In the present study, the indentation testing with a flat cylindrical indenter on typical multi-layer material systems was simulated successfully by finite element method. The emphasis was put on the methods of extrac...In the present study, the indentation testing with a flat cylindrical indenter on typical multi-layer material systems was simulated successfully by finite element method. The emphasis was put on the methods of extracting the yield stresses and strain-hardening modulus of upper and middle-layers of three-layer material systems from the indentation testing. The slope of the indentation depth to the applied indentation stress curve was found to have a turning point, which can be used to determine the yield stress of the upper-layer. Then, a different method was also presented to determine the yield stress of the middle-layer. This method was based on a set of assumed applied indentation stresses which were to be intersected by the experimental results in order to meet the requirement of having the experimental indentation depth. At last, a reverse numerical algorithm was explored to determine the yield stresses of upper and middle-layers simultaneously by using the indentation testing with two different size indenters. This method assumed two ranges of yield stresses to simulate the indentation behavior. The experimental depth behavior was used to intersect the simulated indentation behavior. And the intersection corresponded to the values of yield stresses of upper and middle-layers. This method was also used further to determine the strain-hardening modulus of upper and middle-layers simultaneously.展开更多
Heterogeneous materials are inherently dielectric,and charge distribution and transport in such materials involves complex local fields and polarizations that are remarkably sensitive to morphology and the interaction...Heterogeneous materials are inherently dielectric,and charge distribution and transport in such materials involves complex local fields and polarizations that are remarkably sensitive to morphology and the interaction of conduction and permittivity.Trial and error design of such material systems is time consuming and expensive,and often ineffectual.However,heterogeneous materials are essential for energy conversion and storage,and they have become the foundation for major advances in the performance of devices such as batteries,fuel cells,separation membranes,and solar cells.The present paper presents some relationships in support of rational design based on an extensive experimental validation of the concepts and analysis that form a foundation for that design.Salient results include the prediction and confirmation of volume fraction effects(including nondilute mixtures),and the prediction and direct measurement of surface charge effects at internal interfaces as a function of constituent morphology and orientation.展开更多
Autonomous material exploration systems that integrate robotics,material simulations,and machine learning have advanced rapidly in recent years.Although their number continues to grow,these systemscurrently operate in...Autonomous material exploration systems that integrate robotics,material simulations,and machine learning have advanced rapidly in recent years.Although their number continues to grow,these systemscurrently operate in isolation,limiting the overall efficiency of autonomous material discovery.In analogy to how human researchers advance materials science by sharing knowledge and collaborating,autonomous systems can also benefit from networking and knowledge exchange.Here,we propose a framework in which multiple autonomous material exploration systems form a network via transfer learning,selectively utilizing relevant knowledge from other systems in real time.We demonstrate this approach using three distinct autonomous systems and show that such networking significantly enhances the efficiency of material discovery.Our results suggest that the proposed framework can enable the development of large-scale autonomous material exploration networks,ultimately accelerating progress in material development.展开更多
High-resolution imaging tools have revolutionized energy science by enabling direct visualization of local chemical and physical transformations across scales in highly complex material systems�from atomic rearrangeme...High-resolution imaging tools have revolutionized energy science by enabling direct visualization of local chemical and physical transformations across scales in highly complex material systems�from atomic rearrangements at catalytic surfaces and interfaces to mesoscale heterogeneities within battery electrodes.展开更多
A quadratic yield function which can describe the anisotropic behaviors of sheet metals with tension/compression symmetry and asymmetry is proposed.Five mechanical properties are adopted to determine the coefficients ...A quadratic yield function which can describe the anisotropic behaviors of sheet metals with tension/compression symmetry and asymmetry is proposed.Five mechanical properties are adopted to determine the coefficients of each part of the yield function.For particular cases,the proposed yield function can be simplified to Mises or Hill’s quadratic yield function.The anisotropic mechanical properties are expressed by defining an angle between the current normalized principal stress space and the reference direction with the assumption of orthotropic anisotropy.The accuracy of the proposed yield function in describing the anisotropy under tension and compression is demonstrated.展开更多
