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    SPECIAL TOPIC — Ion beam modification of materials and applications

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    Optical spectroscopy study of damage evolution in 6H-SiC by H$_{2}^{ + }$ implantation
    Yong Wang(王勇), Qing Liao(廖庆), Ming Liu(刘茗), Peng-Fei Zheng(郑鹏飞), Xinyu Gao(高新宇), Zheng Jia(贾政), Shuai Xu(徐帅), and Bing-Sheng Li(李炳生)
    Chin. Phys. B, 2021, 30 (5): 056106.   DOI: 10.1088/1674-1056/abe9a7
    Abstract98)   HTML0)    PDF (1911KB)(73)      
    Lattice defects induced by ion implantation into SiC have been widely investigated in the decades by various techniques. One of the non-destructive techniques suitable to study the lattice defects in SiC is the optical characterization. In this work, confocal Raman scattering spectroscopy and photoluminescence spectrum have been used to study the effects of 134-keV H$_{2}^{ + }$ implantation and thermal treatment in the microstructure of 6H-SiC single crystal. The radiation-induced changes in the microstructure were assessed by integrating Raman-scattering peaks intensity and considering the asymmetry of Raman-scattering peaks. The integrated intensities of Raman scattering spectroscopy and photoluminescence spectrum decrease with increasing the fluence. The recovery of the optical intensities depends on the combination of the implantation temperature and the annealing temperature with the thermal treatment from 700 ℃ to 1100 ℃. The different characterizations of Raman scattering spectroscopy and photoluminescence spectrum are compared and discussed in this study.
    Structure and luminescence of a-plane GaN on r-plane sapphire substrate modified by Si implantation
    Lijie Huang(黄黎杰), Lin Li(李琳), Zhen Shang(尚震), Mao Wang(王茂), Junjie Kang(康俊杰), Wei Luo(罗巍), Zhiwen Liang(梁智文), Slawomir Prucnal, Ulrich Kentsch, Yanda Ji(吉彦达), Fabi Zhang(张法碧), Qi Wang(王琦), Ye Yuan(袁冶), Qian Sun(孙钱), Shengqiang Zhou(周生强), and Xinqiang Wang(王新强)
    Chin. Phys. B, 2021, 30 (5): 056104.   DOI: 10.1088/1674-1056/abd76a
    Abstract87)   HTML0)    PDF (1426KB)(40)      
    We show the structural and optical properties of non-polar a-plane GaN epitaxial films modified by Si ion implantation. Upon gradually raising Si fluences from 5×1013 cm-2 to 5×1015 cm-2, the n-type dopant concentration gradually increases from 4.6×1018 cm-2 to 4.5×1020 cm-2, while the generated vacancy density accordingly raises from 3.7×1013 cm-2 to 3.8×1015 cm-2. Moreover, despite that the implantation enhances structural disorder, the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements. The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1×1015 cm-2, which ceases at the overdose of 5×1015 cm-2 due to the partial amorphization in the surface region. Upon raising irradiation dose, a yellow emission in the as-grown sample is gradually quenched, probably due to the irradiation-induced generation of non-radiative recombination centers.
    Evolution of ion-irradiated point defect concentration by cluster dynamics simulation
    Shuaishuai Feng(冯帅帅), Shasha Lv(吕沙沙), Liang Chen(陈良), and Zhengcao Li(李正操)
    Chin. Phys. B, 2021, 30 (5): 056105.   DOI: 10.1088/1674-1056/abf102
    Abstract96)   HTML0)    PDF (633KB)(57)      
    The relationship between ions irradiation and the induced microstructures (point defects, dislocations, clusters, etc.) could be better analyzed and explained by simulation. The mean field rate theory and cluster dynamics are used to simulate the effect of implanted Fe on the point defects concentration quantitatively. It is found that the depth distribution of point defect concentration is relatively gentle than that of damage calculated by SRIM software. Specifically, the damage rate and point defect concentration increase by 1.5 times and 0.6 times from depth of 120 nm to 825 nm, respectively. With the consideration of implanted Fe ions, which effectively act as interstitial atoms at the depth of high ion implantation rate, the vacancy concentration Cv decreases significantly after reaching the peak value, while the interstitial atom concentration Ci increases significantly after decline of the previous stage. At the peak depth of ion implantation, Cv dropped by 86%, and Ci increased by 6.2 times. Therefore, the implanted ions should be considered into the point defects concentration under high dose of heavy ion irradiation, which may help predict the concentration distribution of defect clusters, further analyzing the evolution behavior of solute precipitation.
