Electron Detection Mode Research Articles

Back-scattered electron visualization of ferroelectric domains in a BiFeO3 epitaxial film

Three-dimensional orientation of the ferroelectric (FE) domain structure of a BiFeO3 epitaxial film was investigated by scanning electron microscopy (SEM) using back-scattered electrons and piezoresponse-force microscopy (PFM). By changing the crystallographic orientation of the sample and the electron collection angle relative to the detector, we establish a link between the orientation of polarization vectors (out-of-plane and in-plane) in the BiFeO3 film and the back-scattered electron image contrast in agreement with PFM investigations. The different FE polarization states in the domains correspond to altered crystalline environments for the impingent primary beam electrons. We postulate that the resultant back-scattered electron domain contrast arises as a result of either differential absorption (through a channelling effect) or through back-diffraction from the sample, which leads to a projected diffraction pattern super-imposed with the diffuse conventional back-scattered electron intensity. We demonstrate that SEM can be sensitive for both out-of-plane and in-plane polarization directions using the back-scattered electron detection mode and can be used as a non-destructive and fast method to determine 3D FE polarization orientation of domains.

Electron detection modes comparison for quantification of secondary phases of Inconel 686 weld metal

Quantitative analyses produce important information concerning the microstructural characteristics of materials, which are reflected in the main properties of the materials. The secondary and backscattered electron modes represent the two main techniques most used in scanning electron microscopy, to produce images and, consequently, realize a quantitative analysis. However, each technique has its advantages and problems. The present work proposed evaluate what is the best SEM technique to quantify secondary phases in a cladding of Inconel 686, which can be extended to the other classes of nickel based alloys rich in Mo. It was performed a quantitative analysis of several images to characterize the microstructure of Inconel 686 weld cladding. The images were obtained using three modes: secondary electron (SE), Z contrast backscattered electron (BSE) and topographic backscattered electron (BSE). The segmentation and quantify of secondary phases was performed by SVRNA software. The statistical results revealed differences between the techniques. The secondary electron mode included several artefacts that reduced the precision of the quantification study. The BSE modes are shown to be the best techniques for quantification.

On the mechanisms of the corrosion of weathering steel by SO2 in laboratory studies: influence of the environmental parameters

We report here on the mechanisms underlying the corrosion of weathering steel in accelerated laboratory tests using artificially polluted SO2-atmospheres. The role of corrosion parameters such as the SO2 concentration, the exposure time, the relative humidity and temperature of the environment are discussed in detail. Through the extensive use of Mossbauer spectroscopy in both its transmission and electron detection modes, as well as with the help of other analysis techniques, the characterization of the different corrosion products at the various stages of the corrosion process has been carried out. The results complement the data obtained in field studies and help to understand the mechanisms involved in this complex phenomenon.

Structure of foliicolous thalli of the Gomphillaceae in a south-western Florida lichen community

AbstractFoliicolous lichens complete their life cycles upon non-deciduous leaves in humid tropical and subtropical environments. The anatomy of these lichens and its adaptations to this specialized niche have received only limited attention. The present work examines the structural organization in seven species of the Gomphillaceae that colonize palm leaves in south-west Florida, USA. Thalli with their leaf substratum were embedded in resin and examined with SEM in backscattered electron detection mode. All species showed a continuous, covering epilayer of fungal origin that consisted of relatively sparse, scattered cell lumina of reduced diameter connected by cell wall-derived material. Fungal cells were intermixed below this layer, with algal cells often resting directly on the substratum. Interactions between symbionts were mainly limited to wall-to-wall contacts without penetration. The epilayer showed continuity with the fungal prothallus at the perimeter of the thalli. Crystalline deposits in the upper portions of thalli were common, particularly in the species of Gyalectidium examined. All thalli were entirely epicuticular; some covered the stomata of the leaf beneath. It is suggested that the prominence of non-living wall materials and mineral crystals in thallus structure might serve to minimize the metabolic cost of fungal tissue in climates where warm temperatures at night result in higher rates of respiration.

Virtual scanning electron microscope. 5. Application in nanotechnology and in micro- and nanoelectronics

The provided examples demonstrate the application of a simulator-based virtual scanning electron microscope (SEM) in certification of test object sizes on a low-voltage SEM and in calibration of a high-voltage SEM operating in the slow secondary electron detection mode. Using the virtual SEM, the problem of comparing different SEM calibration techniques is solved.

