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Your search keyword '"Guo, Xu"' showing total 4 results
Start Over Author "Guo, Xu" Topic surface roughness
4 results on '"Guo, Xu"'

1. Flexible white top-emitting organic light-emitting diode with a MoOxroughness improvement layer

Author

Guo Xu, Chen Shu-Fen, Wu Qiang, Zhao Xiao-Fei, Huang Wei, and Shao Ming

Subjects
Materials science, business.industry, General Physics and Astronomy, Substrate (electronics), Electroluminescence, Cathode, Anode, law.invention, law, OLED, Surface roughness, Optoelectronics, Chromaticity, business, Layer (electronics)
Abstract

In this paper, an MoOx film is deposited on a polyethylene terephthalate (PET) substrate as a buffer layer to improve the surface roughness of the flexible PET substrate. With an optimized MoOx thickness of 100 nm, the surface roughness of the PET substrate can be reduced to a very small value of 0.273 nm (much less than 0.585 nm of the pure PET). Flexible white top-emitting organic light-emitting diodes (TEOLEDs) with red and blue dual phosphorescent emitting layers are constructed based on a low-reflectivity Sm/Ag semi-transparent cathode. The flexible white emission exhibits the best luminance and current injection characteristics with the 100-nm-thick MoOx buffer layer and this result indicates that a smooth substrate is beneficial to the enhancement of device electrical and electroluminescence performances. However, the white TEOLED with a 50-nm-thick MoOx buffer layer exhibits a maximum current efficiency of 4.64 cd/A and a power efficiency of 1.9 lm/W, slightly higher than those with a 100-nm MoOx buffer layer, which is mainly due to an obvious intensity enhancement but limited current increases in 50-nm MoOx-based white TEOLED. The change amplitudes of the Commission International de l'Eclairage (CIE) chromaticity coordinates are less than (0.016, 0.005) for all devices in a wide luminance range over 100 cd/m2, indicating an excellent color stability in our white flexible TEOLEDs. Additionally, the flexible white TEOLED with an MoOx buffer layer shows excellent flexibility to withstand more than 500 bending times under a curvature radius of approximately 9 mm. Research demonstrates that it is mainly attributed to the high surface energy of the MoOx buffer layer, which is conducible to the improvement of the surface adhesion to the PET substrate and the Ag anode.

Published
2013

2. Mechanics of axisymmetric adhesive contact of rough surfaces involving power-law graded materials.

Author

Jin, Fan and Guo, Xu

Subjects
*ADHESIVES, *SURFACE roughness, *MECHANICAL behavior of materials, *AXIAL loads, *ENERGY dissipation, *FRACTURE toughness, *STRENGTH of materials
Abstract

Abstract: In the present paper, the mechanics of axisymmetric adhesive contact of rough surfaces involving power-law graded materials is investigated analytically. A series of general analytical solutions have been obtained with use of the cumulative superposition and equivalent energy release rate approaches. These solutions provide closed-form expressions of equilibrium relations among applied load, indentation depth and contact radius. Based on these solutions, an effective macroscopic description of the contact evolution is obtained for a general punch profile with surface roughness. Our analysis results reveal that the simultaneous presence of surface roughness and graded material properties can influence the pull-off force and energy dissipation due to adhesion hysteresis significantly. Moreover, it is found that both the adhesion strength and toughness can be optimized by adjusting the surface topography and material parameters of power-law graded solids appropriately. The analytical results obtained in this paper include the corresponding solutions for homogeneous isotropic materials as special cases and therefore can also serve as the benchmarks for checking the validity of numerical solution results. [Copyright &y& Elsevier]

Published
2013
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3. A magnification-based multi-asperity (MBMA) model of rough contact without adhesion.

Author

Guo, Xu, Ma, Benben, and Zhu, Yichao

Subjects
*ROUGH surfaces, *ADHESION, *MULTISCALE modeling, *MOLECULAR dynamics, *CONTACT mechanics
Abstract

Contact analysis without adhesion is still a challenging issue, mainly owing to the multiscale and self-fractal characteristics of rough surfaces. One of the most widely used theories for analyzing contact behavior of rough surfaces is the asperity-based Hertz contact models initiated by Greenwood and Williamson. Due to its single-scaled nature, however, G-W models generally output less accurate predictions when indentation is deep. This article aims for proposing a new theoretical model that effectively formulates the contact status of rough surfaces throughout the entire compression process. This is achieved by integrating the idea of magnification, or evolving resolution into the G-W model, and a magnification-based multi-asperity model is thus established where the multiscale nature of rough surface is taken into account properly. In the derived model, the originally complex contact problem is decomposed into a family of sub-problems each defined on a morphologically simpler contact islands, and a number of explicit formulations from existing multi-asperity models can thus be used. The present model not only effectively reproduces the results of G-W models for short indentation distance, but is also shown that when indentation is sufficiently deep, the present model smoothly transits to the regime of elastic interaction between smooth surfaces governed by Hookean-law formulation. Compared to other G-W type models, the proposed framework has also shown its strength in the computation of actual contact area. The proposed model is then compared with existing molecular dynamics simulation and experimental results for validation. [ABSTRACT FROM AUTHOR]

Published
2019
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4. Adhesive contact of a power-law graded elastic half-space with a randomly rough rigid surface.

Author

Jin, Fan, Zhang, Wei, Wan, Qiang, and Guo, Xu

Subjects
*ADHESION, *CONTACT mechanics, *POWER law (Mathematics), *ELASTICITY, *SURFACE roughness, *ENERGY dissipation, *PARAMETER estimation
Abstract

A theoretical model of a power-law graded elastic half-space in contact with a randomly rough rigid surface is established by combining the Greenwood–Williamson rough contact model and the JKR type adhesion model for power-law graded materials. The rough surface is modeled as an ensemble of non-interacting asperities with identical radius of curvature and Gaussian distributed heights. By applying the JKR type theory for power-law graded solids to each individual asperity of the rough surface, the total normal forces for the rough surface are derived for loading and unloading stages, respectively, and a prominent adhesion hysteresis associated with dissipation energy is revealed. Our results include the solutions for homogeneous materials and Gibson solids as special cases and describe the complete transition between these two limiting situations. A dimensionless adhesion parameter, which influences both the total pull-off force and the energy dissipation due to adhesive hysteresis, is also identified. It is found that a small adhesion parameter results in higher energy dissipation and pull-off force, while a large adhesion parameter leads to lower energy dissipation and pull-off force. [ABSTRACT FROM AUTHOR]

Published
2016
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