Subsurface damage is easily induced in machining of hard and brittle materials because of their particular mechani?cal and physical properties. It is detrimental to the strength,performance and lifetime of a machined ...Subsurface damage is easily induced in machining of hard and brittle materials because of their particular mechani?cal and physical properties. It is detrimental to the strength,performance and lifetime of a machined part. To manu?facture a high quality part,it is necessary to detect and remove the machining induced subsurface damage by the subsequent processes. However,subsurface damage is often covered with a smearing layer generated in a machining process,it is rather di cult to directly observe and detect by optical microscopy. An e cient detection of subsur?face damage directly leads to quality improvement and time saving for machining of hard and brittle materials. This paper presents a review of the methods for detection of subsurface damage,both destructive and non?destructive. Although more reliable,destructive methods are typically time?consuming and confined to local damage infor?mation. Non?destructive methods usually su er from uncertainty factors,but may provide global information on subsurface damage distribution. These methods are promising because they can provide a capacity of rapid scan and detection of subsurface damage in spatial distribution.展开更多
Potassium dihydrogen phosphate (KDP) is an important electro-optic crystal, often used for frequency conversion and Pockels cells in large aperture laser systems. To investigate the influence of anisotropy to the de...Potassium dihydrogen phosphate (KDP) is an important electro-optic crystal, often used for frequency conversion and Pockels cells in large aperture laser systems. To investigate the influence of anisotropy to the depth of subsurface damage and the profiles of cracks in subsurface of KDP crystal, an experimental study was made to obtain the form of subsurface damage produced by scratches on KDP crystal in [100], [120] and [110] crystal directions on (001) crystal plane. The results indicated that there were great differences between depth and crack shape in different directions. For many slip planes in KDP, the plastic deformation and cracks generated under pressure in the subsurface were complex. Fluctuations of subsurface damage depth at transition point were attributed to the deformation of the surface which consumed more energy when the surface deformation changed from the mixed region of brittle and plastic to the complete brittle region along the scratch. Also, the process of subsurface damage from shallow to deep, from dislocation to big crack in KDP crystal with the increase of radial force and etch pit on different crystal plane were obtained. Because crystallographic orientation and processing orientation was different, etching pits on (100) crystal plane were quadrilateral while on (110) plane and (120) plane were trapezoidal and triangular, respectively.展开更多
This paper proposes a method for the rapid detection of subsurface damage(SSD)of Si C using atmospheric inductivity coupled plasma.As a plasma etching method operated at ambient pressure with no bias voltage,this meth...This paper proposes a method for the rapid detection of subsurface damage(SSD)of Si C using atmospheric inductivity coupled plasma.As a plasma etching method operated at ambient pressure with no bias voltage,this method does not introduce any new SSD to the substrate.Plasma diagnosis and simulation are used to optimize the detection operation.Assisted by an Si C cover,a taper can be etched on the substrate with a high material removal rate.Confocal laser scanning microscopy and scanning electron microscope are used to analyze the etching results,and scanning transmission electron microscope(STEM)is adopted to confirm the accuracy of this method.The STEM result also indicates that etching does not introduce any SSD,and the thoroughly etched surface is a perfectly single crystal.A rapid SSD screening ability is also demonstrated,showing that this method is a promising approach for the rapid detection of SSD.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
A theoretical model of relationship between subsurface damage and surface roughness was established to realize rapid and non-destructive measurement of subsurface damage of ground optical materials.Postulated conditio...A theoretical model of relationship between subsurface damage and surface roughness was established to realize rapid and non-destructive measurement of subsurface damage of ground optical materials.Postulated condition of the model was that subsurface damage depth and peak-to-valley surface roughness are equal to depth of radial and lateral cracks in brittle surface induced by small-radius(radius≤200 μm)spherical indenter,respectively.And contribution of elastic stress field to the radial cracks propagation was also considered in the loading cycle.Subsurface damage depth of ground BK7 glasses was measured by magnetorheological finishing spot technique to validate theoretical ratio of subsurface damage to surface roughness.The results show that the ratio is directly proportional to load of abrasive grains and hardness of optical materials,while inversely proportional to granularity of abrasive grains and fracture toughness of optical materials.Moreover,the influence of the load and fracture toughness on the ratio is more significant than the granularity and hardness,respectively.The measured ratios of 80 grit and 120 grit fixed abrasive grinding of BK7 glasses are 5.8 and 5.4,respectively.展开更多
