bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of epitaxial diamond on natural diamond substrates by cathodoluminescence
Authors: Malta D.P. , Fitzgerald E.A. , Posthill J.B. , Rudder R.A. , Hudson G.C. , Markunas R.J.
Published: June 2020

A large effort continues in the development of diamond growth technologies for the production of electronic-grade diamond epitaxy. Diamond has several properties such as a wide band gap (5.48 eV) and high thermal conductivity (2000 W m-1K-1) that make it desirable for electronic applications. Characterization of diamond with cathodoluminescence (CL) spectroscopy yields information on impurity and defect distributions with both spatial and energy resolution, providing insight into the growth process.

Diamond films were grown by plasma-enhanced chemical vapor deposition (PECVD) on natural type Ia 1mm × 1mm × 0.25mm diamond substrates. The results of microstructural studies on this type substrate are discussed elsewhere in these proceedings. Two films were selected for CL analysis based on their strikingly different surface morphologies but similar growth conditions. Both were grown for 6 hours at a substrate temperature of ∽ 750°C and a pressure of 5 Torr. The gas mixtures were varied: CO/CH4/H2 was used in one case and CH4/H2 in the other.
An electron microscopy study of high-thermal-conductivity ribbon-shape carbon fibers
Authors: Robinson Kerry E.
Published: June 2020

In an effort to develop a low-cost high thermal conductivity carbon fiber, ribbon-shaped fibers were meltspun from a liquid crystalline, mesophase pitch precursor. Initial tests indicated that the ribbon-shaped fibers could be processed more easily and exhibited improved thermal conductivities when compared to commercial round fibers. Evidently, it is the more linear, polycrystalline structure within these fibers that accounts for their improved thermal conductivities. Thus, studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to fully analyze the transverse and longitudinal structure of these high thermal conductivity fibers.

Ribbon-shaped fibers, melt-spun from a synthetic mesophase pitch and then heat treated, were tested to determine their tensile strengths, tensile moduli and thermal conductivities. A Jeol JSM-I C848 SEM at an accelerating voltage of 20 kV was used to obtain general structural information, such as extent and texture of lamellar organization of the graphitic layers within the fibers, and the microstructure of the fibers was studied by TEM.
An inexpensive, easy to use video imaging system for intracellular Ca2+ and quantitative fluorescence microscopy
Authors: Gruenstein Eric , Luna Jesus
Published: June 2020

Fura-2 is the most commonly used member of a family of calcium sensitive flourescent dyes that allows the measurement of intracellular free calcium (Cai by dual excitation fluorimetry. The use of this dye in conjunction with video imaging microscopy permits visualization of changes in Cai with a high degree of spatial resolution. This resolution in turn allows the detection of Cai gradients, waves, and other localized cellular responses not easily detected by photometric techniques. Despite these advantages, most published reports have utilized photometry rather than imaging, due largely to the higher cost and greater complexity of use of the latter technique. With these problems in mind, we have developed a turnkey calcium imaging system that is both inexpensive and simple enough to use that it can be mastered in 2-3 hours.

Data showing the distribution of free Ca2+ in the cytoplasm of a quiescent human fibroblast and the kinetics of stimulation of these cells with mitogens are illustrated on the next page.
Electron beam damage of Ni3Al
Authors: Muller David A. , Silcox John
Published: June 2020

In recent years, the effect of radiation induced sputtering in electron microscopy at voltages as low as 100 kV has been identified and has emerged as a significant factor in microanalysis. The inhibiting effect of some surface layers has also been noted. More generally, the use of focused electron probes (as in STEM) as a tool for materials modification on the nanoscale has also been developed. We report here observations of electron radiation effects in Ni3Al, a proto-typical high temperature, high strength intermetallic of some considerable interest. This work is comparable to the study of electron radiation damage in aluminium reported by Bullough et.al.

Fig. 1 illustrates the formation of holes in a Ni3Al specimen and the associated nickel rich patches formed after irradiation at 100kV in the Cornell UHV HB501A STEM in spot mode with an estimated 10Å FWHM beam size at a beam current of 0.12 nA for a period of 20 minutes. The somewhat dramatic radiation damage is readily seen.
A field-emission SEM optimized for operation at low beam voltage
Authors: Pawley JB , Ximen J , Lin PS-D , Schippert M.
Published: June 2020

The advantages of operating the SEM at low beam voltage (V0 ) have been recognized for some time. They include: less specimen charging, greater contrast in the fine topographic component of the secondary electron (SE) signal and reduced radiation damage. Although initially it was difficult to obtain high resolution images when using low V0, this limitation can be essentially overcome by employing both a FE source and an immersion objective lens. In an instrument employing both of these features it is possible to produce a beam diameter of about 3 nm @ 1.5 kV. When insulating specimens are viewed under these conditions, the resolution in the image is limited more by the structure of the coating material than by the beam diameter, while on conductors, small structural features produce useful contrast only at low V0.

