The shape of field emitters and the ion trajectories in three-dimensional atom probes

The lateral resolution of three-dimensional atom probes is mainly controlled by the aberrations of the ion trajectories near the specimen surface. For the first time, a simulation program has been developed to reconstruct the ion trajectories near a sharp hemispherical electrode defined at the atomic scale. Surface atoms submitted to the highest field were removed one by one. The consecutive gradual change of the surface topology was taken into account in the calculation of ion trajectories. As the tip was 'field evaporated', the initial spherical shape of the emitter was observed to transform gradually into a polygonal shape. When the tip reached its equilibrium shape, the field distribution at the tip surface was found to be much more uniform compared to the initial distribution. The calculated distribution of ion impacts on the detector exhibits the presence of depleted zones both at the centre of low index poles and along <001> zone axes. These predictions are in excellent agreement with experiments.     

On the coupling efficiency of metal-coated near-field probes

A theory for calculating the optical transmission of nanometric circular apertures in a thick and perfectly conducting screen coated upon an optical fibre has been developed. The theory is intended for the study of near-field probes and differs from other well known theories of radiation transmission through subwavelength apertures in the fact that it includes an optical fibre, making possible to distinguish which part of energy passing through the aperture is effectively coupled in guided modes. In a scanning near-field optical microscope tip, only the guided modes will reach the photodetector, and will contribute to the final read-out. A numerical calculation for different fibre parameters, to show the dependence of the guided transmission coefficient for the guided modes of the fibre, is presented. The agreement of the theory with earlier calculations where the optical fibre is not included is emphasized.     

Analysis conditions of an industrial Al-Mg-Si alloy by conventional and 3D atom probes.

Industrial 6016 Al-Mg-Si(Cu) alloys are presently regarded as attractive candidates for heat treatable sheet materials. Their mechanical properties can be adjusted for a given application by age hardening of the alloys. The resulting microstructural evolution takes place at the nanometer scale, making the atom probe a well suited instrument to study it. Accuracy of atom probe analysis of these aluminium alloys is a key point for the understanding of the fine scale microstructural evolution. It is known to be strongly dependent on the analysis conditions (such as specimen temperature and pulse fraction) which have been widely studied for ID atom probes. The development of the 3D instruments, as well as the increase of the evaporation pulse repetition rate have led to different analysis conditions, in particular evaporation and detection rates. The influence of various experimental parameters on the accuracy of atom probe data, in particular with regard to hydride formation sensitivity, has been reinvestigated. It is shown that hydrogen contamination is strongly dependent on the electric field at the specimen surface, and that high evaporation rates are beneficial. Conversely, detection rate must be limited to smaller than 0.02 atoms/pulse in order to prevent drastic pile-up effect.     

"四大战略"托升方圆集团竞争优势

主圆集团依靠科技创新,优化产品结构,拓展经营领域,开辟全球市场,创造出良好的经济效益和社会效益,2002年完成销售收入8.6亿元,实现利税8600万元,保持着良好的发展势头。     

Standard deviations of composition measurements in atom probe analyses-Part II: 3D atom probe

In a companion paper [F. Danoix, G. Grancher, A. Bostel, D. Blavette, Surf. Interface Anal. this issue (previous paper).], the derivation of variances of the estimates of measured composition, and the underlying hypotheses, have been revisited in the the case of conventional one dimensional (1D) atom probes. In this second paper, we will concentrate on the analytical derivation of the variance when the estimate of composition is obtained from a 3D atom probe. As will be discussed, when the position information is available, compositions can be derived either from constant number of atoms, or from constant volume, blocks. The analytical treatment in the first case is identical to the one developed for conventional 1D instruments, and will not be discussed further in this paper. Conversely, in the second case, the analytical treatment is different, as well as the formula of the variance. In particular, it will be shown that the detection efficiency plays an important role in the determination of the variance.     

Advances in the reconstruction of atom probe tomography data

Key to the integrity of atom probe microanalysis, the tomographic reconstruction is built atom by atom following a simplistic protocol established for previous generations of instruments. In this paper, after a short review of the main reconstruction protocols, we describe recent improvements originating from the use of exact formulae enabling significant reduction of spatial distortions, especially near the edges of the reconstruction. We also show how predictive values for the reconstruction parameters can be derived from electrostatic simulations, and finally introduce parameters varying throughout the analysis.     

原子光刻中的原子沉积数值模拟

近年来,有关原子光刻的实验研究得到了快速发展,并取得了一系列重大的实验进展。在原子光刻中,对不同原子在各种条件下的沉积过程的研究是具有非常重要的意义的。现利用有限差分法求解光与原子作用的薛定谔方程分析了激光功率、失谐量、腰斑大小以及原子纵向速度对汇聚效果的影响,总结了一些原子在驻波场中各项参数对沉积效果的影响。     

Identifying the financial advantages of linking computer systems within manufacturing companies

This paper examines the benefits to production efficiency which can accrue by investing in computer systems, and provides an insight into the trade-offbetween computer links and computer integration.     

