Scanning transmission electron microscopy and atom probe tomography analysis of non-stoichiometry long-period-stacking-ordered structures in Mg-Ni-Y/Sm alloys

The long-period-stacking-ordered(LPSO)structure affects the mechanical,corrosion and hydrolysis properties of Mg alloys.The current work employs high angle annular dark field-scanning transmission electron microscopy(HAADF-STEM)and atom probe tomography(APT)to investigate the structural and local chemical information of LPSO phases formed in Mg-Ni-Y/Sm ternary alloys after extended isothermal annealing.Depending on the alloying elements and their concentrations,Mg-Ni-Y/Sm develops a two-phase LPSO+α-Mg structure in which the LPSO phase contains defects,hybrid LPSO structure,and Mg insertions.HAADF-STEM and APT indicate non-stoichiometric LPSO with incomplete Ni_(6)(Y/Sm)_(8) clusters.In addition,the APT quantitatively determines the local composition of LPSO and confirms the presence of Ni within the Mg bonding layers.These results provide insight into a better understanding of the structure and hydrolysis properties of LPSO-Mg alloys.

High-precision three-dimensional atom localization via probe absorption at room temperature

A scheme is used to explore the behavior of three-dimensional(3D)atom localization in a Y-type hot atomic system.We can obtain the position information of the atom due to the position-dependent atom–field interaction.We study the influences of the system parameters and the temperature on the atom localization.More interestingly,the atom can be localized in a subspace when the temperature is equal to 323 K.Moreover,a method is proposed to tune multiparameter for localizing the atom in a subspace.The result is helpful to achieve atom nanolithography,photonic crystal and measure the center-of-mass wave function of moving atoms.

High-precision three-dimensional Rydberg atom localization in a four-level atomic system

Rydberg atoms have been widely investigated due to their large size,long radiative lifetime,huge polarizability and strong dipole-dipole interactions.The position information of Rydberg atoms provides more possibilities for quantum optics research,which can be obtained under the localization method.We study the behavior of three-dimensional(3D)Rydberg atom localization in a four-level configuration with the measurement of the spatial optical absorption.The atomic localization precision depends strongly on the detuning and Rabi frequency of the involved laser fields.A 100%probability of finding the Rydberg atom at a specific 3D position is achieved with precision of~0.031λ.This work demonstrates the possibility for achieving the 3D atom localization of the Rydberg atom in the experiment.

Three-dimensional Holographic Vector of Atomic Interaction Field(3D-HoVAIF) for the QSPR/QSAR of Polychlorinated Naphthalenes

Three-dimensional holographic vector of atomic interaction field（3D-HoVAIF） is used to describe the chemical structures of polychlorinated naphthalenes（PCNs）.After variable screening by stepwise multiple regression（SMR） technique,the liner relationships between gas-chromatographic relative retention time（RRT）,298 K supercooled liquid pressures（logPL）,n-octanol/air partition coefficient（logKOA）,n-octanol/water partition coefficient（logKOW）,aqueous solubilities（logSW）,relative in vitro potency values（-logEROD） of PCNs and 3D-HoVAIF descriptors have been established by partial least-square（PLS） regression.The result shows that the 3D-HoVAIF descriptors can be well used to express the quantitative structure-property（activity） relationships of PCNs.Predictive capability of the models has also been demonstrated by leave-one-out cross-validation.Moreover,the predicted values have been presented for those PCNs which are lack of experimentally physico-chemical properties and biological activity by the optimum models.

Analysis of Cr Atoms Three-Dimensional Deposition Characteristics

The semi-classical model is used to simulate the three-dimensional trajectory and deposition distribution of the chromium atoms in the Gaussian laser standing wave field using the Runge-Kutta method, and then the three-dimensional deposition stripes are also given, besides, the effects of atomic beam divergence, chromatic aberration and spherical aberration on deposition structure are also analyzed.

