The aluminum foil for high voltage aluminum electrolytic capacitor was immersed in 0.5 mol/L H3PO4 or 0.125 mol/L NaOH solution at 40 ℃ for different time and then DC electro-etched in 1 mol/L HC1＋2.5 mol/L H2SO4 el...The aluminum foil for high voltage aluminum electrolytic capacitor was immersed in 0.5 mol/L H3PO4 or 0.125 mol/L NaOH solution at 40 ℃ for different time and then DC electro-etched in 1 mol/L HC1＋2.5 mol/L H2SO4 electrolyte at 80 ℃. The pitting potential and self corrosion potential of A1 foil were measured with polarization curves （PC）. The potentiostatic current--time curve was recorded and the surface and cross section images of etched A1 foil were observed with SEM. The electrochemical impedance spectroscopy （EIS） of etched A1 foil and potential transient curves （PTC） during initial etching stage were measured. The results show the chemical pretreatments can activate A1 foil surface, facilitate the absorption, diffusion and migration of C1- onto the A1 foil during etching, and improve the initiation rate of meta-stable pits and density of stable pits and tunnels, leading to much increase in the real surface area and special capacitance of etched A1 foil.展开更多
Process technology of multiple cylindrical micro-pins by wire-electrical discharge machining （wire-EDM） and electrochemical etching was presented. A row of rectangular micro-columns were machined by wire-EDM and the...Process technology of multiple cylindrical micro-pins by wire-electrical discharge machining （wire-EDM） and electrochemical etching was presented. A row of rectangular micro-columns were machined by wire-EDM and then machined into cylindrical shape by electrochemical etching. However, the shape of the multiple electrodes and the consistent sizes of the electrodes row are not easy to be controlled. In the electrochemical process, the shape of the cathode electrode determines the current density distribution on the anode and so the forming of multiple electrodes. This paper proposes a finite element method （FEM） to accurately optimize the electrode profile. The microelectrodes row with uniformity diameters with size from hundreds micrometers to several decades could be fabricated, and mathematical model controlling the shape and diameter of multiple microelectrodes was provided. Furthermore, a good agreement between experimental and theoretical results was confirmed.展开更多
It is possible to achieve selective electrochemical etching between different materials,such as p-and n-type silicon.However,achieving selective electrochemical etching on two different regions of the same p-type sili...It is possible to achieve selective electrochemical etching between different materials,such as p-and n-type silicon.However,achieving selective electrochemical etching on two different regions of the same p-type silicon material is a problem that has rarely been considered.Herein,a novel selective electrochemical etching technique for cantilever-type silicon-on-insulator(SOI)wafer-based microswitches is proposed.In this study,a p-type handle layer was selectively etched,and a p-type device layer was passivated.This was achieved using a circuit with two voltage sources:voltages of−1.2 and 0 V were applied to the handle and device layers,respectively.It was found that the proposed etching process can effectively prevent the in-use sticking of a cantilever-type switch.This is accomplished by increasing the gap between the device layer and its underlying handle layer and increasing the roughness of these layers.The technique is applicable to the fabrication of various cantilever-type SOI microelectromechanical systems,irrespective of the resistivity of the SOI wafer.展开更多
One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-s...One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-scale application is limited by their costly chemical synthesis methods.In this work,the niche feature of MXenes was capitalized in the packed-bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste.A simple NH4F solution was employed as the green electrolyte,which could be used repeatedly without any loss in its efficacy.Surprisingly,both fluoride and ammonium were found to play critical roles in the electrochemical etching,functionalization,and expansion of the layered parent materials(MAXs)through which the liberation of ammonia gas was observed.The electrochemically produced MXenes with excellent conductivity,applied as supercapacitor electrodes,could deliver an ultrahigh volumetric capacity(1408 F cm^(−3))and a volumetric energy density(75.8 Wh L^(−1)).This revolutionary green,energy-efficient,and scalable electrochemical route will not only pave the way for industrial-scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.展开更多
