Scintillation SE detector for variable pressure scanning electron microscopes

We present results obtained with a new scintillation detector of secondary electrons for the variable pressure scanning electron microscope. A detector design is based on the positioning of a single crystal scintillator within a scintillator chamber separated from the specimen chamber by two apertures. This solution enables us to decrease the pressure to several Pa in the scintillator chamber while the pressure in the specimen chamber reaches values of about 1000 Pa (7.5 Torr). Due to decreased pressure, we can apply a potential of the order of several kV to the scintillator, which is necessary for the detection of secondary electrons. Simultaneously, the two apertures at appropriate potentials of the order of several hundreds of volts create an electrostatic lens that allows electrons to pass from the specimen chamber to the scintillator chamber. Results indicate a promising utilization of this detector for a wide range of specimen observations.     

Measurement technique for the incident electron current in secondary electron detectors and its application in scanning electron microscopes.

A measurement technique for incident electron current in secondary electron (SE) detectors, especially the Everhart-Thornley (ET) detector, based on signal-to-noise ratio (SNR), which uses the histogram of a digital scanning electron microscope (SEM) image, is described. In this technique, primary electrons are directly incident on the ET detector. This technique for measuring the correlation between incident electron current and SNR is applicable to the other SE detectors. This correlation was applied to estimate the efficiency of the ET detector itself, to evaluate SEM image quality, and to measure the geometric SE collection efficiency and the SE yield. It was found that the geometric SE collection efficiency at each of the upper and lower detectors of a Hitachi S-4500 SEM was greater than 0.78 at all working distances.     

Application of channel electron multipliers in an electron detector for low‐voltage scanning electron microscopy

An electron detector containing channel electron multipliers was built and tested in the range of low‐voltage scanning electron microscopy as a detector of topographic contrast. The detector can detect backscattered electrons or the sum of backscattered electrons and secondary electrons, with different amount of secondary electrons. As a backscattered electron detector it collects backscattered electrons emitted in a specific range of take‐off angles and in a large range of azimuth angles enabling to obtain large solid collection angle and high collection efficiency. Two arrangements with different channel electron multipliers were studied theoretically with the use of the Monte Carlo method and one of them was built and tested experimentally. To shorten breaks in operation, a vacuum box preventing channel electron multipliers from an exposure to air during specimen exchanges was built and placed in the microscope chamber. The box is opened during microscope observations and is moved to the side of the scanning electron microscope chamber and closed during air admission and evacuation cycles enabling storing channel electron multipliers under vacuum for the whole time. Experimental tests of the detector included assessment of the type of detected electrons (secondary or backscattered), checking the tilt contrast, imaging the spatial collection efficiency, measuring the noise coefficient and recording images of different specimens.     

Synthesis and characterization of Ag–Co–Ni nanowires

This work provides an electrodeposition‐based methodology for synthesizing multicomponent nanowires containing Ag, Co and Ni atoms. Nanowire morphology was obtained by using an anodic alumina membrane with cylindrical pores of ～200‐nm diameter. Structural, compositional and magnetic characterization revealed that the as‐synthesized nanowires adopted a core–shell microstructure. The core (axial region) contained pure Ag phase volumes with a plate‐like morphology oriented perpendicular to the nanowire axis. The shell (peripheral region) contained pure Ag nanoparticles along with superparamagnetic Co and Ni rich clusters.     

High‐quality imaging in environmental scanning electron microscopy – optimizing the pressure limiting system and the secondary electron detection of a commercially available ESEM

In environmental scanning electron microscopy applications in the kPa regime are of increasing interest for the investigation of wet and biological samples, because neither sample preparation nor extensive cooling are necessary. Unfortunately, the applications are limited by poor image quality. In this work the image quality at high pressures of a FEI Quanta 600 (field emission gun) and a FEI Quanta 200 (thermionic gun) is greatly improved by optimizing the pressure limiting system and the secondary electron (SE) detection system. The scattering of the primary electron beam strongly increases with pressure and thus the image quality vanishes. The key to high‐image quality at high pressures is to reduce scattering as far as possible while maintaining ideal operation conditions for the SE‐detector. The amount of scattering is reduced by reducing both the additional stagnation gas thickness (aSGT) and the environmental distance (ED). A new aperture holder is presented that significantly reduces the aSGT while maintaining the same field‐of‐view (FOV) as the original design. With this aperture holder it is also possible to make the aSGT even smaller at the expense of a smaller FOV. A new blade‐shaped SE‐detector is presented yielding better image quality than usual flat SE‐detectors. The electrode of the new SE detector is positioned on the sample table, which allows the SE‐detector to operate at ideal conditions regardless of pressure and ED.     

