bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoparticles of Cd(S,Se) grown in silicate glasses study by High Resolution Transmission Electron Microscopy (HRTEM) assisted by image treatment
Authors: Gandais Madeleine , Allais Mireille
Published: June 2020

CdSxSe1-x doped glasses have raised large interest in the recent past years. They are commercially available as sharp cut-off filters with optical absorption edge varying from yellow to deep red as the composition x varies from 1 to 0, according to the properties of bulk Cd(S,Se) compounds, On the other hand glasses prepared in laboratory present different optical properties in relation with excitonic confinement when the semiconductor grains are smaller than 5nm : increase of the third order nonlinear optical susceptibility, shift of the absorption edge toward higher energy, quantum size effects. In order to improve the understanding of the optical properties, it is important to get fine structural informations on the semiconductor phase : crystallographic structure (which may be different than in bulk materials), morphology, size and defects. Comparatively to optical investigations, there have been few structural studies of the semiconductors doped glasses. HRTEM is potentially a powerful method for examining nanocrystals in low concentration within glass. Practically however, the sharpness of the crystal images is reduced by the presence of background signal originating mainly from glass. Numerical treatment of filtering through Fourier transformation presents several advantages. A large part of the signal originating from glass (at low frequencies) and from statiscal noise (at high frequencies) may be suppressed as shown in Figures 1 and 2. The Fourier transform (Figure 2c) may be used for measuring the lattice parameters more easely than the lattice image.
Cross-section preparation of copper/polyimide interfaces for TEM analyses
Authors: Csencsits Roseann , Riel Norman , Rose Jamie , Dion John
Published: June 2020

Copper/polyimide (Cu/PI) structures are used extensively for computer packaging applications. For high circuit density multi-chip substrates, a thin film (typically 2-5μm) of polyimide is used; but the polyimide used to interconnect the multi-chip substrates via tape automated bonding (TAB) is typically 50μm thick to protect the tape leads from the cantilever effect. Although many spectroscopic, adhesion and deformation studies have been published about the bonding of metals to thin polyimide, relatively little has been published regarding the use of metal on thick polyimide.

One factor limiting the analyses of these interfaces derived from the thick polyimide is the difficulty preparing adequate TEM specimens.Due to the greatly differing ion milling rates of metals and polymers, and the thickness of the two layers, a preparation technique was developed on model tape samples.The model samples consisted of 1μm sputtered Cu on 50μm polyimide, with and without Cr adhesion layers.
A novel TEM technique for junction delineation in integrated circuits
Authors: Romano A. , Vanhellemont J. , De Keersgieter A. , Vandervorst W. , Morante J. R. , Van Landuyt J.
Published: June 2020

Ion implantation is a well established technique to dope selectively prespecified regions of silicon substrates. It has the drawback that a thermal treatment is required to activate the dopant and to reconstruct the crystal lattice. This leads to dopant diffusion in depth and also laterally, when the implantation has been preformed through a patterned mask.

In this paper two different approaches to determine the doping profile using chemical etching and TEM are presented. Cross-section specimens are prepared using a technique described elsewhere, followed by preferential etching.

The first approach is well established and is based on the combined action of HF and HNO3.Low concentrations of HF are used to keep the etching rate low enough. Figure 1 shows a cross-section of a boron implanted and annealed sample which has been etched using the solution HF(40%):HNO3(65%)= 1:300 at 5°C for 80 seconds. The etching rate is proportional to the doping level, as shown in figure 2 and it can be observed that the lowest level which one can delineate with this solution is of the order of 1017cm−3, which is in agreement with the delineated level of figure 1, namely 6·1017 cm−3.
Conventional methods of Lorentz microscopy
Authors: Geiss H.Roy
Published: June 2020

Lorentz electron microscopy has been used to study magnetic domain/domain wall structures in thin films since 1959. Initially the contrast was described in terms of the classical Lorentz deflection of the incident electron beam. As a result Lorentz microscopy has become the general designation given to any of the techniques used to study the magnetic structure with electron beams. However, when sufficiently weak interactions are considered, a more rigorous quantum-mechanical description of the electron-specimen is required. It thus becomes necessary to consider the basis of magnetic imaging as following from the interaction between the magnetic vector potential of the specimen and the incident electron beam. This interaction results in a phase change of the propagating electron beam which is proportional to the path integral of the vector potential. Thus Lorentz microscopy, in reality, is simply phase contrast microscopy for a special class of objects.

