The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site（OIS）. A...The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site（OIS）. As the concentration of He atoms in ThO2 increases, the strain induced by the He atoms increases and the octahedral interstitial site is not large enough to accommodate a large cluster, such as a He hexamer. We considered three different Schottky defect（SD） configurations（SD1, SD2, and SD3）. When He atoms are located in the SD sites, the strain induced by the He atoms is released and the incorporation and binding energies decrease. The He trimer is the most stable cluster in SD1. Large He clusters, such as a He hexamer, are also stable in the SDs.展开更多
Density functional theory calculations are conducted to investigate the stability and interactions among small helium （He） clusters in bulk tungsten （W）. The lowest energy structure of each cluster for sizes n= 1 ...Density functional theory calculations are conducted to investigate the stability and interactions among small helium （He） clusters in bulk tungsten （W）. The lowest energy structure of each cluster for sizes n= 1 to 6 is determined. With the formation of He dusters, He defects form in bulk W. Tile thermodynamics of the dusters are investigated in the temperature range of 1000-2300K using molecular dynamics. This study provides the information essential to understand smaB He duster behavior in bulk W.展开更多
We present a scheme for the preparation of one-dimensional （1D） and two-dimensional （2D） cluster states with electrons trapped on a liquid helium surface and driven by a classical laser beam. The two lowest levels...We present a scheme for the preparation of one-dimensional （1D） and two-dimensional （2D） cluster states with electrons trapped on a liquid helium surface and driven by a classical laser beam. The two lowest levels of the vertical motion of the electron act as a two-level system, and the quantized vibration of the electron along one of the parallel directions （the x direction） serves as the bosonic mode. The degrees of freedom of the vertical and parallel motions of the trapped electron can be coupled together by a classical laser field. With the proper frequency of the laser field, the cluster states can be realized.展开更多
The behaviors of helium clusters and self-interstitial tungsten atoms at different temperatures are investigated with the molecular dynamics method. The self-interstitial tungsten atoms prefer to form crowdions which ...The behaviors of helium clusters and self-interstitial tungsten atoms at different temperatures are investigated with the molecular dynamics method. The self-interstitial tungsten atoms prefer to form crowdions which can tightly bind the helium cluster at low temperature. The crowdion can change its position around the helium cluster by rotating and slipping at medium temperatures, which leads to formation of combined crowdions or dislocation loop locating at one side of a helium cluster. The combined crowdions or dislocation loop even separates from the helium cluster at high temperature. It is found that a big helium cluster is more stable and its interaction with crowdions or dislocation loop is stronger.展开更多
Clusters traverse a gas and collide with gas particles. The gas particles are absorbed, and the clusters become hosts. If the clusters are size-selected, the number of guests will be Poisson distributed. We review thi...Clusters traverse a gas and collide with gas particles. The gas particles are absorbed, and the clusters become hosts. If the clusters are size-selected, the number of guests will be Poisson distributed. We review this by showcasing four laboratory procedures that all rely on the validity of the Poisson model. The effects of a statistical distribution of the clusters＇ sizes in a beam of clusters are discussed. We derive the average collision rates. Additionally, we present Poisson mixture models that also involve standard deviations. We derive the collision statistics for common size distributions of hosts and also for some generalizations thereof. The models can be applied to large noble gas clusters traversing doping gas. While outlining how to fit a generalized Poisson to the statistics, we still find even these Poisson models to be often insufficient.展开更多
The accumulation of He on a W surface during keV-He ion irradiation has been simulated using cluster dynamics modeling. This is based mainly on rate theory and improved by involving different types of objects, adoptin...The accumulation of He on a W surface during keV-He ion irradiation has been simulated using cluster dynamics modeling. This is based mainly on rate theory and improved by involving different types of objects, adopting up-to-date parameters and complex reaction processes, as well as considering the diffusion process along with depth. These new features make the simulated results compare very well with the experimental ones. The accumulation and diffusion processes are analyzed, and the depth and size dependence of the He concentrations contributed by different types of He clusters is also discussed. The exploration of the trapping and diffusion effects of the He atoms is helpful in understanding the evolution of the damages in the near-surface of plasma-facing materials under He ion irradiation.展开更多
Behaviors and properties of helium in titanium were explored by molecular dynamics(MD) simulation in this study.The influence of He number,vacancy number and He density(ratio of helium to vacancy) on the thermal stabi...Behaviors and properties of helium in titanium were explored by molecular dynamics(MD) simulation in this study.The influence of He number,vacancy number and He density(ratio of helium to vacancy) on the thermal stability of HenVm clusters(where n and m denote the number of He atoms and vacancies) were investigated.Meanwhile,interactions among He atoms,SIA atoms and vacancies were discussed.The results demonstrate that the binding energies of an interstitial helium atom primarily depend on He and vacancy numbers rather than the helium-to-vacancy ratio(n/m).It is different from the previous report of other researchers.The binding energies of an isolated vacancy and a self-interstitial titanium atom depend on both the number of helium atoms and the helium-to-vacancy ratio(n/m) of clusters.The thermal stability of clusters is decided by the competitive processes among thermal emissions of vacancy,SIA and helium atom.展开更多
基金Project supported by the Program of International S&T Cooperation,China(Grant No.2014DFG60230)the National Natural Science Foundation of China(Grant Nos.11605273,21571185,U1404111,11504089,21501189,and 21676291)+1 种基金the Shanghai Municipal Science and Technology Commission,China(Grant No.16ZR1443100)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA02040104)
文摘The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site（OIS）. As the concentration of He atoms in ThO2 increases, the strain induced by the He atoms increases and the octahedral interstitial site is not large enough to accommodate a large cluster, such as a He hexamer. We considered three different Schottky defect（SD） configurations（SD1, SD2, and SD3）. When He atoms are located in the SD sites, the strain induced by the He atoms is released and the incorporation and binding energies decrease. The He trimer is the most stable cluster in SD1. Large He clusters, such as a He hexamer, are also stable in the SDs.
