Jaroslav Sobota

Multilayer film deposition of TiN/AlN on a rotating substrate holder from reactive sputtering of elemental targets of titanium and aluminum

(Ti,Al)Nx coatings have previously been deposited by reactive sputtering from (TiAl) targets. This article will report on a multilayer approach, where a substrate is rotating successively through sputter zones with targets of elemental Ti and Al. In reactive sputtering of these elements the well-known hysteresis curves of total pressure versus reactive gas flow for constant Ar flow were observed. It was then possible to select certain flow values of nitrogen and to maintain a constant sputtering pressure by using a PC process control. By variation of the substrate holder velocity a multilayer TiNx/AlNx system, with bilayer thicknesses from 1 to 8 nm, was studied. The multilayer film was characterized by the acoustic-emission scratch technique used in adhesion studies. Consistency between the various critical load values were achieved, and adhesion values between 40 and 80 N were measured; wear was also found to depend on the number of multilayers.

C:N and C:N:O films: preparation and properties

Abstract Oxygen pressure and bias voltage affect the mechanical and optical behaviour of r.f. magnetron sputtered C : N films in different ways. At higher oxygen pressures, hydrogen is also incorporated. The adhesion of the film is improved when a suitable metallic buffer layer is deposited prior to carbon coating.

Film growth of nanostructured C–N/TiNx multilayers reactively sputtered in pure nitrogen

The present communication reports on reactive sputtered nanostructured C–N/TiNx multilayers deposited in pure nitrogen. Carbon and titanium sputtering cathodes are operating concurrently in the side by side configuration. Experimental parameters of relevance for the pseudomorphic growth of the carbon nitride multilayer system, for instance, nitrogen flow and the rotation speed of the substrate holder, varying the bilayer thickness, are discussed. Nanostructured composite coatings, typically 2–3 μm thick, were deposited at a pressure ranging from 0.2 to 1 Pa, and seeding with TiN sputtered in pure nitrogen is reported for the C–N/TiNx system. The acoustic emission scratch test was used, both for measurement of coating adhesion and for tribological characterization. Relevant friction parameters, such as friction coefficient and film transfer, when a WC or a Si3N4 ball is reciprocating on the nanostructured multilayer were studied. Further the dynamic impact method was used for testing the coating system, an...

Characterization of quasi-rugate filters using ellipsometric measurements

A sample with a quasi-inhomogeneous refractive index profile has been prepared by r.f. magnetron sputtering by mixing very thin layers of SiO2 and Al2O3. It has been proved that the quasi-inhomogeneous profile is, to the accuracy of our experiment, undistinguishable from the smoothly inhomogeneous profile. This effective inhomogeneous profile was then established from the measured ellipsometric data by the new method based on Tikhonovs regularization technique. As the method uses some a-priori information on the system, the results are rather qualitative but they seem to reveal the depth profiles of the refractive index and extinction coefficient as well as their dispersion.

A study of film growth and tribological characterization of nanostructured C-N/TiNX multilayer coatings

Abstract Coatings of C-N/TiN X composite multilayers, where X ≤ 1 in the nanometer range, have been deposited in a reactive sputtering system with side-by-side cathodes of titanium and carbon. Coatings were deposited on samples of tungsten carbide, and high-speed steel on a substrate holder rotating with variable speed from 2 to 28 rpm. Sputtering was performed in nitrogen/argon with a constant Ar flow of 25 sccm. The individual bilayer thicknesses were derived from the deposition rate and the rotation speed. Power for the Ti and C cathodes was kept constant at 1200 W. Deposition parameters were selected from curves showing total sputtering pressure and the voltages of the Ti and C sputtering cathodes versus the nitrogen gas flow. The acoustic emission scratch test developed for coating-adhesion measurements was used as a coarse test for coating evaluation. Particularly, the acoustic emission signal will be discussed and the friction coefficient for sliding against a Si 3 N 4 ball in a ball-on-disk tribometer was measured, and showed a strong dependence on the deposition parameters.

