| 1. |
- Landälv, Ludvig, 1982-, et al.
(författare)
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Phase evolution of radio frequency magnetron sputtered Cr-rich (Cr,Zr)(2)O-3 coatings studied by in situ synchrotron X-ray diffraction during annealing in air or vacuum
- 2019
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Ingår i: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 34:22, s. 3735-3746
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Tidskriftsartikel (refereegranskat)abstract
- The phase evolution of reactive radio frequency (RF) magnetron sputtered Cr0.28Zr0.10O0.61 coatings has been studied by in situ synchrotron X-ray diffraction during annealing under air atmosphere and vacuum. The annealing in vacuum shows t-ZrO2 formation starting at similar to 750-800 degrees C, followed by decomposition of the alpha-Cr2O3 structure in conjunction with bcc-Cr formation, starting at similar to 950 degrees C. The resulting coating after annealing to 1140 degrees C is a mixture of t-ZrO2, m-ZrO2, and bcc-Cr. The air-annealed sample shows t-ZrO2 formation starting at similar to 750 degrees C. The resulting coating after annealing to 975 degrees C is a mixture of t-ZrO2 and alpha-Cr2O3 (with dissolved Zr). The microstructure coarsened slightly during annealing, but the mechanical properties are maintained, with no detectable bcc-Cr formation. A larger t-ZrO2 fraction compared with alpha-Cr2O3 is observed in the vacuum-annealed coating compared with the air-annealed coating at 975 degrees C. The results indicate that the studied pseudo-binary oxide is more stable in air atmosphere than in vacuum.
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| 2. |
- Serban, Alexandra, 1988-, et al.
(författare)
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Magnetron Sputter Epitaxy of High-Quality GaN Nanorods on Functional and Cost-Effective Templates/Substrates
- 2017
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Ingår i: Energies. - Basel, Switzerland : MDPI AG. - 1996-1073. ; 10:9
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB2/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology.
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| 3. |
- Junaid, Muhammad, 1975-
(författare)
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Magnetron Sputter Epitaxy of GaN Epilayers and Nanorods
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this research, electronic-grade GaN(0001) epilayers and nanorods have been grown onto Al2O3(0001) and Si(111) substrates, respectively, by reactive magnetron sputter epitaxy (MSE) using liquid Ga as a sputtering target. MSE, employing ultra high vacuum conditions, high-purity source materials, and lowenergy ion assisted deposition from substrate biasing, is a scalable method, lending itself to large area GaN synthesis.For the growth of epitaxial GaN films two types of sputtering techniques, direct current (DC) magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) were studied. The GaN epitaxial films grown by DC-MSE directly on to Al2O3(0001) in a mixture of Ar and N2, feature low threading dislocation densities on the order of ≤ 1010 cm-2, as determined by transmission electron microscopy (TEM) and modified Williamson-Hall plots. X-ray rocking curves reveal a narrow full-width at half maximum (FWHM) of 1054 arcsec of the 0002 reflection. A sharp 4 K photoluminescence (PL) peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. GaN(0001) epitaxial films grown on Al2O3 substrates by HiPIMS deposition in a mixed N2/Ar discharge contain both strained domains and almost relaxed domains in the same epilayers, which was determined by a combination of x-ray diffraction (XRD), TEM, atomic force microscopy (AFM), μ-Raman microscopy, μ-PL, and Cathodoluminescence (CL). The almost fully relaxed domains show superior structural and optical properties evidenced by a rocking curves with full width at half maximum of 885 arc sec and a low temperature band edge luminescence at 3.47 eV with the FWHM of 10 meV. The other domain exhibits a 14 times higher isotropic strain component, which is due to higher densities of point and extended defects, resulting from bombardment of energetic species during growth.Single-crystal GaN(0001) nanorods have been grown directly on Si(111) substrates by DC-MSE in a pure N2environment. The as-grown GaN nanorods exhibit very high crystal quality from bottom to the top without any stacking faults, as determined by TEM. The crystal quality is found to increase with increasing working pressure. XRD results show that all the rods are highly 0001 oriented. All nanorods exhibit an N-polarity, as determined by convergent beam electron diffraction methods. Sharp and well-resolved 4 K μ-PL peaks at ~3.474 eV with a FWHM ranging from 1.7 meV to 22 meV are attributed to the intrinsic GaN band edge emission and corroborate the exceptional crystal quality of the material. Texture measurements reveal that the rods have random in-plane orientation when grown on Si(111) with its native oxide while they have an inplane epitaxial relationship of GaN[11̅20] // Si[1̅10] when grown on Si(111) without the surface oxide. The best structural and optical properties of the rods were achieved at N2 partial pressures of 15 to 20 mTorr. By diluting the reactive N2 working gas in DC-MSE with Ar, it is possible to achieve favorable growth conditions for high quality GaN nanorods onto Si(111) at a low total pressure of 5 mTorr. With an addition of small amount of Ar (0.5 mTorr), we observe an increase in nanorod aspect ratio from 8 to ~35, a decrease in average diameter from 74 nm to 35 nm, and a 2-fold increase in nanorod density compared to pure N2 conditions. By further dilution, the aspect ratio continuously decreases to 14 while the diameter increases to 60 nm and the nanorod density increases to a maximum of 2.4×109 cm-1. The changes in nanorod morphology upon Ar-dilution of the N2 working gas are explained by a transition from N-rich growth conditions, promoting the diffusion induced nanorods growth mode, to Ga-rich growth conditions, in qualitative agreement with GaN nanorods growth by MBE. At N2 partial pressure of 2.5 mTorr, the Ga-target is close to a non-poisoned state which gives the most perfect crystal quality which is reflected in an exceptionally narrow band edge emission at 3.479 eV with a FWHM of only 1.7 meV. Such structural and optical properties are comparable to rods previously grown at 3 to 4 time higher total working pressures of pure N2.
