Cathodoluminescence attachment to an electron probe instrument

A simple cathodoluminescence (CL) attachment to a JEOL JSM-840 scanning electron microscope (SEM) is described. It is based on a Si photodiode mounted inside the SEM chamber. The current amplifier of a backscattered electron detector unit, which is a standard feature of this SEM, is used to amplify and display the CL images. Examples of CL panchromatic (integral) images of GaAs, InP, and ZnS crystals are presented.     

Lock-in technique applied to cathodoluminescence of biomedical specimens in the SEM

Very low signals or disturbances by unwanted, foreign signals often lead to a restriction in the application of the cathodoluminescence (CL) method in the scanning electron microscope (SEM). This is even true if one uses an optimal CL detection system. We, therefore, introduced the lock-in-amplification technique, which has proved very successful in investigations of semiconductor materials into the biomedical field. After attaching the lock-in system to our SEM which has a special CL equipment, we found that this technique could remove the disturbance caused by the light emitted from the heated filament, which can be reflected into the CL detector. Specimens on polished Al-stubs or on Au-coated glass slides could be imaged with improved contrast. The same was true if we measured the wavelengths of the CL. A general improvement of the signal-to-noise ratio in all specimens could not be detected. However, the beam current could often be reduced when using the lock-in technique without a decrease in the quality of the CL image. A disadvantage of the commercially available lock-in amplifier is that pictures need a longer exposure time than without lock-in amplification.     

LabVIEW-based control and data acquisition system for cathodoluminescence experiments

Computer automation of cathodoluminescence (CL) experiments using equipment developed in our laboratory is described. The equipment provides various experiments for CL efficiency, CL spectra, and CL time response studies. The automation was realized utilizing the graphical programming environment LabVIEW. The developed application software with procedures for equipment control and data acquisition during various CL experiments is presented. As the measured CL data are distorted by technical limitations of the equipment, such as equipment spectral sensitivity and time response, data correction algorithms were incorporated into the procedures. Some examples of measured data corrections are presented.     

Multiscale iterative voting for differential analysis of stress response for 2D and 3D cell culture models

Focused ion beam-scanning electron microscope (FIB-SEM) tomography is a powerful application in obtaining three-dimensional (3D) information. The FIB creates a cross section and subsequently removes thin slices. The SEM takes images using secondary or backscattered electrons, or maps every slice using X-rays and/or electron backscatter diffraction patterns. The objective of this study is to assess the possibilities of combining FIB-SEM tomography with cathodoluminescence (CL) imaging. The intensity of CL emission is related to variations in defect or impurity concentrations. A potential problem with FIB-SEM CL tomography is that ion milling may change the defect state of the material and the CL emission. In addition the conventional tilted sample geometry used in FIB-SEM tomography is not compatible with conventional CL detectors. Here we examine the influence of the FIB on CL emission in natural diamond and the feasibility of FIB-SEM CL tomography. A systematic investigation establishes that the ion beam influences CL emission of diamond, with a dependency on both the ion beam and electron beam acceleration voltage. CL emission in natural diamond is enhanced particularly at low ion beam and electron beam voltages. This enhancement of the CL emission can be partly explained by an increase in surface defects induced by ion milling. CL emission enhancement could be used to improve the CL image quality. To conduct FIB-SEM CL tomography, a recently developed novel specimen geometry is adopted to enable sequential ion milling and CL imaging on an untilted sample. We show that CL imaging can be manually combined with FIB-SEM tomography with a modified protocol for 3D microstructure reconstruction. In principle, automated FIB-SEM CL tomography should be feasible, provided that dedicated CL detectors are developed that allow subsequent milling and CL imaging without manual intervention, as the current CL detector needs to be manually retracted before a slice can be milled. Due to the required high electron beam acceleration voltage for CL emission, the resolution for FIB-SEM CL tomography is currently limited to several hundreds of nm in XY and up to 650 nm in Z for diamonds. Opaque materials are likely to have an improved Z resolution, as CL emission generated deeper in the material is not able to escape from it.     

Color cathodoluminescence study of oxides subjected to thermal environments

The behavior of cathodoluminescence (CL) from oxides associated with plastic deformation as well as with annealing at different temperatures and atmospheres has been examined. Observations using the real color CL (CCL) mode in a scanning electron microscope show that the annealing temperature rather than the annealing atmosphere is the major factor influencing the observed changes in the spatial distribution of the total CL emission from the microdeformed surface. However, at the same annealing temperature, the spectral composition of the CL depends on the annealing atmosphere. An attempt has been made to explain the obtained results in terms of defect theory and radiation effects in electron microscopy.     