The remaining obstacle to more widespread use of LVSEM for high resolution topographic imaging is the high cost of the equipment.
Applications of virtual objective aperture in TEM
Authors: Fan G.Y. , Deerinck T. , Ahn C.C. , Price J. , Young S.J. , Ellisman M.H.
Published: June 2020

In a special imaging mode (B mode) available on a customized JEM-4000EX microscope, the objective mini lens (OM) is strongly excited so that the back focal plane of the objective lens (OL) is imaged onto the plane of the selected-area aperture (SA), Fig. 1, with a magnification of 3.2x. Thus the S A functions as a virtual objective aperture, the applications of which are summarized below.

1. Improving contrast in imaging thick sections of biological specimens.

The increased inelastic scattering in thick specimens results in image blur due to chromatic aberration present in the magnetic lenses. Such blur degrades image resolution and contrast. The energy loss spectrum in Fig. 2 (curve 1), from a 1 μm section of frog spinal ganglion, suggests that the inelastic contribution to images of this type of specimen is substantial. The use of an objective aperture (OA) can reduce some of the unwanted contributions (curve 2), but the SA in B mode is much more effective, as suggested by Fig. 1 and demonstrated by curved 3.
Second-generation scanning photoemission microscope at the National Synchrotron Light Source
Authors: Ko Cheng-Hao , Kirz Janos , Ade Harald , Johnson Erik , Hulbert Steven , Anderson Erik , Kern Dieter
Published: June 2020

We are commissioning a new generation scanning photoemission microscope (X1-SPEM II) at beamline X1A of the National Synchrotron Light Source (NSLS). Our first generation scanning photoemission microscope (X1-SPEM I) was the first to achieve submicron resolution. One of the major improvements is the replacement of the home-made single pass cylindrical mirror analyzer with a high energy resolution, multi-channel Hemispherical Sector Analyzer (HSA). The alignment scheme for the optical elements has also been redesigned. The advantages of these two major improvements will be discussed.

A photoemission microscope requires a high brightness source and a good focusing scheme. In most cases, a monochromator is placed between the photon source and the focusing optical elements. Our X1-SPEM uses the soft x-ray undulator at the NSLS as a high brightness source. A Fresnel zone plate is coherently illuminated by the monochromatic beam selected by the spherical grating monochromator (250-800 eV range) to form a microprobe, less then 0.2 μm in size.
3D microanalysis of tissue volumes using dual-energy conebeam x-ray microtomography
Authors: Johnson Roger H.
Published: June 2020

Using a modified SEM as a microfocus x-ray source and stimulable phosphor plates as detectors, we have built a conebeam microtomograph for 3D imaging of 1-10mm biological samples (Figure l). For individual projections, the resolution and exposure time are about three microns and two minutes, respectively, with the same parameters in the reconstruction depending on the number of views.

In conventional computed tomography (CT) each detector element integrates the energy incident upon it from all transmitted photons regardless of their wavelength. All spectral information is lost. It can be beneficial to acquire two sets of projections: one using a higher peak x-ray source energy than the other. Figure 2 illustrates that tissue and bone will attenuate the two spectra differentially producing different contrast relationships in the high- and low-energy images. We have previously clinically applied post-processing dual-energy CT to analyze the mineral and fat content of lumbar vertebrae in perimenopausal, osteoporotic women.
Accurate methods for crystal structure determination using aspects of dynamical diffraction theory
Authors: Steeds J W , Vincent R
Published: June 2020

An approach to the solution of crystal structures has been developed over the past ten years which is based on the intensities of high order Laue zone (HOLZ) fine structure lines present in zone axis patterns. It is a common observation that when the individual reflections in a HOLZ ring are studied in detail, several individual excess lines are observed. These individual lines are directly related to the excited branches of the dispersion surface, created by the two dimensional dynamical diffraction which occurs in the zero order Laue zone (ZOLZ). They may either directly correspond to a single branch of the dispersion surface (a unique Bloch state) or else to a cluster of close branches (a small number of distinct Bloch states). It is often the case that the intensities of these lines may be derived from a pseudo-kinematical theory, which greatly simplifies the process of deducing atomic positions from the experimental data.
Improvements in electron diffraction of frozen hydrated crystals by energy filtering and large-area single-electron detection
Authors: Schröder Rasmus R. , Burmester Christoph
Published: June 2020

Diffraction patterns of 3D protein crystals embedded in vitrious ice are critical to record. Inelastically scattered electrons almost completely superimpose the diffraction pattern of crystals if the thickness of the crystal is higher than the mean free path of electrons in the specimen. Figure 1 shows such an example of an unfiltered electron diffraction pattern from a frozen hydrated 3D catalase crystal. However, for thin 2D crystals electron diffraction has been the state of the art method to determine the Fourier amplitudes for reconstructions to atomic level, and in one case the possibility of obtaining Fourier phases from diffraction patterns has been studied. One of the main problems could be the background in the diffraction pattern due to inelastic scattering and the recording characteristics for electrons of conventional negative material.

