bluuebunny/crossref_metadata_2025 huggingface dataset:
Light-cured dental composites characterization by Electron Microscopy
Authors: Culbertson B. M. , Devinev M. L. , Kao E. C.
Published: June 2020

The service performance of current dental composite materials, such as anterior and posterior restoratives and/or veneer cements, needs to be improved. As part of a comprehensive effort to find ways to improve such materials, we have launched a broad spectrum study of the physicochemical and mechanical properties of photopolymerizable or visible light cured (VLC) dental composites. The commercially available VLC materials being studied are shown in Table 1. A generic or neat resin VLC system is also being characterized by SEM and TEM, to more fully understand formulation variables and their effects on properties.

At a recent dental research meeting, we reported on the differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) characterization of the materials in Table 1. It was shown by DSC and DMA that the materials are substantially undercured by commonly used VLC techniques. Post curing in an oral cavity or a dry environment at 37 to 50°C for 7 or more hours substantially enhances the cure of the materials.
Contrast symmetry and defect identification
Authors: Skalicky P.
Published: June 2020

Although the symmetry of the diffraction contrast of defects has received the attention of several authors already some time ago, symmetry rules are mainly based on geometrical arguments without solid proof for their validity in the general case. The symmetry of the diffraction contrast depends on the symmetry of the displacements and on the symmetry of the diffraction conditions (which of course follows from Neumann’s principle). General proofs for thee symmetry of dislocation contrast are given in this paper.

The diffraction contrast of a dislocation (or any number of parallel straight dislocations) which are inclined with respect to the surface of the foil and therefore show the so called “oscillating contrast” can only exhibit one of a limited number of symmetries.

(SAL): symmetry along the (projected) line of the dislocation

(SAM): symmetry about midfoil

(SAC): symmetry about center
Calculations and experimental observations of shadow images from multilayers
Authors: Wang Shiyao , Gajdardziska-Josifovska M. , Cowley J.M.
Published: June 2020

The properties of multilayer thin film materials are strongly influenced by the structure of their interfaces. The numerous applications for these materials motivate electron microscopy studies of cross sectional samples in which the interfaces are observed edge on. High resolution imaging is the most established technique, but other techniques, such as Fresnel fringe method and refraction at interfaces, have also been employed to characterize the structure and abruptness of amorphous/polycrystalline multilayers. The aim of this work is to explore the applicability of shadow images from coherent sources to the studies of multilayers.

Coherent interference effects are readily observable in the diffraction plane of a VG HB-5 STEM which is equipped with a cold field emission gun. The shadow image of the studied Si/Mo multilayer is obtained on the detection plane when the specimen is illuminated by a stationary convergent beam. This beam is formed with a very large or no objective aperture. Low magnification images are produced at large values of defocus (Fig. 1a), while for lower defocus the magnification increases and the shadow images become more and more distorted because of the objective lens aberration (Fig. 1b and 1c). In addition to the high sensitivity to the defocus. spherical aberration and probe position, the shadow images also appear to be dependent on the interface abruptness.
Fresnel fringe effects at interfaces of thin multilayer structures
Authors: Nguyen Tai D. , Gronsky Ronald , Kortright Jeffrey B.
Published: June 2020

Recent developments in the TEM Fresnel-fringe technique have provided an alternative method to the determination of structures and morphology of interfaces in multilayer thin film structures. This method has been employed in the investigation of structures and defects in grain boundaries, dislocations, precipitate platelets, twin boundaries, metal interfaces, and multilayer structures. It has been demonstrated that the fringe spacing primarily relates to the layer thickness, while the fringe contrast as a function of defocus relates to the magnitude of the localized change in the scattering potential and thus to the interfacial composition. The profile of the fringes is more closely related to the abruptness of the composition change at the interface. Other factors affecting the Fresnel fringe intensity are the specimen thickness, aperture size, beam convergence, and degree of tilt of the interface from the incident electron beam.

Fresnel fringes result from the electrons experiencing an abrupt change in the inner scattering potential parallel to the electron beam path. Most previous calculations of the Fresnel contrast with defocus have simulated models based on one square or symmetrical trapezoid-shaped potential well, which are applicable only to a single interface or grain boundary, or to a few layer pairs of the multilayer.
Analysis of a new type of extended defect in αAl2O3
Authors: Sklad P. S. , Bentley J.
Published: June 2020

The recrystallization behavior of amorphous surface layers produced on single crystal [0001] αAl2O3 by implantation at -185°C with 4 x 1016 Al/cm2 at 90 keV and 6 x 1016 O/cm2 at 55 keV is being investigated by transmission electron microscopy (TEM). The microstructural development which occurs during annealing of bulk specimens in the temperature range from 800 to 1200°C has been characterized by conventional imaging and diffraction techniques. These studies demonstrate that the amorphous A12O3 first transforms to γ-Al2O3, a cubic transitional form, which in turn transforms to α-Al2O3 which is epitactical with the substrate. The as-implanted microstructure is characterized by a featureless amorphous region extending from the surface to a depth of 170 nm, Fig. la. The interface between the amorphous region and the crystalline substrate corresponds to the end of the projected range of the implanted ions and is characterized by a high density of small defects. These defects are similar to those seen in Al2O3 after neutron or ion irradiation and are probably small dislocation loops or defect clusters. The dominant microstructural features in specimens annealed to produce α-Al2O3 are a band of dislocation loops near the original crystalline-amorphous interface and a population of faceted cavities distributed throughout the implanted layer, Fig. 1b.
A SISF formation mechanism in Ni3Al
Authors: Lin Dongliang , Hen Mao
Published: June 2020

In the ordered Ll2 structure, the superlattice intrinsic stacking fault (SISF) has often been observed to be formed through two steps, the formation of antiphase boundary (APB) by dissociation of superlattice dislocation at first and then the conversion of the APB to the SISF(1,2). The present paper studied the SISF in NijAl by TEM and found that the SISF can also be formed by superlattice dislocation dipoles.

