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  《npj 计算材料学》是在线出版、完全开放获取的国际学术期刊。发表结合计算模拟与设计的材料学一流的研究成果。本刊由中国科学院上海硅酸盐研究所与英国自然出版集团(Nature Publishing Group,NPG)以伙伴关系合作出版。
  主编为陈龙庆博士,美国宾州大学材料科学与工程系、工程科学与力学系、数学系的杰出教授。
  共同主编为陈立东研究员,中国科学院上海硅酸盐研究所研究员高性能陶瓷与超微结构国家重点实验室主任。
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  《npj 计算材料学》是在线出版、完全开放获取的国际...
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Nanomaterials: A semiconductor with an enhanced signature(新型半导体纳米材料,让待检分子的拉曼信号放大)
Yufeng Shan, Zhihui Zheng, Jianjun Liu, Yong Yang, Zhiyuan Li, Zhengren Huang & Dongliang Jiang
npj Computational Materials
 3, Article number: 11 (2017)
doi:10.1038/s41524-017-0008-0
Published online:15 March 2017
Abstract| Full Text | PDF OPEN
摘要:表面增强拉曼光谱(SERS)是一种强大的高灵敏分析技术,它可以探测和分析物质表层所吸附的分子数量。目前仅限少数几种贵金属纳米结构能够产生如此强度的SERS效应,极大地限制了这一技术的应用。半导体SERS材料可以克服贵金属衬底的一些缺点,有望使得SERS技术在表面科学、光谱和生物医药领域得到进一步应用;但是其探测灵敏度及信号增强效果均受制于半导体衬底较弱的SERS活性。本研究报道了一种新型半导体SERS活性衬底材料Nb2O5,可以高灵敏度地检测染料分子。其在633780nm激光激发下,探测亚甲基蓝染料的SERS增强因子高达107以上,是目前发现的灵敏度最高的半导体衬底材料,甚至可以和具有热点效应的金属纳米结构衬底相媲美。通过密度泛函理论和有限元计算表明,Nb2O5如此之高的SERS活性可以归因于光诱导电荷转移的化学增强机制和电磁场增强机制的叠加作用。在分子Nb2O5体系中,Nb2O5和表面吸附的染料分子,共同产生了新的分子最高占据轨道和最低未占据轨道,因此在长波长的激发光下,电子仍能够轻易跃迁。除此之外,电磁增强也为增强因子贡献了两个数量级。本研究表明,Nb2O5纳米粒子有望作为一种新型半导体SERS材料,取代贵金属,在生物相关领域发挥其巨大应用潜力。 

Abstract: Surface-enhanced Raman scattering technique, as a powerful tool to identify the molecular species, has been severely restricted to the noble metals. The surface-enhanced Raman scattering substrates based on semiconductors would overcome the shortcomings of metal substrates and promote development of surface-enhanced Raman scattering technique in surface science, spectroscopy, and biomedicine studies. However, the detection sensitivity and enhancement effects of semiconductor substrates are suffering from their weak activities. In this work, a semiconductor based on Nb2O5 is reported as a new candidate for highly sensitive surface-enhanced Raman scattering detection of dye molecules. The largest enhancement factor value greater than 107 was observed with the laser excitation at 633 and 780 nm for methylene blue detection. As far as literature review shows, this is in the rank of the highest sensitivity among semiconductor materials; even comparable to the metal nanostructure substrates with “hot spots”. The impressive surface-enhanced Raman scattering activities can be attributed to the chemical enhancement dominated by the photo-induced charge transfer, as well as the electromagnetic enhancement, which have been supported by the density-functional-theory and finite element method calculation results. The chemisorption of dye on Nb2O5 creates a new highest occupied molecular orbital and lowest unoccupied molecular orbital contributed by both fragments in the molecule-Nb2O5 system, which makes the charge transfer more feasible with longer excitation wavelength. In addition, the electromagnetic enhancement mechanism also accounts for two orders of magnitude enhancement in the overall enhancement factor value. This work has revealed Nb2O5 nanoparticles as a new semiconductor surface-enhanced Raman scattering substrate that is able to replace noble metals and shows great potentials applied in the fields of biology related. 

