bluuebunny/crossref_metadata_2025 huggingface dataset:
HREM and LORENTZ Microscopy Studies on Sm(Co,Cu,Fe,Zr)z High Temperature Permanent Magnets
Authors: Zhang Y , Tang W , Hadjipanayis GC , Chen C , Liu JF , Nelson C , Krishnan K , Luo ZP , Miller DJ
Published: July 2020

Sm(Co,Cu,Fe,Zr)z 2:17 based permanent magnets have the highest Curie temperature and the most excellent temperature stability among the current rare-earth permanent magnets. in recent years, the Sm(Co,Cu,Fe,Zr)z magnets have attracted again considerable attention due to the demand of the Department of Defense for high temperature applications such as aircraft, spacecraft and ship systems. Our recent studies have led to the development of new precipitation hardened Sm(Co,Fe,Cu,Zr)z magnets with operating temperatures above 400°C and with coercivities as high as 10 kOe at 500°C. The microstructure of the Sm(Co,Cu,Fe,Zr)z high temperature magnets consists of a cellular structure (2:17 rhomobohedral cells surrounded by 1:5 hexagonal cell walls) superimposed on a lamella phase (2:17 hexagonal). This microstructure is sensitive to processing and to the alloy chemical composition. Magnetic domain structure studies play a critical role in understanding the magnetic hardening behavior of the magnets. in this paper, HREM and magnetic domain structure were studied in these Sm(Co,Cu,Fe,Zr) high temperature permanent magnets.
Future Direction of High-Resolution X-Ray Microanalysis in the AEM
Authors: Watanabe M , Williams DB
Published: July 2020

Current commercial analytical electron microscopes (AEMs) including scanning transmission electron microscopes (STEMs) are a compromise design between the highest spatial, analytical and energy resolutions. in contrast, a VG HB603 STEM at Lehigh University has been designed with a 300 kV cold field-emission gun and twin X-ray detectors to maximize X-ray generation and collection efficiencies [1]. in addition, instrumental features of almost no stray radiation, ultra-high vacuum (<10−7 Pa in the stage and <10−7 Pa in the gun), beam blanking and direct probe-current measurement in the HB 603 have transformed the approaches to quantitative analysis. By using such modern AEMs, it is now possible to perform X-ray microanalysis with the spatial resolution as low as 1.5 nm and the detectability limits of∽2 atoms in the analyzed volume [2]. Furthermore, even quantitative X-ray mapping becomes achievable, while maintaining, high spatial resolution (the original aim of such instruments) [3].
Atomic Scale Characterization of Oxygen Vacancy Ordering in Oxygen Conducting Membranes By Z-Contrast IMAGING and EELS
Authors: Klie RF , Browning ND
Published: July 2020

Mixed conductors have been the focus of many studies in the last decade, leading to a detailed understanding of many of the macroscopic bulk properties of these materials. in particular, although the reduced low temperature phase in rare earth perovskite oxides is commonly explained in terms of ordered brownmillerite structured micro domains, its transition to the high temperature phase remains elusive. in this presentation an investigation of (La, Sr)FeO3, prepared under different reducing conditions through correlated atomic resolution annular dark field imaging and electron energy loss spectroscopy will be shown.

We investigate the (La, Sr)FeO3 material by atomic resolution Z-contrast imaging and EELS using a 200 keV STEM/TEM JEOL2010F with a post column GIF. The combination of these techniques allows us to obtain direct images from the atomic structure of the bulk sample and to correlate this with the atomically resolved EELS information. In-situ heating of the material in a heating double tilt holder in the microscope columns allows us to simulate the highly reducing operating conditions for this oxygen conducting membrane material.
Determination of the Width of the GaN/AlxGa1-xN Heterointerface Using EELS
Authors: Mkhoyan KA , Alldredge ES , Silcox J , Ashcroft NW
Published: July 2020

It is known that wurtzite III-V nitrides are highly polarized in the c-direction, which is usually the growth direction. This polarization (spontaneous and piezoelectric) in GaN/AlxGa1-xN heterostructure field effect transistors (HFET) results in high carrier concentrations at the interfaces, in addition to the large conduction band offset. This high-density 2D electron gas formed at a GaN/AlxGa1-xN heterointerface in its turn increases the mobility of the heterostructure. Therefore, questions about the measurement of the physical width of a GaN/AlxGa1-xN interface and the calculation of its effects on the physical characteristics of devices naturally arise. Since the electrical field distribution, as well as the location and density of the 2D electron gas, depends on the width of the GaN/AlxGa1-xN heterointerface, accurate determination of the width is critical.

Measurements with high spatial resolution EELS using transmission electron spectroscopy with a ∽2Å focused electron beam permits atomic-level studies of such specimens.
Quantitative Measurement of Compositional Enrichment in Strained Alloy Quantum Dots
Authors: Crozier PA , Catalano M
Published: July 2020

High spatial resolution information on the structure and composition of semiconductor quantum dots is necessary to relate microstructure to macroscopic electron-optical properties [1]. Scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) can be used to determine the elemental composition of nanometer-sized particles. Applying these techniques to quantum dots is challenging because the dot nucleates on a very thin wetting layer of similar composition and is embedded in a matrix. Here we present a strategy to extract absolute compositional information on InGaAs dots. The method relies on modeling both the dot shape and the electron probe profile.