Ultra-Micro-Thermal Field-Flow Fractionation

Abstract Micro-thermal field-flow fractionation, proposed conceptually and implemented experimentally several years ago, has developed rapidly in terms of theory, instrumentation, and numerous applications for the analysis and characterization of polymers and particles of synthetic, natural, and biological origin. Although the advances have been important, achieving the ultimate limits of miniaturization imposed by the physics as well as by recent technologies represents a challenge that was explored. The result of the reported experimental study is a new separation channel for ultra-micro-thermal field-flow fractionation, which was compared, in terms of performance, with the existing compact micro-thermal field-flow fractionation unit. The limits of the miniaturization are experimentally demonstrated with the use of suspensions of colloidal particles, which represent a more difficult case of separation than polymers in solution.

CN/MeN nanocomposite coatings, deposition and testing of performance

Abstract The present communication will report on nanostructured multilayer films containing metal nitride (NbN or ZrN) and carbon nitride. Alcatel 650 and Leybold Z550 sputtering systems equipped with two magnetrons and two r.f. generators were used for the deposition of nanocomposite coatings by r.f. reactive sputtering. The composite coatings, typically 2–3 μm thick, were deposited at a total pressure ranging from 0.2 to 1 Pa and at a relatively low substrate temperature not exceeding 200°C. Various substrates, such as silicon, highly polished steel and tungsten carbide were used. The friction coefficient and wear rate were measured at room temperature in a ball-on-disc tribometer. We also investigated the structure of the multilayer by means of low-angle X-ray reflection and high angle X-ray diffraction. We determined the multilayer period and its changes with temperature from X-ray reflection. It follows from the X-ray diffraction that the polycrystalline structure of the multilayer is developed after annealing. Multilayer nanocomposites can be deposited at low substrate temperatures in conventional PVD coaters and they will combine good adhesion, low wear and low friction coefficient in one system.

Stacked Josephson Junction Based on Nb/Si Superlattice

We report on the technology and basic electrical properties of ten-fold stacked Nb/Si/Nb Josephson junction (JJ). The problem of making a large number of stacked JJs with identical properties was solved by metallic superlattice preparation technology. The uniformity of Si barriers thickness was examined by low angle X-ray diffraction and cross-sectional transmission electron microscopy. To prevent pinholes in the Si barriers the Nb/Si superlattice was sputtered at the regime at which smoothing of interfacial roughness occurs. The stacked junction exhibit both ac and dc Josephson effects. In the Ic(B) diffraction pattern there is an extra periodicity of about 2–3 G in addition to a larger period of about 21 G.

Standing-wave effects in grazing-incidence x-ray diffraction from polycrystalline multilayers

The intensity of x-ray diffraction from a polycrystalline multilayer in a grazing-incidence scattering geometry is modulated by a standing wave created by the interference of the radiation transmitted through the multilayer stack with the wave field specularly reflected from the superlattice interfaces. Similarly, the radiation being diffracted from the polycrystalline structure is reflected specularly from the interfaces and a standing-wave interference pattern results as well. This effect is demonstrated by a series of diffraction measurements on C∕Ni periodic multilayers; the experimental data have been modeled using the distorted-wave Born approximation and a very good correspondence with the experiments was achieved. The method was used for the study of the profiles of the crystallite sizes and strains in multilayers.

Trends in Polymer and Particle Characterization by Microfluidic Field-Flow Fractionation Methods: Science or Business?

More than 45 years have passed since the invention of field-flow fractionation (FFF). During this time, several methods and techniques, differing mainly by the nature of the applied field, have been proposed and experimentally implemented. However, only few of them are currently in practical laboratory use. Recent trends of miniaturization of all separation techniques have also been followed in the development of FFF apparatus. The aim of this work is to give an overview of the advances that are important in the practical use of microfluidic FFF techniques. Another aim is a critical evaluation of the crucial characteristics of the most widespread FFF techniques performed in standard-size channels.