Editorial Summary   

中国科学家新近发现了一种能检测痕量生物小分子的新型半导体材料。来自中国科学院上海硅酸盐研究所的杨勇、黄政仁等,发现Nb2O5可以显著增强生物医药领域染料分子的拉曼信号。粗糙衬底上的纳米尺寸效应能增加光场,利用这种增强的光信号来检测特定分子的技术叫表面增强拉曼光谱(SERS)技术。但只有少数几种贵金属材料(如金、银)才能将信号强度提高到实用水平。杨勇等发现了一种目前SERS活性最强的半导体衬底材料,氧化铌纳米晶,可以高灵敏检测亚甲基蓝、甲基紫以及甲基蓝等染料分子。他们在检测亚甲基蓝染料时发现,在633780 nm光激发下,拉曼信号增强了107倍以上。   

A semiconductor that makes recognizing molecules easier is identified by researchers in China. Yong Yang and co-workers from the Shanghai Institute of Ceramics show that niobium pentoxide can strongly enhance the optical signature of the colored dyes used in biomedical applications. Nanometer-sized features on a rough surface can increase optical fields. This phenomenon can enhance the optical signature used to identify a specific molecule in a technique called surface-enhanced Raman spectroscopy (SERS).But only a few materials, notably noble metals such as gold and silver, have demonstrated useful levels of enhancement. Yang et al. find that niobium pentoxide nanoparticles can be used as a most-active SERS semiconductor substrate to detect the dyes methylene blue, methyl violet and methyl blue. They measured a SERS enhancement factor of over ten million using 633 and 780 nano meter light to detect methylene blue.

Mechanical properties of Fe-rich Si alloy from Hamiltonian 用哈密尔顿计算揭示富Fe硅合金的力学性能 
Tetsuo Mohri, Ying Chen, Masanori Kohyama, Shigenobu Ogata, Arkapol Saengdeejing, Somesh Kumar Bhattacharya, Masato Wakeda, Shuhei Shinzato & Hajime Kimizuka
npj Computational Materials 3, Article number: 10 (2017)
doi:10.1038/s41524-017-0012-4
Published online:10 March 2017
Abstract| Full Text | PDF OPEN

摘要:本文结合电子结构计算和统计力学手段(如团族变分方法、分子动力学模拟等),对富Fe硅合金力学性能的内在物理机制问题作了研究,其中团族变分方法、分子动力学模拟用来计算均相和多相系统。首先在均相系统中运用电子结构计算来研究弹性性能,并将Si含量增加时延展性损失的内在物理机制,归因于磁体积和D03排序的组合效应。本文以形成微结构的多相性作为典型实例,重点关注了晶界,并通过高精度电子结构计算研究了Si原子的偏析行为。找到了两种分离位点,即松散位点和紧密位点,发现二者的分离机制因场所而异。最后,本文主要通过电子结构计算,结合分子动力学模拟,对Fe-Si合金中的位错行为进行了研究。以处于螺旋位错线上的扭结成核和迁移的两种能垒,对固溶硬化和软化作了解释。此外,基于动力学蒙特卡罗模拟(KMC),本文还关注了扭结成核触发的滑移面优先选择,讨论了特定加工硬化行为的线索。 

Abstract: The physical origins of the mechanical properties of Fe-rich Si alloys are investigated by combining electronic structure calculations with statistical mechanics means such as the cluster variation method, molecular dynamics simulation, etc, applied to homogeneous and heterogeneous systems. Firstly, we examined the elastic properties based on electronic structure calculations in a homogeneous system and attributed the physical origin of the loss of ductility with increasing Si content to the combined effects of magneto-volume and D03 ordering. As a typical example of a heterogeneity forming a microstructure, we focus on grain boundaries, and segregation behavior of Si atoms is studied through high-precision electronic structure calculations. Two kinds of segregation sites are identified: looser and tighter sites. Depending on the site, different segregation mechanisms are revealed. Finally, the dislocation behavior in the Fe–Si alloy is investigated mainly by molecular dynamics simulations combined with electronic structure calculations. The solid-solution hardening and softening are interpreted in terms of two kinds of energy barriers for kink nucleation and migration on a screw dislocation line. Furthermore, the clue to the peculiar work hardening behavior is discussed based on kinetic Monte Carlo simulations by focusing on the preferential selection of slip planes triggered by kink nucleation. 