For many of the magnetic thin films investigated the coercivity of the film is so low that it must be in a nearly zero field environment in order to retain the domain structure. In order to achieve this condition experimentally, the objective lens is usually turned off and the diffraction lens is used as the image forming lens.
A new method for the observation of Type II magnetic contrast
Authors: Ferrier R.P. , McVitie S.
Published: June 2020

Type II magnetic contrast was first observed by Philibert and Tixier and relies on the change in the effective backscattering coefficient due to interaction of the scattered electrons within the specimen and the local magnetic induction (for a review see Tsuno). Depending on the tilt of the specimen and the position of the backscattered electron detector(s), contrast due to the presence of either or both domains and domain walls can be obtained; in the case of the latter, the standard geometry is for the specimen to be normal to the incident beam and the detectors are positioned above it and close to the optic axis. This is the geometry adopted in our studies, which used a JEOL 2000FX with a special split objective lens polepiece; this permitted the specimen to be in magnetic field-free space, the separate lens gaps above and below allowing good probe forming capabilities combined with excellent Lorentz imaging performance. A schematic diagram is shown in Fig. 1.
Fabrication and characterization - by High Resolution Electron Microscopy and atom probe microanalysis - of Co-based metallic multilayer films
Authors: Petford-Long Amanda K. , Cerezo A. , Hetherington M.G.
Published: June 2020

The fabrication of multilayer films (MLF) with layer thicknesses down to one monolayer has led to the development of materials with unique properties not found in bulk materials. The properties of interest depend critically on the structure and composition of the films, with the interfacial regions between the layers being of particular importance. There are a number of magnetic MLF systems based on Co, several of which have potential applications as perpendicular magnetic (e.g Co/Cr) or magneto-optic (e.g. Co/Pt) recording media. Of particular concern are the effects of parameters such as crystallographic texture and interface roughness, which are determined by the fabrication conditions, on magnetic properties and structure.

In this study we have fabricated Co-based MLF by UHV thermal evaporation in the prechamber of an atom probe field-ion microscope (AP). The multilayers were deposited simultaneously onto cobalt field-ion specimens (for AP and position-sensitive atom probe (POSAP) microanalysis without exposure to atmosphere) and onto the flat (001) surface of oxidised silicon wafers (for subsequent study in cross-section using high-resolution electron microscopy (HREM) in a JEOL 4000EX. Deposi-tion was from W filaments loaded with material in the form of wire (Co, Fe, Ni, Pt and Au) or flakes (Cr). The base pressure in the chamber was around 8×10−8 torr during deposition with a typical deposition rate of 0.05 - 0.2nm/s.
Microdomains in BaFeO3-y (0.35 < y < 0.50)
Authors: Vallet-Regí M. , Parras M. , González-Calbet J.M. , Grenier J.C.
Published: June 2020

BaFeO3-y compositions (0.35<y<0.50) have been investigated by means of electron diffraction and microscopy to resolve contradictory results from powder X-ray diffraction data.

The samples were obtained by annealing BaFeO2.56 for 48 h. in the temperature range from 980°C to 1050°C . Total iron and barium in the samples were determined using chemical analysis and gravimetric methods, respectively.

In the BaFeO3-y system, according to the electron diffraction and microscopy results, the nonstoichiometry is accommodated in different ways as a function of the composition (y):

In the domain between BaFeO2.5+δBaFeO2.54, compositional variations are accommodated through the formation of microdomains. Fig. la shows the ED pattern of the BaFeO2.52 material along thezone axis. The corresponding electron micrograph is seen in Fig. 1b. Several domains corresponding to the monoclinic BaFeO2.50 phase, intergrow with domains of the orthorhombic phase. According to that, the ED pattern of Fig. 1a, can be interpreted as formed by the superposition of three types of diffraction maxima : Very strong spots corresponding to a cubic perovskite, a set of maxima due to the superposition of three domains of the monoclinic phase along [100]m and a series of maxima corresponding to three domains corresponding to the orthorhombic phase along the [100]o.
Radiation damage and charging effects of insulators in Electron Microscopy
Authors: Cazaux Jacques , Jbara Omar , Kim K.H.
Published: June 2020

In the proliferation of papers dealing with charging effects of insulators submitted to an electron bombardment, the macroscopic consequences of charging are quite always considered without any consideration on the microscopic causes. The electric field built up and potential are only the electrostatic consequence of the trapped charge distribution, ρ(r,t), and, consequently of the trapping mechanisms of charged particles. On the other hand, the radiation damage effects are often explained by microscopic mechanisms (such as the Knotek-Feibelmann model) despite the fact that most of these radiation damages occur in insulators where a very large electric field may be established : If all the particles penetrating into the insulators where trapped for a long time the calculated electric field will reach 107 V/cm in less than one second (for a beam density of 1 μA/mm2). The above remark suggests that the (positive or negative) charged particles are not all trapped or, if they are, it is with a very short trapping time τr.)
Is there an electron wind?
Authors: Marks L. D. , Zhang J. P.
Published: June 2020

A not uncommon question in electron microscopy is what happens to the momentum transferred by the electron beam to a crystal. If the beam passes through a crystal and is preferentially diffracted in one direction, is the momentum ’lost’ by the beam transferred to the crystal? Newton’s third law implies that this must be the case. Some experimental observations also indicate that this is the case; for instance, with small particles if the particles are supported on the top surface of a film they often do not line up on the zone axis, but if they are on the bottom they do. However, if momentum is transferred to the crystal, then surely we are dealing with inelastic scattering, not elastic scattering and is not the scattering probability different? In addition, normally we consider inelastic scatter as incoherent, and therefore the part of the electron wave that is inelastically scattered will not coherently interfere with the part of the wave that is scattered; but, electron holography and high resolution electron microscopy work so the wave passing through a specimen must be coherent with the wave that does not pass through the specimen.
Crystallization in highly irradiated poly(vinyl chloride)
Authors: Avalos-Borja M. , Adem E. , Cota L. , Burillo G.
Published: June 2020

Poly (vinyl chloride) is one of the most widely used materials in today’s society, and the study of its properties is relevant to many fields. In the present case, we investigate changes that occured in this material when it was exposed to high doses of gamma rays. Previous studies using electron beam irradiation indicated the possibilities of using this material as a “getter” due to its ability to capture gases like CO2 and CO. The present work deales with preliminary results on the structural characteristics of a carbon rich material obtained using ionizing radiation.

