bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of TEM and STM observations of small silver clusters on different carbon supports
Authors: Tesche Bernd , Schilling Tobias
Published: June 2020

The objective of our work is to determine:

a) whether both of the imaging methods (TEM, STM) yield comparable data and

b) which method is better suited for a reliable structure analysis of microclusters smaller than 1.5 nm, where a deviation of the bulk structure is expected.

The silver was evaporated in a bell-jar system (p 10−5 pa) and deposited onto a 6 nm thick amorphous carbon film and a freshly cleaved highly oriented pyrolytic graphite (HOPG).

The average deposited Ag thickness is 0.1 nm, controlled by a quartz crystal microbalance at a deposition rate of 0.02 nm/sec. The high resolution TEM investigations (100 kV) were executed by a hollow-cone illumination (HCI). For the STM investigations a commercial STM was used. With special vibration isolation we achieved a resolution of 0.06 nm (inserted diffraction image in Fig. 1c). The carbon film shows the remarkable reduction in noise by using HCI (Fig. 1a). The HOPG substrate (Fig. 1b), cleaved in sheets thinner than 30 nm for the TEM investigations, shows the typical arrangement of a nearly perfect stacking order and varying degrees of rotational disorder (i.e. artificial single crystals). The STM image (Fig. 1c) demonstrates the high degree of order in HOPG with atomic resolution.
The influence of surface defects on the catalytic reaction of submonolayer films observed by photoemission electron microscopy
Authors: Mundschau M. , Kordesch M. E. , Rausenberger B. , Engel W. , Bradshaw A. M. , Zeitler E.
Published: June 2020

Defects on surfaces are known to greatly enhance the rate of many catalytic reactions. In some cases, the active sites in catalysis may reside only at defect sites. Surface defects are best characterized by microscopic techniques. It was demonstrated earlier that catalytic reactions can be followed using an ultra high vacuum version of a classical photoemission electron microscope. This technique can image submonolayer coverages because of the extreme sensitivity of photoemission to local work function.

We report here studies on the catalytic oxidation of adsorbed CO on Pt which was followed in situ and in real time. For temperatures below 500 K and for partial pressure ratios of oxygen to CO of less than ∽ 10:1, an adsorbed layer of CO forms which effectively blocks the co-adsorption of oxygen.
Characterization of aluminophosphates: Identification of 18-member ring structure in AlPO4-8
Authors: Ulan J. , Szostak R. , Gronsky R.
Published: June 2020

The first claim in 1987 of an aluminophosphate (VPI-5) with a pore diameter greater than 7 Å regenerated interest in ultra-large pore molecular sieves for which theoretical models have existed since 1969. Large micropore materials are needed, especially in the oil industry, as catalysts which have the high acidity of zeolites, are thermally stable at high temperatures and pressures, and have significant porosity to allow diffusion of heavier feedstocks currently being seen in refineries.

The aluminophosphate VPI-5 is reported to be the first molecular sieve to contain an 18-member ring structure with a pore diameter greater than 12 Å based on X-ray powder diffraction and adsorption data. Researchers at Mobil laboratories have crystallized the silicoaluminophosphate molecular sieve MCM-9 an its X-ray powder diffraction pattern has been shown to match a mixture of VPI-5 and AIPO4-11.
Recent applications of TEM to the study of interfaces
Authors: Barry Carter C.
Published: June 2020

This paper will review the current state of understanding of interface structure and highlight some of the future needs and problems which must be overcome. The study of this subject can be separated into three different topics: 1) the fundamental electron microscopy aspects, 2) material-specific features of the study and 3) the characteristics of the particular interfaces. The two topics which are relevant to most studies are the choice of imaging techniques and sample preparation. The techniques used to study interfaces in the TEM include high-resolution imaging, conventional diffraction-contrast imaging, and phase-contrast imaging (Fresnel fringe images, diffuse scattering). The material studied affects not only the characteristics of the interfaces (through changes in bonding, etc.) but also the method used for sample preparation which may in turn have a significant affect on the resulting image. Finally, the actual nature and geometry of the interface must be considered. For example, it has become increasingly clear that the plane of the interface is particularly important whenever at least one of the adjoining grains is crystalline.

A particularly productive approach to the study of interfaces is to combine different imaging techniques as illustrated in the study of grain boundaries in alumina. In this case, the conventional imaging approach showed that most grain boundaries in ion-thinned samples are grooved at the grain boundary although the extent of this grooving clearly depends on the crystallography of the surface. The use of diffuse scattering (from amorphous regions) gives invaluable information here since it can be used to confirm directly that surface grooving does occur and that the grooves can fill with amorphous material during sample preparation (see Fig. 1). Extensive use of image simulation has shown that, although information concerning the interface can be obtained from Fresnel-fringe images, the introduction of artifacts through sample preparation cannot be lightly ignored. The Fresnel-fringe simulation has been carried out using a commercial multislice program (TEMPAS) which was intended for simulation of high-resolution images.
HREM of the interface between CVD Si3N4 and single-crystal SiC
Authors: Unal O. , Mitchell T. E.
Published: June 2020

Ceramic/ceramic composites are of interest because of their potential structural applications, especially at high temperature. The interface between the components is especially important in influencing the mechanical properties. As part of a program to investigate Si3N4 matrix/SiC whiskers composites, macroscopic Si3N4/SiC interfaces have also been prepared in order to study their mechanical behavior, particularly with regard to crack propagation. These interfaces have also been studied by HREM.

