Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide(4H-SiC),which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers.I...Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide(4H-SiC),which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers.In this work,we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations(TSDs),threading edge dislocations(TEDs)and basal plane dislocations(BPDs)in 4H-SiC.In n-type 4H-SiC,the inclination angles of the etch pits of TSDs,TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°−35°,8°−15°and 2°−4°,respectively.In semi-insulating 4H-SiC,the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°−34°and 21°−24°,respectively.The inclination angles of dislocation-related etch pits are independent of the etching duration,which facilitates the discrimination and statistic of dislocations in 4H-SiC.More significantly,the inclination angle of a threading mixed dislocations(TMDs)is found to consist of characteristic angles of both TEDs and TSDs.This enables to distinguish TMDs from TSDs in 4H-SiC.展开更多
In this work,we propose to reveal the subsurface damage(SSD)of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching.Under UV illumination,SSD acts as a photoluminescence-blac...In this work,we propose to reveal the subsurface damage(SSD)of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching.Under UV illumination,SSD acts as a photoluminescence-black defect.The selective photo-chemical etching reveals SSD as the ridge-like defect.It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion.The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines,which are typical features of scratches.This means that the underlying scratches under mechanical stress give rise to the formation of SSD in 4H-SiC wafers.SSD is incorporated into 4H-SiC wafers during the lapping,rather than the chemical mechanical polishing(CMP).展开更多
Gastrointestinal tumors are common malignant tumors in the digestive tract, of which gastric cancer is the third leading cause of cancer death and colorectal cancer is the fourth most deadly cancer. Nowadays, surgical...Gastrointestinal tumors are common malignant tumors in the digestive tract, of which gastric cancer is the third leading cause of cancer death and colorectal cancer is the fourth most deadly cancer. Nowadays, surgical resection remains to be one of the main measures for treating digestive tract tumors, and gastrointestinal anastomosis remains to be a key step in gastrointestinal surgery. Mg and its alloys have great potentials to be used for gastrointestinal anastomosis as anastomotic nail materials due to their biodegradability, good mechanical properties and biocompatibility. In this study, Mg–2Zn–0.5Nd(ZN20) alloy fine wires showed great potential as surgical staples. When we performed in vitro corrosion experiments, drainage fluid was collected from different parts of the patient’s abdominal cavity after surgery for the first time to replace the traditional simulation fluid and to more realistically simulate the microenvironment required by the anastomotic nail. ZN20 alloy has an ultimate tensile strength of 256 MPa, an elongation rate of 12.56%, a tensile force in anastomosis of 16.8 N, and a rupture pressure after anastomosis at 17 kPa, which means that a sufficient mechanical support was provided after anastomosis.The statistical analysis and histopathological analysis of biochemical tests indicate that ZN20 alloy has no adverse effect on the normal metabolism of liver, kidney and body, but has superior biocompatibility and biosafety. This work confirms that ZN20 possesses a great application potential in the clinical field as a new type of gastrointestinal anastomotic nail material.展开更多
Radiation damage produced in 4H-SiC by electrons of different doses is presented by using multiple characterization techniques. Raman spectra results indicate that SiC crystal structures are essentially impervious to ...Radiation damage produced in 4H-SiC by electrons of different doses is presented by using multiple characterization techniques. Raman spectra results indicate that SiC crystal structures are essentially impervious to 10 Me V electron irradiation with doses up to 3000 kGy. However, irradiation indeed leads to the generation of various defects, which are evaluated through photoluminescence(PL) and deep level transient spectroscopy(DLTS). The PL spectra feature a prominent broad band centered at 500 nm, accompanied by several smaller peaks ranging from 660 to 808 nm. The intensity of each PL peak demonstrates a linear correlation with the irradiation dose, indicating a proportional increase in defect concentration during irradiation. The DLTS spectra reveal several thermally unstable and stable defects that exhibit similarities at low irradiation doses.Notably, after irradiating at the higher dose of 1000 kGy, a new stable defect labeled as R_(2)(Ec-0.51 eV) appeared after annealing at 800 K. Furthermore, the impact of irradiation-induced defects on SiC junction barrier Schottky diodes is discussed. It is observed that high-dose electron irradiation converts SiC n-epilayers to semi-insulating layers. However, subjecting the samples to a temperature of only 800 K results in a significant reduction in resistance due to the annealing out of unstable defects.展开更多