Samples were prepared by depositing four monolayers of In0.5Ga0.5As onto a GaAs substrate giving a nominal wetting layer thickness of 1.2 nm [2]. STEM was performed on a Vacuum Generator's HB501 equipped with a GATAN parallel electron energy-loss spectrometer. An ES Vision system was used to acquire spatially resolved electron energy-loss spectra from the wetting layer and the quantum dots.
Extraction of Quantitative Magnetic Data Using Transmission Lorentz Microscopy
Authors: Chapman J N
Published: July 2020

The study of magnetic thin films by Lorentz microscopy in the transmission electron microscope (TEM) is a well-established technique. However, in many instances, images are recorded with the specimen in its as-grown state or in a single remanent state following application of a magnetic field outside the microscope. Although such images can provide valuable information, they rarely produce insight into the mechanism by which the magnetic material reverses nor do they show the magnetic structures that form during the reversal process. Furthermore, it is not possible to determine, for example, the field range over which a reversal takes place. Given the importance of such elements for magnetic sensing and storage applications, there is considerable incentive to develop techniques which not only yield the magnetisation loop for an individual element but which reveal how the spatial distribution of magnetisation evolves as a function of field.
Fluctuation Microscopy in the STEM
Authors: Voyles P M , Muller D A
Published: July 2020

Fluctuation microscopy is an electron microscopy technique sensitive to medium-range order (MRO) in disordered materials. It has been applied to study amorphous germanium and silicon, leading to the conclusion that these materials exhibit more MRO than the conventional continuous random network model for their structure.

As originally proposed by Treacy and Gibson, fluctuation microscopy utilizes mesoscopicresolution (1.5 nm) hollow-cone dark field (HCDF) imaging in a TEM. The normalized variance of such images,

is a measure of the magnitude of fluctuations in the diffracted intensity from mesoscopic volumes of the sample and is sensitive to MRO via the three- and four-body atom distribution functions. Studying V as a function of the diffraction vector magnitude k gives information about the degree of MRO and the internal structure of ordered regions. V as a function of the inverse resolution Q gives information about the characteristic MRO length scale.
A 2-2-2 200kv Field Emission STEM/TEM System
Authors: Boyes E D , Ringnalda J , Stam M A J van der , Fliervoet T F , Cappellen E Van
Published: July 2020

In many new application areas it is necessary to combine atomic resolution imaging with atomic level chemical and crystallographic analysis. The new applications include microbiology, nanotubes, smart materials and sensor initiatives, and the myriad semiconductor fields. Along with these there are many other valuable applications in older and more established technologies such as chemicals, catalysis, pigments and construction materials for chemical plants, airplanes, pipelines, power generation, and other aspects of societal infrastructure. Analysis down to the atomic level will help to solve recalcitrant problems and open up some reluctant opportunities in these fields. They can be very effective in resolving important and long standing issues with huge potential monetary and societal costs and benefits. Key aspects of environmentally sensitive corrosion and pollution control may also require the support of similarly sophisticated imaging and microanalysis.

We think the capabilities of a new generation high performance instrument should include atomic resolution coherent TEM imaging and also incoherent atomic number (Z) contrast high angle annular dark field (HAADF) STEM imaging.
Quantitative Characterization of Internal Boundaries — What Can Be Achieved with Electron Microscopy?
Authors: Elsasser Christian , Rühle Manfred
Published: July 2020

Internal boundaries in crystalline microstructures, like polycrystals, thin-film or multi-layer composites, essentially control many important material properties and physical phenomena, such as mechanical deformation and fracture, transport processes or phase transformations. This influence is originating from the local atomistic and electronic structures at the boundaries. Hence, for a. science-based technological design and optimisation of structural and functional materials it is of paramount importance to characterize and understand the structure, chemistry and bonding at interfaces.

Transmission electron microscopy (TEM) has matured to one of the most successful experimental approaches for the analysis of extended structural defects like dislocations and interfaces. This presentation discusses scientific and technological ingredients of TEM for quantitative characterisations on the microscopic level. For selected model cases of internal interfaces it illustrates recent achievements of both experiment and theory. A variety of interface properties and corresponding TEM techniques for their characterisation are summarized in TABLE 1.
The Use of Moiré Patterns in TEM Images to Measure Precipitate Composition in Al-Si-Ge Alloys
Authors: Radmilovic V , Mitlin D , Hinderberger S , Dahmen U
Published: July 2020

Moiré patterns are commonly formed in multiphase system when diffracting planes of similar spacing and orientation lead to interference effects. They can be used experimentally to evaluate the stress distribution in materials [1], to analyze orientation relationships and latttice strain in diffraction contrast microscopy, or, combined with the related geometrical phase technique, to analyze displacements in high resolution lattice images [2,3]. The interpretation of moiré fringes is often not straightforward due to the elastic interaction between the crystals at the interface and the dynamical nature of electron diffraction [4]. However, if the two lattices are fully relaxed, or if a small precipitate crystal is embedded in a large matrix, moiré patterns can give a simple and direct measure of orientation and lattice constants. in the present work, the moiré technique has been applied to the quantitative analysis of lath-shaped Ge or Ge-Si precipitates in Al with the aim to determine the composition (the Si:Ge ratio) from the lattice parameter indicated by the moiré fringes.
Quantitative Analysis of Interface Structure by HRTEM
Authors: Ernst Frank
Published: July 2020