The tensile deformation of the directionally solidified Ni3Al (of composition in wt% of 82.88Ni, 8.5A1, 0.8Zr, 7.8Cr, and 0.02B) specimens was performed at room temperature. Thin foils were made normal to the specimen axis (parallel to [001]) and studied at 200 kv in H-800.

As shown in Fig.l, a SISF is formed at the end of a superlattice dislocation dipole, according to the SISF-type dissociation [10] =1/3 [11]+1/3[2l] on (111) plane. In Fig.2, a superlattic dislocation dipole is moving away from a SISF.
Weak beam image of a superlattice dislocation in deformed Ni3 (AlHfB)
Authors: Wu X. F.
Published: June 2020

A number of intermetallic compounds with the L12 structure exhibit a strange increase in the flow stress and work-hardening rate with increasing temperature. Despite the success of some model in explaining macroscopic properties, the detailed dislocation processes of model that are assumed to take place have not been observed in microscope. This work is an attempt to determine how the dislocation fine structure is related to the deformation behaviour of L12.

Single crystal Ni-23Al-1Hf-0.1B(at%) was used in the present study. direction was chosen as compression axis. Samples were deformed to plastic strain of 6%, specimens were cut parallel to by spark erosion. Fined electropolishing was donein solution of 1% perchloric acid in methanol at −50°c and 30V. The g/3g diffraction condition used in weak beam observation.

Fig1 shows the dislocation structure in foil. Long fairly straight screw dislocations with b=a[011] are imaged. The formation of dipoles is regarded as a characteristic and unusual feature of the dislocation structure. This indicates that annihilation is difficult at room temperature deformation. Weak beam images of superlattice dislocations are shown in fig.2 by using different reflections. The dislocation CC is long straight screw dislocation.
HRTEM observations of layer structure and stacking faults in MoS2 crystals
Authors: Shiojiri Makoto , Takahashi Noboru , Enomoto Susumu
Published: June 2020

MoS2 has a six-folded coordinated layer structure represented by the stacking symbol aβ ab ab The Greek letters refer to Mo atoms in the positions (2c) ± (⅓ ⅔ ¼) , and the italic letters refer to S atoms in the positions (4f) ± (⅓ ⅔ 0.629; ⅔ ⅓ 0.129) of the space group C6/mmc. The bonds between two S layers are mainly Van der Waals type and hence considerably weaker than the covalent bonds between Mo and S atoms.

A cleaved flake of MoS2 was embedded in synthetic resin and ultramicrotomed with a diamond knife perpendicular to the cleaved surface. The section was observed with an ABT EM-002B electron microscope having a UHR lens of Cs=0.4 mm.

Fig. 1 shows an observed HRTEM image of an MoS2 crystal and its electron diffraction pattern. The incident beam was parallel to the [2
0] axis.
The use of HREM in studying clay minerals
Authors: Qing Chen Quan , Lu Xing
Published: June 2020

A wider scope of clay research has been opened by investigators in various branches of science and technology due to their increasing interest in such materials. Electron microscope is one of the important methods for studying clay and clay minerals. Although a previous contribution of electron microscopy was to clarify the morphology and later electron diffraction (ED) of fine clay particles.However with the continous improvement of instrument and high resolution electron microscopy (HREM) techniques has provided more detailed information of clay minerals. This paper presents the use of HREM in stúdying clay minerals among our research.

1. Analysis of the structure of clay minerals
Recent advances in crystal structure analysis have indicated that disordered features are commonly revealed to various extents in clay mineral structure, such as polytypes,stacking disorders,mixed-layers.......etc. When the fraction of disordered feature is rather low, which cannot be distinguished by other method such as x-ray diffraction,however by using HREM lattice imaging, ED, and computer simulating (CS), which can be distinguished distinctly and sensitively. Fig.1a shows the structure of kaolinite with enantio morphic types i.e. left-handed and right-handed kaolinite. The computer simulated image (CSI) and electron diffraction pattern (EDP) are included for interpretation. It was also found that dickite is exhibited as intergrowth or stacking faults in the koalinite.
A multislice calculation of asymmetry of the weak-beam images of intrinsic stacking faults
Authors: Liu Z. Q. , Cockayne D. J. H.
Published: June 2020

Weak-beam images of stacking faults with one sign of a reflection can show some contrast changes to the images with the opposite sign of the reflection, that is so called asymmetry. This was first reported by Cullis and Booker, then this research has been carried on. For example. Foil et al and Cockayne et al.

