A novel two-step method is employed, for the first time, to fabricatc nonvolatile memory devices that have metal nanoerystals. First, size-averaged Au nanocrystals are synthesized chemically; second, they are assemble...A novel two-step method is employed, for the first time, to fabricatc nonvolatile memory devices that have metal nanoerystals. First, size-averaged Au nanocrystals are synthesized chemically; second, they are assembled into memory devices by a spin-coating technique at room temperature. This attractive approach makes it possible to tailor the diameter and control the density of nanocrystals individually. In addition, processes at room temperature prevent Au diffusion, which is a main concem for the application of metal nanocrystal-based memory. The experimental results, both the morphology characterization and the electrical measurements, reveal that there is an optimum density of nanocrystal monolayer to balance between long data retention and a large hysteresis memory window. At the same time, density-controllable devices could also feed the preferential emphasis on either memory window or retention time. All these facts confirm the advantages and novelty of our two-step method.展开更多
Radiotherapy(RT)based on X-ray irradiation is a widely applied cancer treatment strategy in the clinic.However,treating cancer based on RT alone usually results in insufficient radiation energy deposition,which inevit...Radiotherapy(RT)based on X-ray irradiation is a widely applied cancer treatment strategy in the clinic.However,treating cancer based on RT alone usually results in insufficient radiation energy deposition,which inevitably has serious side effects on healthy parts of the body.Interestingly,high atomic number(high-Z)metal nanocrystals as X-ray sensitizers can reduce the radiation dose effectively due to their high X-ray absorption,which has attracted increased attention in recent years.High-Z metal nanocrystals produce Auger and photoelectrons electrons under X-ray irradiation,which could generate large amounts of reactive oxygen species,and induce cellular damages.The sensitization effect of high-Z metal nanocrystals is closely related with their composition,morphologies,and size,which would strongly impact their performances in the application of cancer imaging and therapy.In this review,we summarize diverse types of X-ray sensitizers such as bismuth,hafnium,gold,and gadolinium for cancer RT and imaging applications.In addition,current challenges and the outlook of RT based on high-Z metal nanocrystals are also discussed.展开更多
The fundamental thermodynamic functions of enthalpy, entropy, and Gibbs free energy, as functions of the excess free volume at interfaces, temperature, and grain size, have been derived for single-phase metal nanocrys...The fundamental thermodynamic functions of enthalpy, entropy, and Gibbs free energy, as functions of the excess free volume at interfaces, temperature, and grain size, have been derived for single-phase metal nanocrystals. The model was applied to predict the thermal features of nano-grain boundaries and the characteristics of phase transformation in nanocrystalline metals, such as the transformation temperature and the critical grain size for phase transformation at a given temperature. The model predictions have been verified by experimental studies on the β-Co ←→α-Co phase transformation in nanocrystalline Co prepared by ball milling.展开更多
Among the various types of heterogeneous catalysts,supported metal nanocatalysts(SMNCs)have attracted widespread interest in chemistry and materials science,due to their advantageous features,such as high efficiency,s...Among the various types of heterogeneous catalysts,supported metal nanocatalysts(SMNCs)have attracted widespread interest in chemistry and materials science,due to their advantageous features,such as high efficiency,stability,and reusability for catalytic reactions.However,to obtain well-defined SMNCs and inhibit nanoparticle aggregation,traditional approaches generally involve numerous organic reagents,complex steps,and specialized equipment,thus hindering the practical and large-scale synthesis of SMNCs.In this review,we summarize green and sustainable synthetic methodologies for the assembly of SMNCs,including low temperature pyrolysis and solid-state,surfactant-and reductant-free,and ionic liquid assisted syntheses.The conventional application of SMNCs for electrochemical hydrogen evolution and the corresponding achievements are subsequently discussed.Finally,future perspectives toward the sustainable production of SMNCs are presented.展开更多