The development of ‘quantitative’ high-resolution transmission electron microscopy (QHRTEM) has led to considerable progress in analyzing and understanding the atomistic structure of grain boundaries and heterointerfaces, which often control relevant macroscopic properties of materials. The following results of recent experimental studies and the comparison of these results with atomistic modeling demonstrate the strength of QHRTEM:

1.Grain Boundaries in SrTiO3. Some technical applications of SrTiO3 ceramics rely on special electric properties of this material, which originate from segregation of electrically active point defects to grain boundaries. QHRTEM can substantially contribute to understanding the correlation between the atomistic structure of grain boundaries and the segregation of point defects to these interfaces. As an example for a grain boundary structure solved by QHRTEM, FIGs. la and b present an experimental HRTEM image of the Σ= 3, (111) grain boundary in SrTiO3 and the corresponding atomistic structure as obtained by QHRTEM.
Optical Proprties of Tin Thin Film Obtained by Applying a Near Free Elctron Aproximation Using The Eels in Transmission Mode
Authors: González-Valenzuela C , González R , Espinosa-Magaña F , Martínez-Sanchez R , Duarte-Möller A
Published: July 2020

A TiN thin film was grown by the DC-Sputtering technique was characterized by EELS spectroscopy in order to obtain the optical quantities, ε1,ε2 and the refractive index η. Optical properties were obtained analyzing the low loss window located at an energy less to 50 eV respect to the elastic peak. A primary energy of 200 keV and a spot size of 440 nm with an average acquisition time of 5 min were used. The optical properties were calculated using the Kramers - Kronig relations.

Figure 1 shows the PEELS spectra in the low loss region for TiN thin film. As we can see, the most prominent plasmon loss peak characterizing TiN appears at an energy loss of 24 eV. The origin of the loss peak located at 17 eV is interpreted as surface plasmon. in order to obtain a better approximation, we use a near-free electron model and we have compared with the respective optical quantities calculated with the conventional formalism.
Quantitative Evaluation of The Chemical Composition of γ-γ’Interfaces in Ni Superalloys
Authors: Calderon H A , Benyoucef M , Clement N
Published: July 2020

The excellent mechanical properties of Ni based superalloys depend upon the presence of γ’ particles (LI2 structure). Their volume fraction, spatial distribution and size determine the mechanical strength of these alloys. Ni alloys for technological applications make use of large volume fractions of precipitates where processes of coarsening and coalescence take place during service leading in some cases to deterioration of properties. Addition of different alloying elements prevents accelerated coalescence by retarding diffusion and thus improving the mechanical properties of such alloys. Coalescence can also take place under the influence of an applied stress leading to the formation of rafts of the y' phase. For example the microstructure changes during creep deformation, depending on the alloy composition, with the corresponding formation of dislocation networks and rafts of different morphologies [1]. The γ-γ’ interfaces are also different depending on the alloy composition and most likely to the local distribution of alloying elements and their strain fields.
Grain Boundary Structure Analysis of Covalent Bonding Materials by Atomic Resolution Transmission Electron Microscopy
Authors: Ichinose Hideki , Sawada Hidetaka , Takuma Eriko , Saito Hideo
Published: July 2020

Grain boundaries of covalent bonding materials such as silicon, germanium and SiC require rather physical consideration than that of geometry to discuss the result of their electron microscopic observation. Dangling bond, for example, is expected least in number in the stable boundary (least dangling bond rule). [1][2] in practice, further precise consideration must be done both in geometry and in physics in the covalent bonding materials boundary. in the present study, geometrical discussion is combined together with that of the atomic bonding about diamond, SiC and ZnO grain boundaries. Chemical structure image of the modern high-voltage transmission electron microscope enabled to do it. An asymmetrical Σ3 boundary of diamond and a 6H-SiC boundary with 70.5 degree rotation are mainly observed.

The sliced specimen, 0.3mm in thickness, was mechanically thinned down to 0.02 mm and was finally polished using an argon ion milling. Final thickness of the specimen was estimated to be 3 nm in the region close to the edge of the small hole.
Hrem Observation of the Relaxation of Grain Boundaries in Au At Their Intersection with Free Surfaces
Authors: Radetic T , Dahmen U
Published: July 2020

Grain boundaries in fee metals with low stacking fault energy are known to undergo extended relaxations that can at times lead to a thin layer of a different structure. in Cu, for example, it has been found that Σ3{112}} boundaries relax into a 9R phase or even a bec phase. in this work, we have used high resolution electron microscopy to investigate the atomic structure of Σ99 grain boundaries in mazed bicrystal films of Au. On {001} Ge single crystal substrates, Au bicrystals can be grown in two equivalent {110} orientation variants, related to each other by a 90° rotation about the surface normal. There is equal probability to nucleate either orientation variant in early stages of film formation and since there is no reason for preferential growth, the morphology of the bicrystal film consists of many grains in only two orientations. All grain boundaries are of the type Σ99 and display tilt character.

