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Y 2 O 3 coating on Al 2 O 3 substrate was prepared by atmospheric plasma spray (APS). Computational fluid dynamics (CFD) was carried out to predict the state of in-flight Y 2 O 3 particles at different powder feeding rates. Microstructure and mechanical properties were found to be affected by the spray distance and powder feeding rate. In this study, the hardness was calculated using a field emission-scanning electron microscope (FE-SEM) because the indentation in the coating is too small to measure using a hardness test machine. The formation of pores causes a decrease in the mechanical property, and the pore length of over 10 μm substantially decreases the hardness. Meanwhile, the solidification behavior is affected by the maximum temperature of the in-flight particles. Based on computational fluid dynamics (CFD) analysis, the maximum temperature of the in-flight particles was found to decrease with increase of the powder feeding rate at the same spray distance. At the powder feeding rate of 60 g/min, a lower adhesion strength was confirmed than that at feeding rate of 30 g/min because splats were insufficiently spread due to the lower maximum temperature of the in-flight particles. The roughness and height of the coating surface were evaluated by confocal microscopy and atomic force microscopy(AFM) analyses. The roughness is the resultant of accumulated splats and the accumulation mechanism of splats is affected by the state of the in-flight particles. Furthermore, there were nano-scale differences of height on the splat surface, on which the nucleation looks like 'rugged bark' during solidification of splats when the in-flight particles impact the substrate. [ABSTRACT FROM AUTHOR]

Piezoelectric materials are suitable for haptic technology as they can convert mechanical stimuli into electrical signals and vice-versa. However, owing to their disadvantageous mechanical properties such as brittleness (in ceramics) and a low piezoelectric coefficient (in polymers), their application in haptic technology remains challenging. In this paper, we introduce a truss-like 3D hollow nanostructure using zinc oxide (ZnO) that exhibits a drastically improved elastic strain limit while maintaining a piezoelectric coefficient similar to that of single-crystal ZnO. The ZnO hollow nanostructure was fabricated using proximity field nanopatterning (PnP) and atomic layer deposition (ALD) at four different processing temperatures. The piezoelectric characteristics were analyzed through dual AC resonance tracking piezoresponse force microscopy (PFM), and the piezoelectric coefficient was measured to be up to 9.2 pm/V. The nanopillar compression test result showed that the measured elastic strain limit of approximately 10% was at least 3 times greater than the previously reported value. The extended elastic limit of the 3D hollow structure was further supported by finite element simulations. The ZnO hollow nanostructure shows excellent potential for its application to enhanced haptic devices, which mimic the human sense of touch. A 3D ZnO hollow nanostructure exhibits an improved elastic strain limit while maintaining a piezoelectric coefficient similar to that of single-crystal ZnO. This nanostructure is fabricated using atomic layer deposition at four different temperatures. The piezoelectric coefficient of ≈ 9.2 pm/V and elastic strain limit of ≈ 10% are measured by piezoresponse force microscopy and nanopillar compression test, respectively. Image 1 • We developed a 3D ZnO hollow nanostructure through atomic layer deposition and 3D nanolithography. • The effective piezoelectric coefficient of 3D ZnO hollow nanostructure is close to that of a single-crystal bulk ZnO. • The 3D ZnO hollow nanostructure has a high elastic strain limit of 10% which is 3 times greater than the bulk ZnO value. • Our 3D hollow nanostructure can be used in enhanced haptic devices, which mimic the human sense of touch. [ABSTRACT FROM AUTHOR]