The asymmetry for intrinsic stacking faults seems more complicated experimentally and theoretically. This asymmetry was observed (e.g.,Liu), and an example is shown in Fig. 1, where intrinsic stacking fault A shows less contrast with 400 in (a) than with 00 in (b). A multislice calculation was carried for an intrinsic stacking fault inclined on 001 silicon foil. The unit cell has 001 axis down along the incident beam, and is shown in Figure 2. Figure 3 shows the projected potential arrays of several successive slices with the thickness of 2.71 Å. Line A A' separates the arrays into two parts with different projected potentials due to the existence of the fault. The darkened dots which actually have larger values of the potential correspond to the atomic positions in the slices. The shifts of the atoms near the fault can be seen. The calculation were carried for the foil thickness of 271.00 - 371.07Å with relatively large deviation parameter s (.054Å)-1 The Laue center has been carefully chosen so that the weak-beam conditions are obtained. Five successive supercells with the same thickness but with different depths of the fault were used so that the fault is joined up smoothly tor the calculation. The final results of the calculation is shown in Figure 4, where (a) is for 040 and (b) is for 040. Five different symbols represent five different depths of the fault. The periodicity of the fault agrees with 1/s. The contrast ratio for±040 is 0.85.
Interface motion during recrystallization of amorphous NiSi2
Authors: Batstone J. L. , Smith D.A.
Published: June 2020

Recrystallization of amorphous NiSi2 involves nucleation and growth processes which can be studied dynamically in the electron microscope. Previous studies have shown thatCoSi2 recrystallises by nucleating spherical caps which then grow with a constant radial velocity. Coalescence results in the formation of hyperbolic grain boundaries. Nucleation of the isostructural NiSi2 results in small, approximately round grains with very rough amorphous/crystal interfaces. In this paper we show that the morphology of the rccrystallizcd film is dramatically affected by variations in the stoichiometry of the amorphous film.

Thin films of NiSi2 were prepared by c-bcam deposition of Ni and Si onto Si3N4, windows supported by Si substrates at room temperature. The base pressure prior to deposition was 6 × 107 torr. In order to investigate the effect of stoichiomctry on the recrystallization process, the Ni/Si ratio was varied in the range NiSi1.8-2.4. The composition of the amorphous films was determined by Rutherford Backscattering.
In-situ compression of high performance polymeric and related fibers within the Scanning Electron Microscope
Authors: Jeor Var L. St. , Chau C. C. , Thomsen Mark
Published: June 2020

A large portion of the interest currently given high performance polymer fibers stems from their potential use in composite construction. Although many of these fibers display good tensile properties, compressive strength is a major concern. There are many studies which have observed the compressive failure morphology of polymeric fibers. These studies usually involve the postmortem observation of samples which have failed, either partly or completely, following compressive strain. Observations have included such events as kink band formation, brittle failure and other modes as well. But to our knowledge these failure modes have not been recorded, in process, using the scanning electron microscope (SEM). In this article we introduce a technique which allows observation of compressive failure within the SEM, or using light microscopy (LM), in process. We also present some results unique to this procedure. This technique allows us to follow this "process" of compressive failure including both it's initiation and the more advanced stages of failure. Since the compressive failure of polymeric fibers is a process rather than an instantaneous event we have been able to record this process of failure, in it's various stages, in relatively high resolution SEM micrographs. Our methodology involves the use of relatively low accelerating voltages to minimize charging artifacts associated with damaged areas of the fiber. This induced damage can disrupt the 3 - 5nm sputter coating used to prevent such artifact resulting in uncoated fiber being exposed to the electron beam. This technique also lends itself readily to video recording. We have observed compressive failure processes for Kevlar 49®, Spectra 1000®, Hercules AS-4® carbon and various experimental fibers such as Polybenzobisoxazole (PBO). Our observations have included such modes of failure as kink band formation, delamination, buckling and brittle failure. It is noted that some of these processes occur simultaneously in any given fiber, and with the exception of brittle failure, these processes can be recorded at every stage of development visible to the SEM.
In situ investigations of the fcc to hcp martensitic phase transformation in CoNi
Authors: Karnthaler H.P. , Waitz T.
Published: June 2020

CoNi alloys show like pure Co a martensitic phase transformation between the fcc high temperature phase and the hcp low temperature phase. In Co+32%Ni the mean transformation temperature is at room temperature RT. Since the hysteresis is rather large (± 150°C) both phases can be observed in a stable configuration at RT. The two close packed lattices can transform into each other by the movement of a Shockley partial dislocation on every other close packed plane. In the case of the fcc → hcp transition there are four {111} planes which can act as habit planes. Therefore, caused by topological reasons the growing lamellas will hinder each other during their expansion. This seems to be an important difference to the reversed transformation where only one habit plane exists.

Single crystals of Co+32%Ni were grown under vacuum by a modified Bridgeman technique. The crystals were in the fcc phase at RT. Discs of 1mm diameter with 〈112〉 orientation were prepared by spark erosion.
Precipitation in silicon-implanted by oxygen and carbon plus oxygen
Authors: Chen Y. L. , Carpenter R. W. , Sjoreen T. P.
Published: June 2020

Interest in precipitation processes in silicon appears to be centered on oxygen and carbon impurities in thermally aged materials, and on oxygen implanted materials to form buried dielectric layers. The precipitation reaction products are small, and the presence of carbon is often an important consideration. This abstract reports high resolution electron microscopy observations of precipitate morphology in FZ-Si implanted with oxygen (2.3×l020cm-3 concentration at projected range. Rp). and with oxygen plus carbon (both 1.2×l020cm-3concentration at Rp), and then post-implanted annealed at 923K for 120 hours. These oxygen and carbon concentrations are significantly higher than the saturation oxygen and carbon concentrations in Si at the melting point, which are ∼2×l018 cm-3.

