bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of two-photon chromophore excitation to laser scanning microscopy
Authors: Piston David W. , Strickler James H. , Webb Watt W.
Published: June 2020

The non-linear optical technique of two-photon excitation of fluorescence and photochemical reactions makes possible new applications that are not possible using linear one-photon excitation in laser scanning confocal microscopy. The two-photon excitation effect arises from the simultaneous absorption of two red photons, which causes the transition to an excited electronic state with its normal absorption in the ultraviolet. In our fluorescence experiments, this excited state is the same singlet state, S1, that is populated during a conventional fluorescence experiment, and thus exhibits the same emission properties (e.g. wavelength shifts, environmental sensitivity) that are observed in typical biological microscopy studies. Likewise, photochemical reactions such as light induced polymerization and photolytic uncaging that are normally catalyzed by UV light can be generated using two-photon excitation. In practice, twophoton excitation is made possible by the very high local instantaneous intensity that is provided by a combination of the diffraction limited focusing in the microscope and the temporal concentration of a subpicosecond mode-locked laser.
A new microtome approach and its relation to 3D imaging
Authors: Newberry Sterling P.
Published: June 2020

A continuing concern of this laboratory is to improve techniques for acquiring and displaying 3D images of structure over a wide range of magnification from a single, identical piece of tissue. One of the major problems is to slice the sample thin enough in one dimension that ultra structure can be preserved. Slicing is not a serious drawback because computer reconstruction techniques permit us to put the slice images together for comparison with the next lower level of magnification all the way down to the whole specimen. Reembedding techniques have also helped to bridge the gap between magnification levels. Ironically it is at the first level of slicing that thickness prevents adequate preservation making the specimen very difficult to section. For brain tissue the Vibratome® has become the preferred microtome but it does not handle many softer and harder tissues and even neuroscientist tend to prefix their tissue. There still appears to be need for improved methods of cutting a variety of fresh tissues.
Imaging organic aerogels at the molecular level
Authors: Ruben G.C. , Pekala R.W.
Published: June 2020

The sol-gel polymerization of metal alkoxides or certain multifunctional organic monomers leads to the formation of highly crosslinked, transparent gels. If the solvent is simply evaporated from the pores of these gels, large capillary forces are exerted, and a collapsed structure known as a xerogel is formed. In order to preserve the gel skeleton, it is necessary to remove the the aforementioned solvent under supercritical conditions. The low density, microporous material that results from this operation is known as an aerogel. Aerogels have an ultrafine cell/pore size (< 500 Å), connected porosity, high surface areas (400-1000 m2/g), and an ultrastructure composed of interconnected colloidal-like particles or polymeric chains with characteristic dimensions of 100 Å. This ultrastructure is responsible for the unique optical, thermal, and acoustic properties of aerogels. For example, the ultrafine cell/pore size minimizes light scattering; and thus, aerogels are transparent porous solids. The high porosity of aerogels makes them excellent insulators with their thermal conductivity being approximately 100X lower than that of the fully dense matrix. Finally, the aerogel skeleton is responsible for the low sound velocities observed in these materials (i.e. 100-300 m/sec).
New challenges to image processing posed by cryo-Electron microscopy of single particles
Authors: Frank Joachim
Published: June 2020

Compared with images of negatively stained single particle specimens, those obtained by cryo-electron microscopy have the following new features: (a) higher “signal” variability due to a higher variability of particle orientation; (b) reduced signal/noise ratio (S/N); (c) virtual absence of low-spatial-frequency information related to elastic scattering, due to the properties of the phase contrast transfer function (PCTF); and (d) reduced resolution due to the efforts of the microscopist to boost the PCTF at low spatial frequencies, in his attempt to obtain recognizable particle images.
Microscopy of whole cells in ice
Authors: O'Toole E.T. , Mcintosh J.R.
Published: June 2020

Cryomicroscopy of frozen hydrated specimens makes it possible to visualize biological material in a condition that is close to its native state by avoiding chemical fixatives, dehydration or stain. In the past, cryoimaging using a conventional TEM has been limited to thin frozen suspensions of biological material or to thin cryosections of frozen cells and tissues. High voltage electron microscopes (HVEM) offer the advantage of improved penetration of thick samples by the electron beam and thus are suitable for imaging thick frozen samples. Here we describe a comparative method for studying the ultrastructure of freeze substituted, critical point dried cells and frozen hydratpd cells in the HVEM.
Research thrusts employing intermediate-voltage analytical microscopy
Authors: Garratt-Reed Anthony J.
Published: June 2020

Although commercial analytical electron microscopes equipped with field-emission electron guns operating at 100kV have been in routine use in laboratories in many countries for over 15 years, and while there has been a general appreciation that for certain studies (e.g. catalyst research) such instruments are invaluable tools, there has been little consensus on what results can be expected from such microscopes when used for study of more generalized samples, and in particular their ability to resolve chemical detail in the thin-foil samples typical of much materials research.

