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 MaxwellGarnett, 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 600oC, respectively. The results of this study can be considered as a predictive design tool for nanomaterial-based optical coatings in general.

A new cluster tool for in situ real-time processing and depth-resolved compositional, structural and optical characterization of thin films at temperatures from -100 to 800 °C is described. The implemented techniques comprise magnetron sputtering, ion irradiation, Rutherford backscattering spectrometry, Raman spectroscopy, and spectroscopic ellipsometry. The capability of the cluster tool is demonstrated for a layer stack MgO/amorphous Si (∼60 nm)/Ag (∼30 nm), deposited at room temperature and crystallized with partial layer exchange by heating up to 650 °C. Its initial and final composition, stacking order, and structure were monitored in situ in real time and a reaction progress was defined as a function of time and temperature.

The mechanism of graphitic ordering of atomic C on Ni was investigated at temperatures ranging from room temperature to 550 degrees C. The C/Ni films were prepared by ion beam sputtering. Their structure has been determined by Rutherford backscattering spectrometry/nuclear reaction analysis, X-ray photoelectron spectroscopy, Raman spectroscopy and cross-sectional transmission electron microscopy. A temperature-induced and a Ni-induced enhancement of graphitic ordering is demonstrated. The Ni-effect is responsible for the formation of a bi-layer structure of the C films at higher deposition temperatures. In the bi-layers, C forms graphenic planes parallel to the Ni surface within a thickness range of 1-2 nm. Further deposited C grows preferentially perpendicular to the surface. The results are discussed on the basis of hyperthermal atom deposition, surface diffusion, metal-induced crystallization and dissolution-precipitation. Our findings point to a dominating role of surface diffusion-assisted crystallization in the carbon ordering process. (C) 2016 Elsevier Ltd. All rights reserved.

Successive crystallization of amorphous Cr-Zr-O thin films, formation of the (Cr,Zr) 2 O 3 /(Zr,Cr)O 2 nanocomposites and thermally induced changes in the hexagonal crystal structure of metastable (Cr,Zr) 2 O 3 were investigated by means of in situ high-temperature synchrotron diffraction experiments up to 1100°C.The thin films of Cr-Zr-O were deposited at room temperature using reactive ion beam sputtering from zonal Cr-Zr targets under oxygen flow.The resulting amorphous Cr-Zr-O solid solutions contained up to 15 at.%Zr.During the annealing in vacuum, the Cr-Zr-O solid solutions decomposed into two metastable phases, Cr-rich (Cr,Zr) 2 O 3 and Zr-rich (Zr,Cr)O 2 , which crystallized in hexagonal and tetragonal structure, respectively.With increasing Zr content in amorphous Cr-Zr-O, the start of the phase segregation and crystallization was shifted from 600°C at 3 at.%Zr to 1000°C at 15 at.%Zr.With the aid of the in situ high-temperature synchrotron powder diffraction experiments, it was found that the metastable Cr 2-2x Zr x O 3-x can accommodate up to approx.3 at.%Zr.The zirconium atoms occupy partially the Wyckoff positions 6b in the corundum-like crystal structure of Cr 2 O 3 that are empty in the stoichiometric chromium oxide.The incorporation of Zr into the crystal structure of Cr 2 O 3 inflated the elementary cell and modified the thermal expansion of Cr 2-2x Zr x O 3-x .The tetragonal structure of zirconia was stabilized by chromium.The phase segregation during the crystallization led to the formation of (Cr,Zr) 2 O 3 /(Zr,Cr)O 2 nanocomposites.The size of crystallites in these nanocomposites decreased with increasing Zr content from 60 nm to 30 nm and increased only slightly at the highest annealing temperatures.In summary, this contribution illustrates the microstructure design in nanocomposites on the example of metastable chromium and zirconium oxides.

Carbon : nickel (C : Ni) nanocomposite templates (NCTs) were used as catalyst precursors for diametercontrolled 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 pre-defined catalysts for diameter-controlled SWCNT synthesis in comparison to in situ formed catalysts.

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.