The subsurface damage(SSD)layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology.Three ways such as ice-fixed abrasiv...The subsurface damage(SSD)layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology.Three ways such as ice-fixed abrasive,thermosetting fixed abrasive and free abrasive lappings are adopted to lap monocrystalline germanium wafers.The SSD depth was measured by a nanoindenter,and the morphology of SSD layer was observed by an atomic force microscopy(AFM).The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer.Compared with thermosetting fixed abrasive and free abrasive lappings,the SSD depth lapped with ice-fixed abrasive is shallower.Moreover,the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing ways.展开更多
Laser-induced damage in fused silica optics greatly restricts the performances of laser facilities. Gray haze damage,which is always initiated on ceria polished optics, is one of the most important damage morphologies...Laser-induced damage in fused silica optics greatly restricts the performances of laser facilities. Gray haze damage,which is always initiated on ceria polished optics, is one of the most important damage morphologies in fused silica optics.In this paper, the laser-induced gray haze damages of four fused silica samples polished with CeO2, Al2O3, ZrO2, and colloidal silica slurries are investigated. Four samples all present gray haze damages with much different damage densities.Then, the polishing-induced contaminant and subsurface damages in four samples are analyzed. The results reveal that the gray haze damages could be initiated on the samples without Ce contaminant and are inclined to show a tight correlation with the shallow subsurface damages.展开更多
High-speed machining(HSM) has been studied for several decades and has potential application in various industries, including the automobile and aerospace industries. However,the underlying mechanisms of HSM have not ...High-speed machining(HSM) has been studied for several decades and has potential application in various industries, including the automobile and aerospace industries. However,the underlying mechanisms of HSM have not been formally reviewed thus far. This article focuses on the solid mechanics framework of adiabatic shear band(ASB) onset and material metallurgical microstructural evolutions in HSM. The ASB onset is described using partial differential systems. Several factors in HSM were considered in the systems, and the ASB onset conditions were obtained by solving these systems or applying the perturbation method to the systems. With increasing machining speed, an ASB can be depressed and further eliminated by shock pressure. The damage observed in HSM exhibits common features. Equiaxed fine grains produced by dynamic recrystallization widely cause damage to ductile materials, and amorphization is the common microstructural evolution in brittle materials. Based on previous studies, potential mechanisms for the phenomena in HSM are proposed. These include the thickness variation of the white layer of ductile materials. These proposed mechanisms would be beneficial to deeply understanding the various phenomena in HSM.展开更多
As for the ultra-precision grinding of the hemispherical fused silica resonator,due to the hard and brittle nature of fused silica,subsurface damage(SSD)is easily generated,which enormously influences the performance ...As for the ultra-precision grinding of the hemispherical fused silica resonator,due to the hard and brittle nature of fused silica,subsurface damage(SSD)is easily generated,which enormously influences the performance of such components.Hence,ultra-precision grinding experiments are carried out to investigate the surface/subsurface quality of the hemispherical resonator machined by the small ball-end fine diamond grinding wheel.The influence of grinding parameters on the surface roughness(SR)and SSD depth of fused silica samples is then analyzed.The experimental results indicate that the SR and SSD depth decreased with the increase of grinding speed and the decrease of feed rate and grinding depth.In addition,based on the material strain rate and the maximum undeformed chip thickness,the effect of grinding parameters on the subsurface damage mechanism of fused silica samples is analyzed.Furthermore,a multi-step ultra-precision grinding technique of the hemispherical resonator is proposed based on the interaction influence between grinding depth and feed rate.Finally,the hemispherical resonator is processed by the proposed grinding technique,and the SR is improved from 454.328 nm to 110.449 nm while the SSD depth is reduced by 94%from 40μm to 2.379μm.The multi-step grinding technique proposed in this paper can guide the fabrication of the hemispherical resonator.展开更多
