bluuebunny/crossref_metadata_2025 huggingface dataset:
Nano-Sized Catalytic Materials Investigated by a STEM-Based Mass Spectroscopic Technique
Authors: Yang J C , Singhal A , Bradley S , Gibson J M
Published: July 2020

Knowledge of catalysts' sizes and shapes on their support material is crucial in understanding catalytic properties. With increasing interest in nanosized catalytic materials, it is vital to obtain structural information at the nanometer level in order to understand their catalytic behavior. We have recently demonstrated that very high angle (˜100mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the number of atoms of individual nano-sized clusters on a support material We are presently applying this technique to a bimetallic catalyst, PtRu5, where our data suggest that the shape of the PtRu5 particle is, surprisingly, oblate on the carbon substrate.

PtRu5 is of interest for methanol oxidation for applications in batteries. PtRu5 compounds were produced by a molecular precursor method. Imaging was performed on a Field Emission Gun (FEG) Vacuum Generators HB501 STEM operated at 100kV.
Defect Review at 0.25 Micron Electron Optic Requirements and Practical Examples
Authors: Tracy Bryan
Published: July 2020

The sub-micron era in 1C process technology has been characterized by ever shrinking device geometries. When the minimum feature size of 0.5 micron was reached, a significant inflection in the usefulness of optical microscopy occurred. Seemingly routine Fab activities such as the use of the optical microscopes to determine the quality of the metal etch were no longer possible. At the same time, an increased use of defect inspection tools such as KLA and Tencor was required to insure stable process quality. These and other factors combined to hasten the introduction of multiple defect review scanning electron microscopes into the modern 1C Fab. This trend has accelerated during the process development of 0.25 micron technology. Accordingly, as leading 1C manufactures introduce production 0.25 devices, it is not unusual to find as many as six such instruments installed in a modern development or fabrication facility. As such, these instruments, commonly called Defect Review Tools (DRT's) constitute an increasing share of the Fab equipment set.
Imaging and Analytical Challenges for Nanoscale Semiconductor Technology: Breakthrough Needs for Development and Manufacturing
Authors: McDonald Robert C , John Mardinly A , Susnitzky David W
Published: July 2020

The complexity of today’s commercial semiconductors has contributed to tremendous gains in device performance; millions of transistors are now packed into each square centimeter of silicon. The reduction of scale occurring within the semiconductor industry places extraordinary new demands on transmission electron microscopy: TEM is becoming a required precision measurement tool for manufacturing and a necessary analytical tool for R&D and failure analysis support. This paper reviews the industry’s needs for advanced TEM sample preparation, imaging and microanalysis and outlines the challenges presented to the TEM community as device dimensions continue along the National Technology Roadmap.

In the semiconductor industry, TEM is applied to process debugging, yield engineering, tool qualifications, single-bit failure analyses, and new process development. A large fraction of the analysis effort focuses on transistor, metal, interconnect and dielectric structures grown on and into the Si wafer. Fig. 1 shows a TEM image of a multilayer metal in a near-current generation microprocessor to illustrate the scale and nature of complexity.
Characterization of Multilayered Structures Using a FEGSEM and X-Ray Microanalysis
Authors: Gauvin Raynald , Caron Mario , Fortin Vincent , Currie John F
Published: July 2020

Microelectronic processes now involve multilayer structures of different materials. It is important to control accurately the thickness and composition of these materials during their processing. The determination of these two physical parameters are usually performed by Elastic Recoil Detection (ERD), by Auger Electron Spectroscopy (AES) and Transmission Electron Microscopy (TEM). However, these techniques are not suitable for analysis on a routine basis. In this context, a quantitative procedure based on EDS X-ray microanalysis in the Scanning Electron Microscope has been developped because of its availability and its speed of analysis. However, this technique requires several measurement of K ratio taken at different voltages which is time consuming. With the advent of Field Emission Gun Scanning Electron Microscopes (FEGSEM), X-ray line scans taken at low electron beam voltage with an EDS system may be an alternative. In this paper, preliminary results using this technique on multilayered materials are presented.

To investigate this characterization technique, a AlSiCu(200 nm)/TiN(95 nm)/Ti(40 nm) multilayer metallization structure deposited on Si substrate was used. EDS X-ray line scans were obtained with a Hitachi S-4500 FEGSEM coupled with a Link ISIS 300 EDS system.
Comparison of Sputtered Titanium Nitride on Silicon Dioxide and Aluminum-Alloy Thin Films
Authors: Drown JL , Merchant SM , Gross ME , Eaglesham D , Giannuzzi LA , Irwin RB
Published: July 2020

Titanium nitride (TiN) films are used as anti-reflection coatings (ARC) on aluminum (Al) films to facilitate lithography processes during multilevel metallization for the manufacture of integrated circuits on silicon-based (Si) semiconductor devices. It is generally accepted in the literature that the microstructure of multilevel metal stacks is influenced by the texture of the substrate. For the case of interconnect materials used in the semiconductor industry, a typical metal stack is as follows: Titanium/Titanium Nitride/Al-alloy/ARC-Titanium Nitride. The Ti/TiN layer underneath the Al-alloy film is used as a barrier stack to prevent junction spiking. The Ti/TiN underlayer also determines the growth conditions (crystallography and orientation relationships) of the subsequent Al-alloy film.