    Effect of helium concentration on irradiation damage of Fe-ion irradiated SIMP steel at 300 ℃ and 450 ℃
    Zhen Yang(杨振), Junyuan Yang(杨浚源), Qing Liao(廖庆), Shuai Xu(徐帅), and Bingsheng Li(李炳生)
    Chin. Phys. B, 2021, 30 (5): 056107.   DOI: 10.1088/1674-1056/abd6f9
    Abstract94)   HTML0)    PDF (2393KB)(39)      
    SIMP steel is newly developed fully martensitic steel for lead-cooled fast reactors and accelerator-driven systems. It is important to evaluate its radiation resistance via high flux neutron irradiation, where dense He atoms can be formed via (n, α) transmutation reaction. Co-irradiation with Fe and He ions, instead of neutron, was performed. Specimens were irradiated with 6.4-MeV Fe ions to the damage dose of 5 dpa at a depth of 600 nm. Three different helium injection ratios of 60-appm He/dpa (dpa: displacements per atom), 200-appm He/dpa and 600-appm He/dpa at a depth of 600 nm, were performed. Two different irradiation temperatures of 300 ℃ and 450 ℃ were carried out. The effect of helium concentration on the microstructure of Fe-irradiated SIMP steel was investigated. Microstructural damage was observed using transmission electron microscopy. The formed dislocation loops and bubbles depended on the helium injection ratio and irradiation temperature. Lots of dislocation loops and helium bubbles were homogeneously distributed at 300 °C, but not at 450 °C. The causes of observed effects are discussed.
    Effect of tellurium (Te4+) irradiation on microstructure and associated irradiation-induced hardening
    Hefei Huang(黄鹤飞), Jizhao Liu(刘继召), Guanhong Lei(雷冠虹), Ondrej Muránsky, Tao Wei, and Mihail Ionescu
    Chin. Phys. B, 2021, 30 (5): 056108.   DOI: 10.1088/1674-1056/abf039
    Abstract82)   HTML0)    PDF (3151KB)(43)      
    The GH3535 alloy samples were irradiated using 15-MeV Te4+ ions at 650 °C to a dose of 0.5, 3.0, 10, and 20 dpa, respectively. The Te atoms distribution and microstructure evolution were examined by electron probe microanalysis (EPMA) and transmission electron microscopy (TEM). The nano-indenter was then used to measure the nano-hardness changes of samples before and after irradiation. TEM results showed the formation of dislocation loops in the irradiated samples. Their mean diameters increase with the increase of irradiation dose and tends to be saturated when irradiation dose exceeds 10 dpa. The ratio of yield strength increments calculated by dispersed barrier hardening (DBH) model is basically consistent with that of nano-hardness increments measured by nano-indenter. In addition, the relationship between the nano-hardness increments and dpa for the GH3535 alloy irradiated by Te ions has been revealed in the study.
    Corrosion behavior of high-level waste container materials Ti and Ti-Pd alloy under long-term gamma irradiation in Beishan groundwater
    Qianglin Wei(魏强林), Yuhong Li(李玉红), Yanliang Huang(黄彦良), Dongyan Yang(杨冬燕), Bo Yang(杨波), and Yibao Liu(刘义保)
    Chin. Phys. B, 2021, 30 (5): 056109.   DOI: 10.1088/1674-1056/abf03b
    Abstract91)   HTML0)    PDF (3435KB)(38)      
    Titanium and titanium-palladium alloys are important potential materials for nuclear waste container, which will endure both intense γ-irradiation and groundwater erosion. Therefore, it is very important to investigate the corrosion behavior of the container materials. In this research, the cumulative dose effect of TA8-1 type titanium-palladium alloy (TA8-1) and TA2-type pure titanium (TA2) under γ-irradiation was studied based on the geological disposal of nuclear wastes. The irradiation experiments were performed at room temperature using 60Co gamma sources with a 5.0-kGy·h-1 intensity for 40, 80 or 160 days, respectively. The pH value and conductivity of Beishan groundwater were investigated. The results showed that the pH value changed from alkaline (8.22) to acidic (2.46 for TA8-1 and 2.44 for TA2), while the un-irradiated solution remained alkaline (8.17 for TA8-1 and 8.20 for TA2) after 160 days. With the increase of irradiation dose, the conductivity increases rapidly and then tends to become stable, which indicates that the titanium dioxide corrosion layer formed on the surface of the sample surface effectively prevents further corrosion. Meanwhile, XRD and SEM-EDS analysis results show that the main components of corrosion products are TiO2 and TiO. The titanium on the surface of the sample is oxidized, resulting in slight uneven local corrosion. The results show that TA8-1 and TA2 are suitable to be used as candidate materials for high-level waste (HLW) disposal containers due to their excellent performance under long-term and high-dose irradiation corrosion.
