| 1. |
- Chubarov, Mikhail, et al.
(författare)
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Initial stages of growth and the influence of temperature during chemical vapor deposition of sp(2)-BN films
- 2015
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 33:6, s. 061520-
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the structural evolution of thin films, starting by the initial stages of growth, is important to control the quality and properties of the film. The authors present a study on the initial stages of growth and the temperature influence on the structural evolution of sp(2) hybridized boron nitride (BN) thin films during chemical vapor deposition (CVD) with triethyl boron and ammonia as precursors. Nucleation of hexagonal BN (h-BN) occurs at 1200 degrees C on alpha-Al2O3 with an AlN buffer layer (AlN/alpha-Al2O3). At 1500 degrees C, h-BN grows with a layer-by-layer growth mode on AlN/alpha-Al2O3 up to similar to 4 nm after which the film structure changes to rhombohedral BN (r-BN). Then, r-BN growth proceeds with a mixed layer-by-layer and island growth mode. h-BN does not grow on 6H-SiC substrates; instead, r-BN nucleates and grows directly with a mixed layer-by-layer and island growth mode. These differences may be caused by differences in substrate surface temperature due to different thermal conductivities of the substrate materials. These results add to the understanding of the growth process of sp(2)-BN employing CVD. (C) 2015 American Vacuum Society.
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| 2. |
- Chubarov, Mikhail, et al.
(författare)
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Polytype pure sp2-BN thin films as dictated by the substrate crystal structure
- 2015
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Ingår i: Chemistry of Materials. - Washington : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 27:5, s. 1640-1645
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Tidskriftsartikel (refereegranskat)abstract
- Boron nitride (BN) is a promising semiconductor material, but its current exploration is hampered by difficulties in growth of single crystalline phase-pure thin films. We compare the growth of sp2-BN by chemical vapor deposition on (0001) 6H-SiC and on (0001) α-Al2O3 substrates with an AlN buffer layer. Polytype-pure rhombohedral BN (r-BN) with a thickness of 200 nm is observed on SiC whereas hexagonal BN (h-BN) nucleates and grows on the AlN buffer layer. For the latter case after a thickness of 4 nm, the h-BN growth is followed by r-BN growth to a total thickness of 200 nm. We find that the polytype of the sp2-BN films is determined by the ordering of Si-C or Al-N atomic pairs in the underlying crystalline structure (SiC or AlN). In the latter case the change from h-BN to r-BN is triggered by stress relaxation. This is important for the development of BN semiconductor device technology.
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| 3. |
- Henry, Anne, et al.
(författare)
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Early stages of growth and crystal structure evolution of boron nitride thin films
- 2016
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Ingår i: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 55:5, s. 05FD06-
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Tidskriftsartikel (refereegranskat)abstract
- A study of the nucleation and crystal structure evolution at the early stages of the growth of sp(2)-BN thin films on 6H-SiC and alpha-Al2O3 substrates is presented. The growth is performed at low pressure and high temperature in a hot wall CVD reactor, using ammonia and triethylboron as precursors, and H-2 as carrier gas. From high-resolution transmission electron microscopy and X-ray thin film diffraction measurements we observe that polytype pure rhombohedral BN (r-BN) is obtained on 6H-SiC substrates. On alpha-Al2O3 an AlN buffer obtained by nitridation is needed to promote the growth of hexagonal BN (h-BN) to a thickness of around 4 nm followed by a transition to r-BN growth. In addition, when r-BN is obtained, triangular features show up in plan-view scanning electron microscopy which are not seen on thin h-BN layers. The formation of BN after already one minute of growth is confirmed by X-ray photoelectron spectroscopy. (C) 2016 The Japan Society of Applied Physics
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| 4. |
- Music, Denis, et al.
(författare)
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Electrical resistivity modulation of thermoelectric iron based nanocomposites
- 2018
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Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 157, s. 384-390
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Tidskriftsartikel (refereegranskat)abstract
- Iron oxides are promising thermoelectrics, but their high electrical resistivity impedes broader applications. In this work, we have studied Fe oxides with metallic contributions. Pt and Ir additions are also considered to enhance the valence electron concentration and further modify the transport properties. Based on density functional theory explorations, Fe based clusters (Fe-3, Fe-4, and Fe3Pt) are suggested to act as nucleation sites for metallic crystallites, while O leads to formation of an amorphous matrix. This has been validated by transmission electron microscopy and x-ray photoelectron spectroscopy of sputter-grown Fe-Pt-Ir-O thin films. Densely packed bcc Fe grains, approx. 2-3 nm in diameter, are embedded in an amorphous Fe-O matrix in the as-grown state. The Seebeck coefficient reaches even -411 mu V K-1 and the electrical resistivity is up to 5 orders of magnitude lower than that of previously reported literature data on Fe oxides. We suggest that this peculiarity of our films is due to finite states localized at the Fermi level in these nanocomposites.
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| 5. |
- Schmidt, Susann, et al.
(författare)
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A comparative study of direct current magnetron sputtering and high power impulse magnetron sputtering processes for CNX thin film growth with different inert gases
- 2016
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Ingår i: Diamond and related materials. - : ELSEVIER SCIENCE SA. - 0925-9635 .- 1879-0062. ; 64, s. 13-26
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Tidskriftsartikel (refereegranskat)abstract
- Reactive direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS) discharges of carbon in different inert gas mixtures (N-2/Ne, N-2/Ar, and N-2/Kr) were investigated for the growth of carbon-nitride (CNX) thin films. Ion mass spectrometry showed that energies of abundant plasma cations are governed by the inert gas and the N-2-to-inert gas flow ratios. The population of ion species depends on the sputter mode; HiPIMS yields approximately ten times higher flux ratios of ions originating from the target to process gas ions than DCMS. Exceptional are discharges in Ne with N-2-to-Ne flow ratios <20%. Here, cation energies and the amount of target ions are highest without influence on the sputter mode. CNX thin films were deposited in 14% N-2/inert gas mixtures at substrate temperatures of 110 degrees C and 430 degrees C. The film properties show a correlation to the substrate temperature, the applied inert gas and sputter mode. The mechanical performance of the films is mainly governed by their morphology and composition, but not by their microstructure. Amorphous and fullerene-like CN0.14 films exhibiting a hardness of similar to 15 GPa and an elastic recovery of similar to 90% were deposited at 110 degrees C in reactive Kr atmosphere by DCMS and HiPIMS.
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