bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel Methods of Microanalysis Employing Secondary- and Auger-Electron Spectroscopy in Stem
Authors: Kruit P. 
Published: June 2020

Introduction: Electron spectroscopy is a well established technique in physics and material science and merely adding the spatial resolution of a STEM would already open a new field of applications. However, by using the specific advantages of electron microscope optics and the expertise in thin specimen preparation of microscopists, electron spectroscopy in the STEM can yield information that cannot be obtained in any other way.Instrumentation: The feasibility of extracting a large portion of the Auger and secondary electrons from the magnetic field of an immersion condenser objective lens has now been demonstrated. The scheme involves a careful shaping of the magnetic field through which the electrons are guided to a deflector which separates the secondary beam from the primary beam. The parallelizing action of this field forces the electrons into a beam of small opening angle which can be accepted by traditional optics including an electrostatic energy analyser. Results reported in this paper are from a prototype instrument; energy analysers mounted on fully ultra high vacuum microscopes are now also in operation or will become operational very soon. To detect the secondary or Auger electron together with the primary electron which was responsible for its emission requires only small additions to the instrumentation. Single electron sensitivity in both the secondary electron detector and the EELS detector are of course necessary, but this can be done with standard detectors with a timing resolution of better than 5 ns. Commercial electronic equipment can then sort the coincident events.
Stochastic Limitations to Phase and Contrast Determinations in Electron Holography
Authors: Lenz Friedrich , Völkl Edgar 
Published: June 2020

An important step in the evaluation of electron holograms consists in the determination of contrast μ> 0 and phase φ of a distribution functionrecorded using a large but finite number N of electrons. The direction of the interference fringes and their period (‘fringe width’) which is used as length unit are assumed to be known. The x axis runs perpendicular, and the y axis parallel to the fringes. It is assumed that a rectangular area is evaluated, the width of which in x direction is an integer multiple of the fringe width, and that within this area the fringe system is parallel and equidistant, i.e. μ and φ are constant. We shall restrict ourselves to the interval 0 < x ≤ 1. According to (1), the probability for an electron to be recorded within an interval between x and x + dx is W(x, φ,μ) dx. During the practical evaluation of a holographic fringe pattern, however, the x values are not measured but only the numbers of electors recorded within finite sampling areas.
Subunit Arrangement of and Rearrangements in E. coli F1F0 ATP Synthase Determined by Cryoelectron Microscopy
Authors: Gogol Edward. P. , Capaldi Roderick. A. 
Published: June 2020

The F1F0 ATP synthase is the enzymatic complex which interconverts the electrochemical energy of the transmembrane proton gradient, generated by oxidative phosphorylation of metabolic substrates, into the energy currency of ATP. In doing so, it reversibly couples transmembrane proton flow to the catalysis of the high energy terminal phosphate bond of ATP. Even the simplest example of the enzyme, the bacterial F1F0, is a complex assembly of eight subunits in non-unit stoichiometry, five making up the catalytic F1 portion (α3β3γδε) and three the F0, the proton channel (a b2c10‒12) We are attempting to understand the role of subunit interactions in the coupling phenomenon and the catalytic mechanism, which exhibits an extraordinarily high degree of allosteric cooperativity.Three-dimensional reconstruction of negatively stained arrays of the F1 has shown it to be a hexagonal barrel-shaped structure; cryoelectron microscopy of unstained, frozen-hydrated specimens (figure 1a) has revealed an interior cavity partially occluded by an internal structure.Immunolabelling with monoclonal Fab fragments to the α subunit, followed by alignment and averaging of cryoelectron images, has demonstrated the alternating αβ arrangement of subunits around the periphery of the F1. The internal structure has also been localized next to one of the (catalytic) β subunits (see figure 2a,b). Addition of Fab fragments to the carboxy-terminal part of the (single-copy) γ subunit preserves the characteristic triangular appearance and uniform orientation of the Fl-Fab complexes (figure lb).Averages of these images place the additional density of the label at the periphery of the structure, superimposed on a β subunit (figure 2c). Surprisingly, similar results are obtained with readily-binding monoclonal antibodies to each of the single-copy subunits.
T4 Replication Accessory Proteins Visualized as Complexes with DNA by Cryoelectron Microscopy
Authors: Gogol Edward P. , Young Mark C. , Kubasek William L. , Jarvis Thale C. , von Hippel Peter H. 
Published: June 2020

