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Superfluid-Mott-Insulator Transition in an Optical Lattice with Adjustable Ensemble-Averaged Filling Factors
Shifeng Yang, Tianwei Zhou, Chen Li, Kaixiang Yang, Yueyang Zhai, Xuguang Yue, Xuzong Chen
Chin. Phys. Lett. 2020, 37 (4):
040301
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DOI: 10.1088/0256-307X/37/4/040301
We study the quantum phase transition from a superfluid to a Mott insulator of ultracold atoms in a three-dimensional optical lattice with adjustable filling factors. Based on the density-adjustable Bose–Einstein condensate we prepared, the excitation spectrum in the superfluid and the Mott insulator regime is measured with different ensemble-averaged filling factors. We show that for the superfluid phase, the center of the excitation spectrum is positively correlated with the ensemble-averaged filling factor, indicating a higher sound speed of the system. For the Mott insulator phase, the discrete feature of the excitation spectrum becomes less pronounced as the ensemble-averaged filling factor increases, implying that it is harder for the system to enter the Mott insulator regime with higher filling factors. The ability to manipulate the filling factor affords further potential in performing quantum simulation with cold atoms trapped in optical lattices.
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Discriminating High-Pressure Water Phases Using Rare-Event Determined Ionic Dynamical Properties
Lin Zhuang, Qijun Ye, Ding Pan, Xin-Zheng Li
Chin. Phys. Lett. 2020, 37 (4):
043101
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DOI: 10.1088/0256-307X/37/4/043101
Recent discoveries of dynamic ice VII and superionic ice highlight the importance of ionic diffusions in discriminating high-pressure ($P$) water phases. The rare event nature and the chemical bond breaking associated with these diffusions, however, make extensive simulations of these processes unpractical to ab initio and inappropriate for force field based methods. Using a first-principles neural network potential, we performed a theoretical study of water at 5–70 GPa and 300–3000 K. Long-time dynamics of protons and oxygens were found indispensable in discriminating several subtle states of water, characterized by proton's and oxygen ion's diffusion coefficients and the distribution of proton's displacements. Within dynamic ice VII, two types of proton transfer mechanisms, i.e., translational and rotational transfers, were identified to discriminate this region further into dynamic ice VII T and dynamic ice VII R. The triple point between ice VII, superionic ice (SI), and liquid exists because the loosening of the bcc oxygen skeleton is prevented by the decrease of interatomic distances at high $P$'s. The melting of ice VII above $\sim$40 GPa can be understood as a process of two individual steps: the melting of protons and the retarded melting of oxygens, responsible for the forming of SI. The boundary of the dynamic ice VII and SI lies on the continuation line ice VII's melting curve at low $P$'s. Based on these, a detailed phase diagram is given, which may shed light on studies of water under $P$'s in a wide range of interdisciplinary sciences.
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Nonadiabatic and Multielectron Effects in the Attoclock Experimental Scheme
Zhi-Lei Xiao, Wei Quan, Song-Po Xu, Shao-Gang Yu, Xuan-Yang Lai, Jing Chen, Xiao-Jun Liu
Chin. Phys. Lett. 2020, 37 (4):
043201
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DOI: 10.1088/0256-307X/37/4/043201
The problem of how long it takes for an electron to tunnel from one side of a barrier to the other has been debated for decades and the attoclock is a promising experimental procedure to address this problem. In the attoclock experiment, many physical effects will contribute to the experimental results and it is difficult to extract the tunneling time accurately. We numerically investigate a method of measuring the residual equivalent temporal offset (RETO) induced by the physical effects except for tunneling delay. The Coulomb potential effect, the nonadiabatic effect, the multielectron effect, and the Stark effect are considered in the theoretical model. It is shown that the ratio of the RETO of the target atoms to that of H is insensitive to the wavelength and is linearly proportional to (2$I_{\rm p}$)$^{-3/2}$. This work can help to improve the accuracy of the attoclock technique.