Radiation treatment was done in several steps, a) irradiation of 1000 Mrad (at dose rate of 0.95 Mrad/hr) in a Gamma Beam Type 651-PT ( Co) source. b) the sample is then extracted with tetrahydrofuran (THF) in order to separate the homopolymer from the gel that was formed during irradiation. c) the gel fraction (crosslinked polymer) was filtered, dried and weighted, and exposed again for 200 Mrad more
Low-energy displacement damage and the effect on the AEM of Ceramics
Authors: Howitt D. G. , Medlin D.L. , Cluckie M. M.
Published: June 2020

The observation that the signal from light elements such as carbon, oxygen, and nitrogen decreases in strength with time is to be expected for displacement in ceramic materials at high voltage, not only because the momentum transfer from an electron is more favorable, but also because the lattices are often full of defects. Even though the sensitivities of these materials can be below that of close parked metals at high voltage, during analytical electron microscopy the beam currents are sufficiently intense that the effect can be substantial. The loss rates for the signal are however quite predictable in the early stages and need not interfere with quantitative assessments of composition.

An example of the loss of carbon signal from titanium carbide is shown in Figure 1 and a determination of the overall cross-section for carbon loss at 100 keV indicates a value close to 0.3 barns. This is about the cross-section for carbon displacement at 20 eV which is a conservative estimate of the binding energy for carbon in the lattice. Early experiments on vanadium carbide (Venables, 1969) indicate a similar overall cross-section however the threshold energy for the electrons to induce the damage is about only 5 eV. These results are consistent with the transfer of about 5 eV from an incident electron inducing a very small displacement of the carbon atom, of the order of an interatomic distance, with a damage cross-section of about 200 barns. Since the process needs to be repeated several times before the carbon atom is lost from the specimen the measured cross-section is proportionality reduced.
New method for producing double replica for observing and a precipitates
Authors: Spiradek Krystyna , Czyrska-Filemonowicz Aleksandra , Hörl Erwin M.
Published: June 2020

In metallurgy and metal physics it is very often necessary to analyse the types, shapes, sizes etc. of precipitates in a metal or metal alloy. Furthermore it is often of importance to know the distribution of these particles along the grain boundaries and within the grains. For this analysis a new EM technique has been developed.

The procedure of this technicue is the following:

First of all specimens are prepared of the materials to be investigated in such a way that one obtains thin metal plates or foils of a thickness of 0,1 to 0,01 mm. This foils are etched in a H2O solution of 10 % H2CrO3 for revealing the surface structure. Afterwards carbon is avaporated on both sides of the foils. In the next step a square grid of 3 mm х 3 mm is scratched into the foil on both sides in such a way that the grid of the top side is exactly positioned over the grid of the bottom side. After this procedure the specimens are inserted into an ethanol solution of 10 % bromine in a horizontal position till the metallic matrix is solved and the precipitates are left. This step takes approx. 24 hours. Afterwards the replicas consisting of the two carbon layers with the precipitates between them are cleaned using firstly ethanol afterwards 50% ethanol in destilled water and finally just destilled water (.5 hours in each bath). In the next step the replicas are put on EM grids of sandwich type. Great care is necessary in this step in order to avoid shifting of the carbon layers and disturbances of the positions of the precipitates. These replicas are now ready for TEM as well as SEM investigations, as soon as they are dry.
Characterization of active slip systems in Hg0.8Cd0.2Te
Authors: McKeagney D. B. , Campbell T. J.
Published: June 2020

The compound semiconductor Hg0.8Cd0.2Te is commonly used in the production of infrared detection devices. In bulk growth, due to low Hg-Te bond strengths, high dislocation densities are often encountered. These dislocations, which are generated during the crystal growth process, significantly impair the performance of the semiconductor device. To best control this dislocation generation during growth, a knowledge of the active slip systems within the crystal lattice is desirable.

Microhardness tests were performed on two distinct crystal surfaces of Bridgman grown Hg0.8Cd0.2Te crystals. Selected area electron channeling was used to determine trie crystallographic orientations of the surfaces that were tested. The slip lands that were introduced during the indentation process were observed using both the scanning electron and optical microscopes. From the data obtained, using elementary crystallographic techniques, the dominant slip systems active in Hg0.8Cd0.2Te were characterized.
Growth and morphology of NaCl-type crystals prepared by various methods
Authors: Saito Yoshio , Kaito Chihiro , Maeda Shigeo
Published: June 2020

NaCl type crystals generally grow a cube. NaCl-type crystals with rhombic prism shape have been found among the cube crystals. No convincing interpretation for the rhombic prism crystals has been given. The growth mechanisms of some crystals have been clarified by means of potetial energy calculations in previous papers. In the present paper, free energy of NaCl type crystals having various shapes have been calculated in order to make clear the origin of the appearing of the rhombic prism crystals. The growth mechanism is discussed on the basis of the free energy.