Prokaryotic community structure in photosynthetic biofilms from extreme acidic streams, Río Tinto (SW, Spain)

Four algal photosynthetic biofilms were collected from the Rio Tinto (SW Spain) at four localities: AG, Euglena and Pinnularia biofilms; ANG, Chlorella and Pinnularia biofilms; RI, Cyanidium and Dunaliella biofilms; and CEM, Cyanidium , Euglena and Pinnularia biofilms. Community composition and structure were studied by a polyphasic approach consisting of 16S rRNA analysis, scanning electron microscopy by back-scattered electron detection mode (SEM-BSE), and fluorescence in-situ hybridization (FISH). Acidophilic prokaryotes associated with algal photosynthetic biofilms included sequences related to the Alpha-, Beta-, and Gammaproteobacteria (phylum Proteobacteria) and to the phyla Nitrospira, Actinobacteria, Acidobacteria and Firmicutes. Sequences from the Archaea domain were also identified. No more than seven distinct lineages were detected in any biofilm, except for those from RI, which contained fewer groups of Bacteria . Prokaryotic communities of the thinnest algal photosynthetic biofilms ( 200 μm) generate microniches that could facilitate the development of less-adapted microorganisms (coming from the surrounding environment) to extreme conditions, thus resulting in a more diverse prokaryotic biofilm. [ Int Microbiol 2008; 11(4):251-260]

Prokaryotic community structure in algal photosynthetic biofilms from extreme acidic streams in Río Tinto (Huelva, Spain).

Four algal photosynthetic biofilms were collected from the Río Tinto (SW Spain) at four localities: AG, Euglena and Pinnularia biofilms; ANG, Chlorella and Pinnularia biofilms; RI, Cyanidium and Dunaliella biofilms; and CEM, Cyanidium, Euglena and Pinnularia biofilms. Community composition and structure were studied by a polyphasic approach consisting of 16S rRNA analysis, scanning electron microscopy by back-scattered electron detection mode (SEM-BSE), and fluorescence in-situ hybridization (FISH). Acidophilic prokaryotes associated with algal photosynthetic biofilms included sequences related to the Alpha-, Beta-, and Gammaproteobacteria (phylum Proteobacteria) and to the phyla Nitrospira, Actinobacteria, Acidobacteria and Firmicutes. Sequences from the Archaea domain were also identified. No more than seven distinct lineages were detected in any biofilm, except for those from RI, which contained fewer groups of Bacteria. Prokaryotic communities of the thinnest algal photosynthetic biofilms (-100 microm) were more related to those in the water column, including Leptospirillum populations. In general, thick biofilms (200 microm) generate microniches that could facilitate the development of less-adapted microorganisms (coming from the surrounding environment) to extreme conditions, thus resulting in a more diverse prokaryotic biofilm.

Direct Electron Exposed Silicon Detectors in EELS

Abstract Samples to be studied using EELS techniques are more or less sensitive to the effects of the radiation exposed to them by the beam. Quite often the sample is damaged due to the high radiation doses in the areas where the beam has been focused. Secondly, the build up of carbon contamination on the surface of the sample caused by the beam affects the results of the analysis if the sample itself contains carbon. The solution to these problems is to minimize the exposure times needed to record the spectrum, which will lower the radiation-doses on the sample. In addition, problems related to beam instabilities would be reduced due to the shortened acquisition times. However, in order still to achieve an acceptable signal-to-noise ratio the need for a detector with high detective quantum efficiency is essential. We have investigated the possibilities using silicon detectors such as photodiode arrays (PDA) and charge coupled devices (CCD) in direct electron detection mode using 100 keV incident electrons.

Low-profile high-efficiency microchannel-plate detector system for scanning electron microscopy applications

A new design high-efficiency microchannel-plate detector and amplification system is described for use in the scanning electron microscope. This complete detector system consists of four basic units: (1) the microchannel-plate detector; (2) the video amplifier; (3) the high-voltage power supply; and (4) the control unit. The microchannel-plate detector system is efficient at both high and low accelerating voltages, and is capable of both secondary electron and backscattered electron detection modes. The size of the actual detector is approximately 3.5 mm in thickness and 25.4 mm in diameter. Thus, use of this detector system permits using almost all the sample chamber to accommodate large specimens with only the loss of the 3.5 mm of working distance. Another feature is that this system also employs a unique video amplifier where there are no active elements at high voltage. The microchannel-plate detector system enables the investigation of secondary electron induced contrast mechanisms and backscattered electron detection at extremely low accelerating voltages even those below 1.0 keV.

