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Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select Structural evolution and bandgap modulation of layered β-GeSe2 single crystal under high pressure Hengli Xie(谢恒立), Jiaxiang Wang(王家祥), Lingrui Wang(王玲瑞), Yong Yan(闫勇), Juan Guo(郭娟), Qilong Gao(高其龙), Mingju Chao(晁明举), Erjun Liang(梁二军), and Xiao Ren(任霄) Chin. Phys. B, 2022, 31 (7): 076101.   DOI: 10.1088/1674-1056/ac6db8 Abstract （544）   HTML （20）    PDF （1291KB）（211）       Knowledge map    Germanium diselenide (GeSe2) is a promising candidate for electronic devices because of its unique crystal structure and optoelectronic properties. However, the evolution of lattice and electronic structure of $β$-GeSe2 at high pressure is still uncertain. Here we prepared high-quality $β$-GeSe2 single crystals by chemical vapor transfer (CVT) technique and performed systematic experimental studies on the evolution of lattice structure and bandgap of $β$-GeSe2 under pressure. High-precision high-pressure ultra low frequency (ULF) Raman scattering and synchrotron angle-dispersive x-ray diffraction (ADXRD) measurements support that no structural phase transition exists under high pressure up to 13.80 GPa, but the structure of $β$-GeSe2 turns into a disordered state near 6.91 GPa and gradually becomes amorphous forming an irreversibly amorphous crystal at 13.80 GPa. Two Raman modes keep softening abnormally upon pressure. The bandgap of $β$-GeSe2 reduced linearly from 2.59 eV to 1.65 eV under pressure with a detectable narrowing of 36.5%, and the sample under pressure performs the piezochromism phenomenon. The bandgap after decompression is smaller than that in the atmospheric pressure environment, which is caused by incomplete recrystallization. These results enrich the insight into the structural and optical properties of $β$-GeSe2 and demonstrate the potential of pressure in modulating the material properties of two-dimensional (2D) Ge-based binary material. Select Radiation effects of electrons on multilayer FePS3 studied with laser plasma accelerator Meng Peng(彭猛), Jun-Bo Yang(杨俊波), Hao Chen(陈浩), Bo-Yuan Li(李博源), Xu-Lei Ge(葛绪雷), Xiao-Hu Yang(杨晓虎), Guo-Bo Zhang(张国博), and Yan-Yun Ma(马燕云) Chin. Phys. B, 2022, 31 (8): 086102.   DOI: 10.1088/1674-1056/ac5c34 Abstract （541）   HTML （0）    PDF （2809KB）（46）       Knowledge map    Space radiation with inherently broadband spectral flux poses a huge danger to astronauts and electronics on aircraft, but it is hard to simulate such feature with conventional radiation sources. Using a tabletop laser-plasma accelerator, we can reproduce exponential energy particle beams as similar as possible to these in space radiation. We used such an electron beam to study the electron radiation effects on the surface structure and performance of two-dimensional material (FePS3). Energetic electron beam led to bulk sample cleavage and damage between areas of uneven thickness. For the FePS3 sheet sample, electron radiation transformed it from crystalline state to amorphous state, causing the sample surface to rough. The full widths at the half maximum of characteristic Raman peaks became larger, and the intensities of characteristic Raman peaks became weak or even disappeared dramatically under electron radiation. This trend became more obvious for thinner samples, and this phenomenon was attributed to the cleavage of P-P and P-S bonds, destabilizing the bipyramid structure of [P2S6]4- unit. The results are of great significance for testing the maximum allowable radiation dose for the two-dimensional material, implying that FePS3 cannot withstand such energetic electron radiation without an essential shield. Select Nanoscale structural investigation of Zn1-xMgxO alloy films on polar and nonpolar ZnO substrates with different Mg contents Xin Liang(梁信), Hua Zhou(周华), Hui-Qiong Wang(王惠琼), Lihua Zhang(张丽华), Kim Kisslinger, and Junyong Kang(康俊勇) Chin. Phys. B, 2021, 30 (9): 096107.   