In order to eliminate the disadvantages of the keyhole in conventional friction stir spot welding joint and attain the highstrength lap joint of Al/Cu dissimilar metals,a novel welding technique,named as friction stir...In order to eliminate the disadvantages of the keyhole in conventional friction stir spot welding joint and attain the highstrength lap joint of Al/Cu dissimilar metals,a novel welding technique,named as friction stir spot riveting(FSSR),was proposed.A pinless tool and an extra filling stud were employed.The Al/Cu spot joints without keyhole defect were achieved by the FSSR.A Cu anchor-like structure was formed,which greatly increased the mechanical interlocking between the upper Al sheet and lower Cu sheet.The thin intermetallic compounds containing CuAl2 and CuAl at the Al/Cu interface strengthened the joining interface between the Al sheet and the Cu stud.Increasing rotating velocity increased frictional heat and plastic deformation and then eliminated the interfacial joining defects.The FSSR joint with the maximum tensile shear load of 3.50 kN was achieved at a rotating velocity of 1800 rpm and a dwell time of 20 s,whose fracture path passed through the softened region of upper Al sheet.In summary,the novel FSSR technique has the advantages of strong mechanical interlocking and metallurgical bonding between dissimilar materials,thereby attaining the high-strength spot joint.展开更多
This article analyzes the problem of computer network security, and design scheme of the network security system. The scheme uses advanced network security technologies, includes a complete set of physical isolation, ...This article analyzes the problem of computer network security, and design scheme of the network security system. The scheme uses advanced network security technologies, includes a complete set of physical isolation, desktop system security, virus protection, identity authentication, access control, information encryption, message integrity check, non-repudiation, security audit, intrusion detection, vulnerability scanning, electromagnetic leakage emission protection, security management and other security technology and management measures, the purpose is to establish a complete, multi-level three-dimensional, network security defense system.展开更多
Titanium and its alloy are commonly used as surgical staples in the reconstruction of intestinal tract and stomach,however they cannot be absorbed in human body,which may cause a series of complications to influence f...Titanium and its alloy are commonly used as surgical staples in the reconstruction of intestinal tract and stomach,however they cannot be absorbed in human body,which may cause a series of complications to influence further diagnosis.Magnesium and its alloy have great potential as surgical staples,because they can be degraded in human body and have good mechanical properties and biocompatibility.In this study,Mg-2Zn-0.5Nd(ZN20)alloy fine wires showed great potential as surgical staples.The ultimate tensile strength and elongation of ZN20 alloy fine wires were 248 MPa and 13%,respectively,which could be benefit for the deformation of the surgical staples from U-shape to B-shape.The bursting pressure of the wire was about 40 kPa,implying that it can supply sufficient mechanical support after anastomosis.Biochemical test and histological analysis illustrated good biocompatibility and biological safety of ZN20 alloy fine wire.The residual tensile stress formed on the outside of ZN20 fine wire during drawing would accelerate the corrosion.The second phase had a negative influence on corrosion property due to galvanic corrosion.The corrosion rate in vitro was faster than that in vivo due to the capsule formed on the surface of ZN20 alloy fine wire.展开更多
demonstrated to hydrogenate dangling bonds on the surface of crystalline silicon(c-Si),which reduces the interface defect density,thus enabling an outstanding passivation effect[1–3].However,like many other industria...demonstrated to hydrogenate dangling bonds on the surface of crystalline silicon(c-Si),which reduces the interface defect density,thus enabling an outstanding passivation effect[1–3].However,like many other industrial c-Si solar cells that suffer from light-induced degradation and light and elevated temperature induced degradation(LeTID)[4,5],the decay of electrical properties has also been found in thin-film a-Si:H solar cells[6–8],as well as samples of c-Si coated with intrinsic a-Si:H films after light soaking[9].A significant observation reported by Plagwitz et al.[10]suggested that illumination induced an increase in surface recombination velocities for both a-Si:H coated p-type and n-type c-Si substrates.The degradation of performance is generally attributed to the generation of deeplevel defects acting as recombination centers,most likely as single dangling bonds[11,12],which is considered to be related to the Staebler-Wronski effect(SWE)[13].展开更多
Cast-mono crystalline silicon wafers contain crystallographic defects, which can severely impact the electrical performance of solar cells. This paper demon- strates that applying hydrogenation processes at moderate t...Cast-mono crystalline silicon wafers contain crystallographic defects, which can severely impact the electrical performance of solar cells. This paper demon- strates that applying hydrogenation processes at moderate temperatures to finished screen print cells can passivate dislocation clusters within the cast-mono crystalline silicon wafers far better than the hydrogenation received during standard commercial firing conditions. Efficiency enhancements of up to 2% absolute are demonstrated on wafers with high dislocation densities. The impact of illumination to manipulate the charge state of hydrogen during annealing is investigated and found to not be significant on the wafers used in this study. This finding is contrary to a previous study on similar wafers that concluded increased H or H0 from laser illumination was responsible for the further passivation of positively charged dangling bonds within the dislocation clusters.展开更多
基金supported by“Pioneer”and“Leading Goose”R&D Program of Zhejiang(Grant No.2022C01021)National Key Research and Development Program of China(Grant Nos.2018YFB2200101)+3 种基金Natural Science Foundation of China(Grant Nos.61774133)Fundamental Research Funds for the Central Universities(Grant No.2018XZZX003-02)Natural Science Foundation of China for Innovative Research Groups(Grant No.61721005)Zhejiang University Education Foundation Global Partnership Fund.
