bluuebunny/crossref_metadata_2025 huggingface dataset:
Single scattering approximations: the domains of validity for structural analysis of protein crystals by electron diffraction
Authors: Glaeser Robert M. , Jap Bing K. , Hslu Ho Ming
Published: June 2020

Single scattering approximations (the kinematic and the weak phase object approx- imation), because of their simplicity, are perhaps the most attractive formulations for structure analysis by electron diffraction. In these approximations, the diffracted wave function is linearly related to the object potential. The validities of these approximations are, however, limited to very thin crystals at low resolution. In materials science the failure of the single scattering approximations and the impor- tance of the dynamical scattering effect have been well accepted. In biological science, the large unit cell size and the low atomic number (e.g. protein crystals) have lead some to believe that the dynamical scattering effect is insignificant for crystallographic analysis. Contrary to this belief, the number of dynamically interacting beams increases with the crystal unit cell size. It is important to note here that the dynamical scattering effect depends on the values of the excitation errors and on the magnitudes of the Fourier coefficients of the crystal potential.
The dynamical theory of a double crystal electron interferometer
Authors: Buxton B.F. , Rackham G.M. , Steeds J.W.
Published: June 2020

Recently, Rackham et al.(1977) reported the observation of fine fringes in convergent beam patterns obtained from double crystal interferometers consisting of two perfectly aligned crystals separated by a gap D of about 1 μm (Fig. 1). If we assume for simplicity that the reciprocal lattice vectors G of the operating reflections are parallel to the crystals, the many-beam wavefunction Ψ(R,t1) on the exit surface of crystal I due to an incident plane wave eix.r. (Fig. 2), given by

(1)

can be matched onto plane waves propagating in directions K+G between the crystals. In the gap therefore, the wavefunction is

(2)

where

(3)

since x ≫ |K+G| for all reflections of interest. The wavefunction (2) is diffracted by the second crystal, from which emerge waves in directions K+H with amplitudes.
The atomic string approximation in high energy electron diffraction
Authors: Tremewan P.T. , Buxton B. F.
Published: June 2020

It is often useful to study dispersion surfaces in order to understand the complicated diffraction effects which are observed in transmission electron micrographs. To obtain these dispersion surfaces accurately from the many-beam equations in cross-grating high energy electron diffraction it is necessary to diagonalise matrices at least of the order 60×60 even for the simplest structures. Such a method cannot easily be used to relate the form of the dispersion surface to the projected potential U(R) seen by the fast electrons. It is possible, however, to solve an equivalent two-dimensional band structure problem for the fast electrons in the crystal. The KKR method, which exploits the near cylindrical symmetry of the projected potential within each atomic string in order to expand the Bloch waves in terms of angular momentum basis functions eiℓθ, enables such an approach to be made and requires the solution of small secular determinants.

Defining the transverse energy S to be zero at the maxima of the atomic string potentials, the atomic string approximation(ASA) reduces the KKR equations for one string per unit cell of the projected potential to the form

where the eigenvector components C are simply related to the coefficients in the angular momentum expansion of the Bloch waves and the structure constants Mℓℓ'(K) only depend on the arrangement of the atomic strings and the orientation K.
Dependence of critical voltages in Cu-based alloys on composition, temperature and short range order
Authors: Kuroda K. , Tomokiyo Y. , Eguchi T.
Published: June 2020

Introduction Since the critical voltage effect in electron microscopy was discovered [1, 2], a number of its applications have been proposed [3-9]. As the critical voltage Vcof an alloy depends primarily on the scattering factors of constituent atoms, not only the compositional change but also the degree of order and the mean square displacement (msd) of the atoms affect the value of Vc. In the present paper the effect of alloying on Vc is studied in Cu-based alloys containing 14.8 at% Al, 4.9 or 14.9 at% Au. These alloys are of interest because Al is lighter and Au heavier than Cu atom, and furthermore the alloys develop a short range order. The critical voltages were determined using JEM-1000 HVEM by observing of the minimum intensity of 2g Kikuchi line and the reversal of the contrast of middle line at lg spot. The measured Vc was analyzed by the 10-beam dynamical theory.
A method to measure pores and fissures in geologic materials under S.E.M. by digital image processing
Authors: Montoto L. , Montoto M. , Bel-Lan A.
Published: June 2020

INTRODUCTION.- The physical properties of rock masses are greatly influenced by their internal discontinuities, like pores and fissures. So, these need to be measured as a basis for interpretation. To avoid the basic difficulties of measurement under optical microscopy and analogic image systems, the authors use S.E.M. and multiband digital image processing. In S.E.M., analog signal processing has been used to further image enhancement (1), but automatic information extraction can be achieved by simple digital processing of S.E.M. images (2). The use of multiband image would overcome difficulties such as artifacts introduced by the relative positions of sample and detector or the typicals encountered in optical microscopy.

