bluuebunny/crossref_metadata_2025_split huggingface dataset:
Applications of Scanning Tunneling Microscopy in the Materials Characterization Laboratory
Authors: Liu J.B , Clark Boyd , Fisher R.M. 
Published: June 2020

Scanning tunneling microscopy, first developed by G.Binnig, H.Rohrer, Ch.Gerber, and E.Weibel [1] in 1982 as a method of directly observing atom sites at the surface of graphite and other crystalline materials, is now being used in an ever increasing variety of applications as a result of steady and rapid advances in instrumentation, interpretation, and specimen handling techniques [2]. As a result the STM is widely recognized as a powerful method of observing surface structure on an atomic scale and is fast becoming an accessory tool in materials characterization laboratories that are devoted to solving industrial problems. Some examples representative materials characterization studies are described in mis paper.The first STM studies employed its high resolution capabilities for fundamental studies of the topography of atoms at surfaces [2]. More recently the value of the STM to observe both surface topography and electronic structure has been utilized. Figure 1 is a STM image of a charge density wave (CDW) from a TaS3 sample at 143K[3]. In this work the advantage of STM, due to sensitivity to both surface topography and electron structure, is apparent.The development of long scan STMs with scan capabilities of several micrometers or more has opened up a whole new class of materials where the magnifications required are comparable to that of a conventional SEM. The 3-dimensional structure of a processed optical recording disk, as revealed by the STM, is illustrated in Figure 2. The ability of the STM to observe both the course and ultrafine structure of such a sample makes it a powerful tool for relating processing conditions to surface structure defects and hence to the quality and reliability of the optical storage disk itself.
Secondary Electron Imaging of Crystal Surface Steps
Authors: Liu J. , Crazier P. A. , Cowley J. M. 
Published: June 2020

High resolution secondary electron (SE) images can be obtained in a scanning transmission electron microscope (STEM) by collecting the type I secondary electrons generated directly by the incident electron beam. The high resolution SE signal is, in general, localized to about 1 nm in the generation process. The escape depth of the secondary electrons, however, varies from about 1 nm for most metals to about 10 nm for some insulating materials. Surface steps can be imaged by collecting high resolution secondary electrons Among other possible contrast mechanisms for SE imaging of surface steps, topographic contrast plays an important role. The topographic contrast of surface steps depends on: (1) the incident electron probe size; (2) step height to SE escape depth ratio; (3) localization of the generated SE signals and (4) the incident beam angle relative to the specimen surface.In our UHV STEM (MIDAS) instrument, both the entrance and exit surfaces of the sample can be imaged by collecting secondary electrons. For thin samples, the resolution is < lnm for SE images of entrance and exit surfaces but for thicker samples the resolution of the SE image obtained from the exit surface will be degraded by the beam broadening effects. For studying steps on thick or bulk crystal surfaces, secondary electrons emitted from the entrance surfaces are, in general, collected to form images with high contrast and high resolution. In this report, all the SE images are obtained, in MIDAS, by collecting secondary electrons emitted from the entrance surfaces of the samples. Figure 1 is a SE image of a MgO smoke crystal revealing the surface growth steps with high contrast. The parallel straight steps, along <100> directions, constitute the edges of unfinished atomic planes on the MgO {100} crystal surfaces. This image indicates that the {100} surfaces of MgO smoke crystals are flat surfaces. Figure 2 shows a SE image of a MoO3 crystal with surface growth steps spiraling from an end-on screw dislocation (the black dots in the SE image represent electron beam induced reduction products). The dark lines (indicated by D) represent up-steps and the bright lines (indicated by B) represent down-steps. It is interesting to note that the two-dimensional crystal growth around the dislocation is anisotropic, forming terraces with long edges parallel to [010] direction.
Variations in Secondary Electron Emission from MgO Characterized by Secondary Electron Spectroscopy
Authors: Liu J. , Crozier P. A. , Hembree G. G. , Luo F. C. H. , Cowley J. M. , Venables J. A. 
Published: June 2020

