J. Houska

Reactive magnetron sputtering of hard Si-B-C-N films with a high-temperature oxidation resistance

Based on the results obtained for C–N and Si–C–N films, a systematic investigation of reactive magnetron sputtering of hard quaternary Si–B–C–N materials has been carried out. The Si–B–C–N films were deposited on p-type Si(100) substrates by dc magnetron co-sputtering using a single C–Si–B target (at a fixed 20% boron fraction in the target erosion area) in nitrogen-argon gas mixtures. Elemental compositions of the films, their surface bonding structure and mechanical properties, together with their oxidation resistance in air, were controlled by the Si fraction (5–75%) in the magnetron target erosion area, the Ar fraction (0–75%) in the gas mixture, the rf induced negative substrate bias voltage (from a floating potential to −500V) and the substrate temperature (180–350°C). The total pressure and the discharge current on the magnetron target were held constant at 0.5Pa and 1A, respectively. The energy and flux of ions bombarding the growing films were determined on the basis of the discharge characterist...

Atom-by-atom simulations of chemical vapor deposition of nanoporous hydrogenated silicon nitride

Amorphous hydrogenated silicon nitride (SiNH) materials prepared by plasma-enhanced chemical vapor deposition (PECVD) are of high interest because of their suitability for diverse applications including optical coatings, gas/vapor permeation barriers, corrosion resistant, and protective coatings and numerous others. In addition, they are very suitable for structurally graded systems such as those with a graded refractive index. In parallel, modeling the PECVD process of SiN(H) of an a priori given SiN(H) ratio by atomistic calculations represents a challenge due to: (1) different (and far from constant) sticking coefficients of individual elements, and (2) expected formation of N2 (and H2) gas molecules. In the present work, we report molecular-dynamics simulations of particle-by-particle deposition process of SiNH films from SiHx and N radicals. We observe formation of a mixed zone (damaged layer) in the initial stages of film growth, and (under certain conditions) formation of nanopores in the film bulk...

Bonding statistics and electronic structure of novel Si–B–C–N materials: Ab initio calculations and experimental verification

Amorphous silicon-boron-carbon-nitrogen alloys were deposited by reactive magnetron sputtering, and their bonding statistics and electronic structure were investigated using a combined approach of experiment and molecular dynamics simulations. The authors show a difference between Si-based and C-based Si–B–C–N networks, and investigate coordination numbers and behavior of individual atom types. Furthermore, the authors calculate electronic structure and photoconductivity of the materials. The authors find that both a higher Si∕C ratio and an addition of hydrogen increase a band gap of the materials.

Effect of implanted argon on hardness of novel magnetron sputtered Si–B–C–N materials: experiments and ab initio simulations

Amorphous silicon–boron–carbon–nitrogen alloys were deposited by reactive magnetron sputtering in nitrogen–argon gas mixtures, and their structure and resulting mechanical properties were investigated using a combined approach of experiment and molecular-dynamics simulations. We show a difference between structures of the materials deposited with a low substrate bias voltage of −100 V leading to a 2% content of implanted Ar atoms, and a high substrate bias voltage of −500 V, resulting in a 6% content of implanted Ar atoms. We find that, while at the higher Ar content the material is practically homogeneous, at the low Ar content there are similar volumes of Si-rich (around the implanted Ar atoms) and Si-poor zones. This can increase material hardness. We examine a temperature dependence of this phenomenon in the light of experimental results.

Experimental and molecular dynamics study of the growth of crystalline TiO2

Thin films of crystalline TiO2 are of high interest due to their photoactivity and photoinduced hydrophilicity. Previously, preparation of TiO2 has been described in terms of extrinsic process parameters, such as total pressure, oxygen partial pressure, or substrate bias potential. We study the growth of TiO2 phases, rutile and anatase, by atom-by-atom molecular dynamics simulations. We focus on the effect of intrinsic process parameters including particle energy, growth temperature, and growth template. While experiments indicate that the deposition of rutile requires higher temperatures and/or energies compared to anatase, we show that the growth of previously nucleated rutile can take place in a wider range of temperatures and energies compared to anatase. In parallel, we show relationships between crystal growth and the lateral size of a crystal. The results facilitate defining new synthesis pathways for TiO2, and constitute phenomena which may be relevant for other ceramics.