NaCl crystals were grown from aqueous solution in a glass made growth cell thermostated with circulating water(±l⋅C). The NaCl crystals were grown at temperature of 50°C which is equivalent to the supersaturation of 2%. The grown crystals were mounted on a net and were dried with a filter paper as quickly as possible. The specimens were examined by a microscope. PbS crystals are prepared by the two-heater method which have been developed to produce ultrafine particles of low melting materials. The detail of the preparation has been shown in a previous paper. The grown crystals collected on a carbon film supported by an electron microscope grid were observed with a Hitachi H-9000 electron microscope.
EM studies of long-lived fiber gels complemented by solid state 2H-NMR spectroscopy
Authors: Svenson Sönke
Published: June 2020

Aqueous gels (1%) consisting of the amphiphilic N-octyl-D- gluconamide (D-Glu-8) usually crystallize within a few hours.They remain stable for more than five months if 0.4% of sodium dodecylsulfate (SDS) is added. It was shown by electron microscopy that the gels are formed by helical fibers of at least bimolecular thickness (4 nm) and of several micrometers length. Randomly dispersed particles with a mean diameter of 5 nm, which are assumed as micelles, were also observed on micrographs (Fig.1).

To provide evidence for this assumption and to rule out the possibility of artefacts introduced by the preparative method, we applied an additional technique, namely solid state 2H-NMR spectroscopy. The spectra point out the temperature dependent equilibrium between “solid” fibers and micelles, as represented by the Pake powder spectrum and the isotropic central singlet (Fig.2). The micellar part of the equilibrium is strongly enhanced in the presence of detergents such as SDS. High concentrations of SDS micelles extend the gel’s lifetime, presumably because these micelles dissolve the crystallization nuclei of D-Glu-8 and thus, prevent further crystal growth.
Electrothinning of nickel thick films for characterization by TEM with the aid of a conducting polymer film
Authors: Chong Ngee-Sing , Norton Michael L.
Published: June 2020

Existing techniques for the preparation of metallic specimens for examination by transmission electron microscopy consist primarily of jet electrolysis or ion milling. Both of these procedures are well-established and are suitable for thinning metallic specimens of interests from a thickness of 0.1 mm to 30-100 nm. Despite its popularity, the former technique may not be suitable for thinning electrodeposited films of 1-5 um thick because of its rather rapid thinning rate of 0.5-1.0 um/sec. Furthermore, it is difficult to ensure good electrical contact between such a delicate film and the specimen holder. Hence, the older method of “window” electropolishing may be applicable owing to its slower thinning rate despite the troublesome steps of lacquering specimen edges, finding suitable polishing conditions, and making electrical attachment. Ion milling, despite its relatively high cost, may be suitable for thinning the nickel films because of its slow milling rates on the order of 110 um/hr. However, special expertise is required in the manipulation of milling conditions such as ion energy and incident ion beam angle to avoid creating the structural artifacts of ion implantation, atom translocation, and bubbling.
Characterising scale-breakdown mechanisms during high-temperature oxidation using EM
Authors: Rowley P .N. , Brydson R. , Little J. A. , Saunders S. R. J.
Published: June 2020

The microstructure and chemical composition of oxide films formed during the initial stages of high temperature oxidation have long been recognised as having a major effect on subsequent scaling behaviour. For example, the development of thick (>lμm) duplex scales on Fe-Cr alloys is assumed to occur via a mechanism of pore and fissure formation in the initial oxide (Atkinson, Tomlinson and Cory.) However, this process has rarely been observed using electron microscopy.

The investigation of the oxidation behaviour of Fe-9Cr alloys in high temperature steam gives an insight into these scale breakdown processes. Within 3 minutes of the onset of oxidation, significant breakdown of the initially formed thin film occurs due to the development of readily visible fissures and pores at oxide grain boundaries (figure 1). This leads to the ready ingress of oxidant and the rapid development of a thick duplex Fe3O4/(Fe,Cr)3O4 oxide with a thin outer layer of α-Fe2O3 (figure 2). The extremely porous nature of this scale allows further inward diffusion of molecular oxidant, thereby instituting the continued growth of (Fe,Cr)3O4 at the scale/metal interface.
The crystallography characteristic of (Mn,Fe)S single crystal
Authors: Xishan Jiang
Published: June 2020

This paper reports the growth step pattern and morphology at equilibrium and growth states of (Mn,Fe)S single crystal on the wall of micro-voids in ZG25 cast steel by using scanning electron microscope. Seldom report was presented on the growth morphology and steppattern of (Mn,Fe)S single crystal.