Replication of bacteriophage T4 is accomplished by a set of proteins encoded by the T4 genome.Central to replication is the DNA polymerase, the product of gene 43 (g43p); while it contains the intrinsic functions of template-directed DNA synthesis, it requires a set of accessory proteins as a minimal system to function with a rate, fidelity and processivity comparable to those obtainedin vivo.These accessory proteins are g44p, g45p and g62p; g32p, a single-stranded DNA binding protein, also assists in the replication process, bothin vitroandin vivo.In the absence of DNA, g44p and g62p form a 4:1 complex which has a DNA-dependent ATPase activity; g45p is a trimer in solution. Their association state when bound to DNA is however unknown, as is the mechanism by which they dramatically improve the replication activity of g43p.We have examined the complex of the three replication accessory proteins and g32p as a complex with DNA by cryoelectron microscopy, avoiding stains or fixatives which may disrupt the labile structures formed. Under conditions which promote the polymerase-enhancing activity of this four-protein system, distinct "hash mark" structures are visible along strands of replicative form M13 DNA (figure 1). These structures are formed only in the presence of all four proteins and ATP; absence of any one of the proteins or ATP, or substitution of non-hydrolyzable ATP analogues, fails to yield any of the hash marks.
Description of two regular structures associated to the cell envelope of Thermus thermophilus: a structural transformation?
Authors: Carrascosa J.L. , R. Castón José , Faraldo M.M. , Berenguer J. , de Pedro M.A. 
Published: June 2020

Thermus thermophilus HB8 is a Gram-negative thermophilic eubacteria, with a well-defined outer membrane and a thin peptidoglycan layer around the cytoplasmic membrane. There is a S-layer on the cell envelope, whose main component is a protein of Mr around 100.000, masked by a lipopolysaccharide-like outer surface that can be revealed by freeze-fracture and shadowing of the native surface of the cells of T. thermophilus.When membrane fractions of this bacteria are treated with Triton X-100 in presence of EDTA, two-dimensional crystals with a hexagonal ordering could be observed by negative staining (figures 1a, 1b). This structure, called S1, had an unit cell dimensions a = b = 20 nm. Nevertheless, if the treatment is developed without the quelant agent, a structure with p2 symmetry is observed, S2, (figures 1d, 1e) with a = 24 and b = 21 nm. We have characterized both crystals by electron microscopy and two-dimensional analysis by Fourier methods. The resulting images showed very different characteristics; while the p6 structure is a typical S-layer, fig. 1c, the other one is a porin-like or regular outer membrane protein structure, fig. 1f, (2).This is surprising because both fractions contains the same ˝P100˝ protein (revealed by biochemical analysis).
Energy-Filtered Electron Microscopy (EFEM) of Frozen Hydrated Biological Specimens
Authors: Probst Wolfgang , Zellmann Erhard , Bauer Richard 
Published: June 2020

The preparation of hydrated biological specimens for the use in a TEM has made a great stride foreward due to the work of Dubochet et al. on vitrification and Muller et al. on high pressure freezing. Transfer units and cryo stages for the microscopes allow imaging of specimens in the 100K range. Due to simple physical reasons, however, contrast of such kinds of specimen is still a problemm in conventional transmission electron microscopes (CTEM). Solutions as they are provided by an EFEM will be shown and explained in the following.Ice is the main constituent of frozen hydrated specimens. The large ratio of inelastic-to-elastic total cross section of 4.0 in case of ice which is even more than that for carbon results in an unavoidable high amount of inelastically scattered electrons. Blurred images and lacking contrast are due to that fact. The EEL spectra from a frozen hydrated section of biological material before and after freeze drying in the microscope document this fact. (Figure 1). Increased scattering probability and thickness contribute to the inelastic loss. In Figure 2 the EEL spectrum from a thin pure ice layer without any support is compared to the spectrum from thin freeze dried cryo section on a thin support. In case of ice the maximum of the low loss range is clearly shifted towards zero loss, mainly due to oxygen low loss and plasmon and to hydrogen core loss. Thus for the images shown in the following Figures a narrow energy window of 10 eV is used really to cut off all the inelastically scattered electrons.
Ultrastructure of Two Mutants in the H-Subunit of Recombinant Human Ferritin: Ordered Arrays Indicate Altered Surface Properties
Authors: Massover William H. , Levi Sonia , Luzzago Alessandra , Tateo Paola , Arosio Paolo 
Published: June 2020

