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Stability and melting behavior of boron phosphide under high pressure

Wenjia Liang(梁文嘉), Xiaojun Xiang(向晓君), Qian Li(李倩), Hao Liang(梁浩), and Fang Peng(彭放)

Chin. Phys. B, 2024, 33 (4): 046201. DOI: 10.1088/1674-1056/ad23d4

Abstract （24）

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Boron phosphide (BP) has gained significant research attention due to its unique photoelectric and mechanical properties. In this work, we investigated the stability of BP under high pressure using x-ray diffraction and scanning electron microscope. The phase diagram of BP was explored in both B-rich and P-rich environments, revealing crucial insight into its behavior at 5.0 GPa. Additionally, we measured the melting curve of BP from 8.0 GPa to 15.0 GPa. Our findings indicate that the stability of BP under high pressure is improved within B-rich and P-rich environments. Furthermore, we report a remarkable observation of melting curve frustration at 10.0 GPa. This study will enhance our understanding of stability of BP under high pressure, shedding light on its potential application in semiconductor, thermal, and light-transmitting devices.

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In situ observation of the phase transformation kinetics of bismuth during shock release

Jiangtao Li(李江涛), Qiannan Wang(王倩男), Liang Xu(徐亮), Lei Liu(柳雷), Hang Zhang(张航), Sota Takagi, Kouhei Ichiyanagi, Ryo Fukaya, Shunsuke Nozawa, and Jianbo Hu(胡建波)

Chin. Phys. B, 2024, 33 (4): 046401. DOI: 10.1088/1674-1056/ad0ec6

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A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth. Results reveal a retarded transformation from the shock-induced Bi-V phase to a metastable Bi-IV phase during the shock release, instead of the thermodynamically stable Bi-III phase. The emergence of the metastable Bi-IV phase is understood by the competitive interplay between two transformation pathways towards the Bi-IV and Bi-III, respectively. The former is more rapid than the latter because the Bi-V to B-IV transformation is driven by interaction between the closest atoms while the Bi-V to B-III transformation requires interaction between the second-closest atoms. The nucleation time for the Bi-V to Bi-IV transformation is determined to be 5.1±0.9 ns according to a classical nucleation model. This observation demonstrates the importance of the formation of the transient metastable phases, which can change the phase transformation pathway in a dynamic process.

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Local thermal conductivity of inhomogeneous nano-fluidic films:A density functional theory perspective

Zongli Sun(孙宗利), Yanshuang Kang(康艳霜), and Yanmei Kang(康艳梅)

Chin. Phys. B, 2024, 33 (4): 046503. DOI: 10.1088/1674-1056/ad18a9

Abstract （26）

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Combining the mean field Pozhar—Gubbins (PG) theory and the weighted density approximation, a novel method for local thermal conductivity of inhomogeneous fluids is proposed. The correlation effect that is beyond the mean field treatment is taken into account by the simulation-based empirical correlations. The application of this method to confined argon in slit pore shows that its prediction agrees well with the simulation results, and that it performs better than the original PG theory as well as the local averaged density model (LADM). In its further application to the nano-fluidic films, the influences of fluid parameters and pore parameters on the thermal conductivity are calculated and investigated. It is found that both the local thermal conductivity and the overall thermal conductivity can be significantly modulated by these parameters. Specifically, in the supercritical states, the thermal conductivity of the confined fluid shows positive correlation to the bulk density as well as the temperature. However, when the bulk density is small, the thermal conductivity exhibits a decrease-increase transition as the temperature is increased. This is also the case in which the temperature is low. In fact, the decrease—increase transition in both the small-bulk-density and low-temperature cases arises from the capillary condensation in the pore. Furthermore, smaller pore width and/or stronger adsorption potential can raise the critical temperature for condensation, and then are beneficial to the enhancement of the thermal conductivity. These modulation behaviors of the local thermal conductivity lead immediately to the significant difference of the overall thermal conductivity in different phase regions.