It was pointed out before, that the use of an energy filtered TEM (EFTEM) and of the Image Plate as a large area electron detector gives considerable improvement for detection of diffraction patterns.
Structure factor refinement by least-squares inversion of 2D convergent-beam patterns
Authors: Marthinsen K. , Holmestad R. , Høier R.
Published: June 2020

While electron microscopy and diffraction for decades mainly have been a qualitative tool, there has been an increasing trend over the last years for more quantitative work. This trend applies in particular to convergent beam electron diffraction (CBED) where different methods for the retrieval of quantitative structure information from CBED intensities have been proposed. In our group we have aimed at developing a general and automatic method based on the strong parameter dependencies that govern the complicated two-dimensional (2-D) intensity variations in the CBED-disks particularly in the nonsystematic many-beam case. The method is based on least squares fitting between digitized experimental and computed patterns. The advantage of this method as compared with alternative methods is many turning points in the intensity variations, which should give a high parameter sensitivity, and the fact that non-systematic many-beam effects are particularly sensitive to structure factor phases, which should make the method especially suitable to non-centric crystals.
Thickness measurement of glucose-embedded crotoxin complex crystals by EELS
Authors: Leapman R.D. , Brink J. , Chiu W.
Published: June 2020

In three-dimensional structure determination of macromolccules by electron crystallography it is necessary to combine diffraction patterns and images recorded at various tilt angles from different crystals. In order to merge these data sets successfully all the crystals should have the same thickness. It has been proposed that parallel electron energy loss spectroscopy (EELS) might provide a useful means of assessing the thickness of a beam-sensitive organic crystal prior to recording the high-resolution structural data. This can be achieved by measuring the fraction of the total transmitted electrons that do not lose energy, i.e., the zero-loss intensity. If Izis the integrated zero-loss intensity and Itotis the total integrated intensity in the energy loss spectrum, then the specimen thickness, t, is given in terms of the total inelastic mean free path, λi, by, t/λi= ln(Itot/Iz). Results recently obtained fromn-paraffin crystals have shown that it is feasible to determine the number of unit cell layers under low electron dose conditions.
Chemically assisted ion-beam etching in a low-angle ion mill
Authors: Alani R. , Swann P.R.
Published: June 2020

In conventional ion mills, chemically assisted ion beam etching (CAIBE) has become an establish method for TEM specimen preparation of certain materials. CAIBE employs a reactive gas which brought in contact with the specimen through a jet assembly, while an inert gas ion beam is directed on the same area. Therefore, thinning occurs by the combination of chemical reaction and physic sputtering, which leads to enhanced thinning rates. The reactive gas used in the CAIBE technique can generated from a solid source which sublimes e.g. iodine or it can be injected directly from a pressuriz gas bottle e.g. nitrous oxide. Nitrous oxide in combination with a xenon ion beam has been used from cross sectioning TEM specimens of diamond films on silicon.

It is well known that indium-containing compound semiconductors develop indium islands on the surface when thinned with an argon ion beam. It is believed that preferential sputtering enriches the surface with indium and that heating by the ion beam melts the indium which then agglomerates to for small globules on the surface.
Transmission electron microscopy studies of boron nitride thin films produced by pulsed laser deposition
Authors: Medlin D.L. , Friedmann T.A. , Mirkarimi P. B. , McCarty K.F. , Mills M.J.
Published: June 2020

We are synthesizing boron nitride films by pulsed laser ablation in order to study the deposition conditions necessary to produce the cubic phase (cBN) which has a number of useful applications as a hard coating, semiconductor, and optical material. The yield of cubic material is controlled in part by the simultaneous irradiation of the growing film with a low energy beam of N2 and Arions. In order to understand how this transformation process occurs, we are using TEM to investigate how the microstructure and phase distribution varies with film deposition conditions.

In many ways analogous to carbon, boron nitride forms both sp3- and sp2-bonded phases. The cubic phase (cBN), which is sp3 bonded, has the zinc blende structure, and in addition, BN can also form an sp3 bonded hexagonal phase with the wurtzite structure (wBN). An sp2-bonded hexagonal structure (hBN) is the stable room temperature phase, but like its analog, graphite, the sp2-bonded material can also exist in a highly disordered state, often referred to as turbostratic (tBN).
HREM image simulations for supported metal particle catalysts
Authors: Yao Ming-Hui , Smith David J.
Published: June 2020

The chemical properties of catalysts often depend on the size, shape and structure of the supported metal particles. To characterize these morphological features and relate them to catalysis is one of the main objectives for HREM study of catalysts. However, in plan view imaging, details of the shape and structure of ultra-fine supported particles (<2nm) are often obscured by the overlapping contrast from the support, and supported sub-nanometer particles are sometimes even invisible. Image simulations may help in the interpretation at HREM images of supported particles in particular to extract useful information about the size, shape and structure of the particles. It should also be a useful tool for evaluating the imaging conditions in terms of visibility of supported particles. P. L. Gai et al have studied contrast from metal particles supported on amorphous material using multislice simulations. In order to better understand the influence of a crystalline support on the visibility and apparent morphological features of supported fine particles, we have calculated images of Pt and Re particles supported on TiO2(rutile) in both plan view and profile view.
Automated particle analysis in Electron Microscopy
Authors: Vander Wood Tim B.
Published: June 2020