Computational modeling sheds light on structural evolution in metallic glasses and supercooled liquids(计算模拟揭示了金属玻璃和过冷液体的结构演化)
Jun Ding & En Ma
npj Computational Materials 3, Article number: 9 (2017)
doi:10.1038/s41524-017-0007-1
Published online:01 March 2017
Abstract| Full Text | PDF OPEN

摘要:本文概述了目前金属玻璃及其母体过冷液体中无定形结构的演变,涉及该领域三大挑战性问题,重点介绍了近来通过计算分析得出、并有实验结果支持的重要见解。第一个问题是,用局部结构顺序作为指标,尤其用过冷期间局部结构顺序的演化作为指标,来解释实验观察到的粘度随温度的变化,从而提出液体脆性结构可能的起源。第二个问题涉及金属熔体的平均最近-相邻距离在受热时收缩而不是膨胀,并伴有配位数减少的问题。然而,这一看法的依据是分布函数的第一峰最大值的偏移,以及用距离截止指定的最近邻域法确定的平均键长。可是这一现象也可以是相邻原子不对称分布受热恶化时,加宽的第一峰偏斜的结果,因为这些相邻原子可以在非谐性原子间相互作用电位下受激活后移动较短和较长距离。第三个问题涉及金属玻璃的配对分布函数中,类晶体峰值位置。这些峰值位置可以用配位多面体的各种连接方案来解释,并可在亦已存在的无隐藏晶体顺序的高温液体中找到。本文还指出了该领域的发展方向,并呼吁对该领域开展更深入的计算研究,以期最终建立更强的非晶合金的结构-性能关系。   

Abstract: This article presents an overview of three challenging issues that are currently being debated in the community researching on the evolution of amorphous structures in metallic glasses and their parent supercooled liquids. Our emphasis is on the valuable insights acquired in recent computational analyses that have supplemented experimental investigations. The first idea is to use the local structural order developed, and in particular its evolution during undercooling, as a signature indicator to rationalize the experimentally observed temperature-dependence of viscosity, hence suggesting a possible structural origin of liquid fragility. The second issue concerns with the claim that the average nearest-neighbor distance in metallic melts contracts rather than expands upon heating, concurrent with a reduced coordination number. This postulate is, however, based on the shift of the first peak maximum in the pair distribution function and an average bond length determined from nearest neighbors designated using a distance cutoff. These can instead be a result of increasing skewness of the broad first peak, upon thermally exacerbated asymmetric distribution of neighboring atoms activated to shorter and longer distances under the anharmonic interatomic interaction potential. The third topic deals with crystal-like peak positions in the pair distribution function of metallic glasses. These peak locations can be explained using various connection schemes of coordination polyhedra, and found to be present already in high-temperature liquids without hidden crystal order. We also present an outlook to invite more in-depth computational research to fully settle these issues in future, and to establish more robust structure-property relations in amorphous alloys. 

Effective mass and Fermi surface complexity factor from ab initio band structure calculations (基于第一性原理能带计算的有效质量和费米表面复杂因子)
Zachary M. Gibbs, Francesco Ricci, Guodong Li, Hong Zhu, Kristin Persson, Gerbrand Ceder, Geoffroy Hautier, Anubhav Jain & G. Jeffrey Snyder
npj Computational Materials 3, Article number: 8 (2017)
doi:10.1038/s41524-017-0013-3
Published online:23 February 2017
Abstract| Full Text | PDF OPEN
 

 

摘要:有效质量是电子带结构方便的描述参量,可用于表征自由电子模型的态密度和电子传输特征。虽然有效质量在实际系统中是优良的一阶描述参量,但其精确值有不同的定义,每种可描述电子传输的某方面特征。本研究基于第一性原理开展了玻尔兹曼运输计算,不考虑确切的散射机制,而从塞贝克系数提取态密度有效质量、从电导率提取惯性质量来表征带结构。我们以这两个质量比值确定了费米表面复杂性因子,即Nv * K *,在简单体系中它取决于费米表面袋的数量(N v *)及体系的各向异性K *,这两方面都有利于提高热电性能,如热电材料PbTe就具有较高的费米表面复杂性因子值。费米表面复杂性因子可用于高通量搜索有前景的热电材料。  

Abstract: The effective mass is a convenient descriptor of the electronic band structure used to characterize the density of states and electron transport based on a free electron model. While effective mass is an excellent first-order descriptor in real systems, the exact value can have several definitions, each of which describe a different aspect of electron transport. Here we use Boltzmann transport calculations applied to ab initio band structures to extract a density-of-states effective mass from the Seebeck Coefficient and an inertial mass from the electrical conductivity to characterize the band structure irrespective of the exact scattering mechanism. We identify a Fermi Surface Complexity Factor: Nv * K * from the ratio of these two masses, which in simple cases depends on the number of Fermi surface pockets ( N v * ) and their anisotropy K*, both of which are beneficial to high thermoelectric performance as exemplified by the high values found in PbTe. The Fermi Surface Complexity factor can be used in high-throughput search of promising thermoelectric materials.