Precise measurement of a weak radio frequency electric field using a resonant atomic probe

We present a precise measurement of a weak radio frequency electric field with a frequency of ■3 GHz employing a resonant atomic probe that is constituted with a Rydberg cascade three-level atom, including a cesium ground state |6S(1/2)〉,an excited state |6P(3/2)〉, and Rydberg state |nD(5/2)〉. Two radio frequency(RF) electric fields, noted as local and signal fields, couple the nearby Rydberg transition. The two-photon resonant Rydberg electromagnetically induced transparency(Rydberg-EIT) is employed to directly read out the weak signal field having hundreds of k Hz difference between the local and signal fields that is encoded in the resonant microwave-dressed Rydberg atoms. The minimum detectable signal fields of ESmin= 1.36 ± 0.04 mV/m for 2.18 GHz coupling |68D(5/2)〉→ |69P(3/2)〉 transition and 1.33 ± 0.02 mV/m for 1.32 GHz coupling |80D(5/2)〉→ |81P(3/2)〉 transition are obtained, respectively. The bandwidth dependence is also investigated by varying the signal field frequency and corresponding -3 dB bandwidth of 3 MHz is attained. This method can be employed to perform a rapid and precise measurement of the weak electric field, which is important for the atom-based microwave metrology.

Crystallization and impact history of a meteoritic sample of early lunar crust(NWA 3163)refined by atom probe geochronology

Granulitic lunar meteorites offer rare insights into the timing and nature of igneous,metamorphic and impact processes in the lunar crust.Accurately dating the different events recorded by these materials is very challenging,however,due to low trace element abundances (e.g.Sm,Nd,Lu,Hf),rare micrometerscale U-Th-bearing accessory minerals,and disturbed Ar-Ar systematics following a multi-stage history of shock and thermal metamorphism.Here we report on micro-baddeleyite grains in granulitic mafic breccia NWA 3163 for the first time and show that targeted microstructural analysis (electron backscatter diffraction) and nanoscale geochronology (atom probe tomography) can overcome these barriers to lunar chronology.A twinned (-90°/<401>) baddeleyite domain yields a 232Th/208Pb age of 4328 ± 309 Ma,which overlaps with a robust secondary ion mass spectrometry (SIMS) 207Pb/206Pb age of 4308± 18.6 Ma and is interpreted here as the crystallization age for the igneous protolith of NWA 3163.A second microstructural domain,< 2 mm in width,contains patchy overprinting baddeleyite and yields a Th-Pb age of 2175± 143 Ma,interpreted as dating the last substantial impact event to affect the sample.This finding demonstrates the potential of combining microstructural characterization with nanoscale geochronology when resolving complex P-T-t histories in planetary materials,here yielding the oldest measured crystallization age for components of lunar granulite NWA 3163 and placing further constraints on the formation and evolution of lunar crust.

IMPROVED FABRICATION METHOD FOR CARBON NANOTUBE PROBE OF ATOMIC FORCE MICROSCOPY(AFM)

An improved arc discharge method is developed to fabricate carbon nanotube probe of atomic force microscopy （AFM） here. First, silicon probe and carbon nanotube are manipulated under an optical microscope by two high precision microtranslators. When silicon probe and carbon nanotube are very close, several tens voltage is applied between them. And carbon nanotube is divided and attached to the end of silicon probe, which mainly due to the arc welding function. Comparing with the arc discharge method before, the new method here needs no coat silicon probe with metal film in advance, which can greatly reduce the fabrication＇s difficulty. The fabricated carbon nanotube probe shows good property of higher aspect ratio and can more accurately reflect the true topography of silicon grating than silicon probe. Under the same image drive force, carbon nanotube probe had less indentation depth on soft triblock copolymer sample than silicon probe. This showed that carbon nanotube probe has lower spring constant and less damage to the scan sample than silicon probe.