Two major types of polypeptide subunits, H and L, coassemble (n = 24) as heteropolymers to form molecules of the iron-storage protein, ferritin [1]. The significance of the H-type subunits for molecular structure and function remains unclear. The present study has examined the ultrastructure of recombinant human ferritins which are homopolymers of wild-type or mutant H-subunits [2]. Both mutations change the aminoacid sequence along the outer surface of the molecule; 9Cd has a single substitution of glycine for the lysine at position 86, and Ml has a duplication of 18 aminoacids [2].Recombinant ferritins were overexpressed in E. coli. and purified as described by Levi et al [2]. Samples (0.1-0.5 mg/ml) were deposited onto a thin carbon film stripped from freshly cleaved mica and carried on 400 mesh grids; these specimen carriers had been made hydrophilic by glow discharge treatment. After negative staining with 2% sodium silicotungstate (pH 7.0), the specimens were dried and examined at lOOkV with a JEOL 100CX electron microscope.
Studies of Ge/Si(100) and Observation of Atomic Steps on Si(100) using Biassed Secondary Electron Imaging in a UHV STEM
Authors: Krishnamurthy Mohan , Drucker Jeff S. , Venablest John A. 
Published: June 2020

Secondary Electron Imaging (SEI) has become a useful mode of studying surfaces in SEM[1] and STEM[2,3] instruments. Samples have been biassed (b-SEI) to provide increased sensitivity to topographic and thin film deposits in ultra high vacuum (UHV)-SEM[1,4]; but this has not generally been done in previous STEM studies. The recently developed UHV-STEM ( codenamed MIDAS) at ASU has efficient collection of secondary electrons using a 'parallelizer' and full sample preparation system[5]. Here we report in-situ deposition and annealing studies on the Ge/Si(100) epitaxial system, and the observation of surface steps on vicinal Si(100) using b-SEI under UHV conditions in MIDAS.Epitaxial crystal growth has previously been studied using SEM and SAM based experiments [4]. The influence of surface defects such as steps on epitaxial growth requires study with high spatial resolution, which we report for the Ge/Si(100) system. Ge grows on Si(100) in the Stranski-Krastonov growth mode wherein it forms pseudomorphic layers for the first 3-4 ML (critical thickness) and beyond which it clusters into islands[6]. In the present experiment, Ge was deposited onto clean Si(100) substrates misoriented 1° and 5° toward <110>. This was done using a mini MBE Knudsen cell at base pressure ~ 5×10-11 mbar and at typical rates of 0.1ML/min (1ML =0.14nm). Depositions just above the critical thickness were done for substrates kept at room temperature, 375°C and 525°C. The R T deposits were annealed at 375°C and 525°C for various times. Detailed studies were done of the initial stages of clustering into very fine (∼1nm) Ge islands and their subsequent coarsening and facetting with longer anneals. From the particle size distributions as a function of time and temperature, useful film growth parameters have been obtained. Fig. 1 shows a b-SE image of Ge island size distribution for a R T deposit and anneal at 525°C. Fig.2(a) shows the distribution for a deposition at 375°C and Fig.2(b) shows at a higher magnification a large facetted island of Ge. Fig.3 shows a distribution of very fine islands from a 525°C deposition. A strong contrast is obtained from these islands which are at most a few ML thick and mottled structure can be seen in the background between the islands, especially in Fig.2(a) and Fig.3.
High-Resolution Plan View Imaging of Clean and Metal Adsorbed Si Surfaces
Authors: Ozawa S. , Kobayashi K. , Tanaka Y. , Koike H. , Yagi K. 
Published: June 2020

