Instability types at ion-assisted alloy deposition: from two-dimensional to three-dimensional nanopattern growth

Ion irradiation during film growth has a strong impact on structural properties. Linear stability analysis is employed to study surface instabilities during ion-assisted growth of binary alloys. An interplay between curvature-dependent ion-driven and deposition-driven instabilities is investigated. We demonstrate that ion irradiation of growing binary alloys leads to the formation of composition-modulated surface patterns. It is shown that the ion-to-atom arrival ratio R is the pattern control parameter. Close to the instability threshold we identify different regimes of instabilities driven by ion- or deposition-induced surface roughness processes, or roughness-composition feedback interactions. In particular, the synergistic effects of the curvature-dependent displacement and deposition coupling to the preferential sputtering or to the preferential diffusivity are found to induce instabilities and pattern formation. Depending on the film growth and ion-irradiation conditions, the instabilities show stationary or oscillating behavior. The latter one is exclusively connected with ion irradiation. The corresponding phase diagrams are presented in terms of experimentally accessible parameters. This shows an alternative way to control surface patterning and to grow three-dimensional laterally or vertically ordered nanostructures.Comment: 12 pages 3 figures, derivation adde

Fullerenelike arrangements in carbon nitride thin films grown by direct ion beam sputtering

Carbon nitride (CNx) thin films were grown by direct N-2/Ar ion beam sputtering of a graphite target at moderate substrate temperatures (300-750 K). The resulting microstructure of the films was studied by high-resolution transmission electron microscopy. The images showed the presence of curved basal planes in fullerenelike arrangements. The achievement and evolution of these microstructural features are discussed in terms of nitrogen incorporation, film-forming flux, and ion bombardment effects, thus adding to the understanding of the formation mechanisms of curved graphitic structures in CNx materials. (C) 2005 American Institute of Physics

Spin-dependent transport in nanocomposite C:Co films

The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investigated. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range from 200 to 500 degC. Two major effects are reported: (i) a large anomalous Hall effect amounting to 2 \mu ohm cm, and (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves coincide with the rescaled magnetization curves, a finding that is consistent with spin-dependent transport. These findings suggest that C:Co nanocomposites are promising candidates for carbon-based Hall sensors and spintronic devices.Comment: 13 pages, 7 figure

Advanced characterization and optical simulation for the design of solar selective coatings based on carbon: transition metal carbide nanocomposites

Solar selective coatings based on carbon transition metal carbide nanocomposite absorber layers were designed. Pulsed filtered cathodic arc was used for depositing amorphous carbon:metal carbide (a-C:MeC, Me = V, Mo) thin films. Composition and structure of the samples were characterized by ion beam analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The optical properties were determined by ellipsometry and spectrophotometry. Three effective medium approximations (EMA), namely Maxwell-Garnett, Bruggeman, and Bergman, were applied to simulate the optical behaviour of the nanocomposite thin films. Excellent agreement was achieved between simulated and measured reflectance spectra in the entire wavelength range by using the Bergman approach, where in-depth knowledge of the nanocomposite thin film microstructure is included. The reflectance is shown to be a function of the metal carbide volume fraction and its degree of percolation, but not dependent on whether the nanocomposite microstructure is homogeneous or a self-organized multilayer. Solar selective coatings based on an optimized a-C:MeC absorber layer were designed exhibiting a maximum solar absorptance of 96% and a low thermal emittance of ~5% and 15% at 25 and 600 °C, respectively. The results of this study can be considered as a predictive design tool for nanomaterial-based optical coatings in general

Theory of a quodon gas. With application to precipitation kinetics in solids under irradiation

Rate theory of the radiation-induced precipitation in solids is modified with account of non-equilibrium fluctuations driven by the gas of lattice solitons (a.k.a. quodons) produced by irradiation. According to quantitative estimations, a steady-state density of the quodon gas under sufficiently intense irradiation can be as high as the density of phonon gas. The quodon gas may be a powerful driver of the chemical reaction rates under irradiation, the strength of which exponentially increases with irradiation flux and may be comparable with strength of the phonon gas that exponentially increases with temperature. The modified rate theory is applied to modelling of copper precipitation in FeCu binary alloys under electron irradiation. In contrast to the classical rate theory, which disagrees strongly with experimental data on all precipitation parameters, the modified rate theory describes quite well both the evolution of precipitates and the matrix concentration of copper measured by different methodsComment: V. Dubinko, R. Shapovalov, Theory of a quodon gas. With application to precipitation kinetics in solids under irradiation. (Springer International Publishing, Switzerland, 2014

Out-of-plane magnetic patterning on austenitic stainless steels using plasma nitriding

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of ferromagnetic structures with out-of-plane magnetization, embedded in a paramagnetic matrix, can be produced by local plasma nitriding through shadow masks

A combinatorial study of the mechanical and magnetic properties of a gradually nitrided austenitic stainless steel single crystal

The mechanical and magnetic properties of a nitrided austenitic stainless steel are studied using a combinatorial approach. Plasma nitriding of a [100]-oriented 316L single crystal is carried out using a loose shadow mask to produce an in-plane lateral gradient of nitrogen concentration that extends up to 100 μm. The local mechanical and magnetic properties across the gradually nitrided area are resolved by nanoindentation and the polar magneto-optic Kerr effect, respectively. The hardness, reduced Young's modulus and remanence qualitatively depict the nitrogen profile, suggesting that the nitrogen concentration is a central effect for these observed dependencies. Conversely, the coercivity exhibits a non-monotonic behaviour due to the interplay between magnetic anisotropy and the strength of the induced ferromagnetism. Fingerprints of the expected transition from a nitrogen supersaturated solid solution to a multiphase nature of expanded austenite are evidenced along the gradually nitrided area. © 2014 the Partner Organisations

Influence of the surface processes on the mass transport phenomena in the solids under low-energy high-flux ion irradiation at moderate temperatures

Disertacija parašyta Vytauto Didžiojo universitete 2000-2003 metaisBibliogr.: p. 16-18Vytauto Didžiojo universiteta