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Ionic Angular Distributions Induced by Strong-Field Ionization of Tri-Atomic Molecules
Tian Sun, Shi-Wen Zhang, Rui Wang, Shuang Feng, Yang Liu, Hang Lv, Hai-Feng Xu
Chin. Phys. Lett. 2020, 37 (4):
043301
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DOI: 10.1088/0256-307X/37/4/043301
Angular distributions of fragment ions from ionization of several tri-atomic molecules (CO$_{2}$, OCS, N$_{2}$O and NO$_{2}$) by strong 800-nm laser fields are investigated via a time-of-flight mass spectrometer. Anisotropic angular distributions of fragment ions, especially those of atomic ions, are observed for all of the molecules studied. These anisotropic angular distributions are mainly due to the geometric alignment of molecules in the strong field ionization. Distinct different patterns in ionic angular distributions for different molecules are observed. It is indicated that both molecular geometric structure and ionization channels have effects on the angular distributions of strong field ionization/fragmentation.
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Testing the Universality of Free Fall by Comparing the Atoms in Different Hyperfine States with Bragg Diffraction
Ke Zhang, Min-Kang Zhou, Yuan Cheng, Le-Le Chen, Qin Luo, Wen-Jie Xu, Lu-Shuai Cao, Xiao-Chun Duan, Zhong-Kun Hu
Chin. Phys. Lett. 2020, 37 (4):
043701
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DOI: 10.1088/0256-307X/37/4/043701
We perform a precision atom interferometry experiment to test the universality of free fall. Our experiment employs the Bragg atom interferometer with $^{87}$Rb atoms either in hyperfine state $\left| {F = 1,{m_F} = 0} \right\rangle $ or $\left| {F = 2,{m_F} = 0} \right\rangle $, and the wave packets in these two states are diffracted by one pair of Bragg beams alternatively, which is helpful for suppressing common-mode systematic errors. We obtain an Eötvös ratio ${\eta_{1 - 2}} = \left({ 0.9 \pm 2.7} \right) \times {10^{- 10}}$, and set a new record on the precision with improvement of nearly 5 times. This measurement also provides constraint on the difference of the diagonal terms of the mass-energy operator.
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Coaxial Multi-Wavelength Generation in YVO$_{4}$ Crystal with Stimulated Raman Scattering Excited by a Picosecond-Pulsed 1064 Laser
Jing-Jie Hao, Wei Tu, Nan Zong, Yu Shen, Shen-Jin Zhang, Yong Bo, Qin-Jun Peng, Zu-Yan Xu
Chin. Phys. Lett. 2020, 37 (4):
044202
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DOI: 10.1088/0256-307X/37/4/044202
The multiwavelength characteristics of stimulated Raman scattering (SRS) in YVO$_{4}$ crystal excited by a picosecond laser at 1064 nm are investigated theoretically and experimentally. Laser output with seven wavelengths is achieved coaxially and synchronously at 894, 972, 1175, 1312, 1486, 1713 and 2022 nm in a YVO$_{4}$ crystal. The maximum total Raman output energy is as high as 2.77 mJ under the pump energy of 7.75 mJ. A maximum total Raman conversion efficiency of 47.8% is obtained when the pump energy is 6.54 mJ. This is the highest order of Stokes components and the highest output energy generated by YVO$_{4}$ reported up to date. This work expands the Raman spectrum of YVO$_{4}$ crystal to the near-IR regime, with seven wavelengths covered at the same time, paving the way for new wavelength generation in the near-IR regime and its multiwavelength application.
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Optical Properties of Atomic Defects in Hexagonal Boron Nitride Flakes under High Pressure
Xiao-Yu Zhao, Jun-Hui Huang, Zhi-Yao Zhuo, Yong-Zhou Xue, Kun Ding, Xiu-Ming Dou, Jian Liu, Bao-Quan Sun
Chin. Phys. Lett. 2020, 37 (4):
044204
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DOI: 10.1088/0256-307X/37/4/044204
We investigate the pressure spectral characteristics and the effective tuning of defect emissions in hexagonal boron nitride (hBN) at low temperatures using a diamond anvil cell (DAC). It is found that the redshift rate of emission energy is up to 10 meV/GPa, demonstrating a controllable tuning of single photon emitters through pressure. Based on the distribution character of pressure coefficients as a function of wavelength, different kinds of atomic defect states should be responsible for the observed defect emissions.
