| 1. |
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Book of Abstracts : 1st International Workshop on Functional Oxide (FOX) Materials
- 2015
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Proceedings (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Oxide semiconductors are an important part of the functional materials field. Technological accessibility (physical & chemical synthesis), diversity of geometrical shapes (bulk, films, nanostructures) and environmental stability combined with ambience sensitivity makes them promising materials for plenty of future applications. Among other, ZnO, Al2O3, GaO, NiO, TiOx, Gd2O3, Fe3O4 and graphene oxide are considered as materials for both active and passive components in many applications: transparent conductive coatings, gas sensors, biosensors, tomography markers, light emitters, thermoelectric materials, catalysts and many others. We expect the experts to present their latest results on fabrication, characterization and application of the oxide materials.
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| 2. |
- Boosalis, Alexander, et al.
(författare)
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Spectroscopic Mapping Ellipsometry of Graphene Grown on 3C SiC
- 2012
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Ingår i: MRS Proceedings Volume 1407. - : Springer Science and Business Media LLC. ; , s. aa20-43
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Konferensbidrag (refereegranskat)abstract
- Spectroscopic mapping ellipsometry measurements in the visible spectrum (1.25 to 5.35 eV) are performed to determine the lateral variations of epitaxial graphene properties as grown on 3C SiC. Data taken in the visible spectrum is sensitive to both the Drude absorption of free charge carriers and the characteristic exciton enhanced van Hove singularity at 5 eV. Subsequent analysis with simple oscillator models allows the determination of physical parameters such as free charge carrier scattering time and local graphene thickness with a lateral resolution of 50 microns.
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| 3. |
- Eriksson, Jens, et al.
(författare)
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The influence of substrate morphology on thickness uniformity and unintentional doping of epitaxial graphene on SiC
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:24, s. 241607-
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Tidskriftsartikel (refereegranskat)abstract
- A pivotal issue for the fabrication of electronic devices on epitaxial graphene on SiC is controlling the number of layers and reducing localized thickness inhomogeneities. Of equal importance is to understand what governs the unintentional doping of the graphene from the substrate. The influence of substrate surface topography on these two issues was studied by work function measurements and local surface potential mapping. The carrier concentration and the uniformity of epitaxial graphene samples grown under identical conditions and on substrates of nominally identical orientation were both found to depend strongly on the terrace width of the SiC substrate after growth.
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| 4. |
- Johansson, Leif, et al.
(författare)
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Is the Registry Between Adjacent Graphene Layers Grown on C-Face SiC Different Compared to That on Si-Face SiC
- 2013
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 3:1, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- 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 of samples showed formation of μm-sized grains of graphene. The sharp (1 × 1) μ-LEED pattern and six Dirac cones observed in constant energy photoelectron angular distribution patterns from a grain showed that adjacent layers are not rotated relative to each other, but that adjacent grains in general have different azimuthal orientations. Diffraction spots from the SiC substrate appeared in μ-LEED patterns collected at higher energies, showing that the rotation angle between graphene and SiC varied. C 1s spectra collected did not show any hint of a carbon interface layer. A hydrogen treatment applied was found to have a detrimental effect on the graphene quality for both types of samples, since the graphene domain/grain size was drastically reduced. From hydrogen treated samples, μ-LEED showed at first a clear (1 × 1) pattern, but within minutes, a pattern containing strong superstructure spots, indicating the presence of twisted graphene layers. The LEED electron beam was found to induce local desorption of hydrogen. Heating a hydrogenated C-face graphene sample did not restore the quality of the original as-grown sample.
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| 5. |
- Jokubavicius, Valdas, et al.
(författare)
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Effects of source material on epitaxial growth of fluorescent SiC
- 2012
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 522, s. 7-10
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Tidskriftsartikel (refereegranskat)abstract
- The growth of fluorescent SiC using Fast Sublimation Growth Process was demonstrated using different types of SiC source materials. These were prepared by (i) high-temperature hot pressing, (ii) chemical vapor deposition and (iii) physical vapor transport. The optimized growth rates of 50 μm/h, 170 μm/h and 200 μm/h were achieved using the three types of sources, respectively. The best results in respect to growth rates are obtained using higher density sources. Fluorescent SiC layers with mirror-like morphology, very good crystal quality and yellowish or warm white light photoluminescence at room temperature were grown using all three types of the source materials.
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| 6. |
- Jokubavicius, Valdas, et al.
