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Tuning the Water Desalination Performance of Graphenic Layered Nanomaterials by Element Doping and Inter-Layer Spacing
Fuxin Wang, Chao Zhang, Yanmei Yang, Yuanyuan Qu, Yong-Qiang Li, Baoyuan Man, and Weifeng Li
Chin. Phys. Lett.    2020, 37 (11): 116101 .   DOI: 10.1088/0256-307X/37/11/116101
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Through atomic molecular dynamics simulations, we investigate the performance of two graphenic materials, boron (BC$_{3}$) and nitrogen doped graphene (C$_{3}$N), for seawater desalination and salt rejection, and take pristine graphene as a control. Effects of inter-layer separation have been explored. When water is filtered along the transverse directions of three-layered nanomaterials, the optimal inter-layer separation is 0.7–0.9 nm, which results in high water permeability and salt obstruction capability. The water permeability is considerably higher than porous graphene filter, and is about two orders of magnitude higher than commercial reverse osmosis (RO) membrane. By changing the inter-layer spacing, the water permeability of three graphenic layered nanomaterials follows an order of C$_{3}$N $\ge$ GRA $>$ BC$_{3}$ under the same working conditions. Amongst three nanomaterials, BC$_{3}$ is more sensitive to inter-layer separation which offers a possibility to control the water desalination speed by mechanically changing the membrane thickness. This is caused by the intrinsic charge transfer inside BC$_{3}$ that results in periodic distributed water clusters around the layer surface. Our present results reveal the high potentiality of multi-layered graphenic materials for controlled water desalination. It is hopeful that the present work can guide design and fabrication of highly efficient and tunable desalination architectures.
Shear-Banding Evolution Dynamics during High Temperature Compression of Martensitic Ti-6Al-4V Alloy
Xue-Hua Zhang, Rong Li, Yong-Qing Zhao, and Wei-Dong Zeng
Chin. Phys. Lett.    2020, 37 (11): 116201 .   DOI: 10.1088/0256-307X/37/11/116201
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The isothermal compression dynamics of ternary Ti-6Al-4V alloy with initial martensitic structures were investigated in the high temperature range 1083–1173 K and moderate strain rate regime 0.01–10 s$^{-1}$. Shear banding was found to still dominate the deformation mechanism of this process, despite its nonadiabatic feature. The constitutive equation was derived with the aid of Zener–Hollomon parameter, which predicted the apparent activation energy as 534.39 kJ/mol. A combination of higher deformation temperature and lower strain rate suppressed the peak flow stress and promoted the evolution of shear bands. Both experiments and calculations demonstrated that a conspicuous temperature rise up to 83 K could be induced by severe plastic deformation. This facilitated the dynamic recrystallization of deformed martensites, as evidenced by the measured microhardness profiles across shear bands.
Molecular Dynamics Simulations of the Interface between Porous and Fused Silica
Ye Tian, Xiaodong Yuan , Dongxia Hu , Wanguo Zheng , and Wei Han 
Chin. Phys. Lett.    2020, 37 (10): 106101 .   DOI: 10.1088/0256-307X/37/10/106101
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Molecular dynamics simulations are performed to gain insights into the structural and vibrational properties of interface between porous and fused silica. The Si–O bonds formed in the interface exhibit the same lengths as the bulk material, whereas the coordination defects in the interface are at an intermediate level as compared with the dense and porous structures. Clustered bonds are identified from the interface, which are associated with the reorganization of the silica surface. The bond angle distributions show that the O–Si–O bond angles keep the average value of 109$^{\circ}$, whereas the Si–O–Si angles of the interface present in a similar manner to those in porous silica. Despite the slight structural differences, similarities in the vibrations are observed, which could further demonstrate the stability of porous silica films coated on the fused silica.
