SEM imaging of air-sensitive specimens

A device has been built that allows four air-sensitive specimens to be examined in a Philips 501 scanning electron microscope (SEM) without interrupting the vacuum. The specimens are mounted onto a revolving four-faceted stage in an inert atmosphere. The sealed device is then mounted onto the goniometer substage of the SEM and interfaced with the stage rotation drive. After the microscope reaches the operating vacuum condition, the device is opened by turning the stage rotation knob. The device can be viewed with the SEM image during this operation. The same mechanism which opens and closes the device also rotates the four-faceted sample mount to the desired specimen. The x and y translations of the SEM sub-stage are used to move the specimen in the imaging plane. The operation of this device was tested with polyolefin catalysts which are extremely air-sensitive. The main advantage of this device is that it allows air-sensitive specimens to be routinely examined without compromising the other uses of the SEM. Specimens mounted on this device can be viewed from 0 to ± 90° tilt. With a minor adaption, this device can be used to view the total 360° surface of a specimen in a manner similar to that described by Herrmann (1979).     

Cyanide removal of gold from SEM specimens.

The cyanide method is highly recommended for the purposes of the removal of gold coatings from SEM specimens prior to (a) further treatment before further SEM, and (b) staining and mounting for LM.     

An efficient single crystal BSE detector in SEM

Using the optical modifications described, the signal of the wide-angle BSE detector can be increased 3.7-fold compared with the detector type illustrated in Figure 1. The increase was achieved by more fully exploiting the optical phenomena of diffusion, reflection at the critical angle and antireflection, and especially that of their combined effects. A higher photon energy transfer was obtained by specific optical modifications to the scintillator and the light guide. Based on the current modifications, it can be estimated that about 75% of the generated light reaches the PMT. It is necessary, therefore, to revise all values previously published of the DQE coefficient of the YAG scintillator. A general value of DQE is of very limited use depending as it does on the specific conditions under which light emerges from the YAG scintillator. The DQE, therefore, does not permit sufficiently accurate comparison with other scintillation materials. The DQE can be evaluated only for a completed detector configuration in which the laws of geometrical optics apply, or it can be used for making comparisons of scintillation materials used in the same detector configuration.     

高效压电陶瓷加工原理探讨

针对波导管等特殊管状物体内壁的加工,提出了内腔压电超声换能推挤原理,采用了具有频率自动跟踪系统的超声波发生器,自行设计了用于管内腔超声推挤的压电陶瓷换能器,并设计给出了变幅杆--推刀振动子系统的谐振频率、位移节点、放大倍数等计算公式,测出了声学系统的电导--电纳特性,并进行了工艺试验,探讨了超声推挤过程.     

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.     

A simple filter system for processing small or transparent specimens

A novel method of attaching a fine mesh filter to the end of a disposable plastic pipette is described. Such a pipette filter can be used to exclude specimen uptake during specimen preparation procedures, particularly when processing small or transparent materials. The pipette filter-tip does not interfere with fluid exchange and is non-reactive with normal processing fluids.     

Digital image processing of combined SEM and EDX signals

Due to the complexity of biological tissue and man-made materials, the limits of light microscopy in quantitative image analysis are often reached. The scanning electron microscope provides a much higher resolution in such situations, especially when using the low noise secondary electrons signal. However, secondary electrons are sensitive to topography rather than to the elements constituting the specimen. This effect usually makes discrimination of distinct phases or objects by simple grey value thresholding difficult or even impossible. The additional information given by an energy dispersive X-ray system is the step to overcome this problem. The combination of both signals—grey level and energy dispersive information—leads to a masking procedure which eliminates image sections, not belonging to the phase under investigation, from the evaluation.     

Examples of image processing using a computer controlled SEM

Several examples of the use of digital image processing on SEM images are presented. The emphasis is on image enhancement as opposed to pattern recognition. Examples given include non-linear histogram modification, noise filtering, and frame by frame subtraction. Image processing is done on digitally stored images obtained from a modified SEM. The SEM has been modified to allow minicomputer control of the electron/CRT beam position and blanking. Digitization of the sample signals, such as secondary electron, backscattered electron, and absorbed current is done using a 5 MHz voltage to frequency converter and a 100 KHz timer/sealer combination. Software for image storage and manipulation is also described.     

A simple vacuum pipette for processing groups of specimens for electron microscopy.

A standard sink filter pump attached to a special glass adaptor, holding pipettes, enables groups of specimens to be fixed and dehydrated for electron microscopy with speed and safety.     