The relationship between accelerating voltage and electron detection modes to linewidth measurement in an SEM

AbstractThe basic premise underlying the use of the scanning electron microscope (SEM) for linewidth metrology in semiconductor research and production applications is that the video image acquired, displayed, analyzed, and ultimately measured accurately reflects the structure of interest. However, it has been clearly demonstrated that image distortions can be caused by the detected secondary electrons not originating at the point of impact of the primary electron beam and by the type and location of the secondary electron detector. These effects and their contributions to the actual image or linewidth measurement have not been fully evaluated. Effects due to uncertainties in the actual location of electron origination do not affect pitch (line center‐to‐center or similar‐edge‐location‐to‐similar‐edge‐location spacing) measurements as long as the lines have the same edge geometries and similar profiles of their images in the SEM. However, in linewidth measurement applications, the effects of edge location uncertainty are additive and thus give twice the edge detection error to the measured width. The basic intent of this work is to demonstrate the magnitude of the errors introduced by beam/specimen interactions and the mode of signal detection at a variety of beam acceleration voltages and to discuss their relationship to precise and accurate metrology.

Electron detection modes and their relation to linewidth measurement in the Scanning Electron Microscope

The basic premise underlying the use of the scanning electron microscope (SEM) for linewidth measurement for semiconductor research and production applications is that the video image acquired, displayed, and ultimately measured reflects accurately the structure of interest. It should be understood that not all the secondary electrons detected originate at the point of impact with the primary electron beam. Those that do are referred to as Type I electrons. Some of the signal is contributed by re-emergent backscattered electrons creating secondary electrons at the surface of the sample (Type II electrons) and at the final lens polepiece (Type III electrons). Other signal contributions include line-of-sight backscattered electrons and other sources particular to each instrument (Type IV electrons). The effects of these four types of contributions to the actual image or linewidth measurement have not been fully evaluated. In measurement applications, error due to the actual location of signal origination will not affect pitch measurements as the errors cancel. However, in linewidth measurement, the errors are additive and thus give twice the edge detection error to the measured width. The basic intent of this work is to demonstrate the magnitude of these errors relative to the mode of signal detection at a variety of beam acceleration voltages.

The microstructure of ballas (polycrystalline diamond) by electrostatic charging in the SEM

The term "ballas" as used in this paper means a naturally occurring, essentially single phase polycrystalline aggregate of diamond grains with a roughly spherical external shape and with very distinctive grain-boundaries. This is in general agreement with the definitions of others [1-6], but without emphasizing the criterion of a preferred orientation. Ballas has been described both with [1-4] and without [7] a radially aligned structure. The position taken here from our own experience is similar to that of Jeynes [3] in that both these and possibly other characteristic arrangements, such as overgrowth over a larger central grain [2], can be considered as ballas also. Although it has been speculated that ballas could have formed from carbonado [6], ballas is not an aggregate of grains sintered together as in most natural carbonados and especially not as in synthetic materials such as Compax and Syndite. The grain-boundaries are not of the traditional 120 ° equilibrium type characteristic of grains in sintered ceramics and metals, but rather have many aspects of nearly crystallographic, relatively low-angle boundaries some of which appear to be twinned. There are at least five studies that conclude ballas is the result of a crystal growth process rather than sintering [1-5]. The purpose of this letter is to support this conclusion with new evidence from a technique that has proved useful in revealing growth textures at high resolution in single crystal diamond [8]. Several different ballases were polished to various depths at diametrically opposed sites to provide windows into the interior and surfaces for study by reflected light and by SEM. The polishing was done on a cast iron scaife charged with synthetic diamond powder. All samples showed the typical tight grain-boundary structure reported by others [1-7]. In some there is more obvious porosity (usually cracks) at grainboundaries than others. All were remarkably free of second phases. Two 1/8in. diameter roughly spherical samples are described here because of their interesting, but not unusual, microstructure. The polished surfaces were observed with reflected light microscopy including Nomarski interference contrast. The charging in the electron beam of the SEM was the same technique described in the previous paper [8]: let the sample charge up in the beam without a conducting layer and and observe the contrast between areas of higher and lower electron accumulation using primarily the secondary electron detection mode. Two different International Scientific Instruments, Model 40 and a Super III, were used with beam voltages ranging from 15 to 30 kV. In general the samples were examined at a slight tilt, although the patterns did not change with differing degrees of tilt. A simple explanation of the textures revealed by