Editorial Summary

Electronic materials: In search of the right mass (电子材料:寻找合适的质量)

由美国和比利时的研究人员开发了一种用于确定材料热电性能的简单方法。美国西北大学的Snyder及其同事建立的模型,可以简化寻找以废热发电的材料的方法。即便固体内电子的环境非常复杂,电子穿过固体原子晶格的方式仍可看作是在自由空间移动。然而,由于其环境的影响,人们用材料的有效质量,而不是其真实质量,来模拟电子的运动和材料的性能。但有效质量有几种定义方式,与被模拟材料某一性质相关。Snyder等通过对不同电子性质的模拟计算,确定了两种不同有效质量的比值,不仅可用作识别新热电材料的良好方法,还可与电子结构的“复杂性”关联起来。 

A simple method for determining a material’s thermoelectric properties is developed by researchers in the United States and Belgium. Jeffrey Snyder from Northwestern University and his co-workers’ model could simplify the search for materials that efficiently generate electricity from waste heat. Even though the environment of an electron in a solid is very complex, the way an electron moves through a solid’s lattice of atoms can be treated as if it is moving in free space. However, because of the influence of its environment an effective mass, not its true mass, is used to model the movement of electrons and that material’s properties. But this effective-mass can be defined in several ways depending on which material property is being modeled. Snyder et al. determine that the ratio of two different effective masses, as computed from different electronic properties, could be a good method to identify novel thermoelectric materials and can be associated with the “complexity” of the electronic structure

 

Chemomechanical modeling of lithiation-induced failure in high-volume-change electrode materials for lithium ion batteries锂离子电池电极材料锂化过程中高容量变化诱发故障的化学力学建模 

Sulin Zhang
npj Computational Materials 3, Article number: 7 (2017)
doi:10.1038/s41524-017-0009-z
Published online:17 February 2017
Abstract| Full Text | PDF OPEN
摘要:近二十年来,对高效储能系统需求的快速增长,极大地刺激了大容量、高功率、耐使用的锂离子电池的研发。高容量电极材料因在电化学循环期间体积变化较大,引起材料不可避免的降解、失效,导致电池容量快速下降、循环寿命不高。本综述针对锂离子电池高容量阳极材料的降解机制,系统整理了这一机制的连续-电平计算建模的最新进展。据此,我们以硅(Si)为例,重点关注了降解过程中电化学动力学和机械应力之间的强耦合,进一步提出该耦合现象可以通过多种材料设计措施予以控制,减轻材料的降解,这些有效措施包括表面涂层、孔隙率调控等。建模结果得到了实验数据的验证,为高性能锂离子电池工程学、故障诊断和性能优化奠定了基础。   

Abstract: The rapidly increasing demand for efficient energy storage systems in the last two decades has stimulated enormous efforts to the development of high-capacity, high-power, durable lithium ion batteries. Inherent to the high-capacity electrode materials is material degradation and failure due to the large volumetric changes during the electrochemical cycling, causing fast capacity decay and low cycle life. This review surveys recent progress in continuum-level computational modeling of the degradation mechanisms of high-capacity anode materials for lithium-ion batteries. Using silicon (Si) as an example, we highlight the strong coupling between electrochemical kinetics and mechanical stress in the degradation process. We show that the coupling phenomena can be tailored through a set of materials design strategies, including surface coating and porosity, presenting effective methods to mitigate the degradation. Validated by the experimental data, the modeling results lay down a foundation for engineering, diagnosis, and optimization of high-performance lithium ion batteries. 

Atomic structures of twin boundaries in hexagonal close-packed metallic crystals with particular focus on Mg(六方密堆金属晶体的孪生晶界原子结构:特别关注Mg)
Zongrui Pei, Xie Zhang, Tilmann Hickel, Martin Friák, Stefanie andlöbes, Biswanath Dutta & Jörg Neugebauer
npj Computational Materials
 3, Article number: 6 (2017)
doi:10.1038/s41524-017-0010-6
Published online:15 February 2017
Abstract| Full Text | PDF OPEN

摘要:本研究探索了双晶格六方密堆金属材料中的孪生晶界,关注了它们的原子几何形状。结合精确从头算方法和大规模原子模拟,我们解决了以下两个基本问题:1hcp晶体中孪生晶界的本征结构是什么?2)小的形变下这些结构是否稳定?基于实验观察而阐述的孪生晶界原子结构引起了长达十年之久的争论。为了结束这场争论,本研究测定了能量变化、光谱和孪生晶界跃迁机制。所测结果证实,力学稳定性决定了所观察的孪生晶界结构。 

Abstract: We have investigated twin boundaries in double-lattice hexagonal close-packed metallic materials, focusing on their atomic geometry. Combining accurate ab-initio methods and large-scale atomistic simulations we address the following two fundamental questions: (i) What are the possible intrinsic twin boundary structures in hcp crystals? (ii) Are these structures stable against small distortions? In order to help end a decade-long controversy over the experimental observations of the atomic structures of twin boundaries, we have determined the energetics, spectra, and transition mechanisms of the twin boundaries. Our results confirm that the mechanical stability controls structures which are observed. 