Structural Domain Imaging and Direct Determination of Crystallographic Orientation in Noncentrosymmetric Ca$_{3}$Ru$_{2}$O$_{7}$ Using Polarized Light Reflectance
Guoxiong Tang, Libin Wen, Hui Xing, Wenjie Liu, Jin Peng, Yu Wang, Yupeng Li, Baijiang Lv, Yusen Yang, Chao Yao, Yueshen Wu, Hong Sun, Zhu-An Xu, Zhiqiang Mao, and Ying Liu
Chin. Phys. Lett.    2020, 37 (10): 106102 .   DOI: 10.1088/0256-307X/37/10/106102
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The noncentrosymmetricity of a prototypical correlated electron system Ca$_{3}$Ru$_{2}$O$_{7}$ renders extensive interest in the possible polar metallic state, along with multiple other closely competing interactions. However, the structural domain formation in this material often complicates the study of intrinsic material properties. It is crucial to fully characterize the structural domains for unrevealing underlying physics. Here, we report the domain imaging on Ca$_{3}$Ru$_{2}$O$_{7}$ crystal using the reflection of polarized light at normal incidence. The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal, and gives rise to a peculiar contrast. The domain walls are found to be the interfaces between 90$^{\circ}$ rotated twin crystals by complementary magnetization measurements. A distinct contrast in reflectance is also found in the opposite cleavage surfaces, owing to the polar mode of the RuO$_{6}$ octahedra. More importantly, the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain. Such an approach provides an efficient yet feasible method for structural domain characterization, which can also find applications in noncentrosymmetric crystals in general.
Effect of B-Site Ordering on the Magnetic Order in Multifunctional La$_{2}$NiMnO$_{6}$ Double Perovskite
Dexin Yang, Rui Jiang, Yaohua Zhang, Hui Zhang, Senlin Lei, Tao Yang, Xiaoshi Hu, Shuai Huang, Jingyuan Ge, Kunpeng Su, Haiou Wang, and Dexuan Huo
Chin. Phys. Lett.    2020, 37 (10): 106201 .   DOI: 10.1088/0256-307X/37/10/106201
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To obtain various Ni/Mn orderings, we use a low-temperature synthesized method to modulate the Ni/Mn ordering of the ferromagnetic-ferroelastic La$_{2}$NiMnO$_{6}$ compound, and the Ni/Mn ordering is estimated by the low-temperature saturation magnetism. The microstructures, crystal structures and magnetic properties are investigated, and the Landau theory are used to describe the form and magnitude of the coupling effects between Ni/Mn ordering and magnetic order parameters. It is predicted that the Ni/Mn ordering would be a strong coupling effect with the Curie transition temperatures if the La$_{2}$NiMnO$_{6}$ sample stoichiometry is close.
Diffraction-Limited Imaging with a Graphene Metalens
Xueyan Li, Han Lin, Yuejin Zhao, and Baohua Jia
Chin. Phys. Lett.    2020, 37 (10): 106801 .   DOI: 10.1088/0256-307X/37/10/106801
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Planar graphene metalens has demonstrated advantages of ultrathin thickness (200 nm), high focusing resolution (343 nm) and efficiency ($>$32%) and robust mechanical strength and flexibility. However, diffraction-limited imaging with such a graphene metalens has not been realized, which holds the key to designing practical integrated imaging systems. In this work, the imaging rule for graphene metalenses is first derived and theoretically verified by using the Rayleigh-Sommerfeld diffraction theory to simulate the imaging performance of the 200 nm ultrathin graphene metalens. The imaging rule is applicable to graphene metalenses in different immersion media, including water or oil. Based on the theoretical prediction, high-resolution imaging using the graphene metalens with diffraction-limited resolution (500 nm) is demonstrated for the first time. This work opens the possibility for graphene metalenses to be applied in particle tracking, microfluidic chips and biomedical devices.
Controllable Modulation to Quantum Well States on $\beta$-Sn Islands
Ze-Rui Wang, Chen-Xiao Zhao, Guan-Yong Wang, Jin Qin, Bing Xia, Bo Yang, Dan-dan Guan, Shi-Yong Wang, Hao Zheng, Yao-Yi Li, Can-hua Liu, and Jin-Feng Jia
Chin. Phys. Lett.    2020, 37 (9): 096801 .   DOI: 10.1088/0256-307X/37/9/096801
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We investigate the surface structure and electronic properties of $\beta$-Sn islands deposited on a graphitized 6H-SiC (0001) substrate via low temperature scanning tunneling microscopy and spectroscopy. Owing to the confinement of the island geometry, quantum well states (QWSs) are formed, manifesting as equidistant peaks in the tunneling spectra. Furthermore, a distinct strip feature appears on the surfaces of odd-layer Sn islands, ranging from 15–19 layers, which is not present on the surfaces of even-layer Sn islands. The spatial distribution of strips can be modified by applying a bias pulse, using an STM tip. Furthermore, the strip-like structure shows significant impacts on the QWS. An energy splitting of the lowest unoccupied QWSs is observed in strip regions; this may be ascribed to caused the phase shift of the wave functions of the QWSs on the top surface, due to surface distortions created by the aforementioned strips.