The ability to quickly and economically characterize particle samples is increasingly important. A knowledge of particle size distributions can be critical in a wide variety of processes, from powder metallurgy to ethical drug delivery. Powdered materials may be contaminated at levels of only one particle in one thousand and still be unsuitable for use. Particulate samples may represent a variety of materials from many sources, requiring complex analyses for complete characterization. The traditional analytical approach to these problems, dictated by the need for economy, has been the application of batch techniques (e.g. light scattering) to the problem of particle sizing and trace component and bulk techniques (e.g. atomic absorption, x-ray fluorescence) to the problems of particle analysis. Scanning electron microscopy (SEM), combined with energy-dispersive x-ray spectrometry (EDS), is capable of directly measuring the required individual particle sizes, morphologies and compositions but has not been widely applied due to the high cost of analysis of several hundred to thousands of particles which may be required to adequately represent an entire population.
Origins of fine particles in a power-plant plume as determined using individual-particle analysis
Authors: Katrinak Karen A. , Hurley John P.
Published: June 2020

Individual particles from the fine fraction of samples of entrained ash from a coal-burning power plant were analyzed using an automated scanning electron microscope with an energydispersive x-ray spectrometer. The particles were of concern as a probable cause of high levels of opacity in the plant emissions. Both the mass loading and the number size distribution of fine particles peak in the size range of 0.4 to 0.8 μm diameter.

Most of the fine particles are Na-, S-, P-, or Cl-rich. The coal is likely to be the major source for these particles. Minerals and organically-associated metals in the coal can remain in the solid phase during combustion, forming ash particles of varied sizes, including those in the submicron range. Elements are also vaporized during combustion, and Na- and S-bearing particles may form when gas-phase Na2SO4 condenses homogeneously in the convective pass of the boiler. Phosphate and chloride particles may also condense homogeneously.
Structural phenomena in the growth of carbon nanotubes
Authors: Jiao Jun
Published: June 2020

HREM studies of the carbonaceous material deposited on the cathode of a Huffman-Krätschmer arc reactor have shown a rich variety of multiple-walled nano-clusters of different shapes and forms. The preparation of the samples, as well as the variety of cluster shapes, including triangular, rhombohedral and pentagonal projections, are described elsewhere.

The close registry imposed on the nanotubes, focuses attention on the cluster growth mechanism. The strict parallelism in the graphitic separation of the tube walls is maintained through changes of form and size, often leading to 180° turns, and accommodating neighboring clusters and defects. Iijima et. al. have proposed a growth scheme in terms of pentagonal and heptagonal defects and their combinations in a hexagonal graphitic matrix, the first bending the surface inward, and the second outward. We report here HREM observations that support Iijima’s suggestions, and add some new features that refine the interpretation of the growth mechanism. The structural elements of our observations are briefly summarized in the following four micrographs, taken in a Hitachi H-8100 TEM operating at an accelerating voltage of 200 kV and with a point-to-point resolution of 0.20 nm.
The origins of high-resolution secondary-electron microscopy
Authors: Scheinfein M.R. , Drucker J.S. , Weiss J.K.
Published: June 2020

The production or generation of SE by focused, fast electron beams is a multistage process which includes excitation of target electrons by the energetic incident beam, subsequent decay yielding hot SE, transport to the surface, and transmission over the surface potential barrier. The ultimate spatial resolution of a SE image formed by scanning a well focussed probe across a surface is limited by the excitation events' spatial derealization through the transverse momentum transferred to the specimen.

The accepted model for SE production is not well characterized since it is extremely difficult to separate experimentally the generation, transport and transmission processes during a given SE creation event. Here, we examine the SE generation pathway by correlating SE of a given energy produced by an initial inelastic excitation using time coincidence detection. This technique can be used, for example, to isolate the role of plasmon decay in the SE generation process. The experiments were performed in a Vacuum Generators HB501-S UHV scanning transmission electron microscope (STEM), operating at base pressures of 5 × 10−11 torr.
Explanation of the high resolution backscattered electron image in the scanning electron microscope by the twin-population theory historical review
Authors: Wells Oliver C.
Published: June 2020

Several different “twin-population” theories have been proposed to explain the high resolution backscattered electron (BSE) image in the scanning electron microscope (SEM). In all of these, the BSE are divided into local BSE that give an image having a resolution that is significantly better than the electron penetration depth R and diffused BSE that give a less sharp image. Other theories attach more importance to the diffused BSE.

The BSE image was originally proposed by von Ardenne in 1940 with the specimen at right angles to the incident electron beam (Fig. 1). This has been summarised by McMullan. Von Ardenne predicted high resolution secondary electron (SE) imaging by local SE (now called SE-I) and pointed out the advantages of low voltage operation, but failed to realise that there was a high resolution BSE signal also. McMullan distinguished between the BSE image as defined above (Fig. 2(b)) where the principal contrast mechanism is compositional and the reflected electron image in which the sample is tilted by typically 45° and forward-scattered BSE are collected (Fig. 2(a)).
The application of Transmission Electron Microscope to semiconductor device problems
Authors: Cunningham Brian , Daniel Mis J.
Published: June 2020