Transparent single crystals of SiC a few mm in size were obtained as a by-product of the Acheson process. They were mounted on graphite pillars and coated with 5mm of Si3N4 deposited by CVD using a mixture of ammonia, trichorosilane and hydrogen at 1500°C. Cross-sectional specimens were made by the sandwich technique with the final ion-milling at liquid nitrogen temperatures. HREM was performed on a Philips CM3OT.
The role of Electron Microscopy in the study of grain boundaries
Authors: Clark William A. T.
Published: June 2020

Our understanding the nature of interfaces in polycrystalline materials has depended critically on observations obtained in the transmission electron microscope. This is especially true in the case of interfacial structure, where developments in models of atomic and defect structures in interfaces have closely paralleled advances in techniques available for their study. The general acceptance that the crystallography and relative misorientation of the two crystals forming an interface dictate the interfacial structure, and many of its properties, results in large part from direct TEM studies of interfaces.

Grain boundaries were originally considered structureless, amorphous, films, because optical microscopy could not provide information at the necessary resolution, and inferences about the nature of boundaries had to be made from measurements of mechanical properties. However, the development of X-ray methods in the 1920's quickly showed that the crystalline structure of the grains was preserved right up to an interface, and that the boundary could be thought of as a “transition lattice” from one crystal to the other, a concept remarkably similar to many of those still current today. Although there was some earlier optical microscopy of decorated low-angle boundaries in Si, it was not until 1956 that the development of the TEM provided the first detailed picture of dislocations and grain boundaries in opaque materials.
Structure of Nb/Al2O3 interfaces produced by molecular beam epitaxy
Authors: Mayer J. , Flynn C. P. , Rühle M.
Published: June 2020

HREM Studies of the atomistic structure of idealized metal/ceramic interfaces are important for both fundamental and applied reasons. Epitaxial growth by molecular beams allows to produce such interfaces under controlled conditions. Nb/Al2O3 has been chosen as a model system because of the absence of any chemical reactions between the metallic overlayer and the ceramic substrate and since both components possess nearly the same thermal expansion coefficient. Results of x-ray diffraction studies indicate that a unique three-dimensional orientation relationship exists between niobium and sapphire which is established for different choices of surface plane of the sapphire substrate. Aim of the present investigations was to study the orientation relationships and the atomic arrangement at the interface by conventional TEM and HREM.

During MBE growth the sapphire substrates were heated to 1123 K and a vacuum in the 10-7Pa range was maintained. Typical growth rates of 1 monolayer/sec were obtained. Cross-section TEM samples were prepared by a special technique involving cylindrical alumina holders with a diameter of 3mm. Shielding was applied during ion-milling to reduce the effect of the different milling rate of Nb and Al2O3.
Coincidence-site-lattice-pattern (CSL-pattern) of 70.5°/[110] boundary of the 6H-type layer structure
Authors: Kitano Yasuyuki , Takata Masaki
Published: June 2020

The most useful and intuitive model may be a CSL-model to analyze boundary structures. In order to apply the CSL-model to layer structures, we have proposed to use ‘lattice point’ in a wide sence and to add extra lattice points to the Bravais lattice points when interpenetrating(IP)-lattices are drawn. These lattice points will be called ‘extended lattice points’. It is well known that a layer structure is built up with (almost) identical layers stacking on the top of the others with a cirtain amount of shift in a direction perpendicular to the stacking. Each layer consists of one or more atomic planes and has almost (or exactly) the same atomic configuration. The extended lattice points can be defined as the origins in each layer in crystal. The number of such points depends upon the number of layers in a unit cell.

To draw IP-lattices we have adopted all the extended lattice points in addition to the Bravais lattice points. There are three important advantages of doing this extension. First is that the Coincidence-Sites in the IP-lattices drawn do not scatter homogeneously, but gather in a region and make a cluster. They exibit a characteristic pattern of Coincidence-Sites. This pattern is called a CSL-pattern. Second is that the DSC-lattice (Displacement Shift Complete Lattice) provides a set of basic vectors smaller than predicted before extention.
Diffraction contrast images of interphase boundaries in cobalt
Authors: Cheng S.C. , Sheinin S.
Published: June 2020

The boundaries between HCP and FCC phases in cobalt are generally expected to be of the type {111}FCC ‖ {001}HCP. Observations carried out by the authors indicate that the contrast exhibited by this type of boundary is very similar to the contrast exhibited by twin boundaries, as discussed by Sheinin and Corbett. These authors showed that images of twin boundaries consist of two intersecting sets of fringes with the possibility that one set is suppressed under certain diffraction conditions. The purpose of the work presented in this paper is to investigate the contrast exhibited by boundaries between the same two phases but which lie in a different habit plane.