The depth and nature of the subsurface damage in a silicon wafer will limit the performance of IC components. Damage microstructures of the silicon wafers ground by the #325, #600, and #2000 grinding wheels was analyz...The depth and nature of the subsurface damage in a silicon wafer will limit the performance of IC components. Damage microstructures of the silicon wafers ground by the #325, #600, and #2000 grinding wheels was analyzed. The results show that many microcracks, fractures, and dislocation rosettes appear in the surface and subsurface of the wafer ground by the #325 grinding wheel. No obvious microstructure change exists. The amorphous layer with a thickness of about 100 nm, microcracks, high density dislocations, and polycrystalline silicon are observed in the subsurface of the wafer ground by the #600 grinding wheel. For the wafer ground by the #2000 grinding wheel, an amorphous layer of about 30 nm thickness, a polycrystalline silicon layer, a few dislocations, and an elastic deformation layer exist. In general, with the decrease in grit size, the material removal mode changes from micro-fracture mode to ductile mode gradually.展开更多
The last major earthquake in Bantul causing severe damage occurred on May 27th, 2006. The damages in the flat area of Bantul had a certain pattern. The damages pattern controlled the subsurface characteristic below th...The last major earthquake in Bantul causing severe damage occurred on May 27th, 2006. The damages in the flat area of Bantul had a certain pattern. The damages pattern controlled the subsurface characteristic below the flat area. Understanding earthquake damage pattern through geo-morphological approach is important for earthquake hazard analysis. The techniques of remote sensing and Geographical Information Systems were applied to analyze earthquake damage pattern and geomorphological characteristics. Gravity analysis was used to identify the subsurface structure and the basement depth while geoelectric analysis was used to identify sediment depth. Moreover, spatial correlation analysis was used to identify the relationship between the earthquake damage, geomorphological characteristics, and subsurface characteristics. The results show that fluvial, marine, and aeolian landforms have low rock density value based on gravity analysis. These indicate that they were composed by thick unconsolidated material of quaternary alluvium. While denudational, structural, and solutional landforms composed by material of tertiary rocks have high rock density value. The severe damage occurred in the area that has a lower value of local gravity and deeper basement. In contrast, the slight damage occurred in the area that has higher values of local gravity and shallower basement. Moreover, the severe damage occurred in areas of thicker sediment that consist of unconsolidated material. Consequently, the area of unconsolidated material that has deeper basement and thicker sediment is prone to earthquake. They were located on fluvial, marine, and aeolian landforms.展开更多
Subsurface damage(SSD) is an unavoidable problem in the precision mechanical grinding for preparing ultra-thin and flexible silicon chips. At present, there are relatively few studies on the relationship between SSD a...Subsurface damage(SSD) is an unavoidable problem in the precision mechanical grinding for preparing ultra-thin and flexible silicon chips. At present, there are relatively few studies on the relationship between SSD and the bending strength of ultra-thin chips under different grinding parameters. In this study, SSD including amorphization and dislocation is observed using a transmission electron microscope. Theoretical predictions of the SSD depth induced by different processing parameters are in good agreement with experimental data. The main reasons for SSD depth increase include the increase of grit size, the acceleration of feed rate, and the slowdown of wheel rotation speed. Three-point bending test is adopted to measure the bending strength of ultra-thin chips processed by different grinding conditions. The results show that increasing wheel rotation speed and decreasing grit size and feed rate will improve the bending strength of chips, due to the reduction of SSD depth. Wet etching and chemical mechanical polishing(CMP) are applied respectively to remove the SSD induced by grinding, and both contribute to providing a higher bending strength, but in comparison, CMP works better due to a smooth surface profile. This research aims to provide some guidance for optimizing the grinding process and fabricating ultra-thin chips with higher bending strength.展开更多