Surface electron microscopy either in TEM or REM mode has attracted much attention. High resolution (HR) imaging of surfaces in atomic resolution level in profile or plan view imaging mode [1,2] uses surfaces of fine particles grown on peripheries of substrates. Thin self-support films with clean surfaces are generally difficult to make. Therefore, previous observations on clean Si(111)7×7 surfaces [3,4] could resolve only basic lattice fringes of the 7×7 lattice. No details of the unit cell structure have been reported.Scanning Tunneling Microscopy (STM) could reveal details of the 7×7 structure together with electronic structures [5,6]. However, STM is difficult to use for studies of surface dynamic processes. Therefore, HR-TEM is still an important technique. In the present report, HR-TEM observations of clean and metal adsorbed Si(111)7×7 and (001)2×1 with use of a 1 MV HR-UHV-EM [1,2,7] are described. An advantage to use the 1MV electron microscope is to decrease inelastic scattering as in HR-REM observations of Si(111) surfaces [8].The specimens of Si (111) and (001) crystal with thin parts were prepared by a method described previously [9]. They were clamped in a side-entry holder used in a previous REM study [8]. Thinning to a thickness transparent to the electrons were carried out by in-situ flash heating at around 1200°C.
Crystallographic Features of PdO Patches Formed from Pd Film
Authors: Ye H.Q. , Ning X.G. , Smith D.J. 
Published: June 2020

Recently HREM observations of small particles and extended gold as well as oxide surfaces indicated that profile imaging could provide atomic scale information about the morphology of materials. Later studies for other novel metals, such as Ag and Pd, have been reported to oxidate-some surface oxides at vacuum conditions of the used electron microscope. In this presentation, we describe the crystallographic feature of PdO, which was the production of surface reaction during profile imaging observations.The clean surface under intereaction of the incident beam with Pd crystal could obviously result in chemical changes. The series images in Fig.1 of a (001) surface of the Pd crystal(region R) and the edges of holes (P and Q) in the [110] Pd foil illustrate oxide formation at the surface. In Fig.1a, a PdO patch was overlapped onto the region R with rather faint contrast, where the unit cells of the newly formed crystalline and the Pd matrix were outlined. In other hand, two holes P and Q were still full with the amorphous contamination and the surface close to these regions did not changed. After a few minutes, the [001] PdO lattice image became sharp and clear, and then dominated most of the region R (Fig.1b). It was seen that a [111] PdO patch with slight expended lattice spacings and exactly parallel orientation relationships was generated in the region P once carbonaceous materials was removed (Fig. 1b and c). In Fig.1c an [010] PdO patch was well developed in the region Q.
Design of a Spectroscopic Low-Energy Emission Microscope
Authors: Veneklasen Lee H. 
Published: June 2020

This paper discusses some of the unique aspects of a spectroscopic emission microscope now being tested in Clausthal. The instrument is designed for the direct parallel imaging of both elastic and inelastic electrons from flat surfaces. Elastic contrast modes of the familiar LEEM include large and small angle LEED, mirror microscopy, backscatter diffraction contrast (for imaging of surface structure), and phase contrast (for imaging of step dynamics)(1). Inelastic modes include topology sensitive secondary, and work function sensitive photoemission. Most important, the new instrument will also allow analytical imaging using characteristic Auger or soft X-ray emissions. The basic instrument has been described by Bauer and Telieps (2). This configuration has been redesigned to include an airlock, and a LaB6 gun, triple condensor lens, magnetic objective lens, a double focussing separator field, an imaging energy analyzer, and a real time image processor.Fig. 1 shows the new configuration. The basic beam voltage supply Vo = 20 KV, upon which separate supplies for the gun Vg, specimen Vs, lens electrode Vf, and analyzer bias Vb float. The incident energy at the sample can be varied from Vs = 0-1 KV for elastic imaging, or from Vg + Vs = (3 + Vs) KV for inelastic imaging. The image energy window Vs±V/2 may be varied without readjusting either the illumation, or imaging/analyzer optics. The diagram shows conjugate diffraction and image planes. The apertures defining incoming Humiliation and outgoing image angles are placed below the separator magnet to allow for their independent optimization. The instrument can illuminate and image 0.5-100 μm fields at 0-1 keV emission energies with an energy window down to 0.2 eV.
Single-Pole Objective Lens for Low-Voltage SEM High Resolution Wafer Observation
Authors: Yonezawa Akira , Takeuchi Yukio , Kano Takeshi , Ishijima Hiroshi 
Published: June 2020