多齿差摆线针齿行星传动强度分析

多齿差摆线针齿行星传动近几年来在小速比减速机上，特别是在大功率、速比小范畴的使用过程中得到广泛的应用，根据多齿差摆线针齿行星传动受力特点对多齿差摆线针轮的强度进行分析，并与相同速比的一齿差摆线齿轮减速机的摆线轮的强度进行比较。     

Quantitative atom probe analysis of carbides

Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti₂AlC grains in different materials as well as on large M₂₃C₆ precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the ¹³C isotope, and calculating the concentration of ¹²C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) and Ti₂AlC an additional difficulty arises from the overlap between C₂⁺, C₄²⁺ and Ti²⁺ at the mass-to-charge 24 Da.     

Quantitative binomial distribution analyses of nanoscale like-solute atom clustering and segregation in atom probe tomography data

The applicability of the binomial frequency distribution is outlined for the analysis of the evolution nanoscale atomic clustering of dilute solute in an alloy subject to thermal ageing in 3D atom probe data. The conventional chi(2) statistics and significance testing are demonstrated to be inappropriate for comparison of quantity of solute segregation present in two or more different sized system. Pearson coefficient, mu, is shown to normalize chi(2) with respect to sample size over an order of magnitude. A simple computer simulation is implemented to investigate the binomial analysis and infer meaning in the measured value of mu over a series of systems at different solute concentrations and degree of clustering. The simulations replicate the form of experimental data and demonstrate the effect of detector efficiency to significantly underestimate the measured segregation. The binomial analysis is applied to experimental atom probe data sets and complementary simulations are used to interpret the results.     

创新市场管理体系构筑竞争优势

中航电测仪器股份有限公司(以下简称中航电测)自2010年开始搭建市场管理体系的构架以来,建立了以市场为导向的经营管理机制,进一步理顺市场营销管理流程,完善营销组织机构,优化市场资源配置,从而夯实市场营销工作的基础,提高专业管理水平,构筑公司全价值链的竞争优势。之后,持续创新深化市场管理体系,产生了良好的推动效应,取得了喜人业绩。     

加工中心测头的校正

在加工中心上加工工件时,测量刀具直径、长度以及确定工件零点坐标等需占用大量辅助工时,缩短这部分辅助工时对生产效率的提高具有重要意义。为此,我厂在引进辛辛那提公司四轴加工中心的同时,选购了雷尼绍(Ｒｅｎｉｓｈａｗ)公司的ＴＳ27Ｒ型刀具测头和ＭＰ12型主轴测头。刀具测头可快速测量刀具的长度和直径,并将测量值自动输入机床控制系统的刀具表中。主轴测头可准确测量工件表面位置坐标、外角和内角点位置坐标、圆柱中心线、两平行平面的中心面位置坐标,并建立工件零点与程序零点的对应关系。这两种测头操作简便,测量准确。但因两种测…     

新型自动气象站结构特点及其优越性

新型自动气象站是根据当前国际先进的CAN总线技术进行设计的,可结合台站需要自由选择所需传感器,解决当前自动气象站系统无法扩展新要素的问题,其要素设计更为全面科学,对温湿度传感器也进行了改进,并增加称重雨量传感器和0.5mm翻斗雨量传感器。新型自动气象站提高了地面常规要素观测和灾害天气观测的准确度,在软件设计、硬件结构、防雷性能、处理存储能力等方面也比当前运行的自动气象站有较大提升。     

Shape dependence of the capacitance of scanning capacitance microscope probes

The capacitance of approximately conical scanning capacitance microscope probes placed perpendicularly over a conducting plane has been modelled using the finite element method. The dependence on tip/surface distance, radius of curvature of the tip apex, cone angle and height has been analysed. Both shielded and unshielded probes have been considered. The fits of obtained dependences have been combined into an analytic approximation of the capacitance as a function of tip/surface distance, radius of curvature, cone angle and height. The results can be used to estimation of stray capacitance, achievable lateral resolution and contrast.     

浅谈信息技术有利于提高档案利用工作

面临着信息时代档案利用工作要进行技术改革。新技术给档案工作者提出了新要求,要抓基础工作提高档案工作者素质,利用信息技术改进档案利用工作。     

Performance of local electrodes in the local electrode atom probe

The use of a local electrode in atom probe tomography has enabled higher rates of data acquisition and increased field of view compared to other variants of three-dimensional atom probes, but specimen fracture can result in damage to the local electrode. Specimens and local electrodes were examined before and after analyses that resulted in specimen failure. Most specimens were found to be melted after failure and as a result, material was found deposited onto the surface of the local electrode. Material transfer from the specimen to the local electrode was verified by energy dispersive spectrometry in a scanning electron microscope. After the fracture of brittle materials, some remnants were found embedded in the local electrode. For either failure mode, it is likely that the primary specimen rupture produced a sharp protrusion on the specimen or local electrode and this triggered an electrical discharge or uncontrolled field emission that melted a portion of the specimen. The lifetime of the local electrode was found to be dependent on the shape and position of the debris from the specimen failure rather than the number of ions collected or the number of specimens characterized. Local electrodes with smaller apertures were found to be more susceptible to failure.