Two-dimensional atom localization via probe absorption in a four-level atomic system

We have investigated the two-dimensional （2D） atom localization via probe absorption in a coherently driven four-level atomic system by means of a radio-frequency field driving a hyperfine transition. It is found that the detecting probability and precision of 2D atom localization can be significantly improved via adjusting the system parameters. As a result, our scheme may be helpful in laser cooling or the atom nano-lithography via atom localization.

High-precision two-dimensional atom localization via probe absorption in an M-scheme atomic system

In the present paper, we investigate the behavior of two-dimensional atom localization in a five-level M-scheme atomic system driven by two orthogonal standing-wave fields. We find that the precision and resolution of the atom localization depends on the probe field detuning significantly. And because of the effect of the microwave field, an atom can be located at a particular position via adjusting the system parameters.

Re effects in model Ni-based superalloys investigated with first-principles calculations and atom probe tomography

The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom probe tomography.The Re distribution of single,nearest neighbor(NN),next-nearest neighbor(NNN),and cluster configurations are respectively designed in the models withγandγphases.The results show that the Re atoms tend to enteringγphase and the Re atoms prefer to occupy the Al sites inγphase.The Re cluster with a combination of NN and NNN Re-Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys,and the configuration with isolated Re atom is more preferred in the system.Especially,the electronic states are analyzed and the energetic parameters are calculated.The electronic structure analyses show there exists strong Ni-Re electronic interaction and it is mainly contributed by the d-d hybridization.The characteristic features of the electronic states of the Re doping effects are also given.It is also found that Re atoms prefer the Al sites inγside at the interface.The density of states at or near the Fermi level and the d-d hybridizations of NN Ni-Re are found to be important in the systems.

A method for calibrating the confocal volume of a confocal three-dimensional micro-x-ray fluorescence setup

The measurement of the confocal volume of a confocal three-dimensional micro-x-ray fluorescence(3D-XRF)setup is a key step in the field of confocal 3D-XRF analysis.With the development of x-ray facilities and optical devices,3D-XRF analysis with a micro confocal volume will create a great potential for 2D and 3D microstructural analysis and accurate quantitative analysis.However,the classic measurement method of scanning metal foils of a certain thickness leads to inaccuracy.A method for calibrating the confocal volume is proposed in this paper.The new method is based on the basic content of the textbook,and the theoretical results and the feasibility are given in detail for the 3D-XRF mono-chromatic x-ray condition and the poly-chromatic x-ray condition.We obtain a set of experimental confirmation using the poly-chromatic x-ray tube in the laboratory.It is proved that the sensitivity factor of the 3D-XRF can be directly and accurately obtained in a real calibration process.

THEORETICAL ANALYSIS AND EXPERIMENTAL STUDY OF CARBON NANOTUBE PROBE AND CONVENTIONAL ATOMIC FORCE MICROSCOPY PROBE ON SURFACE ROUGHNESS

In this paper, three different tips are employed, i.e., the carbon nanotube tip, monocrystalline silicon tip and silicon nitride tip. Resorting to atomic force microscope （AFM）, they are used for measuring the surface roughness of indium tin oxide （ITO） film and the immunoglobulin G （IgG） proteins within the scanning area of 10 μm×10 μm and 0.5 μm×0.5 μm, respectively. Subsequently, the scanned surface of the ITO film and IgG proteins are analyzed by using fractal dimension. The results show that the ffactal dimension measured by carbon nanotube tip is biggest with the highest frequency components and the most microscopic information. Therefore, the carbon nanotube tip is the ideal measuring tool for measuring super-smooth surface, which will play a more and more important role in the high-resolution imaging field.