This study focuses on the microstructural characterization of the ARC-TiN layer on Si-oxide and Ti/TiN/Al-alloy substrates that are fabricated under similar conditions using conventional physical vapor deposition (PVD - sputtering) techniques. The ARC-TiN microstructure was investigated by transmission electron microscopy (TEM) using a Philips EM430 operating at 300 kV.
Characterization of Variations in Schottky Barrier Height in Semiconductor Devices using EBIC Technique
Authors: Drouin D , Beauvais J , Gauvin R
Published: July 2020

Recent developments in microelectronic devices have increased the need for new investigative techniques. Much of the development on Electron Beam Induced Current (EBIC) occurred in the early 70's. Since that time, much of the work has been devoted to using this technique to investigate defects in semiconductor devices. Less attention has been focused on electrical measurement of semiconductor properties.

A digital EBIC method to characterize semiconductors has been developed and is presented here. The sample current is measured using a Keithley 670 electrometer controlled through a GPIB interface by a standard computer. The electron beam from the scanning electron microscope (SEM) is synchronized with the current acquisition. All the acquisition is controlled by a Labview virtual instrument (Figure 1).

As an example of the performance of this method, a special sample was analyzed. A novel method of resistless lithography process was developed in our laboratory. This technique is dedicated to overcome limits of conventional resist based electron beam lithography.
SIMS of Interfacial Segregation in Ceramics and Composites
Authors: Chabala JM , Gavrilov KL , Mikeska KR , Bennison SJ , Levi-Setti R
Published: July 2020

Trace impurities and dopants in sintered ceramics, often at levels below 100 parts per million, can significantly affect the performance of the materials. In alumina (A12O3), it is believed that calcium and silicon, which are the main background impurities, cause abnormal grain growth. The addition of magnesium to alumina produces several beneficial results, including enhanced densification and improved corrosion resistance of the ceramic. For example, LUCALUX®, which is a dense, transparent ceramic, is made by adding a small amount of MgO (<0.25%) to the alumina. Primarily because they are difficult to detect and image, it has not been easy to determine experimentally the mechanisms by which trace constituents influence the sintering of ceramics. Imaging secondary ion mass spectrometry (SIMS) is a valuable analytical technique for the submicrometer characterization of ceramics. Relevant to this study, magnesium and isotopes of silicon, which have largely eluded detection by traditional techniques, can be measured with SIMS.
Interfacial Segregation Studied With Modern AEM Techniques
Authors: Bentley J
Published: July 2020

For more than 20 years interfacial segregation has been studied by analytical electron microscopy (AEM). Two recent commercial developments should allow more widespread application of 1 nm resolution AEM studies of interfacial segregation. The first is a system for integrated acquisition that in its most sophisticated form allows spectrum imaging [a full spectrum recorded at every pixel of an image (e.g. STEM)] for simultaneous multiple spectroscopies (e.g., EDS and PEELS). A field emission gun (FEG) is necessary for sufficient sensitivity at high spatial resolution. The second commercial development has been imaging energy filters that allow the production of elemental maps from a series of energy-filtered TEM (EFTEM) images at inner shell ionization edges. Resolutions of ∼1 nm can be achieved without an FEG, but analysis is limited to the electron energy-loss signal. Although complex microstructures may require full two-dimensional mapping, for many planar interfaces a one-dimensional profile of composition or chemistry normal to the interface plane is sufficient.
Quantitative Determination of Bi Segregation at Grain Boundaries in Cu Bicrystals
Authors: Alber U , Müllejans H , Rühle M
Published: July 2020

Impurity segregation at grain boundaries (GB) can be detected by EDS in a dedicated STEM. Quantification of the segregation requires not only quantification of the spectra but also consideration of the geometry of the experiment. Our aim was to obtain a value which characterises only the segregation of the impurity and is independent of experimental parameters. The problem is that the specimen composition at the GB is extremely inhomogeneous on an atomic scale in the case of Bi segregation at GBs in Cu. The analysed volume which is defined by the irradiated area and the beam broadening of the primary electron beam inside the specimen contains the interfacial plane as well as neighbouring bulk Cu. One approach is to put the focussed primary electron beam on the interface which is aligned edge on and acquire a spectrum. Both the primary beam diameter and the beam broadening inside the specimen have to be known.
Irradiation-Induced Microstructural Changes in Alloy X-750
Authors: Kenik EA
Published: July 2020

Alloy X-750 is a γ´-strengthened Ni-base alloy that is often used in nuclear power systems for its excellent corrosion resistance and good mechanical properties. However, radiation-induced segregation (RIS) and irradiation-assisted stress corrosion cracking (IASCC) can occur under neutron irradiation. The present study examines the microstructure and composition profiles in a heat of Alloy X-750 before and after neutron irradiation.