Directly Determining the Interface Structure and Band Offset of a Large-Lattice-Mismatched CdS/CdTe Heterostructure
Quanyin Tang, Ji-Hui Yang, Zhi-Pan Liu, and Xin-Gao Gong
Chin. Phys. Lett.    2020, 37 (9): 096802 .   DOI: 10.1088/0256-307X/37/9/096802
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The CdS/CdTe heterojunction plays an important role in determining the energy conversion efficiency of CdTe solar cells. However, the interface structure remains unknown, due to the large lattice mismatch between CdS and CdTe, posing great challenges to achieving an understanding of its interfacial effects. By combining a neural-network-based machine-learning method and the stochastic surface walking-based global optimization method, we first train a neural network potential for CdSTe systems with demonstrated robustness and reliability. Based on the above potential, we then use simulated annealing to obtain the optimal structure of the CdS/CdTe interface. We find that the most stable structure has the features of both bulks and disorders. Using the obtained structure, we directly calculate the band offset between CdS and CdTe by aligning the core levels in the heterostructure with those in the bulks, using one-shot first-principles calculations. Our calculated band offset is 0.55 eV, in comparison with 0.70 eV, obtained using other indirect methods. The obtained interface structure should prove useful for further study of the properties of CdTe/CdS heterostructures. Our work also presents an example which is applicable to other complex interfaces.
Regular Arrangement of Two-Dimensional Clusters of Blue Phosphorene on Ag(111)
Shuo Yang, Zhenpeng Hu, Weihai Wang, Peng Cheng, Lan Chen, and Kehui Wu
Chin. Phys. Lett.    2020, 37 (9): 096803 .   DOI: 10.1088/0256-307X/37/9/096803
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Two-dimensional (2D) blue phosphorene with a honeycomb structure is the phosphorus analog of graphene, and is regarded as a promising 2D material with a large tunable band gap and high charge-carrier mobility. Here, using the molecular beam epitaxy method, we synthesize monolayer blue phosphorene on the Ag(111) surface. Combined with first-principles calculations, scanning tunneling microscopy measurements reveal that the blue phosphorene on the Ag(111) surface consists of 2D clusters with a buckling $1\times 1$ lattice, arranged regularly on the Ag(111). The formation of these phosphorus clusters stems from the strain modulation induced by the lattice mismatch between blue phosphorene and the Ag(111) substrate. Moreover, x-ray photoelectron spectroscopy measurements are performed to study the instability of the blue phosphorene clusters in air. The realization of regular nanoclusters of blue phosphorene with unique sizes and morphology provides an ideal platform for the exploration of the quantum physical properties and applications of blue phosphorene.
Coupling between Particle Shape and Long-Range Interaction in the High-Density Regime
Can-can Zhou, Hongchuan Shen, Hua Tong, Ning Xu, and Peng Tan
Chin. Phys. Lett.    2020, 37 (8): 086301 .   DOI: 10.1088/0256-307X/37/8/086301
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We experimentally probe the coupling between particle shape and long-range interaction, using long-range interacting polygons. For two typical space-filling polygons, square and triangle, we find two types of coupling modes that predominantly control the structure formation. Specifically, the rotational ordering of squares brings a lattice deformation that produces a hexagonal-to-rhombic transition in the high density regime, whereas the alignment of triangles introduces a large geometric frustration that causes an order-to-disorder transition. Moreover, the two coupling modes lead to small and large “internal roughness” of the two systems, and thus predominantly control their structure relaxations. Our study thus provides a physical picture to the coupling between long-range interaction effect and short-range shape effect in the high-density regime unexplored before.