Thin films 10-200nm thick were grown by physical vapor deposition on {001} Ge substrate at 280°C and followed by annealing at 200°C to relieve stresses.
Quantitative Electron Holography - From The Basis of Dynamical Interaction to Holographic Materials Analysis
Authors: Brand Karin , Guo Chengshan , Lehmann Michael , Lichte Hannes
Published: July 2020

Quantitative analysis of a structure means to determine which atoms are where. The where is restricted by the lateral resolution, and the which is related to the sensitivity against differences of the atomic species. Electron holography is on the move to tackle both questions.

• where - Lateral Resolution Electron holography has surmounted conventional electron microscopy in that it has reached atomic resolution both in the amplitude and phase images: with our CM30FEG/UT Special Tuebingen electron microscope, the information limit of 0.09nm and the pixel number of the 2048_ - CCD camera allow to take holograms with image details smaller than 0.095nm; the quality of correction of the aberrations allows an interpretable resolution approaching 0. lnm both in amplitude and phase [1].

• which - Phase Detection Limit (PDL) The phase detection limit describes the minimum phase difference detectable well above a given noise level.
Quantitative Investigations of Interfaces and Grain Boundaries by Phase Contrast Electron Microscopy with Ultra High Resolution
Authors: Kisielowski C , Plitzko JM , Lartigue S , Radetic T , Dahmen U
Published: July 2020

Recent progress in High Resolution Transmission Electron Microscopy makes it possible to investigate crystalline materials by phase contrast microscopy with a resolution close to the 80 pm information limit of a 300 kV field emission microscope'"". A reconstruction of the electron exit wave from a focal series of lattice images converts the recorded information into interpretable resolution. The present contribution illustrates some recent applications of this technique to interfaces.

Fig. 1 shows a reconstructed electron exit wave of a heterophase interface between GaN and sapphire. The experiment takes advantage of three factors: First, we resolved the GaN lattice in projection, which requires at least 0.15 nm resolution. The projection eliminates the stacking fault contrast that usually obscures lattice images in the commonly recorded projection. Thus, image interpretation is drastically simplified. Second, all atom columns at the interface and in the sapphire are resolvable with a smallest projected aluminum - oxygen spacing of 85 pm in the sapphire.
Energy -Loss Fine Structures at the Si-Gd2O3, Interface
Authors: Botton GA , Gupta J A , Landheer D , McCaffrey JP , Sproule GI , Graham MJ
Published: July 2020

In recent years, electron energy loss spectroscopy has provided high spatial resolution information on the elemental composition of interfacial reactions. with the use of field emission guns in conventional TEM or STEM, additional information on the chemical, structural and electronic state at grain boundaries and interfaces can also be obtained (e.g. Ref. 1 and 2). in the study of new types of materials for semiconductor applications such as high-K dielectrics, high spatial resolution information of this type is of critical importance as the dimensions of the structures are reduced and the ultimate electronic properties become size dependent. This paper discusses the analysis of near edge structure information obtained at the Si-Gd2O3 interface, a system with great potential for the next generation of gate material.

The preparation of the thin films and the sample preparation details are given elsewhere3 and only a summary of the characterization method and results are described here.
Electronic Structure Investigations of Metal / SrtiO3 Interfaces Using EELS
Authors: van Benthem Klaus , Scheu Christina , Sigle Wilfried , Elsässer Christian , Rühle Manfred
Published: July 2020

Ni, Pd and Cr thin films were grown on (100)SrTiO3 surfaces by molecular beam epitaxy at substrate temperatures of TNJ, pd=650°C and Tcr =150°C. Electron energy-loss spectroscopy (EELS) and high resolution transmission electron microscopy (HRTEM) were applied to investigate the local electronic structure and the atomic structure of the interfaces, respectively. Analytical microscopy was carried out with a parallel energy-loss spectrometer (PEELS766) attached to a dedicated scanning transmission electron microscope (STEM) operated at 100keV, which has a point resolution of 0.22 nm. HRTEM studies were performed on a Jeol JEM ARM 1250 operated at 1250keV (0.12 nm point resolution). Conventional TEM and HRTEM experiments showed epitaxial orientation relationships between the thin metal films and the substrate for each interface.

The electronic structure of the interfaces in terms of the site- and symmetry projected density of states (PDOS) above the Fermi-level can be extracted from the electron energy-loss near-edge structures (ELNES).
TEM Analysis of an Alumina Bicrystal Section Using a Fib
Authors: Fairer Jeffrey K , Ravishankar N , Michael Joseph R , Barry Carter C
Published: July 2020

Grain boundary migration (GBM) during the sintering and densification of a polycrystalline ceramic material occurs as a result of mass transport across an interface. When there is a liquid film present, either due to additives used for liquid-phase sintering or unavoidable impurities in the material, the mass transport can be visualized in terms of dissolving material from one grain and precipitating it on another. in order to study the effects of crystallography on GBM in the presence of a liquid phase, alumina bicrystals have been fabricated with anorthite (CaA12Si208) glass films at the interface. The alumina-anorthite system in a bicrystal geometry is used because the pseudo-binary phase diagram of the system is well known, the bicrystal geometry allows for control over the original interface misorientation, and the glassy phase of anorthite is the most commonly occurring glass in commercially used alumina.