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| 4. |
- Nyman, Johan, 1992-
(författare)
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Cathodic arc deposition of metal-rich Cr-based coatings
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood and wood-based products have always been key components in the development of human civilization. Nowadays most wood harvesting is done using chainsaws, and their efficient operation helps promote worker safety and reduce emissions. An important factor for efficient operation is the sharpness of the chain – a sharper chain requires less energy for cutting and reduces the risk of dangerous kickback. To reduce the rate of wear and prolong the life of the chains, they are protected by a hard chrome coating. The production of this coating involves compounds in which Cr atoms are in the toxic and carcinogenic hexavalent state. The deposited coatings contain no toxic compounds, however. Consequently, there is a need to develop replacement processes which can produce equally well-performing coatings.In this thesis I investigate the process of cathodic arc deposition of coatings for this purpose. Cathodic arc deposition is a well-established technique for tool coatings, free of toxic compounds. Specifically, elemental Cr coatings, and Cr-rich Cr-N, Cr-C, and Cr-C-N coatings are studied.For the study on elemental Cr, focus is put on the impact of substrate bias on the growth and coating properties. This is important in cathodic arc deposition as the evaporated species are ionized to a high degree. I show that an increasing substrate bias increases the temperature of the substrate and compressive stress of the coatings while decreasing the growth rate because of resputtering. The texture also changes from a preferential [110]- to [100]-orientation, and the hardness is lower than for typical hard chrome coatings.For alloying with N or C, using N2 and C2H2, respectively, the N-/Ccontent is shown to decrease with increasing bias. This process is attributed to preferential resputtering, and ceases at a critical partial pressure, different for N and C, at which point there is no observed difference in N- or C- content at different bias. The incorporation strongly affects the microstructure of the coatings. For N, there is a transition from a columnar structure to a featureless appearance at high N-content, while for C a mixed amorphous/crystalline structure appears at high C-content. For both C and N, the change in microstructure is accompanied by a large increase in hardness, which almost doubles when the alloying concentration reaches ~7 at.%.In a fourth study, combined C- and N-alloying is investigated. Here it is seen that the preferential resputtering persists for N, but for C there is a linear increase in content with partial pressure of C2H2 for all bias levels. This results in the coatings containing more C than N, with a structure like that of Cr-C. At the highest alloying level, a new structure appears which is not seen for the Cr-N and Cr-C studies, consisting of small, elongated grains and columns.In a fifth study, synchrotron-based X-ray adsorption spectroscopy is used to provide structural information about the coatings that is difficult to access with X-ray diffraction. The measurements show that Cr2N and Cr3C2 are the predominant phases forming alongside bcc Cr and reveal changes in bond orientations and strengths at differing alloying concentrations.
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| 5. |
- Nyman, Johan, 1992-, et al.
(författare)
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Substrate bias effects on cathodic arc deposited Cr coatings
- 2023
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Ingår i: Results in Materials. - 2590-048X. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effects of substrate bias on cathodic arc deposition of Cr coatings without external substrate heating at four different substrate bias levels, floating, −30, −50, and −70 V. After 10 min of deposition, the substrate temperature reaches 180, 210, 230, and 260 °C for floating potential, −30, −50, and −70 V, respectively. Time-of-flight energy elastic recoil detection analysis shows that all grown coatings are of high purity, with no coating containing more than 0.2 at.% of C and/or O. Increasing the substrate bias also reduces the number of macroparticles, steers the texture from preferred [110]- to [100]-orientation and induces a residual compressive stress of ∼450 MPa in the coatings. The hardness of the coatings remains at a constant 7.5 GPa irrespective of the substrate bias. The four-point probe resistivity of the grown coatings is 15–17 μΩcm regardless of substrate bias, close to the 12.9 μΩcm of bulk Cr.
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