Single crystal silicon freestanding structures for tensile and fatigue testing were treated with KrF excimer laser to improve surface roughness and accordingly mechanical performance. Sample thickness was 5 μm. Local...Single crystal silicon freestanding structures for tensile and fatigue testing were treated with KrF excimer laser to improve surface roughness and accordingly mechanical performance. Sample thickness was 5 μm. Localized laser treatment was successful in eliminating the scallops developed during Bosch process and in reducing surface roughness. Harsh irradiation at laser energies up to 4 J/cm2 was only possible due to localized treatment without significant vibrations occurring on the freestanding samples that led to fracture in preliminary experiments at energies as low as 0.16 J/cm2. Finite element analysis was used to investigate the temperature distribution on the irradiated structures. Atomic force microscopy (AFM) and Raman spectroscopy were also used to assess surface roughness, crystallinity changes and surface stresses developing on surfaces subjected to perpendicular laser irradiation. At a high energy (3.2 J/cm2) the top surface showed a decrease of roughness compared to fabricated samples. Raman spectroscopy showed the dominance of crystalline silicon after laser irradiation. The effects of laser energy, number of展开更多
This paper presents the estimation of three-dimensional volumetric errors of a machining center by using a tracking interferometer. A tracking interferometer is a laser interferometer with the mechanism to steer the l...This paper presents the estimation of three-dimensional volumetric errors of a machining center by using a tracking interferometer. A tracking interferometer is a laser interferometer with the mechanism to steer the laser direction to follow a target retroreflector. Based on the triangulation principle, the three-dimensional position of the target can be estimated from measured laser displacements. Its capability to measure three-dimensional positioning errors for arbitrary trajectories is important for the indirect measurement of the machine＇s kinematic model. This paper presents experimental investigation of the estimation accuracy of the multilateration-based measurement by a tracking interferometer. A tracking interferometer developed by a part of the authors is used in experiments. In the present experiment, the measured volume of target positions was 100 mm × 100 mm × 100 mm. The estimation accuracy of targets within this volume was not sufficiently high compared to the positioning error of the measured machine tool. The results of the experiment and simulation show that the estimation uncertainty is dependent on tracking interferometer locations relative to target locations. Error sensitivity analysis shows that wider distribution of tracker positions in XY improves the estimation accuracy.展开更多
The piezoresistive effect in graphene ribbon has been simulated based on the first-principles electronic-state calculation for the development of novel piezoresistive materials with special performances such as high f...The piezoresistive effect in graphene ribbon has been simulated based on the first-principles electronic-state calculation for the development of novel piezoresistive materials with special performances such as high flexibility and low fabrication cost. We modified theoretical approach for piezoresistivity simulation from our original method for semiconductor systems to improved procedure applicable to conductor systems. The variations of carrier conductivity due to strain along with the graphene ribbon models (armchair model and zigzag model) have been calculated using band carrier densities and their corresponding effective masses derived from the one-dimensional electronic band diagram. We found that the armchair-type graphene nano-ribbon models have low conductivity with heavy effective mass. This is a totally different conductivity from two-dimensional graphene sheet. The variation of band energy diagrams of the zigzag-type graphene nano-ribbon models due to strain is much more sensitive than that of the armchair models. As a result, the longitudinal and transverse gauge factors are high in our calculation, and in particular, the zigzag-type graphene ribbon has an enormous potential material with high piezoresistivity. So, it will be one of the most important candidates that can be used as a high-performance piezoresistive material for fabricating a new high sensitive strain gauge sensor.展开更多
Repetitive bending fatigue tests were performed using five types of single-crystal silicon specimens with different crystal orientations fabricated from{100}and{110}wafers.Fatigue lifetimes in a wide range between 100...Repetitive bending fatigue tests were performed using five types of single-crystal silicon specimens with different crystal orientations fabricated from{100}and{110}wafers.Fatigue lifetimes in a wide range between 100 and 1010 were obtained using fan-shaped resonator test devices.Fracture surface observation via scanning electron microscope(SEM)revealed that the{111}plane was the primary fracture plane.The crack propagation exponent n was estimated to be 27,which was independent of the crystal orientation and dopant concentration;however,it was dependent on the surface conditions of the etched sidewall.The fatigue strengths relative to the deflection angle were orientation dependent,and the ratios of the factors obtained ranged from 0.86 to 1.25.The strength factors were compared with those obtained from finite element method stress analyses.The calculated stress distributions showed strong orientation dependence,which was well-explained by the elastic anisotropy.The comparison of the strength factors suggested that the first principal stress was a good criterion for fatigue fracture.We include comparisons with specimens tested in our previous report and address the tensile strength,initial crack length,volume effect,and effects of surface roughness such as scallops.展开更多