After mechanical and argon-ion-milling thinning, (001) wafers were examined in [011] cross-section with an LSI 002B at 200kv for HREM and a Philips EM400ST FEG at l00kv for EELS. A typical implanted region is shown in Fig. 1a for O-implanted and Fig. 1b for O-plus-C-implanted specimens.
Copper precipitation on extrinsic defects in silicon
Authors: Rice P.M. , Kim M.J. , Carpenter R.W.
Published: June 2020

The gettering of impurity copper in silicon has been investigated for over a decade because of its technological importance in electronic device fabrication.it is known that Cu can be extrinsically gettered in silicon at deliberately introduced nucleation sites. However, its reaction mechanism and the nature of the reaction product are not well understood. Here we report the interaction of Cu with dislocations in Si created by mechanical abrasion.

A damaged region was introduced into CZ{001} silicon wafers on one side by abrasion. A Cu layer 200nm thick was deposited onto the abraded surface in a UHV chamber at room temperature. After Cu deposition the wafers were sealed immediately into quartz ampules under vacuum and annealed at 1000 C for 24 hrs, followed by quenching. Cross section specimens were prepared by mechanical dimpling and Ar beam ion milling. Diffraction contrast imaging and microdiffraction experiments were done in a JEM-2000FX at 200kV, and a Philips 400TEM/STEM/FEG at 100kV.
Phase separation and silicide formation in the films of Pd-W alloys on Si
Authors: Rozhanski N. , Lifshitz V.
Published: June 2020

Pd-W alloy films are of interest because of their use for contact fabrication in microelectronic devices.

In the present work Pd2 5W7 5, Pd4 0W6 0, Pd9 0W1 0 films were sputter deposited on Si(100) and only Pd9 0W1 0 films were polycrystalline.The amorphization of Pd- W films, possibly due to impurities, was not observed previously. The reaction of Pd9 0W1 0 films with a Si substrate begins at 200°C and leads to the formation of Pd2Si in two equivalent epitaxial orientations: A and B.In contrast to Ni-Nb films the presence of the native SiO2 layer under Pd-W alloy does not prevent the diffusion processes and the formation of silicides both on bulk and on plan-view specimens.

Amorphous Pd-W films do not react with Si up to∼500°C and their crystallisation begins at T∼575°C.The reaction is also followed by the formation of two types of epitaxially oriented Pd2 Si islands as shown in Figure 1.The crystallisation of the films is accompanied by the formation of W grains.Pd crystals were not observed, that is possibly due to Pd precipitation at W grain boundaries.
The reaction of amorphous Ni-Nb films with Si in the presence of a native SiO2 layer
Authors: Rozhanski N. , Barg A.
Published: June 2020

Amorphous Ni-Nb alloys are of potential interest as diffusion barriers for high temperature metallization for VLSI. In the present work amorphous Ni-Nb films were sputter deposited on Si(100) and their interaction with a substrate was studied in the temperature range (200-700)°C. The crystallization of films was observed on the plan-view specimens heated in-situ in Philips-400ST microscope. Cross-sectional objects were prepared to study the structure of interfaces.

The crystallization temperature of Ni5 0 Ni5 0 and Ni8 0 Nb2 0 films was found to be equal to 675°C and 525°C correspondingly. The crystallization of Ni5 0 Ni5 0 films is followed by the formation of Ni6Nb7 and Ni3Nb nucleus. Ni8 0Nb2 0 films crystallise with the formation of Ni and Ni3Nb crystals. No interaction of both films with Si substrate was observed on plan-view specimens up to 700°C, that is due to the barrier action of the native SiO2 layer.
Investigation of the uniformity of well thickness in InP/InGaAs single quantum wells by large-angle convergent beam electron diffraction and dark-field imaging
Authors: Jordan IK , Cherns D. , Hockly M , Spurdens PC
Published: June 2020

The sharpness of interface, and the uniformity of well width, is of great interest in the growth of single quantum well (SQW) structures. These properties are usually investigated using High resolution electron microscopy (HREM) on cross sectioned samples. However this technique allows the imaging of only very small areas, and long Tange structure present in a sample may not be detected.

In the lattice matched InP/InGaAs system discussed here selective etches enable the preparation of plan view samples with up to 1mm2 of flat, electron transparent, area. Large angle convergent beam electron diffraction (LACBED) may then be used on these samples to obtain an extended rocking curve. Analysis of the rocking curve enables a measurement of the mean well width to be made. All structures reported on here were grown using MOVPE.

At large values of deviation parameter, s, typically greater than 0.003Å−1, the main features of rocking curves can be interpreted using the kinematic approximation.
The oval defects on MBE grown GaAs(100)
Authors: Hsu Tung , Petrich G.S. , Cohen P. I.
Published: June 2020

Oval defects were observed on specimens of MBE grown GaAs(100) samples. Substrates were GaAs(100) tilted 2ò toward [011] (A misorientation); chemically etched before growing 0.2μm of GaAs at 600òC, at a rate of 0.4μm/h, and using a 3:1 As:Ga flux ratio. After the growth samples were transferred through air to a JEOL-200CX electron microscope for REM and RHEED study,

Surfaces of the sample exhibited bunched atomic steps and wide atomically flat (100) terraces. There were approximately 100 such defects, large and small, within a specimen surface of 1 mm2.