The recent developments of the in-lens field emission scanning electron microscopes make it possible to image specimen surfaces with subnanometer resolution by collecting high resolution type I secondary electron (SE) signals. SE images with a resolutiori better than 1 nm have also been obtained in scanning transmission electron microscope (STEM) instruments. A problem related to the correct interpretation of these high resolution images is the lack of knowledge on the energies of the collected electrons contributing to the images. On the other hand secondary electron spectroscopy (SES) on clean surfaces has been developed for several years and biased SE imaging of several deposits on metallic and semiconductor crystal surfaces has been demonstrated. The combination of ultra-high resolution SE imaging with SES and Auger electron spectroscopy (AES) can be realized in pur UHV STEM instrument (MIDAS). The description of the performance of the MIDAS is reported elsewhere. We report here some recent results on SE imaging of MgO smoke crystals, in the MIDAS, with energy analysis of the collected secondary electrons.Strong variations of SE signals from different MgO crystals have been observed and the intensity of the collected secondary electrons from some MgO cubes increases under electron beam irradiation. Figure 1 shows a SE image of several MgO cubes, revealing that some of the crystals (indicated by A) have much higher intensity than others (indicated by B) and bright diffuse patches on the dark crystal can be seen (indicated by D). We have used SES to study the variations in SE emission under electron irradiation. The fact that the velocity distribution of the emitted secondary electrons may depend strongly on the surface morphology of the samples studied makes the interpretation of these SE spectra complicated. In order to avoid this problem and other possible complications arising from the detector geometry we acquired SE spectra from a fixed flat area of a single crystal MgO shown in figure 2. The sample was biased at -30 V and the resolution of the SE spectrum is about 1 eV. Figure 3a shows the SE spectra, taken from the exit surface of the crystal. Spectrum 1 was obtained from a poorly emitting MgO cube as that shown in figure 2 (all the spectra were obtained from the circled area). Spectra 2, 3 and 4 were obtained after about 10, 20 and 40 minutes electron irradiation respectively. In order to study spectral shape variations the spectra were normalized so that they all had the same peak intensity. The normalized data were shown in figure 3b.
Experiments on REM and SREM using a Tem/Stem Microscope with a Configurable Angle-Resolving Detector
Authors: Banzhof H. , Daberkow I. 
Published: June 2020

A Philips EM 420 electron microscope equipped with a field emission gun and an external STEM unit was used to compare images of single crystal surfaces taken by conventional reflection electron microscopy (REM) and scanning reflection electron microscopy (SREM). In addition an angle-resolving detector system developed by Daberkow and Herrmann was used to record SREM images with the detector shape adjusted to different details of the convergent beam reflection high energy electron diffraction (CBRHEED) pattern.Platinum single crystal spheres with smooth facets, prepared by melting a thin Pt wire in an oxyhydrogen flame, served as objects. Fig. 1 gives a conventional REM image of a (111)Pt single crystal surface, while Fig. 2 shows a SREM record of the same area. Both images were taken with the (555) reflection near the azimuth. A comparison shows that the contrast effects of atomic steps are similar for both techniques, although the depth of focus of the SREM image is reduced as a result of the large illuminating aperture. But differences are observed at the lengthened images of small depressions and protrusions formed by atomic steps, which give a symmetrical contrast profile in the REM image, while an asymmetric black-white contrast is observed in the SREM micrograph. Furthermore the irregular structures which may be seen in the middle of Fig. 2 are not visible in the REM image, although it was taken after the SREM record.
HREM Observations of Deformation Recovery on and Near Surfaces of Eu2O3
Authors: Ning X.G. , Ye H.Q. 
Published: June 2020

Profile imaging technigue has been achieved very much in the field of surface science since it was first proposed. This work will show the deformation recovery on and near the surfaces of Eu2O3 under electron irradiation. The experiment was carried out in a JEOL-200CX high-resolution electron microscope. The Eu2O3 phase has a complex cubic structure with a=1.087 nm. A projected unit cell has been marked in Fig. la. It has been indicated that only Eu3+ ions , which are located in f.c.c. sublattice, appeared in HR images under certain defocus and in the thin areas of specimen. The structural character of Eu2O3 shown by HR images may be analyzed based upon comparing with that of simple f.c.c. structure.It can be seen from Fig. la that the surfaces of Eu2O3 are clean and Eu3+ ions on the (111) surfaces S1 and S2 moved /12 towards to the right (it is actually surface stacking fault). In Fig.lb the stacking fault on S2 was removed under electron irradiation but remained on S1. The stacking fault energy of Eu2O3 is high in the bulk. From Fig.l it can be known that the stacking fault energy may become lower on the (111) surface due to less constrained factors there. This kind of surface stacking fault is related to surface partial dislocations, and both of them may act as the main forms of surface deformation under electron irradiation.
LVSEM: Past Present and Future
Authors: Pawley James B. 
Published: June 2020