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Giant Broadband One Way Transmission Based on Directional Mie Scattering and Asymmetric Grating Diffraction Effects
Xuannan Wu, Guanwen Yuan, Rui Zhu, Jicheng Wang, Fuhua Gao, Feiliang Chen, Yidong Hou
Chin. Phys. Lett. 2020, 37 (4):
044205
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DOI: 10.1088/0256-307X/37/4/044205
High performance optical diode-like devices are highly desired in future practical nano-photonic devices with strong directional selectivity. We demonstrate a kind of giant broadband reciprocity optical diode-like devices by simultaneously using the directional Mie scattering effect and the asymmetric grating diffraction effect. The maximum asymmetric subtraction and the asymmetric transmission ratio can reach nearly 100% and 40 dB at specified wavelength, respectively. In a wide waveband from 500 nm to 800 nm, the asymmetric subtraction and the ratio keep larger than 80% and 3.5 dB, respectively, even under oblique incidence. To the best of our knowledge, this is the best one-way-transmission effect observed in the reciprocity optical diode-like devices. In addition, we further demonstrate that this one-way-transmission effect can bring an effective absorption enhancement on gold films. The giant, broadband and angle-insensitive one-way-transmission effect demonstrated here is far beyond the well-known anti-reflection effect in the light-trapping devices and will bring new design philosophy for nano-photonic devices.
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Mode Control of Quasi-PT Symmetry in Laterally Multi-Mode Double Ridge Semiconductor Laser
Ting Fu, Yu-Fei Wang, Xue-You Wang, Xu-Yan Zhou, Wan-Hua Zheng
Chin. Phys. Lett. 2020, 37 (4):
044207
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DOI: 10.1088/0256-307X/37/4/044207
In traditional semiconductor lasers, it is usual to obtain single lateral mode operation by narrowing the ridge of waveguide, which is sensitive to fabrication inaccuracies. To overcome this shortcoming, a quasi-PT (parity-time) symmetric double ridge semiconductor laser is proposed to reach single lateral mode operation for an intrinsic multi-mode stripe laser. The coupled mode theory is used to analyze the non-Hermitian modulation of the gain (or loss) of the PT symmetric double ridge laser to obtain the coupling coefficient between the two ridge waveguides. Finally, the mode field distributions of the quasi-PT symmetric double ridge laser are simulated before and after the spontaneous PT symmetry breaking, which keep the laser operating in single lateral mode.
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High-Fidelity Manipulation of the Quantized Motion of a Single Atom via Stern–Gerlach Splitting
Kun-Peng Wang, Jun Zhuang, Xiao-Dong He, Rui-Jun Guo, Cheng Sheng, Peng Xu, Min Liu, Jin Wang, Ming-Sheng Zhan
Chin. Phys. Lett. 2020, 37 (4):
044209
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DOI: 10.1088/0256-307X/37/4/044209
We demonstrate high-fidelity manipulation of the quantized motion of a single $^{87}$Rb atom in an optical tweezer via microwave couplings induced by Stern–Gerlach splitting. The Stern–Gerlach splitting is mediated by polarization gradient of a strongly focused tweezer beam that functions as fictitious magnetic field gradient. The spatial splitting removes the orthogonality of the atomic spatial wavefunctions, thus enables the microwave couplings between the motional states. We obtain coherent Rabi oscillations for up to third-order sideband transitions, in which a high fidelity of larger than $0.99$ is obtained for the spin-flip transition on the first order sideband after subtraction of the state preparation and detection error. The Stern–Gerlach splitting is measured at a precision of better than $0.05$ nm. This work paves the way for quantum engineering of motional states of single atoms, and may have wide applications in few body physics and ultracold chemistry.
