| 1. |
- Eriksson, Anders, et al.
(författare)
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Nanocolumnar Epitaxial Ti1-xSixN (0 ≤ x ≤ 0.18) Thin Films Grown by Dual Reactive Magnetron Sputtering on MgO (001), (011), and (111) Substrates
- 2012
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ti1-xSixNy thin films and multilayers have been grown on single-crystal TiN-templated MgO (001), (011), and (111) substrates kept at 550 °C. Elemental Ti and Si targets were used in UVH reactive dual magnetron sputtering in a mixed Ar/N2 discharge. Composition analysis by time-of-flight energy elastic recoil detection analysis show that the films are close to stoichiometric (0.95 ≤ y ≤ 1.00) with respect to TiN over the wide range of Si concentrations 0 ≤ x ≤ 0.22. High-resolution transmission electron microscopy (TEM) combined with scanning TEM and energy dispersive Xray analysis show that all films grow epitaxially for x ≤ 0.18 and that as much as every fifth Ti atom can be replaced by Si (~10 at.%) in Ti1-xSixN(001). For the (011) and (111)-oriented films, however, only 1-2 at.% Si substitutes for Ti. Instead, Si segregates to form crystalline-to-amorphous SiNz (z ≈ 1) tissue phases, which promote the formation of epitaxial TiN nanocolumns. The nanocolumns have preferred {110} interfaces and {200} top facets and grow several hundreds of nm in length.
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| 2. |
- Fager, Hanna, et al.
(författare)
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Hf-Al-Si-N multilayers deposited by reactive magnetron sputtering from a single Hf0.6Al0.2Si0.2 target using high-flux, low-energy modulated substrate bias : film growth and properties
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Hf1−x−yAlxSiyN (0≤x≤0.14, 0≤y≤0.13) single layers and multilayer films are grown on Si(001) at a substrate temperature Ts=250 °C using ultrahigh vacuum magnetically-unbalanced reactive magnetron sputtering from a single Hf0.6Al0.2Si0.2 target in a 5%-N2/Ar atmosphere at a total pressure of 20 mTorr (2.67 Pa). The composition and nanostructure of Hf1−x−yAlxSiyN is controlled during growth by varying the ion energy (Ei) of the ions incident at the film surface, keeping the ion-to-metal flux ratio (Ji/JMe) constant at 8. By sequentially switching Ei between 10 and 40 eV, Hf0.77Al0.10Si0.13N/Hf0.78Al0.14Si0.08N multilayers with bilayer periods Λ = 2-20 nm are grown, in which the Si2p bonding state changes from predominantly Si-Si bonds for films grown at Ei = 10 eV, to mainly Si-N bonds at Ei = 40 eV. Multilayer hardness values increase monotonically from 20 GPa with Λ = 20 nm to 27 GPa with Λ = 2 nm, while multilayer fracture toughness increases with increasing Λ. Multilayers with Λ = 10 nm have the optimized property combination of being bothrelatively hard, H∼24 GPa, and fracture tough.
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| 3. |
- Fager, Hanna, et al.
(författare)
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Reactive DC magnetron sputtering of amorphous (Ti0.25B0.75)1−xSixNy thin films from TiB2 and Si targets
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- (Ti0.25B0.75)1−xSixNy, 0≤x≤0.89, 0.9≤y≤1.25, thin films were reactively grown on Si(001) substrates by dc magnetron sputtering from compound TiB2 and elemental Si targets. The films can be grown in a fully electron-diffraction amorphous state with x>0.46, as evidenced by XRD and HR-TEM investigations. With x=0, BN form onion-like sheets surrounding TiNnanograins. Substrate temperatures, Ts=100-600 ◦C, has a minor effect of the film structure and properties, due to limited surface diffusion.Ion-assisted growth with substrate bias voltages, Vb, between -50 V and -200 V, favors densification of amorphous structures over nanocrystalline formation, and improves mechanical properties. A maximum hardness value of 26.8±0.7 GPa is found for an amorphous (Ti0.25B0.75)0.39Si0.61N1.15 film grown with substrate temperature Ts=400 °C and substrate bias voltage Vb=-100 V.
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| 4. |
- Halim, Joseph, et al.