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Microscopic growth mechanism and edge states of monolayer 1T'-MoTe₂

Haipeng Zhao(赵海鹏), Yin Liu(刘隐), Shengguo Yang(杨胜国), Chenfang Lin(林陈昉), Mingxing Chen(陈明星), Kai Braun, Xinyi Luo(罗心仪), Siyu Li(李思宇), Anlian Pan(潘安练), and Xiao Wang(王笑)

Chin. Phys. B, 2024, 33 (4): 046801. DOI: 10.1088/1674-1056/ad16d5

Abstract （30）

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Transition metal ditellurides (TMTDs) have versatile physical properties, including non-trivial topology, Weyl semimetal states and unique spin texture. Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications. Here, we demonstrate the epitaxial growth of 1T'-MoTe₂ on Au (111) and graphitized silicon carbide (Gr/SiC) by molecular beam epitaxy (MBE). We investigate the morphology of the grown 1T'-MoTe₂ at the atomic level by scanning tunnelling microscopy (STM) and reveal the corresponding microscopic growth mechanism. It is found that the unique ordered Te structures preferentially deposited on Au (111) regulate the growth of monolayer single crystal 1T'-MoTe₂, while the Mo clusters were preferentially deposited on the Gr/SiC substrate, which impedes the ordered growth of monolayer MoTe₂. We confirm that the size of single crystal 1T'-MoTe₂ grown on Au (111) is nearly two orders of magnitude larger than that on Gr/SiC. By scanning tunnelling spectroscopy (STS), we observe that the STS spectrum of the monolayer 1T'-MoTe₂ nano-island at the edge is different from that at the interior, which exhibits enhanced conductivity.

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Residual stress modeling of mitigated fused silica damage sites with CO₂ laser annealing

Chuanchao Zhang(张传超), Wei Liao(廖威), Lijuan Zhang(张丽娟), Xiaolong Jiang(蒋晓龙), Zhenhua Fang(方振华), and Xiaodong Jiang(蒋晓东)

Chin. Phys. B, 2024, 33 (3): 036101. DOI: 10.1088/1674-1056/acf447

Abstract （33）

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A numerical model based on measured fictive temperature distributions is explored to evaluate the residual stress fields of CO₂ laser-annealed mitigated fused silica damage sites. The proposed model extracts the residual strain from the differences in thermoelastic contraction of fused silica with different fictive temperatures from the initial frozen-in temperatures to ambient temperature. The residual stress fields of mitigated damage sites for the CO₂ laser-annealed case are obtained by a finite element analysis of equilibrium equations and constitutive equations. The simulated results indicate that the proposed model can accurately evaluate the residual stress fields of laser-annealed mitigated damage sites with a complex thermal history. The calculated maximum hoop stress is in good agreement with the reported experimental result. The estimated optical retardance profiles from the calculated radial and hoop stress fields are consistent with the photoelastic measurements. These results provide sufficient evidence to demonstrate the suitability of the proposed model for describing the residual stresses of mitigated fused silica damage sites after CO₂ laser annealing.

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Photostability of colloidal single photon emitter in near-infrared regime at room temperature

Si-Yue Jin(靳思玥) and Xing-Sheng Xu(许兴胜)

Chin. Phys. B, 2024, 33 (3): 036102. DOI: 10.1088/1674-1056/ad1090

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The photostability of a colloidal single photon emitter in near-infrared regime at room temperature is investigated. The fluorescence lifetime, blinking phenomenon, and anti-bunching effect of a single CdTeSe/ZnS quantum dot with an emission wavelength of 800 nm at room temperature are studied. The second-order correlation function at zero delay time is much smaller than 0.1, which proves that the emission from single quantum dots at 800 nm is a highly pure single-photon source. The effects of the irradiation duration on the fluorescence from single quantum dots are analyzed. The experimental results can be explained by a recombination model including a multi-nonradiative recombination center model and a multi-charged model.