Successive crystallization of amorphous Cr-Zr-O thin films, formation of the (Cr,Zr)2O3/(Zr,Cr)O2 nanocomposites and the thermally induced changes in the hexagonal crystal structure of metastable (Cr,Zr)2O3 were investigated by means of in situ high-temperature synchrotron diffraction experiments up to 1100°C. The thin films were deposited at room temperature by using reactive ion beam sputtering, and contained 3–15at.% Zr. At low Zr concentrations, chromium-rich (Cr,Zr)2O3 crystallized first, while the crystallization of zirconium-rich (Zr,Cr)O2 was retarded. Increasing amount of zirconium shifted the onset of crystallization in both phases to higher temperatures. For 3at.% of zirconium in amorphous Cr-Zr-O, (Cr,Zr)2O3 crystallized at 600°C. At 8at.% Zr in the films, the crystallization of (Cr,Zr)2O3 started at 700°C. At 15at.% Zr, the Cr-Zr-O films remained amorphous up to the annealing temperature of 1000°C. Metastable hexagonal (Cr,Zr)2O3 accommodated up to ~3at.% Zr. Excess of zirconium formed tetragonal zirconia, which was stabilized by chromium.

A comparative study of nitrogen depth profiles in low energy ion implantation nitrided austenitic stainless steel 1.4301 by glow discharge optical emission spectroscopy (GDOES), secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA) is presented. All methods require calibration either from reference samples or known scattering or reaction cross sections for the nitrogen concentration, while the methods producing a sputter crater – SIMS and GDOES – need additional conversion from sputter time to depth. NRA requires an assumption of material density for a correct conversion from the ‘natural’ units inherent to all ion beam analysis methods into ‘conventional’ depth units. It is shown that a reasonable agreement of the absolute concentrations and very good agreement of the layer thickness is obtained. The observed differences in broadening between the nitrogen distribution near the surface and the deeper region of the nitrided layer–steel interface are discussed on the basis of surface contaminations, surface roughening and energy straggling effects.

Three-dimensional, ion-induced nanoscale pattern formation in the growth mode is studied for a bicomponent thin film. C:Ni films were grown by dual ion beam cosputtering applying an assisting oblique-incidence low-energy Ar+ ion beam. Their microstructure was determined by scanning electron, atomic force, and transmission electron microscopy, as well as by grazing-incidence small-angle x-ray scattering. The role of ion-induced collisional effects was investigated by binary collision computer simulations. The formation of compositionally modulated ripples on the C: Ni film surface is demonstrated. They consist of metal-enriched topographic crests and carbon-enriched valleys. Since the surface is constantly covered by incoming species, this pattern is transferred into the bulk as a periodic array of Ni3C nanoparticles or of Ni-enriched regions in a carbon matrix. Lateral ripple propagation is shown to be one of the crucial phenomena for the film morphology. The essential experimental features are reproduced by the computer simulations. The results reveal the importance of ion-induced preferential displacements as the driving factor for a surface instability, which gives rise to the observed pattern formation.

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.

Tetrahedral amorphous carbon (ta‐C) is studied as a tribological coating for the valve train's exhaust camshaft of a combustion engine. The coated camshafts were installed in a non‐fired engine, tested in a computerized component test bench under practice‐relevant conditions and analyzed for their frictional behavior. A notable reduction of the valve train's drive torque on the test bench is demonstrated. Namely, on a roller cam system with ta‐C‐coated camshaft the reduction is about 15% in average within the entire engine‐map. The ta‐C coatings were extensively characterized under laboratory conditions before and after the investigations on the test bench. Mechanistic understanding of the tribological behavior of ta‐C coatings under dry or starving lubricated conditions was achieved by atomistic simulations of the tribological contact. Industrial utilization of these results would lead to a significant increase of the energy efficiency of combustion engines.

The structure, the optical and the mechanical properties of carbon: vanadium nanocomposite thin films (similar to 1 at.% to 48 at.% V) grown by direct current magnetron sputtering at 110 degrees C are investigated using X-ray diffraction, Raman spectroscopy, transmission electron microscopy, spectroscopic ellipsometry, and nano-indentation. At all compositions a phase separation into cubic vanadium carbide, VCx, (x <= 1) and carbon is observed, the structure of both phases changing continuously with the vanadium content. The film microstructure consists of statistically distributed spherical VCx particles in a carbon matrix at V concentrations of up to about 35 at.%, and at higher V concentrations of elongated, dendrite-like VCx nanocrystallites, which are separated by a carbon tissue phase. The microstructure hints to a transition from purely repeated nucleation dominated growth to a regime with competing repeated nucleation and surface diffusion. The optical properties are controlled by the phase composition of the films. The hardness is nearly independent of the composition, thus enabling the independent tuning of the absorption behavior at constant hardness.

The influence of the metal content (Cu: 0-28 at.%) on the structural, mechanical and tribological properties of amorphous carbon films grown by pulsed filtered cathodic vacuum arc deposition is investigated. Silicon and AISI 301 stainless steel have been used as substrate materials. The microstructure, composition and bonding structure have been determined by scanning electron microscopy, combined Rutherford backscattered spectroscopy-nuclear reaction analysis, and Raman spectroscopy, respectively. The mechanical and tribological properties have been assessed using nanoindentation and reciprocating sliding (fretting tests) and these have been correlated with the elemental composition of the films. A self-organized multilayered structure consisting of alternating carbon and copper metal nanolayers (thickness in the 25-50 nm range), whose formation is enhanced by the Cu content, is detected. The nanohardness and Young's modulus decrease monotonically with increasing Cu content. A maximum value of the Young's modulus of about 255 GPa is obtained for the metal-free film, whereas it drops to about 174 GPa for the film with a Cu content of 28 at.%. In parallel, a 50% drop in the nanohardness from about 28 GPa towards 14 GPa is observed for these coatings. An increase in the Cu content also produces an increment of the coefficient of friction in reciprocating sliding tests performed against a corundum ball counterbody. As compared to the metal free film, a nearly four times higher coefficient of friction value is detected in the case of a Cu content of 28 at.%. Nevertheless, the carbon-copper composite coatings produced a clear surface protection of the substrate despite an overall increase in wear loss with increasing Cu content in the range 3-28 at.%. (C) 2013 Elsevier B.V. All rights reserved.

The mechanical and tribological properties of nanostructured carbon:nickel films on silicon substrates are investigated using a multi-scale experimental and theoretical approach. The C:Ni nanostructures comprising either tilted columns or three-dimensionally self-organized nanopatterns are grown by ion-beam assisted deposition (IBAD). Complex layer architectures were obtained by sequential deposition by rotating the substrate in relation to the assisting ion beam after each deposition step. Atomic composition of the films was determined by ion beam analysis. The phase structure of carbon was analyzed by Raman spectroscopy, that of nickel by X-ray diffraction. The microstructure of the films was determined by high resolution transmission electron microscopy. The films show good adhesion as probed by scratch tests. The film hardness is on the order of 20 GPa, and the elastic modulus is at about 200 GPa. Friction coefficients on the order of 0.1 are found for oscillating wear conditions under ambient conditions. Atomistic computer simulations were applied to assist the experimental findings. Dry and liquid contacts are considered. The simulation shows a complex behaviour for the carbon-carbon interaction, e.g. resulting in the formation of a tribo-layer. Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379, is gratefully acknowledged. We thank Andrea Scholz (HZDR) for X-ray diffraction measurements and Angela Schneider (HZDR) for the mechanical and tribological measurements.

The effect of the assisting low energy ion beam on the structure of nanocomposite thin films is studied for the carbon:nickel system. The parameter range for the ion beam assisted deposition (IBAD) comprised (i) growth temperatures from room temperature to 500°C, (ii) assisting Ar ion energies from 50 eV to 140 eV, and (iii) nickel concentrations from 5 at.% to 40 at.%. Atomic composition of the films was determined by ion beam analysis. The phase structure of the C:Ni thin films was analysed by Raman spectroscopy and X-Ray diffraction. Scanning electron microscopy was applied for surface analysis, and high resolution transmission electron microscopy was used for microstructure determination. The growth of C:Ni nanocomposites without ion assistance is controlled by the phase separation under kinetic constraints of surface and volume diffusion and the film growth rate. In contrast, ordered nanostructures are formed upon utilizing the energy and momentum input of the assisting ion beam. They consist of nanocolumns with varying tilt angles in relation to the film surface, compositionally modulated surface ripples or three-dimensionally ordered nanopatterns throughout the entire thin film thickness. The correlation between IBAD parameters (temperature, ion energy and flux) and nanocomposite morphological and microstructural features (phase structure, tilting angle, and periodicity) will be presented. Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379, is gratefully acknowledged. We thank Andrea Scholz (HZDR) for X-ray diffraction measurements.

+ion irradiation on the morphology of C-Ni thin films will be reported. Ion-beam assisted deposition (IBAD) promotes the columnar growth of carbon encapsulated metallic nano-columns at low deposition temperatures for Ar + ion energy ranges of 50-100 eV. Moreover, the momentum transfer results in a tilting of the columns relative to the film surface. The potential to grow complex matrix encapsulated metallic structures such as chevrons is demonstrated. Furthermore, a window of deposition conditions will be reported where the ion assistance leads to the formation of regular 3D nanopatterns with welldefined periodicity. The influence of such anisotropic film morphology on the optical properties is highlighted. Acknowledgements: Funding by the European Union, ECEMP-Project D1, Nanoskalige Funktionsschichten auf Kohlenstoffbasis, Projektnummer 13857 / 2379, is gratefully acknowledged.