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...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 （Al2O3） is used to fabricate the nanostep. There are three steps of Al2O3 in this structure including 8 nm, 18 nm and 44 inn. The thickness of Al2O3 film and the height of the step are measured by anellipsometer. The experimental results show that the thickness of Al2O3 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 Physikaliseh-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.展开更多
The energy dissipation of X-shaped flaring gate piers ahead of a stepped spillway was adopted in the Suofengying Hydroplant. Under the circumstance that the first step is higher than others, at the step surface an aer...The energy dissipation of X-shaped flaring gate piers ahead of a stepped spillway was adopted in the Suofengying Hydroplant. Under the circumstance that the first step is higher than others, at the step surface an aerated cavity occured behind piers. The interaction of the weir head, the elevation difference between crest and chamber outlet, the first step height, the slopes of weir end and step, and the size of cavity, was investigated, the expression was derived to characterize their relationship, and the corresponding curves were plotted. The comparison of the calculated and simulated results with the measured data was performed. When the slopes of step and weir end are equivalent, the relative height difference between the first and second steps becomes the main factor influencing the aerated cavity. These findings may be useful in practical applications.展开更多
A coastal forest combined with a backward-facing step is an efficient facility to reduce tsunami damage to residential areas behind sea embankments.This study establishes a generalized model,and experimentally explore...A coastal forest combined with a backward-facing step is an efficient facility to reduce tsunami damage to residential areas behind sea embankments.This study establishes a generalized model,and experimentally explores the water level changes upstream of the vegetation-step mitigation model as well as its energy dissipation effect under different initial Froude numbers,step heights,and vegetation conditions.The results show that the relative backwater rise increases with the growth of vegetation density,patch length and initial Froude number,representing a slowing down of the tsunami inundation.As for energy dissipation,it is mainly caused by the additional resistance of the vegetation and the hydraulic jump.And the vegetation condition not only affects the energy dissipation due to stem-scale turbulence within the patch,but also changes the hydraulic jump process of water falling from the step in cooperation with the step height.As a result,the energy dissipation efficiency always increases with the growth of vegetation density,vegetation patch length and step height.With the criterion that the energy dissipation efficiency and its growth rate can hardly change with vegetation parameters,this study innovatively defines the threshold slope and gives the principle of judging the most cost-effective vegetation conditions at different step heights.These results are expected to provide an important reference for the design of composite tsunami mitigation facilities.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51175418)Major Research Program on Nanomanufacturing of National Natural Science Foundation of China(Grant No.91323303)+1 种基金Fund of the State Key Laboratory of Precision Measuring Technology and Instruments(Tianjin University and Tsinghua University)of China(Grant No.PIL1403)Collaborative Innovation Center of Suzhou Nano Science and Technology of China
文摘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 （Al2O3） is used to fabricate the nanostep. There are three steps of Al2O3 in this structure including 8 nm, 18 nm and 44 inn. The thickness of Al2O3 film and the height of the step are measured by anellipsometer. The experimental results show that the thickness of Al2O3 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 Physikaliseh-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.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50479061).
文摘The energy dissipation of X-shaped flaring gate piers ahead of a stepped spillway was adopted in the Suofengying Hydroplant. Under the circumstance that the first step is higher than others, at the step surface an aerated cavity occured behind piers. The interaction of the weir head, the elevation difference between crest and chamber outlet, the first step height, the slopes of weir end and step, and the size of cavity, was investigated, the expression was derived to characterize their relationship, and the corresponding curves were plotted. The comparison of the calculated and simulated results with the measured data was performed. When the slopes of step and weir end are equivalent, the relative height difference between the first and second steps becomes the main factor influencing the aerated cavity. These findings may be useful in practical applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.52020105006,12272281,U2340216).
文摘A coastal forest combined with a backward-facing step is an efficient facility to reduce tsunami damage to residential areas behind sea embankments.This study establishes a generalized model,and experimentally explores the water level changes upstream of the vegetation-step mitigation model as well as its energy dissipation effect under different initial Froude numbers,step heights,and vegetation conditions.The results show that the relative backwater rise increases with the growth of vegetation density,patch length and initial Froude number,representing a slowing down of the tsunami inundation.As for energy dissipation,it is mainly caused by the additional resistance of the vegetation and the hydraulic jump.And the vegetation condition not only affects the energy dissipation due to stem-scale turbulence within the patch,but also changes the hydraulic jump process of water falling from the step in cooperation with the step height.As a result,the energy dissipation efficiency always increases with the growth of vegetation density,vegetation patch length and step height.With the criterion that the energy dissipation efficiency and its growth rate can hardly change with vegetation parameters,this study innovatively defines the threshold slope and gives the principle of judging the most cost-effective vegetation conditions at different step heights.These results are expected to provide an important reference for the design of composite tsunami mitigation facilities.
