A novel method for acquiring large-scale automated scanning electron microscope data

Recent software and hardware advances in the field of electron backscatter diffraction have led to an increase in the rate of data acquisition. Combining automated stage movements with conventional beam control have allowed researchers to collect data from significantly larger areas of samples than was previously possible. This paper describes a LabVIEW? and AutoIT^© code which allows for increased flexibility compared to commercially available software. The source code for this software has been made available in the online version of this paper.     

Low-cost image-capture system for a scanning electron microscope

We describe a PC-based active-capture system for recording digital images from a scanning electron microscope. The system is based on a National Instruments data-acquisition board and a Pentium computer, controlled by software that we have written in Visual Basic.     

A cassette system for systematic cryostorage of low-temperature scanning electron microscopy stubs

A system is described for the storage of cylindrical (10 × 3.5 mm) stubs for low-temperature scanning electron microscopy. The system facilitates rapid retrieval of mounted specimens, maximizes the capacity of the low-temperature (liquid nitrogen) specimen store, locates each stub exactly in a protected well, and eliminates the possibility of specimen damage from conventional hazards during transport between the storage facility and microscope.     

Secondary electron imaging in the variable pressure scanning electron microscope

Secondary electron imaging is not possible in the variable pressure scanning electron microscope because the mean free path of the secondaries in the gas is too short to permit them to reach the detector. This paper therefore investigates an alternative strategy for producing an image containing significant amounts of secondary electron contrast. This involves modifying the microscope by the addition of a biased electrode above the sample and then collecting a specimen current signal. This system, originally described by Farley and Shah (1988), is found to produce true secondary electron detail over a wide range of conditions.     

Transmission EBSD from 10 nm domains in a scanning electron microscope

The spatial resolution of electron diffraction within the scanning electron microscope (SEM) has progressed from channelling methods capable of measuring crystallographic characteristics from 10 μm regions to electron backscatter diffraction (EBSD) methods capable of measuring 120 nm particles. Here, we report a new form of low‐energy transmission Kikuchi diffraction, performed in the SEM. Transmission‐EBSD (t‐EBSD) makes use of an EBSD detector and software to capture and analyse the angular intensity variation in large‐angle forward scattering of electrons in transmission, without postspecimen coils. We collected t‐EBSD patterns from Fe–Co nanoparticles of diameter 10 nm and from 40 nm‐thick Ni films with in‐plane grain size 15 nm. The patterns exhibited contrast similar to that seen in EBSD, but are formed in transmission. Monte Carlo scattering simulations showed that in addition to the order of magnitude improvement in spatial resolution from isolated particles, the energy width of the scattered electrons in t‐EBSD is nearly two orders of magnitude narrower than that of conventional EBSD. This new low‐energy transmission diffraction approach builds upon recent progress in achieving unprecedented levels of imaging resolution for materials characterization in the SEM by adding high‐spatial‐resolution analytical capabilities.     

Transient analysis of gaseous electron-ion recombination in the environmental scanning electron microscope

Most of the work carried out in relation to contrast mechanisms and signal formation in an environmental scanning electron microscope has yet to consider the time dependent aspects of image generation at a quantitative level. This paper quantitatively describes gaseous electron‐ion recombination (also known as ‘signal scavenging’) in an environmental scanning electron microscope at a transient level by utilizing the dark shadows/streaks seen in gaseous secondary electron detector images of alumina (Al₂O₃) immediately after a region of enhanced secondary electron emission is encountered by a scanning electron beam. The investigation firstly derives a theoretical model of gaseous electron‐ion recombination that takes into consideration transients caused by the time constant of the gaseous secondary electron detector electronics and external circuitry used to generate images. Experimental data of pixel intensity versus time of the streaks are then simulated using the model enabling the relative magnitudes of (i) ionization and recombination rates, (ii) recombination coefficients and (iii) electron drift velocities, as well as absolute values of the total time constant of the gaseous secondary electron detection system and external circuitry, to be determined as a function of microscope operating parameters such as gaseous secondary electron detector bias, sample‐electrode separation, imaging gas pressure, and scan speed. The results revealed, for the first time, the exact dependence that the effects of secondary electron‐ion recombination on signal formation has on reduced electric field and time in an environmental scanning electron microscope. Furthermore, the model implicitly demonstrated that signal loss as a consequence of field retardation due to ion space charges, although obviously present, is not the foremost phenomenon causing streaking in images, as previously thought.     

