PolyU IR Collection: MRC Journal/Magazine Articles
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Relationship between the microstructure and nanoindentation hardness of thermally evaporated and magnetron-sputtered electrochromic tungsten oxide films
http://hdl.handle.net/10397/6022
Title: Relationship between the microstructure and nanoindentation hardness of thermally evaporated and magnetron-sputtered electrochromic tungsten oxide films<br/><br/>Authors: Ong, C. W.; Wong, H. Y.; Pang, Geoffrey Kin-hung; Baba-Kishi, K. Z.; Choy, Chung-loong<br/><br/>Abstract: Tungsten oxide (WOₓ) films were fabricated by (i) reactive thermal evaporation (RTE) at room temperature with oxygen ambient pressure Pₒ₍₂₎ as a parameter, and (ii) reactive magnetron sputtering (RMS) with substrate temperature T[sub s] as a parameter. The film structure revealed by x-ray photoelectron spectroscopy, x-ray diffraction, density measurements, infrared absorption, and atomic force microscopy was correlated with the nanoindentation hardness H. The RTE WOₓ films deposited at high Pₒ₍₂₎ were amorphous and porous, while H depended appreciably on normalized penetration depth h[sub D] (indentation depth/film thickness) due to the closing of the pores at the point of indentation. Decrease in Pₒ₍₂₎ from 10 to 2 × 10⁻³ retort led to smaller porosity, weaker h[sub D] dependence of H, and higher average H (measured at h[sub D] ≈ 0.2 to 0.3, for example). The RMS WOₓ film deposited at room temperature was amorphous and denser than all RTE films. The rise in substrate temperature T[sub s] first densified the film structure (up to 110 °C) and then induced crystallization with larger grain size for T[sub s] ≥ 300 °C. Correspondingly, the h D dependence of H became weaker. In particular, H of the RMS sample deposited at 110 °C showed a peak at h[sub D] slightly above 1 owing to pileup at the contact point of indentation. For higher T[sub s], pileup occurred at shallower h[sub D] and the average H (measured at h[sub D] ≈ 0.2 to 0.3, for example) rose, accompanied by the increase of grain size.<br/><br/>Description: DOI: 10.1557/JMR.2001.0214Tensile strength of zinc oxide films measured by a microbridge method
http://hdl.handle.net/10397/6020
Title: Tensile strength of zinc oxide films measured by a microbridge method<br/><br/>Authors: Ong, C. W.; Zong, D. G.; Aravind, M.; Choy, Chung-loong; Lu, D. R.<br/><br/>Abstract: Double-layered ZnO/silicon nitride microbridges were fabricated for microbridge tests. In a test, a load was applied to the center of the microbridge specimen by using a microwedge tip, where the displacement was recorded as a function of load until the specimen broke. The silicon nitride layer in the structure served to enhance the robustness of the specimen. By fitting the data to a theory, the elastic modulus, residual stress, and tensile strength of the ZnO film were found to be 137 ± 18 GPa, -0.041 ± 0.02 GPa, and 0.412 ± 0.05 GPa, respectively. The analysis required the elastic modulus, internal stress, and tensile strength of the silicon nitride layer. They were measured separately by microbridge tests on single-layered silicon nitride microbridges. The measured tensile strength of the ZnO films represents the maximum tolerable tensile stress that the films can sustain when they are used as the functional component in devices.<br/><br/>Description: DOI: 10.1557/JMR.2003.0343New relationship between Young's modulus and nonideally sharp indentation parameters
http://hdl.handle.net/10397/6019
Title: New relationship between Young's modulus and nonideally sharp indentation parameters<br/><br/>Authors: Ma, Dejun; Ong, C. W.; Wong, Sing-fai<br/><br/>Abstract: Both analysis and numerical calculations have been carried out to investigate the relationship between Young's modulus and nonideally sharp indentation parameters. The results confirm that there exists an approximate one-to-one correspondence between the ratio of nominal hardness/reduced Young's modulus (H[sub n]/E[sub r]) and the ratio of elastic work/total work (Wₑ/W) for any definite bluntness ratio (Δh/h[sub m]) of a nonideally sharp indenter. Based on this relationship, the Young's modulus of the indented material can be determined just from the values of H[sub n], Wₑ, and W, which are directly measurable quantities in an indentation test.<br/><br/>Description: DOI: 10.1557/JMR.2004.0274New method for determining Young's modulus by non-ideally sharp indentation
http://hdl.handle.net/10397/6018
Title: New method for determining Young's modulus by non-ideally sharp indentation<br/><br/>Authors: Ma, Dejun; Ong, C. W.; Wong, Sing-fai; He, Jiawen<br/><br/>Abstract: In a previously developed method for estimating Young's modulus E by depth-sensing indentation with spherical-tipped Berkovich indenter, the E value is deduced from several functional relationships (established by finite element analysis) relating nominal hardness/reduced elastic modulus ratio (H[sub n]/E[sub r]) and elastic work/total work ratio (Wₑ/W). These relationships are specified for different absolute bluntness/maximum displacement ratios (Δh/h[sub m]). This paper reports the generalization of the method by proposing a function to replace all the above mentioned H[sub n]/E[sub r]-Wₑ/W relationships. The function contains only a parameter V[sub r] ≡ V[sub ideal]/V[sub blunt] instead of Δh/h[sub m], where V[sub ideal] is defined as the indented volume bounded by the cross-sectional areas measured at the maximum displacement hm for an ideally sharp indenter, and V [sub blunt] is that of the real indenter. The use of V[sub r] to replace Δh/h[sub m] is for the purpose of extending the application of the method for non-spherical tipped Berkovich indenters. The effectiveness of the method for materials of prominent plasticity was demonstrated by performing tests on carbon steel and aluminum alloy using three Berkovich indenters with different tip shapes.<br/><br/>Description: DOI: 10.1557/JMR.2005.0193