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Electronic effects on radiation damage in α-iron: A molecular dynamics study

Lin Jiang(江林), Min Li(李敏), Bao-Qin Fu(付宝勤), Jie-Chao Cui(崔节超), and Qing Hou(侯氢)

Chin. Phys. B, 2024, 33 (3): 036103. DOI: 10.1088/1674-1056/ad0ec4

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Iron (Fe)-based alloys, which have been widely used as structural materials in nuclear reactors, can significantly change their microstructure properties and macroscopic properties under high flux neutron irradiation during operation, thus, the problems associated with the safe operation of nuclear reactors have been put forward naturally. In this work, a molecular dynamics simulation approach combined with electronic effects is developed for investigating the primary radiation damage process in α-Fe. Specifically, the influence of electronic effects on the collision cascade in Fe is systematically evaluated based on two commonly used interatomic potentials for Fe. The simulation results reveal that both electronic stopping (ES) and electron-phonon coupling (EPC) can contribute to the decrease of the number of defects in the thermal spike phase. The application of ES reduces the number of residual defects after the cascade evolution, whereas EPC has a reverse effect. The introduction of electronic effects promotes the formation of the dispersive subcascade: ES significantly changes the geometry of the damaged region in the thermal spike phase, whereas EPC mainly reduces the extent of the damaged region. Furthermore, the incorporation of electronic effects effectively mitigates discrepancies in simulation outcomes when using different interatomic potentials.

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Molecular dynamics study of primary radiation damage in TiVTa concentrated solid-solution alloy

Yong-Peng Zhao(赵永鹏), Yan-Kun Dou(豆艳坤), Xin-Fu He(贺新福), Han Cao(曹晗),Lin-Feng Wang(王林枫), Hui-Qiu Deng(邓辉球), and Wen Yang(杨文)

Chin. Phys. B, 2024, 33 (3): 036104. DOI: 10.1088/1674-1056/ad0146

Abstract （36）

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The primary radiation damage in pure V and TiVTa concentrated solid-solution alloy (CSA) was studied using a molecular dynamics method. We have performed displacement cascade simulations to explore the generation and evolution behavior of irradiation defects. The results demonstrate that the defect accumulation and agglomeration in TiVTa CSA are significantly suppressed compared to pure V. The peak value of Frenkel pairs during cascade collisions in TiVTa CSA is much higher than that in pure V due to the lower formation energy of point defects. Meanwhile, the longer lifetime of the thermal spike relaxation and slow energy dissipation capability of TiVTa CSA can facilitate the recombination of point defects. The defect agglomeration rate in TiVTa CSA is much lower due to the lower binding energy of interstitial clusters and reduced interstitial diffusivity. Furthermore, the occurrence probability of dislocation loops in TiVTa CSA is lower than that in pure V. The reduction in primary radiation damage may enhance the radiation resistance of TiVTa CSA, and the improved radiation tolerance is primarily attributed to the relaxation stage and long-term defect evolution rather than the ballistic stage. These results can provide fundamental insights into irradiation-induced defects evolution in refractory CSAs.

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Comparative study on phase transition behaviors of fractional molecular field theory and random-site Ising model

Ting-Yu Liu(刘婷玉), Wei Zhao(赵薇), Tao Wang(王涛), Xiao-Dong An(安小冬), Lai Wei(卫来), and Yi-Neng Huang(黄以能)

Chin. Phys. B, 2024, 33 (3): 036403. DOI: 10.1088/1674-1056/ad0cc7

Abstract （44）

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Fractional molecular field theory (FMFT) is a phenomenological theory that describes phase transitions in crystals with randomly distributed components, such as the relaxor-ferroelectrics and spin glasses. In order to verify the feasibility of this theory, this paper fits it to the Monte Carlo simulations of specific heat and susceptibility versus temperature of two-dimensional (2D) random-site Ising model (2D-RSIM). The results indicate that the FMFT deviates from the 2D-RSIM significantly. The main reason for the deviation is that the 2D-RSIM is a typical system of component random distribution, where the real order parameter is spatially heterogeneous and has no symmetry of space translation, but the basic assumption of FMFT means that the parameter is spatially uniform and has symmetry of space translation.

