| 181. |
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Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots
- 2016
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 6:11
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Tidskriftsartikel (refereegranskat)abstract
- Tuning the emission energy of graphene quantum dots (GQDs) and understanding the reason of tunability is essential for the GOD function in optoelectronic devices. Besides material-based challenges, the way to realize chemical doping and band gap tuning also pose a serious challenge. In this study, we tuned the emission energy of GQDs by substitutional doping using chlorine, nitrogen, boron, sodium, and potassium dopants in solution form. Photoluminescence data obtained from (Cl- and N-doped) GQDs and (B-, Na-, and K-doped) GQDs, respectively exhibited red- and blue-shift with respect to the photoluminescence of the undoped GQDs. X-ray photoemission spectroscopy (XPS) revealed that oxygen functional groups were attached to GQDs. We qualitatively correlate red-shift of the photoluminescence with the oxygen functional groups using literature references which demonstrates that more oxygen containing groups leads to the formation of more defect states and is the reason of observed red-shift of luminescence in GQDs. Further on, time resolved photoluminescence measurements of Cl- and N-GQDs demonstrated that Cl substitution in GQDs has effective role in radiative transition whereas in N-GQDs leads to photoluminescence (PL) quenching with non-radiative transition to ground state. Presumably oxidation or reduction processes cause a change of effective size and the bandgap.
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| 182. |
- Tuominen, M., et al.
(författare)
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Investigation of domain evolution in sublimation epitaxy of SiC
- 1998
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 193:1-2, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- High resolution X-ray diffractometry has been applied to study domain misorientation in SiC epi-layers grown by the sublimation epitaxy method. A pronounced effect of the growth conditions on the mosaicity of the epi-layer has been observed. The results are discussed in terms of domain evolution and structural changes during the epi-growth under different growth conditions.
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| 183. |
- Tzalenchuk, Alexander, et al.
(författare)
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Engineering and metrology of epitaxial graphene
- 2011
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Ingår i: Solid State Communications. - : Elsevier. - 0038-1098 .- 1879-2766. ; 151:16, s. 1094-1099
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Tidskriftsartikel (refereegranskat)abstract
- ere we review the concepts and technologies, in particular photochemical gating, which contributed to the recent progress in quantum Hall resistance metrology based on large scale epitaxial graphene on silicon carbide.
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| 184. |
- Tzalenchuk, Alexander, et al.
(författare)
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Towards a quantum resistance standard based on epitaxial graphene
- 2010
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Ingår i: NATURE NANOTECHNOLOGY. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 5:3, s. 186-189
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Tidskriftsartikel (refereegranskat)abstract
- The quantum Hall effect(1) allows the international standard for resistance to be defined in terms of the electron charge and Plancks constant alone. The effect comprises the quantization of the Hall resistance in two-dimensional electron systems in rational fractions of R-K = h/e(2) = 25 812.807 557(18) Omega, the resistance quantum(2). Despite 30 years of research into the quantum Hall effect, the level of precision necessary for metrology-a few parts per billion-has been achieved only in silicon and III-V heterostructure devices(3-5). Graphene should, in principle, be an ideal material for a quantum resistance standard(6), because it is inherently two-dimensional and its discrete electron energy levels in a magnetic field (the Landau levels(7)) are widely spaced. However, the precisions demonstrated so far have been lower than one part per million(8). Here, we report a quantum Hall resistance quantization accuracy of three parts per billion in monolayer epitaxial graphene at 300 mK, four orders of magnitude better than previously reported. Moreover, by demonstrating the structural integrity and uniformity of graphene over hundreds of micrometres, as well as reproducible mobility and carrier concentrations across a half-centimetre wafer, these results boost the prospects of using epitaxial graphene in applications beyond quantum metrology.
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| 185. |
- Unéus, Lars, et al.
(författare)
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The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1419-1422, s. 1419-1422
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Konferensbidrag (refereegranskat)abstract
- We present here the effect of a hydrogen anneal at 600degreesC for Schottky sensor devices based on n- and p-type 4H SiC. The devices have gate contacts of Ta/Pt, or TaSix/Pt. The catalytic metal gate dissociates hydrogen and thus promotes diffusion of hydrogen atoms into the SiC, where the atoms will trap or react with different impurities, defects or surface states. This will change parameters such as the carrier concentrations, the defect density of the material or the surface resistivity at the SiC/SiO2 interface. The current-voltage and the capacitance-voltage characteristics were measured before and after annealing in hydrogen and oxygen containing atmosphere, and the results show a reversible effect in the I-V characteristics.
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| 186. |
- Vagin, Mikhail, et al.
(författare)
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Bioelectrocatalysis on Anodized Epitaxial Graphene and Conventional Graphitic Interfaces
- 2019
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Ingår i: ChemElectroChem. - : WILEY-V C H VERLAG GMBH. - 2196-0216. ; 6:14, s. 3791-3796
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Tidskriftsartikel (refereegranskat)abstract
- Graphitic materials exhibit significant anisotropy due to the difference in conductivity in a single layer and between adjacent layers. This anisotropy is manifested on epitaxial graphene (EG), which can be manipulated on the nanoscale in order to provide tailor-made properties. Insertion of defects into the EG lattice was utilized here for controllable surface modification with a model biocatalyst and the properties were quantified by both electrochemical and optical methods. A comparative evaluation of the electrode reaction kinetics on the enzyme-modified 2D material vs conventional carbon electrode materials revealed a significant enhancement of mediated bioelectrocatalysis at the nanoscale.
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| 187. |
- Vagin, Mikhail, et al.
(författare)
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Monitoring of epitaxial graphene anodization
- 2017
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Ingår i: Electrochimica Acta. - : Pergamon Press. - 0013-4686 .- 1873-3859. ; 238, s. 91-98
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Tidskriftsartikel (refereegranskat)abstract
- Anodization of a graphene monolayer on silicon carbide was monitored with electrochemical impedance spectroscopy. Structural and functional changes of the material were observed by Raman spectroscopy and voltammetry. A 21 fold increase of the specific capacitance of graphene was observed during the anodization. An electrochemical kinetic study of the Fe(CN)(6)(3) (/4) redox couple showed a slow irreversible redox process at the pristine graphene, but after anodization the reaction rate increased by several orders of magnitude. On the other hand, the Ru(NH3) (3+/2+)(6) redox couple proved to be insensitive to the activation process. The results of the electron transfer kinetics correlate well with capacitance measurements. The Raman mapping results suggest that the increased specific capacitance of the anodized sample is likely due to a substantial increase of electron doping, induced by defect formation, in the monolayer upon anodization. The doping concentration increased from less than 1 x 10(13) of the pristine graphene to 4-8 x 10(13) of the anodized graphene. (C) 2017 Elsevier Ltd. All rights reserved.
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| 188. |
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| 189. |
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| 190. |
- Vasiliauskas, Remigijus, et al.
(författare)
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Cubic SiC formation on the C-face of 6H-SiC (0001) substrates
- 2012
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 348:1, s. 91-96
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Tidskriftsartikel (refereegranskat)abstract
- Nucleation and subsequent growth of cubic SiC (111) on Si- and C-faces of nominally on-axis 6H-SiC substrates was investigated. More uniform nuclei and twin boundary distribution was observed when 3C-SiC was grown on the C-face. This was attributed to a lower critical supersaturation ratio. A new type of defects which appear as pits in the C-face 3C-SiC layers related to homoepitaxial 6H-SiC spiral growth was found and described. The evaluation of the growth driving force for both polar faces showed that the homoepitaxial 6H-SiC spirals were not overgrown on the C-face due to low maximum supersaturation ratio. The XRD ω-rocking characterization shows a better structural quality of the 3C-SiC was grown on the Si-face, however on the C-face the uniformity over the whole sample was higher. Unintentional doping by N (~1016 cm-3) was slightly higher on the C-face while Al doping was higher (~1014 cm-3) on the Si-face of the grown material, similarly to the doping of hexagonal SiC polytypes.
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