DOI: 10.1088/1674-1056/ac11e1 Abstract （540）   HTML （0）    PDF （5625KB）（176）       Knowledge map    Zn1-xMgxO alloy films are important deep ultraviolet photoelectric materials. In this work, we used plasma-assisted molecular beam epitaxy to prepare Zn1-xMgxO films with different magnesium contents on polar (0001) and nonpolar (1010) ZnO substrates. The nanoscale structural features of the grown alloy films as well as the interfaces were investigated. It was observed that the cubic phases of the alloy films emerged when the Mg content reached 20% and 37% for the alloy films grown on the (0001) and (1010) ZnO substrates, respectively. High-resolution transmission electron microscopy images revealed cubic phases without visible hexagonal phases for the alloy films with more than 70% magnesium, and the cubic phases exhibited three-fold and two-fold rotations for the alloy films on the polar (0001) and nonpolar (1010) ZnO substrates, respectively. This work aims to provide references for monitoring the Zn1-xMgxO film structure with respect to different substrate orientations. Select Preparation of graphene on SiC by laser-accelerated pulsed ion beams Danqing Zhou(周丹晴), Dongyu Li(李东彧), Yuhan Chen(陈钰焓), Minjian Wu(吴旻剑), Tong Yang(杨童), Hao Cheng(程浩), Yuze Li(李昱泽), Yi Chen(陈艺), Yue Li(李越), Yixing Geng(耿易星), Yanying Zhao(赵研英), Chen Lin(林晨), Xueqing Yan(颜学庆), and Ziqiang Zhao(赵子强) Chin. Phys. B, 2021, 30 (11): 116106.   DOI: 10.1088/1674-1056/abfc3c Abstract （525）   HTML （1）    PDF （1930KB）（124）       Knowledge map    Laser-accelerated ion beams (LIBs) have been increasingly applied in the field of material irradiation in recent years due to the unique properties of ultra-short beam duration, extremely high beam current, etc. Here we explore an application of using laser-accelerated ion beams to prepare graphene. The pulsed LIBs produced a great instantaneous beam current and thermal effect on the SiC samples with a shooting frequency of 1 Hz. In the experiment, we controlled the deposition dose by adjusting the number of shootings and the irradiating current by adjusting the distance between the sample and the ion source. During annealing at 1100 ℃, we found that the 190 shots ion beams allowed more carbon atoms to self-assemble into graphene than the 10 shots case. By comparing with the controlled experiment based on ion beams from a traditional ion accelerator, we found that the laser-accelerated ion beams could cause greater damage in a very short time. Significant thermal effect was induced when the irradiation distance was reduced to less than 1 cm, which could make partial SiC self-annealing to prepare graphene dots directly. The special effects of LIBs indicate their vital role to change the structure of the irradiation sample. Select Pressure-induced phase transitions in the ZrXY (X= Si, Ge, Sn;Y= S, Se, Te) family compounds Qun Chen(陈群), Juefei Wu(吴珏霏), Tong Chen(陈统), Xiaomeng Wang(王晓梦), Chi Ding(丁弛), Tianheng Huang(黄天衡), Qing Lu(鲁清), and Jian Sun(孙建) Chin. Phys. B, 2022, 31 (5): 056201.   DOI: 10.1088/1674-1056/ac5989 Abstract （524）   HTML （5）    PDF （6039KB）（384）       Knowledge map    Pressure is an effective and clean way to modify the electronic structures of materials, cause structural phase transitions and even induce the emergence of superconductivity. Here, we predicted several new phases of the ZrXY family at high pressures using the crystal structures search method together with first-principle calculations. In particular, the ZrGeS compound undergoes an isosymmetric phase transition from P4/nmm-I to P4/nmm-II at approximately 82 GPa. Electronic band structures show that all the high-pressure phases are metallic. Among these new structures, P4/nmm-II ZrGeS and P4/mmm ZrGeSe can be quenched to ambient pressure with superconducting critical temperatures of approximately 8.1 K and 8.0 K, respectively. Our study provides a way to tune the structure, electronic properties, and superconducting behavior of topological materials through pressure. Select Doping effect on the structure and physical properties of quasi-one-dimensional compounds Ba9Co3(Se1-xSx)15 (x = 0-0.2) Lei Duan(段磊), Xian-Cheng Wang(望贤成), Jun Zhang(张俊), Jian-Fa Zhao(赵建发), Wen-Min Li(李文敏), Li-Peng Cao(曹立朋), Zhi-Wei Zhao(赵志伟), Changjiang Xiao(肖长江), Ying Ren(任瑛), Shun Wang(王顺), Jinlong Zhu(朱金龙), and Chang-Qing Jin(靳常青) Chin. Phys. B, 2021, 30 (10): 106101.   