The Al foil for high voltage Al electrolytic capacitor usage was immersed in 5.0%NaOH solution containing trace amount of Zn2＋and Zn was chemically plated on its surface through an immersion-reduction reaction. Such ...The Al foil for high voltage Al electrolytic capacitor usage was immersed in 5.0%NaOH solution containing trace amount of Zn2＋and Zn was chemically plated on its surface through an immersion-reduction reaction. Such Zn-deposited Al foil was quickly transferred into HCl-H 2 SO 4 solution for DC-etching. The effects of Zn impurity on the surface and cross-section etching morphologies and electrochemical behavior of Al foil were investigated by SEM, polarization curve （PC） and electrochemical impedance spectroscopy （EIS）. The special capacitance of 100 V formation voltage of etched foil was measured. The results show that the chemical plating Zn on Al substrate in alkali solution can reduce the pitting corrosion resistance, enhance the pitting current density and improve the density and uniform distribution of pits and tunnels due to formation of the micro Zn-Al galvanic local cells. The special capacitance of etched foil grows with the increase of Zn2＋concentration.展开更多
Separation technology is an indispensable step in the preparation of freestanding GaN substrate. In this paper, a largearea freestanding GaN layer was separated from the substrate by an electrochemical liftoff process...Separation technology is an indispensable step in the preparation of freestanding GaN substrate. In this paper, a largearea freestanding GaN layer was separated from the substrate by an electrochemical liftoff process on a sandwich structure composed of an Fe-doped GaN substrate, a highly conductive Si-doped sacrificial layer and a top Fe-doped layer grown by hydride vapor phase epitaxy(HVPE). The large difference between the resistivity in the Si-doped layer and Fe-doped layer resulted in a sharp interface between the etched and unetched layer. It was found that the etching rate increased linearly with the applied voltage, while it continuously decreased with the electrochemical etching process as a result of the mass transport limitation. Flaky GaN pieces and nitrogen gas generated from the sacrificial layer by electrochemical etching were recognized as the main factors responsible for the blocking of the etching channel. Hence, a thick Si-doped layer grown by HVPE was used as the sacrificial layer to alleviate this problem. Moreover, high temperature and ultrasonic oscillation were also found to increase the etching rate. Based on the results above, we succeeded in the liftoff of ~ 1.5 inch GaN layer. This work could help reduce the cost of freestanding GaN substrate and identifies a new way for mass production.展开更多
The interconnection of wires is an important issue in vacuum-packaged microelectromechanical systems devices because of the difficulties of hermetical sealing and electrical insulation.This paper presents an approach ...The interconnection of wires is an important issue in vacuum-packaged microelectromechanical systems devices because of the difficulties of hermetical sealing and electrical insulation.This paper presents an approach of Au film selective patterning on highly uneven surfaces for wire interconnections of devices in which silicon-oninsulator(SOI)wafers are anodically bonded to glass.The Au film on the handle layer,functioned as an anode,was selectively removed with electrochemical dissolution in a chloride solution.The choice of etchant solution and etching conditions were optimized to improve the process efficiency,resulting in a high yield of gold portions within the via holes for wire interconnection.The proposed wire interconnection technology was employed to fabricate a vacuum-packaged resonant pressure sensor as a proof-of-concept demonstration.Reliable wire bonding and vacuum package were achieved as well as a Q factor that does not decrease over a year.As a platform technology,this method provides a new approach of wire interconnection for vacuum-packaged devices based on SOI–glass anodic bonding.展开更多
The fabrication of ordered, high aspect-ratio microstructures in silicon by use of photo-assisted electrochemical etching is an important technology, where voltage and current density are significant factors. In this ...The fabrication of ordered, high aspect-ratio microstructures in silicon by use of photo-assisted electrochemical etching is an important technology, where voltage and current density are significant factors. In this paper, disordered walls appear in 5-inch n-type silicon wafers when a large current density is used. Based on the theory of space charge region, these disordered walls are caused by the contradiction between the protection from dissolution by a high applied voltage and the dissolution by a high current density. To verify this point, wall arrays were fabricated at different applied voltages and current densities. Moreover, the critical voltage was kept constant and different current densities were applied to obtain conditions for avoiding disordered walls and achieving uniform wall arrays. Finally, a wall array with a period of 5.6 μm and a depth of 55 μm was achieved at an applied voltage of 3 V and a monotonically increasing current density ranging from 22.9 to 24.5 mA/cm^2.展开更多