The material was in the HTH commercial heat treatment (lh at 1121°C + air cooling + 20h at 704°C). Specimens were prepared from both control material and material irradiated at 360°C to a fluence of 2.3 × 1020 n/cm2 (E > 1 MeV), which was estimated to produce -0.4 displacements per atom. High spatial resolution analytical electron microscopy was performed in a Philips EM400T/FEG operated in the STEM mode with a probe diameter of ∼1.4 nm (FWHM). Composition profiles were acquired in two different ways: all energy dispersive X-ray spectrometry (EDS) and some parallel-detection electron energy-loss spectrometry (PEELS) profiles were acquired as individual spot analyses, whereas the majority of the PEELS profiles were acquired as spectrum lines with ∼10 s acquisition times per point. The quoted compositions are as measured (wt%); no deconvolution for the effect of the excited volume was performed.
Texture and Grain Boundaries in Epitaxial Oxide Multilayers, Including Superconductors, on Biaxially Textured Metal Substrates
Authors: Goyal A , Specht E D , Norton D P , Paranthaman M , List F A , Park C , Christen D K , Kroeger D M
Published: July 2020

A new technique, referred to as rolling-assisted-biaxially-textured-substrates (RABiTS) has recently been proposed by Goyal et al., to fabricate long-range, biaxially textured substrates with suitable metal/ceramic surfaces for epitaxial growth of electronic devices [1]. Using standard thermomechanical processing, long lengths of flexible, biaxially oriented substrates with smooth surfaces (rms∼50nm) are obtained [1]. Epitaxial metal and/or oxide layers which can serve both as a chemical as well as a structural buffer are deposited on the biaxially textured metal. The metal with a suitable set of epitaxial, multi-layers comprises the substrate which is expected to have many potential applications, including superconductivity, photovoltaics and ferroelectrics [1].

When high temperature superconductors are deposited on a set of epitaxial multilayers on biaxially textured RABiT substrates, extremely high critical current densities, approaching 106 A/cm2 at 77K have been obtained [2].
In-Situ Observation of Deformation Processes by OIM
Authors: Weiland Hasso
Published: July 2020

The thermo-mechanical response of single crystals has been studied in detail since the discovery of X-ray and electron diffraction. While an extensive knowledge exists on the effect of crystallographic orientation on deformation and recrystallization behavior of single crystals, the thermo-mechanical response of grains of different orientations embedded in a polycrystalline matrix are not well understood. With the emergence of microstructure based models predicting the structure evolution during deformation or recrystallization, data validating the predicted structure changes are essential. This requires to study the evolution of microstructural attributes such as morphology or orientation of an individual grain within a specific grain neighborhood during mechanical or thermal exposure. Interrupted coupon scale testing, with a separation of testing and microstructural observation is not sufficient due to the small size of the objects to be observed. Thus, the structure evolution of selected grains has to be followed in-situ.
Strain Estimation by Electron Back Scattered Diffraction
Authors: Baudin T , Chastel Y , Pennelle R
Published: July 2020

The quality of the Kikuchi patterns obtained for example by electron backscattered diffraction decreases when the dislocation density increases in strained materials, and consequently, it can theoretically be correlated to the strain through the average dislocation density measurement particularly for monotonic deformation paths. For that purpose, in a first step it is necessary to define a quality factor defined in the Hough space or with the Burns method currently used when the Kikuchi patterns are automatically analyzed. Then, and it is the most important point, the quality factor must be linked to the strain through a calibration curve independent of crystallographic orientation.

The main objective of this study is to test the reliability of this method in the simple case of the hardness test. This test is simulated using the finite element method and the obtained results are compared to those measured by electron backscattered diffraction. Several calibration methods are defined.
Application of Microdiffraction in Sem for Assessing Intrinsic Materials Susceptibility to Intergranular Corrosion and Stress Corrosion Cracking
Authors: Palumbo G , Lehockey EM , Lin P
Published: July 2020

Intergranular degradation processes (e.g., corrosion, stress corrosion cracking) are a frequent cause of premature and unpredictable service failure of engineering components. Since these processes cause component failure via propagation through the intercrystalline network, they are strongly dependent upon the distribution of specific grain boundary structures in the material. Previous studies have shown that grain boundaries crystallographically described by low Σ (Σ≤29) Coincidence Site Lattice (CSL) relationships can often selectively display a high resistance (and often immunity) to corrosion and fracture. Recent advances in automated microdiffraction techniques (e.g., EBSP) in SEM have now made it possible to readily evaluate grain boundary character distributions in conventional polycrystalline materials. by utilizing this technique, and by formulating and applying simple stochastic models for the propagation of intergranular cracking and corrosion processes, the opportunity now exists for (1) improved component lifetime prediction, and (2) the optimization of materials synthesis techniques to yield intergranular-degradation resistant microstructures.
Ultrahigh-Vacuum Field-Emission Electron Microscope as Applied to Observation and Analysis of Crystal Surface
Authors: Takeguchi M , Honda T , Ishida Y , Kersker M , Tanaka M , Furuya K
Published: July 2020

UHV(ultrahigh-vacuum) TEM has long been used as a powerful tool for studying crystal surfaces, particularly for both the direct imaging of the surface structure and for in-situ observation of surface reaction processes with atomic resolution.

This paper reports a newly developed 200kV UHV TEM equipped with a field emission gun(FEG). The instrument is designed to obtain information about elemental or bonding states of surfaces in addition to observation of surface atomic structure with high contrast. Basic performances of the UHV FE-TEM includes a specimen vacuum of 2.0X10-8Pa, probe size less than 1.0nm Ø with 0.5nA probe current, point-to-point resolution of 0.21 nm, and a lattice resolution of 0.10nm.