Fig. 1 is a secondary-electron SEM image of an alumina bicrystal recorded using a field-emission SEM (Hitachi S900) operating at 5 kV.
Nonorthogonal Twining in Epitaxial SrRuO3 Thin Films Grown on (001) LaAlO3
Authors: Tian W , Jiang J C , Pan X Q
Published: July 2020

Nonorthogonal twinings have commonly been observed in perovskite oxides such as SrTi03 and BaTi03. Among them, the ﹛111﹜ Σ3 type twining exists with a relative large amount of population and has been extensively studied. By combining quantitative high resolution transmission electron microscopy (HRTEM) and spatially resolved electron energy loss spectroscopy (EELS), one was able to determine the atomic structure of the ﹛111﹜Σ3 twin boundary in these oxides.[l] On the other hand, nonorthogonal twinings in SrRuO3 have been much less studied. SrRu03, a ternary ruthenium metal oxide, has a perovskite-compatible structure and exhibits low electrical resistivity (10-4 Ω•cm), showing an unparallel technique importance in microelectronic applications. Since the properties of material strongly depend on the microstructure and defect configurations, it is important to study the twining structures and their formation mechanisms in SrRuO3 thin films.

Transmission electron microscopy (TEM) was used to study the SrRuO3 thin films grown on (001) LaAlO3 by 90° off-axis rf sputtering.
Crystal Polarity Determination by Electron Channeling
Authors: Tafto J
Published: July 2020

Multilayers, heterostructures, nanostructures and composites are of great interest to the materials scientists, and frequently we encounter crystals lacking centrosymmetry. Thus crystal polarity determination on a microscopic scale is becoming increasingly important in describing interface structures and the internal defects in small crystals. in many cases the polarity of a crystallite can be determined by convergent beam electron diffraction, CBED. Powerful alternatives are to monitor the electron induced x-ray emission, EDS, or electron energy losses, EELS, under channeling conditions. While the determination of the phase of the structure factors, and thus the determination of the crystal polarity, relies on many beam diffraction effects when the CBED technique is used, two-beam experiments provide information about the phase of the structure factor when localized EDS or EELS signals are detected under channeling conditions.

The experimental conditions used to determine the polarity and absolute orientation from electron channeling are similar to those used in ALCHEMI experiments to locate small amounts of atoms by electron channeling.
Dechanneling Effects in EELS and EDXS Analysis of Ybacu-Oxides
Authors: Miller Peter
Published: July 2020

Quantitative analysis in the TEM by EELS or EDXS depends on the K-factor method in which uniform ionization, independent of specimen orientation and thickness, is assumed. This assumption is of limited validity for crystals, where channeling of the electron wave ψ affects the ionization rate as observed in both energy loss and X-ray signals. Both EELS and EDXS are sensitive to changes in ψψ*near the atomic sites, and this variation as a function of crystal orientation forms the basis for ALCHEMI. Simultaneously recorded EELS and EDXS spectra were used to monitor changes in Cu/Ba ratio from YBaCu-oxides using L2,3/M4,5 ionization edges or K/L X-rays respectively. Although the acceptance aperture for EELS (11 mrad at 300 keV) may not be sufficiently large to mask double-channeling effects, it is small enough that momentum transfer is sufficiently limited to enhance derealization. Thus it is expected that the EELS signal should be less sensitive to crystal orientation than EDXS (an estimate of impact parameters yields 0.73 and 0.61 Å for the Ba and Cu energy loss signals, reducing to 0.06 and 0.04 Å respectively for X-ray emissions).
Atomic Site Occupancy of Platinum Group Metals in the γ’ (Ll2) Phase of a γ-γ’ Complex Nickel Base Superalloy Using Alchemi (Atomic Location by Channnelling Enhanced Microanalysis)
Authors: Ofori A P , Humphreys C J
Published: July 2020

Nickel-base superalloys (NBSAs) have remarkable mechanical properties (and corrosion resistance) at elevated temperatures. Single crystal NBSAs have found major use as turbine blades in aeroengines, where there is a large world market because the turbine blades have to be replaced at regular intervals. in order to develop engines with higher efficiency, considerable efforts are being devoted to enhance the temperature capabilities of superalloys. The two phase γ-γ’ structure that is crucial to NBSA characteristics is primarily produced by the presence of Al in combination with Ni: above a critical concentration the Ll2 γ’ phase based on Ni3Al precipitates out of the γ Ni-base solution. However, superalloys usually contain many other alloying elements such as Cr, Co, Mo, W and Ta to enhance strength and impart higher temperature performance. Among these alloying additions, much attention has recently been paid to Re because of its contribution to the improvement of both creep and corrosion properties.
The Role of Simulation in ALCHEMI
Authors: Rossouw Chris
Published: July 2020