The laser-induced damage threshold(LIDT)of plate laser beam splitter(PLBS)coatings is closely related to the subsurface absorption defects of the substrate.Herein,a two-step deposition temperature method is proposed t...The laser-induced damage threshold(LIDT)of plate laser beam splitter(PLBS)coatings is closely related to the subsurface absorption defects of the substrate.Herein,a two-step deposition temperature method is proposed to understand the effect of substrate subsurface impurity defects on the LIDT of PLBS coatings.Firstly,BK7 substrates are heat-treated at three different temperatures.The surface morphology and subsurface impurity defect distribution of the substrate before and after the heat treatment are compared.Then,a PLBS coating consisting of alternating HfO2–Al2O3 mixture and SiO2 layers is designed to achieve a beam-splitting ratio(transmittance to reflectance,s-polarized light)of approximately 50:50 at 1053 nm and an angle of incidence of 45◦,and it is prepared under four different deposition processes.The experimental and simulation results show that the subsurface impurity defects of the substrate migrate to the surface and accumulate on the surface during the heat treatment,and become absorption defect sources or nodule defect seeds in the coating,reducing the LIDT of the coating.The higher the heat treatment temperature,the more evident the migration and accumulation of impurity defects.A lower deposition temperature(at which the coating can be fully oxidized)helps to improve the LIDT of the PLBS coating.When the deposition temperature is 140◦C,the LIDT(s-polarized light,wavelength:1064 nm,pulse width:9 ns,incident angle:45◦)of the PLBS coating is 26.2 J/cm2,which is approximately 6.7 times that of the PLBS coating deposited at 200◦C.We believe that the investigation into the laser damage mechanism of PLBS coatings will help to improve the LIDT of coatings with partial or high transmittance at laser wavelengths.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51575084)the Science Fund for Creative Research Groups of NSFC(Grant No.51621064)the Science Challenge Project(Grant No.JCKY2016212A506–0101)
文摘Subsurface damage is easily induced in machining of hard and brittle materials because of their particular mechani?cal and physical properties. It is detrimental to the strength,performance and lifetime of a machined part. To manu?facture a high quality part,it is necessary to detect and remove the machining induced subsurface damage by the subsequent processes. However,subsurface damage is often covered with a smearing layer generated in a machining process,it is rather di cult to directly observe and detect by optical microscopy. An e cient detection of subsur?face damage directly leads to quality improvement and time saving for machining of hard and brittle materials. This paper presents a review of the methods for detection of subsurface damage,both destructive and non?destructive. Although more reliable,destructive methods are typically time?consuming and confined to local damage infor?mation. Non?destructive methods usually su er from uncertainty factors,but may provide global information on subsurface damage distribution. These methods are promising because they can provide a capacity of rapid scan and detection of subsurface damage in spatial distribution.
基金supported by Key National Natural Science Foundation of China (Grant No. 50535020)
文摘Potassium dihydrogen phosphate (KDP) is an important electro-optic crystal, often used for frequency conversion and Pockels cells in large aperture laser systems. To investigate the influence of anisotropy to the depth of subsurface damage and the profiles of cracks in subsurface of KDP crystal, an experimental study was made to obtain the form of subsurface damage produced by scratches on KDP crystal in [100], [120] and [110] crystal directions on (001) crystal plane. The results indicated that there were great differences between depth and crack shape in different directions. For many slip planes in KDP, the plastic deformation and cracks generated under pressure in the subsurface were complex. Fluctuations of subsurface damage depth at transition point were attributed to the deformation of the surface which consumed more energy when the surface deformation changed from the mixed region of brittle and plastic to the complete brittle region along the scratch. Also, the process of subsurface damage from shallow to deep, from dislocation to big crack in KDP crystal with the increase of radial force and etch pit on different crystal plane were obtained. Because crystallographic orientation and processing orientation was different, etching pits on (100) crystal plane were quadrilateral while on (110) plane and (120) plane were trapezoidal and triangular, respectively.