Editorial Summary

Structural materials: at the boundary between twins(结构材料:孪晶晶界)

德国和捷克共和国的研究人员研究了一组对普通金属机械性能至关重要的原子缺陷。来自Eisenforschung马普研究所的Zongrui Pei及其同事确定了镁、锆和钛等材料中可能存在的结构畸变类型。孪晶发生在某一区域原子规则排列的错排,例如对六方密堆积结构中的孪晶,其缺陷原子结构的形成至今难以解释。Pei等运用从头算方法和大规模原子模拟揭示了镁中可能出现两种类型的孪晶:滑移孪晶和反射孪晶。他们的研究表明力学不稳定性使前者很难在实验中观察到。 

A group of atomic defects that are critical to the mechanical properties of common metals is investigated by researchers in Germany and the Czech Republic. Zongrui Pei from the Max-Planck-Institut für Eisenforschung and co-workers identify the types of structural aberration that can exist in materials such as magnesium, zirconium and titanium. A twin boundary occurs where the regular atomic structure in one region becomes misaligned from that in the next. For one specific atomic arrangement, known as a hexagonal close-packed structure, the atomic structures of such defects are not very well understood. Pei et al. use ab-initio methods and large-scale atomistic simulations to show that two types of twin boundaries can occur in magnesium: glide twin boundaries and reflection twin boundaries. They show that mechanical instability makes the former difficult to see experimentally.  

Experimental verification of the ab initio phase transition sequence in SrZrO3 and comparisons with SrHfO3 and SrSnO3 (实验验证从头算的SrZrO3相变序列及其与SrHfO3SrSnO3的比较) 
Ashok Kumar, Shalini Kumari, Hitesh Borkar, Ram S Katiyar & James Floyd Scott
npj Computational Materials
 3, Article number: 2 (2017)
doi:10.1038/s41524-016-0002-y
Published online:19 January 2017
Abstract| Full Text | PDF OPEN

摘要:本研究报道了对SrZrO3SZO)所作Raman研究的细致结果,SZO Raman光谱有三个异常特点:1)在ω频率处有小的跳动区,2)有强度消失区,3)有一个温度导数dω(T)/dT急剧变化,该区从低于T = 600 K的单调区,到高于600 KCurie–Weiss依赖区,一直外推到已知相变温度T = 970 K时的零频率区,从而证明急剧变化具有移位性。此外,预测的高应力下P4mm铁电相从极化-电压实验获得了初步支持。在600 - 650 K范围内的新相推断结果与中子研究不符。本研究还对SZO与其家族成员SrSnO3SrHfO3作了比较,并讨论了Kennedy Knight所得结论的不同之处。我们发现,SrHfO3的一个已知相变也是带有通用模式的移位。 

Abstract: We present detailed Raman studies of SrZrO3 (SZO) that show three anomalies in Raman modes: One has a small jump in frequency ω, one has its intensity vanish, and a third has a sharp change in temperature derivative dω(T)/dT from flat below T = 600 K to a Curie–Weiss dependence above 600 K with extrapolation to zero frequency at the known transition temperature T = 970 K, thereby proving the latter to be displacive. In addition, the P4mm ferroelectric phase predicted at high stresses has preliminary support from polarization-voltage experiments. The inference of a new transition in the temperature region 600–650 K is in disagreement with neutron studies. Comparisons are given for family member SrSnO3 and SrHfO3, and we discuss the different conclusions of Kennedy and Knight. We show that a known transition in SrHfO3 is also displacive with a well-behaved soft mode. 

Editorial Summary

Dielectrics: into a new phase 绝缘体:研究进入新阶段

由印度、英国和美国的研究人员共同确定了一种具有意外原子排列结构的材料,有望应用于电子器件。来自CSIR国家物理实验室的Ashok Kumar及其同事观察到锆酸锶在650 K的相变。锆酸锶是电绝缘体,因其有较大的介电常数而在半导体技术领域有很大应用潜力。它具有钙钛矿结构,受热后其原子结构在不同的温度发生相应的改变。但相变所带来的效应仍是一个争论的问题。Kumar及其同事通过测定与原子振动相关的拉曼光谱和介电光谱,研究了锆酸锶的结构。从光谱结果中他们确定了锆酸锶的三个异常特征,并由此推断了一个新相变的存在。 