Atomic force microscopy(AFM)-based electrochemical etching of a highly oriented pyrolytic graphite(HOPG)surface is studied toward the single-atomic-layer lithography of intricate patterns.Electrochemical etching is pe...Atomic force microscopy(AFM)-based electrochemical etching of a highly oriented pyrolytic graphite(HOPG)surface is studied toward the single-atomic-layer lithography of intricate patterns.Electrochemical etching is performed in the water meniscus formed between the AFM tip apex and HOPG surface due to a capillary effect under controlled high relative humid-ity(~75%)at otherwise ambient conditions.The conditions to etch nano-holes,nano-lines,and other intricate patterns are investigated.The clectrochemical reactions of HOPG etching should not generatc debris duc to the conversion of graphite to gaseous CO and CO_(2)based on etching reactions.However,debris is observed on the etched HOPG surface,and incom-plete gasification of carbon occurs during the etching process,resulting in the generation of solid intermediates.Moreover,the applied potential is of critical importance for precise etching,and the precision is also significantly influenced by the AFM tip wear.This study shows that the AFM-based electrochemical etching has the potential to remove the material in a single-atomic-layer precision.This result is likely because the etching process is based on anodic dissolution,resulting in the material removal atom by atom.展开更多
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 produ...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.展开更多
Macroporous silicon arrays（MSA） have attracted much attention for their potential applications in photonic crystals,silicon microchannel plates,MEMS devices and so on.In order to fabricate perfect MSA structure,phot...Macroporous silicon arrays（MSA） have attracted much attention for their potential applications in photonic crystals,silicon microchannel plates,MEMS devices and so on.In order to fabricate perfect MSA structure,photo-electrochemical （PEC） etching of MSA and the influence of etching current on the pore morphology were studied in detail.The current-voltage curve of a polished n-type silicon wafer was presented in aqueous HF using back-side illumination.The critical current density J_（PS） was discussed and the basic condition of etching current density for steady MSA growth was proposed.An indirect method was presented to measure the relation of J_（PS） at the pore tip and etching time.MSA growth was realized with the pore diameter constant by changing the etching current density according to the measuring result of J_（PS）.MSA with 295μm of depth and 98 of aspect ratio was obtained.展开更多
The influence of voltage on photo-electrochemical etching（PEC） of macroporous silicon arrays（MSA） was researched.According to the theory of the space charge region,I-V scan curves and the reaction mechanism of the...The influence of voltage on photo-electrochemical etching（PEC） of macroporous silicon arrays（MSA） was researched.According to the theory of the space charge region,I-V scan curves and the reaction mechanism of the n-type silicon anodic oxidation in HF solution under different current densities,the pore morphology influenced by the working voltage were studied and analyzed in detail.The results show that increasing the etching voltage will lead to distortion of the pore morphology,decreasing etching voltage will result in an increase in the blind porosity, and the constant etching voltage for a long time will cause gradual bifurcation.Through the optimization of the process parameters,the perfect MSA structure with a pore depth of 317μm,a pore size of 3μm and an aspect ratio of 105 was obtained.展开更多
Hierarchical porous patterns have been fabricated on the C face, Si face, and cross section of n-type 6H-SiC crystal via photo-electrochemical etching using HF/C2H5OH and HF/H2O2 as electrolytes. The porous layer disp...Hierarchical porous patterns have been fabricated on the C face, Si face, and cross section of n-type 6H-SiC crystal via photo-electrochemical etching using HF/C2H5OH and HF/H2O2 as electrolytes. The porous layer displayed multiple and multiscale microstructures on different faces, including stalactite-like, sponge-like and dendritic porous structures on C face, echinoid micro-patterns on Si face, and columnar and keel-shaped micro-patterns on the cross section. The formation of hierarchical porous pattern is ascribed to the dynamic competition balance between the electrochemical oxidation rate and the oxide removal rate. It was found that increasing the ionic strength of the electrolyte can obviously disturb the surface morphology of the porous SiC during the photo-electrochemical etching. Possible mechanisms for selective etching were further discussed.展开更多
Although an increasing interest has been attracted to further develop heterostructured catalysts from metallic glasses(MGs) by heat treatment, overcoming surface oxidation effect is still a critical problem for such e...Although an increasing interest has been attracted to further develop heterostructured catalysts from metallic glasses(MGs) by heat treatment, overcoming surface oxidation effect is still a critical problem for such environmental catalysts. Herein, a short-time electrochemical etching of partially crystallized Febased ribbons in 0.3 M H3 PO4 electrolyte enables the formation of honeycomb-like nanoporous structure as effective catalytic active sites in Fenton-like process. Studies of structure and surface morphologies reveal that the formation of nanoporous structure by potentiostatic etching originates from electrochemical potential difference of nanocrystals(a-Fe(Si) and Fe2 B) and residual amorphous phase in partially crystallized ribbons, where Fe2 B having a lower open circuit potential tends to be selectively dissolved.Simultaneously, thin oxide layer after electrochemical etching exposes more active sites for H2 O2 activation and provides an effective protection of nanocrystals from massive loss during etching. Investigation of optimal processing conditions suggests that the selection of electrolyte plays an important role;dye degradation rates of etched ribbons in HNO3 and Na2 SO4 electrolytes can also achieve at least 2 times higher than that of as-annealed ribbons. This work holds the promise to develop novel environmental catalysts by effective electrochemical etching of partially crystallized ribbons.展开更多