As a kind of material with excellent performance and low cost,plastics have been widely used,and their global annual production reaches 400 million tons,of which approximately 90%derives from non-renewable fossil fuel...As a kind of material with excellent performance and low cost,plastics have been widely used,and their global annual production reaches 400 million tons,of which approximately 90%derives from non-renewable fossil fuels[1].Since plastics are difficult to degrade under natural conditions and their castoff poses a high risk of causing environmental pollution and resource waste[2],constructing efficient material recovery systems to re-integrate end-of-life plastics into the chemical/material industry is a promising strategy for achieving sustainability[3].展开更多
Materials have driven human progress from the Stone Age to the Silicon Age,and a new age of multifunctional assembled materials is coming.Designing these materials with precisely tailored properties is essential to so...Materials have driven human progress from the Stone Age to the Silicon Age,and a new age of multifunctional assembled materials is coming.Designing these materials with precisely tailored properties is essential to solve problems that the current generation of materials cannot handle.展开更多
Modeling the response of material and chemical systems to electric fields remains a longstanding challenge.Machine learning interatomic potentials(MLIPs)offer an efficient and scalable alternative to quantum mechanica...Modeling the response of material and chemical systems to electric fields remains a longstanding challenge.Machine learning interatomic potentials(MLIPs)offer an efficient and scalable alternative to quantum mechanical methods,but do not by themselves incorporate electrical response.Here,we show that polarization and Born effective charge(BEC)tensors can be directly extracted from longrange MLIPs within the Latent Ewald Summation(LES)framework,solely by learning from energy and force data.Using this approach,we predict the infrared spectra of bulk water under zero or finite external electric fields,ionic conductivities of high-pressure superionic ice,and the phase transition and hysteresis in ferroelectric PbTiO_(3)perovskite.This work thus extends the capability of MLIPs to predict electrical response–without training on charges or polarization or BECs–and enables accurate modeling of electric-field-driven processes in diverse systems at scale.展开更多
Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction DoubleDrift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, devel- oped by t...Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction DoubleDrift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, devel- oped by the authors, for operation in the Ka-, V- and W-band frequencies. The results are further compared with corresponding Si and Ge homo-junction devices. The study shows high values of device efficiency, such as 23%, 22% and 21.5%, for n-Ge/p-Si IMPATTs at the Ka, V and W bands, respectively. The peak device negative con- ductances for n-Si/p-Ge and n-Ge/p-Si hetero-junction devices found to be 50.7× 10^6 S/m^2 and 71.3× 106 S/m^2, which are -3-4 times better than their Si and Ge counterparts at the V-band. The computed values of RF powerdensity for n-Ge/p-Si hetero-junction IMPATTs are 1.0 ×10^9, 1.1 × 10^9 and 1.4× 10^9 W/m^2, respectively, for Ka-, V- and W-band operation, which can be observed to be the highest when compared with Si, Ge and n-Si/p-Ge devices. Both of the hetero-junctions, especially the n-Ge/p-Si hetero-junction diode, can thus become a superior RF-power generator over a wide range of frequencies. The present study will help the device engineers to choose a suitable material pair for the development of high-power MM-wave IMPATT for applications in the civil and defense-related arena.展开更多
We report a new nBn photodetector(nBn-PD)design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for midwavelength infrared(MWIR)applications.In this structure,delta-doped compositionally graded barrier(δ-DCGB...We report a new nBn photodetector(nBn-PD)design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for midwavelength infrared(MWIR)applications.In this structure,delta-doped compositionally graded barrier(δ-DCGB)layers are suggested,the advantage of which is creation of a near zero valence band ofset in nBn photodetectors.The design of theδ-DCGB nBn-PD device includes a 3µm absorber layer(n-InAs0.81Sb0.19),a unipolar barrier layer(AlSb),and 0.2μm contact layer(n-InAs0.81Sb0.19)as well as a 0.116µm linear grading region(InAlSb)from the contact to the barrier layer and also from the barrier to the absorber layer.The analysis includes various dark current contributions,such as the Shockley-Read-Hall(SRH),trap-assisted tunneling(TAT),Auger,and Radiative recombination mechanisms,to acquire more precise results.Consequently,we show that the method used in the nBn device design leads to difusion-limited dark current so that the dark current density is 2.596×10^(−8)A/cm^(2)at 150 K and a bias voltage of−0.2 V.The proposed nBn detector exhibits a 50%cutof wavelength of more than 5µm,the peak current responsivity is 1.6 A/W at a wavelength of 4.5µm and a−0.2 V bias with 0.05 W/cm2 backside illumination without anti-refective coating.The maximum quantum efciency at 4.5µm is about 48.6%,and peak specifc detectivity(D*)is of 3.37×10^(10)cm⋅Hz1/2/W.Next,to solve the refection concern in this nBn devices,we use a BaF_(2)anti-refection coating layer due to its high transmittance in the MWIR window.It leads to an increase of almost 100%in the optical response metrics,such as the current responsivity,quantum efciency,and detectivity,compared to the optical response without an anti-refection coating layer.展开更多
基金the National Natural Science Foundation of China （No. 10472094） the Research Fund for the Doctoral Program of Higher Education （N6CJ0001） Doctorate Fund of Northwestern Polytechnical University.