Noble metallic nanocrystals are used in a wide variety of applications,such as catalysis,batteries,and bio-and chemical sensors.Most of the previous studies focus on the preparation of thermodynamically stable nanocry...Noble metallic nanocrystals are used in a wide variety of applications,such as catalysis,batteries,and bio-and chemical sensors.Most of the previous studies focus on the preparation of thermodynamically stable nanocrystals enclosed by low-index facets and discuss their corresponding catalytic properties.Recently,researchers have found that the nanocrystals with high-index facets(HIFs)are of more interest for electrocatalysis.Herein,we review recent key progress in the synthesis of noble metallic nanoparticles enclosed with HIFs and their facetdependent electrocatalytic behaviors.First,we introduce the concept of HIFs,and establish the correlation between their surface structure and catalytic activity.Then,we discuss various synthetic approaches for controlling the shapes and composition of the nanocrystals enclosed by HIFs.Afterwards,we showcase the enhanced electrocatalytic performance realized by HIF-based nanostructures.Finally,we provide guidance on how to improve the electrocatalysis by engineering HIFs on noble metallic nanocrystals.展开更多
Crystallization kinetics and phase transformation of bulk Fe64Co7Zr6Nd3B20 metallic glass were studied by X-ray diffractometry （XRD）, differential scanning calorimetry （DSC） and transmission electron microscopy （...Crystallization kinetics and phase transformation of bulk Fe64Co7Zr6Nd3B20 metallic glass were studied by X-ray diffractometry （XRD）, differential scanning calorimetry （DSC） and transmission electron microscopy （TEM）. Based on the Kissinger analyses, the activation energies for the nucleation and growth during the first, second and third crystallization-stages of the metallic glass are determined to be 294, 475 and 365 kJ/mol, respectively, and the activation energy for the glass transition is determined to be 1 242 kJ/mol. The Johnson-Mehl-Avrami （JMA） analysis under the isothermal condition reveals that the crystallization process is a three-dimensional controlled growth of nuclei at a constant nucleation rate. The crystalline grains are in the size of less than 50 nm after the selected annealing treatments. In the completely crystallized state, the alloy exhibits the maximum coercivity （Hc） of 34.8 kA/m and corresponding energy product of 11 kJ/m3.展开更多
文摘A novel two-step method is employed, for the first time, to fabricatc nonvolatile memory devices that have metal nanoerystals. First, size-averaged Au nanocrystals are synthesized chemically; second, they are assembled into memory devices by a spin-coating technique at room temperature. This attractive approach makes it possible to tailor the diameter and control the density of nanocrystals individually. In addition, processes at room temperature prevent Au diffusion, which is a main concem for the application of metal nanocrystal-based memory. The experimental results, both the morphology characterization and the electrical measurements, reveal that there is an optimum density of nanocrystal monolayer to balance between long data retention and a large hysteresis memory window. At the same time, density-controllable devices could also feed the preferential emphasis on either memory window or retention time. All these facts confirm the advantages and novelty of our two-step method.
基金We gratefully acknowledge support by the National Natural Science Foundation of China(Nos.21674116 and 21874024)the joint research projects of Health and Education Commission of Fujian Province(No.2019-WJ-20).
文摘Radiotherapy(RT)based on X-ray irradiation is a widely applied cancer treatment strategy in the clinic.However,treating cancer based on RT alone usually results in insufficient radiation energy deposition,which inevitably has serious side effects on healthy parts of the body.Interestingly,high atomic number(high-Z)metal nanocrystals as X-ray sensitizers can reduce the radiation dose effectively due to their high X-ray absorption,which has attracted increased attention in recent years.High-Z metal nanocrystals produce Auger and photoelectrons electrons under X-ray irradiation,which could generate large amounts of reactive oxygen species,and induce cellular damages.The sensitization effect of high-Z metal nanocrystals is closely related with their composition,morphologies,and size,which would strongly impact their performances in the application of cancer imaging and therapy.In this review,we summarize diverse types of X-ray sensitizers such as bismuth,hafnium,gold,and gadolinium for cancer RT and imaging applications.In addition,current challenges and the outlook of RT based on high-Z metal nanocrystals are also discussed.