The low-voltage in-lens FE-SEM can observe a 10nm diameter pinhole on Si polycrystal film and etch residue which cannot be observed by a typical SEM. However,this in-lens SEM cannot observe a large size specimen such as a wafer. A new single pole objective lens was recently designed for this purpose. Because of the small bore diameter (2∼3mm),when using this lens,a negative potential must be given to the specimen holder to improve the efficiency of the secondary electron detection.From researching of a single pole magnetic lens system used for observing a wafer with high resolution, we obtained the secondary electron image. Fig.1 shows the single pole objective lens mounted on the specimen chamber. L is the distance between the pole face and the opposite iron wall,R is the radius of the outer yoke,and WD is the working distance. The design features are as follows:
Low-Voltage Scanning Electron Microscope (LVSEM) with a Single-Polepiece Lens
Authors: Müllerová I. , Lenc M. 
Published: June 2020

The advantages of the LV SEM are well known. Recently a lot of interesting results from this field were presented which were obtained thanks to development of field emission guns and to the enourmous progress in the computation techniques in electron optics.One of the simplest arrangements of the LVSEM is shown in Figure 1. The Tesla SEM BS 350 with a field emission gun and the TF-W/100-Zr cathode was used for our experiment. The gun provides 10−10 A current in the diffraction limited spot (for the angular density 0.20mA sr−1). If a potential Usp is applied to the specimen the energy E of the electrons that strike the specimen is Ep-eUsp (Ep-primary beam energy, e-elementary charge). The produced secondary (SE) and backscattered (BSE) electrons are accelerated towards the semiconductor detector by the electrostatic field and their energy spectrum extends from eUsp to Ep. The final energy of the SE and BSE can then be sufficient for achieving a reasonable amplification of the semiconductor detector which is directly proportional to the energy of the electrons that strike the detector. We calculated optical properties for a combination of the electrostatic and magnetic lenses of the basic geometry shown in Figure 1 and for an arrangement with the single polepiece lens shown in Figure 2. We particularly investigated coefficients of the chromatic (Cc) and spherical (Cs) aberrations as functions of the ratio of the primary beam energy to the energy of the electrons that strike the specimen Ep/E for some optimum position of the specimen, electropstatic and magnetic field. Our results are shown in Table 1. The coefficients Cs and Cc do not change with the energy Epor E if the ratio Ep/E is maitained the same and aberrations are lower for larger ratios Ep/E, so that the influence of the contribution of the electrostatic lens aberrations is negligible for our geometry. For example, if we require a resolution limit r=2nm and an energy of the electrons that strike the specimen E=300eV, it is possible to calculate that the coefficient of the aberrations must be Cs<0.21mm and Cc<0.14mm for an energy width AE=0.2eV, so that we need the ratio Ep/E≥150 for the arrangement shown in Figure 1 (i.e.Ep≥45keV) and Ep/E≥33 for the arrangement shown in Figure 2 (i.e.Ep≥10keV).The advantages of the combination of the magnetic lens with the electrostatic cathode lens for the high resolution very low energy electron microscopy are well known . We assume that for the LVSEM only a medium electrostatic field strength is admitted at the specimen surface. Nevertheless, our experimental arrangements should certainly be optimized in the future.
Fast Fourier Transform Techniques for Measuring SEM Resolution
Authors: Dodson A. , Joy D. C. 
Published: June 2020

Precise knowledge of a particular SEM's resolution is important for at least two reasons to the microscopist operating the instrument. First, accurate interpretation of micrographs obtained in the course of daily operation depends on knowing the performance limits of the instrument. Second, it is important for the microscopist to be able to verify instrumental performance.Spatial resolution is typically determined using micrographs of materials containing structures having a “known” spacing. By showing that two objects in the micrograph are separated by some distance, it is claimed that the instrument is capable of resolving this spacing. This method is passable for instruments whose maximum resolution resolves only features of known spacing. However, for High Resolution SEM's (HRSEM) this method is not adequate. It is difficult to identify specimens with surface structure that can be verified to exist at the ultimate limits of today's HRSEM resolution. The fact that verifying resolution by this method depends on being able to verify the spacing of surface structure on a particular specimen leads to an interesting paradox - the resolution of a given instrument can be verified only after a better instrument is available to characterize the structure spacing.