SiBCN materials for high-temperature applications: Atomistic origin of electrical conductivity

The paper contains a detailed discussion of the electronic structure of the novel hard and thermally stable amorphous SiBCN materials. We focus on the weight of individual electronic states on different elements, bond types, bonds of different lengths, and the number of atoms and clusters of atoms the states are localized on. A special attention is paid to the states around the Fermi level. We show in detail the effect of individual elements and bond types on the (non)conductivity of the materials. The results provide a detailed insight into the complex relationships between the material composition and the electronic properties, and allow one to tailor SiBCN compositions which can combine different functional properties, such as high thermal stability with electrical conductivity.

Reactive high-power impulse magnetron sputtering of ZrO2 films with gradient ZrOx interlayers on pretreated steel substrates

High-power impulse magnetron sputtering with a pulsed O2 flow control was used for reactive deposition of densified stoichiometric ZrO2 films with gradient ZrOx interlayers onto floating Si and steel substrates at low substrate temperatures (less than 150 °C). The depositions were performed using a strongly unbalanced magnetron with a planar Zr target of 100 mm diameter in Ar + O2 gas mixtures at the total pressure close to 2 Pa. Two kinds of gradient ZrOx interlayers with different depth profiles of the stoichiometric coefficient, x, from x ≅ 0 to 2, were deposited using the feedback pulsed O2 flow control. Prior to deposition, a modification of the substrate surfaces was performed by high-power impulse magnetron sputtering of the Zr target in Ar gas at the same pressure of 2 Pa and a direct current substrate bias from −965 to −620 V in a target pulse and low substrate temperatures (less than 150 °C) for 10 min. It was shown that the pretreatment of the steel substrates is a necessary condition for good adhesion of the zirconium oxide (both pure ZrO2 and ZrO2 + ZrOx interlayer) films and that the adhesion of the ZrO2 films is substantially higher when the gradient ZrOx interlayers are used. The densified stoichiometric ZrO2 films (refractive index of 2.21 and extinction coefficient of 4 × 10−4 at the wavelength of 550 nm) deposited onto the gradient ZrOx interlayers exhibited a high hardness (15–16 GPa) and an enhanced resistance to cracking.High-power impulse magnetron sputtering with a pulsed O2 flow control was used for reactive deposition of densified stoichiometric ZrO2 films with gradient ZrOx interlayers onto floating Si and steel substrates at low substrate temperatures (less than 150 °C). The depositions were performed using a strongly unbalanced magnetron with a planar Zr target of 100 mm diameter in Ar + O2 gas mixtures at the total pressure close to 2 Pa. Two kinds of gradient ZrOx interlayers with different depth profiles of the stoichiometric coefficient, x, from x ≅ 0 to 2, were deposited using the feedback pulsed O2 flow control. Prior to deposition, a modification of the substrate surfaces was performed by high-power impulse magnetron sputtering of the Zr target in Ar gas at the same pressure of 2 Pa and a direct current substrate bias from −965 to −620 V in a target pulse and low substrate temperatures (less than 150 °C) for 10 min. It was shown that the pretreatment of the steel substrates is a necessary condition for good ...

Relationships between the distribution of O atoms on partially oxidized metal (Al, Ag, Cu, Ti, Zr, Hf) surfaces and the adsorption energy: A density-functional theory study

We investigate the oxidation of selected metal (Al, Ag, Cu, Ti, Zr, and Hf) surfaces by the density functional theory. We go through a wide range of (233 per metal) distributions of O atoms on a partially oxidized metal surface. First, we focus on the qualitative information whether the preferred distribution of O atoms is heterogeneous (stoichiometric oxide + metal) or homogeneous (substoichiometric oxide). We find that the former is energetically preferred, e.g., for Al, while the latter is energetically preferred, e.g., for Ti, Zr, and Hf. Second, we provide the quantitative values of adsorption energies corresponding to the energetically preferred O atom distributions for various partial coverages of various metals by O. Third, we discuss and show an example of implications of the aforementioned findings for the understanding and simulations of sputtering.