A New Cu-Based Metallic Glass Composite with Excellent Mechanical Properties
Dong-Mei Li, Lan-Sheng Chen, Peng Yu, Ding Ding, and Lei Xia
Chin. Phys. Lett.    2020, 37 (8): 086401 .   DOI: 10.1088/0256-307X/37/8/086401
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A new Cu-based bulk metallic glass composite of nominal composition (at.%) Cu$_{41}$Ni$_{27}$Ti$_{25}$Al$_{7}$ with excellent plasticity and a strong work-hardening behavior is fabricated. Strength above 1859 MPa and plasticity more than 11% are achieved under compression and tension modes. The deformation mechanism is proposed to the structural heterogeneities of the composite that promotes multiple shear bands meanwhile inhibits their free propagation, which results in the macroscopically plastic strain and work hardening. The alloy contains relatively cheap metals and has a low cost, which is beneficial to industrial applications.
Large Barocaloric Effect with High Pressure-Driving Efficiency in a Hexagonal MnNi$_{0.77}$Fe$_{0.23}$Ge Alloy
Qingqi Zeng, Jianlei Shen, Enke Liu, Xuekui Xi, Wenhong Wang, Guangheng Wu, and Xixiang Zhang
Chin. Phys. Lett.    2020, 37 (7): 076101 .   DOI: 10.1088/0256-307X/37/7/076101
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The hydrostatic pressure is expected to be an effective knob to tune the magnetostructural phase transitions of hexagonal MM'X alloys (M and M' denote transition metals and X represents main group elements). We perform magnetization measurements under hydrostatic pressure on an MM'X martensitic MnNi$_{0.77}$Fe$_{0.23}$Ge alloy. The magnetostructural transition temperature can be efficiently tuned to lower temperatures by applying moderate pressures, with a giant shift rate of $-151$ K/GPa. A temperature span of 30 K is obtained under the pressure, within which a large magnetic entropy change of $-23$ J$\cdot$kg$^{-1}$K$^{-1}$ in a field change of 5 T is induced by the mechanical energy gain due to the large volume change. Meanwhile, a decoupling of structural and magnetic transitions is observed at low temperatures when the martensitic transition temperature is lower than the Curie temperature. These results show a multi-parameter tunable caloric effect that benefits the solid-state cooling.
Comparison of Cavities Formed in Single Crystalline and Polycrystalline $\alpha$-SiC after H Implantation
Qing Liao, Long Kang, Tong-Min Zhang, Hui-Ping Liu, Tao Wang, Xiao-Gang Li, Jin-Yu Li, Zhen Yang, and Bing-Sheng Li
Chin. Phys. Lett.    2020, 37 (7): 076102 .   DOI: 10.1088/0256-307X/37/7/076102
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Cavities and extended defects formed in single crystalline and polycrystalline $\alpha$-SiC implanted with H$^{+}$ ions are compared. The samples are investigated by cross-sectional transmission electron microscopy. H$_{2}$ bubbles are formed during H implantation and H$_{2}$ molecules escape the sample to form cavities during thermal annealing at 1100℃. Microcracks and the extended defects prefer to nucleate in single crystalline $\alpha$-SiC, but not polycrystalline $\alpha$-SiC. Grain boundaries can account for the experimental results. The formation of cavities on grain boundaries is investigated.
Pressure Effects on the Transport and Structural Properties of Metallic Glass-Forming Liquid
Qi-Long Cao, Duo-Hui Huang , Jun-Sheng Yang , and Fan-Hou Wang 
Chin. Phys. Lett.    2020, 37 (7): 076201 .   DOI: 10.1088/0256-307X/37/7/076201
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Transport and structural properties of metallic glass-forming liquid Cu$_{50}$Zr$_{50}$ are investigated by molecular dynamics simulation, under high pressures from 1 bar to 70 GPa. The following results have been obtained: (i) reversals of component diffusion coefficients ($D_{\rm Cu}$ and $D_{\rm Zr}$) are observed at the reversion pressure. At low pressures below the reversion pressure, $D_{\rm Cu}/D_{\rm Zr}$ decreases from about 1.4 to 1.0. At high pressures above the reversion pressure, $D_{\rm Cu}/D_{\rm Zr}$ decreases more rapidly from 1.0 to about 0.7. (ii) Component diffusion coefficients decay exponentially with pressure up to reversion pressure, then the strength of the exponential dependence changes, while the pressure-dependent behavior of viscosity can be well described by a single exponential relation over the full range of pressure. (iii) The Stokes–Einstein relation (SER) works well at low pressures and starts to be violated at the breakdown pressure. For glass-forming liquid Cu$_{50}$Zr$_{50}$ along the 2000 K isotherm, the breakdown pressure equals the reversion pressure of component diffusion coefficients and is about 35 GPa. (iv) The pressure dependences of the ratio between component diffusion coefficients can be used to predict the breakdown pressure of SER along isotherm. The validity of SER and the reversals of component diffusion coefficients are found to be related to the pressure dependence of the relative total fractions of predominant Voronoi polyhedrons around individual components.