基金supported by the National Natural Science Foundation of China(52035009,52005243)the Science and Technology Innovation Committee of Shenzhen Municipality(JCYJ20200109141003910,GJHZ20180928155412525)。
文摘This paper proposes a method for the rapid detection of subsurface damage(SSD)of Si C using atmospheric inductivity coupled plasma.As a plasma etching method operated at ambient pressure with no bias voltage,this method does not introduce any new SSD to the substrate.Plasma diagnosis and simulation are used to optimize the detection operation.Assisted by an Si C cover,a taper can be etched on the substrate with a high material removal rate.Confocal laser scanning microscopy and scanning electron microscope are used to analyze the etching results,and scanning transmission electron microscope(STEM)is adopted to confirm the accuracy of this method.The STEM result also indicates that etching does not introduce any SSD,and the thoroughly etched surface is a perfectly single crystal.A rapid SSD screening ability is also demonstrated,showing that this method is a promising approach for the rapid detection of SSD.
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).
基金Project(50375156) supported by the National Natural Science Foundation of China
文摘A theoretical model of relationship between subsurface damage and surface roughness was established to realize rapid and non-destructive measurement of subsurface damage of ground optical materials.Postulated condition of the model was that subsurface damage depth and peak-to-valley surface roughness are equal to depth of radial and lateral cracks in brittle surface induced by small-radius(radius≤200 μm)spherical indenter,respectively.And contribution of elastic stress field to the radial cracks propagation was also considered in the loading cycle.Subsurface damage depth of ground BK7 glasses was measured by magnetorheological finishing spot technique to validate theoretical ratio of subsurface damage to surface roughness.The results show that the ratio is directly proportional to load of abrasive grains and hardness of optical materials,while inversely proportional to granularity of abrasive grains and fracture toughness of optical materials.Moreover,the influence of the load and fracture toughness on the ratio is more significant than the granularity and hardness,respectively.The measured ratios of 80 grit and 120 grit fixed abrasive grinding of BK7 glasses are 5.8 and 5.4,respectively.
基金supported by the National Natural Science Foundation of China(No.51375237)the Postdoctoral Science Foundation of China(No.2015T80547)
文摘The subsurface damage(SSD)layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology.Three ways such as ice-fixed abrasive,thermosetting fixed abrasive and free abrasive lappings are adopted to lap monocrystalline germanium wafers.The SSD depth was measured by a nanoindenter,and the morphology of SSD layer was observed by an atomic force microscopy(AFM).The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer.Compared with thermosetting fixed abrasive and free abrasive lappings,the SSD depth lapped with ice-fixed abrasive is shallower.Moreover,the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing ways.
文摘Laser-induced damage in fused silica optics greatly restricts the performances of laser facilities. Gray haze damage,which is always initiated on ceria polished optics, is one of the most important damage morphologies in fused silica optics.In this paper, the laser-induced gray haze damages of four fused silica samples polished with CeO2, Al2O3, ZrO2, and colloidal silica slurries are investigated. Four samples all present gray haze damages with much different damage densities.Then, the polishing-induced contaminant and subsurface damages in four samples are analyzed. The results reveal that the gray haze damages could be initiated on the samples without Ce contaminant and are inclined to show a tight correlation with the shallow subsurface damages.
