The article reports on the enhanced hardness of nanocomposite coatings, their thermal stability, protection of the substrate against oxidation at temperatures above 1000 °C, X-ray amorphous coatings thermally stable above 1000 °C and new advanced hard nanocomposite coatings with enhanced toughness which exhibit (i) low values of the effective Young's modulus E ⁎ satisfying the condition H/E ⁎  > 0.1, (ii) high elastic recovery W e  ≥ 60%, (iii) strongly improved tribological properties, and (iv) enhanced resistance to cracking; here E ⁎  = E(1−ν 2 ), E is the Young's modulus and ν is the Poison's ratio. At the end trends of next development of hard nanocomposite coatings are briefly outlined.

Hard nanocomposite coatings: Thermal stability, oxidation resistance and toughness

The electronic structure of the perovskite LaCoO$_3$ for different spin states of Co ions was calculated in the LDA+U approach. The ground state was found to be a nonmagnetic insulator with Co ions in a low-spin state. Somewhat higher in energy we found two intermediate-spin states followed by a high-spin state at significantly higher energy. The calculation results show that Co 3$d$ states of $t_{2g}$ symmetry form narrow bands which could easily localize whilst $e_g$ orbitals, due to their strong hybridization with the oxygen 2$p$ states, form a broad $\sigma^*$ band. With the increase of temperature which is simulated by the corresponding increase of the lattice parameter, the transition from the low- to intermediate-spin states occurs. This intermediate-spin (occupation $t_{2g}^5e_g^1$) can develop an orbital ordering which can account for the nonmetallic nature of LaCoO$_3$ at 90 K$<$T$<$500 K. Possible explanations of the magnetic behavior and gradual insulating-metal transition are suggested.

https://arxiv.org/pdf/cond-mat/9709060.pdf

Intermediate-spin state and properties of LaCoO_3

Hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10−6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K) CuO thin films. The Cu2O thin films are p-type and show enhanced properties: grain size (54.7 nm), optical transmission 72% (at 600 nm) and Hall mobility 51 cm2/Vs. The bulk and surface Valence band spectra of Cu2O and CuO thin films are studied by temperature dependent Hall effect and Ultra violet photo electron Spectroscopy (UPS). CuO thin films show a significant band bending downwards (due to higher hole concentration) than Cu2O thin films.

Synthesis of Cu2O from CuO thin films: Optical and electrical properties

An extended structure zone diagram is proposed that includes energetic deposition, characterized by a large flux of ions typical for deposition by filtered cathodic arcs and high power impulse magnetron sputtering. The axes are comprised of a generalized homologous temperature, the normalized kinetic energy flux, and the net film thickness, which can be negative due to ion etching. It is stressed that the number of primary physical parameters affecting growth by far exceeds the number of available axes in such a diagram and therefore it can only provide an approximate and simplified illustration of the growth condition?structure relationships.

/pdf/a-structure-zone-diagram-including-plasma-based-deposition-2p0bkpz4ru.pdf

A structure zone diagram including plasma based deposition and ion etching - eScholarship

A review of high-temperature selective absorbing coatings for solar thermal applications

Cu2O thin films have been grown on glass substrates at room temperature by reactive magnetron sputtering. As-deposited films exhibit high electrical resistivity and low optical transmittance. To improve the film properties, post annealing treatments in air at various temperatures have been performed. Low temperature annealing (<300 °C) avoids the film oxidation into CuO and the films remain single-phased. In this temperature range, the annealing in air enhances the transmittance in the visible region due to the decrease of the defect scattering. Moreover, the optical band gap of Cu2O thin films is enlarged from 2.38 to 2.51 eV with increasing annealing temperature. The increase of optical band gap accompanying the reduction of Urbach energy indicates that the widening of optical band gap may result from the partial elimination of defect band tail after thermal annealing in air. Combining experimental results with recent reported calculations, the peak at about 1.7 eV in photoluminescence spectra is assign...