Toward structural/chemical cotailoring of phase‐change Ge–Sb–Te in a transmission electron microscope

Ge₂Sb₂Te₅, as the prototype material for phase‐change memory, can be transformed from amorphous phase into nanoscale rocksalt‐type GeTe provided with an electron irradiation assisted by heating to 520°C in a 1250 kV transmission electron microscope. This sheds a new light into structural and chemical cotailoring of materials through coupling of thermal and electrical fields.     

A transformation anomaly in a Cu–Zn–Al alloy

A comparison is described of the structures of an M9R Cu–Zn–Al alloy as quenched directly into the martensitic state, and as stabilized, with the structure of the material after up-quenching into the β₁ state after which treatment the martensitic memory transformation occurs thermoelastically. Preliminary results on the increased tendency for the stabilized alloy to form f.c.c. stacking sequence regions are given and discussed.     

New scintillation detector of backscattered electrons for the low voltage SEM

The new scintillation detector of backscattered electrons that is capable of working at primary beam energy as low as 0.5 keV is introduced. Low energy backscattered electrons are accelerated in order to generate a sufficient number of photons. Secondary electrons are deflected back by the energy filter so that the true compositional contrast of the specimen is obtained. The theoretical models of the detector function are described and first demonstration images are presented.     

A high-speed area detector for novel imaging techniques in a scanning transmission electron microscope

A scanning transmission electron microscope (STEM) produces a convergent beam electron diffraction pattern at each position of a raster scan with a focused electron beam, but recording this information poses major challenges for gathering and storing such large data sets in a timely manner and with sufficient dynamic range. To investigate the crystalline structure of materials, a 16×16 analog pixel array detector (PAD) is used to replace the traditional detectors and retain the diffraction information at every STEM raster position. The PAD, unlike a charge-coupled device (CCD) or photomultiplier tube (PMT), directly images 120–200 keV electrons with relatively little radiation damage, exhibits no afterglow and limits crosstalk between adjacent pixels. Traditional STEM imaging modes can still be performed by the PAD with a 1.1 kHz frame rate, which allows post-acquisition control over imaging conditions and enables novel imaging techniques based on the retained crystalline information. Techniques for rapid, semi-automatic crystal grain segmentation with sub-nanometer resolution are described using cross-correlation, sub-region integration, and other post-processing methods.     

An optical configuration for fastidious STEM detector calibration and the effect of the objective‐lens pre‐field

In the scanning transmission electron microscope, an accurate knowledge of detector collection angles is paramount in order to quantify signals on an absolute scale. Here we present an optical configuration designed for the accurate measurement of collection angles for both image‐detectors and energy‐loss spectrometers. By deflecting a parallel electron beam, carefully calibrated using a diffraction pattern from a known material, we can directly observe the projection‐distortion in the post‐specimen lenses of probe‐corrected instruments, the 3‐fold caustic when an image‐corrector is fitted, and any misalignment of imaging detectors or spectrometer apertures. We also discuss for the first time, the effect that higher‐order aberrations in the objective‐lens pre‐field has on such an angle‐based detector mapping procedure.     

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 simple backscattered electrons and specimen current detection device for the scanning electron microscope

A simple, low-investment device has been developed that allows the collection of backscattered electrons (BSEs) and specimen current (SC) signals for imaging purposes and current measurement. Originally, this system was designed for detection, measurement, and display of specimen current, with a video signal output whose level was modulated by this current. Eventually, a BSE detector was developed, using a graphite disk (about 8 cm in diameter) to collect the BSEs. The disk was mounted on a Philips SEM 5O5, attached and concentrically to the final lens aperture. This configuration gives a large solid angle of collection. The collected charge is further processed by the same electronics used in the aforementioned SC detection system. Electron channeling, topographic contrast with BSE, and material contrast with BSE and SC images can be obtained with reasonably good edge definition.     

A critical evaluation of film thickness‐derived pressure–viscosity coefficients

A single parameter, the pressure–viscosity coefficient, α, quantifies the pressure dependence of the viscosity of the liquid in elastohydrodynamic lubrication (EHL). Most published values of α have not been obtained from measurements of viscosity as a function of pressure. Rather, these effective pressure–viscosity coefficients have been derived from the measurement of the EHL film thickness, a more difficult procedure. In this article, five well‐characterized liquids that should be Newtonian in the EHL inlet are identified for which film‐derived coefficients have been reported. These coefficients are compared with coefficients derived from published viscosity correlations and new viscosity measurements. The film‐derived coefficients are found to not be an accurate representation of the piezoviscous response. The procedure of deriving a pressure–viscosity coefficient from a film thickness measurement does not offer an alternative to the simpler and easier viscometer measurement. Copyright © 2014 John Wiley & Sons, Ltd.     