文摘In the present study, the indentation testing with a flat cylindrical indenter on typical multi-layer material systems was simulated successfully by finite element method. The emphasis was put on the methods of extracting the yield stresses and strain-hardening modulus of upper and middle-layers of three-layer material systems from the indentation testing. The slope of the indentation depth to the applied indentation stress curve was found to have a turning point, which can be used to determine the yield stress of the upper-layer. Then, a different method was also presented to determine the yield stress of the middle-layer. This method was based on a set of assumed applied indentation stresses which were to be intersected by the experimental results in order to meet the requirement of having the experimental indentation depth. At last, a reverse numerical algorithm was explored to determine the yield stresses of upper and middle-layers simultaneously by using the indentation testing with two different size indenters. This method assumed two ranges of yield stresses to simulate the indentation behavior. The experimental depth behavior was used to intersect the simulated indentation behavior. And the intersection corresponded to the values of yield stresses of upper and middle-layers. This method was also used further to determine the strain-hardening modulus of upper and middle-layers simultaneously.
文摘Heterogeneous materials are inherently dielectric,and charge distribution and transport in such materials involves complex local fields and polarizations that are remarkably sensitive to morphology and the interaction of conduction and permittivity.Trial and error design of such material systems is time consuming and expensive,and often ineffectual.However,heterogeneous materials are essential for energy conversion and storage,and they have become the foundation for major advances in the performance of devices such as batteries,fuel cells,separation membranes,and solar cells.The present paper presents some relationships in support of rational design based on an extensive experimental validation of the concepts and analysis that form a foundation for that design.Salient results include the prediction and confirmation of volume fraction effects(including nondilute mixtures),and the prediction and direct measurement of surface charge effects at internal interfaces as a function of constituent morphology and orientation.
文摘Autonomous material exploration systems that integrate robotics,material simulations,and machine learning have advanced rapidly in recent years.Although their number continues to grow,these systemscurrently operate in isolation,limiting the overall efficiency of autonomous material discovery.In analogy to how human researchers advance materials science by sharing knowledge and collaborating,autonomous systems can also benefit from networking and knowledge exchange.Here,we propose a framework in which multiple autonomous material exploration systems form a network via transfer learning,selectively utilizing relevant knowledge from other systems in real time.We demonstrate this approach using three distinct autonomous systems and show that such networking significantly enhances the efficiency of material discovery.Our results suggest that the proposed framework can enable the development of large-scale autonomous material exploration networks,ultimately accelerating progress in material development.
文摘High-resolution imaging tools have revolutionized energy science by enabling direct visualization of local chemical and physical transformations across scales in highly complex material systems�from atomic rearrangements at catalytic surfaces and interfaces to mesoscale heterogeneities within battery electrodes.
基金supported by the National Natural Science Foundation of China (Grant Nos.51475003 and 51205004)Beijing Natural Science Foundation (Grant No.3152010)+1 种基金open project of "State Key Laboratory of Solidification Processing" of Northwestern Polytechnical University (No.SKLSP201635)Beijing Education Committee Science and Technology Program (Grant No.KM201510009004)
文摘A quadratic yield function which can describe the anisotropic behaviors of sheet metals with tension/compression symmetry and asymmetry is proposed.Five mechanical properties are adopted to determine the coefficients of each part of the yield function.For particular cases,the proposed yield function can be simplified to Mises or Hill’s quadratic yield function.The anisotropic mechanical properties are expressed by defining an angle between the current normalized principal stress space and the reference direction with the assumption of orthotropic anisotropy.The accuracy of the proposed yield function in describing the anisotropy under tension and compression is demonstrated.