    Degradation of β-Ga2O3 Schottky barrier diode under swift heavy ion irradiation
    Wen-Si Ai(艾文思), Jie Liu(刘杰), Qian Feng(冯倩), Peng-Fei Zhai(翟鹏飞), Pei-Pei Hu(胡培培), Jian Zeng(曾健), Sheng-Xia Zhang(张胜霞), Zong-Zhen Li(李宗臻), Li Liu(刘丽), Xiao-Yu Yan(闫晓宇), and You-Mei Sun(孙友梅)
    Chin. Phys. B, 2021, 30 (5): 056110.   DOI: 10.1088/1674-1056/abf107
    Abstract102)   HTML0)    PDF (1008KB)(54)      
    The electrical characteristics and microstructures of β-Ga2O3 Schottky barrier diode (SBD) devices irradiated with swift heavy ions (2096 MeV Ta ions) have been studied. It was found that β-Ga2O3 SBD devices showed the reliability degradation after irradiation, including turn-on voltage Von, on-resistance Ron, ideality factor n, and the reverse leakage current density Jr. In addition, the carrier concentration of the drift layer was decreased significantly and the calculated carrier removal rates were 5×106-1.3×107 cm-1. Latent tracks induced by swift heavy ions were observed visually in the whole β-Ga2O3 matrix. Furthermore, crystal structure of tracks was amorphized completely. The latent tracks induced by Ta ions bombardments were found to be the reason for the decrease in carrier mobility and carrier concentration. Eventually, these defects caused the degradation of electrical characteristics of the devices. In terms of the carrier removal rates, the β-Ga2O3 SBD devices were more sensitive to swift heavy ions irradiation than SiC and GaN devices.
    Influence of temperature and alloying elements on the threshold displacement energies in concentrated Ni-Fe-Cr alloys
    Shijun Zhao(赵仕俊)
    Chin. Phys. B, 2021, 30 (5): 056111.   DOI: 10.1088/1674-1056/abf10d
    Abstract81)   HTML0)    PDF (3382KB)(55)      
    Concentrated solid-solution alloys (CSAs) have demonstrated promising irradiation resistance depending on their compositions. Under irradiation, various defects can be produced. One of the most important parameters characterizing the defect production and the resulting defect number is the threshold displacement energies (Ed). In this work, we report the results of Ed values in a series of Ni-Fe-Cr concentrated solid solution alloys through molecular dynamics (MD) simulations. Based on several different empirical potentials, we show that the differences in the Ed values and its angular dependence are mainly due to the stiffness of the potential in the intermediate regime. The influences of different alloying elements and temperatures on Ed values in different CSAs are further evaluated by calculating the defect production probabilities. Our results suggest a limited influence of alloying elements and temperature on Ed values in concentrated alloys. Finally, we discuss the relationship between the primary damage and Ed values in different alloys. Overall, this work presents a thorough study on the Ed values in concentrated alloys, including the influence of empirical potentials, their angular dependence, temperature dependence, and effects on primary defect production.