The defects were of various sizes, indicating that they were at different stages of growth, but had the same general shape. After shooting a series of pictures from different azimuth angles, a three demensional computer model is then constructed and the model is tilted and rotated to simulated the views from different directions. There is a good agreement between the simulated and the experimental pictures.
The characterization of Ga0.5In0.5P/GaAs solar cells grown on Si substrates
Authors: Jones K.M. , Al-Jassim M.M. , Olson J.M. , Kurtz S.R. , Kibbler A.E. , Vernon S.M.
Published: June 2020

Multijunction solar cells have the potential of achieving conversion efficiencies in excess of 30%. It has been recently demonstrated that Ga0.5In0.5P/GaAs tandem solar cells can achieve efficiencies higher than 27%, These devices are grown on GaAs substrates. However, there is an increasing need for a cheaper, lighter substrate with higher thermal conductivity than GaAs for space solar cell applications. In this work, we have investigated the structural and luminescent properties of GaAs/GaInP multilayers grown on Si substrates. All layers were grown by MOCVD on (100), n-type Si substrates misoriented by 2° towards (110). The TEM examination was performed in a Philips CM-30 TEM operating at 300 KeV.

The first part of this study focussed on the growth of GaAs on Si for further use as a substrate for growing GaAs/GaInP cell structures. GaAs layers grown under standard MOCVD conditions exhibited dislocation densities in the 2-4 x 108 cm−2 range for 2μm thick layers. On the other hand, thermal cycle growth (TCG) gave rise to layers with significantly improved structural quality. This was carried out by several repetitions of deposition-annealing-cool down cycles during the growth. The effect of annealing on dislocation propagation is quite evident in TEM cross-sections (Fig. 1). The majority of defects are confined to a relatively thin region close to the interface. Wafers that had been in situ annealed 3 or 4 times exhibited a heavily faulted interface region, approximately 5000 Å thick, with the rest of the GaAs layer having a dislocation density in the 7-9 x 106 cm−2 range.
Spin-polarized Scanning Electron Microscopy
Authors: Koike Kazuyuki , Matsuyama Hideo
Published: June 2020

Spin-polarized scanning electron microscopy (spin SEM), where the secondary electron spin polarization is used as the image signal, is a novel technique for magnetic domain observation. Since its first development by Koike and Hayakawa in 1984, several laboratories have extensively studied this technique and have greatly improved its capability for data extraction and its range of applications. This paper reviews the progress over the last few years.

Almost all the high expectations initially held for spin SEM have been realized. A spatial resolution of several hundreds angstroms has been attained, which is nearly one order of magnitude higher than that of conventional methods for thick samples. Quantitative analysis of magnetization direction has been performed more easily than with conventional methods. Domain observation of the surface of three-dimensional samples has been confirmed to be possible. One of the drawbacks, a long image acquisition time, has been eased by combining highspeed image-signal processing with high speed scanning, although at the cost of image quality. By using spin SEM, the magnetic structure of a 180 degrees surface Neel wall, magnetic thin films, multilayered films, magnetic discs, etc., have been investigated.
Characterisation of planar crystal defects in Y2Fe17Cx (0.6 ≤ x ≤ 1.6) magnetic material by High Resolution Electron Microscopy
Authors: Coene W. , Hakkens F. , Jacobs T.H. , Buschow K.H.J.
Published: June 2020

Intermetallic compounds of the type RE2Fe17Cx (RE= rare earth element) are promising candidates for permanent magnets. In case of Y2Fe17Cx, the Curie temperature increases from 325 K for x =0 to 550 K for x = 1.6 . X ray and electron diffraction reveal a carbon - induced structural transformation in Y2Fe17Cx from the hexagonal Th2Ni17 - type (x < 0.6 ) to the rhombohedral Th2Zn17 - type ( x ≥ 0.6). Planar crystal defects introduce local sheets of different magnetic anisotropy as compared with the ordered structure, and therefore may have an important impact on the coercivivity mechanism .

High resolution electron microscopy ( HREM ) on a Philips CM30 / Super Twin has been used to characterize planar crystal defects in rhombohedral Y2Fe17Cx ( x ≥ 0.6 ). The basal plane stacking sequences are imaged in the [100] - orientation, showing an ABC or ACB sequence of Y - atoms and Fe2 - dumbbells, for both coaxial twin variants, respectively . Compounds resulting from a 3 - week annealing treatment at high temperature ( Ta = 1000 - 1100°C ) contain a high density of planar defects.
Electron-beam patterning of materials with nanometer resolution
Authors: Berger S.D. , Macaulay J.M. , Brown L.M.
Published: June 2020

It was first reported in 1978 that intense electron irradiation of thin films of NaCl leads to the formation of holes with a diameter of the order of the probe. Since that time the same phenomena has been observed in a variety of materials, typical examples being AlF3, MgO and Al2O3. Quantitative and qualitative descriptions of the damage have been given by a number of workers in an attempt to understand the underlying mechanisms. While groups of chemically or structurally similar materials often show the same general sequence of events in the hole formation process, it is a common observation that polymorphs or different preparation techniques result in very different behavior, Furthermore, examples of hole formation have been given which appear to show characteristics specific to that material system.

In an effort to gain insight into the hole formation process we decided to concentrate on a set of observations which are reasonably common.
Elemental mass loss in silicate minerals during x-ray analysis
Authors: Champness P.E. , Devenish R.W.
Published: June 2020

It has long been recognised that silicates can suffer extensive beam damage in electron-beam instruments. The predominant damage mechanism is radiolysis. For instance, damage in quartz, SiO2, results in loss of structural order without mass loss whereas feldspars (framework silicates containing Ca, Na, K) suffer loss of structural order with accompanying mass loss. In the latter case, the alkali ions, particularly Na, are found to migrate away from the area of the beam. The aim of the present study was to investigate the loss of various elements from the common silicate structures during electron irradiation at 100 kV over a range of current densities of 104 - 109 A m−2. (The current density is defined in terms of 50% of total current in the FWHM probe). The silicates so far ivestigated are:- olivine [(Mg, Fe)SiO4], a structure that has isolated Si-O tetrahedra, garnet [(Mg, Ca, Fe)3Al2Si3AO12 another silicate with isolated tetrahedra, pyroxene [-Ca(Mg, Fe)Si2O6 a single-chain silicate; mica [margarite, -Ca2Al4Si4Al4O2O(OH)4], a sheet silicate, and plagioclase feldspar [-NaCaAl3Si5O16]. Ion- thinned samples of each mineral were examined in a VG Microscopes UHV HB501 field- emission STEM. The beam current used was typically - 0.5 nA and the current density was varied by defocussing the electron probe. Energy-dispersive X-ray spectra were collected every 10 seconds for a total of 200 seconds using a Link Systems windowless detector. The thickness of the samples in the area of analysis was normally 50-150 nm.
The buckling of thin EM specimens
Authors: Thölén A.R.
Published: June 2020

Thin electron microscope specimens often contain irregular bend contours (Figs. 1-3). Very regular bend patterns have, however, been observed around holes in some ion-milled specimens. The purpose of this investigation is twofold. Firstly, to find the geometry of bent specimens and the elastic properties of extremely thin foils and secondly, to obtain more information about the background to the observed regular patterns.

The specimen surface is described by z = f(x,y,p), where p is a parameter, eg. the radius of curvature of a sphere. The beam is entering along the z—direction, which coincides with the foil normal, FN, of the undisturbed crystal surface (z = 0). We have here used FN = [001]. Furthermore some low indexed reflections are chosen around the pole FN and in our fcc crystal the following g-vectors
are selected:
SEM study of quartz grains from recent sediments: Western Iraq
Authors: Al-Kufaishi F.
Published: June 2020

Two localities (Al-Marij and Laik) were selected to investigate the type of Quartz Grains from crustal material formed by evaporation of waters discharged by springs in Hit area, western Iraq, Previous studies on the crustal material (1,2) showed that the water discharged by these springs are associated with Abu-Jir fault system which run parallel to the Euphrates river,

Factor analyses of the crustal and soil materials (50 samples analysed for 16 variables)(2) showed five factors; the first factor includes SiO2, Al2O3 and TiO2 with positive factor loading, and CaO, L.O.I. with negative loading and hence lead to the conclusion that the distribution of these variables is a reflection of transported clay material.

This study concentrates on the use of SEM to investigate the contribution of Quartz grains found in the crustal material on two selected
sites.
Modelling of the electron beam scattering by fine-dispersed structures and calculation of topographical contrast of cathodoluminescent images in the SEM
Authors: Viskov M.V. , Nikolaev A.G. , Obyden S.K. , Saparin G.V. , Meleshkin S.M.
Published: June 2020

A three-dimensional model of the scattering of a high-energy electron beam in a fine-dispersed structure (FDS) is developed. The model is intended for calculating, by the Monte-Carlo method, the color and black-and-white contrast of the image formed in the course of investigations of powdered structures in the cathodoluminescence (CL) mode in the SEM. The theory is developed in the approximation of an infinitely thin electron beam, which limits the minimum sizes of FDS crystals by the value of the order of 10μm under the experimental conditions (the electron beam diameter of 0.8 to 1.0 μm).

The model takes account of: 1) elastic and inelastic interactions, and the absorption of the electrons of the primary beam scattered during the whole succession of the acts of interaction with FDS crystals; 2) secondary electron emission: the “birth”, elastic and inelastic scattering, and the absorption of secondary electrons during the whole succession of the acts of interaction with FDS crystals; 3) a change in the intensity and wavelength of the detected monochromatic CL-radiation of each of the FDS crystals with allowance made for the elastic and Raman scattering and the absorption of CL photons; 4) a stochastic character of the volume distribution of the FDS crystals, as well as their random orientation and possible defects of their shape; the requirement of the identical size of the crystals being kept in force; 5) the geometry of the light-collecting system, namely, the angular aperture of the luminescence collector.
The orientation relationships between widmanstatten cementite and austenite
Authors: Farooque M. , Edmonds D. V.
Published: June 2020

Cementite has a complex orthorhombic crystalline structure with lattice parameters 4.52, 5.08 and 6.74 Å. Its crystallographic orientation relationship with austenite was first determined by Pitsch using a Hadfields Manganese Steel (nominally Fe-13Mn-1.2C (wt%))and this was later confirmed by Dippenaar and Honeycombe. This is within 5° of

(where the subscripts c and a denote cementite and austenite respectively).

The present study has also been carried out in Hadfields Manganese Steel, which has the advantage that it is austenitic at room temperature but can be partially decomposed to Widmanstatten cementite, among other structures, by annealing at intermediate temperatures in the approximate range 300-650 °C.

An alloy of nominal composition Fe-12Mn-0.8C (wt%) was prepared as a 50 g argon arc melt and homogenised at 1200 °C. Samples were hot-rolled,cold swaged and machined to 3 mm diameter rod. Short lengths of rod were encapsulated in silica tube under a partial pressure of argon and solution treated at 1200 °C for 15 min, quenched to room temperature, and then annealed at 375 °C for 96 hours.
Correlation between dislocation, grain boundary and interface of duplex SS in stress corrosion cracking(SCC)
Authors: Zheng-fang Wang , Wang Z.F.
Published: June 2020

The main purpose of this study highlights on the evaluation of chloride SCC resistance of the material,duplex stainless steel,OOCr18Ni5Mo3Si2 (18-5Mo) and its welded coarse grained zone(CGZ).18-5Mo is a dual phases (A+F) stainless steel with yield strength:512N/mm2 .The proportion of secondary Phase(A phase) accounts for 30-35% of the total with fine grained and homogeneously distributed A and F phases(Fig.1).After being welded by a specific welding thermal cycle to the material,i.e. Tmax=1350°C and t8/5=20s,microstructure may change from fine grained morphology to coarse grained morphology and from homogeneously distributed of A phase to a concentration of A phase(Fig.2).Meanwhile,the proportion of A phase reduced from 35% to 5-10°o.For this reason it is known as welded coarse grained zone(CGZ).In association with difference of microstructure between base metal and welded CGZ,so chloride SCC resistance also differ from each other.

Test procedures:Constant load tensile test(CLTT) were performed for recording Esce-t curve by which corrosion cracking growth can be described, tf,fractured time,can also be recorded by the test which is taken as a electrochemical behavior and mechanical property for SCC resistance evaluation. Test environment:143°C boiling 42%MgCl2 solution is used.Besides, micro analysis were conducted with light microscopy(LM),SEM,TEM,and Auger energy spectrum(AES) so as to reveal the correlation between the data generated by the CLTT results and micro analysis.
Precipitation of chromium borides in annealed nickel aluminides
Authors: Carro G. , Wittig J.E. , Kenik E.A. , Flanagan W.F.
Published: June 2020

Alloys based on the intermetallic phase, Ni3Al, are a class of materials noted for superior elevated temperature mechanical properties and oxidation resistance. Boron has been shown to increase ductility in these alloys and chromium additions to boron-doped nickel aluminide alloys have been reported to improve the high temperature properties by reducing dynamic embrittlement in oxidizing environments. However, a potential problem with these Ni-Al-Cr-B alloys is the depletion of chromium and boron at grain boundaries from chromium boride precipitation.

Two alloys were investigated for elevated temperature chromium boride precipitation. The first, IC-218, has the composition (at%): 16.4 Al, 8.0 Cr, 0.4 Zr, 0.1 B, Ni bal., and the second, OR3B contains 15.0 Al, 10.0 Cr, 0.1 B, Ni bal.. Samples of both alloys were rapidly solidified into circular foils, 0.25 mm thick, by splat quenching between two copper plates. Also, cold rolled and recrystallized sheet, 3 mm thick, of IC-218 was used for comparison.
Stability of the T2 phase during low-dose ion milling
Authors: Reed J. R. , Michel D. J. , Howell P. R.
Published: June 2020

Recent studies have shown that the T2 (Al6CuLi3) phase particles in dilute Al-Li-Cu alloys transform to microcrystalline aggregates during TEM examination, during ion-beam thinning, or during in- situ heating in the TEM. Other studies, however, have noted that the T2 phase particles exhibit an ‘apparent’ five-fold symmetry suggesting that microcrystalline or twinned regions, rather than ‘single crystal’ regions, were responsible for the five-fold diffraction patterns. As a consequence, additional work was considered necessary to investigate further the stability of the T2 phase in dilute Al-Li-Cu alloys.

The 3-mm diameter TEM disc specimens were prepared from a specially melted Al-2.5%Li-2.5%Cu alloy produced by conventional procedures. The TEM specimen thermal treatment and electropolishing procedures were previously reported. The electropolished disc specimens were examined in a JEOL 200CX microscope operated at 200 kV. Selected disc specimens containing the T2 phase were then subjected to ion beam thinning in a Gatan precision ion-milling system, operated with an argon ion beam, at accelerating voltage of 6 kV and a beam current of lμA.
HREM studies on twinning behaviour of eutectic silicon in unmodified and Sr- modified Al-Si alloys
Authors: Sharazuzzoha M. , Hogan L.M. , Smith David J. , Deymier P.A.
Published: June 2020

The addition of trace amounts of sodium or strontium to commercial Al-Si alloys promotes a massive increase in twin density in the eutectic silicon which is associated with a change in morphology of the silicon phase from a flake to a fibrous form. In the flake form the internal twins are always parallel to external faces of an individual flake as in Fig. 1a, resulting in a consistent <112> growth direction by the twin-plane reentrant edge (TPRE) growth mechanism. In the fibrous form the high twin density promotes a zigzag alternation of <112> growth directions, as in Fig. 1b, with a net <001> growth axis,so that twins can be parallel to any of four <110> axes. In the flake form all twins lie in a single <110> zone. The essential morphological features of flake and fibrous growth are conveyed in two dimensions by Figs. 1a and 1b. HREM has been employed in the present study to investigate further the nature of the twinning in eutectic silicon of flake and fibrous morphologies.
Orientation and morphology variants of the α2 phase in B2 parent matrix in a super α2 titanium aluminide alloy
Authors: Edelson Lawrence H.
Published: June 2020

Titanium aluminides are potential low density, high stiffness, high-temperature materials that use ordered crystal lattices to retain strength at elevated temperatures. The super α2 system is based on the hexagonal DO19 α2 phase (Ti3Al), but has sufficient β (BCC, high temperature phase) stabilizing elements (Nb, V and Mo) so that a continuous B2 ordered cubic phase is retained to room temperature. Transmission electron microscopy (TEM) images and selected area electron diffraction (SAD) patterns were used to analyze the crystallography and morphology of the α2 phase that forms when 100% B2 phase is aged at 1000°C for one hour. TEM is the only technique that provides both precise crystallographic and morphological analysis of the phase transformation.