DOI: 10.1088/1674-1056/ac1f03 Abstract （523）   HTML （0）    PDF （1668KB）（140）       Knowledge map    A series of samples of Ba9Co3(Se1-xSx)15 (x = 0, 0.05, 0.1, 0.15, 0.2) with quasi-one-dimensional (1D) structure were successfully synthesized under high-temperature and high-pressure conditions. The influence of partial substitution of S for Se on the structure, electronic transport, and magnetic properties of Ba9Co3(Se1-xSx)15 has been investigated in detail. The x-ray diffraction data shows that the lattice constant decreases linearly with increasing S-doping level, which follows the Vegrad's law. The doped S atoms preferentially occupy the site of Se atoms in CoSe6 octahedron. Physical properties measurements indicate that all the samples of Ba9Co3(Se1-xSx)15 are semiconducting and display spin glass behavior. As the replacement of Se by smaller size S, although the inter-chain distance decreases, the electronic hopping between CoSe/S6 chains is weakened and leads to an increase of band gap from 0.75 eV to 0.86 eV, since the S-3p electrons are more localized than Se-4p ones. Ba9Co3(Se1-xSx)15 exhibits 1D conducting chain characteristic. Select Structural and electrical transport properties of charge density wave material LaAgSb2 under high pressure Bowen Zhang(张博文), Chao An(安超), Xuliang Chen(陈绪亮), Ying Zhou(周颖), Yonghui Zhou(周永惠), Yifang Yuan(袁亦方), Chunhua Chen(陈春华), Lili Zhang(张丽丽), Xiaoping Yang(杨晓萍), and Zhaorong Yang(杨昭荣) Chin. Phys. B, 2021, 30 (7): 076201.   DOI: 10.1088/1674-1056/abf643 Abstract （493）   HTML （8）    PDF （1119KB）（214）       Knowledge map    Layered lanthanum silver antimonide LaAgSb2 exhibits both charge density wave (CDW) order and Dirac-cone-like band structure at ambient pressure. Here, we systematically investigate the pressure evolution of structural and electronic properties of LaAgSb2 single crystal. We show that the CDW order is destabilized under compression, as evidenced by the gradual suppression of magnetoresistance. At PC～ 22 GPa, synchrotron x-ray diffraction and Raman scattering measurements reveal a structural modification at room-temperature. Meanwhile, the sign change of the Hall coefficient is observed at 5 K. Our results demonstrate the tunability of CDW order in the pressurized LaAgSb2 single crystal, which can be helpful for its potential applications in the next-generation devices. Select Optically-controlled resistive switching effectsof CdS nanowire memtransistor Jia-Ning Liu(刘嘉宁), Feng-Xiang Chen(陈凤翔), Wen Deng(邓文), Xue-Ling Yu(余雪玲), and Li-Sheng Wang(汪礼胜) Chin. Phys. B, 2021, 30 (11): 116105.   DOI: 10.1088/1674-1056/ac16ce Abstract （490）   HTML （1）    PDF （1569KB）（69）       Knowledge map    Since it was proposed, memtransistors have been a leading candidate with powerful capabilities in the field of neural morphological networks. A memtransistor is an emerging structure combining the concepts of a memristor and a field-effect transistor with low-dimensional materials, so that both optical excitation and electrical stimuli can be used to modulate the memristive characteristics, which make it a promising multi-terminal hybrid device for synaptic structures. In this paper, a single CdS nanowire memtransistor has been constructed by the micromechanical exfoliation and alignment lithography methods. It is found that the CdS memtransistor has good non-volatile bipolar memristive characteristics, and the corresponding switching ratio is as high as 106 in the dark. While under illumination, the behavior of the CdS memtransistor is similar to that of a transistor or a memristor depending on the incident wavelengths, and the memristive switching ratio varies in the range of 10 to 105 with the increase of the incident wavelength in the visible light range. In addition, the optical power is also found to affect the memristive characteristics of the device. All of these can be attributed to the modulation of the potential barrier by abundant surface states of nanowires and the illumination influences on the carrier concentrations in nanowires. Select Phase transition-induced superstructures of β-Sn films with atomic-scale thickness Le Lei(雷乐), Feiyue Cao(曹飞跃), Shuya Xing(邢淑雅), Haoyu Dong(董皓宇), Jianfeng Guo(郭剑锋), Shangzhi Gu(顾尚志), Yanyan Geng(耿燕燕), Shuo Mi(米烁), Hanxiang Wu(吴翰翔), Fei Pang(庞斐), Rui Xu(许瑞), Wei Ji(季威), and Zhihai Cheng(程志海) Chin. Phys. B, 2021, 30 (9): 096804.   