Isotropic etching polishing(IEP)based on the merging of isotropic etch pits has been proposed as a generic metal finishing approach.In this work,the tuning of the etching isotropy of various metals,which is the key to...Isotropic etching polishing(IEP)based on the merging of isotropic etch pits has been proposed as a generic metal finishing approach.In this work,the tuning of the etching isotropy of various metals,which is the key to realizing the finishing effect of IEP,is studied by theoretical analysis and etching experiments.The isotropic etching of various metals can be realized through mass transfer polarization by adjusting the electrochemical parameters.The addition of sulfuric acid in the electrolyte is the most effective for tuning the isotropy of electrochemical etching.It can decrease the diffusion coefficient of metal ions,thereby increasing the resistance of mass transfer and transforming the electrochemical dissolution of metal into mass transfer polarization.In this study,the atomic and close-to-atomic scale surface finishing of various metals and alloys has been successfully achieved through isotropic etching.After etching at a current of 1.5 A for 3 min,the surface Sa roughness of TA2 is drastically reduced from 242 to 3.98 nm.After etching for 1 min at a current of 3 A,the surface Sa roughness of pure tungsten,NiTi,and CoCrNi decreases from 9.33,76.4,and 37.6 nm,respectively,to 1.16,2.01,and 2.51 nm,respectively.展开更多
基金Project supported by University New Materials Disciplines Constructions Program of Beijing Region,ChinaProject(51172102/E020801) supported by the National Natural Science Foundation of China
文摘The aluminum foil for high voltage aluminum electrolytic capacitor was immersed in 0.5 mol/L H3PO4 or 0.125 mol/L NaOH solution at 40 ℃ for different time and then DC electro-etched in 1 mol/L HC1＋2.5 mol/L H2SO4 electrolyte at 80 ℃. The pitting potential and self corrosion potential of A1 foil were measured with polarization curves （PC）. The potentiostatic current--time curve was recorded and the surface and cross section images of etched A1 foil were observed with SEM. The electrochemical impedance spectroscopy （EIS） of etched A1 foil and potential transient curves （PTC） during initial etching stage were measured. The results show the chemical pretreatments can activate A1 foil surface, facilitate the absorption, diffusion and migration of C1- onto the A1 foil during etching, and improve the initiation rate of meta-stable pits and density of stable pits and tunnels, leading to much increase in the real surface area and special capacitance of etched A1 foil.
基金the financial support from China Aviation Science Foundation (04H52055).
文摘Process technology of multiple cylindrical micro-pins by wire-electrical discharge machining （wire-EDM） and electrochemical etching was presented. A row of rectangular micro-columns were machined by wire-EDM and then machined into cylindrical shape by electrochemical etching. However, the shape of the multiple electrodes and the consistent sizes of the electrodes row are not easy to be controlled. In the electrochemical process, the shape of the cathode electrode determines the current density distribution on the anode and so the forming of multiple electrodes. This paper proposes a finite element method （FEM） to accurately optimize the electrode profile. The microelectrodes row with uniformity diameters with size from hundreds micrometers to several decades could be fabricated, and mathematical model controlling the shape and diameter of multiple microelectrodes was provided. Furthermore, a good agreement between experimental and theoretical results was confirmed.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51575248 and 32071900).
文摘It is possible to achieve selective electrochemical etching between different materials,such as p-and n-type silicon.However,achieving selective electrochemical etching on two different regions of the same p-type silicon material is a problem that has rarely been considered.Herein,a novel selective electrochemical etching technique for cantilever-type silicon-on-insulator(SOI)wafer-based microswitches is proposed.In this study,a p-type handle layer was selectively etched,and a p-type device layer was passivated.This was achieved using a circuit with two voltage sources:voltages of−1.2 and 0 V were applied to the handle and device layers,respectively.It was found that the proposed etching process can effectively prevent the in-use sticking of a cantilever-type switch.This is accomplished by increasing the gap between the device layer and its underlying handle layer and increasing the roughness of these layers.The technique is applicable to the fabrication of various cantilever-type SOI microelectromechanical systems,irrespective of the resistivity of the SOI wafer.