(författare)
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Geometrical Control of 3C and 6H-SiC Nucleation on Low Off-Axis Substrates
- 2011
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 679-680, s. 103-106
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Tidskriftsartikel (refereegranskat)abstract
- Growth of 3C or 6H-SiC epilayers on low off-axis 6H-SiC substrates can be mastered by changing the size of the on axis plane formed by long terraces in the epilayer using geometrical control. The desired polytype can be selected in thick (~200 µm) layers of both 6H-SiC and 3C-SiC polytypes on substrates with off-orientation as low as 1.4 and 2 degrees. The resultant crystal quality of the 3C and the 6H-SiC epilayers, grown under the same process parameters, deteriorates when lowering the off-orientation of the substrate.
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| 7. |
- Jokubavicius, Valdas, et al.
(författare)
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On stabilization of 3C-SiC using low off-axis 6H-SiC substrates
- 2012
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Konferensbidrag (refereegranskat)abstract
- Heteroepitaxial growth of 3C-SiC on 0.8 and 1.2 degree off-oriented 6H-SiC substrates was studied using a sublimation growth process. The 3C-SiC layers were grown at high growth rates with layer thickness up to 300 µm. The formation and the quality of 3C-SiC are influenced by the off-orientation of the substrate, the growth temperature (studied temperature range from 1750 oC to 1850oC), and the growth ambient (vacuum at 5*10-5 mbar and nitrogen at 5*10-1 mbar). The largest domains of 3C-SiC and the lowest number of double positioning boundaries were grown using nitrogen ambient and the highest growth temperature. The combined use of low off-axis substrate and high growth rate is a potential method to obtain material with bulk properties.
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| 8. |
- Ou, Yiyu, et al.
(författare)
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Characterization of donor-acceptor-pair emission in fluorescent 6H-SiC
- 2012
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Ingår i: Physica Scripta. - : Institute of Physics Publishing Ltd. - 0031-8949 .- 1402-4896. ; T148, s. 014003-
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Tidskriftsartikel (refereegranskat)abstract
- We investigated donor-acceptor-pair emission in N-B-doped 6H-SiC samples by using photoluminescence (PL) and angle-resolved PL. It is shown that n-type doping with concentrations larger than 10(18) cm(-3) is favorable for observing luminescence, and increasing nitrogen results in stronger luminescence. A dopant concentration difference greater than 4x10(18) cm(-3) is proposed to help achieve intense PL. Angular-dependent PL was observed that was attributed to the Fabry-Perot microcavity interference effect, and a strong luminescence intensity in a large emission angle range was also achieved. The results indicate that N-B-doped fluorescent SiC is a good wavelength converter in white LED applications.
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| 9. |
- Ou, Yiyu, et al.
(författare)
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Omnidirectional luminescence enhancement of fluorescent SiC via pseudoperiodic antireflective subwavelength structures
- 2012
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 37:18, s. 3816-3818
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, an approach of fabricating pseudoperiodic antireflective subwavelength structures (ARS) on fluorescent SiC by using self-assembled etch mask is demonstrated. By applying the pseudoperiodic (ARS), the average surface reflectance at 6° incidence over the spectral range of 390–785 nm is dramatically suppressed from 20.5% to 1.62%, and the hydrophobic surface with a large contact angle of 98° is also achieved. The angle-resolved photoluminescence study presents a considerable omnidirectional luminescence enhancement with an integral intensity enhancement of 66.3% and a fairly preserved spatial emission pattern.
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| 10. |
- Ou, Y., et al.
(författare)
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Photoluminescence and Raman spectroscopy characterization of boron-and nitrogen-doped 6H silicon carbide
- 2012
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Ingår i: Silicon Carbide and Related Materials 2011. - : Trans Tech Publications Inc.. - 9783037854198 ; , s. 233-236
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Konferensbidrag (refereegranskat)abstract
- Nitrogen-boron doped 6H-SiC epilayers grown on low off-axis 6H-SiC substrates have been characterized by photoluminescence and Raman spectroscopy. The photoluminescence results show that a doping larger than 10 18 cm -3 is favorable to observe the luminescence and addition of nitrogen leads to an increased luminescence. A dopant concentration difference larger than 4×10 18 cm -3 is proposed to achieve intense photoluminescence. Raman spectroscopy further confirmed the doping type and concentrations for the samples. The results indicate that N-B doped SiC can serve as a good wavelength converter in white LEDs applications.
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