Pavel Souček

Laser desorption ionisation quadrupole ion trap time‐of‐flight mass spectrometry of titanium‐carbon thin films

RATIONALE Titanium-carbon (Ti-C) ceramic thin films (abbreviated as n-TiC/a-C:H) are very important for industrial applications. However, their chemical structure is still not completely resolved. The aim of this study was to determine the chemical composition of such n-TiC/a-C:H layers prepared by balanced magnetron sputtering under various experimental conditions. METHODS Mass spectrometric analysis of Ti-C thin films was carried out via laser desorption ionisation (LDI) using a quadrupole ion trap and reflectron time-of-flight analyser. The stoichiometry of clusters formed via laser ablation was determined, and the relative abundances of species for which the isotopic patterns overlaps were estimated using a least-squares program. RESULTS Ti-C films were found to be composites of (i) pure and hydrogenated TiC, (ii) titanium oxycarbides, and (iii) titanium oxides of various degrees of hydrogenation (all embedded in an amorphous and/or diamond-like carbon matrix). Hydrogenated titanium oxycarbide was the main component of the surface layer, whereas deeper layers were composed primarily of TiC and titanium oxides (also embedded in the carbon matrix). CONCLUSIONS Mass spectrometry proved useful for elucidating the chemical structure of the hard ceramic-like Ti-C layers produced by magnetron sputtering. The Ti-C layers were found to be complex composites of various chemical entities. Knowledge of the resolved structure could accelerate further development of these kinds of materials.

Atmospheric dry hydrogen plasma reduction of inkjet-printed flexible graphene oxide electrodes

This study concerns a low-temperature method for dry hydrogen plasma reduction of inkjet-printed flexible graphene oxide (GO) electrodes, an approach compatible with processes envisaged for the manufacture of flexible electronics. The processing of GO to reduced graphene oxide (rGO) was performed in 1-64 s, and sp2 /sp2 +sp3 carbon concentration increased from approximately 20 % to 90 %. Since the plasma reduction was associated with an etching effect, the optimal reduction time occurred between 8 and 16 s. The surface showed good mechanical stability when deposited on polyethylene terephthalate flexible foils and significantly lower sheet resistance after plasma reduction. This method for dry plasma reduction could be important for large-area hydrogenation and reduction of GO flexible surfaces, with present and potential applications in a wide variety of emerging technologies.

Investigation of the Influence of Ni Doping on the Structure and Hardness of Ti-Ni-C Coatings

Nanocomposite nc-TiC/a-C:H thin films exhibit unique combination of mechanical properties, high hardness, low friction, and wear. Selective doping by weak-carbide forming element can be used in order to specifically design the physical and chemical properties of nc-TiC/a-C:H coatings. In this paper we report on an effect of nickel addition on structure and hardness of the nc-TiC/a-C:H coatings. The effect of Ni alloying on the coating structure under conditions of DCMS and HiPIMS depositions was studied. The coating structure was correlated with the coating hardness. The grain size, the grain carbon vacancy concentration, and the mean grain separation were found to be the key parameters determining the coating hardness. Ni doping proved to have a significant effect on the coating microstructure which resulted in changes of the hardness of the deposited coatings.

Characterization of Ta-B-C nanostructured hard coatings

Microstructure and mechanical properties of Ta-B-C nanocrystalline layers prepared by magnetron sputtering were studied. DC magnetron sputtering was used to prepare thin layers on rotated substrates. Various deposition parameters were tested. Microstructure of layers was studied by means of scanning and transmission electron microscopy on thin lamellar cross sections prepared using a focussed ion beam. Both undisturbed layers and the volume under relatively large indentation prints (load of 1 N) were observed. The microstructure observations were correlated with mechanical properties characterized by means of nanoindentation experiments in both the static and the dynamic loading regime. Elastic modulus, indentation hardness and fracture resistance of prepared nanostructured coatings were evaluated and discussed.

Study of Fracture Resistance of Nanolaminate Coatings Using Indentation and Impact Tests

The aim of the present work was to study the mechanical properties of thin nanocomposite Mo-B-C coatings consisting of nanocrystalline Mo2BC embedded in amorphous Mo-B-C matrix. Magnetron sputtering of three targets, B4C, C and Mo, was used for coatings preparation. The Mo-B-C coatings were deposited on high speed steel substrates. The fracture resistance of Mo-B-C coatings was studied by both indentation and dynamic impact tests. The impact tests enabled us to predict the load limit causing the coating destruction.

Fracture Resistance Enhancement in Hard Mo-B-C Coatings Tailored by Composition and Microstructure

State-of-the-art protective coatings often suffer from brittleness. Therefore, the coatings are intensively sought which would simultaneously exhibit high hardness and stiffness with moderate ductility and fracture resistance. In this paper, we report on the nanostructure designing of coatings containing metal, boron, and carbon enabling the simultaneous presence of stiff boridic and carbidic bonds together with weaker metallic bonds to provide coatings with these desirable properties. Three designs are presented with different relative amounts of nanocrystalline and amorphous phases, ranging from near-amorphous to prevalently crystalline microstructure. All presented coatings exhibit an unusual combination of high fracture resistance and high hardness that cannot be achieved with state-of-the-art protective coatings. Indentation tests at high loads revealed that no cracks are present at the surface of the investigated coatings while state-of-the-art ceramic protective coatings already exhibit significant cracking. Cracks in the bulk of the presented coating are detected only when the deformation is so severe that the substrate itself fails.

W-B-C Nanostructured Layers - Microstructure and Mechanical Properties

Several W-B-C layers were prepared by magnetron sputtering. The microstructure of thin layers was observed by means of scanning and transmission electron microscopy on cross sections prepared using a focused ion beam. Both undisturbed layers and the volume under indentation prints were inspected. The W-B-C layers are fine nanostructured materials about 2 μm thick and indents with loads up to 1 N do not cause any visible defects (cracks, delamination etc). The results were correlated with mechanical properties characterized by means of nanoindentation experiments in both the static and the dynamic loading regime using a Berkovich indenter. Elastic modulus, indentation hardness and fracture resistance of prepared nanostructured coatings were evaluated and discussed.

Mo-B-C and Ta-B-C Nanostructured Layers with Promising Fracture Toughness

X-B-C (X=Mo, Ta) layers prepared by magnetron sputtering were tested. Mechanical properties were characterized by means of nanoindentation experiments in both the static and the dynamic loading regime. The results were correlated with observations of the microstructure under indentation prints by means of scanning and transmission electron microscopy on cross sections prepared using a focussed ion beam. An excellent fracture resistance of prepared nanostructured coatings was found.

Study of the Local Mechanical Properties of Magnetron Sputtered Nanolaminate Coatings

Nanostructure coatings based on boroncarbide were prepared using magnetron sputtering technique. The mechanical properties of the coatings were tested using quasi-static and dynamic nanoindentation tests with Berkovich and cube-corner indenters. The fracture resistance of the coatings and the coating/substrate interface was studied. Moreover, the dynamic wear and scratch resistance of the coatings was evaluated by means of impact and scratch tests.

Study of the Nanoindentation Induced Defects in Nanocomposite n-TiC/a-C:H Films

The aim of the present work is to study the nanoindentation induced defects in as-deposited and annealed nanocomposite n-TiC/a-C:H coatings. Furthermore, the resistance of the coatings against indentation induced defect creation was studied using TEM analysis of lamellas prepared using a focused ion beam for both as-deposited and annealed samples.