bluuebunny/crossref_metadata_2025 huggingface dataset:
TEM Characterization of a Highly Oriented Diamond Film Deposited on (100) Silicon by Bias-Enhanced Nucleation (BEN) and Textured Growth
Authors: Chawla A K , Jeon S-J , Sung C , Baik Y-J
Published: July 2020

Currently, the aim of research in diamond film synthesis on silicon substrates is to gain an understanding of the mechanisms responsible for the development of highly oriented film and for the formation of epitaxial nuclei. With this as our goal we have applied plan-view transmission electron microscopy (TEM) for analysis of a diamond film grown on Si at various stages of film growth.

An ASTeX™ MPCVD system was used to deposit diamond on a single-crystal (100) Si substrate under the following conditions: 970°C, 700W microwave power, 2% CH4 in H2, 90 torr., and 4 hours. The growth step was preceded by a BEN stage in which a negative potential of 200V was applied to the substrate for 25 minutes at 600°C, 700W, 4% CH4 in H2, and 20 torr.. Three different types of plan-view TEM samples were prepared. For one the common procedure of backthinning, dimpling, and ion milling was applied to produce a specimen which reveals microstructures at the film surface.
Characterization of Chemically Vapor Deposited GaN on Sic on a Simox Substrate
Authors: Zhou WL , Pirouz P
Published: July 2020

GaN has been intensively studied because of its potential applications for the fabrication of blue- or ultraviolet-light emitting devices. Sapphire (α-Al2O3) is generally used as the substrate for growth of GaN film. However, the large lattice mismatch between GaN and Al2O3is a possible cause of the large defect density in the GaN films. Consequently, alternative substrates are being studied with the aim of growing films of lesser defect densities and improved opto-electronic properties. In this paper, we report a transmission electron microscopy (TEM) study of a GaN film grown on cubic SiC which has been obtained by carbonization of the top silicon layer of a SIMOX substrate, i.e. the system GaN/SiC/Si/SiO2/Si.

Cross-sectional TEM specimens were prepared by the conventional sandwich technique with the foil surface normal to the Si[l10] direction. The composite sample was ground and dimpled to a thickness of ∼ 10μm, and subsequently ion thinned to electron transparency.
TEM Investigation of Nitrogen-Doped Amorphous Carbon Coated Field Emitters
Authors: Myers AF , Steel EB , Ding M Q , Cuomo JJ
Published: July 2020

Amorphous carbon coatings, including highly sp3-bonded amorphous diamond (a-D), also referred to as tetrahedral amorphous carbon (ta-C), and diamond-like carbon (DLC), have recently been explored for field emission applications [1-3]. These coatings can be deposited uniformly at low temperatures, and possess chemical and mechanical properties similar to those of diamond. They also can be doped with nitrogen to form n-type semiconductors [4]. Diamond coatings, on the other hand, are microscopically nonuniform, usually require deposition temperatures greater than 600 °C, and cannot be doped to produce shallow donor levels [2]. Diamond, a-D, and DLC coated emitters all show enhanced electron emission properties [1-3].

The major emphasis of the work presented here is on the parallel electron energy loss spectroscopy (PEELS) characterization of the sp2 and sp3 bonded carbon in the coatings. PEELS spectra and TEM images were recorded with a Philips CM300 FEG TEM, equipped with a Gatan model 666 parallel acquisition EELS spectrometer. The operating voltage was 300 keV.
Microstructure of Pvd Al Deposition on CVD Tin
Authors: Zhang Na , McNicholas Mark , Anderhalt Bob , Slow Evan , Colvin Neil
Published: July 2020

CVD TiN films offer promise as a barrier to Al deposition as a result of the improved conformai step coverage of this film in 0.25 μm contact holes. As an underlayer, the TiN performs a secondary role by improving electromigration (EM) resistance. This is a result of the crystal orientation of the TiN film and its influence on the orientation of the subsequent Al layer. A <111>Al orientation shows improved EM resistance; however, CVD TiN has a preferred <200> orientation as opposed to a <111>PVD TiN orientation.

In this study, two parts were investigated: 1) obtain a qualified PVD Al film on a CVD <200> TiN barrier in terms of sheet resistance and reflectivity utilizing MRC's Eclipse™ Mark II PVD system; 2) examine the texture of the Al film utilizing Philips XL30 SEM equipped with EDAX-DX4 EDS system and Electron Back Scatter Pattern (EBSP) system.
The Effect of Fe Layer Width on the Electron Structure of Ferromagnetic Face Centered Tetragonal Fe-Cu Multilayers
Authors: Lloyd SJ , Dunin-Borkowski RE
Published: July 2020

The mean specimen potentials across a series of short period coherent face centered ferromagnetic Fe-Cu multilayers, grown on (001) Cu by UHV DC magnetron getter sputtering, have been measured using Fresnel contrast analysis1 in the transmission electron microscope. Multilayers A, B and C nominally had 100 repeats of (Fe2/Cu15), (Fe4Cu13) and (Fe6/Cu9) in units of atomic layers, and saturation magnetizations at 0K of 1.7, 0.7 and 0.8μB/Fe atom, respectively. X-ray diffraction measurements showed that the average (002) spacing in each multilayer was much greater than conventional elasticity theory would predict from the bulk elastic constants of face centered Fe and Cu.

