| 1. |
- Beshkova, Milena, et al.
(författare)
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Atomic Layer Deposition of AlN on Graphene
- 2021
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Ingår i: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 218:17
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Tidskriftsartikel (refereegranskat)abstract
- Graphene is a material with great promise for several applications within electronics. However, using graphene in any such application requires its integration in a stack of thin layers of materials. The ideal structure of graphene has a fully saturated surface without any binding sites for chemisorption of growth species, making film growth on graphene highly challenging. Herein, an attempt to deposit very thin layers of AlN using an atomic layer deposition approach is reported. It is demonstrated using X-ray photoelectron spectroscopy that Al-N are formed in the films deposited on graphene and shown by scanning electron microscopy and atomic force microscopy that the films have an island morphology. These results may be considered promising toward the development of a growth protocol for AlN on graphene and possibly also for 2D AlN fabrication.
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| 2. |
- Beshkova, Milena, et al.
(författare)
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Low-pressure sublimation epitaxy of AlN films - growth and characterization
- 2004
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 76, s. 143-146
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial layers of aluminum nitride have been grown at temperatures 1900-2400degreesC on 10 x 10 mm(2) 4H-SiC substrate via sublimation recondensation in an RF heated graphite furnace. The source material was polycrystalline sintered AlN. A maximum growth rate of about 100 mum/h was achieved at 2400degreesC and seed to source distance of 1 mm. The surface morphology reflects the hexagonal symmetry of the seed suggesting an epitaxial growth. This was confirmed by X-ray diffraction (XRD). The spectra showed very strong and well-defined (0002) reflection position at around 36.04degrees in symmetric Theta-2Thetascans for all samples. Micro-Raman spectroscopy reveals that the films have a wurtzite structure. It is evidenced by the appearance of the A(1) (TO) (at 601 cm(-1)) and E-2((2)) (at 651 cm(-1)) lines in the spectra. Secondary-ion mass spectroscopy (SIMS) results showed a low concentration of carbon incorporation in the AlN films. A correlation between the growth conditions and properties of the AlN layers was established.
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| 3. |
- Beshkova, Milena, et al.
(författare)
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Properties and potential applications of two-dimensional AlN
- 2020
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Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 176
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Forskningsöversikt (refereegranskat)abstract
- The success of Graphene has triggered the research interest in other stable, single and few-atom-thick layers of van der Waals materials, which can possess attractive and technologically useful properties. Other complex structures, such as boron nitride, MXenes and metal chalcogenides have been successfully synthesized as layered materials showing advanced properties. Here, after an introduction briefing novel 2D materials, we focus on 2D AlN and present a review covering theoretical considerations on the stability of an infinite hexagonal AlN (h-AlN) sheet, differences that occur in the electronic structure between bulk AlN and single layer and discuss possible methods of tuning their electronic and magnetic properties by manipulating the surface and strain using DFT (density functional theory) computations. We address potential applications of 2D-AlN with an emphasis on gas sensing for CO2, CO, H-2, O-2, NO and NO2 in the presence of NH3. Further, we discuss some growth strategies of AlN single layer and few layers on different substrates. 2D AlN layers and nanotubes with ultrawide bandgap (9.20-9.60 eV) which shows a great potential to support innovative and front-end development of deep-ultraviolet optoelectronic devices are illustrated.
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| 4. |
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| 5. |
- Beshkova, Milena, et al.
(författare)
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Properties of 3C-SiC Grown by Sublimation Epitaxy on Different Type of Substrates
- 2010
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Ingår i: Materials Science Forum, Vols. 645-648. - : Transtec Publications; 1999. ; , s. 183-186
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Konferensbidrag (refereegranskat)abstract
- 3C-SiC layers have been grown by using sublimation epitaxy at a temperature of 2000 degrees C, on different types of on-axis 6H-SiC(0001) substrates. The influence of the type of substrate on the morphology of the layers investigated by Atomic Force Microscopy (AFM) is discussed. Stacking faults are studied by reciprocal space map (RSM) which shows that double positions domains exists.
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| 6. |
- Beshkova, Milena, et al.
(författare)
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Properties of AlN layers grown by sublimation epitaxy
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 995-998
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Konferensbidrag (refereegranskat)abstract
- Epitaxial layers of aluminum nitride (AlN)less than or equal to 80 mum thick have been grown at the temperatures 1900 and 2100 degreesC on 10x10mm(2) 4H-SiC substrates via sublimation recondensation in a RF heated graphite furnace. The source material was polyerystalline sintered AlN. A maximum growth rate of 80 mum/h was achieved at 2100degreesC and seed to source separation of I mm. The surface morphology reflects the hexagonal symmetry of the seed that suggesting an epitaxial growth. All crystals show strong and well defined single crystalline XRD patterns. Only the (002) reflection positioned at around 36.04 was observed in symmetric Theta-2Theta scan. The rocking curves FWHM (full width half maximum) and peak positions arc reported.