基金Australian Research Council,Grant/Award Numbers:DP190100120,FT200100015National Key Research and Development Program,Grant/Award Number:2021YFA1600800Shenzhen Science and Technology Program,Grant/Award Numbers:RCJC20200714114434086,JCYJ20190808142001745,JCYJ20200812160737002,20180921273B。
文摘One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-scale application is limited by their costly chemical synthesis methods.In this work,the niche feature of MXenes was capitalized in the packed-bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste.A simple NH4F solution was employed as the green electrolyte,which could be used repeatedly without any loss in its efficacy.Surprisingly,both fluoride and ammonium were found to play critical roles in the electrochemical etching,functionalization,and expansion of the layered parent materials(MAXs)through which the liberation of ammonia gas was observed.The electrochemically produced MXenes with excellent conductivity,applied as supercapacitor electrodes,could deliver an ultrahigh volumetric capacity(1408 F cm^(−3))and a volumetric energy density(75.8 Wh L^(−1)).This revolutionary green,energy-efficient,and scalable electrochemical route will not only pave the way for industrial-scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.
基金Project (51172102) supported by the National Natural Science Foundation of ChinaProject (BS2011CL011) supported by Promotive Research Fund for Young and Middle-aged Scientists of Shandong Province(doctor fund),China
文摘The Al foil for high voltage Al electrolytic capacitor usage was immersed in 5.0%NaOH solution containing trace amount of Zn2＋and Zn was chemically plated on its surface through an immersion-reduction reaction. Such Zn-deposited Al foil was quickly transferred into HCl-H 2 SO 4 solution for DC-etching. The effects of Zn impurity on the surface and cross-section etching morphologies and electrochemical behavior of Al foil were investigated by SEM, polarization curve （PC） and electrochemical impedance spectroscopy （EIS）. The special capacitance of 100 V formation voltage of etched foil was measured. The results show that the chemical plating Zn on Al substrate in alkali solution can reduce the pitting corrosion resistance, enhance the pitting current density and improve the density and uniform distribution of pits and tunnels due to formation of the micro Zn-Al galvanic local cells. The special capacitance of etched foil grows with the increase of Zn2＋concentration.
基金supported by the National Key R&D Program of China (Grant Nos. 2017YFB0404100 and 2017YFB0403000)the National Natural Science Foundation of China (Grant No. 61704187)the Key Research Program of the Frontier Science of the Chinese Academy of Sciences (Grant No. QYZDB-SSWSLH042)。
文摘Separation technology is an indispensable step in the preparation of freestanding GaN substrate. In this paper, a largearea freestanding GaN layer was separated from the substrate by an electrochemical liftoff process on a sandwich structure composed of an Fe-doped GaN substrate, a highly conductive Si-doped sacrificial layer and a top Fe-doped layer grown by hydride vapor phase epitaxy(HVPE). The large difference between the resistivity in the Si-doped layer and Fe-doped layer resulted in a sharp interface between the etched and unetched layer. It was found that the etching rate increased linearly with the applied voltage, while it continuously decreased with the electrochemical etching process as a result of the mass transport limitation. Flaky GaN pieces and nitrogen gas generated from the sacrificial layer by electrochemical etching were recognized as the main factors responsible for the blocking of the etching channel. Hence, a thick Si-doped layer grown by HVPE was used as the sacrificial layer to alleviate this problem. Moreover, high temperature and ultrasonic oscillation were also found to increase the etching rate. Based on the results above, we succeeded in the liftoff of ~ 1.5 inch GaN layer. This work could help reduce the cost of freestanding GaN substrate and identifies a new way for mass production.