Contrast in zone axis channelling patterns, formed by variations in characteristic X-ray emission rates as an electron beam is scanned in angle, is related to projected sublattice site symmetries of ionized atoms within the unit cell. Whereas overall Brillouin zone geometry is identical to that observed in large angle convergent beam patterns, this incoherent X-ray channelling contrast is related to ADF or BSE contrast by integration over thickness of the signal generated within the specimen. Contrast is thus relatively stable and easily interpretable.1 This is useful in separating the response of dilute atoms from abundant atomic species, since the specific channelling pattern of each atom has its own overall fingerprint. Correlation of patterns formed from Ta-doped TiAl with bright field LACBED is shown in Fig. 1 (clearly Ta occupies Ti sublattice sites). No simulation of channelling contrast is necessary if minority atomic species are distributed over sublattice sites in a way that can be reconstructed from a linear superposition of majority (or host) atom sites that form part of the regular lattice structure. The distribution over sublattice sites may be determined by any one of a variety of analysis methods.2,3
A Routine to Determine the Shift of Kikuchi Bands in EBSD to Sub-pixel Resolution
Authors: Tao Xiaodong , Eades Alwyn
Published: July 2020

The long-term aim of our research is to detect and image dislocations in the SEM with EBSD. We will apply it first to the characterization of threading dislocations in Si/Si-Ge structures. As an initial step, we set out to detect the shift of the Kikuchi bands in EBSD patterns to sub-pixel precision.

In the standard analysis of EBSD patterns, to find the positions of Kikuchi bands, it is usual to use the Hough transform. This transform displays the intensity along all lines in the EBSD pattern, as a function of the position and the angle of the line. Thus linear features in the pattern (Figure 1) appears as peaks in the transform (Figure 2a). in normal EBSD analysis, the aim is to determine the orientation of the grain to a precision of perhaps a degree or two. Therefore, many simplifications are made in the software with the aim of gaining speed.
How Accurate is Qcbed ? -- the Case of Rutile (TiO2)
Authors: Jiang B , Friis J , Spence JCH
Published: July 2020

An accuracy of better than 1% is needed to measure the changes in charge density due to bonding. Here we report an accuracy up to 0.025% (random error) obtained in rutile crystal structure factors measurement by QCBED. This error is the standard deviation in the mean value obtained from ten data sets. Systematic errors may be present. Figure 1 gives an example of the (200) refinement results. Table 1 lists several low order structure factor refinement results. The accuracy of the measured electron structure factors was 0.1-0.2% but after conversion to x-ray structure factors, the accuracy for low orders improved due to the Mott formula [1] For (110) and (101) reflections, the accuracy in x-ray structure factors became 0.025% and 0.048% respectively. This accuracy is equivalent to that of the X-ray single crystal Pendellosung method on silicon crystals [2].

The experiments were done on a Leo 912 Omega TEM.
ProcessDiffraction VI.2: New possibilities in manipulating electron diffraction ring patterns
Authors: Lábár János L , Adamik Miklós
Published: July 2020

A free computer program was introduced recently to process electron diffraction ring patterns. The program (called ProcessDiffraction) produces XDR-like output from the digitized version of the measured diffraction patterns. The enhanced functionality of V1.2 is summarized in the present paper.

1. The program starts with a hint-window giving suggestions what can be done next. Hints change permanently as processing progresses. The hint-window can be switched off optionally. It is a complement to the Windows-style Help-system. 2. The center of the rings is found by manually shifting the measured pattern until it overlaps with a generated reference circle. The computer can further refine the position of the center. 3. Elliptical distortion of the measured pattern (NOT of the display, which is irrelevant) is corrected by adjusting the eccentricity and axis direction of the reference ellipse (distorted from the reference circle) until visually coincide with the measured ring.
Designing Advanced Ceramic Structures with Novel Environmental Microscopy and Related Methods
Authors: Gai Pratibha L
Published: July 2020

Silica and titania based ceramics and their analogs are some of the most fundamental in crystal chemistry and ceramic science Our interests include applications of nanostructures and chemical composites of the ceramics in nanoelectronics, chemical processes and as scaffolds in biotechnologies. Finely divided titania is used in a vast array of products including paper, paint, food and clothing. Novel microscopy methods including dynamic environmental-high resolution transmission EM (EHREM) at the atomic level, FESEM and cathodoluminescence are leading to striking progress in the development of the ceramic nanotechnologies.

Phase transformations in the cristobalite form of silica, from the tetragonal a phase (low or room temperature form) to the cubic β phase (high temperature, (270°C) form) result in discontinuous thermal expansion and are not conducive to nanotechnology. Here we report fundamental in situatomic resolution studies of the phase transformations using EHREM and have used the results to design a number of stable, single-phase structures at room temperature (RT).
Manipulation of Nanodiamond Clusters for Nanoscale Applications
Authors: Tyler T , Kvit A , Jaeger D , Zhirnov V , Hren J
Published: July 2020

One objective of the present work is to study the processes of assembly/self assembly of diamond clusters into nanostructures such as dots, wires,and filmsunder the influence of high electric fields. Diamond nanoparticles (∼2-5 nm in size) in a suspension of ethyl alcohol were deposited by pulsed electrophoresis onto sharp metal needles, such as those employed for field electron emission applications [1,2]. A custom designed sample holder has been constructed for a JEOL 2010 F, which allows for the convenient transfer of the sharp metal wires for analysis at high resolution, and then for removal (e.g. for re-deposition). These procedures allow us to precisely control the deposition thickness and morphology. They are capable of building a variety of deposition structures, even an isolated nanodiamond particle. The geometry of the deposits depends upon the applied voltage, the concentration of the suspension, the pulse duration, and the local electric field (which in turn depends on tip geometry, e.g. see Fig. 1).
Extreme SEM
Authors: Boyes E D
Published: July 2020