Experimental observations were carried out on boundaries in wedge crystals of cobalt, as shown schematically in Fig.1. The orientations of the crystals on either side of the boundary were obtained from selected area diffraction. For the bright and dark field images in Figs. 3a and 4a the orientations were found to be (12
)FCC on the left of the boundary and (100)HCP on the right. The boundary was found to be of the {111}FCC ‖ {312}HCP type. In the diffraction pattern obtained from the region containing the boundary shown in Fig. 2, the reflections (111)FCC and (002)HCP are identified.
The role of interfaces in the creep-deformation of a Sic whisker-reinforced Si3N4 composite
Authors: More K.L. , Koester D.A. , Davis R.F.
Published: June 2020

The high temperature mechanical properties of a SiC whisker-reinforced composite are currently being investigated. The deformation characteristics of the composite are controlled not only by the distribution of the constituent phases, but also by the interfaces between phases. The material is a hot pressed 30 vol.% SiC whisker-reinforced Si3N4 containing sintering aids of 1.5 wt.% A12O3 and 6.0 wt.% Y2O3. Constant compressive stress creep experiments were conducted in a continuously purified 0.11 MPa nitrogen atmosphere in a system described elsewhere. This work focussed on two creep experiments conducted at temperatures of 1470 K and 1620 K, both in the stress range 50-350 MPa. Figure 1 shows the stress exponent, n, for creep of the composite at both 1470 K and 1620 K. At 1620 K, n exhibited a bi-linear behavior. However, this behavior was not observed for creep at 1470 K.

In the as-hot pressed state, the composite had an amorphous grain boundary phase containing N, O, Al, Si, and Y as determined by energy dispersive spectroscopy. Prior to loading, the specimens were annealed for 4 hr at the creep temperature. During the anneal, the grain boundary phase crystallized and underwent a change in composition as determined by X-ray diffraction and transmission electron microscopy (TEM).
Investigation of the microstructure of hetero-epitaxial Si/CoSi2/Si (001) and (111) structures by TEM
Authors: Bulle-Lieuwma C.W.T. , van Ommen A.H.
Published: June 2020

Hetero-epitaxial Si/CoSi2/Si structures have been formed by high dose implantation of Co+ ions into (001) and (111) Si substrates and subsequent annealing of the substrates. Such structures are of interest due to their application as metal base base and permeable base transistors. We have studied the microstructure of both as-implanted and annealed structures by transmission electron microscopy (TEM), including high-resolution electron microscopy (HREM). HREM was performed using a Philips 300 kV electron microscope with a point resolution of approximately 0.19 nm. CoSi2 layers have been formed by implantation of 170 keV Co+ ions at a temperature of 450°C and to doses of 1× 1017 and 2× 1017 Co+ / cm2. The wafers were annealed for 30 minutes in a N2/H2 ambient at a temperature of 1000°C. In the as implanted structures, the Co is present in the form of epitaxial CoSi2 precipitates. Precipitates occur both in an aligned (A-type) and twinned (B-type) orientation. Annealing of the implanted structures results in the formation of a buried CoSi2 layer of aligned orientation. A striking observation is that the CoSi2 layer has an aligned orientation with respect to the Si matrix, whereas CoSi2 grown on top of (111) Si has a twinned orientation. The mechanism behind this phenomenon is not fully understood. We think that geometrical aspects play a crucial role. Therefore we have studied in detail the geometry of the coordination of coherent CoSi2 precipitates.
The staining of carboxylated latex with cesium hydroxide
Authors: Shaffer O.L. , Stanislawczyk V. , El-Aasser M.S.
Published: June 2020

Various staining techniques of polymers have been developed for transmission electron microscopy. The ability to diferentiate polymer phases is crucial in the understanding latex particle morphology. A new technique has been developed to study the acidic groups on the surface as well as in the interior of acrylic latex particles.

A 2% aqueous solution of cesium hydroxide(CsOH) is used as a swelling and staining agent. The alkali metal hydroxides are the most basic of all the hydroxides and CsOH is the strongest base in the group. A drop of latex is diluted in 1 to 2 cc of freshly prepared 2% aqueous CsOH. A drop of the dispersion is placed on a 200 mesh formvar-carbon coated copper TEM grid. Most of the drop is removed with filter paper leaving a thin film of the dispersion. The grid is then positioned in a Philips cold stage which is filled with liquid nitrogen after placement in a Philips 400 TEM.
Measurement of microscopic displacements in graphite/epoxy composite materials using a SEM-generated surface map
Authors: Burghardt R.C. , Ehrman J.M. , Stephens T.C. , Hibbs M.F.
Published: June 2020

Graphite fiber-reinforced resin composite materials have a wide use in aerospace, automotive and sporting goods applications where high strength to weight ratios are requisite. Many of these materials use highly cross-linked epoxy resins as the matrix material. Unfortunately these resins have a low resistance to crack propagation and as a result research efforts have been directed towards reducing this tendency.