基金support of the Shenzhen Science and Technology Innovation Commission under Project Numbers KQTD20190929172505711,JSGG20210420091802007, and JCYJ20210324115413036Guangdong Provincial Department of Science and Technology under Project Number K22333004。
文摘High-speed machining(HSM) has been studied for several decades and has potential application in various industries, including the automobile and aerospace industries. However,the underlying mechanisms of HSM have not been formally reviewed thus far. This article focuses on the solid mechanics framework of adiabatic shear band(ASB) onset and material metallurgical microstructural evolutions in HSM. The ASB onset is described using partial differential systems. Several factors in HSM were considered in the systems, and the ASB onset conditions were obtained by solving these systems or applying the perturbation method to the systems. With increasing machining speed, an ASB can be depressed and further eliminated by shock pressure. The damage observed in HSM exhibits common features. Equiaxed fine grains produced by dynamic recrystallization widely cause damage to ductile materials, and amorphization is the common microstructural evolution in brittle materials. Based on previous studies, potential mechanisms for the phenomena in HSM are proposed. These include the thickness variation of the white layer of ductile materials. These proposed mechanisms would be beneficial to deeply understanding the various phenomena in HSM.
基金This work was supported by the National Key Research and Development Program of China(No.2022YFB3403600)the National Natural Science Foundation of China(No.52293403)Self-Planned Task of State Key Laboratory of Robotics and System(HIT)(No.SKLRS202204C).
文摘As for the ultra-precision grinding of the hemispherical fused silica resonator,due to the hard and brittle nature of fused silica,subsurface damage(SSD)is easily generated,which enormously influences the performance of such components.Hence,ultra-precision grinding experiments are carried out to investigate the surface/subsurface quality of the hemispherical resonator machined by the small ball-end fine diamond grinding wheel.The influence of grinding parameters on the surface roughness(SR)and SSD depth of fused silica samples is then analyzed.The experimental results indicate that the SR and SSD depth decreased with the increase of grinding speed and the decrease of feed rate and grinding depth.In addition,based on the material strain rate and the maximum undeformed chip thickness,the effect of grinding parameters on the subsurface damage mechanism of fused silica samples is analyzed.Furthermore,a multi-step ultra-precision grinding technique of the hemispherical resonator is proposed based on the interaction influence between grinding depth and feed rate.Finally,the hemispherical resonator is processed by the proposed grinding technique,and the SR is improved from 454.328 nm to 110.449 nm while the SSD depth is reduced by 94%from 40μm to 2.379μm.The multi-step grinding technique proposed in this paper can guide the fabrication of the hemispherical resonator.
基金This study was financially supported by the National Natural Science Foundation of China in Major Project Program (No. 50390061)the National Science Fund for Distinguished Young Scholars (No. 50325518).
文摘The depth and nature of the subsurface damage in a silicon wafer will limit the performance of IC components. Damage microstructures of the silicon wafers ground by the #325, #600, and #2000 grinding wheels was analyzed. The results show that many microcracks, fractures, and dislocation rosettes appear in the surface and subsurface of the wafer ground by the #325 grinding wheel. No obvious microstructure change exists. The amorphous layer with a thickness of about 100 nm, microcracks, high density dislocations, and polycrystalline silicon are observed in the subsurface of the wafer ground by the #600 grinding wheel. For the wafer ground by the #2000 grinding wheel, an amorphous layer of about 30 nm thickness, a polycrystalline silicon layer, a few dislocations, and an elastic deformation layer exist. In general, with the decrease in grit size, the material removal mode changes from micro-fracture mode to ductile mode gradually.
