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

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

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

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 metaisSu bibliogrVytauto Didžiojo universiteta

Nitruration par faisceau d'ions des aciers austénitiques inoxydables (étude du transport atomique d'azote, des effets de flux et des effets structuraux)

POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Influence of surface preparation and ion flux on the nitriding efficiency of austenitic stainless steel

Surface and coatings technology : 13th International Conference on surface modification of materials by ion beams San Antonio, Texas, 21-26 September 2003Ion beam nitriding of an austenitic stainless steel (ASS) at moderate temperatures (similar to 400 degrees C) produces a supersaturated nitrogen solid solution that has beneficial effects on the mechanical properties. The nitriding efficiency cannot be improved by increasing the treatment temperature in order to preserve the stainless character contrary to other parameters such as surface pretreatment, ion flux, etc. The effect of flux and pretreatment with argon is investigated in ion beam nitriding of 304L ASS. The ion energy and temperature were 1.2 keV and 400 degrees C, respectively, the ion current densities were 0.5, 0.67, and 0.83 mA(.)cm(-2). The obtained results show that nitrogen uptake increases with increasing the ion flux. The pretreatment with argon beam for I min at RT increases nitrogen uptake at early stages of nitriding and longer pretreatment times do not provide any improvement. The results are discussed in relation with surface effects and atomic transport mechanismVytauto Didžiojo universiteta

Flux effect on the ion-beam nitriding of austenitic stainless-steel AISI 304L

The effect of flux and Ar pretreatment during ion-beam nitriding of austenitic stainless steel is investigated. The ion energy and temperature were 1.2 keV and 400 °C, respectively, the ion current densities were 0.5, 0.67, and 0.83 mA cm–2. The nitrogen distribution profiles were measured using nuclear reaction analysis. The obtained nitrogen distribution profiles were analyzed by the means of the nitrided layer thickness evolution due to sputtering and diffusion and the model of trapping–detrapping. Both approaches could fit well the experimental results, however, different diffusion coefficients have to be assumed for each current density. In addition, the diffusion coefficients are higher for higher current densities. On the other hand, it is shown that the pretreatment with Ar-ion beam at nitriding temperatures produces only a thermal effect without any other influence on the following nitrogen diffusion. The results are discussed in relation with surface and temperature effects and atomic transport mechanismsVytauto Didžiojo universiteta

Ion beam nitriding of single and polycrystalline austenitic stainless steel

Article Number: 083531Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 degrees C with 1.2 keV nitrogen ions using a high current density of 0.5 mA cm(-2). The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the being more preferential for nitrogen diffusion than . In both type of samples, XRD analysis shows the presence of the phase usually called "expanded" austenite or gamma(N) phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stressVytauto Didžiojo universiteta

A comparative study of ion beam nitriding of single-crystalline and polycrystalline 316L austenitic stainless steel

Surface and coatings technology: 13th international conference on surface modification of materials by ion beams, San Antonio, Texas, 21-26 September, 2003Nitriding of an austenitic stainless steel (ASS) at moderate temperature (400 °C) increases significantly its hardness without loss of corrosion resistance. This study presents the first comparison between single crystalline ([001], [011] and [013] orientations) and polycrystalline 316L ASS ion beam nitriding. The current density, ion energy and temperature were 0.5 mA·cm−2, 1.2 keV and 400 °C, respectively. The nitrogen distribution profiles were measured by nuclear reaction analysis (NRA). A notable difference of nitrogen penetration between polycrystalline and single-crystalline samples is observed, depending on the orientation of the single crystals. The nitrogen penetration is higher for [100] and [013] oriented single crystals. X-ray diffraction (XRD) reveals the presence of the γN phase in both types of samples. Moreover, it shows that the nitrided layer in single crystals exhibits disorientations in relation to the matrixVytauto Didžiojo universiteta

Carbon:nickel nanocomposite templates-predefined stable catalysts for diameter-controlled growth of single-walled carbon nanotubes

Carbon : nickel (C : Ni) nanocomposite templates (NCTs) were used as catalyst precursors for diameter-controlled growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD). Two NCT types of 2 nm thickness were prepared by ion beam co-sputtering without (type I) or with assisting Ar+ ion irradiation (type II). NCT type I comprised Ni-rich nanoparticles (NPs) with defined diameter in an amorphous carbon matrix, while NCT type II was a homogenous C : Ni film. Based on the Raman spectra of more than 600 individual SWCNTs, the diameter distribution obtained from both types of NCT was determined. SWCNTs with a selective, monomodal diameter distribution are obtained from NCT type I. About 50% of the SWCNTs have a diameter of (1.36 ± 0.10) nm. In contrast to NCT type I, SWCNTs with a non-selective, relatively homogeneous diameter distribution from 0.80 to 1.40 nm covering 88% of all SWCNTs are obtained from NCT type II. From both catalyst templates predominantly separated as-grown SWCNTs are obtained. They are free of solvents or surfactants, exhibit a low degree of bundling and contain negligible amounts of MWCNTs. The study demonstrates the advantage of predefined catalysts for diameter-controlled SWCNT synthesis in comparison to in situ formed catalysts.ISSN:2040-3364ISSN:2040-337