    Cathodic shift of onset potential on TiO2 nanorod arrays with significantly enhanced visible light photoactivity via nitrogen/cobalt co-implantation
    Xianyin Song(宋先印), Hongtao Zhou(周洪涛), and Changzhong Jiang(蒋昌忠)
    Chin. Phys. B, 2021, 30 (5): 058505.   DOI: 10.1088/1674-1056/abee07
    Abstract83)   HTML0)    PDF (1195KB)(45)      
    Despite anionic doping has been widely implemented to increase the visible light activity of TiO$_{2}$, it often gives rise to a dramatical anodic shift in current onset potential. Herein, we show an effective method to achieve the huge cathodic shift of TiO$_{2}$ photoanode with significantly enhanced visible light photo-electrochemical activity by nitrogen/cobalt co-implantation. The nitrogen/cobalt co-doped TiO$_{2}$ nanorod arrays (N/Co-TiO$_{2}$) exhibit a cathodic shift of 350 mV in onset potential relative to only nitrogen-doped TiO$_{2}$ (N-TiO$_{2}$). Moreover, the visible-light ($\lambda >420 $ nm) photocurrent density of N/Co-TiO$_{2}$ reaches 0.46 mA/cm$^{2}$, far exceeding 0.07 mA/cm$^{2}$ in N-TiO$_{2}$ at 1.23 V $versus$ reversible hydrogen electrode (RHE). Systematic characterization studies demonstrate that the enhanced photo-electrochemical performance can be attributed to the surface synergic sputtering of high-energy nitrogen/cobalt ions.
    Evolution of helium bubbles in nickel-based alloy by post-implantation annealing
    Rui Zhu(朱睿), Qin Zhou(周钦), Li Shi(史力), Li-Bin Sun(孙立斌), Xin-Xin Wu(吴莘馨), Sha-Sha Lv(吕沙沙), and Zheng-Cao Li(李正操)
    Chin. Phys. B, 2021, 30 (8): 086102.   DOI: 10.1088/1674-1056/ac0783
    Abstract66)   HTML0)    PDF (3497KB)(25)      
    Nickel-based alloys have been considered as candidate structural materials used in generation IV nuclear reactors serving at high temperatures. In the present study, alloy 617 was irradiated with 180-keV helium ions to a fluence of 3.6×1017 ions/cm2 at room temperature. Throughout the cross-section transmission electron microscopy (TEM) image, numerous over-pressurized helium bubbles in spherical shape are observed with the actual concentration profile a little deeper than the SRIM predicted result. Post-implantation annealing was conducted at 700 ℃ for 2 h to investigate the bubble evolution. The long-range migration of helium bubbles occurred during the annealing process, which makes the bubbles of the peak region transform into a faceted shape as well. Then the coarsening mechanism of helium bubbles at different depths is discussed and related to the migration and coalescence (MC) mechanism. With the diffusion of nickel atoms slowed down by the alloy elements, the migration and coalescence of bubbles are suppressed in alloy 617, leading to a better helium irradiation resistance.
    Microstructure evolution of T91 steel after heavy ion irradiation at 550 ℃
    Ligang Song(宋力刚), Bo Huang(黄波), Jianghua Li(李江华), Xianfeng Ma(马显锋), Yang Li(李阳), Zehua Fang(方泽华), Min Liu(刘敏), Jishen Jiang(蒋季伸), and Yanying Hu(胡琰莹)
    Chin. Phys. B, 2021, 30 (8): 086103.   DOI: 10.1088/1674-1056/ac0a64
    Abstract71)   HTML0)    PDF (7682KB)(32)      
    Fe-Cr ferritic/martensitic (F/M) steels have been proposed as one of the candidate materials for the Generation IV nuclear technologies. In this study, a widely-used ferritic/martensitic steel, T91 steel, was irradiated by 196-MeV Kr+ ions at 550 ℃. To reveal the irradiation mechanism, the microstructure evolution of irradiated T91 steel was studied in details by transmission electron microscope (TEM). With increasing dose, the defects gradually changed from black dots to dislocation loops, and further to form dislocation walls near grain boundaries due to the production of a large number of dislocations. When many dislocation loops of primary a0/2<111> type with high migration interacted with other defects or carbon atoms, it led to the production of dislocation segments and other dislocation loops of a0<100> type. Lots of defects accumulated near grain boundaries in the irradiated area, especially in the high-dose area. The grain boundaries of martensite laths acted as important sinks of irradiation defects in T91. Elevated temperature facilitated the migration of defects, leading to the accumulation of defects near the grain boundaries of martensite laths.