Probe Knots and Hopf Insulators with Ultracold Atoms

Knots and links are fascinating and intricate topological objects. Their influence spans from DNA and molecular chemistry to vortices in superfluid helium, defects in liquid crystals and cosmic strings in the early universe. Here we find that knotted structures also exist in a peculiar class of three-dimensional topological insulators—the Hopf insulators. In particular, we demonstrate that the momentum-space spin textures of Hopf insulators are twisted in a nontrivial way, which implies the presence of various knot and link structures. We further illustrate that the knots and nontrivial spin textures can be probed via standard time-of-flight images in cold atoms as preimage contours of spin orientations in stereographic coordinates. The extracted Hopf invariants, knots, and links are validated to be robust to typical experimental imperfections. Our work establishes the existence of knotted structures in Hopf insulators, which may have potential applications in spintronics and quantum information processing.

Quantitative Structure Activity Relationship Studies of Benzoxazinone Derivative Antithrombotic Drug Using New Three-dimensional Structure Descriptors

A novel three-dimensional holographic vector of atomic interaction field（3D-HoVAIF） was used to describe the chemical structures of 23 benzoxazinone derivatives as antithrombotic drugs.Here a quantitative structure activity relationship（QSAR） model was built by partial least-squares（PLS） regression.The estimation stability and prediction ability of the model were strictly analyzed by both internal and external validations.The correlation coefficients of established PLS model,leave-one-out（LOO） cross-validation,and predicted values versus experimental ones of external samples were R2=0.899,RCV2=0.854 and Qext2=0.868,respectively.These values indicated that the built PLS model had both favorable estimation stability and good prediction capabilities.Furthermore,the satisfactory results showed that 3D-HoVAIF could preferably express the information related to the biological activity of benzoxazinone derivatives.

Experimental Investigation of the Early Stage of Precipitation on Binary Al-Li, Al-Cu Alloys and Ternary Al-Li-Cu Alloys by Means of Atom Probe Tomography

Aluminum-based alloys play a key role in modern engineering and are widely used in construction components in aircraft, automobiles and other means of transportation due to their light weight and superior mechanical properties. Introduction of different nano-structure features can improve the service and the physical properties of such alloys. An improvement of an Al-based alloy has been performed based on the understanding of the relationships among compositions, processing, microstructural characteristics and properties. Knowledge of the decomposition process of the microstructure during the precipitation reaction is particularly important for future technical developments. The objective of this study is to investigate the nano-scale chemical composition in the Al-Cu, Al-Li and Al-Li-Cu alloys during the early stage of the precipitation sequence and to describe whether this compositional difference correlates with variations in the observed precipitation kinetics. Investigation of the fine scale segregation effects of dilute solutes in aluminum alloys which were experienced different heat treatments by using atom probe tomography has been achieved. The results show that an Al-1.7 at.% Cu alloy requires a long ageing time of approximately 8 h at 160°C to allow the diffusion of Cu atoms into Al matrix. For the Al-8.2 at.% Li alloy, a combination of both the natural ageing condition (48 h at room temperature) and a short artificial ageing condition (5 min at 160°C) induces increasing on the number density of the Li clusters and hence increase number of precipitated particles. Applying this combination of natural ageing and short artificial ageing conditions onto the ternary Al-4 at.% Li-1.7 at.% Cu alloy induces the formation of a Cu-rich phase. Increasing the Li content in the ternary alloy up to 8 at.% and increasing the ageing time to 30 min resulted in the precipitation processes ending with δ' particles. Thus the results contribute to the understanding of Al-alloy design.

三维原子探针的电场结构模拟研究

本文针对目前世界上被广泛使用的局部电极原子探针的样品及局部电极几何结构,通过有限元方法,结合多物理场仿真技术,研究了局部电极与针状样品的距离z、样品尖端曲率半径ρ、局部电极的入口直径φ、厚度w、开口角度α和入口长度h等参数对样品尖端附近的局部电场的影响。模拟结果表明:当z与φ的取值满足z/φ≥1时,既能在样品尖端得到较高的蒸发电场强度,又能降低局部电极对离子轨迹的影响;局部电极的厚度w和开口角度α的取值对样品尖端的电场影响较小;增大局部电极入口长度h的值有利于提高样品尖端电场强度;随着原子的蒸发(样品尖端曲率半径ρ增大),为维持原子蒸发所需的电场强度,施加在样品上的电压V与样品尖端的曲率半径ρ成正比,且所需维持的电场强度越高,施加的电压V越大。