Monte Carlo simulation of CL and EBIC contrasts for isolated dislocations

Electron beam-induced current (EBIC) and cathodoluminescence (CL) are widely used to investigate semiconductor materials and devices, particularly to obtain information on the recombination properties and the geometry of defects. This report describes a simple formulation of CL and EBIC contrasts based on the Born approximation of excess carrier density in the presence of a pointlike defect. Quantitative interpretation of the CL and EBIC images is often difficult because of a lack of accurate theory treating simultaneously both the details of the electron beam penetration in the semiconductor and the generation of EBIC and CL signals. To overcome this difficulty, the Monte Carlo approach to the phenomenon of the electron beam penetration in solids has been developed to calculate the CL and EBIC signals during a simulation of the electron trajectory. Results for an inclined dislocation in GaAs are presented.     

A method of normalizing cathodoluminescence images of electron transparent foils for thickness contrast applied to InGaN quantum wells

The uniformity of panchromatic cathodoluminescence (CL) from In_0.09Ga_0.91N/GaN quantum wells at 100 K was investigated using a combined transmission electron microscope–cathodoluminescence instrument. A technique for correcting CL images of electron‐transparent wedge specimens for thickness contrast artefacts is presented. The foil thickness was estimated using the dynamical formulation of the relationship between the thickness and the (experimentally observed) transmitted electron intensity. For a given thickness the CL intensity was calculated using the Everhart–Hoff depth‐dose function and also taking into account surface recombination losses. Experimental CL images were normalized by dividing by the calculated CL value at each point. The procedure was successful in calculating the underlying materials contrast in CL images of thin specimens of InGaN single quantum wells. Non‐uniformities in the CL emission on the scale of ～0.7 µm were observed.     

SEM characterization of silicon nanostructures: can we meet the challenge?

The current semiconductor technology road map for device scaling champions a 4.5 nm gate length in production by 2022. The scanning electron microscope (SEM) as applied to critical dimensions (CD) metrology and associated characterization modes such as electron beam-induced current and cathodoluminescence (CL) has proved to be a workhorse for the semiconductor industry during the microelectronics era. We review some of the challenges facing these techniques in light of the silicon nanotechnology road map. We present some new results using voltage contrast imaging and CL spectroscopy of top-down fabricated silicon nanopillar/nanowires (<100 nm diameter), which highlight the visualization challenge. However, both techniques offer the promise of providing process characterization on the 10-20 nm scale with existing technology. Visualization at the 1 nm scale with these techniques may have to wait for aberration-corrected SEM to become more widely available. Basic secondary electron imaging and CD applications may be separately addressed by the He-ion microscope.     

Application of a new detector for cathodoluminescence measurements in the wavelength range to 1.8 μm

The energetic gap structure of semiconductors or insulators can strongly be influenced by the local appearance of inhomogenities, impurities, dopants or vacancies. A high spatial resolution cathodoluminescence (CL) measuring technique makes it possible to investigate this gap structure via spectral analysis of the emitted CL. This can lead to a detailed knowledge of the local defect distribution. The wavelength range which could be detected by CL measurements has, up to the present, been limited to values less than 1 μm, because no detectors were available for higher wavelengths. By use of a new germanium detector, the measuring range could be extended to 1.8 μm. This makes it possible to analyse the CL properties, both of materials with small gap energies and of deep impurities. The detector properties which are important for CL measurements are presented. The efficiency of the detector is demonstrated by CL investigations of barium titanate ceramics and silicon. The results are discussed and compared to results obtained using conventional detectors.     

A new approach to generating arc length parameterized NURBS tool paths for efficient three-axis machining of smooth, accurate sculptured surfaces

With the development of a new function of computer numerical control controllers, nonuniform rational B-spline (NURBS) interpolation, NURBS tool path generation for sculptured surface machining is under extensive research. The common procedures of the current NURBS tool path planning methods are as follows: first, to find a group of cutter contact points on a sculptured surface; second, to calculate their corresponding cutter locations (CLs); then, to fit a NURBS tool path to the CLs within a prescribed tolerance; and finally, to inspect the tool path for possible gouge by the tool and delete the invalid path segments, if any. However, the NURBS tool path has the following problems: (a) although it passes through the discrete CLs of the theoretical CL path, the deviation along the two paths could be larger than the tolerance; (b) its parameter is not the arc length of the path; and (c) it is difficult to detect gouge along the NURBS path and to remove the invalid segments from it. Consequently, NURBS tool paths generated with the current methods of commercial computer-aided design/computer-aided manufacturing (CAD/CAM) software cannot be used to make smooth and accurate surfaces. To address these problems, this work proposes a new approach to generating arc length parameterized NURBS tool paths with high accuracy in terms of the theoretical CL paths and without gouge and interference. Two practical examples in this work clearly demonstrate the feasibility of this approach and the advantages of the generated NURBS tool paths. Therefore, this approach can be implemented into the CAD/CAM software to promote NURBS machining in industry.     