A UHV Energy Dispersive X-ray Spectrometer (EDS) originally developed by JEOL Ltd. and a Parallel Electron Energy Loss Spectrometer (PEELS) are attached to the UHV FE-TEM, which combined with a fine focused probe of 1.Onm Ø allows atomic scale spectroscopy of surfaces.
In-SituEELS Analysis of Cobalt Valence in La1-xSrxCoO3-y
Authors: Yin JS , Wang ZL
Published: July 2020

Transition and rare earth metal elements have played a vital role in synthesis of functional and smart materials because of their unique electronic structures and mixed valences. Experimental measurement of the valence states is thus important for understanding the mechanism which drives the functional properties. Lai1.xSrxCoO3-y(LSCO), for example, is an ionic conductor with potential applications in fuel cells and many other fields. In this type of materials, the anion deficiency is directly associated with the ratio of Co2+/Co3+ (or Co3+/Co4+) present in the specimen. It is known that the anion deficiency of the material depends on the operation temperature, but a direct measurement of anion deficiency is a challenge to existing microscopy techniques. In this paper, we present the in-situ analysis of Co valence in LSCO using electron energy-loss spectroscopy (EELS) in a transmission electron microscope.

LSCO thin films (with x = 0.5) were grown on polished MgO(00l) substrate by liquid source metal-organic chemical vapor deposition (MOCVD) method [1].
ESEM Hot Stage Evaluation of Sol-Gel Insulation Coatings for High Field HTS Magnets.
Authors: Mutlu I H , Goddard R E , Hascicek Y S
Published: July 2020

High temperature, thin ceramic insulation coatings are necessary for the application of High Temperature Superconductors (HTS) in high field magnet technology. Especially in the so called “wind and react” technology, insulation coatings have to withstand the final heat treatment at about 900°C, otherwise turn to turn insulation will be broken. We have developed a sol-gel coating method for HTS tape conductors at NHMFL. Excellent adhesion at the interface due to the significant interfacial reactions, indicates that this sol-gel route is a feasible method for applying zirconia coatings. Sol-gel technology is a low temperature chemical route of preparing inorganic material. The stability and the coating characteristics of a organozirconium compound have been investigated to coat ZrO2 films on silver sheathed HTS tape conductors. This method was used to coat stainless steel with ZrO2.

The ZrO2 coatings were obtained by dipping the silver sheathed HTS tape in a solution of zirconiumtetrabutoxide, isopropanol and acetylacetone.
In Situ Nitride Growth Studies by Low Energy Electron Microscopy (LEEM) and Low Energy Electron Diffraction (LEED)
Authors: Bauer E , Pavlovska A , Tsong IST
Published: July 2020

Nitride films play an increasing role in modern electronics, for example silicon nitride as insulating layer in Si-based devices or GaN in blue light emitting diodes and lasers. For this reason they have been the subject of many ex situ electron microscopic studies. A much deeper understanding of the growth of these important materials can be obtained by in situ studies. Although these could be done by SEM, LEEM combined with LEED is much better suited because of its excellent surface sensitivity and diffraction contrast. We have in the past studied the high temperture nitridation of Si(l11) by ammonia (NH3)and the growth of GaN and A1N films on Si(l11) and 6H-SiC(0001) by depositing Ga and Al in the presence of NH3 and will report some of the results of this work for comparison with more recent work using atomic nitrogen instead of NH3.
A High Voltage Scanning Electron Microscope for the In-SituObservation and Recording of Electromigration Voids in Metal Lines on Integrated Circuits.
Authors: Flinn P A , Lee S , Doan J C , Bravman J C , Marieb T , Madden C
Published: July 2020

The passing of current through thin metal lines results in the formation of voids which will eventually cause the line to fail electrically. Gathering of experimental data on electromigration has been limited by two facts: The dimensions of the metal lines on modern integrated circuits are on the order of the resolution limit of light microscopy; and voids in these lines behave quite differently when they are surrounded by a protective film of SiO2 or other dielectric. This dielectric protects the metal surface and constrains the line, pushing back on the metal displaced by void formation. Several additional factors further complicate experimental analysis: the sample test current must be precisely controlled during observation; the sample must be accurately heated to several hundred degrees; the metal lines must be long and narrow (typically 0.2-3.0 (am wide by 300 μm long); testing is often lengthy, sometimes extending over several days even under conditions selected to minimize the time to failure; and electromigration failures are characterized by long incubation periods during which no changes are observed followed by rapid and complex behavior.
Unveiling Novel Reaction Processes in Catalysis by Environmentalhrem (EHREM)
Authors: Gai Pratibha L
Published: July 2020

Dynamic interactions between gas molecule and solid surfaces are central to heterogeneous catalytic processes. Recently, we have developed a novel in-situ environmental high resolution electron microscopy (EHREM) method, capable of probing live gas-catalyst reactions at elevated temperatures directly (in-situ) on the atomic scale1. A Philips CM30 (S)TEM has been modified with an integrated environmental cell maintaining atomic resolution in controlled gas environments, upto ∼ 1000 °C. Using this method, we have studied important real-life catalysts, vanadyl pyrophosphates ((VO)2P2O7, hereafter referred to as VPO), used in n-butane oxidation to maleic anhydride (MA with end uses in furans.