An unexpected atomic arrangement in a material useful for electronics is identified by researchers in India, the UK, and the USA. Ashok Kumar from the CSIR-National Physical Laboratory and co-workers observe a phase change in strontium zirconate at 650 K. Strontium zirconate is an electrical insulator that has great potential in the semiconductor-technology because of its large dielectric constant. As this so-called perovskite is heated, its atomic structure changes at specific temperatures. But the sequence of these phase changes is still a matter of debate. Kumar and colleagues study the structure of strontium zirconate by measuring the optical emission associated with atomic vibrations—a method known as Raman spectroscopy and dielectric spectroscopy. They identify three anomalous features in these results that infer the presence of a new phase transition. 

Quantum–continuum simulation of underpotential deposition at electrified metal–solution interfaces (带电金属–溶液界面处欠电位沉积的量子–连续体模拟)
Stephen E. Weitzner & Ismaila Dabo
npj Computational Materials
 3, Article number: 1 (2017)
doi:10.1038/s41524-016-0004-9
Published online:12 January 2017
Abstract| Full Text | PDF OPEN

摘要:过渡金属离子的欠电位沉积是许多电合成途径的关键步骤。虽然欠电位沉积在原子水平上已得到深入研究,但运用第一性原理在真空条件下的计算结果有可能严重低估了欠电位沉积金属的稳定性。最近的研究结果表明,将共吸附阴离子考虑进来对欠电位沉积反应的描述更为可靠。除此之外,其他一些环境因素如电压引起的界面带电、溶液的离子活度等对欠电位沉积的影响等还亟待研究。本研究采用电化学界面的量子连续体模型,探讨了真实电化学条件下,铜在金上的欠电位沉积。本研究报道了界面带电、浓度效应、阴离子共吸附对铜在金(100)表面的欠电位沉积层的稳定性所造成的影响。 

Abstract: The underpotential deposition of transition metal ions is a critical step in many electrosynthetic approaches. While underpotential deposition has been intensively studied at the atomic level, first-principles calculations in vacuum can strongly underestimate the stability of underpotentially deposited metals. It has been shown recently that the consideration of co-adsorbed anions can deliver more reliable descriptions of underpotential deposition reactions; however, the influence of additional key environmental factors such as the electrification of the interface under applied voltage and the activities of the ions in solution have yet to be investigated. In this work, copper underpotential deposition on gold is studied under realistic electrochemical conditions using a quantum–continuum model of the electrochemical interface. We report here on the influence of surface electrification, concentration effects, and anion co-adsorption on the stability of the copper underpotential deposition layer on the gold (100) surface.

Editorial Summary 

Thin films: How to overachieve at underpotentials (薄膜:不同欠电位条件下如何实现超稳定) 

金属离子在欠电位条件下沉积在惰性金属表面形成可用于催化或传感的纳米材料。但在这个过程中所沉积的金属不稳定,常会被周围的液体所溶解。对此,来自美国宾州大学的Stephen WeitznerIsmaila Dabo发展了一种程序解决量子-机械模拟方法中令人困扰的不稳定性。该方法可用来估计欠电位沉积时,铜离子在金表面沉积的稳定性。研究人员采用量子-连续体方法解释了溶剂效应,采用蒙特卡洛模拟理解带电金-水界面的带电状况对沉积的影响。这些计算结果提示了考虑界面电荷和共吸附离子等因素对精确模拟欠电位沉积的必要性。 

The deposition of atomically thin metal films can be predicted with a comprehensive model incorporating realistic environmental factors. Nanomaterials used as catalysts and sensors are often produced by the spontaneous attachment of metal ions onto inert metal surfaces in the underpotential regime, where the depositing metal would normally dissolve in the surrounding liquid environment. Stephen Weitzner and Ismaila Dabo from the Pennsylvania State University have developed a procedure to resolve the perplexing inability of quantum-mechanical simulations to estimate the stability of underpotential deposits, such as copper ions onto gold surfaces. The researchers used a quantum–continuum approach to account for solvent effects and Monte Carlo simulations to understand how electrification of the gold–water interface impacts deposition. These computations revealed the need to include the interfacial charge and co-adsorbed ions to accurately simulate underpotential deposition.