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Theoretical characterization of the adsorption configuration of pyrrole on Si(100) surface by x-ray spectroscopy

Hao-Qing Li(李好情), Jing Ming(明静), Zhi-Ang Jiang(姜志昂), Hai-Bo Li(李海波), Yong Ma(马勇), and Xiu-Neng Song(宋秀能)

Chin. Phys. B, 2024, 33 (2): 026102. DOI: 10.1088/1674-1056/aceaeb

Abstract （59）

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The possible configurations of pyrrole absorbed on a Si(100) surface have been investigated by x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectra. The C-1s XPS and NEXAFS spectra of these adsorption configurations have been calculated by using the density functional theory (DFT) method and full-core hole (FCH) approximation to investigate the relationship between the adsorption configurations and the spectra. The result shows that the XPS and NEXAFS spectra are structurally dependent on the configurations of pyrrole absorbed on the Si(100) surface. Compared with the XPS, the NEXAFS spectra are relatively sensitive to the adsorption configurations and can accurately identify them. The NEXAFS decomposition spectra produced by non-equivalent carbon atoms have also been calculated and show that the spectral features vary with the diverse types of carbon atoms and their structural environments.

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Floquet spectrum and universal dynamics of a periodically driven two-atom system

Wenzhu Xie(谢文柱), Zhengqiang Zhou(周正强), Xuan Li(李轩), Simiao Cui(崔思淼), and Mingyuan Sun(孙明远)

Chin. Phys. B, 2024, 33 (2): 026702. DOI: 10.1088/1674-1056/ad0623

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We investigate the Floquet spectrum and excitation properties of a two-ultracold-atom system with periodically driven interaction in a three-dimensional harmonic trap. The interaction between the atoms is changed by varying the s-wave scattering length in two ways, the cosine and the square-wave modulations. It is found that as the driving frequency increases, the Floquet spectrum exhibits two main features for both modulations, the accumulating and the spreading of the quasienergy levels, which further lead to different dynamical behaviors. The accumulation is associated with collective excitations and the persistent growth of the energy, while the spread indicates that the energy is bounded at all times. The initial scattering length, the driving frequency and amplitude can all significantly change the Floquet spectrum as well as the dynamics. However, the corresponding relation between them is valid universally. Finally, we propose a mechanism for selectively exciting the system to one specific state by using the avoided crossing of two quasienergy levels, which could guide preparation of a desired state in experiments.

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Effect of surface modification on the radiation stability of diamond ohmic contacts

Lian-Xi Mu(牟恋希), Shang-Man Zhao(赵上熳), Peng Wang(王鹏), Xiao-Lu Yuan(原晓芦), Jin-Long Liu(刘金龙), Zhi-Fu Zhu(朱志甫), Liang-Xian Chen(陈良贤), Jun-Jun Wei(魏俊俊), Xiao-Ping Ou-Yang(欧阳晓平), and Cheng-Ming Li(李成明)