Past: In 1960 Thornley published the first description of SEM studies carried out at low beam voltage (LVSEM, 1-5 kV). The aim was to reduce charging on insulators but increased contrast and difficulties with low beam current and frozen biological specimens were also noted. These disadvantages prevented widespread use of LVSEM except by a few enthusiasts such as Boyde. An exception was its use in connection with studies in which biological specimens were dissected in the SEM as this process destroyed the conducting films and produced charging unless LVSEM was used.In the 1980’s field emission (FE) SEM’s came into more common use. The high brightness and smaller energy spread characteristic of the FE-SEM’s greatly reduced the practical resolution penalty associated with LVSEM and the number of investigators taking advantage of the technique rapidly expanded; led by those studying semiconductors. In semiconductor research, the SEM is used to measure the line-width of the deposited metal conductors and of the features of the photo-resist used to form them. In addition, the SEM is used to measure the surface potentials of operating circuits with sub-micrometer resolution and on pico-second time scales. Because high beam voltages destroy semiconductors by injecting fixed charges into silicon oxide insulators, these studies must be performed using LVSEM where the beam does not penetrate so far.
Real Color Cathodoluminescence (CL) in the SEM: Physics, Color Display and Applications
Authors: Saparin G.V. , Obyden S.K. 
Published: June 2020

This paper is concerned with a novel technique of investigating the CL of solids in SEM by means of spectral topographical analysis (use of real color contrast determined by the local CL spectrum).The present-day black-and-white visualizing systems allow images with the number of brightness gradations more than 100. The observer is capable of distinguishing no more than 16 levels of monochrome color (grey levels) at a time. The situation differs when color contrast is used. In the color image, the elements of the same brightness can be discriminated by color contrast. Generally, color image elements can be discriminated both by brightness contrast and by color contrast. For example, only three primary colors (red, green and blue) are employed in commercial television, and the total number of hues approaches 16. If white is used as the reference color, the number of hues amounts to 12000, of which only one third can be displayed by the standard color monitor. The knowledge of color discrimination thresholds allows one to determine the number of colors discernable by eye, this number being about 1300. Thus, color contrast in SEM increases the information content of the image by about two orders, as compared with its black-and-white counterpart. This method of information representation does not practically allow any loss of information in forming the CL image in the visible region. SEM allows the formation of the image in real colors determined by the local CL spectra of the object. The color of the point is determined by the total power of all the detected spectral bands and lines. Thus, the color CL image represents spectral topographical information about the object surface. The signal forming this image for one color channel can be presented as.
Approaches to Quantitative Electron Detection in the Scanning Electron Microscope for Topographic Studies
Authors: Hejna Jan 
Published: June 2020

An electron signal in the scanning electron microscope (SEM) usually consists of contributions caused by different contrast mechanisms. The most common in practice are material and topographic contrasts. Quantification of material contrast is rather a simple matter. A backscattered electron detector placed over a specimen gives mainly material contrast which can be quantified by the use of a multichannel analyser like in the energy-dispersive x-ray spectrometry.In case of topographic contrast two problems arise. One of them is dimensional metrology, especially linewidth measurements in microelectronics, the second is reconstruction of a surface relief. The first problem needs detection conditions at which the results of SEM measurements correspond exactly with real dimensions, the second needs a signal which is related with a known formula to a local surface inclination and a procedure for converting the signal into the surface relief.Experiments in the SEM and Monte-Carlo calculations have shown that results of dimensional measurements depend on an energy of a primary beam, on a type of detected electrons (secondary electrons (SE) or backscattered electrons (BSE)) and on a type of a detector.The use of low primary beam voltages and BSE is advisable, The problem of a poor efficiency of BSE detectors at low primary beam voltages can be overcome by accelerating BSE, after they have passed through a grid rejecting SE, by high voltage applied to a scintillator in a BSE detector.
In-Lens Low-Loss Electron Detector for the Upper Specimen Stage in the Scanning Electron Microscope
Authors: Wells Oliver C. , LeGoues Françoise K. , Hodgson Rodney T. 
Published: June 2020

For the best resolution in either the scanning electron microscope (SEM) or the transmission electron microscope (TEM) the sample must be mounted in the high-field region of a condenser-objective lens. Detectors for either the secondary electrons (SE) or the backscattered electrons (BSE) in the SEM must allow for the fact that both of these are strongly deflected by the focusing magnetic field of the lens. Typically the SE are collected above the lens, while the BSE are collected using either diode(s) or scintillator(s) between the polepieces.Low-loss electrons (LLE) are scattered from a solid target with an energy loss of less than a few percent of the incident beam energy. These can be collected from a steeply tilted sample from below the exit polepiece of a condenser-objective lens. A suggestion to use the second half of the lens field as an energy filter was shown to by Munro to be unlikely to work because the chromatic dispersion of this part of the lens field is insufficient.The magnetic field of a condenser-objective lens can provide energy filtering as follows.A flat sample is mounted at typically 25° to 30° from the horizontal at or near the center of the lens. Figure 1 shows the trajectories of the electrons scattered with no loss of energy as calculated by Munro. These electrons are confined within a “containment region” with a well-defined boundary beyond which they cannot go. If a suitable detector is placed just inside the surface of this region then it will collect LLE. The slower BSE are confined within a smaller region and so are not collected.
Scattering of Electrons at High - Pressure and Restoration of Image Contrast in High Pressure Scanning Electron Microscopy
Authors: Shah J. S. , Durkin R. , Farley A. N. 
Published: June 2020