DIGITAL IMAGE PROCESSING.- The studied rock specimens were in the form of flat deformation-free surfaces observed under a Phillips SEM model 500. The SEM detector output signal was recorded in picture form in b&w negatives and digitized using a Perkin Elmer 1010 MP flat microdensitometer.
Correlation analysis of radiation damage
Authors: Hegerl R. , Feltynowski A. , Grill B.
Published: June 2020

Till now correlation functions have been used in electron microscopy for two purposes: a) to find the common origin of two micrographs representing the same object, b) to check the optical parameters e. g. the focus. There is a third possibility of application, if all optical parameters are constant during a series of exposures. In this case all differences between the micrographs can only be caused by different noise distributions and by modifications of the object induced by radiation.

Because of the electron noise, a discrete bright field image can be considered as a stochastic series Pm,where i denotes the number of the image and m (m = 1,.., M) the image element. Assuming a stable object, the expectation value of Pmwould be Ηmfor all images. The electron noise can be introduced by addition of stationary, mutual independent random variables nmwith zero expectation and the variance. It is possible to treat the modifications of the object as a noise, too.
3-D reconstruction from conically tilted projections
Authors: Radermacher M. , Hoppe W.
Published: June 2020

As shown earlier, reconstruction from conically tilted projections has the advantage of delivering a smoother background around the elongated image point than reconstruction from single axis tilted projections, because of the smaller blind region in Fourier space. In this paper a weighted backprojection for conical tilting is presented. In contrast to the iterative techniques of the ART-type the shape of the image point and its clutter are defined and predictable.

Let S with x, y, z be the coordinate system fixed to the object, and S'j with x'j, y'j, z'j be the system with the x'j, y'j -plane on the j-th projection. Let ϑ be the polar angle and φj be the azimuthal angle between S and S'j. The j-th projection then is
Off-axis electron holography by field emission electron microscope
Authors: Tonomura A. , Matsuda T. , Komoda T.
Published: June 2020

Although the feasibility of electron holography has been verified by several authors, it has not yet been put to practical use. This is because of the lack of a coherent electron source, such as optical laser. In practice, the number of interference fringes produced with a biprism is 200 at most, the exception being one dimensional cases. Off-axis holography requires 5,000∼100,000 interference fringes. Therefore, the useful application of electron holography in higher resolution and phase contrast electron microscopy hinges on development of a coherent electron source capable of producing 5,000 fringes or more.

To realize a coherent electron source, a 100 kV field emission electron gun was developed and attached to an electron microscope. In designing the microscope,special care was taken in the column and electric supply. This was done to minimize movement of the small beam spot, which is easily disturbed from outside, so as to maintain the field emission electron beam.
Discrimination of individual atoms in the molecular images of chlorinated copper phthalocyanine
Authors: Uyeda N. , Fujiyoshi Y. , Kobayashi T.
Published: June 2020

For the establishment of solid approaches to the target of discriminating individual atoms in molecular images, it still seems to be necessary to deal with radiation resistant compounds with known structures. The use of thin specimen crystals renders several advantages, as they keep molecules in suitable orientations with tolerably small atomic displacements due to the thermal vibration. Rows of stacked molecules increase the contrast in the projected images, although the thickness must be such that the specimen can be regarded as a thin phase object. Two dimensional periodicity of projected images facilitates the spacial averaging which increases the s/n ratio as predicted by Kuo and Glaeser, reducing the exposure time and consequently the radiation damage. In order to realize the atomic resolution, the improvement in the instrumental characteristics is indispensable as well. The 500kV electron microscope constructed by Kobayashi et al. has the capability of achieving the ultimate resolution of 1.5A, and played the principal role in the present attempt to reach the atomic resolution.
High resolution phase contrast electron microscopy:imaging of single atoms and “amorphous state”
Authors: Iijima Sumio
Published: June 2020

Using very thin films of graphite crystals as support films, we demonstrated some bright-field CTEM images of single tungsten atoms and surface structures of the graphite films. Theoretical calculation on these objects using phase object approximation supported the validity of our interpretation of the images.

We made a further investigation on the similar phase objects by utilizing a JEOL-UHP objective pole-piece (Cs= 0.7mm) installed in a JEM-100B microscope. This lens gives an “interpretable resolution”,, of 2.6Å. Practically, however, the attainable resolution is restricted by chromatic aberration and illumination angle, barring operational faults. These parameters modify the ideal image transfer functions in the higher frequency region and thus become important for discussing the high resolution details. The resolution measured for the new lens from the optical diffractograms was around 3.2Å, which is slightly better than the value 3.8Å for our old lens (BLG-pole-piece, Cs= 2.0mm).
Imaging of the crystal structure of a new WO3, phase by high-resolution electron microscopy
Authors: Gerand B. , Figlarz M.
Published: June 2020

A new hydrate of tungsten trioxide with the formula WO3,1/3 H2O was found by hydrothermal treatment in an autoclave either of crystalline WO3,2 H2O or of a tungstic acid gel. By dehydration of this hydrate in the air and by subsequent reductions a set of new compounds of tungsten were obtained : a polymorph of WO3 and two other oxides, all unknown. Their structures have in general a higher symmetry than the compounds already known. The detailed procedure for preparing these phases, their analysis, their structures and properties will be reported elsewhere (1).