Chin. Phys. B, 2024, 33 (2): 026801. DOI: 10.1088/1674-1056/ace61e

Abstract （63）

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The ohmic contact interface between diamond and metal is essential for the application of diamond detectors. Surface modification can significantly affect the contact performance and eliminate the interface polarization effect. However, the radiation stability of a diamond detector is also sensitive to surface modification. In this work, the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated. Before radiation, the specific contact resistivities ($\rho_{\rm c}$) between Ti/Pt/Au-hydrogen-terminated diamond (H-diamond) and Ti/Pt/Au-oxygen-terminated diamond (O-diamond) were $2.0 \times 10^{-4}$ $\Omega \cdot $cm$^{2}$ and $4.3 \times 10^{-3}$ $\Omega \cdot $cm$^{2}$, respectively. After 10 MeV electron radiation, the $\rho_{\rm c}$ of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were $5.3 \times 10^{-3}$ $\Omega \cdot $cm$^{2}$ and $9.1 \times 10^{-3}$ $ \Omega \cdot $cm$^{2}$, respectively. The rates of change of $\rho_{\rm c}$ of H-diamond and O-diamond after radiation were 2550% and 112%, respectively. The electron radiation promotes bond reconstruction of the diamond surface, resulting in an increase in $\rho_{\rm c}$.

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Growth and characterization of Bi(110)/CrTe₂ heterostructures: Exploring interplay between magnetism and topology

Zhenyu Yuan(袁震宇), Fazhi Yang(杨发枝), Baiqing Lv(吕佰晴), Yaobo Huang(黄耀波), Tian Qian(钱天), Jinpeng Xu(徐金朋), and Hong Ding(丁洪)

Chin. Phys. B, 2024, 33 (2): 026802. DOI: 10.1088/1674-1056/ad082a

Abstract （77）

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The interplay between topology and magnetism is vital for realizing exotic quantum phenomena, significant examples including quantum anomalous Hall effect, axion insulators, and high-order topological states. These states host great potential for future applications in high-speed and low-consumption electronic devices. Despite being extensively investigated, practical platforms are still scarce. In this work, with molecular beam epitaxy (MBE), we provide the first experimental report on high-quality Bi(110)/CrTe$_{2}$ magnetic heterostructure. By employing in-situ high-resolution scanning tunneling microscopy, we are able to examine the interaction between magnetism and topology. There is a potential edge state at an energy level above the Fermi level, but no edge states observed near the Fermi level The absence of high-order topological corner states near $E_{\rm F}$ highlights the importance of lattice matching and interface engineering in designing high-order topological states. Our study provides key insights into the interplay between two-dimensional magnetic and topological materials and offers an important dimension for engineering magnetic topological states.

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Sensitivity investigation of 100-MeV proton irradiation to SiGe HBT single event effect

Ya-Hui Feng(冯亚辉), Hong-Xia Guo(郭红霞), Yi-Wei Liu(刘益维), Xiao-Ping Ouyang(欧阳晓平), Jin-Xin Zhang(张晋新), Wu-Ying Ma(马武英), Feng-Qi Zhang(张凤祁), Ru-Xue Bai(白如雪), Xiao-Hua Ma(马晓华), and Yue Hao(郝跃)

Chin. Phys. B, 2024, 33 (1): 016104. DOI: 10.1088/1674-1056/acf303

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The single event effect (SEE) sensitivity of silicon—germanium heterojunction bipolar transistor (SiGe HBT) irradiated by 100-MeV proton is investigated. The simulation results indicate that the most sensitive position of the SiGe HBT device is the emitter center, where the protons pass through the larger collector-substrate (CS) junction. Furthermore, in this work the experimental studies are also carried out by using 100-MeV proton. In order to consider the influence of temperature on SEE, both simulation and experiment are conducted at a temperature of 93 K. At a cryogenic temperature, the carrier mobility increases, which leads to higher transient current peaks, but the duration of the current decreases significantly. Notably, at the same proton flux, there is only one single event transient (SET) that occurs at 93 K. Thus, the radiation hard ability of the device increases at cryogenic temperatures. The simulation results are found to be qualitatively consistent with the experimental results of 100-MeV protons. To further evaluate the tolerance of the device, the influence of proton on SiGe HBT after gamma-ray (⁶⁰Coγ) irradiation is investigated. As a result, as the cumulative dose increases, the introduction of traps results in a significant reduction in both the peak value and duration of the transient currents.