基金Supported by the National Natural Science Foundation of China under Grant No 11605007the Funding from the China Scholarship Council under Grant No 201506465019
文摘Density functional theory calculations are conducted to investigate the stability and interactions among small helium （He） clusters in bulk tungsten （W）. The lowest energy structure of each cluster for sizes n= 1 to 6 is determined. With the formation of He dusters, He defects form in bulk W. Tile thermodynamics of the dusters are investigated in the temperature range of 1000-2300K using molecular dynamics. This study provides the information essential to understand smaB He duster behavior in bulk W.
基金supported by the National Natural Science Foundation of China (Grant No. 60978009 )the National Basic Research Program of China (Grant Nos. 2009CB929604 and 2007CB925204)
文摘We present a scheme for the preparation of one-dimensional （1D） and two-dimensional （2D） cluster states with electrons trapped on a liquid helium surface and driven by a classical laser beam. The two lowest levels of the vertical motion of the electron act as a two-level system, and the quantized vibration of the electron along one of the parallel directions （the x direction） serves as the bosonic mode. The degrees of freedom of the vertical and parallel motions of the trapped electron can be coupled together by a classical laser field. With the proper frequency of the laser field, the cluster states can be realized.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.11705157)the Henan Provincial Key Research Projects,China(Grant No.17A140027)the Ninth Group of Key Disciplines in Henan Province of China(Grant No.2018119).
文摘The behaviors of helium clusters and self-interstitial tungsten atoms at different temperatures are investigated with the molecular dynamics method. The self-interstitial tungsten atoms prefer to form crowdions which can tightly bind the helium cluster at low temperature. The crowdion can change its position around the helium cluster by rotating and slipping at medium temperatures, which leads to formation of combined crowdions or dislocation loop locating at one side of a helium cluster. The combined crowdions or dislocation loop even separates from the helium cluster at high temperature. It is found that a big helium cluster is more stable and its interaction with crowdions or dislocation loop is stronger.
文摘Clusters traverse a gas and collide with gas particles. The gas particles are absorbed, and the clusters become hosts. If the clusters are size-selected, the number of guests will be Poisson distributed. We review this by showcasing four laboratory procedures that all rely on the validity of the Poisson model. The effects of a statistical distribution of the clusters＇ sizes in a beam of clusters are discussed. We derive the average collision rates. Additionally, we present Poisson mixture models that also involve standard deviations. We derive the collision statistics for common size distributions of hosts and also for some generalizations thereof. The models can be applied to large noble gas clusters traversing doping gas. While outlining how to fit a generalized Poisson to the statistics, we still find even these Poisson models to be often insufficient.
基金supported by the Special Funds for Major State Basic Research Project of China(973)(Nos.2007CB925004 and 2008CB717802)the Knowledge Innovation Program of the Chinese Academy of Sciences(No.KJCX2-YW-N35)+2 种基金National Natural Science Foundation of China(No.11005124)the China Postdoctoral Science Foundation Funded Project(No.20100470863)Director Grants of CASHIPS.Part of the calculations were performed in the Center for Computational Science of CASHIPS
文摘The accumulation of He on a W surface during keV-He ion irradiation has been simulated using cluster dynamics modeling. This is based mainly on rate theory and improved by involving different types of objects, adopting up-to-date parameters and complex reaction processes, as well as considering the diffusion process along with depth. These new features make the simulated results compare very well with the experimental ones. The accumulation and diffusion processes are analyzed, and the depth and size dependence of the He concentrations contributed by different types of He clusters is also discussed. The exploration of the trapping and diffusion effects of the He atoms is helpful in understanding the evolution of the damages in the near-surface of plasma-facing materials under He ion irradiation.
基金Supported by the National Natural Science Foundation of China (Grant No 10775101)
文摘Behaviors and properties of helium in titanium were explored by molecular dynamics(MD) simulation in this study.The influence of He number,vacancy number and He density(ratio of helium to vacancy) on the thermal stability of HenVm clusters(where n and m denote the number of He atoms and vacancies) were investigated.Meanwhile,interactions among He atoms,SIA atoms and vacancies were discussed.The results demonstrate that the binding energies of an interstitial helium atom primarily depend on He and vacancy numbers rather than the helium-to-vacancy ratio(n/m).It is different from the previous report of other researchers.The binding energies of an isolated vacancy and a self-interstitial titanium atom depend on both the number of helium atoms and the helium-to-vacancy ratio(n/m) of clusters.The thermal stability of clusters is decided by the competitive processes among thermal emissions of vacancy,SIA and helium atom.