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Effects of Total-Ionizing-Dose Irradiation on Single-Event Burnout for Commercial Enhancement-Mode AlGaN/GaN High-Electron Mobility Transistors
Si-Yuan Chen, Xin Yu, Wu Lu, Shuai Yao, Xiao-Long Li, Xin Wang, Mo-Han Liu, Shan-Xue Xi, Li-Bin Wang, Jing Sun, Cheng-Fa He, Qi Guo
Chin. Phys. Lett. 2020, 37 (4):
046101
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DOI: 10.1088/0256-307X/37/4/046101
We investigate the synergism effect of total ionizing dose (TID) on single-event burnout (SEB) for commercial enhancement-mode AlGaN/GaN high-electron mobility transistors. Our experimental results show that the slight degradation of devices caused by gamma rays can affect the stability of the devices during the impact of high energy particles. During heavy ion irradiation, the safe working values of drain voltage are significantly reduced for devices which have already been irradiated by $^{60}$Co gamma rays before. This could be attributed to more charges trapped caused by $^{60}$Co gamma rays, which make GaN devices more vulnerable to SEB. Moreover, the electrical parameters of GaN devices after $^{60}$Co gamma and heavy-ion irradiations are presented, such as the output characteristic curve, effective threshold voltages, and leakage current of drain. These results demonstrate that the synergistic effect of TID on SEB for GaN power devices does in fact exist.
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Wettability and Surface Energy of Hydrogen- and Oxygen-Terminated Diamond Films
Zi-Cheng Ma, Nan Gao, Shao-Heng Cheng, Jun-Song Liu, Ming-Chao Yang, Peng Wang, Zhi-Yuan Feng, Qi-Liang Wang, Hong-Dong Li
Chin. Phys. Lett. 2020, 37 (4):
046801
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DOI: 10.1088/0256-307X/37/4/046801
The contact angle and surface energy values of diamond are systemically investigated in terms of surface treatments (hydrogen- and oxygen-terminations), structure feature (single crystal diamonds and polycrystalline diamond films), crystal orientation ((100), (111) and mixed (100)/(111) orientations), different fluids (probes of polar deionized water and nonpolar di-iodomethane). It is found that the hydrophobic/hydrophilic characteristic and surface energy values of diamond are mainly determined by the surface hydrogen/oxygen termination, and less related to the structural features and crystal orientation. Based on the contact angle values with polar water and nonpolar di-iodomethane, the surface energies of diamond are estimated to be about 43 mJ/m$^{2}$ for hydrogen-termination and about 60 mJ/m$^{2}$ for oxygen-termination. Furthermore, the varying surface roughness of diamond and fluids with different polarities examined determine the variation of contact angles as well as the surface energy values. These results would be helpful for a more detailed understanding of the surface properties of diamond films for further applications in a broad number of fields, such as optical and microwave windows, biosensors, and optoelectronic devices, etc.
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Pressure-Induced Metallization and Structural Phase Transition in the Quasi-One-Dimensional TlFeSe$_{2}$
Zi-Yi Liu, Qing-Xin Dong, Peng-Fei Shan, Yi-Yan Wang, Jian-Hong Dai, Rajesh Jana, Ke-Yu Chen, Jian-Ping Sun, Bo-Sen Wang, Xiao-Hui Yu, Guang-Tong Liu, Yoshiya Uwatoko, Yu Sui, Huai-Xin Yang, Gen-Fu Chen, Jin-Guang Cheng
Chin. Phys. Lett. 2020, 37 (4):
047102
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DOI: 10.1088/0256-307X/37/4/047102
We report a comprehensive high-pressure study on the monoclinic TlFeSe$_{2}$ single crystal, which is an antiferromagnetic insulator with quasi-one-dimensional crystal structure at ambient pressure. It is found that TlFeSe$_{2}$ undergoes a pressure-induced structural transformation from the monoclinic phase to an orthorhombic structure above $P_{\rm c} \approx 13$ GPa, accompanied with a large volume collapse of $\Delta V/V_{0}=8.3{\%}$. In the low-pressure monoclinic phase, the insulating state is easily metallized at pressures above 2 GPa; while possible superconductivity with $T_{\rm c}^{\rm onset} \sim 2$ K is found to emerge above 30 GPa in the high-pressure phase. Such a great tunability of TlFeSe$_{2}$ under pressure indicates that the ternary $A$FeSe$_{2}$ system ($A$ = Tl, K, Cs, Rb) should be taken as an important platform for explorations of interesting phenomena such as insulator-metal transition, dimensionality crossover, and superconductivity.