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Effect of grain size on gas bubble evolution in nuclear fuel: Phase-field investigations

Dan Sun(孙丹), Qingfeng Yang(杨青峰), Jiajun Zhao(赵家珺), Shixin Gao(高士鑫), Yong Xin(辛勇), Yi Zhou(周毅), Chunyu Yin(尹春雨), Ping Chen(陈平), Jijun Zhao(赵纪军), and Yuanyuan Wang(王园园)

Chin. Phys. B, 2024, 33 (1): 016105. DOI: 10.1088/1674-1056/ad08a6

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Numerous irradiation-induced gas bubbles are created in the nuclear fuel during irradiation, leading to the change of microstructure and the degradation of mechanical and thermal properties. The grain size of fuel is one of the important factors affecting bubble evolution. In current study, we first predict the thermodynamic behaviors of point defects as well as the interplay between vacancy and gas atom in both UO₂ and U₃Si₂ according to ab initio approach. Then, we establish the irradiation-induced bubble phase-field model to investigate the formation and evolution of intra- and inter-granular gas bubbles. The effects of fission rate and temperature on the evolutions of bubble morphologies in UO₂ and U₃Si₂ have been revealed. Especially, a comparison of porosities under different grain sizes is examined and analyzed. To understand the thermal conductivity as functions of grain size and porosity, the heat transfer capability of U₃Si₂ is evaluated.

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Simulation of space heavy-ion induced primary knock-on atoms in bipolar devices

Bin Zhang(张彬), Hao Jiang(姜昊), Xiao-Dong Xu(徐晓东), Tao Ying(应涛), Zhong-Li Liu(刘中利), Wei-Qi Li(李伟奇), Jian-Qun Yang(杨剑群), and Xing-Ji Li(李兴冀)

Chin. Phys. B, 2024, 33 (1): 016106. DOI: 10.1088/1674-1056/acd3e1

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Bipolar junction transistors (BJTs) are often used in spacecraft due to their excellent working characteristics. However, the complex space radiation environment induces primary knock-on atoms (PKAs) in BJTs through collisions, resulting in hard-to-recover displacement damage and affecting the performance of electronic components. In this paper, the properties of PKAs induced by typical space heavy ions (C, N, O, Fe) in BJTs are investigated using Monte Carlo simulations. The simulated results show that the energy spectrum of ion-induced PKAs is primarily concentrated in the low-energy range (17 eV—100 eV) and displays similar features across all tested ions. The PKAs induced by the collision of energetic ions have large forward scattering angles, mainly around 88°. Moreover, the distribution of PKAs within a transistor as a function of depth displays a peak characteristic, and the peak position is linearly proportional to the incident energy at a certain energy range. These simulation outcomes serve as crucial theoretical support for long-term semiconductor material defect evolution and ground testing of semiconductor devices.

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Hamiltonian system for the inhomogeneous plane elasticity of dodecagonal quasicrystal plates and its analytical solutions

Zhiqiang Sun(孙志强), Guolin Hou(侯国林), Yanfen Qiao(乔艳芬), and Jincun Liu (刘金存)

Chin. Phys. B, 2024, 33 (1): 016107. DOI: 10.1088/1674-1056/acfaf3

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A Hamiltonian system is derived for the plane elasticity problem of two-dimensional dodecagonal quasicrystals by introducing the simple state function. By using symplectic elasticity approach, the analytic solutions of the phonon and phason displacements are obtained further for the quasicrystal plates. In addition, the effectiveness of the approach is verified by comparison with the data of the finite integral transformation method.