    Mechanism of defect evolution in H+ and He+ implanted InP
    Ren-Jie Liu(刘仁杰), Jia-Jie Lin(林家杰), N Daghbouj, Jia-Liang Sun(孙嘉良), Tian-Gui You(游天桂), Peng Gao(高鹏), Nie-Feng Sun(孙聂枫), and Min Liao(廖敏)
    Chin. Phys. B, 2021, 30 (8): 086104.   DOI: 10.1088/1674-1056/abf640
    Abstract62)   HTML0)    PDF (1486KB)(34)      
    The defect evolution in InP with the 75 keV H+ and 115 keV He+ implantation at room temperature after subsequent annealing has been investigated in detail. With the same ion implantation fluence, the He+ implantation caused much broader damage distribution accompanied by much higher out-of-plane strain with respect to the H+ implanted InP. After annealing, the H+ implanted InP did not show any blistering or exfoliation on the surface even at the high fluence and the H2 molecules were stored in the heterogeneously oriented platelet defects. However, the He molecules were stored into the large bubbles which relaxed toward the free surface, creating blisters at the high fluence.
    Ion track-based nanowire arrays with gradient and programmable diameters towards rational light management
    Ran Huang(黄冉), Jiaming Zhang(张家明), Fangfang Xu(徐芳芳), Jie Liu(刘杰), Huijun Yao(姚会军), Yonghui Chen(陈永辉), and Jinglai Duan(段敬来)
    Chin. Phys. B, 2021, 30 (8): 086105.   DOI: 10.1088/1674-1056/ac078a
    Abstract56)   HTML0)    PDF (1192KB)(43)      
    Integrating nanowires with nonuniform diameter and random spatial distribution into an array can afford unconventional and additional means for modulating optical response. However, experimental realization of such a nanowire array is quite challenging. In this work, we propose a new fabrication strategy which takes advantage of ion track technology, via sequential swift heavy ion irradiation and ion track etching. Based on this strategy, we unprecedentedly realize nanowire arrays, using gold as an example, with gradient and programmable diameters in a controlled manner. We further demonstrate that such nanowire arrays can support broadband, tunable, and enhanced plasmonic responses. We believe that our new type of nanowire arrays will find great potential in applications such as light management and optoelectronic devices.
    Helium-hydrogen synergistic effects on swelling in in-situ multiple-ion beams irradiated steels
    Haocheng Liu(刘昊成), Jia Huang(黄嘉), Liuxuan Cao(曹留煊), Yue Su(苏悦), Zhiying Gao(高智颖), Pengfei Ma(马鹏飞), Songqin Xia(夏松钦), Wei Ge(葛伟), Qingyuan Liu(刘清元), Shuang Zhao(赵双), Yugang Wang(王宇钢), Jinchi Huang(黄金池), Zhehui Zhou(周哲辉), Pengfei Zheng(郑鹏飞), and Chenxu Wang(王晨旭)
    Chin. Phys. B, 2021, 30 (8): 086106.   DOI: 10.1088/1674-1056/abfcca
    Abstract70)   HTML1)    PDF (7236KB)(59)      
    The development of reliable fusion energy is one of the most important challenges in this century. The accelerated degradation of structural materials in fusion reactors caused by neutron irradiation would cause severe problems. Due to the lack of suitable fusion neutron testing facilities, we have to rely on ion irradiation experiments to test candidate materials in fusion reactors. Moreover, fusion neutron irradiation effects are accompanied by the simultaneous transmutation production of helium and hydrogen. One important method to study the He-H synergistic effects in materials is multiple simultaneous ion beams (MSIB) irradiation that has been studied for decades. To date, there is no convincing conclusion on these He-H synergistic effects among these experiments. Recently, a multiple ion beam in-situ transmission electron microscopy (TEM) analysis facility was developed in Xiamen University (XIAMEN facility), which is the first triple beam system and the only in-running in-situ irradiation facility with TEM in China. In this work, we conducted the first high-temperature triple simultaneous ion beams irradiation experiment with TEM observation using the XIAMEN facility. The responses to in-situ triple-ion beams irradiation in austenitic steel 304L SS and ferritic/martensitic steel CLF-1 were studied and compared with the results in dual- and single-ion beam(s) irradiated steels. Synergistic effects were observed in MSIB irradiated steels. Helium was found to be critical for cavity formation, while hydrogen has strong synergistic effect on increasing swelling.
