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The piezotronic effect and piezo-phototronic effect on materials and devices have been widely studied in binary semiconductors. Wide-band ternary semiconductors are a great class of materials with potential application in nano/microdevices, because of their continuously tunable physical properties with composition. Here, we first demonstrate the piezo-photronics effect of ternary wurtzite structured nanowires (NWs), opening an innovative materials system. Single-crystal ternary CdS x Se 1−x (x = 0.85, 0.60, and 0.38) NWs were synthesized with site-controlled compositions via a chemical vapor deposition process, and high-performance visible photodetectors (PDs) with fast response speed (<2 ms), high photosensitivity, high responsivity, and broadened photoresponse region (than CdS NW) were fabricated based on these ternary materials. By introducing an external tensile strain, the performance of PDs is enhanced by 76.7% upon 0.2 mW/cm 2 442 nm light illumination for CdS 0.85 Se 0.15 by the piezo-phototronic effect. The composition effect of materials in ternary materials on light detecting and piezo-phototronics was also first investigated systematically. The results indicate that in the CdS x Se 1−x system, as the value of x decreases, the photocurrent and responsivity experience an increase, while the enhancement of the piezo-phototronic effect was weakened. The change in piezoelectric coefficient and carrier screening effect are proposed for the observed phenomenon. This study reports a high-quality ternary CdS x Se 1−x NWs system used for high-performance PDs, broadens the family of piezotronic materials, offers an innovative material for high-performance visible PD, and provides a new pathway to modulate the performance of piezo-phototronic devices by tuning the atomic ratios of ternary wurtzite semiconducting materials. This is essential for developing a full understanding of piezotronics on a broader scope, and it also enables the development of the better performance of optoelectronic devices.

In contrast with dimple textures, surface roughness is a texture at the micro-scale, essentially which will influence the load-bearing capacity of lubricant film. The numerical simulation was carried out to investigate the influence of surface roughness on friction property of textured surface. The lubricant film pressure was obtained using the method of computational fluid dynamics according to geometric model of round dimple, and the renormalization-group k-e turbulent model was adopted in the computation. The numerical simulation results suggest that there is an optimum dimensionless surface roughness, and near this value, the maximum load-bearing capacity can be achieved. The load-bearing capacity is determined by the surface texture, the surface roughness, and the interaction between them. To get information of friction coefficient, the experiments were conducted. This experiment was used to evaluate the simulation. The experimental results show that for the frequency of 4 and 6 Hz, friction coefficient decreases at first and then increases with decreasing surface roughness, which indicates that there exists the optimum region of surface roughness leading to the best friction reduction effect, and it becomes larger when area fractions increase from 2% to 10%. The experimental results agree well with the simulation results.

Abstract:Friction experiments are conducted on a ring-on-disk tribometer, and friction noise produced during the friction process is extracted by a microphone. The phase trajectory and chaotic parameters of friction noise are obtained by phase-space reconstruction, and its attractor evolution is analyzed. The results indicate that the friction noise is chaotic because the largest Lyapunov exponent is positive. The phase trajectory of the friction noise follows a "convergence-stability-divergence" pattern during the friction process. The friction noise attractor begins forming in the running-in process, and the correlation dimension D increases gradually. In the stable process, the attractor remains steady, and D is stable. In the last step of the process, the attractor gradually disappears, and D decreases. The friction noise attractor is a chaotic attractor. Knowledge of the dynamic evolution of this attractor can help identify wear state changes from the running-in process to the steady and increasing friction processes.

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