In the last 5-10 years there has been a large increase in the application of TEM to semiconductor device problems. This increase is due to several factors. Higher density chips and decreasing device dimensions have led to structural components which are frequently in the nanometer range. The ease with which present day microscopes can measure nanometer dimensions along with the advances in specimen preparation techniques now make the TEM invaluable as a tool for routine constructional analysis. As device dimensions shrink, the structure and composition of thin interfacial layers becomes increasingly important to device performance. In fact, in some cases, such as the emitter polysilicon to single crystal interface in bipolar transistors, the interface can dominate device parametrics such as current gain and emitter resistance. The ability to examine these interfaces in actual devices is therefore extremely important, and TEM is again proving to be uniquely suited to this task.
A TEM study of low-temperature Ge growth on Ge(001)2×1
Authors: Xiao H.Z. , Xue G. , Robertson I.M. , Birnbaum H.K. , Greene J.E.
Published: June 2020

One approach to a solution of the doping problem in the molecular beam epitaxy (MBE) growth of the group IV semiconductors, e.g., segregation, low incorporation, and control of the dopants, is to lower the growth temperatures. It has been found that the room temperature Si deposition becomes amorphous after growth of a limiting epitaxial thickness which increases rapidly with the growth temperature. However, the mechanism for this structural transition is not well understood. In the present paper, we report the preliminary results of a study on the mechanism of the low temperature MBE growth of Ge on Ge(001)2×1 over the temperature range of 20-100 °C at deposition rates R=0.05 and 0.1 nm s−1 in an MBE system which has a bass pressure of 5xl0−11 Torr which increases to about 2xl0−9 Torr during deposition. The structural transitions were investigated using a combination of in-situ reflection high-energy electron diffraction (RHEED) and post-deposition high resolution cross-sectional transmission electron microscopy (XTEM).
A study of ordered domains in Ga0.5In0.5P Grown by MOVPE
Authors: Zhu Jane G. , Friedman D. J. , Al-Jassim M. M. , Olson J. M.
Published: June 2020

Atomic ordering in III-V alloys is known to influence the physical properties of these materials. Therefore, the understanding and the control of the formation of ordered alloys are very important. Ordering in Ga0.5In0.5P, which is lattice matched to GaAs, occurs on two out of four {111} planes, i.e., . The substrate orientation can affect the selection between the two ordered variants. Studies on atomic ordering in III-V alloys have been carried out during the past several years.

Transmission electron microscopy (TEM) and selected-area diffraction have been used in this study to investigate the ordered domains in Ga0.5In0.5P layers. The samples were grown on misoriented (100) GaAs substrates, mostly 2° towards [001] unless otherwise specified, by metalorganic vapor phase epitaxy at 670°C with a growth rate ∼5 μm/hr. The layer thicknesses range from 1.5 to 12 μm. Plan-view specimens were prepared by chemical etching from the substrate sides and examined using a Philips CM30 microscope operated at 300 kV.
In situ HREM of interface interactions
Authors: Sinclair Robert , Konno Toyohiko J.
Published: June 2020

We have applied in situ high-resolution electron microscopy (HREM) to the study of interface reactions, particularly in metal-semiconductor systems. There is contrasting behavior whether or not the manufactured interface undergoes a chemical reaction. The in situ technique allows determination of the reaction mechanisms on an atomic scale.

Reactive interfaces are characterized by systems in which new chemical compounds are formed (e.g., silicides for metal-silicon interfaces, metal gallides and arsenides for GaAs, etc.). We found that the equilibrium phase formation is often preceded by a solid-state amorphization reaction. In situ observations allow very precise measurement of the reaction rate in a sufficient temperature range to confirm that this process is diffusion controlled. Crystallization of the amorphous material can be followed as well as the development of any crystallographic orientation relationships. A ledge growth mechanism can easily be distinguished from a random process.

It might be expected that non-reactive interfaces are stable upon heating.
HREM and AEM study of Pt/SiC interface annealed at high temperature
Authors: Bow J.S. , Porter L.M. , Kim M.J. , Carpenter R.W. , Davis R.F.
Published: June 2020

High temperature applications of SiC semiconductor devices will be essentially limited by the metal/SiC interface interconnect properties. Pt/SiC was reported to have more stable and better electrical properties than other metal/6H-SiC after annealing above 700°C under UHV condition. Some work on the Pt/SiC interface has been conducted by AES and other low spatial resolution surface techniques, but there is no detailed direct image data reported. Here, we characterize the microstructure of the Pt/SiC interface after high temperature annealing in UHV at near atomic resolution and reported the first nanospectroscopic energy loss data for the system.

As-deposited Pt film is polycrystalline with grain size of 10 ± 3 nm (Fig.l). The thin amorphous layer visible at the interface in Fig.l, gradually disappearing in the thick regions, was attributed to oxygen-induced ion-milling damage. Similar results were observed frequently in other metal/ceramic system. We consider the amorphous layer to be due to residual oxygen on the ceramic surface during synthesis, since trace oxygen was only detected at the as-deposited Pt/6H-SiC interface.
Thin-specimen preparation for heterophase interfaces
Authors: Lyman C. E. , Anderson R. , Malis T.
Published: June 2020

Imaging and analysis of heterophase interfaces in cross-sectional view requires demanding thin specimen preparation techniques. The term heterophase refers to the juxtaposition of a heavy and a light element or a metal and an insulator on either side of the interface. No single thinning method can be recommended for all such interfaces in all materials. In fact, the desired information might, of necessity, only be obtained by the use of several methods. This paper provides an overview of three different thinning methods for heterophase interfaces: conventional ion-beam thinning (IBT), tripod polishing (TP), and ultramicrotomy (UM).