The catalyst samples were prepared using V2O5, anhydrous phosphoric acid in isobutyl alcohol and benzyl alcohol followed by calcination and activation. VPO is orthorhombic with a ∼ 16.59Å, b ∼ 7.76Å and c ∼ 9.58 Å. An EHREM lattice image of the fresh catalyst with electron diffraction (ED) and ‘rose’ morphology, is shown in Fig 1(a).
In SituHigh-Resolution Electron Spectroscopic Imaging and Real-Time Image Simulation of Precipitate Growth Mechanisms
Authors: Howe J M , Tsai M M , Csontos A A
Published: July 2020

Precipitate interfaces are ideal for studying the relationship between atomic bonding, structure and composition at internal interfaces and the mechanisms and kinetics of their motion as a function of temperature or driving force for reaction. The crystallography between coherent and semicoherent precipitates and the matrix is well-defined and the precipitate interfaces are often planar and grow by a terrace-ledge-kink mechanism, making them well-suited for study by conventional and high-resolution transmission electron microscopy (HRTEM).

Motion of precipitate interfaces, or more generally, interphase boundaries, involves a change in lattice, composition or both. In order to understand the mechansims of interfacial motion, it is necessary to determine the structural and compositional changes that occur at the highest possible resolution, i.e., as close to the atomic level as possible, and also, to determine the corresponding kinetics of interface motion. HRTEM is an excellent technique for determining the atomic structure of transformation interfaces and in situhot-stage HRTEM is deal for determining interface dynamics at the atomic level, provided the transformation mechanisms are not altered by the thinness of the TEM foil.
Atomic Structure Determination of Nio-Y2O3 Interfaces by HRTEM
Authors: Bailey GW , Dimlich RVW , Alexander KB , McCarthy JJ , Pretlow TP , Dickey EC , Dravid VP
Published: July 2020

The investigation of interfaces between NiO and Y2O3 is part of a research initiative to understand low-energy heterophase interface structures between different oxide materials. In-situ oxide composites formed by the directional solidification of pseudo-binary eutectics are used as model materials in this study because they are amenable to chemical and structural characterization at the atomic length-scale. Previously, interfaces in NiO-ZrO2(cubic) directionally solidified eutectics (DSEs) were examined by various electron imaging and spectroscopy techniques to reveal the three-dimensional interface structure.[l] The second DSE system studied, NiO-Y2O3,[2] was chosen because it is very similar in crystallography to NiO-ZrO2(cubic). The goal of this second, analogous study is not only to understand the NiO-Y2O3 interface structure but, by comparing the results to NiO-ZrO2, is to draw more general conclusions about low energy oxide-oxide interfaces. Table one compares the crystallography of the NiO-ZrO2 and the NiO-Y2O3 DSEs.
Electron Spectroscopy and Holography of Electrically Active Electroceramic Interfaces
Authors: Bailey GW , Dimlich RVW , Alexander KB , McCarthy JJ , Pretlow TP , Johnson Kevin , Ravikumar V , Rodrigues R , Dravid Vinayak P
Published: July 2020

Many electroceramics derive their technologically useful and scientifically appealing properties through electrically active grain boundaries (GBs). Examples of such properties include traditional nonlinear current-voltage relationship (i.e. varistor behavior) and positive temperature of coefficient of resistance (PTCR effect), to recently “rediscovered” phenomena of space-charge formation across functional interfaces, including ferroeletric thin films.

In many such cases, the transport of charge across these interfaces is mediated through potential barriers which form at the core of these interfaces. For example, varistor behavior is attributed to formation of Schottky barriers at GBs which modify the transport of electrons, leading to the nonlinearity in I-V characteristics. The formation of Schottky barrier at the GB core, in turn, is attributed to the formation of space-charge across GBs. The formation of space-charge, further, is clearly attributable to decoration of GB core with charged defects with compensating opposite charge across the GB. The presence, sign, magnitude and spatial distribution of space-charge form the key to understand the Schottky barriers, thus the transport properties of interfacial systems.
Determining Atomic Structure-Property Relationships at Grain Boundaries in High-Tc Superconductors
Authors: Browning N D , Buban J P , Prouteau C , Duscher G , Chisholm M F , Pennycook S J
Published: July 2020

The short coherence length in high-Tc superconductors (5-15Å) makes an atomic scale understanding of the electronic properties at defects and interfaces essential for device applications. This understanding is particularly relevant for grain boundaries in YBa2CU3O7-δ (YBCO), where although extensive studies have shown a clear exponential decrease in critical current with misorientation angle, the absolute value can vary by several orders of magnitude at any given misorientation angle.

