V. Moraes

Bio: V. Moraes is an academic researcher from Vienna University of Technology. The author has contributed to research in topics: Thermal stability & Thin film. The author has an hindex of 8, co-authored 13 publications receiving 262 citations.

Ab initio inspired design of ternary boride thin films.

Abstract: The demand to discover new materials is scientifically as well as industrially a continuously present topic, covering all different fields of application. The recent scientific work on thin film materials has shown, that especially for nitride-based protective coatings, computationally-driven understanding and modelling serves as a reliable trend-giver and can be used for target-oriented experiments. In this study, semi-automated density functional theory (DFT) calculations were used, to sweep across transition metal diborides in order to characterize their structure, phase stability and mechanical properties. We show that early transition metal diborides (TiB2, VB2, etc.) tend to be chemically more stable in the AlB2 structure type, whereas late transition metal diborides (WB2, ReB2, etc.) are preferably stabilized in the W2B5−x structure type. Closely related, we could prove that point defects such as vacancies significantly influence the phase stability and even can reverse the preference for the AlB2 or W2B5−x structure. Furthermore, investigations on the brittle-ductile behavior of the various diborides reveal, that the metastable structures are more ductile than their stable counterparts (WB2, TcB2, etc.). To design thin film materials, e.g. ternary or layered systems, this study is important for application oriented coating development to focus experimental studies on the most perspective systems.

Thermal conductivity and mechanical properties of AlN-based thin films

Abstract: While many research activities concentrate on mechanical properties and thermal stabilities of protective thin films, only little is known about their thermal properties being essential for the thermal management in various industrial applications. Based on the 3ω-method, we show the influence of Al and Cr on the temperature dependent thermal conductivity of single-phase cubic structured TiN and single-phase wurtzite structured AlN thin films, respectively, and compare them with the results obtained for CrN thin films. The dc sputtered AlN thin films revealed a highly c-axis oriented growth for deposition temperatures of 250 to 700 °C. Their thermal conductivity was found to increase strongly with the film thickness, indicating progressing crystallization of the interface near amorphous regions during the sputtering process. For the 940 nm AlN film, we found a lower boundary for the thermal conductivity of 55.3 W m-1 K-1. By the substitution of only 10 at. % Al with Cr, κ significantly reduces to ∼5.0 W m...

Influence of Tantalum on phase stability and mechanical properties of WB2

Abstract: Based on density functional theory, we recently suggested that metastable α-WB2 is a promising candidate combining very high hardness with high toughness. These calculations further suggested that the addition of Tantalum supports the crystallization of α-structured W1-xTaxB2-z, with only minor reduction in toughness. Thus, various Ta containing WB2-based coatings have been synthesized using physical vapor deposition. With increasing Ta content, the hardness increases from ~41 GPa (WB2) to ~45 GPa (W0.74Ta0.26B2). In situ micromechanical cantilever bending tests exhibit fracture toughness KIC values of 3.7 to 3.0 MPa-√m for increasing Ta content (single-phased up to 26 at.% Ta).

Ab initio inspired design of ternary boride thin films.

Abstract: The demand to discover new materials is scientifically as well as industrially a continuously present topic, covering all different fields of application. The recent scientific work on thin film materials has shown, that especially for nitride-based protective coatings, computationally-driven understanding and modelling serves as a reliable trend-giver and can be used for target-oriented experiments. In this study, semi-automated density functional theory (DFT) calculations were used, to sweep across transition metal diborides in order to characterize their structure, phase stability and mechanical properties. We show that early transition metal diborides (TiB2, VB2, etc.) tend to be chemically more stable in the AlB2 structure type, whereas late transition metal diborides (WB2, ReB2, etc.) are preferably stabilized in the W2B5−x structure type. Closely related, we could prove that point defects such as vacancies significantly influence the phase stability and even can reverse the preference for the AlB2 or W2B5−x structure. Furthermore, investigations on the brittle-ductile behavior of the various diborides reveal, that the metastable structures are more ductile than their stable counterparts (WB2, TcB2, etc.). To design thin film materials, e.g. ternary or layered systems, this study is important for application oriented coating development to focus experimental studies on the most perspective systems.

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

Abstract: 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.

Flexible thermally conductive and electrically insulating silicone rubber composite films with BNNS@Al2O3 fillers

Abstract: With the advent of 5G era, the electronic and electrical industries are in increasingly urgent demand for flexible materials with high thermal conductivity coefficients (λ). In this paper, alumina (Al2O3) was chemically grafted to the surface of boron nitride nanosheets (BNNS) to prepare hetero-structured thermally conductive fillers (BNNS@Al2O3), and two-component room temperature vulcanized silicone rubber (RTV-2SR) was used as the polymer matrix. Then BNNS@Al2O3/RTV-2SR flexible thermally conductive and electrically insulating composite films were prepared by shear-coating. Results of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscope (SEM) showed that the BNNS@Al2O3 hetero-structured thermally conductive fillers with “point-plane” structure were successfully prepared. The BNNS@Al2O3 hetero-structured thermally conductive fillers successfully achieved the synergy of Al2O3 and BNNS and had more significant improvement on λ than single Al2O3, single BNNS, and simply blending BNNS/Al2O3. When the amount of BNNS@Al2O3 was 30 wt% (BNNS/Al2O3, 1:1, wt:wt), the in-plane λ (λ∥) and through-plane λ (λ⊥) of the BNNS@Al2O3/RTV-2SR thermally conductive composite film reached 2.86 W/mK and 0.89 W/mK, 2.8 times λ∥ (1.01 W/mK) and 4.2 times λ⊥ (0.21 W/mK) pure RTV-2SR film, also higher than those of BNNS/RTV-2SR (with single BNNS, λ∥ = 2.46 W/mK, λ⊥ = 0.76 W/mK), Al2O3/RTV-2SR (with single Al2O3, λ∥ = 1.62 W/mK, λ⊥ = 0.49 W/mK), and (BNNS/Al2O3)/RTV-2SR (with simply blending BNNS/Al2O3, 1:1, wt:wt, λ∥ = 2.04 W/mK, λ⊥ = 0.62 W/mK) thermally conductive composite films with the same fillers amount. Meanwhile, the prepared BNNS@Al2O3/RTV-2SR thermally conductive composite film obtained excellent mechanical properties, electrical insulation properties, and thermal properties. Its tensile strength, elongation at break, hardness, dielectric constant (e), dielectric loss (tanδ), volume resistivity (ρv), glass transition temperature (Tg), and heat resistance index temperature (THRI), respectively, reached 0.84 MPa, 175%, 27 HA, 3.89, 0.0088, 5.76 × 1011 Ω·cm, − 40.1 °C and 185.3 °C. This work can provide a new idea for the preparation of hetero-structured thermally conductive fillers and flexible thermally conductive and electrically insulating composite films. Schematic diagrams for hetero-structured BNNS@Al2O3 fillers, BNNS@Al2O3/RTV-2SR thermally conductive composite films and corresponding thermal conduction mechanism.