The microstructure produced from 100% B2 material, formed by ice brine quenching the super-α2 alloy from 1250°C, by aging at 1000°C for 1 hr is shown in the scanning electron micrograph in Figure 1. The dark discontinuous phase is acicular α2, while the light continuous phase is the ordered cubic B2 phase.
Microstructural stability in rapidly solidified ternary iron aluminides
Authors: Morton Allan J. , Décamps Brigitte , Gibson Mark A. , Wolfenden Alan
Published: June 2020

Iron aluminides containing ternary additions of Cr, Si and other alloying elements offer good oxidation and sulphidation resistance at a relatively low cost but these alloys have only moderate strength at elevated temperatures and are of limited ductility. The generation of a distribution of fine dispersoids throughout the matrix of these alloys can provide increased strength and also improve ductility by reducing grain size.

We report a study of the microstructural stability of rapidly solidified strip of iron aluminides containing chromium and minor additions of both titanium and boron. As cast strip thickness was in the range 80-120μm.

Figure 1 shows the grain structure near the centre of the as cast strip of a 66.5Fe-28.5Al-5.0Cr (at.%) alloy. The grain size in this view of the strip is quite small (2-5μm) although optical metallography of the longitudinal and transverse cross sections show that the grain structure is columnar through much of the strip thickness.
Aging behaviour of U-6.0Wt.% Nb at temperatures above 350°C
Authors: Beverini G. , Edmonds D.V.
Published: June 2020

Large strength increments accompanied by severe ductility losses are observed upon ageing U-6Nb at temperatures between 350°C and 450°C. This study attempts to characterize the fine scale morphological and compositional changes observed upon ageing this alloy in this temperature regime. Precipitation of Nb-rich particles having a tetragonal crystal structure is believed to be the mechanism responsible for age hardening in this alloy.

Material supplied by AWE, Aldermaston, U.K. was received in the as-water quenched (WQ) condition in the form of 3 mm. diameter rods. Material was aged in sealed silica tubes containing a partial pressure of argon. The aged rods were then sliced to 0.5 mm. thick disks and subsequently ground down to a thickness of 90 μm. using 1200 grit SiC paper. Electropolishing was carried out in a Fischione twin-jet electropolishing unit using a solution of 5% HClO in methanol cooled to -60°C at a voltage of 40V.
Processing and characterization of B4C-Al laminated cermets
Authors: Yasrebi Mehrdad , Kim Gyeung H. , Milius David L. , Sarikaya Mehmet , Aksay Ilhan A.
Published: June 2020

B4C-Al composites show enhanced fracture strength and fracture toughness values over monolithic B4C.1-2 A controlled change in structural morphologies such as lamination further enhances mechanical properties of the composite over the B4C-Al composites processed to form a monolithic morphology. This paper summarizes microstructure-property correlations studied in B4C-Al laminated composites.

The laminated composite is formed either by metal infiltration of B4C tapes sandwiched with Al sheets, type (a), (Fig. 1a) or by lamination of B4C tapes of different porosity and then subjected to metal infiltration of the laminated body, type (b), (Fig. 1b). In the first method, after thin tapes of B4C were formed, each tape was individually sintered between polished graphite discs, then layered with Al sheets, and the entire stack was heated to induce infiltration. In the second method, tapes of B4C with different green densities were stacked and laminated under pressure and temperature. The laminated body was then sintered and subsequently infiltrated with Al.
TEM study of lanthanum aluminate
Authors: Yang C.Y. , Huang Z.R. , Zhou Y.Q. , Li C.Z. , Yang W.H. , Fung K.K.
Published: June 2020

Lanthanum aluminate(LaAlO3) single crystal as a substrate for high Tc superconducting film has attracted attention recently. We report here a transmission electron microscopy(TEM) study of the crystal structure and phase transformation of LaAlO3 by using Philips EM420 and EM430 microscopes. Single crystals of LaAlO3 were investigated first by optical microscope. Stripe-shaped domains of mm size are clearly seen(Fig.1a), and 90° domain boundary is also obvious. TEM specimens were prepared by mechanical grinding and polishing followed by ion-milling.

Fig.lb shows μm size stripe domains of LaAlO3. Convergent beam electron diffraction patterns (CBED) from single domain were taken.Fig. 2a and Fig. 2c are [001] zone axis patterns which show a 4mm symmetry, and the (200) dark field of this zone axis gives 2mm symmetry(fig.2b). Therefore the point group of this crystal is either 4/mmm or m3m. The projection of the first order Laue zone(FOLZ) reflections on zero layer (fig. 2c) shows that the unit cell is face centered. A tetragonal unit ceil is chosen, with a=0.532nm and c=0.753nm, c being determined from the FOLZ ring diameter.