Possible Tricritical Behavior and Anomalous Lattice Softening in van der Waals Itinerant Ferromagnet Fe$_{3}$GeTe$_{2}$ under High Pressure
Jie-Min Xu, Shu-Yang Wang, Wen-Jun Wang, Yong-Hui Zhou, Xu-Liang Chen, Zhao-Rong Yang, and Zhe Qu
Chin. Phys. Lett.    2020, 37 (7): 076202 .   DOI: 10.1088/0256-307X/37/7/076202
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We present a high-pressure study of van der Waals ferromagnetic metal Fe$_{3}$GeTe$_{2}$ through electrical transport and Raman scattering measurements in diamond anvil cells at pressures up to 22.4 GPa. Upon compression, the ferromagnetic transition temperature $T_{\rm c}$ manifested by a kink in resistance curve decreases monotonically and becomes undiscernable around $P_{\rm c} = 10$ GPa, indicative of suppression of the itinerant ferromagnetism. Meanwhile, by fitting the low temperature resistance to the Fermi liquid behavior of $R =R_{0} + AT^{2}$, we found that $R_{0}$ shows a cusp-like anomaly and the coefficient $A$ diverges around $P_{\rm c}$. These transport anomalies imply a tricritical point as commonly observed in itinerant ferromagnets under pressure. Unexpectedly, the Raman-active $E_{2g}$ and $A_{1g}$ modes soften remarkably after an initial weak hardening and the peak widths of both modes broaden evidently on approaching $P_{\rm c}$, followed by complete disappearance of both modes above this critical pressure. A possible underlying mechanism for such anomalous lattice softening near $P_{\rm c}$ is discussed.
Synthesis of Highly Stable One-Dimensional Black Phosphorus/h-BN Heterostructures: A Novel Flexible Electronic Platform
Jingyan Song, Shuai Duan, Xin Chen, Xiangjun Li , Bingchao Yang , and Xiaobing Liu
Chin. Phys. Lett.    2020, 37 (7): 076203 .   DOI: 10.1088/0256-307X/37/7/076203
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Layered black phosphorus (BP) has recently emerged as a promising semiconductor because of its tunable band gap, high carrier mobility and strongly in-plane anisotropic properties. One-dimensional (1D) BP materials are attractive for applications in electronic and thermal devices, owing to their tailored charge and phonon transports along certain orientations. However, the fabrication of 1D BP materials still remains elusive thus far. We herein report the successful synthesis and characterization of nanotube-like BP for the first time by a selective composite with hexagonal boron nitride (h-BN) nanotubes under high pressure and high temperature conditions. The produced 1D BP/h-BN composites possess flexible diameter, length and thickness by adjusting the experimental synthesis parameters. Interestingly, it is important to notice that the stability of our BP sample has been significantly improved under the formation of heterostructures, which can actively promote their commercial applications. Our experimental work, together with first-principles calculations, presents a new scalable strategy of designing 1D tube-like BP/h-BN heterostructures that are promising candidates for flexible and high efficiency electronic platform.