基金The work was financially supported by the National Natural Science Foundation of China (No. 50401001) and the Pro-gram of Beijing New Star of Science and Technology (No. 2004B04).
文摘The fundamental thermodynamic functions of enthalpy, entropy, and Gibbs free energy, as functions of the excess free volume at interfaces, temperature, and grain size, have been derived for single-phase metal nanocrystals. The model was applied to predict the thermal features of nano-grain boundaries and the characteristics of phase transformation in nanocrystalline metals, such as the transformation temperature and the critical grain size for phase transformation at a given temperature. The model predictions have been verified by experimental studies on the β-Co ←→α-Co phase transformation in nanocrystalline Co prepared by ball milling.
文摘Among the various types of heterogeneous catalysts,supported metal nanocatalysts(SMNCs)have attracted widespread interest in chemistry and materials science,due to their advantageous features,such as high efficiency,stability,and reusability for catalytic reactions.However,to obtain well-defined SMNCs and inhibit nanoparticle aggregation,traditional approaches generally involve numerous organic reagents,complex steps,and specialized equipment,thus hindering the practical and large-scale synthesis of SMNCs.In this review,we summarize green and sustainable synthetic methodologies for the assembly of SMNCs,including low temperature pyrolysis and solid-state,surfactant-and reductant-free,and ionic liquid assisted syntheses.The conventional application of SMNCs for electrochemical hydrogen evolution and the corresponding achievements are subsequently discussed.Finally,future perspectives toward the sustainable production of SMNCs are presented.
基金This work was financially supported by the Beijing Natural Science Foundation(JQ18005)the National Natural Science Foundation of China(NSFC)(No.51671003)+2 种基金National Basic Research Program of China(No.2016YFB0100201)the China Postdoctoral Science Foundation(No.2017M620518)Open Project Foundation of State Key Laboratory of Chemical Resource Engineering,the start-up supports from Peking University and Young Thousand Talented Program.
文摘Noble metallic nanocrystals are used in a wide variety of applications,such as catalysis,batteries,and bio-and chemical sensors.Most of the previous studies focus on the preparation of thermodynamically stable nanocrystals enclosed by low-index facets and discuss their corresponding catalytic properties.Recently,researchers have found that the nanocrystals with high-index facets(HIFs)are of more interest for electrocatalysis.Herein,we review recent key progress in the synthesis of noble metallic nanoparticles enclosed with HIFs and their facetdependent electrocatalytic behaviors.First,we introduce the concept of HIFs,and establish the correlation between their surface structure and catalytic activity.Then,we discuss various synthetic approaches for controlling the shapes and composition of the nanocrystals enclosed by HIFs.Afterwards,we showcase the enhanced electrocatalytic performance realized by HIF-based nanostructures.Finally,we provide guidance on how to improve the electrocatalysis by engineering HIFs on noble metallic nanocrystals.
文摘Crystallization kinetics and phase transformation of bulk Fe64Co7Zr6Nd3B20 metallic glass were studied by X-ray diffractometry （XRD）, differential scanning calorimetry （DSC） and transmission electron microscopy （TEM）. Based on the Kissinger analyses, the activation energies for the nucleation and growth during the first, second and third crystallization-stages of the metallic glass are determined to be 294, 475 and 365 kJ/mol, respectively, and the activation energy for the glass transition is determined to be 1 242 kJ/mol. The Johnson-Mehl-Avrami （JMA） analysis under the isothermal condition reveals that the crystallization process is a three-dimensional controlled growth of nuclei at a constant nucleation rate. The crystalline grains are in the size of less than 50 nm after the selected annealing treatments. In the completely crystallized state, the alloy exhibits the maximum coercivity （Hc） of 34.8 kA/m and corresponding energy product of 11 kJ/m3.