Energy-filtered through focal image series of each multilayer (examined in cross-section) were obtained at 397kV using a JEOL 4000FX microscope equipped with a Gatan imaging filter, and a 3.4mrad objective aperture. Fig.1 shows two of the images obtained from multilayer A. The intensity in selected regions of each such image was projected parallel to the layers, the specimen thicknesses (t) of the regions were measured and the contrast of the resulting one dimensional fringe profiles was compared with calculations in order to determine both the shapes and the magnitudes of the potential profiles across the Fe layers.
Characterization of the Interface in a TiC Reinforced Ti-6%A1-4%V Composite Using Monte Carlo Simulations and FEGSEM.
Authors: Gauvin Raynald , Wanjara Priti , Drew Robin AL , Yue Steve
Published: July 2020

Metal matrix composite (MMC) materials are promising materials because of their higher specific mechanical properties (e.g. strength-to-weight ratio) relative to conventional metallic alloys. However, during the processing of these materials, the development of an interfacial reaction zone between the reinforcing material (generally a ceramic) and the metallic matrix may occur, which typically degrades the mechanical properties of these materials if not controlled. Since these interfaces are generally quite small (from 5 to 500 nm), Transmission Electron Microscopy (TEM) is the technique of choice for characterization because of its outstanding spatial resolution. However, specimen preparation for TEM (e.g. ion milling) is quite difficult for MMC materials, due to the combination of two completely different material types, specifically a hard and brittle reinforcement phase incorporated in a relatively soft metallic matrix. Also, since there is only a small amount of the material which is transparent to electrons after specimen preparation, TEM as a materials characterization technique suffers from a lack of statistical robustness, which is a serious drawback.

To characterize materials with a spatial resolution close to that of TEM, low voltage field emission scanning electron microscopy is an option because of the small interaction volume of low energy electrons, as well as the small probe size of these microscopes (typically < 5 nm).
Application of Crystal Orientation Mapping to Intra-Grain Misorientations
Authors: Davies Robert , Randlè Valerie
Published: July 2020

Crystal orientation mapping (COM), which is also referred to as orientation imaging microscopy (OIM), is a powerful tool which opens up enormous possibilities for investigation of materials. The principle of COM is that the microstructure is displayed or mapped according to the orientation of sampled volumes of crystal. These data are obtained in the scanning electron microscope by moving either the electron beam or the specimen stage through predetermined steps and collecting an electron back-scatter diffraction (EBSD) pattern. Typically, a null orientation is represented by a black pixel and colours are used to depict orientations, thus allowing discrete orientation changes such as grain boundaries to be plotted directly in a map format. This is exemplified in figure 1 which shows an orientation map generated from pure aluminium which has undergone 5% cold rolling. The diffiiseness of EBSD patterns further permits strain changes to be mapped.
Chemical Restructuring of Metal Surfaces Studied by Scanning Tunneling Microscope (STM)
Authors: Tanaka Ken-ichi
Published: July 2020

Metal surfaces undergo structural change by the dissociative adsorption of O2, where the reconstructuring is caused by either of the two distinctive mechanisms depending on the temperature and/or the crystalographic planes, one is the “adsorption induced reconstruction” and the other is the “formation of quasi-compounds and their array over the surface”.

The oxygen induced reconstruction of Cu(100) is the former case. When a Cu(100) surface is exposed to O2, oxygen atoms are adsored by making nano-size c(2x2) structure to avoid the convergence of the stress induced by the adsorption. When the oxygen coverage exceeds a critical value of ca 0.3 ML, Cu atoms are missed from the substrate surface to release the stress and the R45 reconstruction is established. In contrast to the Cu(l00) surface, an entirely different process takes place on a Cu( 110) surface exposed to O2, where the (-Cu-O-) string is formed and by a chemical array over the terrace occur.
Formation of Novel Cluster Compounds from Ternary Molybdenum Oxides by In- Situ Deintercalation
Authors: Ramlau R , Simon A , McCarley R E
Published: July 2020

Comprehensive studies by HREM, SAED, and EDXS have been recently devoted to the real structure of the ternary reduced molybdenum oxides in the series Mn±δMo4n+2O6n+4 with M = Sn,In. These compounds contain condensed clusters Mo4n+2O8n+10 with a core of n transedge-sharing molybdenum octahedra. The individual clusters are interconnected via common oxygen atoms. of course, the appropriate choice of counter-cations M is essential for the stability of the clusters, whose core of condensed molybdenum octahedra is a more or less extended metal-metal bonded structure. In tin oxomolybdates condensed clusters with n = 2,3 have been observed, in indium oxomolybdates with n = 3,4,5,6. In Sn2Mo10O16 and Sn2.8Mo14O22 each Sn atom provides 2 electrons to the cluster, in In5Mo18O28, e.g., with n = 4 an In5  7+ polycation, a metal-metal bonded unit itself, provides 7 electrons.

It became obvitalicous that both tin and indium oxomolybdates undergo a structure transformatitalicon when irradiated a 300kV electron mitaliccroscope (Philips CM30/ST, Cs = 1.15mm).
Size-Dependent Equilibrium Shapes of Solid Pb Inclusions in Al
Authors: Dahmen U , Johnson E , Xiao SQ , Paciornik S , Johansen A
Published: July 2020

Small Pb inclusions in Al have been studied by a number of investigators because the alloy system offers the possibility of observing the processes of melting and solidification directly. Both solids are fee, and the mutual solubility of solid Pb and Al is negligible. Despite a large difference in lattice parameter, it has been found that inclusions follow a parallel-cube orientation relationship and their equilibrium shape is a cuboctahedron, bounded by ﹛111﹜ and ﹛100﹜ facets [1]. Following Herring, the relative extent of the two types of facet directly indicates a ratio of interfacial energies γl00/γ111- However, recent investigations have shown that for inclusions in the range of a few to a few tens of nanometers the equilibrium shape becomes a function of size [2].

