energy electron diffraction images and electron reflectivity curves. The diffraction patterns were distinctly different from a monolayer thickness up to three layers. At a larger thickness only the graphitelike spot was visible. The electron reflectivity curve showed a nice oscillation behavior with kinetic energy and as a function of the number of graphene layers. The graphene sheets prepared were found to be very inert and the interface between the substrate and the layer(s) was found to be quite abrupt. No free Si could be detected in or on the graphene layers or at the interface.

  • 57.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Zakharov, A.A.
    Balasubramanian, T.
    Single Layer Graphene Growth on 6H-SiC(0001)2009Konferensbidrag (Refereegranskat)
  • 58.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Watcharinyanon, Somsakul
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Zakharov, A A
    Lund University.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Epitaxial graphene on 6H-SiC and Li intercalation2010Ingår i: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 82, nr 20, s. 205402-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 time. Formation of a dipole layer at the interface, interpreted to originate from Li-Si bonding, is observed directly after Li deposition, and manifested by a 2 eV shift of the C 1s and Si 2p bulk SiC peaks. This indicates that Li atoms penetrate through the graphene and carbon buffer layer directly after deposition at room temperature since three pi bands are then moreover observed at the K point, instead of the single pi band for monolayer graphene. The existence of three pi bands is interpreted as a mixture of bilayer and monolayer graphene plus a difference in doping levels due to an uneven distribution of Li atoms. Li gives rise to electron doping of the graphene and results in a lowering of the Dirac point. After annealing to a few hundred degrees Celsius, a more even Li distribution and intercalation is obtained since then two distinct pi bands appear at the K point.

  • 59.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Uhrberg, Roger
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Zakharov, A A
    Lund University.
    Substrate orientation: A way towards higher quality monolayer graphene growth on 6H-SiC(0001)2009Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 15, s. L87-L90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 a smaller mis-orientation from on-axis (0.03 degrees) than on those with a larger (0.25 degrees). Two different types of a carbon atom networks, honeycomb and three-for-six arrangement, were atomically resolved in the graphene monolayer. These findings are of relevance for various potential applications based on graphene-SiC structures.

  • 60.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Zakharov, A A
    Lund University.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Large homogeneous mono-/bi-layer graphene on 6H-SiC(0001) and buffer layer elimination2010Ingår i: JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN 0022-3727, Vol. 43, nr 37, s. 374010-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 access to high-quality graphene sheets on a suitable substrate plays a crucial role for future electronics applications involving patterning. Different techniques used to characterize the graphene grown are summarized. We moreover show that atomic hydrogen exposures can convert a monolayer graphene sample on SiC(0 0 0 1) to bi-layer graphene without the carbon buffer layer. Thus, a new process to prepare large, homogeneous stable bi-layer graphene sheets on SiC(0 0 0 1) is presented. The process is shown to be reversible and should be very attractive for various applications, including hydrogen storage.

  • 61.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Zakharov, A A
    Lund University.
    Watcharinyanon, Somsakul
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    A low-energy electron microscopy and x-ray photo-emission electron microscopy study of Li intercalated into graphene on SiC(0001)2010Ingår i: NEW JOURNAL OF PHYSICS, ISSN 1367-2630, Vol. 12, nr 125015Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 pi-cones at the six equivalent K-points in the Brillouin zone before Li deposition but the presence of two pi-cones (pi-bands) after Li deposition and after heating to a few hundred degrees C. For 0 ML samples, no pi-band could be detected close to the Fermi level before deposition, but distinct pi-cones at the K-points were clearly resolved after Li deposition and after heating. Thus Li intercalation was revealed in both cases, transforming the carbon buffer layer (0 ML) to graphene. On 1 ML samples, but not on 0 ML, a (root 3 x root 3) R30 degrees diffraction pattern was observed immediately after Li deposition. This pattern vanished upon heating and then wrinkles/cracks appeared on the surface. Intercalation of Li was thus found to deteriorate the quality of the graphene layer, especially for 1 ML samples. These wrinkles/cracks did not disappear even after heating at temperatures andgt;= 500 degrees C, when no Li atoms remained on the substrate.

