National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Sputter deposited p-NiO/n-SnO2 porous thin film heterojunction based NO2 sensor with high selectivity and fast response

Abstract: In this work, we report fabrication and characterization of porous, single layer n-SnO2, p-NiO and bilayer thin film heterojunction devices developed using pulsed DC magnetron sputtering for NO2 detection. Template-free, NiO/SnO2 heterojunction devices were deposited both in top-bottom and in-plane electrode configurations. All the devices showed an optimum sensing temperature of 200 °C. Systematic comparison of the fabricated devices revealed that the heterojunction devices with top-bottom electrodes improved performance. Electrical characterization confirmed the formation of heterojunction across the interface. The response values of the heterojunction sensor ranged from 57 to 144 % for the NO2 concentration range of 2–10 ppm. The heterojunction device showed high selectivity against CO and NH3 with selectivity coefficients of 90 and 26, respectively. The heterojunction sensor exhibited fast response and recovery times of 37 and 98 s, respectively. The device showed excellent stability with

Mechanical and tribological properties of sputter deposited nanostructured Cr–WS2 solid lubricant coatings

Abstract: Solid lubricant coatings of WS 2 and Cr–WS 2 (15–50 at.% Cr) prepared using an unbalanced magnetron sputtering system were evaluated for their mechanical and tribological properties. Nanoindentation results indicated that addition of Cr helped in improving the mechanical properties and the elastic recovery ability of Cr–WS 2 coatings. The adhesive strengths of Cr–WS 2 coatings were evaluated using a nanoscratch tester and from the nanoscratch profiles, critical load values and optical images, it was evident that the adhesion of Cr–WS 2 coatings increased with an increase in the Cr content. Further analysis of the nanoscratch data indicated that WS 2 coatings exhibited large amount of plastic deformation compared to Cr–WS 2 coatings which showed a combination of elastic–plastic deformation. However, micro-tribometer measurements at a load of 2 N showed that the tribological properties of Cr–WS 2 coatings deteriorated with an increase in the Cr content. For example, Cr–WS 2 coatings prepared at Cr content ≥ 33 at.% failed after a sliding distance of 1 m. On the other hand, WS 2 and Cr–WS 2 coatings prepared at low Cr contents (15–23 at.% Cr) exhibited a stable friction coefficient (50–60% relative humidity) in the range of 0.10–0.13 for a sliding distance of 14 m. Micro-Raman spectroscopy data of the worn films taken after a sliding distance of 14 m indicated the presence of WS 2 transfer films for WS 2 and Cr–WS 2 coatings prepared at low Cr contents. For Cr–WS 2 coatings with Cr content ≥ 33 at.%, the worn films consisted predominantly of WO 3 . After an extended sliding distance of 50 m, Cr–WS 2 coatings (15–23 at.% Cr) outperformed WS 2 coating which failed after 20 m. Further, the coatings prepared at low Cr contents did not show any failure even after a sliding distance of 200 m. At a higher load of 7 N, Cr–WS 2 coating with 15 at.% Cr exhibited the best performance with a friction coefficient of 0.07 up to a sliding distance of 72 m. These results indicate that the amount of Cr in the WS 2 matrix needs to be controlled judiciously to obtain improved mechanical and tribological properties in Cr–WS 2 solid lubricant coatings.