bluuebunny/crossref_metadata_2025_split huggingface dataset:
Principles and Utilization of the Electron Beam Damage of Synthetic Polymers
Authors: Vesely D. 
Published: June 2020

The rapid decomposition of polymeric samples is a major problem in structural investigations of these materials, as the crystallographic information and mass/thickness contrast can be quickly lost. The X-ray elemental analysis can also be affected by loss of elements and often extrapolation to zero exposure is necessary. It is thus of great interest to know how quickly this decomposition occurs for a given polymer.The beam damage rate can be measured by loss of crystallinity, loss of mass or loss of elements. The measured decay curves can be approximated by a double exponential function for which only three constants are needed. This describes the behaviour of most polymers very well, however an accurate experimental evaluation of these constants is not easy. The most important and difficult parameters to measure are the initial intensity, exposure and size of the irradiated area. It is not clear why the double exponential function is suitable, if it is a chemical law or if it fits purely by coincidence.
Characteristic X-ray Emission from SrTiO3 by Channeling Electrons
Authors: Ohshima Kiyoshi , Endoh Hisamitsu , Shimizu Ryuichi 
Published: June 2020

Count rate of characteristic x ray changes with the incident condition of electron beames to a crystal. The phenomena is utilized by ALCHEMI to determine the positin of impurity atoms in unit cell. Ionization of atoms, which causes the emission of characteristic x ray, depends on localization of incident electrons. The present paper shows the relation between count rates of characteristic x ray and incident condition of electron beams.Experiment was performed by using JEM_4000EX electron microscope with TN-2000 EDX system. Specimen was prepared by cleaving SrTiO3 and observed from 110 direction. As shown in Fig. 1, 1ll-planes consist of two kinds of atomic planes, Sr-plane and Ti-plane, which are arranged alternatively. Figure 2 shows x-ray spectra of SrTiO3 illuminated by 200keV electrons in such an incident condition that 111-systematic reflections were excited, and particulaly in (a) symmetric incidence and in (b) 222-Bragg reflecting condition. Counts, NT i and Ns r, of characteristic x ray excited by Ti and Sr K-shell ionization respectively are obtained by measuring the areas under the corresponding peaks of the spectra.
Practical Importance of Spatial Resolution and Analytical Sensitivity in AEM X-ray Microanalysis
Authors: Zhang J. , Williams D.B. , Goldstein J.I. 
Published: June 2020

Analytical sensitivity and spatial resolution are important and closely related factors in x-ray microanalysis using the AEM. Analytical sensitivity is the ability to distinguish, for a given element under given conditions, between two concentrations that are nearly equal. The analytical sensitivity is directly related to the number of x-ray counts collected and, therefore, to the probe current, specimen thickness and counting time. The spatial resolution in AEM analysis is determined by the probe size and beam broadening in the specimen. A finer probe and a thinner specimen give a higher spatial resolution. However, the resulting lower beam current and smaller X-ray excitation volume degrade analytical sensitivity. A compromise must be made between high spatial resolution and an acceptable analytical sensitivity. In this paper, we show the necessity of evaluating these two parameters in order to determine the low temperature Fe-Ni phase diagram.A Phillips EM400T AEM with an EDAX/TN2000 EDS/MCA system and a VG HB501 FEG STEM with a LINK AN10 EDS/MCA system were used.
Simultaneous Evaluation of Weight Factors and k Factors for Quantitative x-ray Microanalysis of Thin Specimens
Authors: Heng Yew-Meng , Simon Gerard 
Published: June 2020

Quantitative analyses of elemental content in thin specimens using X-ray energy dispersive spectroscopy (XEDS) in the TEM are commonly effected by the Cliff-Lorimer elements ratio approach or the Hall’s peak-to-continuum normalization method. The former method is mainly used in metallurgy, while the latter is favoured in biology. These two methods require accurate proportionality factors in order to convert the characteristic X-ray intensities, Ia and Ib, to the concentrations of the elements, Ca and Cb.
Nevertheless, both factors can be related as followswhere Ic is the intensity of a fixed continuum region and Eqn.(3) assumes that the Z2 of the compositions of the two standards are not significantly different.This study evaluates the accuracy of the WP and Wca which were determined using standards. To accomplish this, these factors were used to determine kPca, which was then compared to that measured from compounds of known stoichiometry, as well as that calculated theoretically.
Spatial Resolution and Detectability Limits in Thin-Film X-ay Microanalysis
Authors: Goldstein J. I. , Lyman C. E. , Zhang J. 
Published: June 2020

The major advantage of performing x-ray microanalysis in the analytical electron microscope (AEM) is the high compositional spatial resolution and the chemical analysis sensitivity. The spatial resolution (R) is dependent on the size of the focused electron probe (d) and the amount of electron beam broadening (b). The spatial resolution across a discrete interface is:The amount of beam broadening is directly proportional to the thickness (t) to the 3/2 power and inversely proportional to the beam voltage (E). Optimizing d and b involve a consideration of the minimum x-ray intensity necessary for analysis since the x-ray intensity is decreased by minimizing d and t. To obtain the optimum spatial resolution one should use the thinnest possible specimen, a high kV AEM and a high brightness field emission gun (FEG). Figure 1 shows a Ni composition profile across a planar lOnm precipitate in the plessite region of the Grant iron meteorite. A spatial resolution of 2.5nm was obtained from a 20nm thick sample analyzed in a VG Microscopes, Ltd. HB 501 FEG AEM (probe diameter 1.8nm (FWTM)).
Problems in Thin-Film X-ray Quantification
Authors: Chapman J N , Nicholson W A P 
Published: June 2020

Energy dispersive x-ray microanalysis (EDX) is widely used for the quantitative determination of local composition in thin film specimens. Extraction of quantitative data is usually accomplished by relating the ratio of the number of atoms of two species A and B in the volume excited by the electron beam (nA/nB) to the corresponding ratio of detected characteristic photons (NA/NB) through the use of a k-factor. This leads to an expression of the form nA/nB = kAB NA/NB where kAB is a measure of the relative efficiency with which x-rays are generated and detected from the two species.Errors in thin film x-ray quantification can arise from uncertainties in both NA/NB and kAB. In addition to the inevitable statistical errors, particularly severe problems arise in accurately determining the former if (i) mass loss occurs during spectrum acquisition so that the composition changes as irradiation proceeds, (ii) the characteristic peak from one of the minority components of interest is overlapped by the much larger peak from a majority component, (iii) the measured ratio varies significantly with specimen thickness as a result of electron channeling, or (iv) varying absorption corrections are required due to photons generated at different points having to traverse different path lengths through specimens of irregular and unknown topography on their way to the detector.
Determination of the Lattice parameter for TiCl-x and TiNl-x by Use of HOLZ Lines in CBED [114] zonP Axis Patterns
Authors: Lenvig Hansen Poul , Madsen Kristian 
Published: June 2020

TiC and TiN are very hard and wear resistant materials. They are used as thin wear protecting films on tools working in abrasive environments and as powders for grinding. Furthermore, whiskers of TiC and TiN are used as fibre reinforcement in composite materials.
The crystal structure is fcc with lattice parameter a = 0.4240 nm for TiN and a = 0.4328 nm for TiC. Understoichiometric forms, TiN1-x and TiC1-x ( 0 ≤ x ≤ 0.5 ), are common. Their lattice parameter decreases with increasing x. As the understoichiometric forms have inferior mechanical properties compared with the stoichiometric forms, it is of interest to develop methods to measure the composition of the phases.It is the objective of this paper to show that the HOLZ lines in [114] zone axis CBED patterns can be used to measure the local lattice parameter in TiC and TiN in order to distinguish the two phases and in order to assess understoichiometry.
Identification of Several New Ferromagnetic and Antiferromagnetic Rare Earth Cuprates
Authors: Fendorf M. , Keller S.W. , Stacy A.M. , Gronsky R. 
Published: June 2020

Several new rare earth cuprates having the chemical form RxCuyOz (where R represents the rare earths La, Nd, Sm, Eu, and Gd) have recently been synthesized using a NaOH flux at 400°C. The materials are polycrystalline, and contain varying amounts of R2CuO4 and CuO. During subsequent susceptibility measurements using a SQUID magnetometer, it was found that the Gd material orders antiferromagnetically at approximately 14K, while the other compounds become ferromagnetic between 18K and 28K. Treatment of the powders with 12M HC1 for several minutes dissolves the impurity R2CuO4 and CuO phases, thus facilitating efforts to determine the composition and crystal structure of the new ferromagnetic and antiferromagnetic cuprates. Details of synthesis and magnetic behavior of these materials are to be published elsewhere. In this study, a first attempt is made to characterize the Eu and Gd materials.Energy dispersive x-ray analysis carried out during scanning electron microscopy work indicates that the R:Cu ratio in the Gd material is 1:1.70 (close to 3:5) and that in the Eu material is 1:1.96 (close to 1:2).
The Low-Temperature Structure of Magnetite Studied by CBED
Authors: Zuo J.M. , Spence J.C.H. , Petuskey W. 
Published: June 2020

Magnetite (Fe3O4) has the cubic inverse spinel structure for T > TV = 119 K and undergoes a firstorder metal-insulator Verwey transition below TV. The transition from hopping conductivity to insulating behaviour below TV is believed to be due to a condensation of localised electrons onto the Fe++ and Fe+++ ions on the octahedral (B) sites. Tetrahedral (A) sites contain only Fe+++ ions. The aim of this research is to determine this unknown charge ordering below TV by CBED, taking advantage of the high sensitivity of low-angle electron diffraction to ionicity. Below TV the c axis of the cubic cell doubles, and there is a small monoclinic distortion.Previous CBED work established that the space-group is Cc (C centering, glide plane normal to b, displacement along c). Anderson proposed that the building block for the low-temperature structure consists of two Fe++ and two Fe+++ ions per tetrahedron (see, e.g. figure 1).
Analytical Calculation of Complex Lattice Potentials for Electron Diffraction
Authors: Weickenmeier A. 
Published: June 2020

For the quantitative interpretation of electron microscopical diffraction patterns it is often indispensable to perform simulations to get insight into the contrast mechanisms. If the inelastic mean free path length is not small compared with the crystal thickness the diffraction patterns are affected by absorption phenomena. In this case a realistic calculation must include these effects. Within the dynamical theory this can be done by adding an absorptive part to the Fourier coefficients Vg of the lattice potential .Because there are only few experimental data available the absorptive part must be computed. In the most cases the dominant contribution to arises from the thermal diffuse scattering since plasmon excitations and electron excitations contribute in good approximation only to the mean absorption potential .
Then all branches of the dispersion surface are similiar attenuated.Extensive numerical calculations have been performed by Radi for many crystals. Nevertheless it is impossible to tabulate the for all crystals even for only few temperatures and acceleration voltages.
Progress in design and applications of CCD cameras for Electron Microscopy
Authors: Downing Kenneth H. 
Published: June 2020

Over the last several years the long-awaited revolution in direct-digital readout systems has begun, with the introduction of efficient slow-scan CCD cameras. Earlier, the introduction of video cameras to electron microscopes had brought a quantum leap in the speed and efficiency of carrying out a host of operations. The high sensitivity of the video cameras provided the ability to see the image in much more detail and at a lower beam intensity than had been possible previously by viewing the fluorescent screen. The ability to assess, on line, characteristics such as specimen quality and image focus, even qualitatively, gave feedback to the operator that previously took hours to obtain. Due to the low resolution of these video systems, however, they were rarely useful for data recording.The current generation of CCD cameras goes a long way toward meeting the needs of data recording in many, though certainly not all, applications.
Semi-automated methods for 3-D reconstruction of macromolecular complexes
Authors: Carragher B. , Whittaker M. 
Published: June 2020

Techniques for three-dimensional reconstruction of macromolecular complexes from electron micrographs have been successfully used for many years. These include methods which take advantage of the natural symmetry properties of the structure (for example helical or icosahedral) as well as those that use single axis or other tilting geometries to reconstruct from a set of projection images. These techniques have traditionally relied on a very experienced operator to manually perform the often numerous and time consuming steps required to obtain the final reconstruction. While the guidance and oversight of an experienced and critical operator will always be an essential component of these techniques, recent advances in computer technology, microprocessor controlled microscopes and the availability of high quality CCD cameras have provided the means to automate many of the individual steps.During the acquisition of data automation provides benefits not only in terms of convenience and time saving but also in circumstances where manual procedures limit the quality of the final reconstruction.
SOPHIE, a helium cooled superconducting Electron Microscope with a Schottky field emitter
Authors: Stark H. , Beckmann E. , Henderson R. , Zemlin F. 
Published: June 2020

High-resolution cryo-electron microscopy yielded remarkable results in biological molecular structure research. These successes encouraged to proceed in developing even better instruments and procedures. In our laboratory we built the cryo-electron microscope "SOPHIE", a modified Philips CM 20 FEG. SOPHIE stands as an acronym for Superconducting Objective in a PHIlips Electronmicroscope. The main features of this microscope are the following:
1.200kV acceleration voltage2.Schottky field emitter3.Helium cooled superconducting objective
The Helium-cooled cryo-objective from the former microscope SULEIKA was adapted into the column of the original Philips CM20 FEG [Fig. 1], This new SOPHIE microscope, thus, combines two important features: a modern computer controlled electron microscope with a high coherent beam source and the proven advantages of the superconducting cryo-objective. The advantage of the field emission gun at 200 kV over a thermionic cathode at 100 kV can be best visualized while comparing the respective phase-contrast-transfer functions at Scherzer focus [Fig.2]. Moreover, SOPHIE is equipped with the small spot scanning procedure.
A systematic ALCHEMI study of Fe-doped NiAl alloys
Authors: Anderson I.M. , Duncan A.J. , Bentley J. 
Published: June 2020

ALCHEMI site-occupation studies of alloying additions to ordered aluminide intermetallic alloys have been performed with varying degrees of success, depending on the ionization delocalization correction procedure applied to the data. Most published studies have been applied to just one or two alloys in order to ascertain qualitatively the site-preference of the alloying element. However, quantitative siteoccupancies can be extracted from carefully performed ALCHEMI experiments as long as the data are properly treated for ionization delocalization and anti-site occupancies. Systematic studies can therefore yield the dependence of site-occupancies in alloys on independent thermodynamic variables. The purpose of the present study is to examine the variation in the site-occupancy of Fe in B2-ordered NiAl as a function of solute concentration and alloy stoichiometry.Twelve different alloys were prepared for this study with stoichiometrics Ni50-xAl50Fex (Ni-deficient), Ni50-x/2Al50-x/2Fex (intermediate), and Ni50-xAl50Fex (Al-deficient), with x = 0.25, 2, 5, and 10. All alloys were homogenized at 1300°C for 5 h, step-cooled to room temperature, then annealed at 800°C for 72 h and water quenched.
Use of direct phasing in determination of atomic co-ordinates of anthanthrene, C22H12
Authors: Leslie C. E. , Fryer J. R. , Gilmore C. J. , Nicolson W. 
Published: June 2020

Imaging of organic crystals in the electron microscope is limited by their sensitivity to the electron beam, with even the most stable molecules only giving a resolution of ~3Å. By contrast, electron diffraction requires a lower beam intensity, and so can give much better resolution, down to ~lÅ under favourable conditions. Intensities may be measured directly from the diffraction pattern, and the phase determination problem can be surmounted by applying the maximum entropy method, which chooses phases by likelihood estimation.It was decided to apply this method to the organic molecule anthanthrene, C22H12 (fig. 1), since x-ray studies found that the crystals were monoclinic with a = 12.10Å, b = 10.34Å, c = 10.74Å, β = 92.2°, space group P21/a and Z = 4, but no details of the atomic co-ordinates were given in the literature. A previous study of the molecule, using KC1 as the substrate, produced epitaxial layers showing the acprojection being most common at room temperature.
Unitarity and the real world: applications of direct phasing to electron diffraction data
Authors: Tivol W. F. 
Published: June 2020

The Sayre equation can be derived as a special case of unitarity, and recently it was shown that the derivation applies to dynamical scattering and electron diffraction. Since both the triplet formula and the tangent formula can be derived from the Sayre equation, use of these direct methods to find the phases for electron diffraction amplitudes is fully justified.The most transparent form of the unitary equation iswhere Â is the scattering amplitude operator, f is the final state, i the initial state, and n is a complete set of intermediate states; the sum over these states becomes an integral where the intermediate states form a continuum.If there is Friedel symmetry, the form of the Sayre equation derived from equation (1) isThe prime on the sum meansK ≠ 0.If Friedel symmetry is violated, Σ' | A(K) |2becomesThis equation is a quantitative relationship which not only has an essentially unique solution for the phases, but which also constrains the magnitudes of the intensities.
High-angle electron scattering from amorphous silicon
Authors: Libera M. , Ott J.A. , Siangchaew K. , Tsung L. 
Published: June 2020

Channeling occurs when fast electrons follow atomic strings in a crystal where there is a minimum in the potential energy (1). Channeling has a strong effect on high-angle scattering. Deviations in atomic position along a channel due to structural defects or thermal vibrations increase the probability of scattering (2-5). Since there are no extended channels in an amorphous material the question arises: for a given material with constant thickness, will the high-angle scattering be higher from a crystal or a glass?Figure la shows a HAADF STEM image collected using a Philips CM20 FEG TEM/STEM with inner and outer collection angles of 35mrad and lOOmrad. The specimen (6) was a cross section of singlecrystal Si containing: amorphous Si (region A), defective Si containing many stacking faults (B), two coherent Ge layers (CI; C2), and a contamination layer (D). CBED patterns (fig. lb), PEELS spectra, and HAADF signals (fig. lc) were collected at 106K and 300K along the indicated line.
Closed graphene nanostructures
Authors: Iijima Sumio 
Published: June 2020

Graphene is named a single sheet of graphite, or a 2-D carbon hexagons network. The graphene structure has been observed in partially graphitized carbon which is familiar to electron microscopists and its HRTEM image properties were analyzed previously in detail. C60 molecules, which has brought a great excitements in interdisciplinary fields of science and technology, is basically the same graphene structure with a curvature. The individual C60 molecule can be imaged without difficulty by HRTEM. Many of fundamental problems with the molecule however are not solved by the HRTEM technique. On the other hand, carbon nanotubes, a family of the fullerene and discovered serendipitously by the present author5, are an ideal subject for the HRTEM investigation and in fact their structural details can only be analyzed by this technique. The present talk reviews the carbon nanotubes and related structures with an emphasis of usefulness of the HRTEM.Search for the multi-shell graphite particles leads to unexpected discovery of carbon nanotubes which grow on a cathode in a carbon-arc chamber for the C60 production.
The breakup of the intermediate gold aggregates
Authors: Yao Nan , Shih Wan Y. , Dabbs Daniel M. , Aksay Ilhan A. 
Published: June 2020

The synthesis of nanometer scale gold particles is well known historically. Stable and highly colored suspensions result from the reduction of gold cations in solution. But the formation of the gold particles is not monotonic, that is, the mechanism is not simply nucleation and growth. Rather, the pronounced color changes in the evolving suspension indicate that the mechanism is nucleation, aggregation, deaggregation, and growth. Until recently, the structure of the intermediate aggregate had been assumed to be an aggregation of primary particles, each 4-7 nm in diameter. HRTEM studies have shown that the intermediates are continuous ramified structures (Figure 1) which undergo a desintering process to form the final particles (~24-26 nm diameter). In this paper, we discuss a model which explains the role of the surfactant on the gold intermediate in the breakup of the intermediate structure.Gold colloids were prepared by reducing AuIIICl3 (aq) with sodium citrate as in previous studies:
Scanning force microscope Z-calibration using steps on chemically etched mica
Authors: Fei L. , Fraundorf P. 
Published: June 2020

Obtaining reliable dimensional information in all three directions is very important in scanning force microscopy (SFM). Calibration standards for SFM should be easy to produce and reliable. For example, mica is often used as a lateral calibration standard, because lattice fringes are relatively easy to obtain. However, reliable height information is hard to get. Pits formed by lithography (180 nm in depth) are used for vertical calibration by some SFM manufacturers.1 These standards have 10variability and are large on the size scale of monolayers. Colloidal gold particles have been proposed as one kind of SFM vertical standard, but the size variability of these particles (e.g. ranging from 5 to 24 nm) makes their use of limited practical value.One solution to the problem is to use chemically etched mica as height calibration standard. Mica has a layered structure, and its c-axis is well denned and weakly bonded. In this study, we used muscovite mica which has c-axis lattice spacing of 10 Å.