In the present work, this size dependence of the equilibrium shape has been investigated further. Al alloys with about lat.% Pb were prepared by rapid solidification or by ion implantation, and equilibrated by annealing at about 300°C.
Creation of Stacking Faults at Substrate Steps in Zns Thin Films Epitaxially Grown on GaAs (001)
Authors: Arnold Marcel , Wang ZL , Tong W , Wagner BK , Schön S , Summers CJ
Published: July 2020

Electroluminescence (EL)-based displays are an emerging technology for next generation flat panel displays. ZnS is an important component material for light emitting devices and EL-displays. To make this material useful for high efficiency and low voltage EL applications, the density of dislocations is required to be low. High quality single crystalline ZnS thin films have recently been grown by chemical beam epitaxy [1]. This paper focuses on studying the formation mechanism of stacking faults in the film and its relation with the interface structure between the substrate and the film [2].

Stacking faults are the main defects present in the film (Fig. 1). All four stacking faults (sf) are intrinsic and sf1, growing towards the left-hand side from the interface, is only of short range since after crossing sf2 the defect is terminated by a Shockley partial dislocation and the normal stacking sequence is restored. This is the mechanism that annihilates most of the stacking faults generated from the interface within the first 70 nm thickness range.
Atomic Structure of a Symmetric 27°[001] Tilt Grain Boundary in MgO
Authors: Yan Yanfa , Chisholm M F , Pennycook S J
Published: July 2020

The atomic structure of a symmetric 27° [001] tilt grain boundary in MgO has been determined by high-resolution Z-contrast imaging using a 300 kV VG HB603U scanning transmission electron microscope with a 1.3 Å probe. The atomic configuration in the grain boundary core is found to be considerably less open than the structures proposed earlier for similar materials.

Fig. 1 shows the Z-contrast image of the grain boundary and the projected structure derived from the image. It is clearly seen that the boundary is a shared plane of atoms with the same atomic column density as a bulk crystal {100} plane. The boundary consists of an array of separated perfect edge dislocation cores with Burgers vector b= a<100>. It is interesting to point out that the spacing between dislocation cores in the boundary is not uniform (as seen in Fig. 2). The arrangement, which follows the Fibonacci sequence, can be accurately predicted.
Electronic Structure Studies of Impurities In Fe.
Authors: Alvarez Jose R , Rez Peter
Published: July 2020

Small concentrations of impurities can dramatically change mechanical properties of metals and alloys since they modify bonding and cohesion at grain boundaries. In particular, impurities like B, C, P and S have received considerable attention for their effect on the mechanical properties of Fe. It is known that B and C behave as cohesive enhancers, whereas P and S tend to embrittle iron. Ab initio electronic structure calculations for supercell models of Fe crystals with B, C, P and S impurities have been performed to understand how these impurities modify the electronic states on surrounding atoms The calculations give the charge density distribution, localized densities of states (LDOS) and the total energy of the system. The angular momentum resolved LDOS, when multiplied by slowly varying matrix elements, can be directly related to the experimentally measured electron energy loss near edge structure.

The calculations have been performed using two different methods. One is the Linearized Augmented Plane Wave (LAPW) method, in which the Kohn-Sham equations of density functional theory are self-consistently solved within the Local Density Approximation (LDA) to obtain energies and charge distributions of a crystalline system.
Transformation Twinning and Twinning Crystallography in PrCo2Cx Magnets
Authors: Wu Lijun , Zhu Yimei
Published: July 2020

Pr-Co permanent magnets have attracted much attention recently due to their excellent magnetic properties and low cost; these properties can be further improved by adding small amount of carbon. In this paper, we describe the mechanism of structural transformation resulting from carbon doping in PrCo2 crystals.

We identified the heavily twinned PrCo2Cx (x=0.05-0.25) as a rhombohedral phase with space group Rm. Fig.1 shows its typical morphology of the (110) and (211) primary twins and (110)(211) secondary twins together with the corresponding diffraction patterns. We note that the Bragg spots split along the [hh0]* direction, and that the splitting increases with distance from the [110]* row. The splitting (or α angle of the rhombohedral lattice) also varies with carbon concentration.

Because PrCo2 is an untwinned FCC phase (Fdm), the formation of a twin in PrCo2Cx caused by adding carbon atoms apparently is driven by a minimization in lattice strain, which also is the origin of the cubic-rhombohedral phase-transformation.
Atomic Structure of [110] Tilt Grain Boundaries in FCC Materials
Authors: Merkle L , Thompson L J
Published: July 2020

High-resolution electron microscopy (HREM) has been used to study the atomic-scale structure and localized relaxations at grain boundaries (GBs) in Au, Al, and MgO. The [110] tilt GBs play an important role in polycrystalline fee metals since among all of the possible GB geometries this series of misorientations as a whole contains the lowest energies, including among others the two lowest energy GBs, the (111) and (113) twins. Therefore, studies of the atomic-scale structure of [110] tilt GBs in fee metals and systematic investigations of their dependence on misorientation and GB plane is of considerable importance to materials science. [110] tilt GBs in ceramic oxides of the fee structure are also of considerable interest, since in this misorientation range polar GBs exist, i.e. GBs in which crystallographic planes that are made up of complete layers of cations or anions can join to form a GB.