(författare)
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X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Herein, we report X-ray Photoelectron Spectroscopy (XPS) analysis for cold pressed exfoliated 2D nanocrystals of transition metal carbides, MXenes. MXenes are a recently discovered family of 2D materials produced by selective chemical etching of the A element from MAX phases which are ternary metal carbides and nitrides. The latter has the formula of Mn+1AXn, where M is an early transition metal, A is an A-group element, and X is C and/or N. This study is a comparison between two MXenes, Ti3C2Tx and Ti2CTx, where Tx stands for surface termination groups such as –O, –OH, and –F. Ti3C2Tx and Ti2CTx were prepared by immersion of Ti3AlC2 and Ti2AlC powders in 50% conc. HF. A thorough XPS analysis was performed through peak fitting of high resolution XPS spectra and valence band, VB, spectra analysis. The effect of Ar sputtering as well as the number of layers n was the primarily interest of this study. According to the peak fitting analysis, both phases contain the following species, Ti–C, C–C, Ti–F, Ti–O and Ti–OH resulting in the following chemical formulas: Ti3C2(OH)x(O)y(F)z and Ti2C(OH)x(O)y(F)z. Comparing the VB spectra with the DOS calculations show the valance band spectra is actually a mixture of MXene with various terminations of OH, O and F. Before Ar+ sputtering both phases show a large percentage of fluorinated-TiO2 which is due to MXene surface oxidation as well as CHx, C-O and COO groups arising from either surface contaminations or due to drying the etched powders in ethanol after washing the powder of the HF acid. According to the VB spectra, it is shown that the fluorinated TiO2 is actually a mixture of anatase and rutile. The number of layers, n, also plays a role; the lower n, the more the MXene is prone to oxidation.
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| 5. |
- Hsiao, Ching-Lien, et al.
(författare)
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Composition tunable Al1-xInxN nanorod arrays grown by ultra-high-vacuum magnetron sputter epitaxy
- 2011
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembled ternary Al1-xInxN nanorod arrays with variable In concentration, 0.10 ≤ x ≤ 0.32 have been realized onto c-plane sapphire substrates by ultra-high-vacuum magnetron sputter epitaxy with Ti0.21Zr0.79N or VN seed layers assistance. The formation of nanorods was very sensitive to the applied seed layer. Without proper seed layer assistance a continuous Al1-xInxN film was grown. The nanorods exhibit hexagonal crosssections with preferential growth along the c axis. A coaxial rod structure with higher In concentration in the core was observed by (scanning) transmission electron microscopy in combination with low-loss electron energy loss spectroscopy and energy dispersive xray spectroscopy. 5 K cathodoluminescence spectroscopy of Al0.86In0.14N nanorods revealed band edge emission at ~5.46 eV, which was accompanied by a strong defectrelated emission at ~ 3.38 eV.
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| 6. |
- Hsiao, Ching-Lien, et al.
(författare)
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Curved-lattice epitaxial growth of chiral AlInN twisted nanorods for optical applications
- 2012
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Despite of using chiral metamaterials to manipulate light polarization states has been demonstrated their great potential for applications such as invisible cloaks, broadband or wavelength-tunable circular polarizers, microreflectors, etc. in the past decade [1-6], operating wavelength in ultraviolet-visible range is still a challenge issue. Since these chiral structures often consist of metallic materials, their operation is designed for the infrared and microwave regions [2-4]. Here, we show how a controlled curved-lattice epitaxial growth (CLEG) of wide-bandgap AlInN semiconductor curved nanocrystals [7] can be exploited as a novel route for tailoring chiral nanostructures in the form of twisted nanorods (TNRs). The fabricated TNRs are shown to reflect light with a high degree of polarization as well as a high degree of circular polarization (that is, nearly circularly polarized light) in the ultravioletvisible region. The obtained polarization is shown to be dependent on the handedness of the TNRs.
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| 7. |
- Khromov, Sergey, et al.
