| 431. |
- Hellgren, Niklas, et al.
(författare)
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Fullerene-like B C N thin films a computational andexperimental study
- 2004
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Ingår i: Materials Science and Engineering B. - : Elsevier. ; 113:3, s. 242-247
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio calculations show that the energy cost for incorporating lattice defects such as pentagons and heptagons is significantly reduced for BCN compared to BN, thus promoting bending of basal planes in these compounds. Boron–carbon–nitride (Bsingle bondCsingle bondN) thin films with a fullerene-like (FL) microstructure were then deposited by dual cathode magnetron sputtering from C and B4C targets. Up to 1 μm thick films were grown at a total gas pressure of 3 mTorr (0.4 Pa) in varying Ar/N2 ratios, and substrate temperatures between 225 and 350 °C. Compositional and microstructural studies were performed using RBS, SEM and HREM, respectively. Depending on the deposition condition, ternary BxCyNz films with fullerene-like microstructure could be prepared in agreement with the calculations within the composition range 0 ≤ x ≤ 53, 15 ≤ y ≤ 62, and 24 ≤ z ≤ 50 at.%. Fullerene-like structures also tend to form at lower temperatures in the case of BCN compared to CN. Nanoindentation measurements show that all BxCyNz films exhibited a highly elastic response independent of elemental composition. In addition, the calculations suggest a driving force for C and BN phase separation.
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| 432. |
- Hellgren, N., et al.
(författare)
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Growth, structure, and mechanical properties of CNxHy films deposited by dc magnetron sputtering in N2/Ar/H2 discharges
- 2000
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 18:5, s. 2349-2358
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Tidskriftsartikel (refereegranskat)abstract
- Reactive direct current magnetron sputtering was used to deposit the hydrogenated carbon nitride films in mixed nitrogen (N2)/argon (Ar)/ hydrogen (H2) discharges. Growth and structure evolution of films was found to be affected by chemical sputtering effects. The hydrogen were found to be bonded to nitrogen and hydrogen incorporation decreases the elasticity and hardness.
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| 433. |
- Hellgren, N, et al.
(författare)
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Influence of plasma parameters on the growth and properties of magnetron sputtered CNx thin films
- 2000
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Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:1, s. 524-532
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride CNx thin films were grown by unbalanced dc magnetron sputtering from a graphite target in a pure N-2 discharge, and with the substrate temperature T-s kept between 100 and 550 degrees C. A solenoid coil positioned in the vicinity of the substrate was used to support the magnetic field of the magnetron, so that the plasma could be increased near the substrate. By varying the coil current and gas pressure, the energy distribution and fluxes of N-2(+) ions and C neutrals could be varied independently of each other over a wide range. An array of Langmuir probes in the substrate position was used to monitor the radial ion flux distribution over the 75-mm-diam substrate, while the flux and energy distribution of neutrals was estimated through Monte Carlo simulations. The structure, surface roughness, and mechanical response of the films are found to be strongly dependent on the substrate temperature, and the fluxes and energies of the deposited particles. By controlling the process parameters, the film structure can thus be selected to be amorphous, graphite-like or fullerene-like. When depositing at 3 mTorr N-2 pressure, with T-s> 200 degrees C, a transition from a disordered graphite-like to a hard and elastic fullerene-like structure occurred when the ion flux was increased above similar to 0.5-1.0 mA/cm(2). The nitrogen-to-carbon concentration ratio in the films ranged from similar to 0.1 to 0.65, depending on substrate temperature and gas pressure. The nitrogen film concentration did, however, not change when varying the nitrogen ion-to-carbon atom flux ratios from similar to 1 to 20. (C) 2000 American Institute of Physics. [S0021-8979(00)00413-8].
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| 434. |
- Hellgren, Niklas, et al.
(författare)
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Interpretation of X-ray photoelectron spectra of carbon-nitride thin films: New insights from in situ XPS
- 2016
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Ingår i: Carbon. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0008-6223 .- 1873-3891. ; 108, s. 242-252
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Tidskriftsartikel (refereegranskat)abstract
- We report on angular-resolved x-ray photoelectron spectroscopy (XPS) studies of magnetron sputtered CNx thin films, first in situ (without air exposure), then after air exposure (for time periods ranging from minutes to several years), and finally after Ar ion etching using ion energies ranging from 500 eV to 4 keV. The as-deposited films typically exhibit two strong N1s peaks corresponding to pyridine-like, and graphite-like, at similar to 398.2 eV and similar to 400.7 eV, respectively. Comparison between in situ and air-exposed samples suggests that the peak component at similar to 402-403 eV is due only to quaternary nitrogen and not oxidized nitrogen. Furthermore, peak components in the similar to 399-400 eV range cannot only be ascribed to nitriles or pyrrolic nitrogen as is commonly done. We propose that it can also be due to a polarization shift in pyridinic N, induced by surface water or hydroxides. Argon ion etching readily removes surface oxygen, but results also in a strong preferential sputtering of nitrogen and can cause amorphization of the film surface. The best methods for evaluating and interpreting the CNx film structure and composition with ex-situ XPS are discussed. (C) 2016 Elsevier Ltd. All rights reserved.
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| 435. |
- Hellgren, N, et al.