Thin singlecrystalline films of (110) Au were prepared by vacuum evaporation of Au onto (110) NaCl.
Origin of Robust Superconductivity at Twist Boundary in Bi/2212 Bicrystals
Authors: Bailey GW , Dimlich RVW , Alexander KB , McCarthy JJ , Pretlow TP , Zhu Yimei , Li Q , Tsay YN , Sabatini R , Suenaga M
Published: July 2020

We systematically investigated the structure and properties of [001] twist boundaries using Bi2Sr2CaCu2O8+δ (Bi/22112) bicrystals. Contrary to conventional wisdom, all these boundaries, regardless of their misorientation angle, carried the same critical current as their constituent single crystals in magnetic fields up to 9 tesla. Fig. 1 shows the ratio of the critical currents across a grain boundary to that within the grain interior as a function of misorientation of the boundaries. In striking contrast to the results of Dimos et al. with YBa2Cu3O7−δ, the twist boundaries in our bicrystals are not a limiting obstacle for supercurrent.

The origin of the robust superconducting behavior at these twist boundaries was sought by detailed structural characterization using various TEM techniques. Several notable structural features were observed: 1) all the boundaries were clean, structurally intact without any visible amorphous materials; 2) nano-probe EDS and EELS measurements showed that there was no detectable off-stochiometric composition, including oxygen/hole concentration along and across the boundaries; 3) HREM image simulation revealed that the boundaries were located in the middle of the double BiO layers without exception (Fig.2); 4) there was no detectable boundary expansion, contrary to general expectation, and the inter-planar distance of the double BiO layer {dBio =0.309± 0.005nm, measured with line-scan (Fig.3)) at the boundary was the same as those far from the boundary within measurement error; and 5) very often, there was an intercalation of a Ca/CuO2 bi-layer near the boundary, either on one, or both sides, forming a local Bi/2223 structure (Fig.2).
{111} Planar Faults in a Quenced and Annealed NiAl-0.3Hf Single Crystal Alloy
Authors: Garg A , Noebe R D , Hull D R
Published: July 2020

Quenched-in vacancies, vacancy agglomeration and solute-vacancy association can play a significant role in affecting the mechanical behavior of an alloy. It is well known that B2- NiAl can retain a high supersaturation of thermal vacancies which has been shown to manifest itself as dislocation loops, voids, or spiral dislocations. Dislocation climb loops formed in NiAl have been observed to emanate from impurity particles as concentric {100} loops which are prismatic in nature1. Impurity particles have also been shown to be responsible for nucleating faceted voids. However, addition of alloying elements can alter this mode of vacancy condensation and depending upon the degree of interaction between alloying element and vacancies, a completely different defect structure can result. In a recent study, addition of Boron to Fe-35 mol. % Al has been shown to produce complex {100} planar faults having both APB and stacking fault character, whereas Cr, Pd and W produced APBs on {111} planes.
Observation of Ordered Ti3Al5 Precipitates in Slightly Aluminum Rich γ-TiAl
Authors: Jayanthi S , Wiezorek JMK , Swaminathan S , Fraser HL
Published: July 2020

It is the accepted wisdom that off-stoichiometric TiAl alloys with slightly Aluminum rich compositions, e.g. Ti-52 at.% Al and Ti-54 at.% Al, exist as single phase materials. However, previous studies have reported that Ti3Al5 ordering occurs in Al rich γ-TiAl of compositions 54-63 at.% Al [1,2]. The Ti3Al5 ordering involves the substitution of excess Al into selected Ti sites on the pure Ti plane (001) [1]. In the current work such Ti3Al5 ordering has been observed in TiAl alloys of compositions ranging from Ti-52 at.% Al to Ti-56 at.% Al which have been produced as described in earlier reports [e.g. 3].

Experimental and simulated selected area diffraction patterns (SAD) for the [111] zone axis of TiAl are shown in figure 1. A row of extra reflections which appears between the reflections corresponding to the Ll0 structure are clearly visible in the diffraction patterns obtained from the Ti-54 and 56 at.% Al alloys (Fig. 1b,1c).
HRTEM Study of a Modulated Structure in Homologous Compounds In2O3(ZnO)m
Authors: Bando Yoshio , Li Chunfei , Nakamura Masaki , Kimizuka Noboru
Published: July 2020

The structure of the homologous compounds InMO3(ZnO)m (M=In, Fe, Ga, and Al, m=integer) is considered to be a layered structure, consisting of InO2  1− layer (In-O) ) interleaved with MZnmOm+1  1+ layers (M/Zn-O) along the c-axis. In the M/Zn-O layers, the distribution of two kinds of metal atoms is considered to be random fashion from X-ray diffraction analysis. However, in the previous HRTEM study of InFeO3(ZnO)m with m larger than 6, we found a modulated structure, where the image contrast showed a sinusoidal modulation curve present only in the Fe/Zn-O layers. Elemental analysis by EDS clarified that the modulated structure was caused by the ordering of Fe atoms within the Fe/Zn-O layers. In the present study, we try to observe In2O3(ZnO)m compounds, where Fe3+ atoms are replaced by In3+ atoms which have larger ionic radii. We are interested in whether the replacement of Fe3+ by In3+ atoms may cause any structural changes between In2O3(ZnO)m and InFeO3(ZnO)m.