A modification of the Jones–Harris method for deep-groove ball bearings

This study presents a modification of the Jones–Harris method (JHM) for the determination of deflection in deep-groove ball bearings. The finite element method (FEM) and curve fitting have been utilized to modify the load–deflection relationships of Hertz contact formulas in JHM. Several cases of deep-groove bearings are simulated to determine contact deflection. Results obtained from the modified JHM (MJHM) are more accurate than the JHM results demonstrated by the comparison between FEM and experimental results.     

In situ TEM studies of micron‐sized all‐solid‐state fluoride ion batteries: Preparation,prospects, and challenges

Trustworthy preparation and contacting of micron‐sized batteries is an essential task to enable reliable in situ TEM studies during electrochemical biasing. Some of the challenges and solutions for the preparation of all‐solid‐state batteries for in situ TEM electrochemical studies are discussed using an optimized focused ion beam (FIB) approach. In particular redeposition, resistivity, porosity of the electrodes/electrolyte and leakage current are addressed. Overcoming these challenges, an all‐solid‐state fluoride ion battery has been prepared as a model system for in situ TEM electrochemical biasing studies and first results on a Bi/La_0.9Ba_0.1F_2.9 half‐cell are presented. Microsc. Res. Tech. 79:615–624, 2016. © 2016 Wiley Periodicals, Inc.     

A testing device for rolling–sliding behavior in harsh environments: the twin-disk cryotribometer

Understanding the mechanical behavior of angular contact ball bearing contacts in extremely harsh environments has led to the development of specialized apparatus. This device simulates the rolling–sliding behavior of elliptical contacts where the dynamic and kinematic conditions are perfectly controlled. Such a device facilitates several types of analyses: that of mechanically induced surface damage, that of transfer film, that of characterizing surface treatments and surface coatings, and that of thermal phenomena at the contact. Moreover the testing device allows the experimental confirmation of theoretical models developed for determining bearing lifetimes. First we shall describe the testing device end afterwards we shall present results for each type of analysis mentioned above.     

A systematic investigation of the charging effect in scanning electron microscopy for metal nanostructures on insulating substrates

Scanning electron microscopy is perhaps the most important method for investigating and characterizing nanostructures. A well‐known challenge in scanning electron microscopy is the investigation of insulating materials. As insulating materials do not provide a path to ground they accumulate charge, evident as image drift and image distortions. In previous work, we have seen that sample charging in arrays of metal nanoparticles on glass substrates leads to a shrinkage effect, resulting in a measurement error in the nanoparticle dimension of up to 15% at 10 kV and a probe current of 80 ± 10 pA. In order to investigate this effect in detail, we have fabricated metal nanostructures on insulating borosilicate glass using electron beam lithography. Electron beam lithography allows us to tailor the design of our metal nanostructures and the area coverage. The measurements are carried out using two commonly available secondary electron detectors in scanning electron microscopes, namely, an InLens‐ and an Everhart–Thornley detector. We identify and discriminate several contributions to the effect by varying microscope settings, including the size of the aperture, the beam current, the working distance and the acceleration voltage. We image metal nanostructures of various sizes and geometries, investigating the influence of scan‐direction of the electron beam and secondary electron detector used for imaging. The relative measurement error, which we measure as high as 20% for some settings, is found to depend on the acceleration voltage and the type of secondary electron detector used for imaging. In particular, the Everhart–Thornley detectors lower sensitivity to SE₁ electrons increase the magnitude of the shrinkage of up to 10% relative to the InLens measurements. Finally, a method for estimating charge balance in insulating samples is presented.     

V-shaped metal–oxide–semiconductor transistor probe with nano tip for surface electric properties

We design and fabricate a V-shaped metal–oxide–semiconductor (MOS) transistor probe with the focused-ion-beam (FIB) nano tip to measure surface electric properties. The V-shaped structure is selected for its better lateral stiffness, and the specific dimensions are determined using the parallel beam approximation (PBA). The deposition conditions for the nano tip are also investigated for better tip sharpness. The high working frequency of the MOS transistor improves the scanning speed and the high sensitivity reduces the additional equipment required. The detection properties of the device are investigated with PZT poling patterns. The measured results show well-defined patterns, promising that the device can detect surface electric properties with high sensitivity and high working frequency.     

Use of backscattered electron detector arrays for forming backscattered electron images in the scanning electron microscope

The backscattered electron (BSE) signal in the scanning electron microscope (SEM) can be used in two different ways. The first is to give a BSE image from an area that is defined by the scanning of the electron beam (EB) over the surface of the specimen. The second is to use an array of small BSE detectors to give an electron backscattering pattern (EBSP) with crystallographic information from a single point. It is also possible to utilize the EBSP detector and computer-control system to give an image from an area on the specimen--for example, to show the orientations of the grains in a polycrystalline sample ("grain orientation imaging"). Some further possibilities based on some other ways for analyzing the output from an EBSP detector array, are described.