Figure 1 shows Z-contrast images of an [001] low-angle tilt boundary and a 30° [001] asymmetric tilt grain boundary. An interesting feature of both of these boundaries is that there appear to be sites where two atom columns are too close together. However, the problem of like-ion repulsion can be avoided if the columns are taken to be partially occupied. Insight into the effect of this partial occupancy can be obtained through the use of bond-valence sum analysis. Here, the formal valence of an atom is made up of contributions from all of its nearest neighbors, the magnitude of which are determined by the bond length.
Iterative Structure Retrieval Techniques for Aperiodic Defects (e.g. Dislocations) using QHREM
Authors: Bailey GW , Dimlich RVW , Alexander KB , McCarthy JJ , Pretlow TP , Möbus G , Schweinfest R , Bernath S , Wagner T
Published: July 2020

The determination of unknown crystal defect structures by iterative digital image matching (“quantitative HREM”) has previously been successfully applied to grain boundaries (e.g. in niobium [1]) or phase boundaries with small misfit (e.g. Nb-sapphire [2]), which offer several advantages: (i) the supercell is small leading to fast cycle times in iterative structure refinement and thus to a secure global optimum, (ii) noise-filtering is possible by translation symmetry, (iii) the interface structure is mostly planar (i.e. perfectly columnar). For dislocations and other aperiodic defects all these three issues are missing and curved atomic columns from surface strains especially cause problems [3]. Any progress in this area must therefore address (i) - (iii) separately and estimate the change of the confidence level of the retrieved structure when switching from interface-refinement to dislocation-refinement. First results of this project address questions of convergency and speed.

Since each HREM-Lab is only concerned with a limited number of materials (and elements) as well as with a few microscope-voltages only, it is advisable to calculate transmission functions for single atoms for each element and voltage a single time, and store these data files in a library.
Characterization of Precipitate Distributions in Modified S5 Tool Steels
Authors: Hsieh KC , Kenik EA
Published: July 2020

There has been increasing interest from industry to characterize the different precipitate distributions in ferrous materials to account for different mechanical properties that are observed. For this study, two different heat treatments were chosen for the experimental S5 tool steel, modified to have 0.24 wt% C. Alloy S5-1 received 1 hour of austenitizing at 970°C, was quenched at rate of 140°C/s and tempered for 1 hour at 200°C. Alloy S5-2 received 40 minutes of austenitizing at 940°C, was quenched at rate of 16°C/s and tempered for 1 hour at 200 °C. In this relatively low hardenability steel, both S5-1 and S5-2 show mixed microstructures of tempered martensite and bainite (Fig. 1, 2). Not surprisingly, the slower cooling rate for S5-2 created an alloy with inferior microstructure and mechanical properties. Even though these differences in precipitate distributions, could not directly account for differences in mechanical properties, it is of interest to study how the different heat treatments affected the precipitate distributions in S5-1 and S5-2.
Microstructural Characterization of Crystalline and Quasicrystalline Phases in AlCuFe Alloys.
Authors: Rosas G , Reyes-Gasga J , Pérez R
Published: July 2020

Recent interest in the literature on ternary compounds of the AlCuFe type has been prompted by the discovery of stable quasicrystalline phases in these type of alloys (1). Therefore, different investigationes have been carried out in the past, related with the structural characteristics and also the mechanical properties of these compounds (2). It is interesting to point out that very few studies have been carried out on the structural characteristics of the phases which commonly coexist with the icosahedral phase in this ternary alloy (3). In this investigation an assessment of the chemical and structural properties of the phases obtained in alloys of AlCuFe is carried out.

Ternary alloys with approximately 20 different compositions have been prepared. The compositional ranges were: Al(60-65%at), Cu(20-25%at) and Fe(10-15%at). The preparation of the alloys used two different casting process; a gravity chill casting technique and also the spin wheel casting method. These casting techniques were able to provide different cooling velocities in the final ingots or metallic strips.
Crystallography and Phase Transitions in the Ta-Ru and Nb-Ru Shape Memory Alloys
Authors: Fonda R W , Vandermeer R A
Published: July 2020

A new class of shape memory alloys, based on near-equiatomic compositions of Ta-Ru and Nb-Ru, was recently discovered at the Naval Research Laboratory. These alloys exhibit transformation temperatures ranging up to 1400 °C for Ta-Ru and 1100 °C for Nb-Ru, making them the highest transition temperature shape memory alloys yet discovered. Other shape memory alloys typically have transition temperatures within a couple hundred degrees of room temperature. These two alloy systems are quite similar in their transformation behavior. Near the equiatomic composition, the high temperature β phase of both systems has a B2-ordered cubic crystal structure. During cooling, the cubic lattice of β undergoes a slight tetragonal distortion to form the β' phase. Continued cooling of the tetragonal β'(within specific composition ranges) causes a transformation to β'', which is reported to have an orthorhombic crystal structure. The effect of alloy composition on the temperatures, hysteresis, and strains of these transformations was determined by dilatometry.
Microstructural Investigation of Strength Degradation in A Developmental Cvd Sic Fiber At 2000° C
Authors: Garg A , Hull D R , Bhatt R T
Published: July 2020

SiC fibers fabricated by chemical vapor deposition (CVD) methods are being used as reinforcement for metal and ceramic matrix materials because of their high modulus, high strength and good corrosion resistance. These fibers have a complex composite microstructure consisting of a pyrolytic-carbon coated graphite core and a SiC sheath which is often protected by a single or a double layer of carbon-rich coating. Commercially available SCS-6 SiC fibers with a diameter of ˜ 140 μm have been most widely in use for composite fabrication. However, with an ever increasing demand for thinner and stronger fibers, an experimental SiC fiber with a diameter of ˜ 50 μm and having a C-rich SiC sheath was developed by Textron Specialty Materials. The as-fabricated tensile strength of this fiber was found to be ˜ 6 GPa, which is ˜ 50 % higher than that of the SCS-6 fiber.While the room temperature tensile strengths of these fibers heat treated for 1 h in Ar to temperatures ≤ 1600° C were better than those of the SCS-6 fiber, strength of the 2000° C heated fibers decreased to < 1 GPa.
Corrosion of a Plutonium-Bearing Titanate Ceramic
Authors: Buck E C , DiSanto T , Bakel A J , Bates J K
Published: July 2020