文摘Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide(4H-SiC),which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers.In this work,we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations(TSDs),threading edge dislocations(TEDs)and basal plane dislocations(BPDs)in 4H-SiC.In n-type 4H-SiC,the inclination angles of the etch pits of TSDs,TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°−35°,8°−15°and 2°−4°,respectively.In semi-insulating 4H-SiC,the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°−34°and 21°−24°,respectively.The inclination angles of dislocation-related etch pits are independent of the etching duration,which facilitates the discrimination and statistic of dislocations in 4H-SiC.More significantly,the inclination angle of a threading mixed dislocations(TMDs)is found to consist of characteristic angles of both TEDs and TSDs.This enables to distinguish TMDs from TSDs in 4H-SiC.
基金supported by “Pioneer” and “Leading Goose”R&D Program of Zhejiang (Grant No. 2022C01021)National Key Research and Development Program of China (Grant No.2018YFB2200101)+3 种基金National Natural Science Foundation of China (Grant Nos. 91964107, 61774133)Fundamental Research Funds for the Central Universities (Grant No.2018XZZX003-02)Natural Science Foundation of China for Innovative Research Groups (Grant No. 61721005)Zhejiang University Education Foundation Global Partnership Fund
文摘In this work,we propose to reveal the subsurface damage(SSD)of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching.Under UV illumination,SSD acts as a photoluminescence-black defect.The selective photo-chemical etching reveals SSD as the ridge-like defect.It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion.The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines,which are typical features of scratches.This means that the underlying scratches under mechanical stress give rise to the formation of SSD in 4H-SiC wafers.SSD is incorporated into 4H-SiC wafers during the lapping,rather than the chemical mechanical polishing(CMP).
文摘Gastrointestinal tumors are common malignant tumors in the digestive tract, of which gastric cancer is the third leading cause of cancer death and colorectal cancer is the fourth most deadly cancer. Nowadays, surgical resection remains to be one of the main measures for treating digestive tract tumors, and gastrointestinal anastomosis remains to be a key step in gastrointestinal surgery. Mg and its alloys have great potentials to be used for gastrointestinal anastomosis as anastomotic nail materials due to their biodegradability, good mechanical properties and biocompatibility. In this study, Mg–2Zn–0.5Nd(ZN20) alloy fine wires showed great potential as surgical staples. When we performed in vitro corrosion experiments, drainage fluid was collected from different parts of the patient’s abdominal cavity after surgery for the first time to replace the traditional simulation fluid and to more realistically simulate the microenvironment required by the anastomotic nail. ZN20 alloy has an ultimate tensile strength of 256 MPa, an elongation rate of 12.56%, a tensile force in anastomosis of 16.8 N, and a rupture pressure after anastomosis at 17 kPa, which means that a sufficient mechanical support was provided after anastomosis.The statistical analysis and histopathological analysis of biochemical tests indicate that ZN20 alloy has no adverse effect on the normal metabolism of liver, kidney and body, but has superior biocompatibility and biosafety. This work confirms that ZN20 possesses a great application potential in the clinical field as a new type of gastrointestinal anastomotic nail material.
基金supported by the Open Fund(2022E10015)of the Key Laboratory of Power Semiconductor Materials and Devices of Zhejiang Province&Institute of Advanced Semiconductors,ZJU-Hangzhou Global Scientific and Technological Innovation Center。
文摘Radiation damage produced in 4H-SiC by electrons of different doses is presented by using multiple characterization techniques. Raman spectra results indicate that SiC crystal structures are essentially impervious to 10 Me V electron irradiation with doses up to 3000 kGy. However, irradiation indeed leads to the generation of various defects, which are evaluated through photoluminescence(PL) and deep level transient spectroscopy(DLTS). The PL spectra feature a prominent broad band centered at 500 nm, accompanied by several smaller peaks ranging from 660 to 808 nm. The intensity of each PL peak demonstrates a linear correlation with the irradiation dose, indicating a proportional increase in defect concentration during irradiation. The DLTS spectra reveal several thermally unstable and stable defects that exhibit similarities at low irradiation doses.Notably, after irradiating at the higher dose of 1000 kGy, a new stable defect labeled as R_(2)(Ec-0.51 eV) appeared after annealing at 800 K. Furthermore, the impact of irradiation-induced defects on SiC junction barrier Schottky diodes is discussed. It is observed that high-dose electron irradiation converts SiC n-epilayers to semi-insulating layers. However, subjecting the samples to a temperature of only 800 K results in a significant reduction in resistance due to the annealing out of unstable defects.