DOI: 10.1088/1674-1056/ac11e8 Abstract （480）   HTML （0）    PDF （1842KB）（162）       Knowledge map    The ultrathin β-Sn(001) films have attracted tremendous attention owing to its topological superconductivity (TSC), which hosts Majorana bound state (MBSs) for quantum computation. Recently, β-Sn(001) thin films have been successfully fabricated via phase transition engineering. However, the understanding of structural phase transition of β-Sn(001) thin films is still elusive. Here, we report the direct growth of ultrathin β-Sn(001) films epitaxially on the highly oriented pyrolytic graphite (HOPG) substrate and the characterization of intricate structural-transition-induced superstructures. The morphology was obtained by using atomic force microscopy (AFM) and low-temperature scanning tunneling microscopy (STM), indicating a structure-related bilayer-by-bilayer growth mode. The ultrathin β-Sn film was made of multiple domains with various superstructures. Both high-symmetric and distorted superstructures were observed in the atomic-resolution STM images of these domains. The formation mechanism of these superstructures was further discussed based on the structural phase transition of β to α-Sn at the atomic-scale thickness. Our work not only brings a deep understanding of the structural phase transition of Sn film at the two-dimensional limit, but also paves a way to investigate their structure-sensitive topological properties. Select Prediction of scandium tetraboride from first-principles calculations: Crystal structures, phase stability, mechanical properties,and hardness Bin-Hua Chu(初斌华) and Yuan Zhao(赵元) Chin. Phys. B, 2021, 30 (7): 076107.   DOI: 10.1088/1674-1056/abe116 Abstract （465）   HTML （2）    PDF （1562KB）（105）       Knowledge map    Using the evolutionary methodology for crystal structure prediction, we have predicted the orthorhombic Cmcm and Pnma phases for ScB4. The earlier proposed CrB4-, FeB4-, MnB4-, and ReP4-type structures for ScB4 are excluded. It is first discovered that the Cmcm phase transforms to the Pnma phase at about 18 GPa. Moreover, both phases are dynamically and mechanically stable. The large bulk modulus, shear modulus, and Young's modulus of the two phases make it an optimistic low compressible material. Moreover, the strong covalent bonding nature of ScB4 is confirmed by the ELF analysis. The strong covalent bonding contributes greatly to its stability. Select Anomalous bond-length behaviors of solid halogens under pressure Min Wu(吴旻), Ye-Feng Wu(吴烨峰), and Yi Ma(马毅) Chin. Phys. B, 2021, 30 (7): 076401.   DOI: 10.1088/1674-1056/abf4bd Abstract （458）   HTML （1）    PDF （4332KB）（56）       Knowledge map    The three halogen solids (Cl2, Br2, and I2) have the isostructural diatomic molecular phase I with a space group of Cmca at ambient pressure. At high pressure, they all go through an intermediate phase V with incommensurate structures before eventually dissociating into the monatomic phase Ⅱ. However, a new structural transition between phase I and V with anomalous bond-length behavior was observed in bromine under pressure, which, so far, has not been confirmed in iodine and chlorine. Here, we perform first-principles calculations for iodine and chlorine. The new structural transition was predicted to be common to all three halogens under pressure. The transition pressures might be systematically underestimated by the imperfect van der Waals correction method, but they follow the order Cl2 > Br2 > I2, which is consistent with other pressure-induced structural transitions such as metallization and the molecular-to-monatomic transition. Select Bandgap evolution of Mg3N2 under pressure: Experimental and theoretical studies Gang Wu(吴刚), Lu Wang(王璐), Kuo Bao(包括), Xianli Li(李贤丽), Sheng Wang(王升), and Chunhong Xu(徐春红) Chin. Phys. B, 2022, 31 (6): 066205.   