 

Wide-range ideal 2D Rashba electron gas with large spin splitting in Bi2Se3/MoTe2 heterostructure (Bi2Se3/MoTe2异质结构中大自旋分裂的宽幅理想二维Rashba电子气)
Te-Hsien Wang & Horng-Tay Jeng
npj Computational Materials
 3, Article number: 5 (2017)
doi:10.1038/s41524-017-0011-5
Published online:09 February 2017
Abstract| Full Text | PDF OPEN

摘要:能实际应用的理想二维Rashba电子气(几乎所有的传导电子占据Rashba带)是应用半导体自旋电子的关键。本研究证实,这样带有大Rashba劈裂的理想二维Rashba电子气可以在拓扑绝缘体Bi2Se3薄膜上实现,该薄膜可在过渡金属硫化物MoTe2基板上按第一性原理计算结果指导生长得到。研究结果显示,Rashba带专处于MoTe2半导体带隙中一个较大的、约0.6  eV费米能级间隔中。如此宽幅的理想二维Rashba电子气具有大的自旋分裂,为实际利用Rashba效应提供了可能,之前从未做到。由于强自旋-轨道耦合,其Rashba分裂强度与重金属(如AuBi)表面的差不多,所引起的自旋进动距离小到10 nm左右。近Γ点的内(外)Rashba带平面内自旋极化最大约为70%60%)。室温下相干距离至少数倍于自旋进动长度,为采用自旋加工设备提供了良好的一致性。这种二维拓扑绝缘体/过渡金属硫化物异质结构中的理想Rashba带,具有能量范围宽、自旋进动长度短、相干距离长的特点,为室温下制造超薄纳米自旋电子器件(如Datta–Das自旋晶体管)铺平了道路。

Abstract: An application-expected ideal two-dimensional Rashba electron gas, i.e., nearly all the conduction electrons occupy the Rashba bands, is crucial for semiconductor spintronic applications. We demonstrate that such an ideal two-dimensional Rashba electron gas with a large Rashba splitting can be realized in a topological insulator Bi2Se3 ultrathin film grown on a transition metal dichalcogenides

Editorial Summary

2D electron gas for nanoscale spintronic deviceseditor (制造纳米自旋电子设备编辑器的二维电子气)

该研究通过计算揭示了纳米自旋电子晶体管在室温下工作的可能性。来自中国台湾清华大学的T. H. WangH. T. Jeng通过第一性原理计算,证实了一种理想的二维电子气(半导体自旋电子实现应用的关键)可在硒化铋超薄膜绝缘体中实现,该超薄膜用半导体MoTe2衬底、在室温下生长即可制备。超薄器件中形成的二维电子气表现出大的自旋分裂(两种状态的电子自旋间的分离),这正是晶体管之类的设备所需要的特性。采用电子自旋的电子器件来处理信息,用的是电子固有的自旋特性,而不象目前常规电子器件那样用的是电子的电荷特性。这会使设备在更小的空间内存储更多的数据,消耗更少的电能,使用更便宜的材料。 

Calculations reveal the potential for a nanoscale spintronic transistor that works at room temperature. T. H. Wang and H. T. Jeng of Taiwan’s National Tsing Hua University demonstrated through ‘first-principle’ calculations that an ideal two-dimensional electron gas, crucial for semiconductor spintronic applications, can be realized at room temperature in an insulating bismuth selenide ultrathin film grown on a semiconducting molybdenum titelluride substrate. The 2D electron gas formed in the ultrathin device demonstrated large ‘spin-splitting’, a separation between the two states of electron spin, which is needed for transistor-like devices. Spintronic devices use the intrinsic spinning property of electrons to process information instead of the electron charge used in conventional electronics. They could lead to devices that can store more data in a smaller space while consuming less power and using cheaper materials.

 
MoTe2 substrate through first-principle calculations. Our results show the Rashba bands exclusively over a very large energy interval of about 0.6 eV around the Fermi level within the MoTe2 semiconducting gap. Such a wide-range ideal two-dimensional Rashba electron gas with a large spin splitting, which is desirable for real devices utilizing the Rashba effect, has never been found before. Due to the strong spin–orbit coupling, the strength of the Rashba splitting is comparable with that of the heavy-metal surfaces such as Au and Bi surfaces, giving rise to a spin precession length as small as ~10 nm. The maximum in-plane spin polarization of the inner (outer) Rashba band near the Γ point is about 70% (60%). The room-temperature coherence length is at least several times longer than the spin precession length, providing good coherency through the spin processing devices. The wide energy window for ideal Rashba bands, small spin precession length, as well as long spin coherence length in this two-dimensional topological insulator/transition metal dichalcogenides heterostructure pave the way for realizing an ultrathin nano-scale spintronic device such as the Datta–Das spin transistor at room-temperature. 