Theoretical Simulation of the Temporal Behavior of Bragg Diffraction Derived from Lattice Deformation
Cong Guo, Shuai-Shuai Sun, Lin-Lin Wei, Huan-Fang Tian, Huai-Xin Yang, Shu Gao, Yuan Tan, and Jian-Qi Li
Chin. Phys. Lett.    2020, 37 (7): 076301 .   DOI: 10.1088/0256-307X/37/7/076301
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A theoretical study on the structural dynamics of the temporal behavior of Bragg diffraction is presented and compared with experimental results obtained via ultrafast electron crystallography. In order to describe the time-dependent lattices and calculate the Bragg diffraction intensity, we introduce the basic vector offset matrix, which can be used to quantify the shortening, lengthening and rotation of the three lattice vectors (i.e., lattice deformation). Extensive simulations are performed to evaluate the four-dimensional electron crystallography model. The results elucidate the connection between structural deformations and changes in diffraction peaks, and sheds light on the quantitative analysis and comprehensive understanding of the structural dynamics.
Quantum Droplets in a Mixture of Bose–Fermi Superfluids
Jing-Bo Wang, Jian-Song Pan, Xiaoling Cui, and Wei Yi
Chin. Phys. Lett.    2020, 37 (7): 076701 .   DOI: 10.1088/0256-307X/37/7/076701
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We study the formation of quantum droplets in the mixture of a single-component Bose–Einstein condensate (BEC), and a two-species Fermi superfluid across a wide Feshbach resonance. With repulsive boson-boson and attractive boson-fermion interactions, we show that quantum droplets can be stabilized by attractive fermion-fermion interactions on the Bardeen–Cooper–Schrieffer (BCS) side of the resonance, and can also exist in the deep BEC regime under weak boson-fermion interactions. We map out the phase diagram for stable droplets with respect to the boson-boson and boson-fermion interactions, and discuss the role of different types of quantum fluctuations in the relevant regions of the BCS-BEC crossover. Our work reveals the impact of fermion pairing on the formation of quantum droplets in Bose–Fermi mixtures, and provides a useful guide for future experiments.
Ultrathin Al Oxide Seed Layer for Atomic Layer Deposition of High-$\kappa$ Al$_{2}$O$_{3}$ Dielectrics on Graphene
Hang Yang, Wei Chen, Ming-Yang Li, Feng Xiong, Guang Wang, Sen Zhang, Chu-Yun Deng, Gang Peng, and Shi-Qiao Qin
Chin. Phys. Lett.    2020, 37 (7): 076801 .   DOI: 10.1088/0256-307X/37/7/076801
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Due to the lack of surface dangling bonds in graphene, the direct growth of high-$\kappa$ films via atomic layer deposition (ALD) technique often produces the dielectrics with a poor quality, which hinders its integration in modern semiconductor industry. Previous pretreatment approaches, such as chemical functionalization with ozone and plasma treatments, would inevitably degrade the quality of the underlying graphene. Here, we tackled this problem by utilizing an effective and convenient physical method. In detail, the graphene surface was pretreated with the deposition of thermally evaporated ultrathin Al metal layer prior to the Al$_{2}$O$_{3}$ growth by ALD. Then the device was placed in a drying oven for 30 min to be naturally oxidized as a seed layer. With the assistance of an Al oxide seed layer, pinhole-free Al$_{2}$O$_{3}$ dielectrics growth on graphene was achieved. No detective defects or disorders were introduced into graphene by Raman characterization. Moreover, our fabricated graphene top-gated field effect transistor exhibited high mobility ($\sim $6200 cm$^{2}$V$^{-1}$s$^{-1}$) and high transconductance ($\sim $117 μS). Thin dielectrics demonstrated a relative permittivity of 6.5 over a large area and a leakage current less than 1.6 pA/μm$^{2}$. These results indicate that Al oxide functionalization is a promising pathway to achieve scaled gate dielectrics on graphene with high performance.
Velocity and Stability of Condensed Polymorphic SiH$_{4}$: A High-Temperature High-Pressure Brillouin Investigation
Jiayu Wang , Qiang Zhou , Siyang Guo , Yanping Huang , Xiaoli Huang , Lu Wang, Fangfei Li, Tian Cui 
Chin. Phys. Lett.    2020, 37 (6): 066201 .   DOI: 10.1088/0256-307X/37/6/066201
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Silane (SiH$_{4}$) is a promising hydrogen-rich compound for pursing high temperature superconducting. Previous high pressure measurements of Raman, x-ray diffraction and theoretical studies on SiH$_{4}$ mainly focused on its polymorphic structures above 50 GPa, while the structure and the stability