Titanium(Ti) alloys are widely used in aerospace industry due to the low density and high corrosion resistance. However, machining and polishing remain great challenges because of the hardness and chemical stability. With a home-made electrochemical machining workstation, cyclic voltammetry is performed at a wide potential range of [0 V, 20 V] to record the details of passivation and depassivation processes under a hydrodynamic mode. The results show that the thickness of viscous layer formed on the alloy surface plays a crucial effect on the electropolishing quality. The technical parameters, including the mechanical motion rate, polishing time and electrode gap, are optimized to achieve a surface roughness less than 1.9 nm, which shows a prospective application in the electrochemical machining of Ti and it alloys.
The current techniques used for the fabrication of nanosteps are normally done by layer growth and then ion beam thinning. There are also extra films grown on the step surfaces in order to reduce the roughness. So the whole process is time consuming. In this paper, a nanoscale step height structure is fabricated by atomic layer deposition(ALD) and wet etching techniques. According to the traceable of the step height value, the fabrication process is controllable. Because ALD technology can grow a variety of materials, aluminum oxide(Al_2O_3) is used to fabricate the nanostep. There are three steps of Al_2O_3 in this structure including 8 nm, 18 nm and 44 nm. The thickness of Al_2O_3 film and the height of the step are measured by anellipsometer. The experimental results show that the thickness of Al_2O_3 film is consistent with the height of the step. The height of the step is measured by AFM. The measurement results show that the height is related to the number of cycles of ALD and the wet etching time. The bottom and the sidewall surface roughness are related to the wet etching time. The step height is calibrated by Physikalisch-Technische Bundesanstalt(PTB) and the results were 7.5±1.5 nm, 15.5±2.0 nm and 41.8±2.1 nm, respectively. This research provides a method for the fabrication of step height at nanoscale and the nanostep fabricated is potential used for standard references.
WANG ChenyingYANG ShumingJING WeixuanREN WeiLIN QijingZHANG YijunJIANG Zhuangde
By introducing the mechanical motion into the confined etchant layer technique(CELT), we have developed a promising ultraprecision machining method, termed as electrochemical mechanical micromachining(ECMM), for producing both regular and irregular three dimensional(3 D) microstructures. It was found that there was a dramatic coupling effect between the confined etching process and the slow-rate mechanical motion because of the concentration distribution of electrogenerated etchant caused by the latter. In this article, the coupling effect was investigated systemically by comparing the etchant diffusion, etching depths and profiles in the non-confined and confined machining modes. A two-dimensional(2 D) numerical simulation model was proposed to analyze the diffusion variations during the ECMM process, which is well verified by the machining experiments. The results showed that, in the confined machining mode, both the machining resolution and the perpendicularity tolerance of side faces were improved effectively. Furthermore, the theoretical modeling and numerical simulations were proved valuable to optimize the technical parameters of the ECMM process.
The sulfate ions modified YAG:Ce^(3+) phosphors were prepared by co-precipitation method and characterized by X-ray diffraction,transmission electron microscopy,and photoluminescence.Effects of sulfate ions on the photoluminescence(PL) property of the as-prepared YAG:Ce^(3+) phosphors were studied,with sodium dodecyl sulfate(SDS) being added to R^(3+)(Ce^(3+),Y^(3+),Al^(3+)) ions.Results indicated that pure YAG:Ce^(3+) phosphors with different ratios of sulfate ions could be easily obtained by calcining the as-synthesized precursor at 950 ℃ for 2 h,the YAG:Ce^(3+) phosphors with an optimal mass ratio of 3.5 wt.%SDS had the highest emission intensity and the best dispersion behavior,and the fluorescence decay of the as-obtained YAG:Ce^(3+) phosphors was related to the lattice defect,reabsorption and cross correlation.Furthermore,thermal quenching properties of the YAG:Ce^(3+) phosphors and the YAG:Ce^(3+) phosphors with 3.5 wt.%SDS were also discussed,indicating that the YAG:Ce^(3+) with SDS phosphors could have potential applications in the daylight LEDs or warm white LEDs.
Current stretchable surface electrodes have attracted increasing attention owing to their potential applications in biological signal monitoring, wearable human-machine interfaces(HMIs) and the Internet of Things. The paper proposed a stretchable HMI based on a surface electromyography(sEMG) electrode with a self-similar serpentine configuration. The sEMG electrode was transfer-printed onto the skin surface conformally to monitor biological signals, followed by signal classification and controlling of a mobile robot. Such electrodes can bear rather large deformation(such as >30%) under an appropriate areal coverage. The sEMG electrodes have been used to record electrophysiological signals from different parts of the body with sharp curvature, such as the index finger,back of the neck and face, and they exhibit great potential for HMI in the fields of robotics and healthcare. The electrodes placed onto the two wrists would generate two different signals with the fist clenched and loosened. It is classified to four kinds of signals with a combination of the gestures from the two wrists, that is, four control modes. Experiments demonstrated that the electrodes were successfully used as an HMI to control the motion of a mobile robot remotely.