The ability to measure microscopic displacements and calculate strain fields in the vicinity of a fracture crack tip under experimental conditions was needed in order to help predict the fracture resistance of various composite materials being tested. A technique was developed that made it possible to derive displacement measurements on a micrometer scale in the region of a crack tip from observations of epoxy-based composites being fractured using a tensile stage equipped scanning electron microscope (SEM). Samples were polished on the surface to be observed and sputter coated with 5 to 10 nanometers of either gold or 60:40 gold-palladium prior to mounting on the TS-2 tensile stage of a JEOL JSM-35CF. This instrument was also equipped with a Krisel beam interceptor, a beam current meter, a Tracor Northern TN-2000 x-ray analyzer and a TN-1310 digital beam control system. Using the digital beam and x-ray mapping capabilities a matrix of small dots was “written” onto the surface of the sample as shown in figure 1.
The use of weak-beam dark-field Electron Microscopy in the analysis of defects in intermetallics
Authors: Veyssière Patrick , Hug Gilles
Published: June 2020

Defect contrast under weak-beam (WB) conditions was understood in the late sixties. Until then, details on dislocation dissociation below a resolution of about ξg/3 was only matter of speculation. WB elucidated a number of problems on dissociation at a resolution of 2 to 6nm. WB became much less fashionable in the late seventies, leaving considerable domains almost undocumented. At this time, WB remained used mostly by materials scientists in the area of semiconductors and ceramics. A renewed WB activity took place in the mid eighties with the initiation of R & D projects on ordered intermetallics in several countries. Ordered metal alloys are attractive since they offer high specific strengths that may increase with increasing test temperature above ambient up to 600°C-850°C. Unfortunately, most of these systems are so brittle that none of the expected substitutes for superalloys has been designed so far. Presently, Ti-Al is the system that receives the largest attention. Dislocation analysis is important in intermetallics since, excepted in multicomponent systems, the mobility of dislocations is dictated (i) by dissociation symmetries, (ii) by the transitions that dissociation may undergo dynamically and (iii) by the role of temperature on these. In view of the splitting distances that are currently observed, WB is perfectly adapted to this prospect. As a matter of facts, the potential of WB was originally exemplified by a report on four-fold dissociation in ordered Fe3Al. Upon request of the organizers of this session, the present contribution focuses on instrumental electron microscopy and on some aspects of contrast analysis under WB conditions. General information on the implications of core structure analysis on the mechanical properties of alloys together with limitations of dislocation analysis in TEM are reviewed elsewhere.
Shear structures in the Al5CuLi3 frank-fasper phase
Authors: Zhou D. S.
Published: June 2020

Stacking faults and shear structures are often observed in the Frank—Kasper phases, especially in those composed of juxtaposed pentagonal antiprisms (or icosahedral chains) and/or juxtaposed hexagonal antiprisms. Their relationship with the quasicrystals has been extensively studied and leads to some structural models for quasicrystals. Recently, the transformation from icosahedral quasicrystals to crystalline (Frank—Kasper) phases has been studied upon heating. The current paper focuses on the defect structures of the Frank—Kasper phase, which is believed to have the same basic building units as quasicrystals.

The alloy used in the present investigation was made from high purity (>99.99 at%) constituent elements. They were melted in an induction furnace in a graphite crucible under partial argon atmosphere and then were poured into a stainless steel mold. Rapid solidification was carried out by a melt spinner in a helium atmosphere. X-ray diffraction only revealed the presence of icosahedral quasicrystals. Heat treatment was done by encapsulating the samples in quartz tubes and transforming at 397°C for 20 seconds to obtain crystalline phases. The heat treated samples were first examined in a Philips EM400T microscope and then in a JEOL-4000EX microscope for atomic imaging.
Dislocation microstructures in boron-doped Ni3Al
Authors: H.F. Yu , Jones I.P. , Smallman R.E.
Published: June 2020

Despite its relative engineering eclipse (at least in aeronautical terms), Ni3Al is still a rewarding area for scientific research, primarily because so much is already known about it. Many of its mechanical properties, however, are still not understood in terms of secondary defect populations and behaviour. For example, the fundamental Kear-Wilsdorf mechanism, wherein cross slip from {111} to {100} planes provides an increase in strength with temperature, has received intensive microscopic scrutiny recently, and it now appears that the movement of the superpartials on {100} is far more than the atom spacing or so envisaged in Paidar et al. Whether delocking occurs, however, and if so how often, is still not clear. Examples of other problems which remain are:

a) What are the relative contributions to work hardening of the Kear-Wilsdorf mechanism, APB tube formation and SISF formation?

b) Although the yield stress increases with temperature it also increases slightly with strain rate, whereas a negative strain rate dependence might have been expected.
In-situ studies in the high-voltage Electron Microscope
Authors: Westmacott K.H.
Published: June 2020

The principal advantages of high voltage electron microscopes are the ability to 1) attain higher resolution by virtue of the shorter wavelength, and 2) penetrate thicker specimens to observe dynamic behavior representative of bulk material. Some recent examples of in-situ HVEM research, representing the latter category, will be summarized in this contribution, and future directions discussed. Included in the most active research areas are phase transitions, deformation, high temperature reactions and environmental cell studies.