The ideal thin specimen of a heterophase interface is rarely achieved. Regardless of the final thinning method, the information obtainable often depends on the mechanical alignment of the interface prior to final thinning. Typical alignment parameters are: 1) angle between interface and specimen surface, 2) crystallographic orientation about the normal to the interface, and 3) lateral location of thinned area along interface.
Nucleation and initial growth of Pd2Si crystals on Si(111)
Authors: Tong Xianghong , Pohland Oliver , Murray Gibson J.
Published: June 2020

The nucleation and initial stage of Pd2Si crystals on Si(111) surface is studied in situ using an Ultra-High Vacuum (UHV) Transmission Electron Microscope (TEM). A modified JEOL 200CX TEM is used for the study. The Si(111) sample is prepared by chemical thinning and is cleaned inside the UHV chamber with base pressure of 1x10−9 τ. A Pd film of 20 Å thick is deposited on to the Si(111) sample in situ using a built-in mini evaporator. This room temperature deposited Pd film is thermally annealed subsequently to form Pd2Si crystals. Surface sensitive dark field imaging is used for the study to reveal the effect of surface and interface steps.

The initial growth of the Pd2Si has three stages: nucleation, growth of the nuclei and coalescence of the nuclei. Our experiments shows that the nucleation of the Pd2Si crystal occurs randomly and almost instantaneously on the terraces upon thermal annealing or electron irradiation.
Orientation relationship between Γ phase and α–Fe in commercial galvanneal steel coating
Authors: Lin C. S.
Published: June 2020

The steel coatings' forming technology and their resulting mechanical performance are of primary concern to the automobile and appliance industries, for they determine directly the long-term structural integrity of the final products. In automobile industry, steel coating plays a crucial role for extended warranty of their product. The recent trend in coatings is an increase in galvannealed coatings.

The iron-zinc compound coatings produced by galvannealing bring about a dramatic improvement, in terms of coating performance, compared to pure zinc coatings. The improvement includes corrosion resistance, weldability and paintability in addition to energy and material efficiency. However, there is still one serious obstacle which prevents the industry-wide use of galvannealing as the dominant steel coating technology: Its powdering and flaking tendency during press forming processes. There are a number of empirical hypotheses which propose that the presence of various Fe-Zn intermetallic phases influences the powdering/flaking tendency of galvannealed coatings. Nevertheless, not enough microstructural information is available except those obtained by SEM and X-ray diffraction.
The application of high-resolution SEM and EPMA to the study of coatings and interfaces of materials
Authors: Goldstein Joseph I.
Published: June 2020

Microchemical and micro-structural analysis are often required when characterizing coatings and interfaces in materials. For coatings the interface between substrate and coating and between coating and the surface are of particular interest. The scanning electron microscope (SEM) and electron probe microanalyzer (EPMA) are often employed in characterizing interfaces in materials particularly because solid samples can be studied and sample preparation is usually restricted to developing a suitable flat polished surface for analysis. Both these instruments are essentially the same although the EPMA is equipped with wavelength dispersive detectors (WDS) and is dedicated to quantitative microchemical analysis.

The spatial resolution for high resolution SEM where microstructural analysis of the surface is desired is now in many ways comparable to the transmission electron microscope (TEM). Magnifications of over 100,000 X are available in SEMs equipped with a field emission gun using the secondary electron mode. Figure 1 shows the interface region of a retained austenite region in the Tazewell iron meteorite shown in both TEM and SEM mode and Figure 2 shows the morphology of crystals, 0.3 μm wide by 1.5 μm long containing ledges 30-50 nm wide in an electrodeposited Zn coating on a steel in both TEM and SEM mode.
Electron microscopy of pulsed-laser-deposited thin films for tribological applications
Authors: Walck Scott D. , Zabinski Jeffrey S. , Donley Michael S.
Published: June 2020

Pulsed laser deposition (PLD) is a novel thin film deposition technique which has recently been applied to tribological materials with great success. PLD has several inherent advantages over conventional deposition techniques, including excellent film adhesion, replication of target chemistry, and low film deposition temperature. Because load-bearing materials are typically hardened, heat treated alloys, these properties of PLD are ideally suited for tribological applications. In addition to being a relatively simple deposition technique, considerable processing flexibility is inherent with PLD. Dense, nonporous, stoichiometric films of solid lubricants, such as MoS2, have been grown having long wear lives with low coefficients of friction. Hard coating materials, such as TiC, have been grown at room temperature that were polycrystalline and had excellent wear properties.