文摘Single crystal silicon freestanding structures for tensile and fatigue testing were treated with KrF excimer laser to improve surface roughness and accordingly mechanical performance. Sample thickness was 5 μm. Localized laser treatment was successful in eliminating the scallops developed during Bosch process and in reducing surface roughness. Harsh irradiation at laser energies up to 4 J/cm2 was only possible due to localized treatment without significant vibrations occurring on the freestanding samples that led to fracture in preliminary experiments at energies as low as 0.16 J/cm2. Finite element analysis was used to investigate the temperature distribution on the irradiated structures. Atomic force microscopy (AFM) and Raman spectroscopy were also used to assess surface roughness, crystallinity changes and surface stresses developing on surfaces subjected to perpendicular laser irradiation. At a high energy (3.2 J/cm2) the top surface showed a decrease of roughness compared to fabricated samples. Raman spectroscopy showed the dominance of crystalline silicon after laser irradiation. The effects of laser energy, number of
文摘This paper presents the estimation of three-dimensional volumetric errors of a machining center by using a tracking interferometer. A tracking interferometer is a laser interferometer with the mechanism to steer the laser direction to follow a target retroreflector. Based on the triangulation principle, the three-dimensional position of the target can be estimated from measured laser displacements. Its capability to measure three-dimensional positioning errors for arbitrary trajectories is important for the indirect measurement of the machine＇s kinematic model. This paper presents experimental investigation of the estimation accuracy of the multilateration-based measurement by a tracking interferometer. A tracking interferometer developed by a part of the authors is used in experiments. In the present experiment, the measured volume of target positions was 100 mm × 100 mm × 100 mm. The estimation accuracy of targets within this volume was not sufficiently high compared to the positioning error of the measured machine tool. The results of the experiment and simulation show that the estimation uncertainty is dependent on tracking interferometer locations relative to target locations. Error sensitivity analysis shows that wider distribution of tracker positions in XY improves the estimation accuracy.
文摘The piezoresistive effect in graphene ribbon has been simulated based on the first-principles electronic-state calculation for the development of novel piezoresistive materials with special performances such as high flexibility and low fabrication cost. We modified theoretical approach for piezoresistivity simulation from our original method for semiconductor systems to improved procedure applicable to conductor systems. The variations of carrier conductivity due to strain along with the graphene ribbon models (armchair model and zigzag model) have been calculated using band carrier densities and their corresponding effective masses derived from the one-dimensional electronic band diagram. We found that the armchair-type graphene nano-ribbon models have low conductivity with heavy effective mass. This is a totally different conductivity from two-dimensional graphene sheet. The variation of band energy diagrams of the zigzag-type graphene nano-ribbon models due to strain is much more sensitive than that of the armchair models. As a result, the longitudinal and transverse gauge factors are high in our calculation, and in particular, the zigzag-type graphene ribbon has an enormous potential material with high piezoresistivity. So, it will be one of the most important candidates that can be used as a high-performance piezoresistive material for fabricating a new high sensitive strain gauge sensor.
文摘Repetitive bending fatigue tests were performed using five types of single-crystal silicon specimens with different crystal orientations fabricated from{100}and{110}wafers.Fatigue lifetimes in a wide range between 100 and 1010 were obtained using fan-shaped resonator test devices.Fracture surface observation via scanning electron microscope(SEM)revealed that the{111}plane was the primary fracture plane.The crack propagation exponent n was estimated to be 27,which was independent of the crystal orientation and dopant concentration;however,it was dependent on the surface conditions of the etched sidewall.The fatigue strengths relative to the deflection angle were orientation dependent,and the ratios of the factors obtained ranged from 0.86 to 1.25.The strength factors were compared with those obtained from finite element method stress analyses.The calculated stress distributions showed strong orientation dependence,which was well-explained by the elastic anisotropy.The comparison of the strength factors suggested that the first principal stress was a good criterion for fatigue fracture.We include comparisons with specimens tested in our previous report and address the tensile strength,initial crack length,volume effect,and effects of surface roughness such as scallops.