  • 62.
    Virojanadara, Chariya
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Zakharov, A A
    Lund University.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Buffer layer free large area bi-layer graphene on SiC(0001)2010Ingår i: SURFACE SCIENCE, ISSN 0039-6028, Vol. 604, nr 2, s. L4-L7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of hydrogen exposures on monolayer graphene grown on the silicon terminated SiC(0 0 0 1) surface is investigated using photoelectron spectroscopy (PES), low-energy electron microscopy (LEEM) and micro low-energy electron diffraction (mu-LEED). Exposures to ionized hydrogen are shown to have a pronounced effect on the carbon buffer (interface) layer. Exposures to atomic hydrogen are shown to actually convert/transform the monolayer graphene plus carbon buffer layer to bi-layer graphene, i.e. to produce carbon buffer layer free bi-layer graphene on SiC(0 0 0 1). This process is shown to be reversible, so the initial monolayer graphene plus carbon buffer layer situation is recreated after heating to a temperature of about 950 degrees C. A tentative model of hydrogen intercalation is suggested to explain this single to bi-layer graphene transformation mechanism. Our findings are of relevance and importance for various potential applications based on graphene-SiC structures and hydrogen storage.

  • 63.
    Watcharinyanon, Somsakul
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Xia, Chao
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Changes in structural and electronic properties of graphene grown on 6H-SiC(0001) induced by Na deposition2012Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, nr 8, s. 083711-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 in between the graphene and the buffer layer and some go even further into the substrate interface as indicated by the shift of the bulk SiC component in the C 1s and Si 2p core level spectra. The ARPES spectrum exhibits a lowering of the Dirac point indicating increased n-type doping of the monolayer graphene induced by the deposited Na atoms. Upon subsequently heating the sample, we found that a slightly elevated temperature is essential in order to promote Na intercalation. A fully Na intercalation at the graphene-SiC interface is obtained after heating at a temperature of about 75 degrees C. The intercalated Na decouples the buffer layer and transforms it into a second graphene layer so two pi-bands are observed in the ARPES spectra. Interestingly, the two bands show different locations of the Dirac point but both exhibit linear dispersion in the vicinity of the (K) over bar point and not the hyperbolic dispersion observed for AB stacked bi-layer graphene. When heating the sample to about 125 degrees C or higher, Na is found to leave the interface and the second graphene layer is transformed back to the carbon buffer layer.

  • 64.
    Watcharinyanon, Somsakul
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Xia, Chao
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Ytterbium oxide formation at the graphene-SiC interface studied by photoemission2013Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 31, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Synchrotron-based core level and angle resolved photoemission spectroscopy was used to study the formation of ytterbium (Yb) oxide at the graphene-SiC substrate interface. Oxide formation at the interface was accomplished in two steps, first intercalation of Yb into the interface region and then oxygen exposure while heating the sample at 260 degrees C to oxidize the Yb. After these processes, core level results revealed the formation of Yb oxide at the interface. The Yb 4f spectrum showed upon oxidation a clear valence change from Yb2+ to Yb3+. After oxidation the spectrum was dominated by emission from oxide related Yb3+ states and only a small contribution from silicide Yb2+ states remained. In addition, the very similar changes observed in the oxide related components identified in the Si 2p and Yb 4f spectra after oxidation and after subsequent heating suggested formation of a Si-Yb-O silicate at the interface. The electronic band structure of graphene around the (K) over bar -point was upon Yb intercalation found to transform from a single pi band to two pi bands. After Yb oxide formation, an additional third pi band was found to appear. These pi bands showed different locations of the Dirac point (E-D), i.e., two upper bands with E-D around 0.4 eV and a lower band with E-D at about 1.5 eV below the Fermi level. The appearance of three pi-bands is attributed to a mixture of areas with Yb oxide and Yb silicide at the interface.

  • 65.
    Watcharinyanon, Somsakul
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Zakharov, A. A.
    MAX-lab, Lund University.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Studies of Li intercalation of hydrogenated graphene on SiC(0001)2012Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 606, nr 3-4, s. 401-406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 to disappear after annealing. Some other Li atoms are found to penetrate through the bilayer graphene sample and into the interface where H already resides. This is revealed by the existence of shifted components, related to H–SiC and Li–SiC bonding, in recorded core level spectra. The Dirac point is found to exhibit a rigid shift to about 1.25 eV below the Fermi level, indicating strong electron doping of the graphene by the deposited Li. After annealing the sample at 300–400 °C formation of LiH at the interface is suggested from the observed change of the dipole layer at the interface. Annealing at 600 °C or higher removes both Li and H from the sample and a monolayer graphene sample is re-established. The Li thus promotes the removal of H from the interface at a considerably lower temperature than after pure H intercalation.