A significant feature of pulsed laser deposited (PLD) thin films is the incorporation of spherical particles within the films. Figure 1 shows these particles embedded in a film of PLD MoS2 deposited at room temperature.
Intergranular segregation in pressure-vessel steels
Authors: Burke M.G. , Kenik E.A.
Published: June 2020

The degradation of low alloy pressure vessel steels in the presence of neutron irradiation is of fundamental importance in the nuclear industry. Numerous studies have been performed to evaluate the irradiation-induced changes in mechanical properties, and to a lesser extent, the changes in microstructure, of these pressure vessel materials. Irradiation results in an increase in the ductile to brittle transition temperature and a decrease in the upper shelf energy of the steels. The exact contribution of intergranular segregation to the concomitant degradation in mechanical properties is, however, unclear. To understand the microstructural changes caused by neutron irradiation and to clarify this contribution, it is important to fully characterize the material prior to irradiation. In this initial investigation, the techniques of analytical electron microscopy (AEM), high spatial resolution field emission gun scanning transmission electron microscopy (FEG-STEM) and energy dispersive x-ray spectroscopy (EDS) microanalysis have been employed to evaluate the microstructure of a low alloy steel as a first step in addressing this issue.
Ion microscope and microprobe studies of surfaces and interfaces
Authors: Newbury Dale E.
Published: June 2020

Secondary ion mass spectrometry (SIMS) in its spatially-resolved forms, the ion microscope and ion microprobe, offers elemental, isotopic, and molecular detection, wide dynamic intensity range spanning major to trace concentrations in the part per million (ppm) range or lower, high lateral spatial resolution in the micrometer to sub-micrometer range, shallow sampling depths to the nanometer range, and the possibility of "microanalytical tomography", the reconstruction of three-dimensional distributions. With this broad range of capabilities, SIMS has special advantages for the characterization of surfaces and interfaces that complement the measurement capabilities of other microanalysis/surface analysis techniques such as electron probe x-ray microanalysis (EPMA), analytical electron microscopy (AEM), Raman and infrared microscopy, scanning Auger electron microanalysis (SAM/AES), and spatially-resolved x-ray photoelectron spectroscopy (XPS). Examples of applications will highlight the special contributions of SIMS to surface/interface characterization studies.

1. Surface studies

Figure 1 shows an example of characterization with extreme surface sensitivity. Changes in surface chemistry induced on a passivated silicon surface by scanning tunneling microscopy in air are revealed by time-of-flight secondary ion mass spectrometry (TOF-SIMS).
Low-voltage high-resolution SEM: A valuable resource for the polymer morphologist
Authors: Vezie D. L. , Adams W. W. , Thomas E. L.
Published: June 2020

The elucidation of polymer morphology has historically been accomplished using optical microscopy (OM), conventional transmission electron microscopy (TEM), X-ray scattering and more recently for crystalline polymers, high resolution TEM (HRTEM). Significant work using scanning electron microscopy (SEM) to study synthetic polymers began in the late 1960's, but for twenty years after these first studies, the smallest features imaged by SEM in polymer samples have typically been 1-10 μm. The evolution of the low voltage high resolution SEM (LVHRSEM) now provides polymer scientists with the opportunity to image structures topographically on the order of 50-100 Å, a level of microstructure important in basic polymer physics research. The potential for improved understanding of polymer morphology is significant, especially when HRSEM data is combined with information from other complementary techniques such as TEM, X-ray scattering, and the scanning probe microscopies (SPM, AFM, STM).

The advantages of LVHRSEM over conventional thermionic source SEM as a polymer characterization technique include: i) low keV operation reduces or eliminates charging in uncoated insulating polymers, ii) the high brightness, low energy spread, small spot size field emission gun allows for operation at low keV without significant loss of resolution (practically, resolution on the order of 50 Å at 1.0 keV in a polymer sample is attainable), iii) imaging of surface topography is improved at low keV as the beam/sample interaction volume is smaller and closer to the surface, resulting in more secondary electrons being generated within the secondary electron escape depth, and iv) the immersion lens system improves the signal to noise ratio by decreasing the noise component in the secondary electron signal.
Cryo-TEM study of novel morphology in mixed surfactant-lipid systems
Authors: Chiruvolu S.
Published: June 2020

Microstructured fluids arise in a number of biological, chemical, and physical systems as interfaces, films, emulsions, membranes, gels, and liquid crystals. We have recently discovered a wealth of new types of microstructure formed by mixed surfactant systems in water, including the first system of spontaneous, equilibrium vesicles formed by simple cationic and anionic surfactant mixtures. Many of these systems present unusual rheological or phase behavior, and accompanying technological opportunities. However, these systems do not lend themselves to simple characterization by conventional light, X-ray, or neutron scattering, NMR, etc. This is due to the indirect nature of these probes; structural information is inferred from these measurements, and a model is often necessary to infer structural information. For mixed surfactant systems, the microstructure is often so unexpected as to make it impossible to construct a model; or worse, a model built on simple structural concepts leads to erroneous interpretation. Cryo-electron microscopy is a necessary alternative to these techniques as the structural information provided is much more direct and model independent.
A quantitative image analysis method for the determination of cocontinuity in polymer blends
Authors: Heeschen William A.
Published: June 2020

Two new morphological measurements based on digital image analysis, CoContinuity and CoContinuity Balance, have been developed and implemented for quantitative measurement of morphology in polymer blends. The morphology of polymer blends varies with phase ratio, composition and processing. A typical morphological evolution for increasing phase ratio of polymer A to polymer B starts with discrete domains of A in a matrix of B (A/B < 1), moves through a cocontinuous distribution of A and B (A/B ≈ 1) and finishes with discrete domains of B in a matrix of A (A/B > 1). For low phase ratios, A is often seen as solid convex particles embedded in the continuous B phase. As the ratio increases, A domains begin to evolve into irregular shapes, though still recognizable as separate domains. Further increase in the phase ratio leads to A domains which extend into and surround the B phase while the B phase simultaneously extends into and surrounds the A phase.
EELS of laser-irradiated kapton polymide
Authors: Bentley J. , Phillips H.M. , Callahan D.L. , Sauerbrey R.
Published: June 2020

It has recently been demonstrated that the electrical resistivity of a high temperature polymer, polyimide, can be changed permanently from 1017 Ωcm to 10-1 Ωcm by KrF (248 nm) excimer laser irradiation. Further, using a holographic technique, an array of 500-nm-wide electrically conducting wires has been produced on polyimide by direct laser ablation. There is obvious interest in exploiting this phenomenon to create integrated microelectronic devices with conventional polymers as both dielectrics and conductors. The imaging of such patterned nanostructures by scanning and transmission electron microscopy (SEM and TEM) is reported elsewhere. Knowledge of compositional changes that accompany the structural changes is necessary for understanding formation mechanisms, but analytical electron microscopy (AEM) of polymers is usually severely limited by electron beam damage effects, especially when high spatial resolution microanalysis is attempted with focussed probes. However, parallel-detection electron energy-loss spectrometry (PEELS) has been successfully used to investigate laser-induced compositional changes in polyimide (Kapton™, E.I. Dupont) with no apparent signs of beam damage.
Dislocation decomposition and dissociation in molybdenum disilicide
Authors: Maloy S. A. , Petrovic J. J. , Mitchell T. E.
Published: June 2020

Molybdenum disilicide(MoSi2) is being investigated as a potential high temperature structural material. It has the tetragonal C11b crystal structure, space group I4/mmm, with a=3.204Å and c=7.848Å. The shortest Burgers vector is <100> and such dislocations are commonly observed. The {110} planes have pseudo-hexagonal symmetry and so the next larger Burgers vectors, 1/2<111> and <110>, both have b = 4.531Å, followed by 1/2<331> and <001> both with b = 7.848Å. The easiest slip systems are {011}<100> and {110}l/2<111>. These have zero Schmid factors for crystals deformed along [001], forcing other systems such as {103}l/2<331> into operation. Here we will describe and discuss TEM observations of dislocations produced in Czochralski-grown MoSi2 single crystals by deformation along the [001] compression axis at temperatures from 1000 to 1500°C.

Specimens tested at 1000°C yielded in a series of load drops starting at a stress of 680MPa and continuing to 1400MPa (the limit of the machine) when the plastic strain was 0.3%.
Electron diffraction study of thin cobalt oxide films grown by pulsed laser deposition on zirconia substrates
Authors: McKernan Stuart , Ramamurthy Sundar , Barry Carter C.
Published: June 2020

The technique of pulsed laser deposition (PLD) has been applied to many different materials systems. Thin films of metal, ceramic, semiconductor and polymer material have successfully been deposited on different substrates. The nature of the deposited film varies according to the target used and the exact conditions under which the deposition occurred. Among other properties, the films may be amorphous or fully crystalline, they may be homogeneous or contain particulates from the target, and the films may be smooth or textured. Because of the nature of the deposition process the films need not be in the thermodynamically lowest energy state. Following earlier work, we have grown several ceramic films on single crystal oxide targets, to characterize the interfacial reactions involved.

In this study crystalline cobalt oxide ceramic films have been grown on (001) zirconia substrates by PLD. The deposition was performed in an oxygen partial pressure of ∼ 6 mtorr, with the substrate heated to 750°C.
TEM characterization of synthetic hillebrandite: Structure, microstructure, and dehydration
Authors: Kim Y. J. , Kriven W. M.
Published: June 2020

Hillebrandite (Ca2SiO4•H2O) occurs in nature as a white, fibrous mineral. Synthetic hillebrandite was prepared hydrothemally from calcia and silica. On heating, hillebrandite dehydrated to β-Ca2SiO4 which is stable at room temperature. The crystal structure, microstructures and the dehydration mechanism of the synthetic hillebrandite prepared by Ishida et. al were investigated by conventional TEM, HREM, and in situ hot-stage TEM.

Most hillebrandite fibers showed their fiber axis to be parallel to the b axis and tended to lie on {001} cleavage planes. SADP’s frequently displayed continuous streaking, and corresponding dark field images revealed stacking disorders perpendicular to the fiber axis (Fig. 1). The observed [001] SADP (Fig. 2) was very different from the expected [001] SADP based on published XRD data (space group, P21/a). For all hk0 reflections, (i) if k = odd, no individual spots are shown but weak continuous streaking exists, (ii) if k = 2, reflections of h = even are extinct, and (iii) if k = 4, reflections of h = odd are extinct.