Magnetic contrast in the scanning electron microscope: An appraisal of techniques and their applications

The SEM represents a comparatively new technique for the imaging of magnetic domains and a “state of the art” review of its applications and potential is given. A simple account of electron scattering, presented initially, serves as a basis to explain the physical origin and characteristics of the two principal modes of magnetic contrast. Simple models of the imaging process are discussed as well as the instrumental factors necessary to optimize contrast and resolution.The SEM has been used to investigate the domain structures of recording tape, cobalt and many magnetic oxides, including bubble materials. It also yields quantitative information about field distributions such as those found in recording heads. Domain and domain wall images may also be observed in cubic materials and this is particularly useful for studying the behaviour of transformer grain oriented silicon-iron, especially at high accelerating voltages where the coating can be penetrated to reveal the magnetic structure beneath.When allied with its versatility in other fields of operation it is concluded that the SEM constitutes a valuable tool for domain observation and will find increasing use as such.     

An electron microscope investigation of domain structures in thin terbium foils

Thin foils have been prepared from a high quality terbium single crystal for investigation in the transmission electron microscope. The preparation process involved spark machining, chemical polishing and ion beam thinning. The electron microscope was used to examine both the foil microstructure and its magnetic domain structure down to a temperature of 150 K. Below 230 K a narrow periodic magnetic structure running parallel to the in-plane b-axis was formed. This persisted over a temperature range of 10 K before giving way to a less regular pattern. As the temperature was lowered to 150 K the density of domain walls decreased and their deviation from the b-direction became more pronounced. A qualitative explanation of the observations is given.     

掺杂半导体扫描电镜二次电子像

综述了用扫描电镜的二次电子像获得掺杂半导体衬度剖析的方法．实验发现掺杂半导体扫描电镜像对杂质浓度的灵敏度可以达到1016cm^-3，且空间分辨率高达nm量级，是最有可能发展成为下一代掺杂剖析成像的主流技术．文中还探讨了半导体掺杂衬度的可能的机理，详细介绍了两种主要机理：表面能带弯曲和样品外局域电场的出现．     

Differential amplitude contrast imaging in the scanning optical microscope

A split detector is used in a scanning optical microscope to produce high-quality differential amplitude contrast images. A slight lateral offset in the detector position is shown to introduce information about object height variations to the image. These results are compared with images obtained by electrical differentiation.     

Characterization of a nano line width reference material based on metrological scanning electron microscope

The line width (often synonymously used for critical dimension, CD) is a crucial parameter in integrated circuits. To accurately control CD values in manufacturing, a reasonable CD reference material is required to calibrate the corresponding instruments. We develop a new reference material with nominal CDs of 160 nm, 80 nm, and 40 nm. The line features are investigated based on the metrological scanning electron microscope which is developed by the National Institute of Metrology (NIM) in China. Also, we propose a new characterization method for the precise measurement of CD values. After filtering and leveling the intensity profiles, the line features are characterized by the combination model of the Gaussian and Lorentz functions. The left and right edges of CD are automatically extracted with the profile decomposition and k-means algorithm. Then the width of the two edges at the half intensity position is regarded as the standard CD value. Finally, the measurement results are evaluated in terms of the sample, instrument, algorithm, and repeatability. The experiments indicate efficiency of the proposed method which can be easily applied in practice to accurately characterize CDs.     

Beam analysis of scanning electron microscope according to the mirror effect phenomenon

In a scanning electron microscope the influence of electronic beam parameters on the electron-mirror images has been investigated. A simple theoretical model for scanning electron beam behavior in terms of beam and surface potentials is presented. The derived expression relates the scanning beam parameters and parameters of an irradiation region. Influence of a beam (the size and current), scanning potential, working distance, trapped charge and the irradiated area on electron mirror images are defined. Results show that the electron beam current has a considerable effect on the deduced mirror images in comparison with the other beam parameters. So it could be adapted for adjusting the phenomena of mirror effect. Moreover, the trapped charges have been calculated and the results examined in comparison with experimental data.     

Measurements of scan nonlinearity in a scanning electron microscope

A method for measuring the scan nonlinearity of a scanning electron microscope is discussed. This method is tested using a mass-produced microscope and demonstrates good results.     

Image contrast in the backscattered electron mode in scanning electron microscopy and microtomography

The problem of image contrast production in the backscattered electron (BSE) mode in a scanning electron microscope (SEM) in bulk and film structures is discussed. The considerable influence of the parameters of a semiconductor detector on the image contrast is shown. Calculations for contrast in dependence on the composition of target sections, the energy of primary electrons, and the signal detection technique are presented.     