Comparison of cleaning methods for delicate insect specimens for scanning electron microscopy

The objective of the present study was to compare cleaning methods for delicate insect specimens for investigations with scanning electron microscopy (SEM). As typical specimens we used aquatic larvae of mosquitoes, springtails, larvae of mayflies and caterpillars because they are very fragile and large parts of their body consist of soft tissue. Additionally their cuticle is very often covered with dirt, soil particles or other materials. Cleaning with ultrasonic sound, as the most common cleaning method used for SEM, will destroy fragile insects. Therefore we tested different procedures to remove the dirt particles. In a first approach we compared cleaning with Potassium hydroxide (KOH), Proteinase K, and Triton X in aquatic larvae of flies, which were available in numbers and kept under the same conditions. As our results showed that the treatment with KOH gives the best results we treated in a second approach springtails, larvae of mayflies and caterpillars only with KOH. The springtails and caterpillars were largely free of particles after treatment with KOH; however, the larvae of mayflies were still covered with remnants of diatoms and precipitates of calcium carbonate of the algae. KOH dissolves organic impurities, on the other hand silicon dioxide and lime crusts are not solved. With this limitation, treatment with KOH is a simple technique for routine use as cleaning method for fragile insect specimens for SEM.     

Chemical etching in processing cortical bone specimens for scanning electron microscopy

Transverse and longitudinal sectioning of undecalcified cortical bone is a commonly employed technique for investigating the lamellar structure of the osteons. Since a flat surface is required, the specimen has to be grinded and then polished. Whereas the smear of debris and inorganic/organic deposits left by these treatments cannot be removed by ultrasonication alone, a chemical treatment of the specimen surface with either a basic or an acid etching solution is currently employed. A further effect of the latter can be the enhancement of the lamellar bone pattern. The kind of etching solution, its pH, the concentration of etchants, and the contact time significantly affect the sectioned surface when it is observed with scanning electron microscopy (SEM). The etching procedures can severely influence the obtained images. Homogeneous cortical bone specimens were sampled from the first metatarsal of two fresh human subjects. One or two cut surfaces were exposed to different acid and basic solutions in bonded conditions. Considering the type of chemical agents, the solution pH, and the exposure time of the specimens, the effects of several etching media have been investigated and compared. Strong etching, either acid or basic produced surface decalcification and severe damage of the collagen matrix, compromising any morphological or morphometric analysis. Weak acid etching (for example citric and acetic acid), even though causing distinctive alteration of the sample, enhanced the visibility of the lamellar pattern, while the polyphosphate treatment of the surface decalcified a thin layer matrix, ensuring a good visibility of fibrils and avoiding rough distortions. Microsc. Res. Tech. 77:653–660, 2014. © 2014 Wiley Periodicals, Inc.     

An inexpensive and highly efficient device for observing a transmitted electron image in SEM

An inexpensive, efficient device that supplies a transmission mode to the conventional SEM has been developed. The transmitted electrons strike a metal plate, and these generate secondary electrons that are proportional to the quantity of the transmitted electrons. The generated electrons are collected by the secondary electron detector. Hence, the performance of this device is influenced by the number of secondary electrons generated in the metal plate. In order to construct a device that can attain the best transmitted electron image, the signal-to-noise ratio of images, obtained from various trial devices, were measured by a newly-developed digital image processing program. When the material and shape of the device are selected, to produce high-secondary emission, the efficiency of the device compares with that of a relatively expensive standard detector system (scintillator detector).     

An efficient spectroscopic detection system for cathodoluminescence mode scanning electron microscopy (SEM)

A detection system for analytical cathodoluminescence (CL) mode scanning electron microscopy (SEM) is described. This incorporates a cold stage, an efficient light collector, a monochromator and a photomultiplier and used the photon counting technique. The efficiency of the component subsystems was optimized and calibrated, and the performance of alternative light collecting and monochromating equipment is compared. The operation of the photon counter is discussed. The digital output of the photon counter was fed into a multichannel scaler and thence to a computer. This was used to correct the observed count rate with the calibrated spectral variations in the performance of the detection system. Spectra obtained at both room temperature and liquid nitrogen temperacure and monochromatic and panchromatic SEM micrographs are given as examples illustrating the value of this technique. The factors governing the performance of the system are discussed. The forms of noise in the signal and in the detection system are described and the means for minimizing, avoiding or correcting for them are dealt with. Sources of spurious signals in the SEM are treated.     

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