A new method for low-magnification in the environmental scanning electron microscope

A device has been developed and used successfully on two models of the environmental scanning electron microscope that allows low-magnification imaging of about 30x, significantly better than the original 200x low-magnification imaging limit. This was achieved by using an additional aperture to limit the pressure at a point where it will not block the electron beam, and a larger aperture plate for the combination final aperture/secondary electron signal collection surface that also does not block the electron beam significantly.     

A new correction method for high-resolution energy-dispersive x-ray analyses in the environmental scanning electron microscope

Spurious x-ray signals, which previously prevented high-resolution energy-dispersive x-ray analysis (EDS) in the environmental scanning electron microscope (ESEM), can be corrected using a simple method presented here. As the primary electron beam travels through the gas in the ESEM chamber, a significant fraction of the primary electrons is scattered during collisions with gas molecules. These scattered electrons form a broad skirt that surrounds the primary electron beam as it impacts the sample. The correction method assumes that changes in the width of the electron skirt with pressure are less important than changes in the skirt intensity; this method works as follows: The influence of the gas on the overall x-ray data is determined by acquiring EDS spectra at two pressures. Subtracting the two spectra provides us with a difference spectrum which is then used to correct the original data, using extrapolation, back to the x-ray spectrum expected under high-vacuum conditions. Low-noise data are required to resolve small spectral peaks; however, the principle should apply equally to x-ray maps and even to low-magnification images.     

A fluorescence scanning electron microscope

Fluorescence techniques are widely used in biological research to examine molecular localization, while electron microscopy can provide unique ultrastructural information. To date, correlative images from both fluorescence and electron microscopy have been obtained separately using two different instruments, i.e. a fluorescence microscope (FM) and an electron microscope (EM). In the current study, a scanning electron microscope (SEM) (JEOL JXA8600 M) was combined with a fluorescence digital camera microscope unit and this hybrid instrument was named a fluorescence SEM (FL-SEM). In the labeling of FL-SEM samples, both Fluolid, which is an organic EL dye, and Alexa Fluor, were employed. We successfully demonstrated that the FL-SEM is a simple and practical tool for correlative fluorescence and electron microscopy.     

A robust focusing and astigmatism correction method for the scanning electron microscope

This paper discusses a new approach to focusing and astigmatism correction based on the fast fourier transforms (FFTs) of scanning electron microscopy (SEM) images. From the FFTs, it is possible to obtain information on the severity of the defocus and astigmatism. This information is then processed by an algorithm to perform real-time focusing and astigmatism correction on the SEM. The algorithm has been tested on defocused and astigmatic images of different samples, including those with highly directional features. Experiments show that the images obtained after running the algorithm can be as good as those that an experienced SEM operator can achieve.     

影响扫描电镜图像质量的因素分析

本文介绍影响扫描电镜图像质量的因素及其对图像质量的影响,分别从加速电压、扫描速度和信噪比、束斑直径、探针电流、消像散校正、工作距离以及反差对比等分析图像质量的变化原因,提出提高图像质量的方法。     

A mirror electron microscope for surface analysis

The principle of mirror microscopy has been adapted to provide a relatively low resolution surface microscope (<1000 ×), a large transfer width low energy electron diffractometer and a photoelectron analyser in k_|| space. A focused electron beam of ? 10 kV is decelerated through a Johansson lens, reflected in front of the sample and reaccelerated back through the lens to produce an electron image over a field of view of a few microns. The image can be interpreted as a micrograph of work function variations on the surface if other effects (geometry, magnetic field) are uniform. In the LEED mode, diffracted beams virtually retain their positions on the screen over the whole impact energy range used (0.160 V). Secondary electrons are preferentially focused around the lens-gun electro-optic axis, thus effectively filtering them out from the diffraction pattern. The design has an inherently large coherence length, of up to 10⁴ Å. Photoelectrons can similarly be imaged in k_|| space on the detector plane. The addition of energy filtering at the screen allows the two-dimensional Fermi surface to be imaged.     