    Formation of nano-twinned 3C-SiC grains in Fe-implanted 6H-SiC after 1500-℃ annealing
    Zheng Han(韩铮), Xu Wang(王旭), Jiao Wang(王娇), Qing Liao(廖庆), and Bingsheng Li(李炳生)
    Chin. Phys. B, 2021, 30 (8): 086107.   DOI: 10.1088/1674-1056/abff43
    Abstract55)   HTML0)    PDF (5811KB)(31)      
    A nano-twinned microstructure was found in amorphous SiC after high-temperature annealing. Grazing incidence x-ray diffraction, high-resolution transmission electron microscopy, and electron diffraction were performed to characterize the microstructure and phase transition in the recrystallization layer. After 1500 ℃ or 2-h annealing, 3C-SiC grains and numerous stacking faults on the {111} planes were visible. Some 3C-SiC grains have nano-twinned structure with {011} planes. Between the nano-twinned 3C-SiC grains, there is a stacking fault, indicating that the formation mechanisms of the nano-twinned structure are related to the disorder of Si atoms. The increase in the twin thickness with increasing annealing temperature demonstrates that the nano-twinned structure can sink for lattice defects, in order to improve the radiation tolerance of SiC.
    Influence of helium on the evolution of irradiation-induced defects in tungsten: An object kinetic Monte Carlo simulation
    Peng-Wei Hou(侯鹏伟), Yu-Hao Li(李宇浩), Zhong-Zhu Li(李中柱), Li-Fang Wang(王丽芳), Xingyu Gao(高兴誉), Hong-Bo Zhou(周洪波), Haifeng Song(宋海峰), and Guang-Hong Lu(吕广宏)
    Chin. Phys. B, 2021, 30 (8): 086108.   DOI: 10.1088/1674-1056/abf7ac
    Abstract66)   HTML0)    PDF (930KB)(36)      
    Understanding the evolution of irradiation-induced defects is of critical importance for the performance estimation of nuclear materials under irradiation. Hereby, we systematically investigate the influence of He on the evolution of Frenkel pairs and collision cascades in tungsten (W) via using the object kinetic Monte Carlo (OKMC) method. Our findings suggest that the presence of He has significant effect on the evolution of irradiation-induced defects. On the one hand, the presence of He can facilitate the recombination of vacancies and self-interstitial atoms (SIAs) in W. This can be attributed to the formation of immobile He-SIA complexes, which increases the annihilation probability of vacancies and SIAs. On the other hand, due to the high stability and low mobility of He-vacancy complexes, the growth of large vacancy clusters in W is kinetically suppressed by He addition. Specially, in comparison with the injection of collision cascades and He in sequential way at 1223 K, the average sizes of surviving vacancy clusters in W via simultaneous way are smaller, which is in good agreement with previous experimental observations. These results advocate that the impurity with low concentration has significant effect on the evolution of irradiation-induced defects in materials, and contributes to our understanding of W performance under irradiation.
    In-situ TEM observation of the evolution of helium bubbles in Mo during He+ irradiation and post-irradiation annealing
    Yi-Peng Li(李奕鹏), Guang Ran(冉广), Xin-Yi Liu(刘歆翌), Xi Qiu(邱玺), Qing Han(韩晴), Wen-Jie Li(李文杰), and Yi-Jia Guo(郭熠佳)
    Chin. Phys. B, 2021, 30 (8): 086109.   DOI: 10.1088/1674-1056/abff48
    Abstract64)   HTML0)    PDF (5196KB)(24)      
    The evolution of helium bubbles in purity Mo was investigated by in-situ transmission electron microscopy (TEM) during 30 keV He+ irradiation (at 673 K and 1173 K) and post-irradiation annealing (after 30 keV He+ irradiation with the fluence of 5.74×1016 He+/cm2 at 673 K). Both He+ irradiation and subsequently annealing induced the initiation, aggregation, and growth of helium bubbles. Temperature had a significant effect on the initiation and evolution of helium bubbles. The higher the irradiation temperature was, the larger the bubble size at the same irradiation fluence would be. At 1173 K irradiation, helium bubbles nucleated and grew preferentially at grain boundaries and showed super large size, which would induce the formation of microcracks. At the same time, the geometry of helium bubbles changed from sphericity to polyhedron. The polyhedral bubbles preferred to grow in the shape bounded by {100} planes. After statistical analysis of the characteristic parameters of helium bubbles, the functions between the average size, number density of helium bubbles, swelling rate and irradiation damage were obtained. Meanwhile, an empirical formula for calculating the size of helium bubbles during the annealing was also provided.