DOI: 10.1088/1674-1056/ac4cbe Abstract （454）   HTML （3）    PDF （1125KB）（94）       Knowledge map    Wide bandgap semiconductors are crucially significant for optoelectronic and thermoelectric device applications. Metal nitride is a class of semiconductor material with great potential. Under high pressure, the bandgap of magnesium nitride was predicted to grow. Raman spectra, ultra-violet-visible (UV-Vis) absorption spectra, and first-principles calculations were employed in this study to analyze the bandgap evolution of Mg3N2. The widening of the bandgap has been first detected experimentally, with the gap increasing from 2.05 eV at 3 GPa to 2.88 eV at 47 GPa. According to the calculation results, the enhanced covalent component is responsible for the bandgap widening. Select Structural, magnetic, and dielectric properties of Ni-Zn ferrite and Bi2O3 nanocomposites prepared by the sol-gel method Jinmiao Han(韩晋苗), Li Sun(孙礼), Ensi Cao(曹恩思), Wentao Hao(郝文涛), Yongjia Zhang(张雍家), and Lin Ju(鞠林) Chin. Phys. B, 2021, 30 (9): 096102.   DOI: 10.1088/1674-1056/ac0904 Abstract （452）   HTML （0）    PDF （3036KB）（108）       Knowledge map    Ni-Zn ferrite and Bi2O3 composites were developed by the sol-gel method. The structural, magnetic, and dielectric properties were studied for all the prepared samples. X-ray diffraction (XRD) was performed to study the crystal structure. The results of field emission scanning electron microscopy (FE-SEM) showed that the addition of Bi2O3 can increase the grain size of the Ni-Zn ferrite. Magnetic properties were analyzed by a hysteresis loop test and it was found that the saturation magnetization and coercivity decreased with the increase of Bi2O3 ratio. In addition, the dielectric properties of the Ni-Zn ferrite were also improved with the addition of Bi2O3. Select Atomic and electronic structures of p-type dopants in 4H-SiC Lingyan Lu(卢玲燕), Han Zhang(张涵), Xiaowei Wu(吴晓维), Jing Shi(石晶), and Yi-Yang Sun(孙宜阳) Chin. Phys. B, 2021, 30 (9): 096806.   DOI: 10.1088/1674-1056/ac1e22 Abstract （447）   HTML （0）    PDF （1294KB）（253）       Knowledge map    Using hybrid density functional calculation, we study the atomic and electronic structures of p-type dopants, B, Al and Ga, in 4H-SiC. For B, depending on the growth condition, it can occupy both Si and C sites. In contrast, Al and Ga on the C sites exhibit too high formation energy to exist in a significant amount. In 4H-SiC, there exist two types of Si sites in wurtzite-like and zincblende-like local coordination, respectively. Our calculations suggest that the dopant atoms have negligible preference occupying the two sites. In neutral charge state, all the dopants exhibit significant distortions from the structure in the negatively charged state. For most cases, our calculations yield three distorted structures, in which the most stable one has the dopant atom displaced along its bond with one of the surrounding equatorial Si or C atoms, lowering the C3v symmetry to Cs symmetry (i.e., a mirror symmetry only). Among the three dopant elements, Al on Si sites exhibits overall the lowest formation energy and the shallowest acceptor level. Nevertheless, it is not a hydrogenic dopant with the acceptor level 0.12 eV above the valence band maximum based on calculation using a 400-atom supercell. Its corresponding defect state exhibits apparent localization along the [0001] direction, but it is relatively delocalized in the (0001) plane. Select Structural modulation and physical properties of cobalt-doped layered La2M5As3O2 (M= Cu, Ni) compounds Lei Yang(杨蕾), Yan-Peng Song(宋艳鹏), Jun-Jie Wang(王俊杰), Xu Chen(陈旭), Hui-Jing Du(杜会静), and Jian-Gang Guo(郭建刚) Chin. Phys. B, 2021, 30 (7): 076106.   