In the present paper, we examine the structure of the new polymorph of WO3. This compound is white. A study by powder X-ray diffraction shows that this compound is hexagonal with the space group P6/mmm and the lattice parameters a = 7.296 and c = 3.899 A°. The structure, which can be imagined by analogy with the hexagonal bronze structures (2), is shown in figure 1.
The observation of edge dislocation loops by high resolution lattice imaging
Authors: Howitt D.G. , Mitchell T.E.
Published: June 2020

Introduction

The characterization of small defects by diffraction contrast methods in the electron microscope becomes uncertain when the image widths approach the dimensions of the defect. In the case of small defect aggretates, it becomes difficult not only to distinguish between interstitial and vacancy character but also between volume and planar defects.

These small defect aggregates, or rather the disturbances that they produce, can also be investigated by lattice imaging where the interference of two or more beams, whose phases have been disturbed by the defect, produces an image. The images obtained in this way, although not a one-to-one mapping of the atomic arrangement, do bear an unique relationship to it; however, this uniqueness is lost in an electron micrograph since the phase relationships are not recorded. The image interpretation therefore relies upon the effect that the phase relationships have on the image intensity being sufficient to distinguish between likely candidates for the atomic distribution, since the image intensities from this type of microscopy are not in general straightforward to predict.
A theoretical analysis of lattice fringe imaging
Authors: Rez Peter
Published: June 2020

Lattice fringe spacing measurements have been used as a method of estimating local chemical composition. It is possible that, due to dynamical scattering, the fringe profile is influenced by atomic number difference and changes in specimen thickness and tilt as well as atomic displacements. Even if these other effects are negligible it is especially important to know whether the fringe spacing changes in the image exactly correspond to the lattice plane displacements in the specimen. In most experiments tilted illumination is used and the crystal is set at a Bragg condition for a low order reflection. In a high resolution microscope (Cs≃1.5mm) the transfer function should be sufficiently flat in the region of interest and aberrations can be neglected. Some insight into the nature of lattice fringes can be gained from a two-beam theory. Using the standard notation w = cot B = sξg, where s is the excitation error and ξg the extinction distance, the intensity of the fringes becomes:
Electron lattice image interpretation of V2O3 wedge shaped crystal
Authors: Tanaka M. , Rocher A. , Ayroles R. , Jouffrey B.
Published: June 2020

The thickness dependence of a two dimensional lattice image with small lattice spacings (< 5 Å) has been discussed in the theoretical aspect by some authors(1) (2),(3) in the case of zone axis orientation. Our intention is to compare the experimental image with the theoretical one for a vanadium sesquioxide (V2O3) crystal not in the zone axis orientation but in more general orientations. This crystal, one of those which show the metal-insulator transition, is metallic and belongs to the space group at room temperature. The unit cell dimensions in the hexagonal system are a = 4.951 Å and c = 14.003 Å (4). The electron microscope used is a JEM-100C equipped with the fixed specimen stage and operated at 100 kV (Cs = 1.4 mm).

Figure 1 shows a lattice image from a wedge shaped crystal. Especially remarkable is the recurrence of similar contrast in three thicknesses regions : < 50 Å,∽ 250Å,and ∽ 450Å.
High resolution studies of dislocations in lattices
Authors: Bourret A. , Penisson J.M.
Published: June 2020

The study of dislocation by lattice images in crystals was initiated by PARSONS and PHILLIPS using tilted beam illumination. However this method was not extensively used for two reasons : i) it is difficult to correctly assess the Burgers vector and control the orientation of a given dislocation in a deformed material, ii) a good correspondance between object and image is only obtained for dislocations seen end-on. Recently a new development of this method started when dislocations were produced in controlled conditions in the low angle grain boundary of a bicrystal. Two kinds of materials were selected : germanium (diamond structure) with rather large lattice parameter d111 = 3.26 Å and aluminium (fee structure) with d111 = 2.3 Å. Both materials have rather high stacking fault energy and consequently low splitting distances when dislocations are dissociated. For germanium the imaging conditions is easy to set properly : an axial beam in a high voltage electron microscope is the best.
Transmission electron microscopy of SI-AL-O-N alloys
Authors: Kirn M. , Rühle M. , Schmid H. , Gauckler L.J.
Published: June 2020

It is expected that Si-Al-O-N alloys are important high temperature construction materials. The phase diagrams for Si-Al-O-N alloys were studied systematically mainly by X-ray diffraction work (for a summary see). Different stable phases were found. For the understanding of the physical and mechanical properties it is of great interest to know for the different stable phases the microstructure and the morphology, which can be obtained by TEM observations. Results of some TEM studies are reported here utilizing not only the conventional TEM but also the lattice fringe imaging technique.

Specimens of the different phases were produced as described in They were prepared for TEM observations. For high resolution work a Siemens ELMISKOP 102 (operating voltage 125 kV) was used fitted with a double tilting stage (± 45°), for conventional TEM studies the specimens were examined in an AEI EM7 high voltage EM operated at 1 MeV.
Anisotropy of damage productions in electron irradiated molybdenum
Authors: Izui K. , Furuno S. , Otsu H. , Nishida T. , Maeta H.
Published: June 2020

Anisotropy of damage productions in crystals due to high energy electron bombardment are caused from two different origins. One is an anisotropic displacement threshold energy, and the other is an anisotropic distribution of electron flux near the atomic rows in crystals due to the electron channeling effect. By the n-beam dynamical calculations for germanium and molybdenum we have shown that electron flux at the atomic positions are from ∽4 to ∽7 times larger than the mean incident flux for the principal zone axis directions of incident 1 MeV electron beams, and concluded that such a locally increased electron flux results in an enhanced damage production. The present paper reports the experimental evidence for the enhanced damage production due to the locally increased electron flux and also the results of measurements of the displacement threshold energies for the <100>,<110> and <111> directions in molybdenum crystals by using a high voltage electron microscope.
Effect of cascade energy density on the defect cluster type in heavy-ion-irradiated gold
Authors: Jäger W. , Merkle K. L.
Published: June 2020

For the quantification of defect production by energetic displacement cascades in metals, a knowledge of the types and numbers of defects created is required. In Au a considerable fraction of the defects generated in such cascades is present in large enough clusters to be observed by transmission electron microscopy (TEM) and analysed as to their structure, sizes, and types (interstitial or vacancy clusters). Heavy ion bombardments have provided an efficient means to study the defect production in cascades as a function of cascade energy. An important problem concerns the question whether visible interstitial clusters are formed in individual displacement cascades in addition to the vacancy clusters that are formed by collapse of the depleted zones. Two conditions may enhance the formation of interstitial clusters formed in cascades:1) An increase in displacement density as produced by overlapping two low energy cascades is expected to lead to a higher interstitial concentration in close vicinity of the depleted zones.
Defect clusters in heavy-ion irradiated nickel and nickel alloys
Authors: Robinson T.M. , Jenkins M.L.
Published: June 2020

Low-dose (≲1012ions/cm2) heavy-ion irradiation gives a convenient method of studying some aspects of fast-neutron radiation damage and has now been studied using transmission electron microscopy in a wide variety of metals and alloys (e.g. see the reviews by Eyre 1973 and Wilkens 1975). From these studies a consistent picture of the development of the damage structure has emerged. In most cases small vacancy loops are observed, produced heterogeneously at the sites of displacement cascades by the collapse of vacancy-rich ‘depleted zones’. The interstitial component of the damage is usually lost to the foil surfaces and is not observed. There have been surprisingly few investigations of heavy-ion damage in materials of technological importance. However, it has been noted that cascade collapse appears to take place less readily in complex alloys such as steels than in pure metals such as copper (e.g. Williams and Eyre 1976) but few attempts have been reported to explore this effect systematically.
Simulation of electron displacement damage in the high voltage electron microscopy
Authors: Ono S. , Kanaya K.
Published: June 2020

By applying the fundamental theory of the neutron cooling to the conservation law of energy and momentum, the average transferred energy Ea of an atom caused by high energy electrons is given by Ea=Em/2.72, where Emis the maximum energy transferred in a head-on collision.

The threshold energy ETHof the incident electron for the displaced atom is obtained from, where Ed is the average displacement energy of an atom with mass M, Essublimation energy instead of the binding energy by Cosslett, m electron rest mass and c light velocity (Fig.1).

When the energy of the incident electron exceeds the threshold energy ETHof displacements the concentration Cdof displaced atoms produced can be given by Cd=σDΦN, where σDis the cross section for the knock-on process, Φ the electron dose, and the total number N of displaced atoms summing over all collisions giving by Keywell as
The voids formation of Cu-1.5%Fe alloy during irradiation in HVEM
Authors: Ohnuki S. , Takahashi H. , Takeyama T.
Published: June 2020

Introduction

The high voltage electron microscope (HVEM) is a method useful for simulating the effects of fusion and fission reactor and has the advantage that direct observation can be made of the void and other defects of the specimen during irradiation. Also, the determination of the conditions under which voids can be nucleated and grown by electron irradiation ought to be helpful in separating the effects of the various parameters involved. This paper presents the effects of aging on void formation in Cu-Fe alloy during irradiation in the HVEM.

Experimental Procedure

Alloy was quenched into water from 1263 K and aged at 973 K for 1 hr, 4hrs and 4 days. Electron irradiation was performed at 523 K by using a 650 kV HVEM in a flux of 3xl023e/m2 (9xl0-4 displacement/atom/s). The foil plane was a (110). For comparison with the alloy, pure Cu also irradiated under the same dcondition.
Radiation damage mechanisms in some organic molecular crystals
Authors: Clark W.R.K. , Chapman J.N. , Ferrier R.P.
Published: June 2020

Since the relative intensities of electron diffraction spots are a very sensitive measure of the long range order within a crystal, we have designed and built a digital Scanning electron diffractometer to record them as irradiation proceeds. This system is connected to a JEOL JEM 100C electron microscope and generates deflection signals which tilt the illumination incident on the specimen, causing the electron diffraction pattern to be scanned across a scintillator-photomultiplier assembly located below the microscope. The signals are digital, so that the scan consists of a series of discrete steps, with variable but accurately controlled time intervals between. In this work it has been found most convenient to scan along a single row of diffraction spots. To this end the step size is set so that after each step either a spot or an intermediate continuous background region is coincident with the optic axis. During the time interval between steps the detector output (proportional to the current in the spot) is integrated, digitised, and stored in a solid state memory prior to output to the computer for analysis.
Defect clusters of molybdenum alloys bombarded by HVEM
Authors: Igata N. , Kohyama A. , Murakami H. , Itadani K. , Tsunakawa H.
Published: June 2020

As a simulation study of heavy radiation damage by neutrons, in-situ observation of damage process in molybdenum alloys was performed by a high voltage electron microscope. The objectives of this study are to clarify the processes of defect cluster nucleation and growth, and the role of alloying elements on these in the temperature range from 300K to 1300K.

The used molybdenum alloys were Mo-(150-1000)at.ppm.C, Mo-(0.06-0.6)at.%Nb, MO-0.29at.%Hf, MO-(0.026-26)at.%Re and Mo-0.56at.%Ni. The used materials were electron-beam melted and hot rolled at 200-400°C and annealing was performed in the vacuum of l×l0-7torr. at 1800°C for 1.0 hr. The standard irradiation conditions were as follows,

Accelerating voltage: 1250KV, Beam intensity: l-6×l019e/cm2sec, Incident beam direction: <100>, g-vector: {110},

The density of defect clusters was determined by the thickness gradient method.

The logarithmic density of interstitial dislocation loops, logNi, increased with the reciprocal irradiation temperature, 1/T. The relation between logNiand 1/T was divided into two Arrhenius type relations above and below 500K.
High-resolution TEM of grain boundaries in silicon
Authors: FÖll H. , Ast D.G.
Published: June 2020

In contrast to grain boundaries in metals, little is known about the structure and the properties of grain boundaries in covalent crystals, especially in semiconductors. The reason for this lack of knowledge is that grain-boundary-free crystals of, e.g., silicon, are easy to grow; commercially used silicon crystals are free of dislocations and thus nearly perfect. It was not until after the use of polycrystalline silicon had been proposed for the large scale production of cheap solar cells that grain-boundary properties in silicon gained considerable interest. In particular their electronic properties and their influence on device performance is important in this case. Moreover, “grain boundary devices”, i.e., devices with a grain boundary as the active element and with rather interesting properties, are conceivable - provided the relationship between the grain boundary structure and their electronic behaviour can be understood (cf. /l/). In addition, the study of grain boundaries in silicon, with an electronic structure and a binding configuration very different from metals, may provide a valuable tool to test competing grain boundary models (see, e.g., /2,3/) and may lead to a deeper insight into the crystal parameters governing the grain boundary properties.
Electron microscopy investigation of polyethylene single crystals
Authors: Boudet A. , Kubin L.P.
Published: June 2020

The main limitation in the electron microscopy observation of polyethylene single crystals, like other polymers, is the damage created by the electron beam (1). An image intensifier can be used in order to increase the life-time of the crystals (2); however, the eye adapted to darkness for half an hour still gives better results, and we used the latter method. The images were recorded on Kodirex films of high sensitivity which reduce the exposure times by a factor of 20 with respect to electron image plates (3). With the 100 kV electron beam set to an intensity of about 0.1 A/m2 (measured with a Faraday cage), the lifetime of the PE single crystals was as long as half an hour or one hour, allowing ten to fifteen micrographs to be taken in bright, dark field or diffraction. The beam divergence and condenser apertures were set up in such a way that only the observed area was irradiated.
Sources of background X-radiation in analytical electron microscopy
Authors: Headley T.J. , Hren J.J.
Published: June 2020

It is well known that a major barrier to quantitative energy dispersive (EDS) measurements of thin films is the background X-radiation generated from stray electrons and X-rays from a variety of internal sources. A number of sources have been reported in a variety of microscopes and there is disagreement over their relative importance. Clearly the sources from each type of microscope must be systematically investigated and suppressed. We report here one such study of a JEM 100C/SEG microscope. Although our data are specific to this instrument, analogous results should be obtained from other analytical transmission microscopes. The major sources of spectral background in the JEM 100C were found to be: 1) the fixed condenser (Cl) aperture, 2) the variable condenser (C2) aperture, and 3) the specimen holder. Other potential background sources such as the objective lens pole pieces and the anticontamination device did not contribute a measurable signal. Still others, such as the objective aperture, could be eliminated simply by prudent operation (e.g. removal during EDS counts).
Limits of AES microanalysis in SEM
Authors: Delong A. , KolaŘÍk V.
Published: June 2020

Auger electron spectroscopy Is a well known method of chemical analysis of solid surfaces. For its application the following features are important:

i) highest sensitivity when measuring small concetrations

ii) smallest diameter of the analyzed area

It is clear that these two requirements are contradictory. For many applications the second condition is predominant in spite of the fact that it is necessary to take into account the concentration of the element analyzed as high as nearly 100%. As the Auger electrons posses energies in the range of some tens to a few hundred eV, it can be supposed that the smallest surface area from which they can be generated due to scattering will not differ from the area involved in the emission of secondary electrons, i.e. it will not be larger than 100 Å.

There are two other important conditions :

i) the use of a very small electron probe (100 Å)

ii) the attainment of very high current density in the probe
Microanalysis of amorphous semiconductor films
Authors: Schröder B. , Geiger J. , Müller H.W.
Published: June 2020

In a previous paper /l/ it has been pointed out that electron energy loss spectroscopy in the infrared spectral region is a very sensitive tool for the study of structure and composition of thin films. Here as a further example the energy loss study of amorphous silicon films is presented. In the case of amorphous semiconductors where most of the optical and electrical properties are still strongly influenced by impurities an analytical test is substantial.

Silicon films have been investigated which have been prepared by different methods and under different conditions: by evaporation, by decomposition of silane (SiH4) in a rf glow discharge and by sputtering. The influence of the substrate temperature has been studied for films produced by silane decomposition.

Fig. 1 shows a typical spectrum of amorphous silicon prepared by the glow discharge method obtained by 30 keV electrons with a resolution of 3 to 4 meV.
On the problem of filtered images in chemical analysis
Authors: Zanchi G. , Sevely J. , Jouffrey B.
Published: June 2020

As was proposed in several recent review papers (for instance 1-3) it is interesting to use electron energy losses corresponding to inner shell excitations by incident electrons to perform chemical analysis. One of the main advantages of the inner shell excitation spectroscopy (ISES) is that it is essentially available for light elements, contrary to characteristic X ray emission spectroscopy.

Two methods can be used :

- energy analysis : energy loss spectra are obtained from selected projected area of the sample and elemental characteristic energy losses are detected;

- image energy filtering : images are formed by selecting electrons in an energy loss range which contains a characteristic energy loss. They show a map of the distribution of a given element in the object with a high spatial resolution.

Combining these two methods is quite essential to perform chemical analysis. Such studies can be achieved in CTEM by means of an energy filtering system preserving the imaging properties of the microscope.
Spatial resolution of X-ray microanalysis in thin foils
Authors: Hutchings R. , Jones I.P. , Loretto M.H. , Smallman R.E.
Published: June 2020

There is increasing interest in X-ray microanalysis of thin specimens and the present paper attempts to define some of the factors which govern the spatial resolution of this type of microanalysis. One of these factors is the spreading of the electron probe as it is transmitted through the specimen. There will always be some beam-spreading with small electron probes, because of the inevitable beam divergence associated with small, high current probes; a lower limit to the spatial resolution is thus 2αst where 2αs is the beam divergence and t the specimen thickness.

In addition there will of course be beam spreading caused by elastic and inelastic interaction between the electron beam and the specimen. The angle through which electrons are scattered by the various scattering processes can vary from zero to 180° and it is clearly a very complex calculation to determine the effective size of the beam as it propagates through the specimen.
Elemental analysis in a V-Ti-C alloy using electron energy loss spectroscopy
Authors: Fraser Hamish L.
Published: June 2020

There has been considerable interest in the recent past concerning the application of refractory metal-interstitial systems as high temperature materials. it is important to understand the behavior of the interstitial component, and thus the determination of precipitation processes has been an area of study. in addition to making observations in simple binary systems, there is a need to characterize the changes that occur when other substitutional alloying elements are added. recently, bruemmer has studied the precipitation of carbides in a v-8Ti-c alloy over a range of temperatures. it is particularly interesting to characterize the carbides that precipitate at temperatures when the ti can diffuse rapidly (e.g. 1000°c), and determine not only the structure of the carbide but also perform microchemistry on as fine a scale as possible using analytical electron microscopy. bruemmer used a scanning transmission electron microscope (stem) (jeol jsem 200) coupled with an ortec energy dispersive x-ray analyzer to make measurements of the v:ti ratio in the carbide.
Large-angle-electron-channeling-pattern: generation and applications
Authors: Brunner M. , Erlenwein P.
Published: June 2020

A tilting stage /1/ was used for obtaining large angle electron channeling patterns (ECP) /2/ (fig. 1). The stage is driven by two step motors and tilted in synchronism with the movement of an electron beam of a Vistascan storage device or of a light emitting diode, writing the pattern on a photographic film in an xy-recorder. An electron beam with a divergence of 0.03° is produced by a thermal cathode and two diaphragms. The backscattered electrons are registrated by two scintillation detectors which are mounted on opposite sides to reduce shadowing effects. After amplification and regulation the produced electronic signal controls the writing or storage device. This method allows to record ECPs from areas of 200 μm in diameter at a tilting range of ±75° in both directions with a resolution of 0.05°.

This rocking crystal method has been applied already to investigations of the temperature dependence of the ECP-contrast /3/.
Heavy ion irradiation damages in crystals
Authors: Yoshida H. , Sakuramoto N. , Kawai K.
Published: June 2020

Accelerator irradiations are recently of interest in the field of radiation damages, because of the simulation studies for high dose neutron irradiations as well as the fundamental studies for atomic collision processes. The characteristic phenomena associated with ion irradiation such as sputtering,blistering and flaking are considered to be very important for plasma walls of fusion reactors. Since the penetration depth of ions in materials is very small, highly dense lattice defects are produced by ion irradiation in the shallow regions from the surface, and also the projected ions may accumlate within the projected ranges except channelled ions. Such the phenomena can be detected by means of the pulse-thining technique for SEM and TEM observations. Electron channelling pattern (ECP) is also useful for studying about the phenomena, because of its sensitiveness to lattice distortion of the surface layer.

The accelerator irradiations with inert gas and metal ions were performed for bcc, fcc and diamond crystals.
In situ study of collective dislocation movements in a Ni-Cr alloy
Authors: Clement N. , Caillard D. , Martin J.L.
Published: June 2020

Properties of groups of moving dislocations have to be considered in various deformation processes especially those of concentrated alloys (1). Indeed, the strain rate dependence on stress and temperature of such materials cannot be interpreted in terms of simple models postulating homogeneous deformation. Nevertheless experimental studies of these dynamic properties are rare and consist mostly of etch pit studies of the sequences of dislocation pile ups at various stages of the stress strain curve (2) or the dynamic recording of macroscopic slip trace development by high speed cinematography (3).

We report here some microscopic properties of moving groups of dislocations in a FCC Ni-30 wt%Cr alloy observed directly during deformation tests in the high voltage electron microscope. This alloy has a rather low stacking fault energy (γ/Gb≃3.5xlO-3) and exhibits short range order after 100 hours of annealing treatment at 600°C. Between 77 K and 400 K, conventional deformation tests lead to rather small activation volumes indepedent of strain and a high athermal stress, incompatible with the intersection mechanism (4).
Shock deformation twinning in molybdenum and a comparison of deformation twinning in shock-loaded BCC and FCC metals
Authors: Murr L.E. , Wongwiwat K.
Published: June 2020

Verbraak reported deformation twins to have been formed in shock-loaded molybdenum from observations by optical metallography. Attempts to verify the existence of deformation twins in shock-loaded molybdenum by Murr, et al. were unsuccessful at pressures ranging up to 21 GPa (210 kbars) at a constant pulse duration of 2 μs. Since the conditions under which Verbraak originally observed deformation twins were not well documented, a study was undertaken to reinvestigate the shock deformation of molybdenum in a range of pressures and pulse durations.

Molybdenum sheets (0.0025 cm thick and 0.025 cm thick) were annealed to produce several grain sizes and shock loaded in molybdenum sandwiches and assemblies (spall plates and momentum traps) by impacting them with stainless steel flyer plates as outlined previously. Pressure experiments were performed at 140, 260, and 350 kbars (corrected pressure values using impedance matching techniques) at a constant pulse duration of 2 μs while two additional experiments were conducted at 260 kbars by shock loading test assemblies at pulse durations of 0.5 μs and 8 μs.
Interactive effect of repeated loading, pressure, and pulse duration on residual martensite in shock-loaded 304 stainless steel
Authors: Murr L.E. , Moin E. , Staudhammer K.P.
Published: June 2020

Murr and Staudhammer have shown that the residual microstructure in shock loaded stainless steel contains increasing amounts of martensite as the pulse duration is increased at constant pressure. Ma and Murr have derived a simple expression for the so-called dynamic negative shear strain or dynamic back shear strain generated along the slip planes in a shock-loaded material of the form Es ≅ ΔP' Δt/2b, where ΔP' is related to the peak shock pressure and At is the shock pulse duration. The principles behind the theoretical development of this relationship also suggest that at a fixed pulse duration, the resultant dynamic back shear strain of a metal should not only be a function of pressure but also its magnitude will not be the same whether the metal is subjected to the fixed duration of shock stress continuously or intermittently. That is, if the total shock stress duration is divided into several subdurations, say t1 + t2 + t3, the term ΔP' Δt will not be equal to ΔP' (t1 + t2 + t3)even though Δt =(t1, t2, t3).
Aspects of intergranular fracture of CuBi studied in the scanning electron microscope
Authors: Biggin S.
Published: June 2020

IntroductionKossel X-ray diffraction within the SEM can be used to obtain orientation relationships (to 0.2° routinely) and crystal perfection information from microvolumes (5μm)3, this being the principal feature of the technique1. A study of the cracking behaviour of CuBi alloys has been made in an attempt to understand the mechanism by which intergranular fracture occurs due to the addition of down to 0.001at.% Bi2. Orientation relationships (angle/axis pairs) were needed for cracked boundaries but can only be found from Kossel patterns from annealed materials. Thus orientation work was done on annealed material, which was then deformed in a 4-point bending machine. Observations of changes in crystal perfection were made at various strains, as cracks appeared, at positions within grains and at boundaries. Finally, optical study of slip lines at boundaries and fracture surfaces was made.

A Cu0.02 wt.% Bi sample was given a maximum embrittlement heat treatment (1073K,10min,air-cooled; 773K, 4h, furnace-cooled) which caused a large percentage of the Bi to segregate to the boundaries.
Dislocations in alumina deformed by prismatic slip
Authors: Cadoz J. , Castaing J. , Philibert J.
Published: June 2020

Plastic deformation of alumina has been much studied; basal slip occurs and dislocation structures have been investigated by transmission electron microscopy (T.E.M.) (1). Non basal slip has been observed (2); the prismatic glide system <1010> {1210} has been obtained by compression tests between 1400°C and 1800°C (3). Dislocations with <0110> burgers vector were identified using a 100 kV microscope(4).

We describe the dislocation structures after prismatic slip, using high voltage T.E.M. which gives much information.

Compression tests were performed at constant strainrate (∿10-4s-1); the maximum deformation reached was 0.03. Thin sections were cut from specimens deformed at 1450°C, either parallel to the glide plane or perpendicular to the glide direction. After mechanical thinning, foils were produced by ion bombardment. Details on experimental techniques can be obtained through reference (3).
In situ investigation of the primary recrystallization of alpha titanium in HVEM
Authors: Naka S. , Penelle R. , Valle R.
Published: June 2020

The in situ experimentation technique in HVEM seems to be particularly suitable to clarify the processes involved in recrystallization. The material under investigation was unidirectionally cold-rolled titanium of commercial purity. The problem was approached in two different ways. The three-dimensional analysis of textures was used to describe the texture evolution during the primary recrystallization. Observations of bulk-annealed specimens or thin foils annealed in the microscope were also made in order to provide information concerning the mechanisms involved in the formation of new grains. In contrast to the already published work on titanium, this investigation takes into consideration different values of the cold-work ratio, the temperature and the annealing time.

Two different models are commonly used to explain the recrystallization textures i.e. the selective grain growth model (Beck) or the oriented nucleation model (Burgers). The three-dimensional analysis of both the rolling and recrystallization textures was performed to identify the mechanismsl involved in the recrystallization of titanium.
Freeze-fracturing in ultrahigh vacuum: Low-temperature sample holder (4.8 K) and microtome sample holder UHV compatible
Authors: Escaig J.
Published: June 2020

The protection of fracture faces against contamination by residual hydrocarbons can be obtained by pumping the vacuum chamber under ultrahigh vacuum or by surrounding the preparation by a shroud cooled by liquid nitrogen. Both means help in reducing the partial pressure of water vapour. Nevertheless even if ultrahigh vacuum is combined with a cooling shroud, water vapour remains the main residual gas, as can be seen in the mass spectrum shown by Gross or in that of Fig. 1a. Selective condensation of water vapour on specific sites of fractured membranes can create artefacts resembling intramembranous particles. The most efficient way to reduce the partial pressure of H2O is to bake the whole of the vacuum system (vacuum chamber valve, pump) at temperatures between 200 and 400°C. An ion pump is best suited for that purpose as it maintains its pumping rate at high temperature. Contrary to cryopumps, it does not require a cooled screen, which simplifies the construction and keeps running costs down. Curve 1b shows that after 8 hours of baking (overnight) the partial pressure of water vapour is reduced to 2.10-10 Torr and that the residual atmosphere is mainly composed of hydrogen which, because of its high vapour pressure, cannot be condensed at temperatures over a few Kelvin degrees (peak 28 is mainly produced by the filament of the mass spectrometer itself).
Complementary freeze-fracture and freeze-etch preparations
Authors: Steere Russell L. , Erbe Eric F. , Bartle Bryan K.
Published: June 2020

Whereas freeze-etching technology was introduced in 1957 (1) and the first freeze-etching equipment to be made available commercially was developed in 1961 (2), the need for complementary replicas was not recognized until Branton (3) proposed that the two membrane faces seen in freeze-etched specimens were not the inner and outer surfaces of membranes but represented two new faces which resulted from the splitting of membranes between the two lipid layers. Several indirect methods were developed to test Branton's hypothesis and most of them provided confirming evidence. It became obvious that complementary replicas could provide the indisputable answer to this theory; wherever one membrane fracture face appeared on one specimen the other fracture face should appear in the same position on the complementary specimen. Several devices were developed to make possible the preparation of complementary replicas (4, 5, 6, 7).
The “rediscovery” of polyethylene glycol, and its use as an embedding matrix
Authors: Wolosewick J. J.
Published: June 2020

Polyethylene glycols are liquid or solid polymers of the general formula H(OCH2CH2)nOH, where n is greater than or equal to 4. They are readily miscible in water and in a variety of solvents and are nontoxic. The higher molecular weight polymers (e.g., PEG 4000, 6000) are brittle and melt at 55°-65°C, while the lower molecular weight polymers are soft gummy solids or liquids. These polymers have been used as embedding matrices for light and electron microscopy since the 1940's, although their use has been overshadowed by the now standard embedments (e.g., paraffin and epoxy resins).

The procedures for embedding in PEG have been described in detail. Briefly, specimens are fixed according to standard procedures, washed in an appropriate buffer, dehydrated either in PEG-H2O solutions, or in ethyl alcohol. For embedding, the specimens are transferred to capsules filled with the pure polymer and solidified at room temperature, or by rapid cooling in liquid nitrogen. The blocks are mounted onto suitable stubs (e.g., Epon blanks), trimmed and sectioned “dry” on glass or diamond knives. The sections are mounted onto polylysine-coated slides or Forrmvar-coated grids in the same manner as are frozen sections.