文摘The last major earthquake in Bantul causing severe damage occurred on May 27th, 2006. The damages in the flat area of Bantul had a certain pattern. The damages pattern controlled the subsurface characteristic below the flat area. Understanding earthquake damage pattern through geo-morphological approach is important for earthquake hazard analysis. The techniques of remote sensing and Geographical Information Systems were applied to analyze earthquake damage pattern and geomorphological characteristics. Gravity analysis was used to identify the subsurface structure and the basement depth while geoelectric analysis was used to identify sediment depth. Moreover, spatial correlation analysis was used to identify the relationship between the earthquake damage, geomorphological characteristics, and subsurface characteristics. The results show that fluvial, marine, and aeolian landforms have low rock density value based on gravity analysis. These indicate that they were composed by thick unconsolidated material of quaternary alluvium. While denudational, structural, and solutional landforms composed by material of tertiary rocks have high rock density value. The severe damage occurred in the area that has a lower value of local gravity and deeper basement. In contrast, the slight damage occurred in the area that has higher values of local gravity and shallower basement. Moreover, the severe damage occurred in areas of thicker sediment that consist of unconsolidated material. Consequently, the area of unconsolidated material that has deeper basement and thicker sediment is prone to earthquake. They were located on fluvial, marine, and aeolian landforms.
基金supported by the National Natural Science Foundation of China (Grant Nos. U20A6001, 11625207, 11902292, and 11921002)the Zhejiang Province Key Research and Development Project (Grant Nos.2019C05002, 2020C05004, and 2021C01183)。
文摘Subsurface damage(SSD) is an unavoidable problem in the precision mechanical grinding for preparing ultra-thin and flexible silicon chips. At present, there are relatively few studies on the relationship between SSD and the bending strength of ultra-thin chips under different grinding parameters. In this study, SSD including amorphization and dislocation is observed using a transmission electron microscope. Theoretical predictions of the SSD depth induced by different processing parameters are in good agreement with experimental data. The main reasons for SSD depth increase include the increase of grit size, the acceleration of feed rate, and the slowdown of wheel rotation speed. Three-point bending test is adopted to measure the bending strength of ultra-thin chips processed by different grinding conditions. The results show that increasing wheel rotation speed and decreasing grit size and feed rate will improve the bending strength of chips, due to the reduction of SSD depth. Wet etching and chemical mechanical polishing(CMP) are applied respectively to remove the SSD induced by grinding, and both contribute to providing a higher bending strength, but in comparison, CMP works better due to a smooth surface profile. This research aims to provide some guidance for optimizing the grinding process and fabricating ultra-thin chips with higher bending strength.
基金This study was supported by the National Natural Science Foundation of China(61975215)Youth Innovation Promotion Association of the Chinese Academy of Sciences,Strategic Priority Research Program of the Chinese Academy of Sciences(XDA25020206)the Science and Technology Planning Project of Shanghai Municipal Science&Technology Commission(21DZ1100400).
文摘The laser-induced damage threshold(LIDT)of plate laser beam splitter(PLBS)coatings is closely related to the subsurface absorption defects of the substrate.Herein,a two-step deposition temperature method is proposed to understand the effect of substrate subsurface impurity defects on the LIDT of PLBS coatings.Firstly,BK7 substrates are heat-treated at three different temperatures.The surface morphology and subsurface impurity defect distribution of the substrate before and after the heat treatment are compared.Then,a PLBS coating consisting of alternating HfO2–Al2O3 mixture and SiO2 layers is designed to achieve a beam-splitting ratio(transmittance to reflectance,s-polarized light)of approximately 50:50 at 1053 nm and an angle of incidence of 45◦,and it is prepared under four different deposition processes.The experimental and simulation results show that the subsurface impurity defects of the substrate migrate to the surface and accumulate on the surface during the heat treatment,and become absorption defect sources or nodule defect seeds in the coating,reducing the LIDT of the coating.The higher the heat treatment temperature,the more evident the migration and accumulation of impurity defects.A lower deposition temperature(at which the coating can be fully oxidized)helps to improve the LIDT of the PLBS coating.When the deposition temperature is 140◦C,the LIDT(s-polarized light,wavelength:1064 nm,pulse width:9 ns,incident angle:45◦)of the PLBS coating is 26.2 J/cm2,which is approximately 6.7 times that of the PLBS coating deposited at 200◦C.We believe that the investigation into the laser damage mechanism of PLBS coatings will help to improve the LIDT of coatings with partial or high transmittance at laser wavelengths.