200kV field-emission microscopes have already been delivered to customers by Hitachi, and at the time of writing, the first 300kV field-emission STEM is in the final stages of factory test, having already demonstrated an image resolution of 0.3nm point-to-point and excellent x-ray characteristics, and is expected to be delivered to the authors1 laboratory within a few weeks.
High Resolution Scanning Electron Microscopy
Authors: Joy David , Pawley James
Published: June 2020

The scanning electron microscope (SEM) builds up an image by sampling contiguous sub-volumes near the surface of the specimen. A fine electron beam selectively excites each sub-volume and then the intensity of some resulting signal is measured. The spatial resolution of images made using such a process is limited by at least three factors. Two of these determine the size of the interaction volume: the size of the electron probe and the extent to which detectable signal is excited from locations remote from the beam impact point. A third limitation emerges from the fact that the probing beam is composed of a finite number of discrete particles and therefore that the accuracy with which any detectable signal can be measured is limited by Poisson statistics applied to this number (or to the number of events actually detected if this is smaller).
Ultra-high resolution chemical analysis by field-ion atom probe/position sensitive atom probe techniques
Authors: Grovenor C.R.M. , Cerezo A. , Liddle J.A. , Mackenzie R.A.D. , Hetherington M.G. , Smith G.D.W.
Published: June 2020

The use of field ion microscopy based techniques in the study of the structure and chemistry of metallic and semiconducting materials with very high resolution is now well documented. The particular features of these techniques which result in the achievement of very high spatial resolution in images and chemical profiles are; the intrinsic magnification in a conventional field ion microscope of at least 106, the plane-by-plane desorption characteristic of field evaporation processes, and the excellent chemical specificity in a modern atom probe. In addition, we have developed in Oxford a new detector system for field ion based equipment in which both the chemical identity of evaporated ions and the position on the sample surface from which they were evaporated can be established. This allows the reconstruction of the evaporated volume in three dimensions, and this technique has been christened the Position Sensitive Atom Probe, POSAP. This abstract presents the results of two typical experiments illustrating the very high quality of the chemical data that can be obtained in both conventional atom probe and POSAP facilities.
Assessment of resolution in biological electron crystallography
Authors: Glaeser Robert M. , Downing Kenneth H.
Published: June 2020

In the present context the discussion of “biological electron crystallography” will be limited to structural studies of thin, two-dimensional (2-D) crystals, although a broader definition, including even single molecules, is certainly justified. The restriction to 2-D crystals provides the useful simplification that all of the information about the specimen-structure is confined to discrete diffraction spots in the computed Fourier transform of the electron micrographs. The absolute limit of resolution in a structural study is then given by the highest resolution term in the computed Fourier series that is used to synthesize a density-map representation of the specimen, which may be either a 2-D projection or a three-dimensional (3-D) reconstruction. The apparent simplicity of the above definition of “limiting resolution” disguises the fact that the structurally useful, or practical limit of resolution must invariably be somewhat poorer than the objectively determined resolution of the “highest resolution spot” included in the Fourier synthesis of a density map.
High-resolution electron holography
Authors: Lichte Hannes
Published: June 2020

The performance of an electron microscope usually is described in Fourier space by means of the wave transfer function WTF(R) = B(R) exp(iχ(R)) with the pupil function B(R) and the wave aberration χ(R). R means the spatial frequency, rotational symmetry is assumed.

The exp(iχ(R)) term describes the coherent transfer of the object wave a(r)exp(iφ(r)) into the image wave A(r)exp(iФ(r)). For weak specimen (a≈1 and φ<<27π) this transfer can be sketched by means of fig. 1 which shows that a mixing occurs between the amplitudes and phases according to the respective transfer functions cosχ and sinχ. Usually, it is desirable to direct by an appropriate wave aberration x the phase of the object wave - containing the most interesting information about the object structure - into the image intensity A2. This is achieved best at Scherzer focus, however, only a comparably narrow band of spatial frequencies is evenly transferred. Lower spatial frequencies (“Large area phase contrast“) are not found in the image.
Electron penetration effects in the Scanning Electron Microscope applied to Cu/Ta thin films
Authors: Bailey P. , Holloway K. , Clevenger L. , Bojarczuk N.
Published: June 2020

Current semi-conductor technology uses low-resistivity metals, as Cu, for integrated circuit conductor lines and contact structures. Copper, however, is quite mobile in silicon at elevated processing temperatures and a diffusion barrier such as Ta, is therefore required between the Si and Cu. The interdiffusion of Cu and Si with Ta as a diffusion barrier was studied in samples annealed between 500°C and 800“C, using scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Secondary electron images obtained in the SEM, from 5keV to 25keV accelerating voltages were correlated to the structural information obtained by cross-section TEM. This work showed that annealing produced a compositionally non-uniform underlayer beneath the Ta film, and that the technique of varying the accelerating voltage in the SEM provides a means of quickly obtaining such information about underlying structures.
Microscopy studies of flower structures
Authors: Hess W. M. , Hess Carla A. , Gardner John S.
Published: June 2020