New analytical methods have been implemented with novel instrumentation designed to extend, to explore and to exploit an expanded performance envelop for high resolution imaging, EDX chemical microanalysis and chemical imaging with robust and representative bulk samples in a scanning electron microscope (SEM). A key contribution is the integrated and innovative design of the in-lens electron optics, sample holders, detectors including for EDX, specimen chamber and vacuum system. Each component has been improved individually over previous practice and they have been made to work together much better, especially with respect to combining advanced electron imaging at low voltages with efficient x-ray analysis and mapping.

Compared to a conventional out-of-lens/semi-in-lens FESEM the secondary electron image (SEI) resolution at the widely used low voltage of 1 kV is improved by a factor of almost 2x to <1.5nm and this facilitates low voltage imaging at primary magnifications of 250,000x (Fig.1) or more.
Synthesis and Characterization of Carbon Nanotubes on Porous Silicon Substrates
Authors: Dong Lifeng , Jiao Jun , Tuggle David W , Foxley Sean
Published: July 2020

Carbon nanotubes have many unique properties, including a tensile strength greater than that of steel and current-carrying capacity greater than any known metal or superconductor. Many applications have been identified, including field-emission displays and ultra-small transistors. At present, the main barrier to such applications is the ability to synthesize the nanotubes in a large scale with controlled properties'.

The work reported here is an effort for growing carbon nanotubes on porous silicon with a designed pattern. Experimental procedures include (1) a liquid catalyst was prepared by mixing AlCl3.6H2O, SiCl4, FeCl3.6H2O, MoO2Cl2,P-123 chemical components; (2) a flat piece of polydimethylsiloxane (PDMS) elastomer stamp containing a designed pattern was etched in the oxygen plasma, followed by spin coating the catalyst on the patterned stamp;(3) the inked stamp was printed onto a porous silicon substrate. This substrate was then heated in air at 70°C for 10 minutes to stabilize the catalytic pattern on the surface of porous silicon.
Atomic Scale Analysis of a YSZ Bicrystal Grain Boundary
Authors: Lei Y , Ito Y , Browning N D
Published: July 2020

Yttria-stabilized zirconia (YSZ) has been the subject of many experimental and theoretical studies, due to the commercial applications of zirconia-based ceramics in solid state oxide fuel cells. Since the grain boundaries usually dominate the overall macroscopic performance of the bulk material, it is essential to develop a fundamental understanding of their structure-property relationships. Previous research has been performed on the atomic structure of grain boundaries in YSZ, but no precise atomic scale compositional and chemistry characterization has been carried out. Here we report a detailed analytical study of an [001] symmetric 24° bicrystal tilt grain boundary in YSZ prepared with ∼10 mol % Y2O3 by Shinkosha Co., Ltd by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS).

The experimental analysis of the YSZ sample was carried out on a 200kV Schottky field emission JEOL 201 OF STEM/TEM4.
Direct Observation of Single Displacement Cascade in Pyrochlore by Tv-Rate In-Situ TEM and Ex-Situ HRTEM
Authors: Lian J , Wang L M , Wang S X , Ewing R C
Published: July 2020

The ion irradiation-induced crystalline-to-amorphous transformation has been studied in many complex ceramics. Direct impact amorphization has been considered to be one of the fundamental amorphization mechanisms for complex ceramics under heavy ion irradiation. Based on the directimpact model, a highly energetic incident ion transfers its kinetic energy to the target as a thermal spike within 10“13 sec creating a “molten-like” displacement cascade, typically nanometer-scaled in diameter (as indicated by the result of a computer simulation in Fig. 1). This “molten” zone quickly quenches to a small amorphous domain within a few pico-seconds. Epitaxial recrystallization occurs around the amorphous/crystalline interface, so that the size of amorphous domains decrease with time. The accumulation and overlap of small amorphous domains eventually leads to complete amorphization of the irradiated material. Although the in-situTEM technique with the setup shown in Fig. 2 has been extensively applied to the study of the amorphization process in complex ceramics, most of the previous studies relied on in-situobservation of the electron diffraction pattern, and there has been a lack of solid evidence of direct impact amorphization due to the small nature of the cascades and the rapid kinetics of its evolution.
Surface Steps on Flux-Grown Alumina
Authors: Ravishankar N , Barry Carter C
Published: July 2020

The utility of a surface to serve as a substrate depends upon its surface structure. The presence of steps on the surface affects the quality of the deposited material. The basal surface of alumina is one of the most widely used substrate materials and hence considerable effort has been directed towards the study of this surface. The mechanism of formation of a stepped structure on the basal surface of alumina has been investigated using atomic force microscopy. The evolution of steps on the basal surface as a function of temperature has been reported. Flux growth is an attractive route for producing alumina because of the low temperatures required for processing and the extremely low dislocation densities that can be obtained. in the present study, the structure of steps on flux-grown alumina has been investigated. Formation of low-index macrofacets as a result of crystal growth has been observed.
Electron Microscopy in Optimizing Microstructure and Mechanical Properties of Hot-Pressed Silicon Carbide
Authors: Zhang XF , Sixta ME , Yang Q , Chen D , Ritchie RO , De Jonghe LC
Published: July 2020