Fig.1 shows the front half of the polyhedron of(Mn,Fe)S single crystal,its central area being the square crystal plane,the two pairs of hexagons symmetrically located in the high and low, the left and right with a certain, angle to the square crystal plane.According to the symmetrical relationship of crystal, it was defined that the (Mn,Fe)S single crystal at equilibrium state is tetrakaidecahedron consisted of eight hexagonal crystal planes and six square crystal planes. The macroscopic symmetry elements of the tetrakaidecahedron correpond to Oh—n3m symmetry class of fcc structure,in which the hexagonal crystal planes are the { 111 } crystal planes group,square crystal plaits are the { 100 } crystal planes group. This new discovery of the (Mn,Fe)S single crystal provides a typical example of the point group of Oh—n3m.
TEM study on fine carbide precipitates and dislocation cell structure
Authors: Chen Mengzhe , Wang Siqin , Ke Jun
Published: June 2020

A series of investigations have been conducted into the nature and origin of the dislocation cell structure. R.J.Klassen calculated that the dislocation cell limiting size in pure ferrite matrix is about 0.4 μm. M.N.Bassion estimated the size of dislocation cell in deformed ferrite of HSLA steels to be of the same order.

In this paper, TEM observation has been concentrated on the interaction of fine carbide precipitates with dislocation cell structure in deformed Fe-C-V (0.05%C, 0.13% and 0.57%V) and Fe-C-Nb (0.07 %C and 0.04%Nb) alloys and compared with that in Fe-C (0.05%). Specimens were austenitized at 1500 “C/20 min and followed by isothermal treatment at 750 °C and 800 “C for 20, 40 and 120 minutes . The carbide particle sizes in these steels are from 9 to 86nm measured from carbon extraction replicas. Specimens for TEM were cut from differently deformed areas of tensile specimens deformed at room temperture. The thin foils were jet electropolished at -20 C in a solution of 10% perchloric acid and 90% ethanol. The TEM observation was carried out in JEM 100CX , EM420 at 100kv and JEM 2000FX at 200kv.
Devitrification products of rapidly solidified Ni-Nb amorphous alloys.
Authors: Bertero G. A. , Hofmeister W.H. , Evans N.D. , Wittig J.E. , Bayuzick R.J.
Published: June 2020

Rapid solidification of Ni-Nb alloys promotes the formation of amorphous structure. Preliminary results indicate promising elastic properties and high fracture strength for the metallic glass. Knowledge of the thermal stability of the amorphus alloy and the changes in properties with temperature is therefore of prime importance. In this work rapidly solidified Ni-Nb alloys were analyzed with transmission electron microscopy (TEM) during in-situ heating experiments and after isothermal annealing of bulk samples. Differential thermal analysis (DTA), scanning electron microscopy (SEM) and x-ray diffraction (XRD) techniques were also used to characterize both the solidification and devitrification sequences.

Samples of Ni-44 at.% Nb were electromagnetically levitated, melted, and rapidly solidified by splatquenching between two copper chill plates. The resulting samples were 100 to 200 μm thick discs of 2 to 3 cm diameter. TEM specimens were either ion-milled or alternatively electropolished in a methanol-10% sulphuric acid solution at 20 V and −40°C.
Characterization of the microstructures produced by different solutionizing quench rates in aluminum-lithium alloys
Authors: Miyasato Shelly
Published: June 2020

The microstructure in lightweight aluminum-lithium alloys produced by two different quench rates after solution heat treatment were investigated using conventional transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). The formation mechanism, size and distribution of the phase δ’ (Al3Li) were compared, since the precipitate affects many of the mechanical properties in the age- hardening Al-Li system. The metastable δ’ phase has the L12 ordered structure based on the fcc lattice with a lattice parameter difference of -0.08% with the aluminum matrix. The equilibrium phase δ (AlLi) nucleates independently with the B32 structure. TEM yields direct evidence of δ’ formation, size and distribution which is unattainable by other methods due to the size of the precipitates and the presence of isostructural β’ (Al3Zr) dispersoids. Small blocks of Al-2.4Li-0.lZr and Al-2.6Li-lCu-0.5Mg-0.5Zr (wt.%) were solutionized at 550°C for 2 hrs, then either quenched in 0°C water or in still, ambient air. Electropolished foils were viewed in a Philips 301 (l00kV) or JEM 200CX (200 kV).
Processing and microstructure correlations of aluminum alloys for thin-film metallizations
Authors: Park M. , Krause S. J. , Wilson S. R.
Published: June 2020

Aluminum alloys, such as Al-Cu and Al-Cu-Si are the most extensively used metals for interconnects in integrated circuit. The beneficial effect of the Cu addition is to increase the resistance to electromigration and hillock growth. Si is also often added to minimize the erosion in contact windows and enhance the metal corrosion resistance in the wet photoresist development process. Due to the importance of grain boundary transport in electromigration failure, factors such as grain size and grain size distribution, have an important influence on the failure threshold in conjunction with the level of Cu. In addition, the level of Cu and Si has many detrimental effects, such as microcorrosion caused by the galvanic action of Al2Cu precipitates and the occurrence of Si precipitates, which result in points of high resistance. It is not clear what deposition conditions and what quantities of Cu and Si would lead to the optimum properties, in relation to the grain size and the size and distribution of Al2Cu and Si precipitates. Reductions of Cu and Si content can help to decrease the formation of Al2Cu and Si precipitates, but it is believed that these precipitates are readily formed due to the large surface to volume ratio. In the present study, the specific correlations between processing conditions, the amount of Cu and Si additions, and the microstructure of the Al alloy thin film are evaluated for the development of an improved alloy system.
Deformation and fracture behavior of an Al-Li-Cu-Mg-Zr alloy 8090
Authors: Jiang D.M. , Hong B.D.
Published: June 2020

Aluminum-lithium alloys have been recently got strong interests especially in the aircraft industry. Compared to conventional high strength aluminum alloys of the 2000 or 7000 series it is anticipated that these alloys offer a 10% increase in the stiffness and a 10% decrease in density, thus making them rather competitive to new up-coming non-metallic materials like carbon fiber reinforced composites.