Comparison of dissimilarity measures for cluster analysis of X-ray diffraction data from combinatorial libraries 组合数据库中X射线衍射数据对团簇分析的不同方法比较 

Yuma Iwasaki, A. Gilad Kusne & Ichiro Takeuchi
npj Computational Materials
 3, Article number: 4 (2017)
doi:10.1038/s41524-017-0006-2
Published online:03 February 2017
Abstract| Full Text | PDF OPEN

摘要:机器学习技术已被证明在管理全方位不断增长的材料研究数据量方面,拥有难以估量的作用,包括管理不断增长的高通量材料模拟、制造和表征所产生的数据。尤其是机器学习技术已被证明可用于快速自动识别材料组成、结构数据库中潜在新材料的元素组成相图,能使人们快速进行新材料的制备-结构-性能一体化分析及功能材料的发现。自动相图测定方法改进的一个关键问题是,选择不同措施或软件核心功能。所选的措施要能减少复杂结构数据问题对性能分析的影响。该关键问题包括,某个材料的晶格常数改变后,峰高的变化和峰值的移位。在本研究中,我们考察了基于X-射线衍射的结构分析方法以及不同方法对相组成描绘结果的差异。本研究分析了Fe–Co–Ni三元合金成分扩散状态的X-射线衍射结果,比较了9种不同方法对结果的影响。采用余弦、Pearson相关系数和Jensen–Shannon发散方法,在未知峰值位移幅度的情况下,得出了峰高变化和峰值移位(由于晶格常数的改变)时的最佳结果。随着已知的最大峰值移位,动态时间扭曲的归一化约束模式提供了最好的结果。本研究结果也可作为快速分析大量X射线衍射结果(超出组合库数据)的通用策略。 

Abstract: Machine learning techniques have proven invaluable to manage the ever growing volume of materials research data produced as developments continue in high-throughput materials simulation, fabrication, and characterization. In particular, machine learning techniques have been demonstrated for their utility in rapidly and automatically identifying potential composition–phase maps from structural data characterization of composition spread libraries, enabling rapid materials fabrication-structure-property analysis and functional materials discovery. A key issue in development of an automated phase-diagram determination method is the choice of dissimilarity measure, or kernel function. The desired measure reduces the impact of confounding structural data issues on analysis performance. The issues include peak height changes and peak shifting due to lattice constant change as a function of composition. In this work, we investigate the choice of dissimilarity measure in X-ray diffraction-based structure analysis and the choice of measure’s performance impact on automatic composition-phase map determination. Nine dissimilarity measures are investigated for their impact in analyzing X-ray diffraction patterns for a Fe–Co–Ni ternary alloy composition spread. The cosine, Pearson correlation coefficient, and Jensen–Shannon divergence measures are shown to provide the best performance in the presence of peak height change and peak shifting (due to lattice constant change) when the magnitude of peak shifting is unknown. With prior knowledge of the maximum peak shifting, dynamic time warping in a normalized constrained mode provides the best performance. This work also serves to demonstrate a strategy for rapid analysis of a large number of X-ray diffraction patterns in general beyond data from combinatorial libraries. 

Editorial Summary

Machine learning: Spying enhanced materials with x-ray vision 机器学习技术:增强X射线的视力以更好地窥探材料

来自美国国家标准局的A. Gilad Kusne及其同事通过不同措施,量化材料结构的关键数据(如X-射线衍射峰强度和位置,以及样品的组成变化),研究了机器学习技术,以使其能够简化新型合金的合成。利用大量X射线衍射数据集的自动变化计算,可以改善多组分合金的设计。合金中含三个或更多金属时,有可能出现大量不同组合的材料,每种材料都具有不同的性能。科学家们首先制备了成分扩散的铁--镍合金薄膜,然后用不同软件分析X射线的异同,评估处理的速度和准确性。研究鉴定了几种适用于高通量生成彩色编码图样的算法,这些算法能显示合金成分和相位在两个和三个维度之间的关系。 

Using algorithms to automatically spot variations in massive X-ray diffraction data sets may improve design of multi-component alloys. Having three or more metals in an alloy can lead to overwhelming combinations of possible materials, each with different properties. A. Gilad Kusne from the National Institute of Standards and co-workers examined how machine learning techniques could simplify alloy discovery through ‘dissimilarity measures’ that quantify how key structural data points, such as the positions and intensities of X-ray peaks, change with sample makeup.

The team fabricated a compositional spread of iron–cobalt–nickel thin film alloys, and then evaluated different software approaches to finding X-ray dissimilarities for both processing speed and accuracy. Several algorithms suitable for high-throughput generation of color-coded maps that display relations between alloy composition and phase in both two and three-dimensions were identified. 
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