Irradiation with high energy electrons in an HVEM provides a convenient alternative to thermal treatments for inducing phase transitions in alloys. An illustration of how ordering or disordering of the same material can occur under electron irradiation is shown in Figure 1. In this example, a Pt7C ordered phase was formed in a Pt-C alloy at 500°C with a defocused beam (outer region) and subsequently disordered at 30°C with a focussed beam (inner spot).
In-situ high-voltage Electron Microscopy of defect ordering under high-dose irradiation
Authors: Jin N.Y. , Phillipp F. , Seeger A.
Published: June 2020

High-dose irradiation of metals employing dpa values (= displacements per atom) substantially larger than unity may lead to ordered arrangements of defects at temperatures well below the temperature of void formation. We report on a systematic study of defect-ordering phenomena in three fcc metals with markedly different stacking-fault energies, viz. Cu, Ag, and Ni.

5N-pure foils of Cu, Ag and Ni were prepared for in-situ electron microscopy in the conventional way. They were irradiated in an AEI-EM7 high-voltage electron microscope (HVEM) with lMeV electrons (e-) at various temperatures (Tirr) between 20 and 500K (Ag and Cu) or between 300 and 600K (Ni). The electron flux density and the total dose, Φ, were typically 7×l023e-m-2s-1 and 1x1027e-m-2, respectively. The development of the defect patter was investigated in the HVEM during the irradiation.

In all three metals a temperature regime has been found in which visible defects are regularly arranged along <100> directions after a minimum dose of ∼1026 e-m-2 (Fig.l).
The evolution of damage structures under simultaneous dual beam irradiation by ions and electrons in a HVEM
Authors: Takahashi Heishichiro , Ohnuki Soumei , Suzuki Takashi , Hidaka Yasuyoshi , Hishinuma Akimichi
Published: June 2020

It is well-kncwn that the materials for fusion reactor are damaged by high energy neutrons and other energy particles , and that due to nuclear reaction of (n,α) and (n,p) helium and hydrogen are introduced in the materials. Therefore, it is inportant to see the simultaneous effects of these fission productes and damage defects in materials to develope the fusion materials. To simulate the behaviors of damage structure in fusion reactor, the simultaneous dual beam irradiation is the most convenient method.

In order to investigate the effects of hydrogen and helium on the behaviors of defect clustering and void (cavity) formation under the dual beam irradiation, i. e. the simultaneous irradiation with hydrogen or helium ions and electrons was carried out using a high voltage electron microscope with 1000 KeV in the temperature range of 673 k and 823 K for the cold worked and annealed 316 stainless steels. Also, to see the effect of the ratio of hydrogen per dpa,H+ (or He+)/dpa ratio was changed between 0 and 300 appm H+ or He.
“In Situ” observation by Transmission Electron Microscope of the deformation and fracture micromechanisms in 7050 aluminum alloy
Authors: Monteiro W.A. , Alarcon O.E. , Nazar A.M.M.
Published: June 2020

During the last ten years the "in situ" deformation experiments by transmission electron microscopy have been used in metals to study the micromechanism of plastic deformation and fracture propagation mode occuring from the crack tip.These studies were performed in mono and policrystals metals with the aim to investigate the dislocation emission from crack tip phenomena relating it with the ductil versus brittle behavior of materials.

The material used in this experiment was a high strength aluminum alloy 7050 contained recrystal1ized and unrecrystal1ized microstructures, as the obtained by thermomechanical treatment in previous work .Due to the small dimensions of the miniature tensile specimens (2.7 × 6.8 × 0.02 mm ) and the requisite to obtain a lot of samples without introduction of strain during manufacture, the specimens was performed using a lithographic process.
The threshold energy for atom displacement in fcc metals
Authors: Sigle Wilfried , Hohenstein Matthias , Seeger Alfred
Published: June 2020

Prolonged electron irradiation of metals at elevated temperatures usually leads to the formation of large interstitial-type dislocation loops. The growth rate of the loops is proportional to the total cross-section for atom displacement,which is implicitly connected with the threshold energy for atom displacement, Ed . Thus, by measuring the growth rate as a function of the electron energy and the orientation of the specimen with respect to the electron beam, the anisotropy of Ed can be determined rather precisely. We have performed such experiments in situ in high-voltage electron microscopes on Ag and Au at 473K as a function of the orientation and on Au as a function of temperature at several fixed orientations.

Whereas in Ag minima of Ed are found close to <100>,<110>, and <210> (13-18eV), (Fig.1) atom displacement in Au requires least energy along <100>(15-19eV) (Fig.2). Au is thus the first fcc metal in which the absolute minimum of the threshold energy has been established not to lie in or close to the <110> direction.
Crystallization of amorphous ceramics during electron irradiation in high voltage microscope
Authors: Ohnuki S. , Takahashi H. , Kanamura R. , Nakaoka T. , Kinoshita H.
Published: June 2020

Transmission electron microscopy (TEM) has been a conventional method for studying for ceramics materials, therefore, the structural change induced by electron beam is a serious subject. It is well known that some ceramics with covalent bonding are able to change to amorphous structure during the charged particle-irradiation, and also Al2O3 has three structures of alpha, amorphous and gamma. Unfortunately, we have no detailed information on the effect of charged particle irradiation on structure of ceramics. The authors have found that Al2O3 amorphous changes easily to gamma crystalline during TEM observation. The aim of this study is to clarify the effect of some factors on the crystallization process, such as accelerating voltage and irradiation temperature.