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Linear magnetoresistance and structural distortion in layered SrCu_4-xP₂ single crystals

Yong Nie(聂勇), Zheng Chen(陈正), Wensen Wei(韦文森), Huijie Li(李慧杰), Yong Zhang(张勇), Ming Mei(梅明), Yuanyuan Wang(王园园), Wenhai Song(宋文海), Dongsheng Song(宋东升), Zhaosheng Wang(王钊胜), Xiangde Zhu(朱相德), Wei Ning(宁伟), and Mingliang Tian(田明亮)

Chin. Phys. B, 2024, 33 (1): 016108. DOI: 10.1088/1674-1056/acf705

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We report a systematic study on layered metal SrCu_4-xP₂ single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30 T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_p ～ 140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near T_p, i.e., ΔL_c/L_c～ 0.062%. The structural characterization confines that there is no structure transition below and above T_p. All these results suggest that the nonmagnetic transition of SrCu_4-xP₂ could be associated with structural distortion.

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Geometries and electronic structures of Zr_nCu(n =2-12) clusters: A joint machine-learning potential density functional theory investigation

Yizhi Wang(王一志), Xiuhua Cui(崔秀花), Jing Liu(刘静), Qun Jing(井群), Haiming Duan(段海明), and Haibin Cao(曹海宾)

Chin. Phys. B, 2024, 33 (1): 016109. DOI: 10.1088/1674-1056/acd5c2

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Zr-based amorphous alloys have attracted extensive attention because of their large glassy formation ability, wide supercooled liquid region, high elasticity, and unique mechanical strength induced by their icosahedral local structures. To determine the microstructures of Zr—Cu clusters, the stable and metastable geometry of Zr_nCu (n=2—12) clusters are screened out via the CALYPSO method using machine-learning potentials, and then the electronic structures are investigated using density functional theory. The results show that the Zr_nCu (n≥ 3) clusters possess three-dimensional geometries, Zr_nCu (n≥ 9) possess cage-like geometries, and the Zr₁₂Cu cluster has icosahedral geometry. The binding energy per atom gradually gets enlarged with the increase in the size of the clusters, and Zr_nCu (n=5, 7, 9, 12) have relatively better stability than their neighbors. The magnetic moment of most Zr_nCu clusters is just 1μ_B, and the main components of the highest occupied molecular orbitals (HOMOs) in the Zr₁₂Cu cluster come from the Zr-d state. There are hardly any localized two-center bonds, and there are about 20 σ-type delocalized three-center bonds.

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Temperature effect on nanotwinned Ni under nanoindentation using molecular dynamic simulation

Xi He(何茜), Ziyi Xu(徐子翼), and Yushan Ni(倪玉山)

Chin. Phys. B, 2024, 33 (1): 016201. DOI: 10.1088/1674-1056/acf997

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Temperature effect on atomic deformation of nanotwinned Ni (nt-Ni) under localized nanoindentation is investigated in comparison with nanocrystalline Ni (nc-Ni) through molecular simulation. The nt-Ni exhibits enhanced critical load and hardness compared to nc-Ni, where perfect, stair-rod and Shockley dislocations are activated at $(1\bar{1}1)$, $(\bar{1}11)$ and $(11\bar{1})$ slip planes in nt-Ni compared to only Shockley dislocation nucleation at $(1\bar{1}1)$ and $(\bar{1}11)$ slip planes of nc-Ni. The nt-Ni exhibits a less significant indentation size effect in comparison with nc-Ni due to the dislocation slips hindrance of the twin boundary. The atomic deformation associated with the indentation size effect is investigated during dislocation transmission. Different from the decreasing partial slips parallel to the indenter surface in nc-Ni with increasing temperature, the temperature-dependent atomic deformation of nt-Ni is closely related to the twin boundary: from the partial slips parallel to the twin boundary (~10 K), to increased confined layer slips and decreased twin migration(300 K—600 K), to decreased confined layer slips and increased dislocation interaction of dislocation pinning and dissociation (900 K—1200 K). Dislocation density and atomic structure types through quantitative analysis are implemented to further reveal the above-mentioned dislocation motion and atomic structure alteration. Our study is helpful for understanding the temperature-dependent plasticity of twin boundary in nanotwinned materials.

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