  • 66.
    Watcharinyanon, Somsakul
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Rb and Cs deposition on epitaxial graphene grown on 6H-SiC(0001)2011Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 605, nr 21-22, s. 1918-1922Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 from the metal to the graphene layer. The Dirac point of the single pi-cone is found to shift downwards away from the Fermi level by ca. 1.0 eV after alkali metal depositions. The adsorbed Rb and Cs atoms do initially disrupt the bonds in the graphene layer but after heating the bonds appear to be recreated when the alkali metal coverage start to decrease due to thermal desorption. None of these two alkali metals do intercalate into the graphene and buffer layer after depositing at room temperature or after heating. This is contrary to the case of Li where intercalation occurred directly after deposition.

  • 67.
    Watcharinyanon, Somsakul
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Osiecki, Jacek
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Zakharov, A A
    Lund University.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Uhrberg, Roger
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hydrogen intercalation of graphene grown on 6H-SiC(0001)2011Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 605, nr 17-18, s. 1662-1668Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atomic hydrogen exposures on a monolayer graphene grown on the SiC(0001) surface are shown to result in hydrogen intercalation. The hydrogen intercalation induces a transformation of the monolayer graphene and the carbon buffer layer to bi-layer graphene without a buffer layer. The STM, LEED, and core-level photoelectron spectroscopy measurements reveal that hydrogen atoms can go underneath the graphene and the carbon buffer layer and bond to Si atoms at the substrate interface. This transforms the buffer layer into a second graphene layer. Hydrogen exposure results initially in the formation of bi-layer graphene islands on the surface. With larger atomic hydrogen exposures, the islands grow in size and merge until the surface is fully covered with bi-layer graphene. A (root 3 x root 3)R30 degrees periodicity is observed on the bi-layer areas. ARPES and energy filtered XPEEM investigations of the electron band structure confirm that after hydrogenation the single pi-band characteristic of monolayer graphene is replaced by two pi-bands that represent bi-layer graphene. Annealing an intercalated sample, representing bi-layer graphene, to a temperature of 850 degrees C. or higher, re-establishes the monolayer graphene with a buffer layer on SiC(0001).

  • 68.
    Watcharinyanon, Somsakul
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Xia, Chao
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Niu, Yuran
    Lund University, Sweden.
    Zakharov, Alexei A.
    Lund University, Sweden.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Soft X-ray Exposure Promotes Na Intercalation in Graphene Grown on Si-Face SiC2015Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 8, nr 8, s. 4768-4777Artikel i tidskrift (Refereegranskat)
    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.

  • 69.
    Xia, Chao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Niu, Yuran
    Lund University, Sweden.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Effects of aluminum on epitaxial graphene grown on C-face SiC2015Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 19, s. 195306-Artikel i tidskrift (Refereegranskat)
    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.

  • 70.
    Xia, Chao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Niu, Yuran
    MAX-lab, Lund University, Sweden .
    Zakharov, Alexei A.
    MAX-lab, Lund University, Sweden .
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    High thermal stability quasi-free-standing bilayer graphene formed on 4H-SiC(0 0 0 1) via platinum intercalation2014Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 79, s. 631-635Artikel i tidskrift (Refereegranskat)
    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.

  • 71.
    Xia, Chao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Zakharov, A A
    MAX-lab, Lund University, Lund, Sweden.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Effects of Al on epitaxial graphene grown on 6H-SiC(0001)2014Ingår i: Materials Research Express, ISSN 2053-1591, Vol. 1, nr 1, s. 1-13, artikel-id 015606Artikel i tidskrift (Refereegranskat)
    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.

  • 72.
    Xia, Chao
    et al.
    Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Tal, Alexey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Olovsson, Weine
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Nationellt superdatorcentrum (NSC).
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Effects of rhenium on graphene grown on SiC(0001)2018Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 222, s. 117-121Artikel i tidskrift (Refereegranskat)
    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.

  • 73.
    Xia, Chao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Watcharinyanon, Somsakul
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Zakharov, A A.
    Lund University, Sweden .
    Johansson, Leif I.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Detailed studies of Na intercalation on furnace-grown graphene on 6H-SiC(0001)2013Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 613, s. 88-94Artikel i tidskrift (Refereegranskat)
    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.