A gripping stub* for the examination of multilaminous biological specimens in the scanning electron microscope

A simple specimen holder has been developed which expedites study of multilaminous biological specimens in the scanning electron microscope. It has the interesting additional property of allowing examination of the top and bottom of a single sample.     

Energy selective scanning electron microscopy to reduce the effect of contamination layers on scanning electron microscope dopant mapping

We demonstrate that energy selective scanning electron microscopy can lead to substantial dopant contrast and resolution improvements (compared to standard SEM) when the energy selection is carried out based on Monte Carlo modelled secondary electron spectra in combination with detector transfer modelling.     

A scanning tunnelling microscope for operation in air

In this paper a scanning tunnelling microscope for operation in air is described with emphasis on the coarse and fine sample positioning mechanism, piezoelectric scanner and vibration isolation. Line scan (amplitude modulation), top view (brightness modulation) and combined shaded topographical images of the surface of highly orientated pyrolitic graphite are shown.     

A scanning electron microscope based new method for determining degree of substitution of sodium carboxymethyl cellulose

Na-CMC or sodium carboxylmethyl cellulose is a water soluble anionic polymer obtained by introducing carboxymethyl groups along the cellulose chain. Na-CMC is usually synthesized by the alkali catalyzed reaction of cellulose with monochloroacetic acid. The functional properties of Na-CMC depend on the degree of substitution of the cellulose structure (i.e. how many of the hydroxyl groups are substituted per monomer unit), and also on the chain length of the cellulose backbone. The degree of substitution of Na-CMC is usually determined according to ASTM D1439 which evolves the conversion of the Na-CMC to free acid then again forming Na-CMC by adding excess alkali and finally titrating the excess alkali with standard hydrochloric acid (0.3 N). The used volume of the standard alkali determines the degree of substitution. These existing chemical methods for determining the degree of substitution are not very convenient and very time-consuming involving the use of hazardous chemicals. In this research, we have evaluated that the scanning electron microscope equipped with Energy Dispersive X-Ray Analysis can be used to directly determine the degree of substitution.     

Measurements of the surface microroughness with the scanning electron microscope

A three-dimensional reconstruction system for scanning electron microscope consisting of a quadruple scintillator detector, a four-channel frame-grabber and PC-based processing unit was developed. The authors explored a method that takes advantage of the angular distribution of secondary electron emission to obtain quantitative topography contrast and surface profiles. Software processing algorithms were developed to carry out the reconstruction process and compensate for several types of errors, inherent in the method. After pre-calibration, the system allows obtaining surface topography with calculation of microroughness and waviness statistical parameters. The roughness estimation procedure was tested on metal roughness standards for machining and etched silicon surfaces. The main advantages of the system are almost real-time operation and reliable, composition-independent reconstruction for a broad class of materials.     

Chemical etching of natural fluorapatite crystals in acid solutions studied with the scanning electron microscope

Different aspects of the chemical etching process for natural fluorapatite (FAP) crystals in pure phosphoric acid solutions and for those with additives of Ca²⁺ and H₂SO₄ have been studied by means of the scanning electron microscope. The resulting experimental data obtained in the etching process are very sensitive to dissolving conditions, type of crystal face, and the presence or absence of any epitaxial coatings on the surface of dissolving crystals. It was found that the pyramidal crystal faces of the FAP have the highest dissolution rate value and, as a result, are not etched at all. The prism and pinacoid faces usually are covered by hexagonal etch pits under the same conditions. Additives of Ca²⁺ to the phosphoric acid solution result in transition from a chemical etching to a chemical polishing process, and additives of H₂SO₄ result in epitaxial coatings of CaSO₄· xH₂O (x = 0,0.5, 2) and shapeless pits formation.