文摘As a kind of material with excellent performance and low cost,plastics have been widely used,and their global annual production reaches 400 million tons,of which approximately 90%derives from non-renewable fossil fuels[1].Since plastics are difficult to degrade under natural conditions and their castoff poses a high risk of causing environmental pollution and resource waste[2],constructing efficient material recovery systems to re-integrate end-of-life plastics into the chemical/material industry is a promising strategy for achieving sustainability[3].
文摘Materials have driven human progress from the Stone Age to the Silicon Age,and a new age of multifunctional assembled materials is coming.Designing these materials with precisely tailored properties is essential to solve problems that the current generation of materials cannot handle.
基金funding from the BIDMaP Postdoctoral Fellowship.
文摘Modeling the response of material and chemical systems to electric fields remains a longstanding challenge.Machine learning interatomic potentials(MLIPs)offer an efficient and scalable alternative to quantum mechanical methods,but do not by themselves incorporate electrical response.Here,we show that polarization and Born effective charge(BEC)tensors can be directly extracted from longrange MLIPs within the Latent Ewald Summation(LES)framework,solely by learning from energy and force data.Using this approach,we predict the infrared spectra of bulk water under zero or finite external electric fields,ionic conductivities of high-pressure superionic ice,and the phase transition and hysteresis in ferroelectric PbTiO_(3)perovskite.This work thus extends the capability of MLIPs to predict electrical response–without training on charges or polarization or BECs–and enables accurate modeling of electric-field-driven processes in diverse systems at scale.
文摘Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction DoubleDrift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, devel- oped by the authors, for operation in the Ka-, V- and W-band frequencies. The results are further compared with corresponding Si and Ge homo-junction devices. The study shows high values of device efficiency, such as 23%, 22% and 21.5%, for n-Ge/p-Si IMPATTs at the Ka, V and W bands, respectively. The peak device negative con- ductances for n-Si/p-Ge and n-Ge/p-Si hetero-junction devices found to be 50.7× 10^6 S/m^2 and 71.3× 106 S/m^2, which are -3-4 times better than their Si and Ge counterparts at the V-band. The computed values of RF powerdensity for n-Ge/p-Si hetero-junction IMPATTs are 1.0 ×10^9, 1.1 × 10^9 and 1.4× 10^9 W/m^2, respectively, for Ka-, V- and W-band operation, which can be observed to be the highest when compared with Si, Ge and n-Si/p-Ge devices. Both of the hetero-junctions, especially the n-Ge/p-Si hetero-junction diode, can thus become a superior RF-power generator over a wide range of frequencies. The present study will help the device engineers to choose a suitable material pair for the development of high-power MM-wave IMPATT for applications in the civil and defense-related arena.
文摘We report a new nBn photodetector(nBn-PD)design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for midwavelength infrared(MWIR)applications.In this structure,delta-doped compositionally graded barrier(δ-DCGB)layers are suggested,the advantage of which is creation of a near zero valence band ofset in nBn photodetectors.The design of theδ-DCGB nBn-PD device includes a 3µm absorber layer(n-InAs0.81Sb0.19),a unipolar barrier layer(AlSb),and 0.2μm contact layer(n-InAs0.81Sb0.19)as well as a 0.116µm linear grading region(InAlSb)from the contact to the barrier layer and also from the barrier to the absorber layer.The analysis includes various dark current contributions,such as the Shockley-Read-Hall(SRH),trap-assisted tunneling(TAT),Auger,and Radiative recombination mechanisms,to acquire more precise results.Consequently,we show that the method used in the nBn device design leads to difusion-limited dark current so that the dark current density is 2.596×10^(−8)A/cm^(2)at 150 K and a bias voltage of−0.2 V.The proposed nBn detector exhibits a 50%cutof wavelength of more than 5µm,the peak current responsivity is 1.6 A/W at a wavelength of 4.5µm and a−0.2 V bias with 0.05 W/cm2 backside illumination without anti-refective coating.The maximum quantum efciency at 4.5µm is about 48.6%,and peak specifc detectivity(D*)is of 3.37×10^(10)cm⋅Hz1/2/W.Next,to solve the refection concern in this nBn devices,we use a BaF_(2)anti-refection coating layer due to its high transmittance in the MWIR window.It leads to an increase of almost 100%in the optical response metrics,such as the current responsivity,quantum efciency,and detectivity,compared to the optical response without an anti-refection coating layer.