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Metal to Orthogonal Metal Transition
Chuang Chen, Xiao Yan Xu, Yang Qi, Zi Yang Meng
Chin. Phys. Lett. 2020, 37 (4):
047103
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DOI: 10.1088/0256-307X/37/4/047103
Orthogonal metal is a new quantum metallic state that conducts electricity but acquires no Fermi surface (FS) or quasiparticles, and hence orthogonal to the established paradigm of Landau's Fermi-liquid (FL). Such a state may hold the key of understanding the perplexing experimental observations of quantum metals that are beyond FL, i.e., dubbed non-Fermi-liquid (nFL), ranging from the Cu- and Fe-based oxides, heavy fermion compounds to the recently discovered twisted graphene heterostructures. However, to fully understand such an exotic state of matter, at least theoretically, one would like to construct a lattice model and to solve it with unbiased quantum many-body machinery. Here we achieve this goal by designing a 2D lattice model comprised of fermionic and bosonic matter fields coupled with dynamic $\mathbb{Z}_2$ gauge fields, and obtain its exact properties with sign-free quantum Monte Carlo simulations. We find that as the bosonic matter fields become disordered, with the help of deconfinement of the $\mathbb{Z}_2$ gauge fields, the system reacts with changing its nature from the conventional normal metal with an FS to an orthogonal metal of nFL without FS and quasiparticles and yet still responds to magnetic probe like an FL. Such a quantum phase transition from a normal metal to an orthogonal metal, with its electronic and magnetic spectral properties revealed, is calling for the establishment of new paradigm of quantum metals and their transition with conventional ones.
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Negative Magnetoresistance in Antiferromagnetic Topological Insulator EuSn$_2$As$_2$$^{*}$
Huan-Cheng Chen, Zhe-Feng Lou, Yu-Xing Zhou, Qin Chen, Bin-Jie Xu, Shui-Jin Chen, Jian-Hua Du, Jin-Hu Yang, Hang-Dong Wang, Ming-Hu Fang
Chin. Phys. Lett. 2020, 37 (4):
047201
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DOI: 10.1088/0256-307X/37/4/047201
The measurements of magnetization, longitudinal and Hall resistivities are carried out on the intrinsic antiferromagnetic (AFM) topological insulator EuSn$_2$As$_2$. It is confirmed that our EuSn$_2$As$_2$ crystal is a heavily hole doping A-type AFM metal with the Néel temperature $T_{\rm N}$ = 24 K, with a metamagnetic transition from an AFM to a ferromagnetic (FM) phase occurring at a certain critical magnetic field for the different field orientations. Meanwhile, we also find that the carrier concentration does not change with the evolution of magnetic order, indicating that the weak interaction between the localized magnetic moments from Eu$^{2+}$ $4f^7$ orbits and the electronic states near the Fermi level. Although the quantum anomalous Hall effect (AHE) is not observed in our crystals, it is found that a relatively large negative magnetoresistance ($-$13%) emerges in the AFM phase, and exhibits an exponential dependence upon magnetic field, whose microscopic origin is waiting to be clarified in future research.
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Anomalous Hall Effect in Layered Ferrimagnet MnSb$_{2}$Te$_{4}$
Gang Shi, Mingjie Zhang, Dayu Yan, Honglei Feng, Meng Yang, Youguo Shi, Yongqing Li
Chin. Phys. Lett. 2020, 37 (4):
047301
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DOI: 10.1088/0256-307X/37/4/047301
We report on low-temperature electron transport properties of MnSb$_{2}$Te$_{4}$, a candidate of ferrimagnetic Weyl semimetal. Long-range magnetic order is manifested as a nearly square-shaped hysteresis loop in the anomalous Hall resistance, as well as sharp jumps in the magnetoresistance. At temperatures below 4 K, a ${\rm ln}T$-type upturn appears in the temperature dependence of longitudinal resistance, which can be attributed to the electron-electron interaction (EEI), since the weak localization can be excluded by the temperature dependence of magnetoresistance. Although the anomalous Hall resistance exhibits a similar ${\rm ln}T$-type upturn in the same temperature range, such correction is absent in the anomalous Hall conductivity. Our work demonstrates that MnSb$_{2}$Te$_{4}$ microflakes provide an ideal system to test the theory of EEI correction to the anomalous Hall effect.