基金financial supports from National Natural Science Foundation of China (Grant No.61431019,61372054)
文摘The interconnection of wires is an important issue in vacuum-packaged microelectromechanical systems devices because of the difficulties of hermetical sealing and electrical insulation.This paper presents an approach of Au film selective patterning on highly uneven surfaces for wire interconnections of devices in which silicon-oninsulator(SOI)wafers are anodically bonded to glass.The Au film on the handle layer,functioned as an anode,was selectively removed with electrochemical dissolution in a chloride solution.The choice of etchant solution and etching conditions were optimized to improve the process efficiency,resulting in a high yield of gold portions within the via holes for wire interconnection.The proposed wire interconnection technology was employed to fabricate a vacuum-packaged resonant pressure sensor as a proof-of-concept demonstration.Reliable wire bonding and vacuum package were achieved as well as a Q factor that does not decrease over a year.As a platform technology,this method provides a new approach of wire interconnection for vacuum-packaged devices based on SOI–glass anodic bonding.
基金Project supported by the National Special Foundation of China for Major Science Instrument (No. 61227802)the National Natural Science Foundation of China (No. 61405120)+1 种基金the National Program on Key Basic Research Project (No. 2012CB825802)the China Postdoctoral Science Foundation (No. 2014M552224)
文摘The fabrication of ordered, high aspect-ratio microstructures in silicon by use of photo-assisted electrochemical etching is an important technology, where voltage and current density are significant factors. In this paper, disordered walls appear in 5-inch n-type silicon wafers when a large current density is used. Based on the theory of space charge region, these disordered walls are caused by the contradiction between the protection from dissolution by a high applied voltage and the dissolution by a high current density. To verify this point, wall arrays were fabricated at different applied voltages and current densities. Moreover, the critical voltage was kept constant and different current densities were applied to obtain conditions for avoiding disordered walls and achieving uniform wall arrays. Finally, a wall array with a period of 5.6 μm and a depth of 55 μm was achieved at an applied voltage of 3 V and a monotonically increasing current density ranging from 22.9 to 24.5 mA/cm^2.
基金The authors would like to thank the support received from the Science Foundation Ireland(SFI)(No.15/RP/B3208)‘111’project by the State Administration of Foreign Experts Affairs and the Ministry of Education of China(No.B07014)+2 种基金the National Natural Science Foundation of China(NSFC)(No.61635008)This project has also received funding from Enterprise Ireland and the European Union's Horizon 2020 Research and Inno-vation Programme under the Marie Sklodowska-Curie Grant(No.713654)from Science Foundation Ireland and the Sustainable Energy Authority of Ireland(SEAI)under the SFI Career Develop-ment Award Grant(17/CDA/4637).
文摘Atomic force microscopy(AFM)-based electrochemical etching of a highly oriented pyrolytic graphite(HOPG)surface is studied toward the single-atomic-layer lithography of intricate patterns.Electrochemical etching is performed in the water meniscus formed between the AFM tip apex and HOPG surface due to a capillary effect under controlled high relative humid-ity(~75%)at otherwise ambient conditions.The conditions to etch nano-holes,nano-lines,and other intricate patterns are investigated.The clectrochemical reactions of HOPG etching should not generatc debris duc to the conversion of graphite to gaseous CO and CO_(2)based on etching reactions.However,debris is observed on the etched HOPG surface,and incom-plete gasification of carbon occurs during the etching process,resulting in the generation of solid intermediates.Moreover,the applied potential is of critical importance for precise etching,and the precision is also significantly influenced by the AFM tip wear.This study shows that the AFM-based electrochemical etching has the potential to remove the material in a single-atomic-layer precision.This result is likely because the etching process is based on anodic dissolution,resulting in the material removal atom by atom.
基金supported by the National Natural Science Foundation of China (21573054, 21327002, 91323303, 21621091)the Joint Funds Key Project of the National Natural Science Foundation of China (U1537214)+2 种基金the State Key Program of National Natural Science of China (51535003)Self-Planned Task (SKLRS201606B) of State Key Laboratory of Robotics and System (HIT)the Open Project of the State Key Laboratory for Manufacturing Systems Engineering (Xi'an Jiaotong University)
文摘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.
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.200801860003).
文摘Macroporous silicon arrays（MSA） have attracted much attention for their potential applications in photonic crystals,silicon microchannel plates,MEMS devices and so on.In order to fabricate perfect MSA structure,photo-electrochemical （PEC） etching of MSA and the influence of etching current on the pore morphology were studied in detail.The current-voltage curve of a polished n-type silicon wafer was presented in aqueous HF using back-side illumination.The critical current density J_（PS） was discussed and the basic condition of etching current density for steady MSA growth was proposed.An indirect method was presented to measure the relation of J_（PS） at the pore tip and etching time.MSA growth was realized with the pore diameter constant by changing the etching current density according to the measuring result of J_（PS）.MSA with 295μm of depth and 98 of aspect ratio was obtained.