DOI: 10.1088/1674-1056/abf349 Abstract （441）   HTML （1）    PDF （3026KB）（162）       Knowledge map    We investigate the structural variation and physical properties of layered La2M5As3O2 (M=Cu, Ni) compound upon Co doping. It is found that the substitution of Co ion just induces the monotonous change of lattice constants without observing the anomalous kink in superconducting La2(Cu1-xNix)5As3O2 solid-solutions. Meanwhile, this doping barely changes As-As bond length in [M5As3]2- subunit (±2%), being significantly smaller than 7% shrinkage of that in La2(Cu1-xNix)5As3O2. Therefore, the doping dependence of crystal structure exhibits similar trend with Ba1-xKxFe2As2 without the interference of As1-As2 bonding, implying that the Co substitution for Cu/Ni is hole-doped. In terms of physical property, La2(Cu1-xCox)5As3O2 turns into itinerant ferromagnetic metal, while La2(Ni1-xCox)5As3O2 shows paramagnetism and suppressed structural phase transition upon Co-doping. The distinct structural variation and absence of superconductivity provide important clues to understand the effect of As-As bond in [M5As3]2- subunit. Select Theoretical and experimental studies on high-power laser-induced thermal blooming effect in chamber with different gases Xiangyizheng Wu(吴祥议政), Jian Xu(徐健), Keling Gong(龚柯菱), Chongfeng Shao(邵崇峰), Yang Kou(寇洋), Yuxuan Zhang(张宇轩), Yong Bo(薄勇), and Qinjun Peng(彭钦军) Chin. Phys. B, 2022, 31 (8): 086105.   DOI: 10.1088/1674-1056/ac6165 Abstract （436）   HTML （0）    PDF （1981KB）（189）       Knowledge map    High-power laser induced thermal blooming effects in a closed chamber with three different gases are investigated theoretically and experimentally in this work. In the theoretical treatment, an incompressible gas turbulent model is adopted. In the numerical simulation the gas refractive index as a function of both the temperature and pressure is taken into consideration. In the experimental study the pump-probe technology is adopted. A high-power 1064-nm fiber laser with maximum output power of 12 kW is used to drive the gas thermal blooming, and a 50-mW high-beam-quality 637-nm laser diode (LD) is used as a probe beam. The influences of the gas thermal blooming in the chamber on the probe beam wavefront and beam quality are analyzed for three different gases of air, nitrogen, and helium, respectively. The results indicate that nitrogen is well suitable for restraining thermal blooming effect for high-power laser. The measured data are in good agreement with the simulated results. Select Ab-initio calculations of bandgap tuning of In1-xGaxY (Y = N, P) alloys for optoelectronic applications Muhammad Rashid, Jamil M, Mahmood Q, Shahid M Ramay, Asif Mahmood A, and Ghaithan H M Chin. Phys. B, 2021, 30 (11): 116301.   DOI: 10.1088/1674-1056/abf128 Abstract （429）   HTML （0）    PDF （7073KB）（36）       Knowledge map    The Ⅲ-V alloys and doping to tune the bandgap for solar cells and other optoelectronic devices has remained a hot topic of research for the last few decades. In the present article, the bandgap tuning and its influence on optical properties of In1-xGaxN/P, where (x = 0.0, 0.25, 0.50, 0.75, and 1.0) alloys are comprehensively analyzed by density functional theory based on full-potential linearized augmented plane wave method (FP-LAPW) and modified Becke and Johnson potentials (TB-mBJ). The direct bandgaps turn from 0.7 eV to 3.44 eV, and 1.41 eV to 2.32 eV for In1-xGaxN/P alloys, which increases their potentials for optoelectronic devices. The optical properties are discussed such as dielectric constants, refraction, absorption, optical conductivity, and reflection. The light is polarized in the low energy region with minimum reflection. The absorption and optical conduction are maxima in the visible region, and they are shifted into the ultraviolet region by Ga doping. Moreover, static dielectric constant ε1(0) is in line with the bandgap from Penn's model. Select Mechanism of microweld formation and breakage during Cu-Cu wire bonding investigated by molecular dynamics simulation Beikang Gu(顾倍康), Shengnan Shen(申胜男), and Hui Li(李辉) Chin. Phys. B, 2022, 31 (1): 016101.   