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High-Pressure Ultrafast Dynamics in Sr$_{2}$IrO$_{4}$: Pressure-Induced Phonon Bottleneck Effect
Yanling Wu, Xia Yin, Jiazila Hasaien, Yang Ding, Jimin Zhao
Chin. Phys. Lett. 2020, 37 (4):
047801
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DOI: 10.1088/0256-307X/37/4/047801
By integrating pump-probe ultrafast spectroscopy with diamond anvil cell (DAC) technique, we demonstrate a time-resolved ultrafast dynamics study on non-equilibrium quasiparticle (QP) states in Sr$_{2}$IrO$_{4}$ under high pressure. On-site in situ condition is realized, where both the sample and DAC have fixed position during the experiment. The QP dynamics exhibits a salient pressure-induced phonon bottleneck feature at 20 GPa, which corresponds to a gap shrinkage in the electronic structure. A structural transition is also observed at 32 GPa. In addition, the slowest relaxation component reveals possible heat diffusion or pressure-controlled local spin fluctuation associated with the gap shrinkage. Our work enables precise pressure dependence investigations of ultrafast dynamics, paving the way for reliable studies of high-pressure excited state physics.
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Chemical Vapor Deposition of Two-Dimensional PbS Nanoplates for Photodetection
Yi-Yi Gu, Yi-Fan Wang, Jing Xia, Xiang-Min Meng
Chin. Phys. Lett. 2020, 37 (4):
048101
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DOI: 10.1088/0256-307X/37/4/048101
Non-layered two-dimensional (2D) lead sulfide (PbS) has attracted growing interest recently due to its direct narrow bandgap (0.4 eV) and broad spectral detection from visible to mid-IR region, which lead to remarkable electronic and optoelectronic properties promising for real applications. We report the chemical vapor deposition growth of highly crystalline 2D PbS crystals on mica substrates. The high quality and uniformity of 2D PbS nanoplates are confirmed by atomic force microscopy, x-ray powder diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy. The morphology and lateral size are controllable by different growth temperatures. Photodetectors made from 2D PbS nanoplates reveal good stability, high photoresponsivity, and fast response time, which indicates their promising applications for ultrathin optoelectronics.
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CH$_{4}$ Gas Extraction by CO$_{2}$: Substitution in Clathrate Hydrate through Bimolecular Iteration
Xiao-Hui Yu, Yuan Liu, San-Ya Du, Xu Zheng, Jin-Long Zhu, Hong-Wu Xu, Jian-Zhong Zhang, Shi-Yu Du, Xiao-Cheng Zeng, J. S. Francisco, Chang-Qing Jin, Yu-Sheng Zhao, Hui Li
Chin. Phys. Lett. 2020, 37 (4):
048201
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DOI: 10.1088/0256-307X/37/4/048201
Methane clathrate hydrate (MCH) is a promising energy resource, but controllable extraction of CH$_{4}$ from MCH remains a challenge. Gradually replacing CH$_{4}$ in MCH with CO$_{2}$ is an attractive scheme, as it is cost efficient and mitigates the environmentally harmful effects of CO$_{2}$ by sequestration. However, the practicable implementation of this method has not yet been achieved. In this study, using in situ neutron diffraction, we confirm that CH$_{4}$ in the 5$^{12}6^{2}$ cages of bulk structure-I (sI) MCH can be substituted by gaseous CO$_{2}$ under high pressure and low temperature with a high substitution ratio ($\sim $44%) while conserving the structure of the hydrate framework. First-principles calculations indicate that CO$_{2}$ binds more strongly to the 5$^{12}6^{2}$ cages than methane does, and that the diffusion barrier for CH$_{4}$ is significantly lowered by an intermediate state in which one hydrate cage is doubly occupied by CH$_{4}$ and CO$_{2}$. Therefore, exchange of CO$_{2}$ for CH$_{4}$ in MCH is not only energetically favorable but also kinetically feasible. Experimental and theoretical studies of CH$_{4}$/CO$_{2}$ substitution elucidate a method to harness energy from these combustible ice resources.
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31 articles
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