基金financially supported by the National Natural Science Foundation of China (Nos.51705339 and 51905355)。
文摘In order to eliminate the disadvantages of the keyhole in conventional friction stir spot welding joint and attain the highstrength lap joint of Al/Cu dissimilar metals,a novel welding technique,named as friction stir spot riveting(FSSR),was proposed.A pinless tool and an extra filling stud were employed.The Al/Cu spot joints without keyhole defect were achieved by the FSSR.A Cu anchor-like structure was formed,which greatly increased the mechanical interlocking between the upper Al sheet and lower Cu sheet.The thin intermetallic compounds containing CuAl2 and CuAl at the Al/Cu interface strengthened the joining interface between the Al sheet and the Cu stud.Increasing rotating velocity increased frictional heat and plastic deformation and then eliminated the interfacial joining defects.The FSSR joint with the maximum tensile shear load of 3.50 kN was achieved at a rotating velocity of 1800 rpm and a dwell time of 20 s,whose fracture path passed through the softened region of upper Al sheet.In summary,the novel FSSR technique has the advantages of strong mechanical interlocking and metallurgical bonding between dissimilar materials,thereby attaining the high-strength spot joint.
文摘This article analyzes the problem of computer network security, and design scheme of the network security system. The scheme uses advanced network security technologies, includes a complete set of physical isolation, desktop system security, virus protection, identity authentication, access control, information encryption, message integrity check, non-repudiation, security audit, intrusion detection, vulnerability scanning, electromagnetic leakage emission protection, security management and other security technology and management measures, the purpose is to establish a complete, multi-level three-dimensional, network security defense system.
基金the Key Program of China on Biomedical Materials Research and Tissue Organ Replacement(No.2016YFC1101804,2016YFC1100604)National Natural Science Foundation of China(No.51971222,51801220).
文摘Titanium and its alloy are commonly used as surgical staples in the reconstruction of intestinal tract and stomach,however they cannot be absorbed in human body,which may cause a series of complications to influence further diagnosis.Magnesium and its alloy have great potential as surgical staples,because they can be degraded in human body and have good mechanical properties and biocompatibility.In this study,Mg-2Zn-0.5Nd(ZN20)alloy fine wires showed great potential as surgical staples.The ultimate tensile strength and elongation of ZN20 alloy fine wires were 248 MPa and 13%,respectively,which could be benefit for the deformation of the surgical staples from U-shape to B-shape.The bursting pressure of the wire was about 40 kPa,implying that it can supply sufficient mechanical support after anastomosis.Biochemical test and histological analysis illustrated good biocompatibility and biological safety of ZN20 alloy fine wire.The residual tensile stress formed on the outside of ZN20 fine wire during drawing would accelerate the corrosion.The second phase had a negative influence on corrosion property due to galvanic corrosion.The corrosion rate in vitro was faster than that in vivo due to the capsule formed on the surface of ZN20 alloy fine wire.
基金the National Natural Science Foundation of China(61974129,62025403,and 61721005)the Natural Science Foundation of Zhejiang Province(LD22E020001)Lingyan Research and Development Project of Zhejiang Province(022C01215).
文摘demonstrated to hydrogenate dangling bonds on the surface of crystalline silicon(c-Si),which reduces the interface defect density,thus enabling an outstanding passivation effect[1–3].However,like many other industrial c-Si solar cells that suffer from light-induced degradation and light and elevated temperature induced degradation(LeTID)[4,5],the decay of electrical properties has also been found in thin-film a-Si:H solar cells[6–8],as well as samples of c-Si coated with intrinsic a-Si:H films after light soaking[9].A significant observation reported by Plagwitz et al.[10]suggested that illumination induced an increase in surface recombination velocities for both a-Si:H coated p-type and n-type c-Si substrates.The degradation of performance is generally attributed to the generation of deeplevel defects acting as recombination centers,most likely as single dangling bonds[11,12],which is considered to be related to the Staebler-Wronski effect(SWE)[13].
文摘Cast-mono crystalline silicon wafers contain crystallographic defects, which can severely impact the electrical performance of solar cells. This paper demon- strates that applying hydrogenation processes at moderate temperatures to finished screen print cells can passivate dislocation clusters within the cast-mono crystalline silicon wafers far better than the hydrogenation received during standard commercial firing conditions. Efficiency enhancements of up to 2% absolute are demonstrated on wafers with high dislocation densities. The impact of illumination to manipulate the charge state of hydrogen during annealing is investigated and found to not be significant on the wafers used in this study. This finding is contrary to a previous study on similar wafers that concluded increased H or H0 from laser illumination was responsible for the further passivation of positively charged dangling bonds within the dislocation clusters.