The samples were prepared by heating powders of In2O3 and ZnO sealed in Pt tube at 1350 °C for about 3 days and then rapidly cooled down to room temperature. The electron microscope observation was performed by using JEM-2000EX, operated at an accelerating voltage of 200 kV.
Microstructural Characterization of Annealed Samples of Pure-Yttria Using Electron Microscopy
Authors: Banerjee S , Gouma P I , Mills M J
Published: July 2020

Yttria is an electroceramic material that has a negative temperature coefficient of resistivity (i.e. it is an NTC type semiconductor). This property, along with its high melting point and good stability, makes yttria a potential sensor material (thermistor) for measuring temperature differences in demanding applications. Recently there has been increasing interesting in studying this ceramic material. How-ever, there is very limited published information on the microstructural characteristics of pure yttria processed under various conditions. Furthermore, reported evidence on the effect of processing conditions on the electrical response of the material is still lacking. Studies within our Center have revealed a correlation between aging time and electrical behaviour in pure yttria samples. The present study examines the evolution of the microstructure of sintered yttria powder during different annealing treatments.

Yttria pellets (6mm diameter, 2mm height) were cold pressed and then sintered at 1550°C for 24h in air. The sintered pellets were then annealed at 1100°C for different times. Specimens for SEM examination were prepared by grinding the surface of the pellets (using grit paper up to 400) and subsequently polishing them using l μm alumina powders.
The Formation Process of the Microstructure of Al2O3-Al3Ti-Al In-Situ Composite
Authors: Luo HH , Wang DZ , Peng HX , Liu Cheng , Yao CK
Published: July 2020

In the last decade, new in-situ processing techniques, such as DIMOX™, XD™, VLS and SHS, for fabricating metal and intermetallic matrix composites have emerged. It is expected that the in-situ formed composites may reveal not only excellent dispersion of fine reinforcing particles, but high thermodynamical stability and high temperature performance. The fully dense Al2O3-Al3Ti-57Vol%Al composite was in-situ processed by combing combustion synthesis with squeeze casting utilizing the reaction between TiO2 powder (with average diameter of 0.6μm and volume fraction of 14%) and pure Al (99.5%). First, the 14Vol%TiO2/Al bulk materials were fabricated via squeeze casting method, subsequently, the TiO2/Al materials were heat treated to form final in-situ composites. Using XRD, SEM, TEM and HRTEM techniques, the microstructure and its evolution were investigated.

The X-ray diffraction pattern of the composite is shown in Fig.1 which indicates that the composite is composed of A12O3, Al3Ti and Al. According to the reaction formula between TiO2 and Al the volume fraction of Al in the composite is about 57%. Fig.2 is a typical scanning electron micrograph of the composite.
The Stability of BN Interfacial Coatings in CFCC Systems During Oxidation and Exposure to Moisture
Authors: Ailey KS , More KL , Lowden RA
Published: July 2020

The mechanical reliability of ceramic matrix composites (CMCs) at elevated temperatures in oxidative environments is primarily dependent upon the chemical and structural stability of the fiber/matrix interface. Graphitic carbon coatings have traditionally been used to control the interfacial properties in CMCs, however, their use is limited in high temperature oxidative environments due to the loss of carbon and subsequent oxidation of the fiber and matrix. Thus, BN is being investigated as an alternative interfacial coating since it has comparable room temperature properties to carbon with improved oxidation resistance. The stability of BN interfaces in SiC/SiC composites is being investigated at elevated temperatures in either flowing oxygen or environments containing water vapor. The effect of several factors on BN stability, including crystallographic structure, extent of BN crystallization, and impurity content, are being evaluated.

Nicalon™ fiber preforms were coated with ≈ 0.4 μm of BN by CVD using BCl3, NH3, and H2 at 1373 K. The coated preforms were densified using a forced-flow chemical vapor infiltration (FCVI) technique developed at ORNL.
A Microstructural Study of Hot Pressed and Reactive Sintered Beta-Silicon Nitride Coated with Alumina
Authors: Ghosh G , Vaynman S , Fine M E
Published: July 2020

Silicon nitride-based or SiAlON ceramics are increasingly being considered for many engineering applications due to their low density, high strength, and high modulus. For many engineering applications SiAlON ceramics are required to have, among many other properties, both high fracture toughness and good tribological properties. Typically, an interlocking microstructure consisted of β-Si3N4 and/or β'-SiAlON grains is produced, by sintering Si3N4 with desirable additive(s), with a residual glassy or partly crystalline grain boundary phase. The fracture process in such a microstructure is predominantly intergranular, the cracks tend to follow a tortuous path. However, the presence of an intergranular glassy phase causes rapid deterioration of properties at temperature above the glass transition temperature. Therefore, in order to improve high-temperature properties of these ceramics it is desirable to minimize, and if possible to eliminate, the intergranular glassy phase. Particle coating techniques are receiving increasing attention as they are convenient ways of incorporating sintering aids/dopants more uniformly than conventional powder blending method.
Cathodoluminescence Investigation of Electron Irradiation Damage in Insulators.
Authors: Stevens Kalceff MA , Phillips MR , Moon AR
Published: July 2020

Cathodoluminescence (CL) is the luminescent emission from a material which has been irradiated with electrons. Cathodoluminescence microanalysis (spectroscopy and microscopy) in an electron microscope complements the average defect structure information available from complementary techniques (e.g. Photoluminescence, Electron Spin Resonance spectroscopy). CL microanalysis enables both pre-existing and irradiation induced local variations in the bulk and surface defect structure to be characterized with high spatial (lateral and depth) resolution and sensitivity. This is possible as electron beam parameters such as the beam energy, may be varied to finely control the penetration depth of the incident electrons and hence the local volume of specimen probed.