SiC, as one of the most promising candidate ceramics for high temperature structural applications, offers many intrinsic advantages, including high melting temperatures, low density, and high elastic modulus. However, the use of SiC to date has been severely limited by its poor fracture toughness (∽ 2-3 MPa√m for commercially available materials) and crack-growth resistance. Our study focuses on the development of silicon carbide as a potentially tough, high-temperature, and damage-tolerant material. The approaches include identifying roles of sintering additives in modifying grain morphology, effects of post-annealing on grain boundary phases, and possibility in introducing nanoscale precipitates in SiC grains. Central in these efforts is structural characterization using state-of-the-art electron microscopy.

The first success was in situtoughening the SiC, by hot pressing in the presence of A1, B and C additions. Elongated and interlocked grains were developed surrounded by an Al-containing amorphous grain boundary film.
Electron Microscopy Analysis of the Intermediate Phases Formed During the Nucleation of Yba2cu3O7-δ Film
Authors: Wu Lijun , Zhu Yimei , Solovyov V F , Wiesmann H J , Suenaga M
Published: July 2020

Recently, considerable efforts have been made in growing bi-axially aligned thick Yba2cu3O7 (YBCO) films on a flexible, textured metallic substrate for electrical power applications. The BaF2 post-deposition annealing process is one of the most promising methods. to understand the nucleation and growth mechanism of YBCO in this process, extended transmission electron microscopy analysis has been made. Here, we report on the evolution of Ba-Y oxy-fluoride which is pertinent to the epitaxial YBCO nucleation process on SrTiO3 (STO) substrate.

The stoichiometric ratio of Y, Cu and BaF2 was evaporated on (00l)-cut STO substrate Subsequently, these films were annealed at 735°C in an O2-H2O-N2 gas atmosphere and quenched after 10, 20, or 40 minutes. The morphology and phase composition of the precursor changed drastically with the annealing times, e.g. after 10 minutes heat treatment, the precursor consisted of fine grained CU2O and Ba-Y(Cu) oxy-fluoride (cubic, a=0.618nm) as shown in fig.la.
Electron Incoherent Scattering from Nanometer-Sized Charge Ordering in Colossal Magnetoresistive La2/3ca1/3mnO3
Authors: Zuo J M
Published: July 2020

Electronic phase separation is known to occur in complex oxides ranging from high-Tc superconductors to colossal magnetoresisitive (CMR) manganites. Accumulating experimental evidences show regions of temperature dependent conducting and insulating regions, whose exact origin is unknown. Theoretically, it is has been shown that these systems are unstable from the strong interplay between the lattice, charge and spin degrees of freedom.

The key to understand the electronic phase separation in complex oxides is the structure. Electron diffraction is the only probe that covers the length scales from angstroms to microns. Characterization at these length scales is critical (electronic phase separations are typically about nanometers in sizes). Traditionally, electron diffraction has been played important roles in discovering the new types of phase separations, but has contributed little to the quantitative understanding. The reason is the strong interaction of electrons with matter, which gives both strong inelastic background and multiple scattering.
Quantitative X-Ray Microanalysis of Uncoated Ceramics
Authors: Lyman Charles E , Carlton Robert A , Roberts James E
Published: July 2020

Uncoated ceramics are difficult to analyze because specimen charging can reduce the energy of the electron beam at the specimen. This effect may decrease the measured k-ratio to a fraction of its expected value. Thin carbon coatings are the usual solution to this problem. However, the coating procedure takes time, and the same coating thickness also must be applied to the standard. in the environmental SEM (ESEM). surface charge can be mitigated at the higher accelerating voltages normally used for x-ray microanalysis. in the ESEM, electrons are accelerated toward an electrically biased electron detector producing a cascade of electrons and ions from the imaging gas (water vapor) as part of the secondary electron imaging process. Positive ions drift toward the specimen and neutralize negative surface charge; however, the degree of neutralization is a function of a number of operating variables.
Chemical and Electron Beam Reduction of Vanadium Oxides Monitored by EELS and NEXAFS
Authors: Su DS , Hävecker M , Willinger M , Schlögl R
Published: July 2020

The application of modern transmission electron microscopes (TEM) in catalytic research has accelerated the progress in understanding the mechanism of catalytic reactions. For instance, using environmental TEM, the novel glide shear defect process was revealed as an efficient mechanism for the release of the structural oxygen of vanadyl pyrophosphate in the n-butane oxidation [1]. On the other hand, electron energy-loss spectroscopy (EELS), which is nowadays commercially available on modern TEM, appears unknown in the catalytic community. in fact, core-loss EELS is a powerful tool to identify the chemical state of elements and to study the modification of this sate in various compounds.

Fig.l shows EELS-spectra of various vanadium oxides in which the oxidation state of vanadium varies from 2+ (VO) to 5+ (V2O5). The first two features, marked as V L3 and V L2 edges, are attributed to the excitations from V 2p3/2and V 2p1/2core levels to the unoccupied V 3dstates, respectively.