(författare)
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Effect of C-doping on near-band gap luminescence in bulk GaN substrates grown by halide vapor phase epitaxy
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Freestanding bulk C-doped GaN substrates grown by halide vapor phase epitaxy were studied by optical spectroscopy and electron microscopy. In cathodoluminescence (CL) the yellow line (YL) was more intense in samples with higher C content and stable in the temperature range 5-300 K. CL mapping in situ a scanning electron microscope revealed pitlike structure of the layers with higher YL intensity in the pits related to higher local oxygen incorporation. Near bandgap (NBG) emission studies of the pits revealed donor-bound excitons (DBE) with broad emission and no significant acceptor bound exciton (ABE) emission. Pit-free areas demonstrate two well-resolved ABEs with DBE quenched. Quenching of the DBE is explained by potential fluctuations in the vicinity of the carbon atoms in the pits-free regions lowering the ionization barrier for DBE.
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| 8. |
- Kindlund, Hanna, et al.
(författare)
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Microstructure and mechanical properties of : V0.5Mo0.5Nx(111)/Al2O3(0001) thin films
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report results of growth, microstructure, and mechanical properties of V0.5Mo0.5Nx thin films deposited on Al2O3(0001) substrates by reactive magnetron sputtering. Sputtering is carried out in 5 mTorr Ar/N2 atmospheres and the growth temperatures Ts are varied between 100 and 900 °C. We find that the V0.5Mo0.5Nx/Al2O3(0001) alloy films are 111-oriented NaCl-structure. In-plane and out-of plane lattice parameters are found to decrease with increasing Ts and indicate that all alloy films are strained. V0.5Mo0.5Nx hardnesses and reduced elastic moduli increase with increasing Ts, and vary between 15-23 GPa, and 220-318 GPa, respectively. The wear resistance of the alloy films is also found to increase with increasing Ts. In addition, scanning electron micrographs of indents performed on V0.5Mo0.5Nx films show material pile-up around the indent edges and no evidence of crack arising from nanoindentation experiments. Coefficients of friction acquired at normal forces of 1000 μN are found to be of the order of 0.09.
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| 9. |
- Kindlund, Hanna, et al.
(författare)
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V0.5Mo0.5Nx/MgO(001) layers grown at 100-900 °C : composition, nanostructure, and mechanical properties
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- V0.5Mo0.5Nx/MgO(001) alloys with the B1-NaCl structure are grown by ultra-highvacuum reactive magnetron sputter deposition in 5 mTorr mixed Ar/N2 atmospheres at temperatures Ts which are varied from 100 and 900 °C. Alloy films grown at Ts ≤ 500 °C are polycrystalline with a strong 002 texture; layers grown at Ts ≤ 700 °C are epitaxial single-crystals. The N/Me ratio x ranges from 0.64±0.05 with Ts = 900 °C to 0.94±0.05 at 700 °C to 1.02±0.05 with Ts = 500 to 100 °C. The N loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter ao from 4.212 Å with x = 1.02 to 4.175 Å with x = 0.94 to 4.121 Å with x = 0.64. V0.5Mo0.5Nx nanoindentation hardnesses H and elastic moduli E increase with increasing Ts from 17±3 GPa and 274±31 GPa at 100 °C to 26±1 GPa and 303±10 GPa at 900 °C. Films deposited at higher Ts also exhibit enhanced wear resistance. Scanning electron micrographs of nanoindents performed in single-crystal V0.5Mo0.5Nx films and films deposited at 100 and 300 °C reveal no evidence of cracking; instead they exhibit material pile-up around the indents characteristic of plastic flow in ductile materials. Valence band x-ray photoelectron spectroscopy analyses show an enhanced volume density of the shear sensitive d-t2g – d-t2g metallic states in V0.5Mo0.5Nx compared to VN and the density of these orbitals increases with increasing deposition temperature, i.e., the metallic states become more populated with the introduction of N vacancies.
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| 10. |
- Olsson, Simon, et al.
(författare)
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Ion-assisted Growth of Quasicrystalline Cu-Al-Sc Directly from the Vapor Phase
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ion assisted depositions have been used to grow the Al38Cu46Sc16 quasicrystalline phase directly from the vapor phase in thin film form. Diffraction experiments reveal that amorphous films are formed at room temperature. The quasicrystalline phase formed at a substrate temperature of 340 °C with an improved quality at higher temperatures up to 460 °C. The quasicrystal film quality is improved by increasing the ion flux during ion-assisted growth with ion energies of 26.7 eV. Increasing the ion energy further was however found to cause resputtering and defects in the film. Electron microscopy reveals a polycrystalline microstructure with crystal grains in the shape of thin needles.
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