DOI: 10.1088/1674-1056/ac0e24 Abstract （427）   HTML （3）    PDF （2127KB）（67）       Knowledge map    Currently, wire bonding is the most popular first-level interconnection technology used between the die and package terminals, but even with its long-term and excessive usage, the mechanism of wire bonding has not been completely evaluated. Therefore, fundamental research is still needed. In this study, the mechanism of microweld formation and breakage during Cu-Cu wire bonding was investigated by using molecular dynamics simulation. The contact model for the nanoindentation process between the wire and substrate was developed to simulate the contact process of the Cu wire and Cu substrate. Elastic contact and plastic instability were investigated through the loading and unloading processes. Moreover, the evolution of the indentation morphology and distributions of the atomic stress were also investigated. It was shown that the loading and unloading curves do not coincide, and the unloading curve exhibited hysteresis. For the substrate, in the loading process, the main force changed from attractive to repulsive. The maximum von Mises stress increased and shifted from the center toward the edge of the contact area. During the unloading process, the main force changed from repulsive to attractive. The Mises stress reduced first and then increased. Stress concentration occurs around dislocations in the middle area of the Cu wire. Select Inverted V-shaped evolution of superconducting temperature in SrBC under pressure Ru-Yi Zhao(赵如意), Xun-Wang Yan(闫循旺), and Miao Gao(高淼) Chin. Phys. B, 2021, 30 (7): 076301.   DOI: 10.1088/1674-1056/abfbcc Abstract （419）   HTML （2）    PDF （4161KB）（231）       Knowledge map    Based on density functional first-principles calculations and anisotropic Eliashberg equations, we have investigated the electronic structure, lattice dynamics, and phonon-mediated superconductivity in newly synthesized layered compound SrBC under pressure. Different from LiBC and MgB2, our calculations surprisingly reveal that SrBC is isotropic in compressibility, due to the accumulation of substantial electrons in the interstitial region. We find that the Sr phonons strongly couple with B-2pz orbital and the interstitial states, giving rise to a two-gap superconductivity in SrBC, whose transition temperature shows an inverted V-shaped dependence on pressure. The maximal transition temperature is about 22 K at 50 GPa. On both sides of 50 GPa, the transition temperature exhibits quasi-linear variation with positive and negative slopes, respectively. Such a variation of transition temperature is infrequent among phonon-mediated superconductors. The competition between enhanced electron-phonon matrix element and hardened phonons plays an essential role in governing the behavior of the critical temperature. Select Direct observation of the scaling relation between density of states and pairing gap in a dirty superconductor Chang-Jiang Zhu(朱长江), Limin Liu(刘立民), Peng-Bo Song(宋鹏博), Han-Bin Deng(邓翰宾), Chang-Jiang Yi(伊长江), Ying-Kai Sun(孙英开), R Wu(武睿), Jia-Xin Yin(殷嘉鑫), Youguo Shi(石友国), Ziqiang Wang(汪自强), and Shuheng H. Pan(潘庶亨) Chin. Phys. B, 2021, 30 (10): 106802.   DOI: 10.1088/1674-1056/ac0903 Abstract （418）   HTML （0）    PDF （3296KB）（124）       Knowledge map    Theories and experiments on dirty superconductors are complex but important in terms of both theoretical fundamentals and practical applications. These activities are even more challenging when magnetic fields are present because the field distribution, electron density of states, and superconducting pairing potentials become nonuniform. Here, we present tunneling microspectroscopic experiments on NbC single crystals and demonstrate that NbC is a homogeneous dirty superconductor. When applying magnetic fields to the samples, we found that the zero-energy local density of states and the pairing energy gap followed the explicit scaling relation proposed by de Gennes for homogeneous dirty superconductors in high magnetic fields. More significantly, our experimental findings indicate that the validity of the scaling relation extends to magnetic field strengths far below the upper critical field, calling for a new nonperturbative understanding of this fundamental property in dirty superconductors. On the practical side, we used the observed scaling relation to derive a simple and straightforward experimental scheme for estimating the superconducting coherence length of a dirty superconductor in magnetic fields. page Page 1 of 12 Total 223 records First page Prev page Next page Last page