Amorphous Al2O3 was prepared by 200 keV Ar+ ion implantation to 5×1016 cm−2 at 170K - room temperature (RT). High voltage and conventional TEMs of 1000 and 200 keV were used in this investigation of crystallization behavior of the amorphous which was produced on [0001] single crystal.
High-resolution microscopy and semiconductor interface structure
Authors: Gibson J. M. , Loretto D.
Published: June 2020

The attainment of interpretable atomic-level resolution transmission electron microscopy in the last two decades has given rise to a flood of papers containing pictures of atoms in semiconductors in a variety of activities. This plethora of detail may leave the feeling in some that "if you"ve seen one atom, you’ve seen them all". The question is: how much information are we really getting from HREM of semiconductors? The answer is a lot: but nothing like as much as we believe. Furthermore, in many cases old-fashioned and pedestrian diffraction and diffraction contrast techniques can give more information, yet are little-applied. In this paper I will try to describe the applications of HREM which are promising, at the same time making no bones where other methods are better, or at least complementary.

One important limit to the resolution of HREM images, which is most often overlooked, arises from the need for an acceptable signal-to-noise ratio. Every electron micrograph contains noise from a variety of sources: surface layers, photographic grains and electron shot noise.
Σ =13 tilt grain boundary in silicon bicrystal
Authors: Kim M.J. , Chen Y.L. , Carpenter R.W. , Barry J.C. , Schwuttke G.H.
Published: June 2020

The structure of grain boundaries (GBs) in metals, semiconductors and ceramics is of considerable interest because of their influence on physical properties. Progress in understanding the structure of grain boundaries at the atomic level has been made by high resolution electron microscopy (HREM) . In the present study, a Σ=13, (510) <001>-tilt grain boundary in silicon was characterized by HREM in conjunction with digital image processing and computer image simulation techniques.

The bicrystals were grown from the melt by the Czochralski method, using preoriented seeds. Specimens for TEM observations were cut from the bicrystals perpendicular to the common rotation axis of pure tilt grain boundary, and were mechanically dimpled and then ion-milled to electron transparency. The degree of misorientation between the common <001> axis of the bicrystal was measured by CBED in a Philips EM 400ST/FEG: it was found to be less than 1 mrad. HREM was performed at 200 kV in an ISI-002B and at 400 kv in a JEM-4000EX.
TEM characterization for material problems in silicon technology
Authors: Oppolzer H. , Cerva H.
Published: June 2020

Continuing increase in integration density requires reduction of minimum feature sizes which have reached a level of 0.8 μm for the 4 Megabit dynamic random access memory (DRAM) and are approaching about 0.5 μm for the next generation DRAMs. The thickness of thin dielectrics will be in the nanometer range. Besides the dimensions of the small device structures also the properties of all involved materials have to be controlled carefully. Due to its capability of providing high-resolution imaging and analytical information material characterization by cross-sectional TEM is getting increasingly important during process development. Several examples related to various process steps will be presented.

For the trench capacitor in 4 Mbit DRAMs thin dielectrics consisting of an SiO2-Si3N4-SiO2 triple layer are employed. While the thickness of the bottom oxide is reduced at the upper trench edge the nitride layer coats this edge uniformly since it is deposited from the vapor phase (Fig.1a). For the capacitor in a 64 Mbit memory cell oxide thicknesses of about 2 nm and 5 nm for the nitride will be required (Fig.1b).
Silicon layers grown over SiO2 by liquid phase epitaxy: Electron Microscopical study
Authors: Banhart F. , Phillipp F.O. , Bergmann R. , Czech E. , Konuma M. , Bauser E.
Published: June 2020

Defect-free silicon layers grown on insulators (SOI) are an essential component for future three-dimensional integration of semiconductor devices. Liquid phase epitaxy (LPE) has proved to be a powerful technique to grow high quality SOI structures for devices and for basic physical research. Electron microscopy is indispensable for the development of the growth technique and reveals many interesting structural properties of these materials. Transmission and scanning electron microscopy can be applied to study growth mechanisms, structural defects, and the morphology of Si and SOI layers grown from metallic solutions of various compositions.

The treatment of the Si substrates prior to the epitaxial growth described here is wet chemical etching and plasma etching with NF3 ions. At a sample temperature of 20°C the ion etched surface appeared rough (Fig. 1). Plasma etching at a sample temperature of −125°C, however, yields smooth and clean Si surfaces, and, in addition, high anisotropy (small side etching) and selectivity (low etch rate of SiO2) as shown in Fig. 2.
STEM characterization of short - Period GaAs-GaP strained superlattices
Authors: Ballesteros C. , Piqueras J. , Laknerb H. , Bollig B. , Ruiz A. , Briones F.
Published: June 2020

In the epitaxial growth of superlattice (SL) structures composed of non lattice-matched materials a large difference in the lattice constants of the components could result in the formation of misfit dislocations at the interfaces. However, high quality structures can be obtained when the thickness of the layers are kept below a critical value and the difference is elastically accomodated by strain. In particular GaAs-GaP short period superlattices (3.7% mismatch) constitute an interesting case of strained SLS because the stress related shifts of the electronic levels can result in novel optical and electronic properties. In the present work the quality of GaAs-GaP SLS is studied by STEM.

Short period GaAs-GaP superlattices were grown on SI (001) GaAs substrates by Atomic Layer Molecular Beam Epitaxy a new modification of the MBE technique capable of a sharp modulation of both group III and group V sources. To study the possibility of using the GaAs-GaP system for SL and Quantum Well structures a 18 monolayer thick GaAs quantum well was confined by two GaAs-GaP superlattices.
The dissociation of dislocations in SixGe1-x alloys
Authors: Stenkamp D. , Jäger W.
Published: June 2020

The knowledge of the structure of dislocations in semiconductors is of importance for an understanding of their mechanical and electrical properties. In electronic devices dislocations are known to act as recombination centers for charge carriers and as traps for impurity atoms. In addition dislocations play an important role in the mechanical relaxation of elastic stresses in lattice-mismatched heterostructures. In Si-based epitactical heterostructures alloys of Si and Ge are used to adjust the lattice parameters by variation of the alloy composition thereby modifying the elastic stresses in a controlled manner. Such strained layer structures are of potential application for electronic components with improved performance.

We have investigated dislocations in SixGe1-x crystals grown from the melt by the Czochralski and Bridgman method, respectively. The dissociation of dislocations into Shockley partials in SixGe1-x. alloys with low (x ≈ 0.05) and high (x ≈ 0.5) Si content was characterized by analytical electron microscopy at 300 kV.
Comparison of ultra high resolution immersion lens CFESEM and TEM for imaging of semiconductor devices
Authors: Reilly Terrence , Pelillo Al , Miner Barbara
Published: June 2020

The use of transmission electron microscopes (TEM) has proven to be very valuable in the observation of semiconductor devices. The need for high resolution imaging becomes more important as the devices become smaller and more complex. However, the sample preparation for TEM observation of semiconductor devices have generally proven to be complex and time consuming. The use of ion milling machines usually require a certain degree of expertise and allow a very limited viewing area. Recently, the use of an ultra high resolution "immersion lens" cold cathode field emission scanning electron microscope (CFESEM) has proven to be very useful in the observation of semiconductor devices. Particularly at low accelerating voltages where compositional contrast is increased. The Hitachi S-900 has provided comparable resolution to a 300kV TEM on semiconductor cross sections. Using the CFESEM to supplement work currently being done with high voltage TEMs provides many advantages: sample preparation time is greatly reduced and the observation area has also been increased to 7mm. The larger viewing area provides the operator a much greater area to search for a particular feature of interest. More samples can be imaged on the CFESEM, leaving the TEM for analyses requiring diffraction work and/or detecting the nature of the crystallinity.
Characterization of lateral bipolar transistor structures
Authors: David Theodore N. , Verdonckt-Vandebroek Sophie , Barry Carter C. , Simon Wong S.
Published: June 2020

Semiconductor devices are being scaled down into the submicron regime in order to meet technological demands for increased device-packing densities. Other factors considered for device design include low power dissipation, noise immunity, speed and high driving capability. Of these factors, high packing densities and low power dissipation can be derived using Coinplementary-Metal-Oxide-Semiconductor (CMOS) schemes. Bipolar-Junction-Transistor (BJT) schemes on the other hand provide driving capability, low noise performance and speed, at the expense however of greater device power- consumption. Combining CMOS and BJT technologies, a compromise can be struck between devicespeed and power dissipation. Most such combinations have resulted in vertical BJT requiring complex fabrication sequences. Recently, simpler lateral BJTs have been proposed for use in Bipolar CMOS processes. The viability of such semiconducting devices depends in part on the absence or controlled presence of structural defects. Diagnostic techniques are therefore required that are capable of high spatial resolution, for investigating the origin, behavior and possible elimination of fabrication-process-induced defects. Transmission electron microscopy (TEM) of device cross-sections can be effectively used for this purpose. In this study, lateral BJT structures are characterized using cross-section TEM and the results are correlated with electrical device-behavior.
Assessment of SixGe1-x epitaxial alloys grown on silicon at 350°C
Authors: Posthill J.B. , Malta D.P. , Hattangad S.V. , Parikh N.R. , Humphreys T.P. , Rudder R.A. , Fountain G.G. , Nemanich R.J. , Markunas R.J.
Published: June 2020

Since an established epitaxial materials system for the fabrication of Si-based heterojuaction bipolar transistors (HBTs) does not currently exist, several groups are now evaluating SixGe1-x epitaxial alloys for the base region of a Si HBT. A reduced band gap with the potential for reduced resistance in a SixGe1-x base are the attractive features of this structure. Additionally, there might be other applications for SixGe1-x epitaxial structures in device technology. However, as with any lattice-mismatched heteroepitaxial system, the potential for creation of deleterious threading dislocations exists. Also, the formation of a planar array of misfit dislocations could prove to be detrimental to HBT device performance and/or longevity. Hence, the investigation of various methods of producing SixGe1-x epitaxial films combined with detailed analytical characterization is necessary before a, viable device technology is realized. This contribution reports briefly on SixGe1-x epitaxial films that have been grown on Si(100) at 350 ° C by remote plasma-enhanced chemical vapor deposition (RPECVD).
TEM studies of pulse electrodeposited Cu-Se and CuInSe2 films
Authors: Veilleux G. , Boumerzoug M. , Saint-Jacques R.G. , Dao Lê H.
Published: June 2020

Photovoltaic technology is considered as one of the major options for large-scale energy production without pollution. Thin-film technologies are seen as a potential approach to produce cost-effective electricity by photovoltaic. Among the different thin-film deposition techniques (CVD, vacuum evaporation, sputtering, etc.), electrodeposition has emerged as a low-cost method. Using a pulsed electrodeposition technique semiconductor thin films of Cu-Se and CuInSe2 with improved uniformity and lower impurity have been prepared. Varying the electrodeposition solution pH, stoichiometric CuSe, Cu3Se2, Cu2 Se and Cu2Se films on Indium Tin Oxide (ITO) coated glass or Ni electrodes were obtained. Their composition and properties varied with heat treatment (3).

This paper reports the detailed study by Energy-Dispersive Spectrometry (EDS) and Transmission Electron Microscopy (TEM) of heat treatment effects on the composition and phase changes. EDS analyses were done on films deposited onto ITO glass using an Hitachi S-530 Scanning Electron Microscope (SEM). Cerac 99.99% pure powders were used to establish EDS calibration spectra. TEM studies were done on films directly deposited onto Ni grids. Selected area diffraction pattern (SADP) analyses were used to identify the structures. Samples were examined in a Philips EM-300 TEM operated at 100 kV.
Growth and microstructure of Cd1-xZnxS films deposited by hot-wall evaporation technique
Authors: Chaudhuri S. , Dhar A. , Pal A.K.
Published: June 2020

Recent developments in the field of solar photovaltaic technology with CdS as window layer indicated that Cd1-x Znx S is more suitable as the window layer because its propeerties may be tailored by simply adjusting the Zn content. It is known that the band gap of (Cd, Zn) S increases linearly with increasing Zn in the film.

We report here our studies on the growth and microstructure of thin films of cadmium zinc sulphide (Cd1-xZnxS) with the values of x in the range (0<x<0.27). Films were deposited by coevaporation of cadmium sulphide and zinc sulphide by the hot wall evaporation. Three different substrates (NaCl, KCl and LiF) were used for deposition of films in the thickness range 70 - 90 nanometer. The substrate, source and hot wall temperatures were 510 K, 1170 K and 480 K respectively.The microstructure of the films (fig. 1 ,2,3) were observed by transmission electron microscope (Hitachi H 600) and scanning electron microscope (Hitachi S-2300).
Electron Microscopy of CuInSe2 polycrystalline films
Authors: Albu-Yaron Ana , Margulis Lev , Hodes Gary , Noufi Rommel
Published: June 2020

Despite the continuing interest in and research on CuInSe2 (CIS) as one of the prime candidate materials for thin film photovoltaics, there are still many gaps in the knowledge and understanding of this material. One area where there is still much to be learned is the microstructural properties of the CIS film and the effect of the substrate on these properties. Relatively few groups have studied these aspects. We have recently described an aggregate macrostructure and its component microstructure. Here we report on the microstructure of individual crystallites in the CIS films grown on different substrate materials.

CIS films were evaporated using 3 separate sources onto heated (350-450°C) substrates of Mocoated (∼ 0.6 μm) Si single crystal, Al2O3 and 7059 Corning glass. For the transmission electron microscopy (TEM) examinations plan-view specimens were prepared by plasma or chemical etching. Cross-sections of the films deposited on Si single crystal slices were prepared by standard mechanical grinding and polishing followed by thinning to perforation by Ar+ ion bombardment. The specimens were examined by TEM using a Philips EM400T microscope operated at 120 kV. The obtained results show the following trends.
Microstructure of polycrystalline diamond film
Authors: Burke M. G. , Witkowski R. E. , Blackham R. T.
Published: June 2020

Diamond films have attracted considerable attention for use in a wide variety of industrial and commercial applications, particularly as coatings. Diamond coatings will enhance the performance of electro-optical systems, space-based photovoltaic power sources, packages for power electronic devices, and wear-limited processing equipment. These films are generally grown via plasma deposition or chemical vapor deposition techniques using a mixture. To characterize the as-grown diamond films, a variety of techniques including transmission electron microscopy are utilized. For this study, films were grown in a 1.5 kW ASTeX High Pressure Microwave Plasma Source equipped with an austenitic stainless steel, quartz lined reaction chamber. The plasma was a mixture of 0.5 or 2.0% CH4 in H2 at a reactor pressure of 30-50 mm Hg. During deposition, the substrate was heatea to ∼900-950°C. It has been reported that variations in the growth conditions will markedly affect the microstructure of the diamond film; several film morphologies have been observed. The quality of the substrate also exerts a strong effect on the nucleation of the diamond. In this on-going study, the influence of film thickness on the microstructure of polycrystalline diamond films has been characterized by analytical electron microscopy.