  • 74.
    Xia, Chao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Watcharinyanon, Somsakul
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Zakharov, A A
    Lund University.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif I
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Si intercalation/deintercalation of graphene on 6H-SiC(0001)2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 4, s. 045418-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 (mu-LEED). After Si deposition on samples kept at room temperature, small Si droplets are observed on the surface, but no intercalation can be detected. Intercalation is revealed to occur at an elevated temperature of about 800. C. The Si is found to migrate to the interface region via defects and domain boundaries. This observation may provide an answer to the problem of controlling homogeneous bi-/multilayer graphene growth on nearly perfect monolayer graphene samples prepared on SiC(0001). Likewise, Si penetrates more easily small monolayer graphene domains because of the higher density of domain boundaries. Upon annealing at 1000-1100 degrees C, formation of SiC on the surface is revealed by the appearance of a characteristic surface state located at about 1.5 eV below the Fermi level. A streaked mu-LEED pattern is also observed at this stage. The SiC formed on the surface is found to decompose again after annealing at temperatures higher than 1200 degrees C.

  • 75.
    Yakimova, Rositsa
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Iakimov, Tihomir
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kakanakova-Gueorguie, Anelia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Jacobson, Henrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Effect of High Temperature Annealing on Surface and Bulk Characteristics of 4H-SiC2001Ingår i: Proc. of the 43rd Electronic Material Conference, 2001Konferensbidrag (Refereegranskat)
  • 76.
    Yakimova, Rositsa
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Jacobson, H
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kakanakova-Georgieva, Anelia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Iakimov, Tihomir
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Virojanadara, Chariya
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Janzén, Erik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Impact of the initial surface conditions on defect appearance in 4H-SiC epilayers2002Ingår i: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, s. 283-286Konferensbidrag (Refereegranskat)
    Abstract [en]

    Effect of surface irregularities on defect nucleation and development in thick epitaxial layers of 4H-SiC has been investigated. It has been shown that during growth extended defects may undergo transformation and thus stacking faults can be formed, which is favored in thicker layers (e.g. 50mum). Network of misfit dislocations appears if the initial surface has a certain critical roughness and a lower surface energy. Evidence has been presented that well ordered graphite layer might form on the substrates during the preheating stage prior to growth via sublimation.

  • 77.
    Yakimova, Rositsa
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Gogova, Daniela
    Leibniz Institute for Crystal Growth, Berlin, Germany.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Siche, D.
    Leibniz Institute for Crystal Growth, Berlin, Germany.
    Larsson, Krister
    Department of Materials Chemistry, Uppsala University, Uppsala, Sweden.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Analysis of the Formation Conditions for Large Area Epitaxial Graphene on SiC Substrates2010Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2 / [ed] Bauer, AJ; Friedrichs, P; Krieger, M; Pensl, G; Rupp, R; Seyller, T, Trans Tech Publications Inc., 2010, Vol. 645-648, s. 565-568Konferensbidrag (Refereegranskat)
    Abstract [en]

    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 in an inductively heated furnace. The epitaxial graphene is characterized by ARPES, LEEM and Raman spectroscopy. Theoretical studies are employed to get better insight of graphene patterns and stability. Reproducible results of single layer graphene on the Si-face of 6H and 4H-SiC polytypes have been attained. It is demonstrated that thickness uniformity of graphene is very sensitive to the substrate miscut.

  • 78.
    Zakharov, A. A
    et al.
    MAX-lab, Lund University.
    Virojanadara, Chariya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Watcharinyanon, Somsakul
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Leif
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Nano-scale 3D (E,kx,ky) band structure imaging on graphene and intercalated graphene2011Ingår i: IBM Journal of Research and Development, ISSN 0018-8646, E-ISSN 2151-8556, Vol. 55, nr 4, s. 6:1-6:6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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) graphene grown ex situ on 6H-SiC(0001) substrates where a carbon buffer layer (zero ML) forms underneath the graphene layer(s). We demonstrate that the interfacial buffer layer can be converted into quasi-free-standing graphene upon intercalation of Li atoms at the interface and that such a graphene is structurally and electronically decoupled from the SiC substrate. High energy and momentum resolution of the X-PEEM, along with short data acquisition times from submicrometer areas on the surface demonstrates the uniqueness and the versatility of the technique and broadens its impact and applicability within surface science and nanotechnology.

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