The object of the present paper is to evaluate the inluence of various microstructural features on the monotonic and cyclic deformation and fracture behaviors of Al-Li based alloy. The material used was 8090 alloy. After solution treated and waster quenched, the alloy was underaged (190°Clh), peak-aged (190°C24h) and overaged (150°C4h+230°C16h). The alloy in different aging condition was tensile and fatigue tested, the resultant fractures were observed in SEM. The deformation behavior was studied in TEM.
Domain structures in rapidly solidified Mn76Fe4Si20 alloys
Authors: Zhou D. S. , Cao W. , Jin Z.X. , Ye H.Q.
Published: June 2020

In the study course of microstructures of the rapidly quenched Mn-Si alloy, 45° rotation twins showing striking eightfold symmetry in the electron diffraction pattern have been reported. These previous investigations interpreted the domain structures in terms of the β-Mn phase. The aim of this work is to show the similar domain structure having pseudo-eightfold symmetry in the reciprocal space in the Mn-Fe-Si system and to ascertain a new structure in the domain structure.

The main phase in this alloy is the β-Mn phase with primitive cubic and a=0.63 nm. Fig.l gives the [001] HR image of the β-Mn phase where a square unit cell has been outlined. A planar fault showing projected rectangle network was also seen.The short edge of the rectangle remains to be the same as the a axis of the p-Mn phase, while its long side is equal to . The planar fault could appear repeatedly and form domain structure as shown in Fig.2.
TEM of twinning in alpha and beta phase plutonium
Authors: Zocco T. G. , Sheldon R. I. , Rizzo H. F.
Published: June 2020

Twinning in α and β phase Pu has been studied by Transmission Electron Microscopy (TEM) to experimentally determine active twinning systems in this complex metal. Twinning in alpha phase Pu was studied in 2 specimens including a triode sputter deposited film, and a partially transformed (α+δ phase) Pu nominally lwt% Ga alloy. A thick film of metastable beta phase was also obtained by triode sputter deposition. Phase identification of all samples was determined from x-ray diffraction patterns. Alpha phase has a monoclinic crystal structure with 16 atoms per unit cell and a P21/m space group. Beta phase has a body-centered monoclinic crystal structure with 34 atoms per unit cell and an I2/m space group.

Parent/twin orientation relationships were determined by electron diffraction pattern analysis, stereographic projection analysis and fundamental crystallographic calculations.A computer program was also developed to search for all possible twinning systems in α Pu.
Microstructural study of dispersed phase ceramic Bn-AlN composite coatings by chemical vapor deposition
Authors: Freeman G. B. , Lee W. Y. , Lackey W. J.
Published: June 2020

Dispersed phase ceramic composites have recently received much attention because of their superior mechanical properties including fracture toughness, strength, hardness, resistance to wear and erosion. Chemical vapor deposition (CVD) offers one avenue of preparing ceramic composites by simultaneous deposition of multiple phases, i.e. codeposition. The major advantage of preparing dispersed phase ceramic composites by CVD is that mechanical as well as chemical, electrical, optical, and thermal properties of the composites can be favorably tailored by controlling the composites’ composition and microstructure via variation and optimization of CVD process variables such as temperature, pressure, reagent concentration, substrate type, reactor geometry, etc.

In this study, the codeposition of boron nitride (BN) and aluminum nitride (AlN) was explored because the BN+AlN composite system (as a deposited coating) offers the promise of tailoring properties such as friction coefficient, hardness, and resistance to wear and erosion for possible radome, electromagnetic window and tribological applications.
Direct observation of microstructural changes in ion-beam modified ceramics
Authors: Grant Norton M. , Fleischer Elizabeth L. , Hertl William , Mayer James W. , Barry Carter C.
Published: June 2020

A technique for the direct observation of microstructural changes in ceramics following ion- implantation is presented. Ion-implantation produces modifications to the mechanical properties of ceramic surfaces. These modifications have been investigated as a means of improving the hardness and wear of such materials. Examples of these changes will be presented for single-crystal specimens of MgO which have been implanted with Xe+ ions. The resultant microstructural changes are a function of ion fluence and are related to structural modifications at or near the surface.