Investigation of fluorescent lamp phosphors using the combined CL and EDS modes of the SEM

The phenomenon of cathodoluminescence (CL) potentially offers the ideal tool for studying the phosphor materials used in fluorescent lamps, since it can be used directly on processed or unprocessed powders, on coatings in tubes, or on sections cut from tubes. Using examples of both single component materials and multi-component blends, it is demonstrated how a relatively unsophisticated dispersive CL system attached to a scanning electron microscope (SEM) can be used expediently in the extensive study of such phosphors. These studies can be significantly enhanced when other complementary modes of the SEM (e. g. the energy-dispersive x-ray analysis facility) are combined with the CL mode. The strength of the combined technique lies in the major role it can play in materials and processing aspects of the powders themselves, in the processing of the lamps (e.g. by optimising such parameters as coating thickness, packing density etc.), and in diagnostic studies of poor materials or lamps (e.g. by locating rogue particles/components and identifying their origin). The technique also provides a convenient method of studying the temperature stability of selected phosphors.     

From quantum-well wires to nanowires as studied by cathodoluminescence imaging and spectroscopy

Cathodoluminescence (CL) imaging and spectroscopy are used to study one-dimensional structures from three different decades. Quantum-well wires were fabricated in the 1980s and CL images are presented here, where the individual wires of a 450 nm grating are resolved. V-grooved quantum wires (QWRs) were fabricated in the 1990s and the structures exhibit a number of emission peaks. CL is used to identify the spatial origin of the various peaks, including the positions of individual impurities in the QWRs. Nanowires from the 2000s show some variations along the length, which are presented here.     

Constant scallop-height tool path generation for three-axis discrete data points machining

This paper presents a new approach for the determination of constant scallop-height tool paths in the machining of discrete data points using three-axis ball-end milling. Compared with the existing approaches for surfaces, this approach avoids offsetting data points, which is complex and time consuming. This paper firstly creates the local coordinate system centered at each CL point of the current path to calculate the corresponding scallop point and then the similar local coordinate system is created at each scallop point to calculate the wanted CL point of the next tool path. The tool paths generated by the approach keep the scallop-height constant and meet the step error requirement. The experiment result indicates that the approach is feasible and efficient and the overall tool path length can be reduced significantly compared with the iso-planar method.     

A cathodoluminescent study of quartz sand grains

Surfaces and cross sections of individual quartz sand grains have been examined in both the emissive and cathodoluminescent (CL) modes using a scanning electron microscope. The cathodoluminescent micrographs reveal sub-surface information not seen in the emissive mode micrographs. The CL features are generally associated with previous stressing, fracturing or abrasion of the grains, and are probably related to the formation of disrupted-lattice and/or amorphous quartz. The sequence of events during the formation of these features can be identified on many grains by studying the spatial distribution of the most common form of CL contrast—narrow dark bands. On other grains, irregularly distributed dark patches are generally observed to be a surface phenomenon, but the distribution, depth and intensity of these features can be studied by examining cross sections of grains. While it is common for the banded features to cross the entire specimen, it is rare for the diffuse areas to penetrate more than 30 μm. Some grains when experimentally heated above the α-β transition temperature show a marked change and even a complete reversal in CL contrast. Such studies of grains in cathodoluminescence can supplement the environmental information obtained from emissive mode micrographs of geological materials.     

A computerized signal acquisition system for the quantitative evaluation of EBIC and CL data in a SEM

Electron beam-induced current (EBIC) and cathodoluminescence (CL) are widely used methods to obtain information about recombination properties of semiconducting materials and their defects on a micrometer length scale. In this article a computerized SEM (scanning electron microscope) setup is described, which enables us to perform simultaneous measurements of several signals and automatic temperature-dependent measurements. As examples for the performance of this system we present results obtained by simultaneous EBIC/CL experiments, allowing a reconstruction of the defect geometry. In a second example, the temperature dependence of the EBIC contrast is analyzed, introducing the method of EBIC spectroscopy.     