It is now possible to perform High Pressure Scanning Electron Microscopy (HPSEM) in the range 10 to 2000 Pa. Here the effect of scattering on resolution has been evaluated by calculating the profile of the beam in high pressure and assessing its effect on the image contrast . An experimental scheme is presented to show that the effect of the primary beam ionization is to reduce image contrast but this effect can be eliminated by a novel use of specimen current detection in the presence of an electric field. The mechanism of image enhancement is discussed in terms of collection of additional carriers generated by the emissive components.High Pressure SEM (HPSEM) instrumentation is establishing itself as commercially viable. There are now a number of manufacturers, such as JEOL, ABT, ESCAN, DEBEN RESEARCH, selling microscopes and accessories for HPSEM. This is because high pressure techniques have begun to yield high quality micrographs at medium resolution.To study the effect of scattering on the incident electron beam, its profile - in a high pressure environment - was evaluated by calculating the elastic and inelastic scattering cross sections for nitrogen in the energy range 5-25 keV. To assess the effect of the scattered beam on the image contrast, the modification of a sharp step contrast function due to scattering was calculated by single scattering approximation and experimentally confirmed for a 20kV accelerated beam.
Dependence Upon Thickness of Passivation in Low Voltage SEM Inspection of Electronic Devices
Authors: Ikeda S. , Maruse S. , Uchikawa Y. 
Published: June 2020

It was reported that SEM observation of micro electronic devices can be made without serious charging disturbances under a condition of low primary electron energy (Ep=1keV). Besides, the SEM can visualize a voltage profile of electrodes under a passivation layer as a contrast in the secondary electron images of the devices. This contrast appears in the first frame of imaging corresponding to the applied voltage, and disappears when the total dose of irradiated electrons exceeds a critical value. By observing the contrast variations, it was found that the total dose (Dm) of electrons is a linear function of the DC voltage (V) applied to the electrodes under the passivation layer. Utilizing this linearity, unknown local electrode voltage can be estimated, even when the electrodes exist under the passivation layer. However the coefficient of linearity depends on thickness of passivation. In this work we investigated into the dependence of Dm-V characteristics upon the thickness.A test specimen for SEM observation was prepared as follows. As shown in Fig.l, copper electrodes separated by a 0.1mm gap in shape of a hair-pin were evaporated on a quartz glass and then a layer of Si-oxide with varied thickness was deposited upon the surface of electrodes by means of the eximer laser abrasion. Selecting four points (A,B,C,D in Fig.l) of different thicknesses (A:4870A, B:4120A, C:3080A, D:2180A) on the surface of Si-oxide, while appling the voltage (V) between inner and outer electrodes under the passivation layer, the total dose (Dm) irradiated over the specimen untill the contrast of secondary electron image diminishes (Fig.2) was measured. As shown in Fig.3, there exist linearities between Dm and V for various values of the thickness (t) of Si-oxide. Futhermore, the rate of the total dose per voltage (Dm/V) changes depending on t (Fig.4). It should be noted that the total rate per voltage decreases linearly against the thickness.
In Situ Scanning Electron Acoustic Microscopy
Authors: Franceschi J.L. , Murillo R. , Bastié A. , Ez-Zejjari M. , El Abdary H. , Boughanmi N. 
Published: June 2020

A mini scanning electron microscope, the MEBIS [1] (“Microscope Electronique à Balayage In situ”) is used to inspect “in situ” bulk specimens. The electron-optical column which has been made small and light, can be placed just over the sample. With a specially designed control circuitry, a chopped electron beam is used as a source of thermoelastic waves at the surface of specimen. The induced thermal and ultrasonic waves are used for detection and, by combining this acoustic signal with the scanned electron beam, imaging of the subsurface is possible.The accelerating potential used is 10 kV and the equivalent source of thermoelastic waves is less than one micrometre in metals. Below the megahertz range for the chopped beam (frequency f), the wavelength of sound λa is greater than that of the thermal waves λg. Approximately, only thermal waves determines the spatial resolution [2]. These waves are damped with an experimental decay dT = Cte.f−1/2, and the spatial resolution is similar to dT, typically five micrometres in metals for the beam modulation frequency of 100 kHz, with linear signal detection [3]. Above the MHz range, submicronic spatial resolution is possible. But the sensitivity is also a function of the frequency. The signal to noise ratio (S/N) is proportionnal to f−1 (low frequency). A compromise must be made between S/N ratio and satisfactory spatial resolution, since for bulk specimens the signal decays with the thickness [4].