Changes of cathodoluminescence emission from MgO in the scanning electron microscope

The effect of electron beam on the cathodoluminescence (CL) from MgO single crystals has been studied in the scanning electron microscope. It has been found that CL intensity and spectrum vary with irradiation time. The behaviour is discussed in terms of impurities and vacancy defects.     

Field emission of individual carbon nanotubes in the scanning electron microscope

The field emission of individual multiwall carbon nanotubes grown by chemical vapor deposition was measured in a scanning electron microscope. By using a sharp anode, we were able to select one nanotube for measurements in carefully controlled conditions. Single nanotubes follow the Fowler-Nordheim law, and the dependence of the field enhancement with interelectrode distance and nanotube radius is in good agreement with the recent model of Edgcombe and Valdré. Our results suggest that only nanotubes with the highest field enhancement factors, i.e., at least 8x higher than those of the average nanotube population, contribute to the emitted current in usual large area measurements.     

Updating of the toroidal electron spectrometer intended for a scanning electron microscope and its new applications in diagnostics of micro- and nanoelectronic structures

A new version of the toroidal electron spectrometer installed in a scanning electron microscope is described. The new instrument has made it possible to carry out fundamental and applied research in the field of local nondestructive inspection of micro- and nanoelectronic materials and devices. The topology control of 3D microstructures by backscattered electron tomography is exemplified. A high efficiency of secondary electron energy filtering in monitoring of semiconductor regions locally doped by p- and n-type impurities is demonstrated. A physical substantiation for the high contrast of the doped regions is given. The feasibility of taking electron spectra using a scanning electron microscope in a wide range from slow secondary electrons to elastically scattered ones is proved.     

Focused ion beam treatment of ZnO nanowires in the scanning electron microscope

We investigated vapor phase epitaxy-grown ZnO nanowires on a Si substrate by scanning electron microscopy. These investigations show that there are single nanowires and ensembles of nanowires, among which we found straight and bend, perfect and non-perfect nanowires, as well as nanowires with clean surfaces and surfaces with the dark spots and features. After focused ion beam polishing and milling we found that nanowires are homogeneous. The sizes of the nanowires were determined: the length is about 2–24 μm, and the width and height are about 200–500 nm.     

Characterization of the response to moisture of talc and perlite in the environmental scanning electron microscope

This article focuses on the application of ESEM to study the dynamic interaction of hydrophobic and hydrophilic filler materials of interest for the cosmetic and pharmaceutical industries. The ability of ESEM to attain different thermodynamic stages was used to record real-time information of hydration and dehydration processes of those materials in the presence of water and sweat (used as a model physiological fluid). This information is of great importance to understand the behavior of a product containing those fillers as well as to identify potential processing issues related to the interaction of the filler with moisture.     

各向同性媒质中的扫描电子声显微镜的信号激发

在前期研究(声学学报;1991;16(3):161—169)的基础上,建立了改进的热源分布模型。利用积分变换和特征函数展开法,求解了强度简谐调制的电子束源在各向同性试样中所激发的各种Lamb波模式,以及耦合在试样背面的压电片的电压输出,并分析了扫描电子声显微镜(SEAM)的信号激发机理。结果表明SEAM是一种高分辨率的近场成像技术,它的最佳横向空间分辨率为22~(1/2)倍的电子束焦斑半径。实验结果表明SEAM的空间分辨率可优于0.5μm,小于试样的热扩散长度,从实验上证实了理论预计的SEAM的近场成像特征。     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

The effect of beam diameter on the electron skirt in a high pressure scanning electron microscope

Helium gas and air are commonly used in the high pressure scanning electron microscope (HPSEM). The presence of a gaseous environment in the specimen chamber modifies the electron beam profile. In order to fully understand the beam-gas interaction, we have investigated the beam-diameter effect for two gases (helium and air) by Monte Carlo simulation. In this calculation, we have assumed that the electron beam is Gaussian and we have explored the influence of the nature of the gas at low voltage. When the beam diameter varies between 1 and 100 nm, there is no influence on the beam profile for these two gases. The resolving power of the HPSEM is not affected by the beam-gas interaction. These theoretical results have been compared with experimental images obtained at low voltage under air and helium gases. The variation of image quality at low voltage has confirmed the interest of helium for use in a Field Emission Gun SEM (FEGSEM) in high pressure (or low vacuum) conditions.     

Tip-induced surface polarization: a new mechanism for contrast in the scanning tunnelling microscope

We propose a new mechanism influencing the contrast in STM images. It involves the polarization of the surface by the electric field from the tip; this affects the contrast when different parts of the surface have different polarizabilities. We demonstrate its importance for the case of ethene (C₂H₄) molecules adsorbed on the Si(001) surface; for this system we are able to obtain qualitative agreement between experiments and ab initio calculations by including the tip-induced field.