采用蛋白质组学技术筛选与肺腺癌转移相关的标志蛋白

本文应用表面增强基质辅助激光解析离子化-飞行时间质谱(SELDI-TOF-MS)对一系列转移能力递增的肺腺癌细胞CL1-0,CL1-2,CL1-3 CL1--5和CL1-5F4进行蛋白质谱检测。采用H4和WCX2两种具有表面修饰的蛋白芯片筛选差异蛋白,Biomarker Wizard软件分析结果显示H4和WCX2芯片共捕获到32个差异蛋白,其中15个蛋白在细胞随着转移能力增强而逐渐表达降低,相反17个蛋白则随着细胞转移能力的增强表达逐渐升高。在上述筛选到的32个差异蛋白中有2个蛋白可被两种芯片共同捕获。上述研究结果将为揭示肺癌发生和转移的分子机理提供有价值的实验数据。     

Combined cathodoluminescence and X-ray analysis of paint pigments

The suitability of cathodoluminescence (CL) measurements for differentiating between different paint pigments is demonstrated with an example of a combined energy-dispersive X-ray (EDX) and CL analysis of different zinc oxide (ZnO) pigments in a paint fragment where the EDX spectra are virtually identical, but where the CL spectra show significant differences. Consequently, it is possible to distinguish different pigments on the basis of CL spectra and monochromatic CL micrographs.     

齿轮表面的在线强化研究

根据现有的齿轮表面处理技术,提出了齿轮表面在线强化新构思,进而得出齿轮在线强化设计的方法。按此方法,在ＣＬ－１００齿累实验机上实现了齿轮表面的在线强化,为齿轮表面的强化处理提供了一种新的思路和方法。     

Prospective scintillation electron detectors for S(T)EM based on garnet film scintillators

The performance of a scintillation electron detector for a scanning electron microscope and/or a scanning transmission electron microscope (S(T)EM) based on new epitaxial garnet film scintillators was explored. The LuGAGG:Ce and LuGAGG:Ce,Mg film scintillators with chemical formula (Ce_0.01Lu_0.27Gd_0.74)_3–wMg_w(Ga_2.48Al_2.46)O₁₂ were prepared and their cathodoluminescence (CL) and optical properties were studied and compared with the properties of current standard bulk single crystal YAG:Ce and YAP:Ce scintillators. More specifically, CL decay characteristics, CL emission spectra, CL intensities, optical absorption coefficients, and the refractive indices of the mentioned scintillators were measured. Furthermore, electron interaction volumes with absorbed energy distributions, photomultiplier (PMT) photocathode matchings, modulation transfer functions (MTF), and the photon transport efficiencies of scintillation detectors with the mentioned scintillators were calculated. A CL decay time for the LuGAGG:Ce,Mg film scintillator as low as 28 ns with an afterglow of only 0.02% at 1 μs after the e‐beam excitation was observed. As determined from calculated MTFs, the scintillation detectors with the new film scintillators lose contrast transfer ability above 0.6 lp/pixel, while the currently commonly used YAG:Ce single crystal scintillators already do so above 0.1 lp/pixel. It was also calculated that the new studied film scintillators have an 8% higher photon transfer efficiency, even for a simple disk shape compared with the standard bulk single crystal YAG:Ce scintillator. The studied LuGAGG:Ce,Mg epitaxial garnet film scintillators were evaluated as prospective fast scintillators for electron detectors, not only in S(T)EM but also in other e‐beam devices.     

类回转体曲面数控加工刀位轨迹规划

针对类回转体曲面高速进给数控加工,提出螺旋线驱动方式下圆环刀具加工轨迹的规划方法。构造螺旋线作为类回转体曲面的导动线,根据曲面上已知接触点轨迹的切线方向估算后续导动点对应的初始接触点。计算初始接触点处圆环刀具的刀心位置,再计算初始刀心位置与后续导动点对应的目标刀位点分别在圆周方向以及轴向的距离差值,利用相邻刀位点与相邻接触点存在的准相似关系,得到接近目标接触点的搜索方向和步长,经过迭代得到目标接触点和刀位点。在分析接触点处曲面曲率和圆环刀曲率的基础上,给出圆环刀加工误差计算方法。将所提出的算法用于鞋楦的五轴数控轨迹规划中,计算结果表明,该算法搜索效率较高,具有理论和实际应用价值,并通过鞋楦的五轴数控加工试验验证了算法的有效性。