A titanate-based ceramic waste form, rich in phases structurally related to zirconolite (CaZrTi2O7), is being developed as a possible candidate for immobilizing excess plutonium from dismantled nuclear weapons. The waste form is made by cold pressing and sintering of CaO, TiO2, ZrO2, A12O3, BaO, and Gd and Pu oxides. A prototype Pu-loaded ceramic that is being tested contains Pu,Gd-zirconolite-(3T), Pu-bearing brannerite, Gd-zirconolite-(4M), zirconolite-(2M) (see Figure 1), rutile (TiO2), Gd-bearing perovskites, various aluminotitanate phases, and undissolved plutonium oxide. Evidence from laboratory testing and natural analogues of titanates suggests that these phases are extremely corrosion resistant. Zirconolite-rich ceramics have also been considered for the disposal of actinide-bearing waste streams, because zirconolite and related polytypes are able to incorporate at least 20 wt% of actinides. However, since each phase in the multiphase ceramic corrodes at a different rate, the release of any one component or the corrosion of the bulk waste form is difficult to predict
Cathodoluminescence Microcharacterization of the Irradiation Sensitive Defect Structure of Amorphous Silicon Dioxide
Authors: Stevens Kalceff MA , Phillips MR , Moon AR
Published: July 2020

Cathodoluminescence (CL) Microscopy (imaging) and Spectroscopy in a Scanning Electron Microscope enables high spatial resolution, high sensitivity detection of defect centers in materials. Cathodoluminescence microanalysis has been used to investigate the irradiation sensitive defect structure of Types I, II, III and IV amorphous silicon dioxide SiO2 (quartz and silica glasses). The CL experiments were performed in a JEOL JSM 35C SEM equipped with Oxford Instruments liquid N and liquid He cryogenic stages, and an Oxford Instruments MonoCL cathodoluminescence imaging and spectral analysis system. The observed CL emissions, were excited with a stationary electron beam at normal incidence and corrected for total instrument response. The corrected CL spectra were fitted with a multiparameter Gaussian function using a non linear least squares curve fitting algorithm and were identified with particular defect structures. The CL emission from high quality pure amorphous silica and quartz glasses is dominated by intrinsic processes (associated with the host lattice). See Table 1.
Polymorphic Transition in Biogenic Calcium Carbonate: Nacre/Prismatic Interface in Abalone Shell
Authors: Freeh Daniel M , Sarikaya Mehmet
Published: July 2020

The research in biological hard tissues offers lessons for biomimetic (structure and processing) strategies, such as for the synthesis of hierarchical architectures tailored for specific engineering applications. These biocomposites, i.e., biogenic materials in which the major phase is an inorganic component associated with macromolecules (proteins and polysaccharides), include bones, dentin, sea-urchin skeletal units, bacterial and algal particles and molluscan shells. Here, a summary is given from a recent TEM study of the interfacial region of nacreous and prismatic sections of red abalone shell to understand the morphological and crystallographic correlations across this transition region.

Many mollusk species have shells made of CaCO3 in various architectures that have evolved under different ecological conditions to produce structures that best protect the organism. The shells of many species contain both aragonite (orthorhombic, Pmnc) and calcite (Rhombohedral, R3m). In red abalone (Haliotis rufescens), the outer section, prismatic (P), is composed of columnar crystallites of calcite (1-5 μm base, 5-10 μm height), and the inner section, nacre (N), is composed of pseudo-hexagonal platelets of aragonite (side 2-5 μm), stacked as 0.25 μm layers, separated by a few nm-thick organic layer (Fig. 1).
Optical Coherence Microscopy: A New Technique for High-Resolution, Non-Invasive Imaging in Bulk Biological Tissues
Authors: Izatt Joseph A , Kulkarni Manish , Wang Hsing-Wen , Sivak Michael V
Published: July 2020

Optical coherence microscopy (OCM) is a novel technique complementary to optical coherence tomography (OCT) which combines low-coherence interferometry with confocal microscopy to achieve micron-scale resolution imaging in highly scattering media. OCM may be implemented using a single-mode fiber-optic low-coherence interferometer (See Fig. 1). A high numerical aperture objective is used to focus sample-arm light into the specimen, and the reference arm length of the interferometer is adjusted to match the sample arm focal plane optical depth. The sample arm of the interferometer comprises a scanning confocal microscope, in which either the sample or the probe beam is laterally scanned in a raster pattern, and the optical fiber acts as a single-mode confocal aperture for combined light illumination and collection. The reference arm length of the interferometer establishes the depth position of an interferometric “coherence gate” in the sample, from which backscattered light is preferentially collected. Initial studies of OCM in scattering phantoms have demonstrated that this technique provides increased optical sectioning depth compared to confocal microscopy alone.
Sub-100nm Axial Resolution in 3D Widefield Optical Microscopy Using Two Opposing Objective Lenses
Authors: Gustafsson Mats GL , Agard David A , Sedat John W
Published: July 2020

It has been understood since the days of Ernst Abbe that an optical microscope can reach higher resolution the wider the set of angles from which it can observe the specimen — this angular range, of course, is what is indicated by the Numerical Aperture (NA) of the objective lens. Over more than a century of objective lens development, this light collecting angle has been increased closer and closer to the full 180° angle available above a microscope slide. There is, however, a second, equally large and easily accessible set of observation angles available on the other side of the specimen slide, and a standard microscope makes no use whatsoever of light emitted in these directions. One might then ask whether there is not a substantial resolution advantage to be had by devising a microscope that does make use of this "back side" light. The answer, in fact, is yes.
Sub-Millisecond Time Resolved Imaging of Voltage Changes in Excitable Cells and Tissues Using Multiple Site Optical Recording of Transmembrane Voltage (Msortv) and Molecular Probes
Authors: Salzberg BM , Obaid AL
Published: July 2020

Molecular indicators of membrane potential may be used to obtain sub-millisecond time resolved images of transient changes in membrane voltage in a variety of biological systems. These probes are small amphipathic molecules having molecular weights of 400-500, and dimensions on the order of 10 Angstroms, which bind to, but do not cross cell membranes, and change either their absorbance or fluorescence in response to membrane voltage. These extrinsic optical signals depend linearly upon membrane potential, and the best of the dyes respond to a step change in voltage in less than 1.5 μsec at room temperature. The salient properties of fast potentiometric probes will be discussed, and the fidelity of optical recordings to transmembrane voltage changes will be considered.

Since voltage changes in excitable cells take place on a time scale that is determined by the kinetics of conformational changes in membrane proteins, and by membrane electrical time constants, these changes tend to be very rapid, and resolving them requires imaging systems that are frequently orders of magnitude faster than usual video rates.
Near-Field Optical Spectroscopy: Enhancing the Light Budget
Authors: Paesler MA , Hallen HD , Yakobson BI , Jahncke CJ , Boykin PO , Meixner A
Published: July 2020

The near-field scanning optical microscope, or NSOM, provides spectroscopists with resolution beneath the diffraction limit. In the NSOM, an optical aperture smaller than the wavelength λ of the probe radiation is scanned in the near-field of a sample. Pixels are serially gathered and then constituted as a computer-generated image. Spectroscopic NSOM investigations demonstrating sub-λ, resolution include studies of photoluminescence, Raman spectroscopy, and single molecule fluorescence. Results of nano-Raman spectroscopy on semiconducting Rb-doped KTP are shown in figure 1. Figure la is a topographic image of the sample showing a square Rb-doped region in an otherwise undoped sample. Figure lc is a NSOM region of the corner of the doped region, and figure lb is an image of the same region taken within a Raman line. While these data do provide sub-λ spectroscopic resolution and other interesting features, the weak signal provided by current NSOM technologies and the low quantum efficiency of the Raman effect necessitated development of a very low-drift microscope and inconveniently long collection times.
Submicron Optical Spectroscopic Surface Characterisation Using Near-Field Probes.
Authors: Webster S , Kerhsaw K , Batchelder DN , Quirke P , Lidzey D , Bradley DDC , Smith DA
Published: July 2020

The development of scanning near-field optical microscopy has provided a submicron optical tool which has important applications in both fundamental studies and in device fabrication and analysis. The strength of the technique lies not only in its resolution of approximately 50nm, which is an order of magnitude improvement on diffractive optical techniques, but also in its ability to allow highly developed optical spectroscopies to be used for chemical analysis at this resolution. We have particular interest in the application of near-field probes to high spatial resolution laser spectroscopy in a range of organic, biological and inorganic systems. In this paper we shall describe the development of instrumentation for luminescence, Raman and time resolved spectroscopy in air and under fluids and will present the results of studies of phase separated polymer mixtures, organic crystals and semiconductor materials.

The current scanning near-field optical microscope is based around a tapered optical fibre, at the end of which a submicron aperture has been defined by a metal coating.
High Spatial and High Spectral Resolution FTIR Spectroscopic Imaging of Biological Materials
Authors: Lewis EN , Kidder LH , Levin IW
Published: July 2020

Infrared spectroscopy has been used to probe a variety of biological systems including for example, the determination of diseased states and the investigation of foreign inclusions in biologicals. The technique generates qualitative and quantitative information on the structure and dynamics of samples, including lipids, proteins, and non-biological constituents. The coupling of imaging modalities with spectroscopic techniques adds a new dimension to sample analysis in both the spectroscopic and spatial domains. Using a spectroscopic imaging system that incorporates a step-scan interferometer, microscope, and infrared sensitive arrays, we have investigated a variety of biological samples. This seamless combination of spectroscopy for molecular analysis with the power of visualization generates chemically specific images while simultaneously obtaining high resolution spectra for each detector pixel. The spatial resolution of the images approaches the diffraction limit for mid-infrared wavelengths, while the spectral resolution is determined by the interferometer and can be 4 cm−1 or higher.