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| 7. |
- Beshkova, Milena, 1975-, et al.
(författare)
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Structural Properties of 3C-SiC Grown by Sublimation Epitaxy
- 2009
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Ingår i: ECSCRM2009,2009. - Materials Science Forum Vols. 615-617 : Trans Tech Publications. - 9780878493340 ; , s. 181-184
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Konferensbidrag (refereegranskat)abstract
- The present paper deals with morphological and structural investigation of 3C-SiC layers grown by sublimation epitaxy on on axis 6H-SiC(0001) at source temperature 2000 °C, under vacuum conditions (<10-5 mbar) and different temperature gradients in the range of 5-8 °C/mm. The layer grown at a temperature gradient 6 °C/mm has the largest average domain size of 0.4 mm2 assessed by optical microscope in transmission mode. The rocking curve full width at half maximum (FWHM) of (111) reflection is 43 arcsec which suggests good crystalline quality. The AFM image of the same layer shows steps with height 0.25 nm and 0.75 nm which are characteristic of a stacking fault free 3C-SiC surface and c-axis repeat height, respectively.
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| 8. |
- Beshkova, Milena, et al.
(författare)
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Sublimation epitaxy of 3C-SiC grown at Si- and C-rich conditions
- 2012
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 86:10, s. 1595-1599
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Tidskriftsartikel (refereegranskat)abstract
- 3C-SiC layers have been grown by using sublimation epitaxy at a source temperature of 2000 degrees C, under vacuum conditions (andlt;10(-5) mbar) on well oriented (on-axis) 6H-SiC (0001) substrates. Close space sublimation growth geometry has been used in a RF-heated furnace employing high-purity graphite crucible with a possibility to change the growth environment from Si vapor-rich to C vapor-rich. The optical microscopy in transmission mode reveals continuous 3C-domains for 3C-SiC with less than 0.4% 6H-inclusions for the layer grown at Si-rich conditions, and separate 3C-SiC domains for the layer grown at C-rich conditions. The type of 6H-inclusions for layers with continuous domain structure investigated by Atomic Force Microscopy (AFM) is discussed. 2Theta-omega scan shows 0006 and 111 peaks coming from the substrate and the layer, respectively with a higher intensity of the 111 peak for 3C-SiC grown at Si-rich conditions which is related with the continuous character of the 3C-SiC domains.
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| 9. |
- Beshkova, Milena, et al.
(författare)
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Sublimation epitaxy of AIN layers on 4H-SiC depending on the type of crucible
- 2003
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Ingår i: Journal of materials science. Materials in electronics. - 0957-4522 .- 1573-482X. ; 14:10-12, s. 767-768
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial layers of aluminum nitride less than or equal to335 mum thick have been grown attemperatures of 1900 and 2100degreesC on 10 x 10 mm(2) (0001)-oriented alpha(4H) silicon carbide (SiC), with growth times of 1 and 4h, via sublimation-recondensation in a RF-heated graphite furnace. The source material was polycrystalline AIN. The sublimation process was performed in three types of graphite (C) crucible: C-1, C-2 with inner diameters of 35 and 51 mm, respectively, and C-3 with the same inner diameter as C-1, but coated with a layer of TaC. The surface morphology reflects the hexagonal symmetry of the substrate, suggesting an epitaxial growth for samples grown in C-1 and C-3 crucibles for all growth conditions. The same symmetry is observed for AIN layers grown in the C-2 crucible, but only at 2100degreesC. X-ray diffraction analyses confirm the epitaxial growth of AIN samples with the expected hexagonal symmetry. A high-resolution X-ray diffractometer was used to assess the quality of the single crystals. A full width at half maximum of 242 arcsec was achieved for an AIN layer grown in the crucible coated with TaC. (C) 2003 Kluwer Academic Publishers.
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| 10. |
- Beshkova, Milena, et al.
(författare)
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Sublimation epitaxy of AlN layers grown by different conditions on 4H-SiC substrates
- 2007
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Ingår i: Journal of Optoelectronics and Advanced Materials. - 1454-4164 .- 1841-7132. ; 9:1, s. 213-216
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial layers of aluminium nitride were grown at temperature 2100 degrees C on 10X10 mm(2) 4H-SiC substrates via a sublimation-recondensation method in an RF heated graphite furnace. The source material was polycrystalline sintered AIN. Growths of AIN layers in vacuum and pure nitrogen at 20 mbar were compared. MA maximum growth rate of 70 mu m/h was achieved in a pure N-2 atmosphere. The surface morphology reveals the hexagonal symmetry of the seeds, suggesting an epitaxial growth. This was confirmed by High-Resolution X-Ray Diffraction. The spectra showed a strong and well defined (0002) reflection positioned at 36.04 degrees in a symmetric theta-2 theta scan for both samples. Micro-Raman spectroscopy revealed that the films had a wurtzite structure. Rutherford Backscattering Spectrometry indicated the quality with a relative chi(min) parameter 0.68.
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| 11. |
- Scajev, P., et al.
(författare)
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On applicability of time-resolved optical techniques for characterization of differently grown 3C-SiC crystals and heterostructures
- 2012
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Ingår i: HETEROSIC and WASMPE 2011. - : Trans Tech Publications Inc.. ; , s. 159-163
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Konferensbidrag (refereegranskat)abstract
- We applied a number of time-resolved optical techniques for investigation of optical and photoelectrical properties of cubic SiC grown by different technologies on different substrates. The excess carriers were injected by a short laser pulse and their dynamics was monitored by free-carrier absorption, light-induced transient grating, and photoluminescence techniques in a wide excitation range. Combining an optical and electrical probe beam delay, we found that free carrier lifetimes in differently grown layers vary from few ns up to 20 mu s. Temperature dependences of carrier diffusivity and lifetime revealed a pronounced carrier trapping in thin sublimation grown layers. In free-standing layers and thick sublimation layers, the ambipolar mobility was found the highest (120 cm(2)/Vs at room temperature). A linear correlation between the room-temperature band edge emission and carrier lifetime in differently grown layers was attributed to defect density, strongly dependent on the used growth conditions.
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| 12. |
- Shtepliuk, Ivan, et al.
(författare)
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Exploring the Interface Landscape of Noble Metals on Epitaxial Graphene
- 2021
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 218:17
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the interaction between noble metals (NMs) and epitaxial graphene is essential for the design and fabrication of novel devices. Within this framework, a combined experimental and theoretical investigation of the effect of vapor-deposited NM (silver [Ag] and gold [Au]) nanostructures on the vibrational and electronic properties of monolayer epitaxial graphene (MLG) on 4H-SiC is presented. Large sets of Raman scattering data are analyzed using supervised classification and statistical methods. This analysis enables identification of the specific Raman fingerprints of Au- and Ag-decorated MLG originating from different dispersion interactions and charge transfer at the metal nanostructure/MLG interface. It is found that Raman scattering spectra of Au-decorated MLG feature a set of allowed phonon modes similar to those in pristine MLG, whereas the stronger Ag physisorption triggers an activation of defect-related phonon modes and electron doping of MLG. A principal component analysis (PCA) and linear discriminant analysis (LDA) are leveraged to highlight the features in phonon dispersion of MLG that emanate from the NM deposition process and to robustly classify large-scale Raman spectra of metal-decorated graphene. The present results can be advantageous for designing highly selective sensor arrays on MLG patches decorated with different metals.
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| 13. |
- Vasiliauskas, Remigijus, 1982-, et al.
(författare)
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Two-dimensional nucleation of cubic and 6H silicon carbide
- 2009
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Ingår i: ECSCRM2008,2008. - Materials Science Forum Vols. 615-617 : Trans Tech Publications. - 9780878493340 ; , s. 189-192
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Konferensbidrag (refereegranskat)abstract
- The initial stage of heteroepitaxial growth of 3C-SiC and homoepitaxial growth of 6H-SiC on nominal 6H-SiC on-axis substrates has been studied. Before 3C-SiC starts to nucleate, 6H-SiC grows in a step-flow growth mode due to a slight off-orientation of the substrate surface already at about 1500oC. In the 1650-1700oC temperature interval 3C-SiC nucleates as 2D islands. A distance away from the 3C-SiC island 6H-SiC grows in step-flow mechanism. In the vicinity of the 3C-SiC islands the 6H-SiC growth steps start to change direction and even split into two steps with the equal height of 0.5 nm, which is approaching the unit cell size of cubic SiC. When the supersaturation is lower in comparison with the conditions for 3C-SiC growth, there is only formation of 6H-SiC, i.e. homoepitaxial growth. The growth mode of 6H-SiC is dependent on temperature. At the lowest temperature there is spiral growth while at higher temperature 2D nucleation is preferred.
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| 14. |
- Zoulis, Georgios, et al.
(författare)
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Investigation of Low Doped n-Type and p-Type 3C-SiC Layers Grown on 6H-SiC Substrates by Sublimation Epitaxy
- 2010
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Ingår i: Silicon Carbide and Related Materials 2009. ; , s. 179-182
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Konferensbidrag (refereegranskat)abstract
- Both, n-type and p-type 3C-SiC samples grown on 6H-SiC substrates by sublimation epitaxy have been investigated. From low temperature photoluminescence studies, we demonstrate a low level of residual (n and/or p-type) doping with weak compensation, which is confirmed by secondary ion mass spectroscopy in the case of p-type samples.
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