Irradiation with charged and neutral energetic radiation produces defects in radiation sensitive materials. The energetic electron beam in an electron microscope may also induce defects in the specimen. Cazaux has characterized the electric field produced by electron irradiation of a insulator with a conductive surface coating
Electron Microscopy Study of Surface Layers of The French Son68 Nuclear Waste Glass Formed During Vapor Phase Alteration At 200 °C
Authors: Gong WL , Wang LM , Ewing RC
Published: July 2020

The objective of this study was to simulate the aqueous corrosion of the nuclear waste glass over extended periods of time using vapor phase alteration by which reaction progress of glass corrosion is accelerated to form a characteristic suite of secondary alteration phases. In this study, extensive SEM/EDS, AEM, and HRTEM have been performed on the French SON68 waste glasses which were reacted in saturated water vapor at 200 °C for 908, 1013, and 1021 days, respectively. In order to study chemistry and microstructure of surface layers, TEM specimens were prepared in cross-section using the ultramicrotomy slicing technique. In this process, small chunks containing the surface layer and a thin layer of unaltered glass were broken off from the sample surface and each of these chunks was then embedded in resin to form a block. Finally, thin sections, approximately 50-90 nm thick, were microtomed from these blocks and were transferred to holey carbon coated copper grids.
High-Resolution Transmission Electron Microscopy of Defects in Todorokite (Oms-1)
Authors: Turner S , Buseck PR
Published: July 2020

Todorokite is a manganese oxide mineral that occurs in widespread terrestrial and marine deposits. It is a major component of manganese nodules which occur in large quantities on ocean and some lake floors (>1012 tons). Todorokite has been linked to the presence of potentially mineable transition elements in manganese nodules. Todorokite is an octahedral molecular sieve material and has been termed by some in the chemical community as OMS-1. Many of the properties of synthetic and natural varieties have been characterized and potential applications include use for adsorption, as oxidation catalysts and in electrochemical devices.

The todorokite structure consists of a framework of MnO6 octahedra that are edge- and corner-linked to form tunnel structures. Several tunnel structures have been found in naturally occurring todorokite ranging from the most basic 3×3 structure to 3×8 and larger structures. Large cations and water occur in the tunnel interiors.
Oxidation Mechanism of Ferritic Stainless Steel Used for Catalytic Converters in Automotive Exhaust Systems Studied by TEM
Authors: Liu Ping , Andersson Jan
Published: July 2020

Emission of pollutants from automobiles is regarded as one of the major causes of air pollution in many cities around the world. However, the pollutants could be almost eliminated by using catalytic purification of exhaust gas, thus making a better environment. The metallic material for catalytic converters made of ferritic stainless steel, Sandvik 0C404 (20.0 Cr-5.0 Al-Fe balance in wt % plus the addition of rare earth elements), offers a number of advantages over a ceramic one: better thermal conductivity, higher mechanical strength and toughness, thinner walls, larger effective area, greater catalytic capacity, smaller and more flexible design; better resistance to thermal shock. The formation of a homogenous A12O3 layer at high temperature is essential for providing corrosion resistance in such applications because of its high corrosive environment.

A prolonged oxidation of ferritic stainless steel Sandvik 0C404 at 1100 °C resulted in an accelerated oxidation (as schematically illustrated in Fig.l).
Characterization of Adhesive-Primer Penetration into Porous Oxides Formed on Anodized Aluminum Using Energy Electron Loss Spectroscopy (Eels)
Authors: Cole J I , Brien D O' , Qian M , Fisher R M
Published: July 2020

The purpose of this investigation is to evaluate the effects that relatively minor changes in phosphoric acid anodizing (PAA) parameters (voltage, temperature, time) have on oxide morphology and the subsequent penetration of an applied adhesive-primer into the porous oxide. This preliminary study examines two cases, one in which industry-standard PAA parameters have been followed, and a second in which the PAA parameters are slightly above industry limits.

Baseline PAA parameters have been developed in the aerospace industry from extensive empirical testing in order to maximize adhesive bond strength and durability in the presence aggressive environments. It has been noted that for effective mechanical strength of structurally bonded elements, penetration of the adhesive primer into the porous oxide formed by an anodizing pre-treatment is critical. Verifying primer penetration is somewhat problematic due to the high spatial resolution required to both structurally and chemically characterize an oxide film on the order of one micron in thickness.
Microstructural Effects on the Scc Morphology of Alloy 600 in Deaerated Water
Authors: Burke MG , Symons DM
Published: July 2020

Previous studies on the stress corrosion cracking (SCC) behavior of Alloy 600 forgings revealed a correlation between the SCC susceptibility and thermomechanical processing (specifically the final annealing temperature). (1) Detailed microstructural analyses using analytical electron microscopy (AEM) techniques showed that the materials containing dendritic-type intergranular M7C3 carbides were also more resistant to SCC initiation and propagation. This type of analysis has been extended to the evaluation of a 0.062 wt.% C Alloy 600 plate in three conditions (as-received, and heat-treated for 1 week at 982°C and water-quenched, and annealed for 24h at 1075°C and furnace-cooled). Tests were performed in PWR environments using fatigue precracked compact tension (CT) samples. In addition, detailed microstructural analyses using light optical metallography (LOM) and AEM were performed to fully characterize each material condition. The SCC fracture morphology was evaluated using scanning electron microscopy (SEM).