The flowers of broad-leaved plants have four floral structures which differ significantly in shape from flower to flower. The sepals, petals, stigmas and pistils all have characteristic shapes and examples of all of them have been studied with scanning electron microscopy (SEM). The petals appear to be the most delicate of these structures and are therefore useful as indicators for senescence, as indicators for pollution effects or for developmental characteristics. Petals of most flowers are stamens which have switched roles during evolution from sexual organ to agents which attract pollinators. Even though they appear to be smooth to the unaided eye, they have fine sculptured detail when observed with SEM. Adaxial surfaces of some petals have closely packed cells which project from the surface and often have fine ridges or points. The reason for this is unknown, but is likely related to the reflection of light from petals.
Quantum noise characteristics in TEM images measured by means of imaging plate
Authors: Oikawa T. , Mori N. , Hosokawa F. , Kawasaki M.
Published: June 2020

In the observation of the beam sensitive specimens, it is required to minimize the electron dose. At a very low electron dose, however, the electrons themselves become quantum noise, thus lowering the image quality regardlessly of the performance of the detectors. In the present study, the relationship of quantum noise with the image signal included in TEM images has been measured by means of the Imaging Plate (IP), which is a high sensitivity detector.

The instrument used was the TEM-IP system, a PIXsysTEM based on the JEM-2000FXII.

Phase contrast images of the amorphous film were taken at a very low dose where quantum noise is dominant. The images were taken using an objective lens with a spherical aberration constant of 2.3 mm and an accelerating voltage of 200 kV. The spatial frequencies included in the images were estimated by Fourier transformation, which was carried out on the IP-processor of the PIXsysTEM, by using the original data from the IP. In this experiment, it was already ascertained that system noise (noise due to the instrument) is negligible.
On the iterative restoration of exit plane wave function from defocus series in HREM
Authors: Gribelyuk M.A. , Hutchison J.L.
Published: June 2020

The validity domain of a Multiple Image MAximum Posteriori (MIMAP) approach has been estimated on UMo5O16 complex oxide structure (Fig.1). Model defocus series (both noise-free and with an additive random noise) have been prepared by multislice method with no objective aperture imposed. Defocus values Δfn=((8n+3)Csλ/2)05 (n=0,...,4) corresponded to plateaus of JEOL-4000EX microscope transfer function operated under U=400kV. The following problems are considered:

Self-consistency. Apart from a wave function MIMAP aims at refinement of translational misalignment, difference in defocus values within series and a “fog” level c0. The latter represents an additive constant to image intensity arising by image recording and manipulation. We assumed that defocus values were known exactly and images were perfectly aligned. If one sets c01 to its exact value c0=0 and starts restoration from noise-free defocus series of a t=12 thin crystal the procedure will diverge (Fig.2).
A linearity test for thick specimens imaged by HVEM over a 180° angular range
Authors: Liu Yu
Published: June 2020

The image obtained in a transmission electron microscope is the two-dimensional projection of a three-dimensional (3D) object. The 3D reconstruction of the object can be calculated from a series of projections by back-projection, but this algorithm assumes that the image is linearly related to a line integral of the object function. However, there are two kinds of contrast in electron microscopy, scattering and phase contrast, of which only the latter is linear with the optical density (OD) in the micrograph. Therefore the OD can be used as a measure of the projection only for thin specimens where phase contrast dominates the image. For thick specimens, where scattering contrast predominates, an exponential absorption law holds, and a logarithm of OD must be used. However, for large thicknesses, the simple exponential law might break down due to multiple and inelastic scattering.
Cold work effect on modulated structure in a FeMnAlC alloy
Authors: Jahn M.T. , Ling P.
Published: June 2020

The FeMnAlC system has attracted many intensive studies in recent years since it is a potential substitute for the conventional Fe-Cr-Ni stainless steel system. This system is age hardenable when the compositions are about 30 pet Mn, 8 to 11 pet Al and about 1 pet C. An interesting phenomenon has been observed by Jahn that the cold work applied prior to aging lengthens the peak-aging time. This observation contradicts with the general enhancing effect of cold work on aging. Preliminary TEM microscopy suggested that cold work reverses the modulated structure in the alloy such that the aging process is retarded. In this report we present more detail and systematic TEM results to further support the suggested reversion effect which leads to the sluggish effect of cold work on aging process.
HREM observation of interface between precipitates and martensite of reversible shape memory alloy Ni-Ti
Authors: Song Zhiyi , Hashimoto Hatsujiro , Sukedai Eiichi
Published: June 2020

Since the reversible shape memory (RSM) alloys were found in 1960, a number of investigations and applications have been carried out and the mechanism have been discussed extensively. Ni-Ti is one of the typical RSM alloys. Many researches were concentrated on martensite structure and the relationship between martensite and austenite. However, the interface structures between martensite and precipitates have been rarely studied. In the present paper, the interface structures between precipitates ( NiTi2 and Ni3Ti) and martensite were investigated in atomic scale by using nigh resolution electron microscopy.