Transmission electron microscopy (TEM) is a powerful technique for examination of microstructure on a nanometer scale. A problem often encountered when conventional methods of specimen preparation, for TEM analysis, are used is the possibility of ion-beam induced damage. Ion-beam damage can be a serious problem especially in the preparation of MgO specimens. In the present study damage resulting from ion-milling can be entirely avoided by ion-implantation directly into an electron-transparent thin-foil specimen.
An electron diffraction study of the tetragonal— monoclinic transformation in 12 mole% ceria-zirconia
Authors: Hugo G.R. , Muddle B.C. , Hannink R.H.J.
Published: June 2020

The tetragonal (t) ↔ monoclinic (m) transformation occurring in 12 mole% CeO2-ZrO2 is a source of significant transformation plasticity and transformation toughening in this ceramic material. The t↔m transformation is martensitic in nature and a quantitative understanding of the transformation plasticity and transformation toughening requires that the crystallography of this martensitic transformation be understood in detail. Crystallographic characteristics of a martensitic phase transformation are:

1. the existence of a unique lattice correspondence between the phases, which specifies the directions in the product crystal lattice into which any given directions in the parent crystal lattice are transformed,
2. a fixed orientation relationship preserved between parent and product phases, and
3. the orientation of the habit plane or interface plane between the parent and product phases.

For the t↔m transformation occurring in ceria-zirconia, three possible lattice correspondences are plausible.
TEM studies of tweed microstructures in annealed amelia albite
Authors: Kim Y. J. , Henderson D. M.
Published: June 2020

Natural Amelia albite (Ab99.3An0.1Or0.6) annealed at 1073° and 924°C for various periods up to 140 days has been studied by NMR. TEM studies of the same sample revealed a distinct tweed microstructure in some samples annealed at both 1073°C and 924°C. On the whole, the quasi-regular tweed has a periodicity of 100 - 200 Å in both directions, one nearly normal to b* and the other approximately parallel to b*, which gives rise to two-directional streaking in SADP’s (Fig. 1 and 2). However, there are some differences in the tweed structure developed on annealing at 1073°C and at 924°C in albite.

Albite samples annealed at 1073° show a systematic trend in their development of tweed structures: the regularity, periodicity, and frequency of occurrence increase with annealing time during the first 3 days, and then decrease gradually until no tweed microstructures are seen in samples annealed for more than 15 days. The tweed structure proceeds locally to form one-directional twin-like microstructures.
Characterization of grain boundary phases in Si3N4 sintered using Y-Si-Al-O-N additives
Authors: Koehler C. , Thomas G.
Published: June 2020

The usefulness of silicon nitride as a high temperature ceramic can be limited by the presence of amorphous phases at the grain boundaries. Dense silicon nitride ceramics are produced using pressureless sintering of Si3N4 with Y-Si-Al-O-N additives. When these additives are left as a glassy phase at the grain boundaries and triple grain junctions, the mechanical properties at elevated temperatures are weakened due to these low viscous glasses. Post-sintering heat treatments and close compositional control can be effective in transforming the glass into crystalline phases at the grain boundaries thereby increasing the refractoriness.

To optimize high temperature mechanical properties, processing must be controlled not only to fully crystallize the grain boundaries but also to avoid certain unstable secondary phases whose oxidation leads to large molar volume changes which causes possible cracking. Transmisssion electron microscopy and x-ray microanalysis (EDS) are significant methods to characterize the amorphous grain boundary pockets and to identify the crystalline grain boundary phases.
The microstructure of functionalized poLyacrylonitrile beads for bioseparations
Authors: Kamenetzky Eduardo A. , Ley David A.
Published: June 2020

The microstructure of polyacrylonitrile (PAN) beads for affinity chromatography bioseparations was studied by TEM of stained ultramicrotomed thin-sections. Microstructural aspects such as overall pore size distribution, the distribution of pores within the beads, and surface coverage of functionalized beads affect performance properties. Stereological methods are used to quantify the internal structure of these chromatographic supports. Details of the process for making the PAN beads are given elsewhere. TEM specimens were obtained by vacuum impregnation with a low-viscosity epoxy and sectioning with a diamond knife. The beads can be observed unstained. However, different surface functionalities can be made evident by selective staining. Amide surface coverage was studied by staining in vapor of a 0.5.% RuO4aqueous solution for 1 h. RuO4does not stain PAN but stains, amongst many others, polymers containing an amide moiety.
Contributions of Electron Microscopy to Environmental Science
Authors: Fisher Robert. M.
Published: June 2020

Heightened concern about the environment, and particularly the increasing rate of dispersion of toxic substances and irritants has placed severe demands on analytical techniques to define the nature and occurrence of potentially hazardous constituents and devise control technologies as well as to determine the risk to human life. In many cases, environmental contamination involves the presence of very fine particulates, which may pose some health risk in their own right or may simply serve as carriers for hazardous chemicals that fall within the respirable range, i.e. 10 microns or less in major dimension. Electron microscopy, widely used to observe and identify fine particulates in the atmosphere, has already contributed significantly to environmental science but advances in instrumentation are needed to overcome technical and economic limitations to its use.