LOM examination of the as-received material indicated a “good” microstructure, with carbide-decorated grain boundaries as well as intragranular carbides.
Correlation of Measured Thermal Conductivity to a Functionally Graded Material's Microstructure
Authors: Phelps John , Slifka Andrew , Filla James
Published: July 2020

Functionally Graded Materials (FGMs) are used in a number of applications as a protective barrier to extreme environments. One such application of FGMs is to protect metal parts from high temperature environments. FGM coatings are plasma spray deposited onto surfaces of both simple and complex machined parts. Knowing the thermal conductivity of the FGM coating allows engineers to effectively develop high temperature designs with accurate estimates of heat transfer and thermal loading.

In this study, a FGM made by Caterpillar, USA, was measured with our steady state thermal conductivity measurement apparatus. The sample measured is a 10 layer graded coating using a Metro* 461 bond coan4 to a Metco* 205 ceria-yittria stabilized zirconia, with a Ni-Co-Cr-Al-Y metal grading. Figure 1 shows a plot of the thermal conductivity (W/m*K) as a function of temperature (K) for this material. The sudden drop in thermal conductivity at approximately 1073K was totally unexpected
Recent Developments in Fluorescence Spectroscopy: Light Quenching and Multi-Photon Excitation with Tir, Two-Color Two-Photon Excitation and Long Lifetime Probes
Authors: Lakowicz Joseph R
Published: July 2020

Fluorescence spectroscopy is presently enjoying explosive growth due to new experimental capabilities. In this talk we summarize some recent advances which can have applications in cell biology and imaging.

We show that evanescent illumination at one wavelength and incident angle, coupled with light quenching at a second wavelength and incident angle (Figure 1), can be used for selective excitation of fluorophores located up to 5000 Å into the aqueous phase. The use of combined evanescent wave excitation and evanescent wave quenching could provide selective excitation of fluorophores in the cytoplasmic region of cells. We also reported the first experimental observation of two-photon excitation using the evanescent wave resulting from total internal reflection. Two-photon excitation of the calcium probe Indo-1 was demonstrated by the quadratic dependence on intensity (Figure 2) as well as by the anisotropy and time-resolved fluorescence measurements.

Two-photon excitation is routinely performed using a single wavelength. We recently observed two-photon excitation of organic fluorophores with two different wavelengths, a phenomenon we refer to as two-color two-photon excitation.
Pulsed Laser Imaging Techniques: Calcium and Exocytosis in Excitable Cells.
Authors: Fernandez JM
Published: July 2020

A rapid Ca++ signal is known to be the main trigger for exocytosis in excitable cells. However, its mode of action is unknown. Recently, it has become clear that the spatial distribution of a Ca++ stimulus is important for exocytosis. To investigate this question we have developed a novel instrument capable of imaging Ca++ gradients in patch clamped cells. We have equipped a standard fluorescence microscope with a CCD camera and an image processing station. This combination can generate a thin section view of the fluorescence of a single cell. We have equipped this microscope with a pulsed laser illumination system. The distribution of intracellular calcium can be obtained by exciting the Ca++ indicator dye (e.g., rhod-2) with a brief laser pulse [300 ns long at 525 nm ], then an image can be formed with the light emitted by the dye. by synchronizing the laser pulse with a depolarizing stimulus in a patch-clamped chromaffin cell loaded with the fluorescent Ca++ indicator rhod-2, we could easily obtain snapshots of the Ca++ distribution at known times after a stimulus.
Design of a Wide Field High Sensitivity Imaging System for Quantitative Analysis of CGHA Micro-Arrays.
Authors: Sudar Damir , van Vliet Lucas , Clark Steve , Segraves Rick , Lockett Stephen , Albertson Donna , Gray Joe , Daniel Pinkel
Published: July 2020

Comparative Genomic Hybridization (CGH) is a quantitative technique for determining relative copy numbers of DNA sequences in whole-genomic test samples. In conventional CGH, test DNA labelled with one fluorochrome and reference DNA labelled with a spectrally different fluorochrome are hybridized to metaphase chromosomes. by measuring the ratio of intensities of the two fluorochromes, a relative copy number of sequences in the test DNA can be calculated for each point along each chromosome. While this approach is very useful for rapid surveying of the entire test genome, the spatial and dynamic resolution are compromised by the dense packing of DNA in the metaphase state. CGHa (array-based CGH) uses spots of cloned DNA arrayed onto a microscope slide which represent the entire genome or interesting sections thereof. Spatial resolution and dynamic range are now only limited by the size of the clones used. See the abstract by Pinkel et al. for more detail.

We designed an imaging system for analyzing fluorescence signals from micro-arrays containing targets on the order of 100μm in diameter spaced at similar intervals.
Two-Photon Laser Scanning Confocal Microscopy
Authors: Cheng PC , Pan SJ , Shih A , Liou WS , Park MS , Watson T , Bhawalkar J , Prasard P
Published: July 2020

Two-photon fluorescence microscopy has become an important research tool in both biological and material sciences. The technique uses long wavelength, typically in the near IR, as the excitation light to obtain shorter wavelength fluorescence (e.g. visible light). Because of the low linear absorption coefficient of most biological and polymeric specimens, this technique allows deeper penetration of the excitation beam, achieving optical sectioning to a depth of 250μm or more into the specimen. As a result of the quadratic dependency of the two-photon induced fluorescence to the excitation intensity, the fluorescent emission and photobleaching are limited to the vicinity of focal spot. This capability of addressing a specimen’s 3D space allows exciting possibilities in biological researches, such as 3D photobleaching recovery experiment.