Transmittance enhancement and optical band gap widening of Cu2O thin films after air annealing

This paper presents the result of the substrate bias voltage effect on the properties of zirconium nitride films, such as structure, morphology, hardness, internal stresses, optical constants and electrical resistivity. The coatings are deposited on steel and silicon substrates by magnetron sputtering of a zirconium target in reactive Ar–N2 mixture. If a bias voltage is applied to the substrate holder, the film texture changes into a [1 1 1] one. For negative bias voltage values higher than −110 V, the lattice constant decreases and porosities are also observed on the films’ surface. These porosities result from a resputtering phenomenon, which occurs only at high values of negative bias voltage. Although the average crystal size is nearly unchanged by the use of a bias voltage, the films present a maximum of hardness (39.5 GPa) vs. this deposition parameter. The optical properties of ZrN films are correlated with the films structure and their hardness. Optical properties close to those of bulk zirconium nitride are obtained for films deposited with a bias voltage of −110 V. Finally, the electrical resistivity of reactively sputtered ZrN coatings has been measured using the four-point probe method.

Reactively sputtered zirconium nitride coatings: structural, mechanical, optical and electrical characteristics

Zr–Si–N films are deposited on silicon and steel substrates by DC magnetron sputtering of a Zr–Si composite target in Ar–N2 reactive mixture, with different Si contents. At very low silicon content, no Si–N bond is observed and Si atoms may be inserted in the lattice of ZrN, as confirmed by the strong increase in the compressive stresses. For intermediate Si contents, nanocomposite films are synthesised: [100] oriented ZrN grains are embedded in an amorphous SiNx phase. For a silicon content higher than 6 at.%, amorphous films are deposited. The variation of the films hardness vs. the silicon concentration is discussed as a function of the films structure and compressive stress level. Finally, the relationship between the hardness and Young's modulus values is also presented.

Structural changes in Zr–Si–N films vs. their silicon content

Thin CrN and CrSiN films were deposited on steel substrates by DC reactive magnetron sputtering. In this paper, the structure and the oxidation resistance of CrN and CrSiN coatings were studied. Whatever the silicon content, CrN was the sole phase evidenced by X-ray diffraction. Silicon introduction into CrN-based coatings did not modify their preferred orientation. On the other hand, a strong effect of the silicon addition on the film oxidation resistance was noticed. Even for silicon concentration as low as 3 at.%, the films thermal stability, the formation of Cr 2 N phase and the carbon accumulation at the film-substrate interface were strongly limited. Finally, this value of silicon concentration was sufficient to increase the film oxidation resistance by nearly 150 °C.

Influence of silicon addition on the oxidation resistance of CrN coatings

Ti–Si–N coatings were deposited on M2 steel by arc evaporation using a Ti–Si composite target in an industrial reactor. The films structure before and after heat treatment at 700 °C was characterised by XRD. In addition, two types of quantitative experiments were performed in thermobalance: oxidation rate was deduced from isothermal thermogravimetric analyses at 800 °C, while the temperature of oxidation beginning ( Tc ) was measured in dynamic mode. Tc was then calculated by a mathematical approximation based on the non-linear least square. The results were compared to those obtained using TiN and SiN x standards. Depending on the deposition conditions, ternary films have been deposited with an atomic ratio Si/Ti of 0.10 and 0.15. The hardness of the films was close to 40 GPa. Only the TiN phase was detected by XRD. The mean crystal size was estimated to be in the 6–8 nm range, which suggested the nanocomposite nature of the coatings. After air oxidation at 700 °C, it was found that this crystal size was not affected by the thermal treatment, indicating a good thermal stability of the structure. Moreover, incorporation of silicon into TiN-based coatings led to a drastic decrease of their oxidation rate, together with a shift of 200 °C of Tc . The high resistance of oxidation of Ti–Si–N films at elevated temperature is attributable to the network of refractory SiN x , which acted as a diffusion barrier for oxygen and insulated TiN nanograins from the aggressive atmosphere.

D. Pilloud

Papers

Transmittance enhancement and optical band gap widening of Cu2O thin films after air annealing

Reactively sputtered zirconium nitride coatings: structural, mechanical, optical and electrical characteristics

Structural changes in Zr–Si–N films vs. their silicon content

Influence of silicon addition on the oxidation resistance of CrN coatings

Oxidation resistance improvement of arc-evaporated TiN hard coatings by silicon addition