(författare)
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Thermal stability of carbon nitride thin films
- 2001
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 16:11, s. 3188-3201
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of carbon nitride films, deposited by reactive direct current magnetron sputtering in N-2 discharge, was studied for postdeposition annealing temperatures T-A up to 1000 degreesC. Films were grown at temperatures of 100 degreesC (amorphous structure) and 350 and 550 degreesC (fullerenelike structure) and were analyzed with respect to thickness, composition, microstructure, bonding structure, and mechanical properties as a function of T-A and annealing time. All properties investigated were found to be stable for annealing up to 300 degreesC for long times (> 48 h). For higher T-A, nitrogen is lost from the films and graphitization takes place. At T-A = 500 degreesC the graphitization process takes up to 48 h while at T-A = 900 degreesC it takes less than 2 min. A comparison on the evolution of x-ray photoelectron spectroscopy, electron energy loss spectroscopy and Raman spectra during annealing shows that for T-A > 800 degreesC, preferentially pyridinelike N and -C equivalent toN is lost from the films, mainly in the form of molecular N-2 and C2N2, while N substituted in graphite is preserved the longest in the structure. Films deposited at the higher temperature exhibit better thermal stability, but annealing at temperatures a few hundred degrees Celsius above the deposition temperature for long times is always detrimental for the mechanical properties of the films.
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| 436. |
- Hogberg, H., et al.
(författare)
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Strain relaxation of low-temperature deposited epitaxial titanium-carbide films
- 2000
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 219:3, s. 237-244
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Tidskriftsartikel (refereegranskat)abstract
- The lattice misfit strain and relaxation during growth of 60-950 angstroms epitaxial TiC carbide films deposited by co-evaporation of C60 and Ti on MgO(0 0 1) have been studied by reciprocal space mapping (RSM) and transmission electron microscopy (TEM). All the films exhibited a strained layer growth behavior with respect to the substrate. The strain e, ranged from 2.1% for the 60 angstroms film to 0.8% for the 950 angstroms film. Initial misfit strain relaxation was by slip on {1 1 0}<1 0 1¯> and {1 1 1}<1 0 1¯>. After dislocation rearrangement the films predominantly exhibited well-developed misfit dislocations of edge type with line direction <1 0 0> along the interface plane and Burgers vectors 1/2[1 0 1¯] inclined to the interface with MgO.
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| 437. |
- Howe, B., et al.
(författare)
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Growth and physical properties of epitaxial metastable Hf1 - xAlxN alloys deposited on MgO(001) by ultrahigh vacuum reactive magnetron sputtering
- 2007
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 202:4-7, s. 809-814
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial metastable Hf1 - xAlxN alloys with 0 ≤ x ≤ 0.50 were grown on MgO(001) substrates at 600 °C by ultrahigh vacuum reactive magnetron sputtering from Hf and Al targets in 90% Ar + 10% N2 discharges at 7 mTorr. X-Ray diffraction and cross-sectional transmission electron microscopy show that Hf1 - xAlxN alloys are single crystals with the B1-NaCl structure. Rutherford backscattering spectroscopy investigations reveal that all films are slightly overstochiometric with N / (Hf + Al) = 1.05 ± 0.05. The relaxed lattice parameter decreased linearly from 0.4519 nm with x = 0 to 0.4438 nm with x = 0.50, compared to 0.4320 nm expected from the linear Vegard's rule. We find a metastable single phase field that is remarkably broad given the large lattice mismatch (≃ 9%) between the two alloy components. Alloying HfN with AlN leads to an increase in hardness (≃ 30% to 32.4 ± 0.7 GPa), as well as nanostructured compositional modulations due to the onset of spinodal decomposition. © 2007 Elsevier B.V. All rights reserved.
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| 438. |
- Howe, B M, et al.
(författare)
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Real-time control of AlN incorporation in epitaxial Hf1-xAlxN using high-flux, low-energy (10-40 eV) ion bombardment during reactive magnetron sputter deposition from a Hf0.7Al0.3 alloy target
- 2011
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Ingår i: ACTA MATERIALIA. - : Elsevier Science B.V., Amsterdam.. - 1359-6454. ; 59:2, s. 421-428
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Tidskriftsartikel (refereegranskat)abstract
- The AlN incorporation probability in single crystal Hf-1 (-) xAlxN(0 0 1) layers is controllably adjusted between similar to 0% and 100% by varying the ion energy (E-i) incident at the growing film over a narrow range, 10-40 eV. The layers are grown on MgO(0 0 1) at 450 degrees C using ultrahigh vacuum magnetically unbalanced reactive magnetron sputtering from a Hf0.7Al0.3 alloy target in a 5%-N-2/Ar atmosphere at a total pressure of 20 mTorr (2.67 Pa). The ion to metal flux ratio incident at the growing film is constant at 8. Epitaxial film compositions vary from x = 0.30 with E-i = 10 eV, to 0.27 with E-i = 20 eV, 0.17 with E-i = 30 eV, and andlt;= 0.002 with E-i andgt;= 40 eV. Thus, the AlN incorporation probability decreases by greater than two orders of magnitude. This extraordinary range in real-time manipulation of film chemistry during deposition is due to the efficient resputtering of deposited Al atoms (27 amu) by Ar+ ions (40 amu) neutralized and backscattered from heavy Hf atoms (178.5 amu) in the film. This provides a new reaction pathway to synthesize, at high deposition rates, compositionally complex heterostructures, multilayers, and superlattices with abrupt interfaces from a single alloy target by controllably switching E-i. For multilayer and superlattice structures, the choice of E-i value determines the layer composition and the switching periods control the individual layer thickness.
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| 439. |
- 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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| 440. |
- 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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