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.200801860003)
文摘The influence of voltage on photo-electrochemical etching（PEC） of macroporous silicon arrays（MSA） was researched.According to the theory of the space charge region,I-V scan curves and the reaction mechanism of the n-type silicon anodic oxidation in HF solution under different current densities,the pore morphology influenced by the working voltage were studied and analyzed in detail.The results show that increasing the etching voltage will lead to distortion of the pore morphology,decreasing etching voltage will result in an increase in the blind porosity, and the constant etching voltage for a long time will cause gradual bifurcation.Through the optimization of the process parameters,the perfect MSA structure with a pore depth of 317μm,a pore size of 3μm and an aspect ratio of 105 was obtained.
基金supported by the National Basic Research Program of China(Nos.2011CB301904 and 2009CB930503)the National Natural Science Foundation of China(Nos. 51021062 and 11134006)
文摘Hierarchical porous patterns have been fabricated on the C face, Si face, and cross section of n-type 6H-SiC crystal via photo-electrochemical etching using HF/C2H5OH and HF/H2O2 as electrolytes. The porous layer displayed multiple and multiscale microstructures on different faces, including stalactite-like, sponge-like and dendritic porous structures on C face, echinoid micro-patterns on Si face, and columnar and keel-shaped micro-patterns on the cross section. The formation of hierarchical porous pattern is ascribed to the dynamic competition balance between the electrochemical oxidation rate and the oxide removal rate. It was found that increasing the ionic strength of the electrolyte can obviously disturb the surface morphology of the porous SiC during the photo-electrochemical etching. Possible mechanisms for selective etching were further discussed.
基金Financial supports from Australian Research Council through Discovery Project(DP130103592)National Natural Science Foundation of China(Grant No.51771103)。
文摘Although an increasing interest has been attracted to further develop heterostructured catalysts from metallic glasses(MGs) by heat treatment, overcoming surface oxidation effect is still a critical problem for such environmental catalysts. Herein, a short-time electrochemical etching of partially crystallized Febased ribbons in 0.3 M H3 PO4 electrolyte enables the formation of honeycomb-like nanoporous structure as effective catalytic active sites in Fenton-like process. Studies of structure and surface morphologies reveal that the formation of nanoporous structure by potentiostatic etching originates from electrochemical potential difference of nanocrystals(a-Fe(Si) and Fe2 B) and residual amorphous phase in partially crystallized ribbons, where Fe2 B having a lower open circuit potential tends to be selectively dissolved.Simultaneously, thin oxide layer after electrochemical etching exposes more active sites for H2 O2 activation and provides an effective protection of nanocrystals from massive loss during etching. Investigation of optimal processing conditions suggests that the selection of electrolyte plays an important role;dye degradation rates of etched ribbons in HNO3 and Na2 SO4 electrolytes can also achieve at least 2 times higher than that of as-annealed ribbons. This work holds the promise to develop novel environmental catalysts by effective electrochemical etching of partially crystallized ribbons.
基金the National Natural Science Foundation of China(52035009,52005243)the Science and Technology Innovation Committee of Shenzhen Municipality(JCYJ20200109141003910,JCYJ20210324120402007,KQTD20170810110250357).
文摘Isotropic etching polishing(IEP)based on the merging of isotropic etch pits has been proposed as a generic metal finishing approach.In this work,the tuning of the etching isotropy of various metals,which is the key to realizing the finishing effect of IEP,is studied by theoretical analysis and etching experiments.The isotropic etching of various metals can be realized through mass transfer polarization by adjusting the electrochemical parameters.The addition of sulfuric acid in the electrolyte is the most effective for tuning the isotropy of electrochemical etching.It can decrease the diffusion coefficient of metal ions,thereby increasing the resistance of mass transfer and transforming the electrochemical dissolution of metal into mass transfer polarization.In this study,the atomic and close-to-atomic scale surface finishing of various metals and alloys has been successfully achieved through isotropic etching.After etching at a current of 1.5 A for 3 min,the surface Sa roughness of TA2 is drastically reduced from 242 to 3.98 nm.After etching for 1 min at a current of 3 A,the surface Sa roughness of pure tungsten,NiTi,and CoCrNi decreases from 9.33,76.4,and 37.6 nm,respectively,to 1.16,2.01,and 2.51 nm,respectively.