49.5at%Ni-50.5at%Ti alloy whose martensitic transformation temperature is 75°C was annealed at 900°C for 2 hours to allow the components to become uniformly distributed, then quenched into water at room temperature. The specimens for electron microscopy observation were prepared by spark cutting and electropolishing. A JEM-2000EX and JEM-4000EX operated at 200kv and 400kv, respectively were used in the present observations.
The microstructure and crystallography of the Cr-Cr3Si eutectic
Authors: Sutlif J.A. , Bewlay B.P. , Chang K.M. , Jackson M.R.
Published: June 2020

New materials for high temperature aircraft engine components should have a good combination of low density and high strength at temperatures as high as 1300-1500°C. This will probably require the use of composite materials. In-situ composites, or directionally solidified eutectics, are good candidates for this demanding application and have major advantages over alternative synthetic composites, such as MoSi2-SiC or carbon-carbon composites. The fabrication of components from eutectic castings is simpler and eutectic alloys offer some intrinsic microstructural stability with no reinforcement-matrix interface reactions at high temperatures. We are investigating the Cr-Si, Nb-Si and V-Si eutectic systems as potential high temperature in-situ composites. In this paper, we present results on the microstructure and crystallography of the Cr-Cr3Si eutectic which has a eutectic composition of ∼15 at% Si and a melting temperature of ∼1705 °C.
UHV Electron Microscopy study of in situ annealed (100) surfaces of MgO
Authors: Gajdardziska-Josifovska M. , McCartney M. R. , Cowley J. M.
Published: June 2020

The (100) surface of magnesium oxide is of considerable interest because of its frequent use as substrate for epitaxial growth of metal films, high Tc superconductors and model catalyst systems. A large number of surface characterization techniques have been used to determine the atomic structure of the cleaved (100) surface. Clean surfaces have been produced either by cleaving MgO crystals in-situ under ultra-high vacuum (UHV) conditions, or more frequently, by cleaving in air and subsequent annealing in UHV. A wide variety of annealing temperatures and times have been used by different researchers, the upper limit on the temperature being set at ≈900°C to avoid segregation of Ca to the surface. Calcium is the main impurity in even the purest MgO crystals and a few studies have dealt with the structure of the Ca-rich (100) surface of MgO. All of the existing studies have used diffraction and spectroscopy techniques without imaging of the surface. It is the purpose of this work to study the topography of the UHV-annealed (100) surface by reflection electron microscopy (REM).
Energy-filtered convergent beam RHEED rocking curves from cleaved (100) surface of MgO
Authors: Gajdardziska-Josifovska M. , Weiss J. K. , Cowley J. M.
Published: June 2020

Reflection high energy electron diffraction (RHEED) has been used extensively to observe changes in surface reconstructions by analyzing the geometry of the RHEED pattern and to monitor growth of layers in MBE systems by measuring the changes of the intensity of the specular spot with time. RHEED is also capable of yielding the structure of the surface by using dynamical diffraction theory to analyze experimental reflection rocking curves. These rocking curves trace the change in the intensity of the RHEED spots as a function of the angle of incident illumination. They are equivalent to the intensity vs. voltage curves (I-V) obtained in low energy electron diffraction (LEED) which have been used to determine most of the known surface structures. The LEED I-V curves are energy filtered and the theoretical calculations consider only the elastically-scattered electrons. The RHEED theory is also developed only for elastic scattering, but the experimental measurements so far have not been energy filtered.
Alternative approaches to ultra-high resolution imaging
Authors: Cowley J.M.
Published: June 2020

By extrapolation of past experience, it would seem that the future of ultra-high resolution electron microscopy rests with the advances of electron optical engineering that are improving the instrumental stability of high voltage microscopes to achieve the theoretical resolutions of 1Å or better at 1MeV or higher energies. While these high voltage instruments will undoubtedly produce valuable results on chosen specimens, their general applicability has been questioned on the basis of the excessive radiation damage effects which may significantly modify the detailed structures of crystal defects within even the most radiation resistant materials in a period of a few seconds. Other considerations such as those of cost and convenience of use add to the inducement to consider seriously the possibilities for alternative approaches to the achievement of comparable resolutions.
Improving the interpretation of high-resolution images
Authors: Van Dyck D.
Published: June 2020

We are living in a very exciting period for structural research using HREM. Indeed, the possibility to “see” the individual atoms of which matter is constituted seems within reach. Recent technological improvements allow to obtain a resolution of about 0.1 nm. However, the potential power of the technique is still severely limited by the problem of quantitative interpretation of the images. For instance, the use of computer simulation images requires much a priori knowledge which makes HREM very dependent on other techniques. The situation can be compared with the early days of X-ray diffraction. Recent developments make it possible to retrieve the object structure directly from the electron micrographs. We will discuss future prospects in this direction.
Imaging bulk insulators with secondary electrons in an UHV STEM
Authors: Liu J. , Hembree G. G. , Venable J. A.
Published: June 2020

When an insulator is bombarded by electrons a surface potential will build up if the total number of electrons entering the sample is not equal to that coming out. This potential can be positive or negative depending on the energy of the incident electrons and the target material. The effects of charging will limit, or at least perturb, the use of electron beam techniques for examining the surface properties of insulators. Various methods have been developed to avoid insulator charging. However none of these methods can be applied to high spatial resolution electron beam studies of clean insulator surfaces. At the electron beam energies typically used in STEM instruments the surface of bulk insulators will always acquire a negative potential. Secondary electron imaging (SEI) and Auger electron spectroscopy (AES) would be possible if the surface potential were stable under electron beam illumination and was small compared with the incident beam potential.
Limits to the determination of the rigid-body translations
Authors: McKernan Stuart , René Rasmussen D. , Barry Carter C.
Published: June 2020

With the advent of the personal computer revolution, the availability of computing power for performing image-processing and image-simulation calculations is widespread. Many programs now exist to perform these functions with a varying amount of approximation, such as using 2-beams only or a systematic row of beams, or calculating the image with and without the column approximation. It is possible to obtain very close agreement between the experimental and the simulated images, depending on the parameters used, and the assumptions made in performing the calculation. The simulation of the images of defects in materials has, in many cases, therefore become a tractable problem.
High-resolution electron holography of MgO
Authors: Tanji T. , Urata K. , Ishizuka K.
Published: June 2020

Electron holography is a useful application of a transmission electron microscope instrument equipped with a field emission gun (FE-TEM). The peculiarity of holography is ability to record and reconstruct the complex amplitude of an electron wave function. This characteristic makes many kinds of image processing applicable, for instance, image restoration and interferometry. Especially the correction of aberrations is expected to overcome the resolution limit owing to the spherical aberration of an electron objective lens. A few preliminary works have been reported, where a laser optical system or a digital computer system was used to reconstruct image waves and to correct the aberrations. The image qualities, however, were not enough to improve the point resolution.
Real-time reconstruction of electron-off-axis holograms recorded by means of a high-pixel CCD camera
Authors: Rau W.D. , Lichte H. , Voelkl E. , Weierstall U.
Published: June 2020

Electron holography using the electron biprism is about to become a powerful tool to overcome the restrictions of the electron microscope, i.e. the lack of large area phase contrast and the limitation of resolution due to the oscillations of the transfer functions for high spatial frequencies. Up to now, the whole process of hologram detection and reconstruction takes a few hours: After a hologram is recorded on photographic plates, it needs development and digitizing. Then a correction of the nonlinear response of the photographic emulsion to electron exposure is indispensable, before the numerical reconstruction procedure can be started.
Microanalysis with a 200keV FEG TEM
Authors: Joy David C
Published: June 2020

Introduction The Hitachi HF-2000 is a 200keV cold field emitter TEM, designed to offer both high resolution imaging performance and a nanometer probe-forming mode for microanalytical operation. The purpose of this paper is to report some initial microanalytical results obtained from the HF-2000 installed at the University of Tennessee.

General Electron-Optical Parameters The cold field emission gun, which runs at about 5x10-9pA pressure, uses an electrostatic lens configuration and a six stage accelerator. The entire electron gun system is under the control of a dedicated microprocessor which permits all of the operational parameters of the gun to be set, monitored, and adjusted through a keyboard and display. The tip emission current can be adjusted up to 40μA, and the gun voltage ratio (that is the ratio between the voltage on the second anode and the tip extraction voltage) can be varied from 4.5 to 7.5, permitting a significant degree of flexibility in optimizing the optics of the emitter.
Sharpening of EELS data by deconvolution
Authors: Batson P.E.
Published: June 2020

The IBM Wien filter spectrometer now delivers 0.1eV resolution with a diode array detector. Figure 1 shows the zero-loss distribution, Z(E), in the IIB501 STEM. Figure 2 shows the Al L2,3 edge obtained at the same time. This report covers a successful application of a suggestion by D. W. Johnson that deconvolution may be possible if Z(E) contains a sharp edge, such as that on the left in Figure 1.

In principle, deconvolution can be done by a simple division of the fourier components of the data D(ω) by Z(ω). In practice, severe amplification of noise results by the naive approach. In this work, I use a modified Wiener filter algorithm:

(1)
Thin-film x-ray quantitation: New insights with the aid of Monte Carlo calculations
Authors: Michael J. R. , Romig A. D. , Goldstein J. I.
Published: June 2020

The determination of chemical composition from a ratio of the characteristic x-ray intensities (ratio technique) measured from thin specimens has become a standard technique in analytical electron microscopy. One of the main assumptions used in this technique is that the normalized distribution of characteristic x-ray intensity with mass depth (ρt), termed φ(ρt), is constant with mass depth and approaches one. If this assumption is violated, the x-ray generation must be calculated as a function of mass depth (i.e., a voltage dependence in the ionization cross section is required and the effect of fast secondary electrons must be included) and the standard absorption equation must be modified (since φ(ρt) is not constant with (ρt)). Φ(ρt) curves have been experimentally determined only for a limited number of elements because of the difficulty of performing the experiment in thin specimens. Monte Carlo electron trajectory simulations are therefore the most tractable way to calculate the depth distribution of x-ray generation.
Improved detection limits with parallel-detection EELS
Authors: Krivanek O.L. , Kundmann M.K.
Published: June 2020

Parallel-detection electron energy-loss spectrometers (PEELS) have improved the detection limits of electron energy-loss spectroscopy (EELS) so much that established comparisons between EELS and energy-dispersive X-ray spectroscopy (EDXS) no longer apply. We have therefore decided to reinvestigate the comparative advantages of EELS as a microanalytical technique.

Two types of detection limits are of interest: minimum detectable mass (MDM), and minimum detectable mass fraction (MMF). MDM has been improved by parallel-detection EELS so much that single atoms of elements with favorable cross-sections have become detectable. Since detecting a single atom requires a probe with at least 0.1 nA of current and a diameter of no more than 1 nm, this level of performance needs an electron microscope equipped with an efficient field-emission gun (FEG). On the other hand, because the ratio of the signal from a uniformly dispersed element to the signal from the matrix does not depend on the size of the probed area, MMF depends on the total available probe current rather than the probe current density. This means that MMF should be better for microscopes equipped with thermionic guns than for ones equipped with FEGs.
Electron microprobe analysis of ream defects in float glass
Authors: Liu D. R. , Park J. S. , Benoit R. E.
Published: June 2020

Ream, or cord, is a compositional inhomogeneity in glass. Its presence in the float glass can cause a vision distortion. Since the thickness of the ream is normally less than 1 mm, and the chemical difference between the ream and the normal glass is small, the electron microprobe seems the only instrument to make an accurate direct chemical analysis on a ream. The analysis was performed on the ream defects appearing in two types of float glass (the samples #1 and #2) with a CAMECA SX-50 probe analyzer. Cross-section samples were cut from the float glass containing reams. A typical ream can be seen under the conventional light or polarized light microscope. Shown in Figs. 1-2 are the reams in the sample #1 and #2. The shape of the two reams are similar, but the contrast of the ream in #1 is weaker.
Microstructures and recording performances of longitudinal media using different atomic mass underlayer materials
Authors: Nguyen Thao A. , Yogi Tadashi , Lambert Steven
Published: June 2020

Magnetic and recording properties of Co-based longitudinal media are strongly influenced by the underlayer and sputtering conditions. We have investigated the relationship between magnetics, recording noise and microstructural characteristics of CoPtCr media on Mo and W underlayers over a sputtering pressure range 3-24 mtorr. complementing our earlier work of Cr underlayer.

The media structure is C/CoPtCr/Mo or W, with thicknesses of 25/25/100 nm respectively. The film structure was sputter-deposited in a DC S-gun magnetron system. The remanence-thickness product, Mft, was kept in the range of 0.6-1.0 10-3 emu/cm2. The films were characterized by a vibrating sample magnetometer for their magnetic properties. Magnetic recording measurements were made with thin film inductive write heads with a track width of about 10 μm at a flying height of about 5 μm. The microstructures were studied using the IEOL JEM 4000 FX and AKASFII 002-B transmission electron microscopes.
Texturescope: An automatic TEM technique for the imaging of preferred orientations
Authors: Weiland H.
Published: June 2020

The distribution of crystallographic orientations, the texture, is one of the basic structural parameters. Knowledge of the texture on a very local scale is necessary to study aspects of processes such as recrystallization and deformation. With an electron microscope, the texture can be determined1 either by measuring the orientations of individual grains or by measuring local pole figures and obtaining in this way the orientation distribution of hundreds of grains. The latter method, however, does not preserve the spatial distribution of the orientations.

The measurement of pole figures in the TEM is based on the same principles used for conventional pole figure determination by X-rays in transmission. The electron microscope has the additional capability that the area of interest can be imaged. For the measurement of local pole figures, the intensity distribution along a selected hkl-diffraction ring is measured, while the specimen is tilted around a specified axis over a large range (e.g. sheet products are usually tilted around the rolling direction). The measured diffracted intensities must be corrected for absorption of the primary and diffracted beams as well as for the change in diffracting volume. Using selected area diffraction, pole figures of specimen areas between 300 μm and 1 μm in diameter can be analyzed quantitatively.
Microscopy of VLSI oxides
Authors: Iwasaki Hiroshi
Published: June 2020

The oxide of silicon and other insulating films form an integral part of every VLSI circuit (e.g. Fig. 1). Thin gate oxide(SiO2) in the thickness range of 10-20 nm (5-10 nm) is needed for submicron (quatermicron) devices. For such devices, characterization of surface roughness at Si/SiO2 interfaces becomes increasingly important because it is expected to affect field-dependent dielectric breakdown (FDDB), time-dependent dielectric breakdown (TDDB) and carrier mobility of MOS FETs more sensitively at necessitated higher operating electric fields. The Si/SiO2 interface is usually considered as the boundary between Si lattice image and granular SiO2 image.

P-type, CZ- Si(001) substrates with resistivity of 10-13 Ωcm were first cleaned by the RCA method and were oxidized in aquartz tube to 16nm thickness: OC2=100% at 900°C for 53 min (dry oxide), O2/H2=1/4 for 11 min (wet oxide). Some MOS structured samples were also studied. Some dry oxide and reoxidized nitrided oxide (ONO) of 7nm thickness were formed by rapid thermal process for electron mobility study.
Structural and compositional mapping at Si-Ge interfaces using Z-contrast STEM
Authors: Jesson D. E. , Pennycook S. J.
Published: June 2020

Z-contrast scanning transmission electron microscopy (STEM) is a new technique capable of producing intuitively interpretable images of crystals and interfaces at atomic resolution. A fine (˜2.2 Å FWHM) electron probe is scanned across the surface of a thin specimen. Simultaneously, transmitted electrons scattered through high angles are collected by an annular detector with a large inner angle. To understand Z-contrast images requires a fundamentally new approach to image interpretation. The high-angle signal we detect is dominated by incoherently generated thermal diffuse scattering which originates very close to the projected atomic sites. This is sensitive to the composition of the column, approaching the atomic number squared or Z2 dependence of unscreened Rutherford scattering. As the probe propagates along a major zone-axis, the beam sharpens up (channels) at the column positions with the incident probe profile as an envelope. Physically, this corresponds to s -type Bloch states of the probe wavefunction adding in-phase over the angular range of the objective aperture which enhances scattering to the high-angle detector.
Characterization of plasma-assisted CVD multilayers/heterostructures
Authors: Burke M.G. , Young R.M. , Freidhoff C.B. , Partlow W.D. , Buhay H.
Published: June 2020

Amorphous refractory materials can be used in a number of optoelectronic applications when fabricated in multilayer structures. When the layers are deposited with very small thicknesses, heterostructures are produced. Such structures have an adjustable optical bandgap because the wavelength of light is much larger than the distance over which the composition of the film varies (layer to layer). Thicker multilayer structures can be fabricated on metallized, high thermal conductivity substrates. The purpose of the structure is to both protect and modify the substrate's properties. Two types of plasma-assisted chemical vapor deposition (PACVD) techniques have been employed to produce these structures.
The use of electron microscopy in chemical vapor deposition of tungsten for VLSI/ULSI applications
Authors: Schmitz J.E.J.
Published: June 2020

Chemical Vapor Deposition of tungsten (CVD-W) is becoming more popular for use as contact fill or interconnect material in high volume production of VLSI/ULSI circuits (see figure 1). The need for contact fill becomes necessary because sputter techniques exhibit certain problems like poor step coverage in deep and narrow contacts (figure 2). Poor step coverage may result in diminished reliability of the circuit. Tungsten technology has been shown to solve many of these problems. In the development of CVD-W technology, electron microscopy proved to be a unique tool contributing substantially to the development of CVD-W. This paper will give an overview of how electron microscopy can and is used in CVD-W IC metallization issues.
Device failure analysis: A perspective for the 1990s
Authors: Anderson Ron
Published: June 2020

Historically, analytical TEM and SEM analysis capability has lagged behind the capability to conduct electrical diagnostics on electronic devices. The problem is one of spatial resolution. It isn't a case of TEM and SEM specimen preparation methods not keeping pace with the rapid and steady decrease in dimensions of modern device structures—in reality, the industry as a whole has not been able to do single-device failure analysis, much less keep pace with shrinking dimensions. The ability to prepare failure analysis specimens of pre-specified individual devices, or small portions of individual devices, has been demonstrated in a very few laboratories only recently. Uncharitably, there has been no pause in diminishing device dimensions. Researchers are now faced with the horrific prospect of the size of the most-meaningful structures in their specimens shrinking well below the one micron spatial resolution of routine light microscopy—just as people are learning how to make specimens of small pre-defined areas.
A superior cathodoluminescence spectral analysis and imaging system for semiconductor characterisation
Authors: Wright P J
Published: June 2020

Cathodoluminescence is a useful technique in the structural and electro optical characterisation of semiconductors. When performed in a electron microscope, both high spatial resolution images and spectra may be obtained by use of the correct equipment.

Many designs for instruments suitable for cathodoluminescence spectral analysis and imaging in electron microscopes have been described in the literature during the past 25 years. These have often exhibited improved performance when compared with commercially available systems. The prime reason for this has been the willingness of the dedicated CL researcher to mount large, heavy monochromators directly to the chamber of their microscope. The result has been a microscope committed to CL analysis. However, many potential CL users have to use shared facilities and may not compromise the performance or appearance of the microscope. Subsequently, many CL systems have had the monochromator decoupled from the CL collection optics by either fibre optic bundles or quartz fibres. This has allowed the monochromator and its associated detectors to be easily decoupled from the SEM when not in use. Considerable transmission losses have been incurred and in many cases, it has been necessary to duplicate detectors to allow both spectral analysis and imaging. This has resulted in instruments which were less than optimum in both efficiency and operation.
A study of GaAs/Sc0.3Er0.7As/GaAs heterostructures grown on novel GaAs substrate orientations
Authors: Zhu Jane G. , Palmstrøm Chris J. , Carter C. Barry
Published: June 2020

Compound metallic materials, such as rare-earth (RE) monopnictides, are thermally stable and have lattice constants close to those of III-V semiconductors. These materials have been studied in the recent a few years. Epitactic ErAs, ScxEr1-xAs, ErPxSb1-x, and ErP0.6As0.4 (ref. 6) have been grown on GaAs by molecular beam epitaxy (MBE). By mixing rare-earth elements or group V elements, or both, rare-earth pnictides can be lattice-matched to almost all group IV, III-V and II-VI semiconductors. Lattice-matched growth of ScxEr1-x As/GaAs, for example, can be obtained using the composition x=0.32. It has been demonstrated that the rare-earth arsenides can be grown on (100) GaAs in a layer-by-layer mode with very good crystal quality, but the GaAs grown on the rare-earth arsenides has far inferior quality to meet the requirement of novel devices. Island growth of GaAs on RE As/GaAs has been reported.
Electron microscopy of GaAs grown on Si- and Ge-based substrates
Authors: Malta D.P. , Posthill J.B. , Timmons M.L. , Sharps P.R. , Venkatasubramanian R. , Markunas R.J.
Published: June 2020

A GaAs-on-Si technology is desirable to take advantage of the mobility and direct bandgap of GaAs in combination with the crystalline quality, low cost and established technology of Si. Differences in lattice constant (4.1%), thermal expansion coefficient (a factor of ~ 3), and bonding polarity between the two materials can lead to problems such as: threading dislocation formation, thermally induced stress and delamination, and antiphase domain boundaries (APBs), respectively. The lattice mismatch is responsible for the formation of (necessary) misfit dislocations which can concurrently create threading dislocations with typical densities in the range of 106 - 108cm-2. This density of electrically active defects in a device region is highly undesirable.

A proposed scheme for lattice mismatch accommodation and potential threading dislocation reduction has previously been reported in which each layer of a SixGe1-x multilayer structure (MLS) is grown beyond the critical thickness with a progressively higher Ge composition than the previous layer.
Phase segregation in GaAs layers grown at low temperature
Authors: Liliental Zuzanna , Kilaas Roar
Published: June 2020

GaAs device and circuit performance may be impaired by substrate conduction. One such effect, called sidegating, leads to undesirable cross-talk between neighboring devices. This problem can be avoided by isolating the active device layer from the substrate with a GaAs buffer layer grown by molecular beam epitaxy (MBE) at low temperatures (LT GaAs). The LT GaAs layers show high resistivity, a large trap density, and breakdown strengths about ten times that of semi-insulating GaAs. These layers are grown at a substrate temperature of ~ 200°C. A large (~1 at.%) excess of As in these as-grown layers causes an increase (~0.1%) in the GaAs lattice parameter.

The crystal structure of these layers is very sensitive to the growth parameters such as: growth temperature, As/Ga flux ratio and growth rate. With decreasing growth temperature a higher As concentration can be incorporated and only a smaller layer thickness of high crystal perfection can be grown.
Microstructure of silicon-on-insulator material produced by multiple oxygen implantation and annealing
Authors: Seraphin Supapan , Cordts Bernhard F.
Published: June 2020

Implantation of oxygen into silicon at a high dose forms a silicon-on-insulator structure that shows promise for the manufacture of circuits in the submicron region. However, the advantages of the SIMOX (Separation by Implanted Oxygen) structure over bulk silicon can only be realized if the top silicon layer is of device quality. In previous studies, SIMOX materials typically contained defect densities as high as 109 cm-2. The last four years have seen considerable progress along the lines of improving the quality of the top layer by a variety of methods. The approach used in this study replaces a single high-dose implantation by multiple cycles of medium-dose implantations followed by anneal steps. The process results in defect densities as low as 103 to 105 cm-2. We are presenting the structural analysis of SIMOX material produced by three subsequent cycles of implantation and anneal. The sample was examined by TEM after each step of the implantation/anneal sequence. Optimizing the process parameters on the basis of the TEM analysis resulted in the identification of defects, and a reduction of their density. The structural evolution of defects throughout the processing steps will be described.
Analysis of 2D and 3D defects associated with precipitation of Cu in silicon
Authors: Rice P.M. , Kim MJ. , Carpenter R.W.
Published: June 2020

Extrinsic gettering of Cu on near-surface dislocations in Si has been the topic of recent investigation. It was shown that the Cu precipitated hetergeneously on dislocations as Cu silicide along with voids, and also with a secondary planar precipitate of unknown composition. Here we report the results of investigations of the sense of the strain fields about the large (~100 nm) silicide precipitates, and further analysis of the small (~10-20 nm) planar precipitates.

Numerous dark field images were analyzed in accordance with Ashby and Brown's criteria for determining the sense of the strain fields about precipitates. While the situation is complicated by the presence of dislocations and secondary precipitates, micrographs like those shown in Fig. 1(a) and 1(b) tend to show anomalously wide strain fields with the dark side on the side of negative g, indicating the strain fields about the silicide precipitates are vacancy in nature. This is in conflict with information reported on the η'' phase (the Cu silicide phase presumed to precipitate within the bulk) whose interstitial strain field is considered responsible for the interstitial Si atoms which cause the bounding dislocation to expand during star colony growth.