Two-photon confocal fluorescence microscopy is ideal for the study of thick biological and material specimen in 3D. For example, Figure 1 shows a three-dimensional isosurface rendered image of a vascular bundle from a maize stem.
Near Edge X-Ray Absorption Fine Structure (NEXAFS) Microscopy: Chemical Analysis at Sub Visible Spatial Resolution
Authors: Ade H
Published: July 2020

Infrared, Raman, and fluorescence/luminescence microspectroscopy/microscopy in many instances seek to provide high sensitivity compositional and functional information that goes beyond mere elemental composition. This goal is shared by NEXAFS microscopy, in which Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is employed to provide chemical sensitivity and can be relatively easily adopted in a scanning transmission x-ray microscope (STXM). In addition to compositional information, NEXAFS microscopy can exploit the dependence of x-ray absorption resonances on the bond orientation relative to the linearly polarized x rays (linear dichroism microscopy). For compositional analysis, NEXAFS microscopy is analogous to Electron Energy Loss Spectroscopy (EELS) in an electron microscope. However, when utilizing near edge spectral features, NEXAFS microscopy requires a considerable lower dose than EELS microscopy which makes it very suitable to studying radiation sensitive materials such as polymers. NEXAFS has shown to have excellent sensitivity to a wide range of moieties in polymers, including sensitivity to substitution isomerism.
Deltascan, a Light Microscope Imaging System for Examining Birefringent Materials.
Authors: Lewis JG , Glazer AM
Published: July 2020

DELTASCAN is a new light microscopy imaging system developed and built in the Department of Physics, Oxford, UK. [1] It is able to separate out the contrast seen in a ‘cross-polars’ image into three components, | sin δ | (a function of the optical retardation), φ (the orientation of a section of the optical indicatrix) and Io (the transmittance). These three variables are plotted as separate coded colour images. With the present computer and apparatus the data is collected, processed and the images simultaneously drawn in approximately 40 seconds.

DELTASCAN has an optical setup [2] based around a polarising microscope (Figure 5). The intensity through this optical setup can be shown to have the form:

I = Io[1 + sin2(ωt−ϕ)sin δ] (1)

where ω = frequency of the analyser, φ = orientation of cross section of the indicatrix and, δ = relative retardation which is related to a samples birefringence by δ = 2πΔnL/λ.
Full Spectrum Raman Imaging of Glasses and Other Materials
Authors: Morris Michael D , Jestel Nancy L , Christensen Kenneth , Shaver Jeremy M
Published: July 2020

Several spectral bands or regions often are required for contrast generation to utilize the full power Raman imaging for mapping compositional or physical property variations. To achieve this, it is most efficient to use a high throughput imaging spectrograph with a two-dimensional detector operated in pushbroom mode as a line imager. Despite data from several bands, univariate data reduction techniques are inadequate when characterizing complex materials. Multivariate statistical procedures, such as factor analysis, are useful for defining weighted sums of intensities from many Raman shifts (frequencies) and this in turn expresses chemically or structurally useful contrast.

We illustrate this approach with silicate and aluminosilicate glasses. In most cases, no single band can unambiguously identify a particular glass composition. If the glass is heterogeneous, then localized compositional and structural differences may be detected by small changes in several bands, all arising from motions of assorted Si-O moieties.
Infrared Microspectroscopy in Earth and Planetary Science: Recent Developments, Including In Situ High-Pressure, High-Temperature Techniques
Authors: Hofmeister AM
Published: July 2020

Vibrational spectroscopy is used in Earth science for both quantitative and qualitative analysis. This report focuses on infrared (IR) spectroscopy, although similar efforts are on-going in Raman spectroscopy.

Qualitative studies utilize the fact that the vibrational spectrum is a characteristic of a material: hence comparison to a set of standards allows for identification of the phase. Most of these types of studies in Earth science involve macrosamples, but measurements of microsamples from meteorites are on interest in order to identify the structure of SiC inclusions and the type of organic compounds in interplanetary dust. As most of these samples are micron sized, which is below the diffraction limit for the mid-IR, the approach has been to compress the sample using a diamond anvil cell (DAC) into a disk of sub-micron thickness, adhere the sample to a KBr plate, and to subsequently remove the disk from the DAC and obtain spectra with the aid of an FTIR microscope.
Application of Epma Area Analysis To Thickness Measurement of Thin-Films
Authors: Takakura M , H.Takahashi  , Kondo Y , Okumura T , Nielsen C
Published: July 2020

Electron Probe Micro Analyzer (EPMA) uses the characteristic X-ray for analysis. Therefore the depth of analysis area is spread to a few micrometer. It is difficult to make the quantitative or state analysis of surface thin-film. However, it is possible to measure the thickness of thin-film by using the X-ray intensity ratio between the film and bulk standard specimen under an assumed X-ray depth distribution function. In this paper, a known composition thin-film was measured by EPMA and the result was applied to thin-film area analysis.

Film thickness was measured as mass thickness (ρz) by the intensity ratio of the characteristic X-ray intensities between the thin-film and bulk standard. As the X-ray distribution function ϕ(ρz) the model due to Packwood and Brown1) was used, which is written as.

(1)

An error is thought to exist in the thickness calculation because the backscattering yield near the interface is different when the difference in the atomic numbers is large between the thin-film and the substrate.