基于大高宽比CD-AFM探针的设计与制备

针对传统原子力显微镜(AFM)探针和关键尺寸原子力显微镜(CD-AFM)探针受限于针尖有效扫描高度较低,无法对深沟槽和大悬垂侧壁结构进行精准扫描成像的问题,提出了一种大高宽比针尖结构的新型CDAFM探针设计与制备方案。开发的新型CD-AFM探针针尖有效高度为5.1~5.8μm,高宽比达到14,相较于传统硅基CD-AFM探针,其有效高度提升了约4倍。利用开发的探针完成了标称深度为2.3μm、深宽比为4.6的深沟槽样品测试。

基于光束偏转法的原子力显微镜探针一致性装配系统研究

为解决原子力显微镜(Atomic Force Microscope,AFM)系统更换探针后光路调整复杂耗时、精度不足的问题,本文首次提出通过精密控制探针与探针夹装配位置来实现更换的探针相对AFM系统原光路位置的一致,进而实现免去AFM系统换针后调整光路步骤。该系统的光路一致性组件采用光束偏转法对探针位置与偏转进行放大与监测,并使用高精度位移与角度调节平台进行探针相对于探针夹的方位调整。通过实物搭建对探针一致性效果进行了验证,并对紫外光(Ultraviolet,UV)胶水固化过程导致探针位置偏移影响;探针不同偏移量时产生的探测器噪音对AFM系统成像质量影响进行了系统分析。实验结果表明:经由该系统装配的探针平均位置精度接近1.1μm;并且在AFM系统中更换一致性探针仅需8 s。该系统实现了高精度且质量稳定的探针一致性装配,极大地简化了AFM系统重新校准光路的操作步骤,其与自动换针装置配合可有效提升工业计量型AFM的操作与测量性能。

深度学习图像识别辅助原子力显微镜单细胞力学特性精准高效探测

目的原子力显微镜(AFM)的出现为生命科学研究提供了强大工具,特别是AFM压痕实验技术已成为细胞力学特性探测的重要方法,从单细胞尺度为生理病理活动过程带来了大量新的认识,是对传统生化集群平均研究方法的有力补充。然而现有AFM压痕实验技术存在着依赖人工、效率低下等不足,严重制约了其在生命科学领域的实际应用。本文通过将光学显微成像自动目标识别技术与AFM压痕技术结合,建立了单个游离态细胞及聚团生长细胞的力学特性精准高效测量方法。方法利用YOLO深度学习算法识别出光学图像中细胞的中心部位,并通过嵌入视觉转换器(ViT)模块的双UNet神经网络模型对细胞边缘部位进行精确分割,同时采用模板匹配算法对光学图像中AFM微球探针进行定位,在此基础上自动确定AFM探针上的微球针尖与细胞不同部位之间的空间位置关系,进而对细胞中心部位和边缘部位的力学特性进行快速测量。选取HEK 293(人胚胎肾细胞)和HGC-27(人未分化胃癌细胞)两种细胞进行验证实验,并利用Hertz模型对获取的力曲线进行分析以得到细胞杨氏模量。结果在深度学习光学图像自动识别导引下可将AFM探针准确移动至细胞不同部位(中心和边缘)进行力学特性测量,同时实验结果表明,本文提出的方法不仅可对单个游离态细胞进行可靠测量,也适用于聚团生长的细胞。结论深度学习图像识别在辅助AFM单细胞力学特性精准高效探测方面具有巨大潜力,将深度学习图像识别与AFM结合有助于发展面向生物医学应用的高通量单细胞力学特性测量方法。