    Modification of short-range repulsive interactions in ReaxFF reactive force field for Fe-Ni-Al alloy
    Huaqiang Chen(陈华强), Lin Lang(稂林), Shuaiyu Yi(易帅玉), Jinlong Du(杜进隆), Guangdong Liu(刘广东), Lixia Liu(刘丽霞), Yufei Wang(王宇飞), Yuehui Wang(王悦辉), Huiqiu Deng(邓辉球), and Engang Fu(付恩刚)
    Chin. Phys. B, 2021, 30 (8): 086110.   DOI: 10.1088/1674-1056/ac0901
    Abstract74)   HTML0)    PDF (7473KB)(28)      
    The short-range repulsive interactions of any force field must be modified to be applicable for high energy atomic collisions because of extremely far from equilibrium state when used in molecular dynamics (MD) simulations. In this work, the short-range repulsive interaction of a reactive force field (ReaxFF), describing Fe-Ni-Al alloy system, is well modified by adding a tabulated function form based on Ziegler-Biersack-Littmark (ZBL) potential. The modified interaction covers three ranges, including short range, smooth range, and primordial range. The short range is totally predominated by ZBL potential. The primordial range means the interactions in this range is the as-is ReaxFF with no changes. The smooth range links the short-range ZBL and primordial-range ReaxFF potentials with a taper function. Both energies and forces are guaranteed to be continuous, and qualified to the consistent requirement in LAMMPS. This modified force field is applicable for simulations of energetic particle bombardments and reproducing point defects' booming and recombination effectively.
    Oxygen vacancies and V co-doped Co3O4 prepared by ion implantation boosts oxygen evolution catalysis
    Bo Sun(孙博), Dong He(贺栋), Hongbo Wang(王宏博), Jiangchao Liu(刘江超), Zunjian Ke(柯尊健), Li Cheng(程莉), and Xiangheng Xiao(肖湘衡)
    Chin. Phys. B, 2021, 30 (10): 106102.   DOI: 10.1088/1674-1056/ac1339
    Abstract70)   HTML2)    PDF (2255KB)(30)      
    Introducing heteroatoms and defects is a significant strategy to improve oxygen evolution reaction (OER) performance of electrocatalysts. However, the synergistic interaction of the heteroatom and defect still needs further investigations. Herein, we demonstrated an oxygen vacancy-rich vanadium-doped Co3O4 (V-Ov-Co3O4), fabricated by V-ion implantation, could be used for high-efficient OER catalysis. X-ray photoelectron spectra (XPS) and density functional theory (DFT) calculations show that the charge density of Co atom increased, and the reaction barrier of reaction pathway from O* to HOO* decreased. V-Ov-Co3O4 catalyst shows a low overpotential of 329 mV to maintain current density of 10 mA·cm-2, and a small Tafel slope of 74.5 mV·dec-1. This modification provides us with valuable perception for future design of heteroatom-doped and defect-based electrocatalysts.
    Investigations on ion implantation-induced strain in rotated Y-cut LiNbO3 and LiTaO3
    Zhongxu Li(李忠旭), Kai Huang(黄凯), Yanda Ji(吉彦达), Yang Chen(陈阳), Xiaomeng Zhao(赵晓蒙), Min Zhou(周民), Tiangui You(游天桂), Shibin Zhang(张师斌), and Xin Ou(欧欣)
    Chin. Phys. B, 2021, 30 (10): 106103.   DOI: 10.1088/1674-1056/ac1416
    Abstract53)   HTML0)    PDF (1033KB)(44)      
    The monocrystalline LiNbO3 (LN) and LiTaO3 (LT) plates have been qualified as a kind of material platform for high performance RF filter that is considerable for the 5G communication. LN and LT thin films are usually transferred on handle wafers by combining ion-slicing and wafer bonding technique to form a piezoelectric on insulator (POI) substrate. The ion implantation is a key process and the implantation-induced strain is essential for the layer transfer. Here, we reported the strain profile of ion implanted rotated Y-cut LN and LT. The ion implantation generates the out-of-plane tensile strain of the sample surface and (006) plane, while both the tensile and compressive strain are observed on the (030) plane. The implanted ions redistributed due to the anisotropy of LN and LT, and induce the main tensile normal to the (006) plane. Meanwhile, the (030) planes are contracted due to the Poisson effect with the interstitial ions disturbing and mainly show a compressive strain profile.