Sources of Environmental Particulates

Atmosphere particulates, popularly considered to originate primarily from heavy industrial operations such as mining, primary metal production or power generation, can also come from natural sources such as volcanoes, forest fires, silt residue from flooding, and botanical emissions (spores, pollen). Paniculate pollutants also derive from smoking, debris from road wear of automobile and truck tires, fragmentation of asbestos-containing insulation and building materials, food processing, earth moving operations, open burning of agricultural residues and waste dumps and unfiltered emissions from incinerators.
Atomic-Resolution Imaging in the STEM
Authors: Liu J.
Published: June 2020

Scanning transmission electron microscopy (STEM) instruments offer a variety of important imaging and diffraction techniques for characterizing materials and for investigating electron beam specimen interactions. Microdiffraction patterns and electron energy loss spectra can be obtained with a probe size about 1-1.5 nm in diameter. Secondary electron images with a resolution approaching the probe size ( 0.5 nm) can be obtained in STEM instruments. Atomic resolution images can also be obtained with bright-field (BF) imaging mode by phase contrast or with high-angle annular dark-field (HAADF) imaging mode by atomic number contrast. We report here some recent results on high resolution imaging of crystal structures in the STEM.

Phase contrast BF STEM lattice fringes can be obtained by placing a detector at any position of the Ronchigram fringe patterns (shown in figure 1a), formed in the diffraction plane with large convergence of the electron beam incident along a principle zone axis of a single crystal. The image interpretation is similar, due to the reciprocity theorem, to that of the conventional HRTEM images. The image contrast depends on defocus, sample thickness and lens aberrations. Figure 1b shows a BF STEM structural image of a GaAs/InAlAs/InGaAs multiple-quantum-well (MQW) crystal projected along the [110] zone axis. This image reveals the interfaces with weak contrast. Although some information about the interfacial structures can be obtained (e.g., interfaces indicated by arrow A seem abrupt while that indicated by B seems diffuse), chemical interpretation at the atomic scale across the interfaces seems unlikely without performing rigorous image simulation.
A Structural Model for a Quasi-Crystalline Material Derived from TEM
Authors: Bovin Jan-Olov , Terasaki Osamu , Malm Jan-Olle , Lidin Sven , Andersson Sten
Published: June 2020

High resolution transmission electron microscopy (HRTEM) is playing an important role in identifying the new icosahedral phases. The selected area diffraction patterns of quasi crystals, recorded with an aperture of the radius of many thousands of Ångströms, consist of dense arrays of well defined sharp spots with five fold dilatation symmetry which makes the interpretation of the diffraction process and the resulting images different from those invoked for usual crystals. The atomic structure of the quasi crystals is not established even if several models are proposed. The correct structure model must of course explain the electron diffraction patterns with 5-, 3- and 2-fold symmetry for the phases but it is also important that the HRTEM images of the alloys match the computer simulated images from the model. We have studied quasi crystals of the alloy Al65Cu20Fe15. The electron microscopes used to obtain high resolution electro micrographs and electron diffraction patterns (EDP) were a (S)TEM JEM-2000FX equipped with EDS and PEELS showing a structural resolution of 2.7 Å and a IVEM JEM-4000EX with a UHP40 high resolution pole piece operated at 400 kV and with a structural resolution of 1.6 Å. This microscope is used with a Gatan 622 TV system with an image intensifier, coupled to a YAG screen. It was found that the crystals of the quasi crystalline materials here investigated were more sensitive to beam damage using 400 kV as electron accelerating voltage than when using 200 kV. Low dose techniques were therefore applied to avoid damage of the structure.
HREM of Rapidly Solidified Al-Li-Zr Based Alloys
Authors: Radmilovic V. , Thomas G. , Kilaas R. , Kim N. J.
Published: June 2020

During aging of Al-Li-Zr based alloys δ'(Al3Li) precipitates heterogeneously around β'(Al3Zr), forming so-called composite precipitate[l-4], that has important effects on the mechanical behavior of these alloys. As has been observed in several investigations, the addition of small amount of Zr results in a fairly large volume fraction of β' in the microstructure, and this suggests that there may be a partitioning of Li in the β'. In the present investigation, high resolution electron microscopy (HREM) and image simulation have been used to perform detailed characterization of the chemistry and structure of β' precipitate.

The alloy Al-3Li-1Cu-0.5Mg-0.5Zr (wt.%) has been heat treated as follows: a) solution treatment at 550°C for 2 hours and water quenching, b) aging treatment at 150°C for 4 hours or at 200°C for 8 hours and c) 10% cold working followed by aging at 175°C for 64 hours. HREM images were taken on a JEOL ARM electron microscope operating at 400 and 800kV. Simulated HREM images of the composite δ'/β' precipitate were calculated using CEMPAS multislice program described by Kilaas[5].
Theoretical and Experimental Analyses of the Effects of Composition and Strain on Image Contrast in High-Resolution Transmission Electron Microscopy
Authors: Sundo D.F. , Howe J.M.
Published: June 2020

Although the effects of composition and strain on amplitude-contrast images in the TEM have been thoroughly developed, similar theory does not exist for phase-contrast images and only a few specific situations have been treated. The purpose of this research is to develop a quantitative understanding of the effects of composition and strain on phase-contrast images and to test this theory experimentally. A simple defect which can cause both a local change in composition and strain is a substitutional atom. Hence, this defect is treated first, with the expectation that results from this analysis can be extended to predict image contrast from larger defects under certain imaging conditions.

X-ray scattering theory indicates that diffuse scattering from point defects due to composition and strain is linearly additive. For small defect concentrations, the scattered intensity Sdiff(k) is given by: