bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of time-varying imaging from phase-contrast microscopy
Authors: Gwydir Stacy , Kirgios Christos , Buettner Helen , Dunn Stanley
Published: June 2020

Quantitative analysis of neurite outgrowth and growth cone (filopodia and lamellipodia) motility provides key information for developing new therapeutic strategies for treating peripheral nerve injury and disease. Neurite outgrowth and growth cone properties will be measured for neurons taken from the dorsal root ganglia of 8-day old chick embryos. Ganglia will be enzymatically dissociated into single neurons and cultured in a serum-free medium. Cultures will be grown on glass coverslips coated with the basement membrane protein laminin. Following a brief incubation period of 4 hr to allow the initiation of neurites from the nerve cell bodies, cultures will be moved to an incubated microscope stage maintained at 37 C. Subsequent growth of the neurites will be recorded at a rate of 2 frames/sec with a time-lapse videocassette recorder connected to the phase-contrast microscope through a high-resolution (800 lines) video camera.

The videotaped growth sequence will be digitized at a specified time interval, using a frame grabber.
Pathways for penetration of iron and negative stain across the protein shell of ferritin: Ultrastructural perspectives
Authors: Massover William H.
Published: June 2020

Molecules of the metalloprotein, ferritin, have an outer shell comprised of a polymeric assembly of 24 polypeptide subunits (apoferritin). This protein shell encloses a hydrated space, the central cavity, within which up to several thousand iron atoms can be deposited as the biomineral, ferrihydrite. The actual pathway taken by iron moving across the protein shell is not known; an analogous question exists for the demonstrated entrance of negative stains into the central cavity. Intersubunit interstices at the 4-fold and 3-fold symmetry axes have been defined with x-ray diffraction, and were hypothesized to provide a pathway for penetration through the outer shell; however, since these channels are only 4Å in width, they are much too small to allow simple permeation of either hydrated iron or stain ions. A different hypothesis, based on studies of subunit dissociation from highly diluted ferritin, proposes that transient gaps in the protein shell are created by a rapid reversible subunit release and permit the direct passage of large ions into the central cavity.
Investigations of monolayers by fluorescence microscopy
Authors: Stine Keith J.
Published: June 2020

Understanding the organization of amphiphilic molecules at interfaces is of fundamental importance in a number of fields of research. Langmuir-Blodgett technology and membrane mimetic chemistry are based on understanding the structural and physical properties of monolayers of amphiphilic compounds. This is a challenging area with numerous unresolved questions. For example, monolayers of amphiphilic compounds as simple as long-chain fatty acids and esters exhibit complex phase behavior which is still under investigation. In order to investigate biomembrane structure and processes, model systems can be constructed. Monolayers of phospholipids at the air/water interface serve as membrane models and have been used to investigate the effects of varying temperature, surface density, and subphase conditions. Study of the interaction of a protein introduced into the subphase with the monolayer can provide insight into a specific membrane process. In this review, fluorescence microscopy studies by a number of research groups of monolayers of fatty acids and esters, phospholipids, and of interactions of proteins with phospholipid monolayers will be discussed.
AFM, LVHRSEM, and cross-sectional TEM of the near-surface morphology of diblock copolymers
Authors: Schwark D. W. , Vezie D. L. , Reffner J. R. , Thomas E. L. , Annis B. K. , Wunderlich B.
Published: June 2020

Application of block copolymers as adhesives and biomedical devices requires an understanding of the surface composition and morphology of these materials. Microscopy techniques offer excellent depth and lateral resolution and therefore can provide direct microstructural and compositional surface data. Previous workers frequently used only a single microscopy technique to investigate the influence of an external surface constraint on the morphology. The implementation of several different microscopy techniques, each with its own strengths, affords a very complete characterization of the surface composition and morphology of self-assembling diblock copolymers.

The investigation of solvent-cast and annealed thick (1 mm) films of two poly(styrene-b-butadiene) (SB) diblock copolymers, which usually self-assemble to form alternating poly(styrene) (PS) and poly (butadiene) (PB) lamellar microdomains, by three complementary microscopy techniques: cross-sectional transmission electron microscopy (CSTEM), low-voltage high-resolution scanning electron microscopy (LVHRSEM), and atomic force microscopy (AFM) is discussed. For CSTEM and LVHRSEM imaging, contrast between the PS and PB phases was enhanced by preferential staining of the PB phase with the vapors of a 4% aqueous osmium-tetroxide (OsO4) solution for 24 hours.
Evaluation of stereo imaging capabilities and parameters when using personal computers: Defining a low-cost high-quality system
Authors: Mackenzie John M.
Published: June 2020

Over the past several years the capabilities of personal computers have advanced at a staggering rate. At the same time, the cost of the hardware has dropped to such a degree that one wonders whether such inexpensive hardware can perform adequately.

The purpose of this discussion is to look at the minimum hardware necessary to do quality stereo imaging on CRT display devices and to discuss several important evaluation criteria in producing these stereo images.

The most important criteria for producing high quality stereo pairs lies in the quality of the digitization of the image. Most TV rate imaging systems even after multiple frames are averaged are quite distorted and lack sufficient image detail. Slow scan imaging systems such as the one developed in this laboratory which use a gated integrator and can digitize at over one thousand pixels square with 256 gray levels produce images which are extremely close to photographic quality.
Application of an image management system in microscopy
Authors: Chemock Richard S.
Published: June 2020

One of the most common tasks in a typical analysis lab is the recording of images. Many analytical techniques (TEM, SEM, and metallography for example) produce images as their primary output. Until recently, the most common method of recording images was by using film. Current PS/2R systems offer very large capacity data storage devices and high resolution displays, making it practical to work with analytical images on PS/2s, thereby sidestepping the traditional film and darkroom steps. This change in operational mode offers many benefits: cost savings, throughput, archiving and searching capabilities as well as direct incorporation of the image data into reports.

The conventional way to record images involves film, either sheet film (with its associated wet chemistry) for TEM or PolaroidR film for SEM and light microscopy. Although film is inconvenient, it does have the highest quality of all available image recording techniques. The fine grained film used for TEM has a resolution that would exceed a 4096x4096x16 bit digital image.
Reconstruction of intracellular and extracellular networks from stereo IVEM images using computer graphic methods
Authors: Peachey Lee D. , Haselgrove John C. , Baradet Timothy , Weisel John , Haselgrove Christian , Porter Keith R.
Published: June 2020

High and intermediate voltage electron microscopes can be used to get good images of many types of thick biological specimens, including sections of embedded material up to several micrometers thick, whole cells, or isolated cellular components mounted on support films, stereoscopic pairs of images can be obtained by tilting the specimen between exposures, and this requires only relatively small tilt angles, often less than 15°. With a high tilt specimen holder, images covering a wider range of tilt angles can be obtained, increasing the amount of 3D information. Computer graphic methods for extracting quantitative 3D information from such images have been under development and use in this laboratory for several years.

Many cellular structures take the form of networks. Examples that we study are transverse tubular networks in muscle, fibrin clots, and the microtrabecular lattice of the cytoplasm. We perform quantitative, 3D reconstruction and analysis of such networks from multiple stereoscopic image sets obtained using a JEOL 4000-EX TEM.
Development of high-vacuum equipment for EM specimen preparation
Authors: Denton Richard A.
Published: June 2020

High-vacuum techniques made electron microscopy possible. In the 1930s vacuum evaporators with glass or metal chambers, diffusion pumps and oil sealed mechanical pumps were used in Europe and the U.S. The earliest systems used mercury pumps with liquid air traps. Oil diffusion pumps were manufactured in the U.S. by D.P.I. from glass or metal. In 1940 the first RCA TEM went into production as the EMB. First shadow casting in the U.S. was by Williams and Wycoff in 1944 and in Europe by Műller in 1942. Due to war secrecy, neither knew about the other. In 1944 RCA built the first production evaporator for EM under the direction of Bob Picard. The system had an 18" dia. glass bell jar and a metal baseplate with an oil diffusion pump backed by a Cenco Hypervac 20 mechanical pump. In 1948 Optical Film Engineering designed a 12" dia. bell jar evaporator for EM. This SC-3 employed a Welch 5 cfm mechanical pump and a 3" diffusion pump. Carbon evaporation for substrates or replicas was invented by D.E. Bradley in England and published in 1954.
Microchemical imaging in biomedical research
Authors: Ingram P.
Published: June 2020

It is well established that unique physiological information can be obtained by rapidly freezing cells in various functional states and analyzing the cell element content and distribution by electron probe x-ray microanalysis. (The other techniques of microanalysis that are amenable to imaging, such as electron energy loss spectroscopy, secondary ion mass spectroscopy, particle induced x-ray emission etc., are not addressed in this tutorial.) However, the usual processes of data acquisition are labor intensive and lengthy, requiring that x-ray counts be collected from individually selected regions of each cell in question and that data analysis be performed subsequent to data collection. A judicious combination of quantitative elemental maps and static raster probes adds not only an additional overall perception of what is occurring during a particular biological manipulation or event, but substantially increases data productivity. Recent advances in microcomputer instrumentation and software have made readily feasible the acquisition and processing of digital quantitative x-ray maps of one to several cells.
Atomic force microscopy using beam fabricated tips: resolution issues
Authors: Zhou Li , Mooney Chuck , Russell Phillip E.
Published: June 2020

A question often arises concerning the resolving power of the AFM compared with that of the scanning electron microscopy (SEM). One of the advantages of AFM is that it gives accurate three dimensional topographic information that the SEM can not provide. Figure 1(a) shows an SEM micrograph of a two level metal integrated circuit with intermetalic dielectric (unpassivated) that has a complicated three dimensional structure. Quantitive feature height information can not be obtained from this picture. But, as shown in Figure 1(b) die AFM perspective image clearly gives us the details of three dimensional information. In Figure 1(c), a line scan taken from the image yields the height of the pattern quantitively. However, the image we obtain with an AFM is often complicated by the nature of the sample and the structure of the tip. If the dimension of the tip is larger than the topography of the sample, the image will reflect the shape of die tip, which is one of die problems associated with pyramidal shapes of commercial AFM tips (5.0 Х 5.0 μm square base and 55° slope of sidewalls).
Parameters controlling contamination tip growth for atomicforce microscopy
Authors: Mooney C. B. , Zhou Li , Russell P. E.
Published: June 2020

An investigation into improving the tip fabrication technique for Atomic Force Microcopy (AFM) tips has been undertaken. The problems addressed here relate to the artifacts that are produced from imaging high aspect ratio (depth/width) features with standard AFM pyramidal tips. Standard tips, while having a regular geometry present a problem: the pyramid's base is 3-5 microns square and the walls are angled at 55°. This tip shape can cause a great deal of “smoothing” to high aspect ratio topological features, whether they are a few nm or a few μm in height. The use of electron beam grown microtips eliminates many of the tip artifacts found when using standard pyramidal tips. Actual growth of tips is quite easy. Once the SEM is set up properly (focused and stigmated) the scan generator for the beam is turned off, placing the microscope in the spot mode. The beam spot is placed at the point where a tip is desired and left for several minutes.
Multi-dimensional microscopy and analysis
Authors: Echlin Patrick
Published: June 2020

Our natural world is multi-dimensional in which the spatial coordinates of an object are, for a given moment of time, fixed relative to each other. These fixed points change, either very rapidly as in the case of most living material, or very slowly as with metals and rocks. The rates of change are influenced by environmental factors such as temperature, pressure, humidity and electromagnetic radiation.

Sight together with the coupled neuro-physiological processes is the most powerful of our noninvasive senses for detecting, imaging and analysing what is happening in our environment. Our memory serves us reasonably well as a short term archiving mechanism. The images we see arise as a consequence of selective scattering and absorption of a small portion of the electromagnetic spectrum as it interacts with the specimen. We quickly learn how to interpret the information-rich images we are presented with in our daily life; we can perceive motion, minute changes in patterns and the three dimensional location of objects.
Applications of AFM and STM: Solvation forces in liquids and inelastic photon excitation
Authors: Welland M. E. , O'Shea S. , McKinnon A. W. , Wong T. M. H.
Published: June 2020

We describe here non-standard applications of scanned probe microscopy; one application making use of the force sensitivity of the AFM to measure solvation forces at the liquid-solid interface and the other application based on the STM where the tunnelling current is used to excite photon emission from a surface.

An interesting aspect of the solid-liquid interface is the molecular order induced in the liquid by the solid surface. This order can give rise to observable changes in the short range forces acting between two solids in a liquid medium; so called “solvation” or “structural” forces. As a first investigation of the local variation of short range forces in liquids we have used an AFM to observe solvation forces near a graphite surface. The AFM is ideal for this work as it can typically measure very small forces (∼10-10N) with high lateral (∼0.3nm) and vertical resolution (∼0.03nm). In this study, an optical deflection type AFM is used in which the movement of a small cantilever is sensed by measuring the deflection of a laser beam focussed on the back of the lever.
The impact of confocal microscopy in biomedical research
Authors: Amos William B.
Published: June 2020

The confocal optical microscope, using laser illumination, has now gained widespread acceptance (see volume edited by Pawley) Its advantage in providing clear optical sections, particularly with fluorescent specimens, is well known. Of the many confocal instruments now in use in cell biology, the applications can be classified into five different categories.

The chief use is to give three-dimensional information about conventionally prepared fluorescent specimens. A notable example is the in vivo mapping of an identified neurone through several days of embryonic life by O'Rourke, Scott Fraser and colleagues at Irvine, USA. There has also been much work on in situ hybridisation, morphometry of solid tumours, oncogene product localisation and many aspects of the cytoskeleton.

The second use has been in reflection imaging of cell surface contacts, of isolated microtubules and microorganisms, of parts of the eye and of reaction products such as peroxidase.

The third application is the measurement of intracellular parameters such as pH and calcium ion concentration within a defined volume.
Structure refinement from systematic row integrated intensities and non-systematic critical voltages
Authors: Gjønnes J. , Ma Y.
Published: June 2020

Renewed interest in the quantitative side of electron diffraction may be due to several factors:

•

convergent beam diffraction is reckognized as a source for precise and useful intensity data for structure determination;

•

structural features where electron diffraction offers high sensitivity, e.g. disorder, defects, transformation structures and microstructures, charge distributions, receive increasing attention in solid state research.

Various approaches and applications of electron diffraction to structure determination and refinement have been reported in recent years,. In our lab we have concentrated on two methods: the non-systematical critical voltage effect applied to a inner reflections from small unit cells; intensity profiles and integrated intensities from reflections in a systematic row. Applications include charge distributions and ionicities, refinement of coordinates and thermal parameters, supplement to X-ray structure determinations.

The studies of charge distribution combine two basic features of electron difraction: the high sensitivity of inner reflections to charge transfer, cf the Mott formula
Measurement of small structure factors by the critical-voltage effect in HEED: The superlattice reflections in β'nial, β'CoAl and γtial
Authors: Fox Alan G. , Tabbernor Mark A.
Published: June 2020

The systematic critical voltage effect, Vc, in high energy electron diffraction has been used for some time to accurately measure low-angle x-ray structure factor structure factor amplitudes (see e.g. 1). It has a significant advantage over other methods for accurate structure factor measurement, such as systematic convergent beam rocking curve or x-ray Pendellösung techniques, in that it is capable of measuring very small structure factors such as the 222 ‘forbidden’ reflections in Si and Ge (see e.g. 2). In the present work the potential of the systematic Vc method for measuring small structure factor amplitudes and average Debye-Waller factors in the intermetallic alloys NiAl, CoAl and TiAl will be demonstrated.

The structure factors, F, for ordered stoichiometric B2 alloys comprising A and B atoms such as Ni (Co)Al are given by
Carbide precipitation and chromium depletion on coherent twin boundaries in deformed 304 stainless steels
Authors: Advani A.H. , Murr L.E. , Matlock D.J. , Fisher W.W. , Tarin P.M. , Romero R.J. , Maldonado J.G. , Cedillo C. M. , Ramos C. , Miller R.L.
Published: June 2020

Coherent annealing-twin boundaries are constant structure and energy interfaces with an average interfacial free energy of ∼19mJ/m2 versus ∼210 and ∼835mJ/m2 for incoherent twins and “regular” grain boundaries respectively in 304 stainless steels (SS). Due to their low energy, coherent twins form carbides about a factor of 100 slower than grain boundaries, and limited work has also shown differences in Cr-depletion (sensitization) between twin versus grain boundaries. Plastic deformation, may, however, alter the kinetics and thermodynamics of twin-sensitization which is not well understood. The objective of this work was to understand the mechanisms of carbide precipitation and Cr-depletion on coherent twin boundaries in deformed SS. The research is directed toward using this invariant structure and energy interface to understand and model the role of interfacial characteristics on deformation-induced sensitization in SS. Carbides and Cr-depletion were examined on a 20%-strain, 0.051%C-304SS, heat treated to 625°C-4.5h, as described elsewhere.
Segregation in a neutron-irradiated Type 316 stainless steel
Authors: Kenik E. A. , Burke M. G.
Published: June 2020

Radiation-induced segregation (RIS) and associated irradiation-assisted stress corrosion cracking (IASCC) of austenitic alloys may be a major factor in limiting component lifetimes in water-cooled nuclear reactors. There are some similarities between radiation-induced sensitization/IASCC and thermally-induced sensitization/intergranular stress corrosion cracking. Both processes are associated with chromium depletion at grain boundaries. Segregation to boundaries in a neutron irradiated type 316 stainless steel has been investigated with both energy-dispersive X-ray spectrometry (EDXS) and parallel detection electron energy loss spectrometry (PEELS).

All specimens were from the same heat of cold-worked type 316 stainless steel. Both unirradiated control material and material irradiated at ∼300°C to a range of fluences 0.3 - 5 × 1026 neutrons/m2 (E>0.1 MeV) were available. The mass of irradiated material was minimized by mechanically polishing 3-mm-diam. disks to ∼75 μm thickness prior to electropolishing. However, the specific radioactivity of the specimens, which increased with neutron fluence, limited the application of EDXS to the unirradiated and the lowest fluence irradiated materials.
Reliability of sublattice occupancies determined by ALCHEMI
Authors: Bentley J.
Published: June 2020

The atom location by channeling enhanced microanalysis (ALCHEMI) technique is an attractive method for sublattice (site) occupancy determination, especially in multiphase materials. It has been applied to a wide range of ceramics, minerals, semiconductors and metallic alloys with varying degrees of success. The simplicity of the method originally proposed has not always been borne out in practice; applications of the technique have revealed limitations due to crystallography, microstructure, specimen preparation, ionization delocalization, and weak channeling discrimination. Some of these limitations have been encountered in work at ORNL on ALCHEMI of intermetallic alloys such as Ll2-ordered Ni3Al-based alloys (with additions of Hf, Co, and Fe) and Ll0-ordered Cu50Au50-y(X)y alloys with X = Pd or Ni. These applications have been motivated by the technological importance of ordered intermetallic alloys. Commercial materials often have complex compositions with ternary (or higher) additions present at substantial levels. The distribution of the various components on the different sublattices is an important facet of characterization for structure property correlations to help guide alloy development.
Trace analysis of transition elements and rare earths by parallel EELS
Authors: Leapman R.D. , Newbury D.E.
Published: June 2020

It has been realized for some years that electron energy loss spectroscopy (EELS) offers the potential for a highly sensitive microanalytical technique. Here, we present measurements from some NIST glass standard reference materials showing that EELS provides both high spatial resolution and trace sensitivity for a wide range of elements including the 3-d transition metals and the lanthanides.

Specimens were prepared by grinding the glass and depositing the powder on to thin carbon support films. The energy loss spectra were collected by means of a Gatan 666 parallel-detection spectrometer attached to a VG Microscopes HB501 scanning transmission electron microscope (STEM) operating at 100 keV beam energy. This arrangement gave an energy resolution of approximately 0.4 eV limited by the spread of the field-emission source. Large spectral intensities were obtained by setting the probe current to about 8 nA and the collection semi-angle to 20 mrad. In order to eliminate possible hydrocarbon contamination the specimens were cooled to -160 C.
Separating the surface and volume plasmon energy loss intensity distributions in MgO and MgAl2O4
Authors: Evans N. D. , Wang Z. L.
Published: June 2020

Broadening on the low energy side of the MgAl2O4 (spinel) volume plasmon, which increases with decreasing sample thickness (Fig. 1a), affected multiple least squares (MLS) fitting when spectra such as these were used in quantitative analysis. The inverse dependency of broadening on thickness is indicative of a surface effect. Potential artifacts from sample preparation (argon milling) were investigated. Spinel stock was ground in methanol on a grinding disk of 15μm-diameter diamond, and the tailings were placed onto a holey-carbon film. Electron-transparent regions of spinel that extended beyond holes in the film were used to obtain the energy loss single scattering distributions (SSD) shown in Fig. 1b. Parallel-detection electron energy loss spectroscopy (PEELS) was performed at 100 kV with a Philips EM400T/FEG analytical electron microscope. These SSD were obtained using the procedures described earlier, and show, relative to those in Fig. 1a, identical broadening on the left side of the plasmon with decreasing specimen thickness. This similarity indicates the broadening effect is not due to milling but to surface plasmon excitation.
Electronic structure changes associated with magnetic transitions in binary alloys: an exploratory seels study
Authors: Krishnan Kannan M.
Published: June 2020

The Curie temperature of a disordered alloy may differ from that of a partially ordered system. Alternatively, magnetism can influence chemical order and produce substantial changes in the phase diagram. These results have been established by a detailed investigation of the Col-xPtx system and the entire phase diagram, including magnetic and chemical effects, have been calculated and shown to be in good agreement with experimental data. In addition, ultrathin multilayers of Co/Pt show perpendicular anisotropy but the origin of this unique property is not well understood. Recently, we have shown that the d-electron density of states of a range of Cul-xPdx alloys, based on measurements of L3,2 transitions (“white lines” - WL) in electron energy-loss spectroscopy (EELS), is critically dependent on short-range order (SRO). In this paper we present results of the combined effect of magnetic and chemical order on the d -hole count, as measured by the normalized Co WL intensities, in four different Co/Pt alloys.
Energy-analyzing setup for backscattered electrons
Authors: Gérard Pascal , Balladore Jean Louis , Martinez Jean Paul , Ouabbou Abdelghafour
Published: June 2020

We present in this paper an experimental device for determining for an electron beam incident normal to a target, the angular and energetic backscattered electron distribution as a function of the emission angle. The originality of our setup lies in the fact that under a normal incidence the particules reach the target which remains stationary. The detection system, placed on a rotating arm around the point of impact of the incident beam consists of a semiconductor detector (PIN diode). To enable its use as a detector of electron whose energy is comprised between 10 and 40 keV, a specially tailored electronic device was required. In order to enhance the energy resolution the PIN diode is cooled down at liquid nitrogen temperature.

Figure 1 gives an example of the type of spectrum obtained. At a low energy, the electronic noise due the measurement setup appears in the form of the peak at 2 keV, irrespective of the nature of the target, the detection angle θ or the incident energy Eo chosen.
High-Resolution stereo imaging of frozen-hydrated biological samples by Cryo-SEM
Authors: Chen Ya , Walther Paul
Published: June 2020

The introduction of cryo-techniques to SEM allowed the biologist to examine frozen-hydrated specimens at low temperatures on a cryo-stage in the SEM. The problems associated with conventional cryo-SEM included ice crystal formation caused by low cooling rate, poor resolution, limited magnification (<10 kX), specimen contamination, beam damage and charging. Recently, the effectiveness of this technique has been improved because a number of new cryo-preparation instruments have become commercially available. The high pressure freezer permits cryo-fixation of large biological specimens (diameter up to about 1mm) without ice crystal artifacts. Cryo-coating units permit fine-grain metal coating of fractured specimens. In addition, microscopes combining a short focal length lens with a fieldemission (FE) source permit high resolution imaging at low beam voltage (Vo). However, for high resolution cryo-SEM, especially for producing stereo pictures, the artifacts caused by electron irradiation remain a critical problem.

The purpose of this work was to evaluate the extent to which beam damage varies with Vo, and to determine the most appropriate Vo for stereo imaging.
Imaging and analysis of submicron single-crystal aluminum whiskers in Al/Cu/Si deposited films
Authors: Schaper Jacob A.
Published: June 2020

The formation of stress-relieving hillocks, also referred to as single-crystal whiskers is a well-known occurrence in the preparation of metallic thin films. In the manufacture of Application Specific Integrated Circuits, devices at the wafer level are often processed through the first metallic thin film process, coated with a plasma enhanced oxide (PEO), then stockpiled either at the manufacturer's site or the customer's to await final option-level programming. Whisker growth has been detected on wafers retrieved from the stockpile inventory. This paper describes the techniques employed for initial detection, subsequent sample preparation, and the composition analysis of submicron diameter whiskers in Al/Cu/Si thin films on inventoried product wafers.

First indications of whisker growth are increased surface defect levels observed during high power optical microscope sample inspection. Typical appearance of the whiskers, as viewed with an optical microscope, are shown in Figure 1. Structures thought to be surface particles are later imaged in the SEM and confirmed to be oxide-covered whiskers, as shown in Figure 2. Imaging of the nonconductive oxide layer is accomplished via a Field Emission SEM.
Low-Voltage scanning electron microscope (LVSEM) determination of nevirapine Crystal Habit in a Pharmaceutical Suspension
Authors: Angel A. , Peischl R. , Hawi A.
Published: June 2020

LVSEM permits the examination of materials with reduced radiation damage and high contrast, factors which are critical to the successful examination of organic crystals. In this study, LVSEM was applied to characterize the structure of a beam sensitive anhydrous crystal form and its subsequent conversion to the hemihydrate form in an aqueous suspension.

Nevirapine, a dipyridodiazepenone compound, is a reverse transcriptase inhibitor currently being developed for the treatment of AIDS. Nevirapine exists as the hemihydrate stable form and as the anhydrous metastable form. The hemihydrate crystals are multifaceted blades (Fig. 1) whereas the anhydrous form exists predominately as large agglomerates of porous “coral like” crystals with high surface area (Fig. 2). When formulated in aqueous suspensions, anhydrous Nevirapine converted into the hemihydrate form, with eventual growth of the hemihydrate crystals. The extent of conversion and rate of growth have been determined to be a function of temperature and time. LVSEM was used to study the anhydrous-to-hemihydrate conversion as the two forms could easily be identified by their characteristic morphology.
Heterojunction band offsets in GE-SI alloys from EELS
Authors: Batson P.E. , Morar J.F. , Tersoff J. , LeGoues F.K.
Published: June 2020

The positions of the band edges on either side of a semi-conductor heterojunction determine the electrical properties of the interface by defining the potential barrier to transport experienced by an electron or hole. This behavior dominates the function, the Schottky Barrier height, for instance, of semi-conductor structures. On the other hand, the band line-up is essentially a microscopic quantity. It depends on the atomic structure averaged over only two or three atomic spacings.

Band offsets can be inferred from transport properties, such as capacitance. However, these methods are subject to problems of charge trapping and recombination effects because they average over large areas of the heterojunction. An alternate method is to measure some reference level on either side of an interface, a core level or a valence band edge, for instance, and then to measure the band edge relative to the reference using another technique. In an important simplification, Shih and Spicer proposed that some situations may occur where a core level is unchanged on either side of a heterojunction.
In situ crystallization of amorphous silicon
Authors: Batstone J.L.
Published: June 2020

The solid state transformation of amorphous silicon (a-Si) to crystalline silicon (c-Si) is a first order phase transformation which is driven by the difference in free energy between the amorphous and crystalline phases. The crystallization occurs at temperatures of 500-700°C which are readily accessible with commercial specimen heating stages for the transmission electron microscope (TEM). In this paper we study the a-c phase transformation dynamically by utilizing the powerful technique of in-situ TEM to monitor the nucleation and growth kinetics of thin films of Si. The propagation of a moving a-c interface is presented and an activation energy for crystal growth is obtained.

400Å of a-Si was prepared by electron beam deposition of Si at room temperature on amorphous Si3,N4 “window” substrates which required no additional sample preparation for TEM. The samples were examined in a plan view orientation to minimize surface effects on the crystallization process. The a-Si films were annealed by in-situ heating in a Gatan single-tilt hot stage which has a temperature accuracy of ±25°C. Crystallization occurred at ∼700°C with the formation of small crystallites which grew to consume the entire amorphous film. Fig. 1 shows a partially transformed region of a-Si after annealing at 710°C for 6 mins.
TEM studies of spots crystallized in amorphous films by electron beam
Authors: Kolosov V. Yu.
Published: June 2020

Electron beam (e-beam) annealing is powerful method for local modifying and crystallization in desired modes of semiconductors and microelectronics components and is also interesting for information storing. Nevertheless, discussed in many papers mechanism of explosive crystallization of amorphous (a-Ge, a-Si) films is still not clear enough and requires new structure studies. It is more relevant for recently discovered growing of micro-crystals with strong internal lattice bending (gradient crystals) in some amorphous films. This paper reports our findings in the structure of spots crystallized in these unusual modes by TEM beam in vacuum deposited (Ge, Se, Se-Te) or prepared by pyrolysis (Fe2O3) unsupported amorphous films. Bendcontour technique was used to analyze the fields of lattice orientation for gradient crystals, including in situ crystal growth studies or videorecord analysis.

Explosively crystallized spots in a-Ge, a-Si films are known to consist of 3 zones, Fig. 1. We observed the same zones for films 400-800Å thick, deposited at rates 1- 100Å/s: polycrystal central zone (O), surrounded by a fan of radially elongated single crystals (zone R) which in turn is surrounded by zone (C), formed by concentric or spiral shells (each subdivided into single-crystal subshell and polycrystal subshell).
In situ tEM observation of C49 to C54 TiSi2 transformation
Authors: Barmak K. , Levine L.E. , Smith D.A. , Komemt Y.
Published: June 2020

The reaction of thin films of Ti with Si results in the formation of the high resistivity (≃150 μΩcm) base-centered orthorhombic C49 phase prior to the low resistivity (≃15-20 μΩcm) face-centered orthorhombic C54 phase. In our experiments, 30 nm of Ti was evaporated onto a < 100 > oriented Si wafer cleaned in a 10:1 H2O:HF solution. The wafer had been previously implanted with As to a dose of 5×l015 cm−2. Mixed C49/C54 phase films were obtained by furnace annealing at 700°C for 10 min. Plan view transmission electron microscopy (TEM) specimens were prepared by dimpling and etching in a 10:6:6 HNO3:HF:CH3COOH solution. The sample was initially studied in a JEOL 4000FX and in situ heating experiments were carried out in a Philips 430 operating at 300 kV. The progress of the transformation was recorded on video tape. The temperature was raised relatively quickly to 700°C and then more slowly to 750°C.
Replica observation by transmission electron microscopy of GaAs surface grown on vicinal Si (001)
Authors: Inoue T. , Kikuchi Y. , Sasaki T. , Eshita T. , Yoshida M.
Published: June 2020

Over the past several years, heteroepitaxy of GaAs on Si substrates has received strong interest because of its potential for monolithic integration of GaAs optical devices with Si integrated circuit technology. For heteroepitaxy of GaAs on Si substrate, Si(001) substrates oriented toward [110] by a few degrees (1) are used, therefore the GaAs epitaxial layer is expected to have a stepped surface. In this study, we characterized the GaAs surface, grown on vicinal Si(001 ) substrates, by replica observation using transmission electron microscopy (TEM).

The Si substrates were oriented 2 degrees off towards [110] and their surface was expected to have a regular array of [110] steps, 8 nm apart. A two-step growth process (1) was employed to grow GaAs on Si(001) by metalorganic chemical vapor deposition (MOCVD). The Ga source was trimetyl gallium (TMG) and As source was AsH3. Following 10 minutes of 1000°C heat treatment in a H2, gas flow to remove the native oxide, 20 nm GaAs buffer layers were grown at 450°C. They were then heated to a growth temperature of 650°C to grow the GaAs epitaxial layers an additional 3 μm.
HREM of low-temperature InP grown by gas source MBE
Authors: Rajesh R. , Kim M.J. , Bow J.S. , Carpenter R.W. , Maracas G.N.
Published: June 2020

In recent times, following the application of MBE GaAs grown at low temperatures as an electrical buffer layer in field effect transistors, there has been a focus of attention on other III-V materials grown at low temperatures. This lead to speculation on the possibility of applications of low temperature (LT) InP in electronic and photonic devices resulting in a need to correlate the structural properties of this material with the electrical and optical measurements. The current endeavour is directed toward studying the structure and the morphology of LT InP synthesized under varying growth conditions in order that a correlation with properties like conductivity and photoluminescence can be effected.

In this present study, InP grown at low temperatures by gas source MBE using for sources solid indium and P2 has been characterized by TEM. Samples were prepared by mechanical grinding, dimpling and low-angle argon ion-milling. The low-angle technique was employed because it greatly mitigates the formation of indium islands during the milling of InP samples with Ar+ ions. Observations were made on an ISI 002B electron microscope, operating at 200 kV.
Formation of defects in boron-implanted PEPBLT structures
Authors: David Theodore N. , Sundaram Sam , Fejes Peter
Published: June 2020

Variations on LOCOS (local-oxidation of silicon) are being explored for device-isolation, to implement further miniaturization of VLSI devices. One such variation involves poly-encapsulated poly-buffered LOCOS + trench-isolation (PEPBLT). The method provides a means to support device scaling and to create self-aligned shallow field-oxide elements with minimal encroachment into active regions. In an earlier study, dislocations were observed to be associated with a combination of high-dose ∼1E15 cm−2 phosphorus implants and PEPBLT isolation. The present study investigates the effect of boron implants on similar PEPBLT structures. The effect of fabrication-related stresses in the structures is of interest because extended-defects, if formed, could electrically degrade transistors.

PEPBLT structures were exposed to varied processing conditions to build high-performance bipolar transistors. Isolated active-device regions from the above structures were characterized using TEM. Some of the active regions were (i) implanted with 80 keV-8.5E15 cm−2 boron with no anneal, (ii) implanted with 80 keV- 8.5E15 cm−2 boron and annealed at 900°C/90’/N2 plus 1050°C/30” RTA during the course of processing, (iii) not implanted.
Geometry-dependence of defects in PBLT serpentines
Authors: Fejes Peter , David Theodore N. , Liang Han-Bin
Published: June 2020

Poly-buffered LOCOS + trench-isolation is a technique being explored for device-isolation on semiconductor substrates. The method creates self-aligned shallow field-oxide elements with minimal encroachment into active regions. In an earlier study/dislocations were observed in PBLT structures, associated with a combination of high-dose [∼1E15 cm−2] phosphorus implants and PBLT isolation. The present study investigates the effect of implant- and isolation-geometries on the formation of extended-defects in PBLT structures. The effect of fabrication-related stresses in the structures is of interest because extended-defects, once formed, can electrically degrade devices.

PBLT structures were fabricated using varied implant- and isolation- geometries. Selected regions of the structures were exposed to 1E15 cm−2 phosphorus implants. Transmission electron microscopy was then used to characterize these regions. Some of the structures investigated were (i) trench with no adjacent implant, (ii) trench with an adjacent trench, but no implant, (iii) trench with a 1E15 cm−2 phosphorus implant placed ∼4 μm from the trench, (iv) trench with a 1E15 cm−2 phosphorus implant placed ∼2 μm from the trench, (v) doubly-kinked trench with a 1E15cm−2 phosphorus implant placed between the kinks.
TEM/AFM correlative studies of thin-film metallization
Authors: David Theodore N. , Sharma Renu , Carrejo Juan
Published: June 2020

Since the invention of AFM (atomic force microscopy) applications of the technique have grown from year to year. It is expected that with time, there will be an increased use of AFM in the semiconductor industry for analysis of surface-topography and microstructure of thin films and heterostructures. However, before the technique can be used on its own for analyzing the behavior of thin films, it is necessary to establish legitimate areas of application of the technique. The present study uses AFM and TEM (transmission electron-microscopy) to study a few examples of thin-film metallizations and then looks at the extent of correlation between the two. It turns out that TEM and AFM work very well as complementary techniques. Caution is required in interpreting AFM micrographs.

As examples of metallization Al(Cu), polysilicon and TiW thin films were investigated using AFM and TEM. Al(1.5%Cu) films were sputtered onto SiO2/Si substrates for ∼1 second (unbiased) at a substrate temperature of 450°C.
Structural and compositional effects on the electron migration properties of Al-Cu alloy
Authors: Liu J.B. , Duan J.Z. , Gronsky R.
Published: June 2020

Aluminium and aluminium-based alloys are typically used as the metallization interconnections in LSI and VLSI silicon-based integrated circuits. Important factors affecting the lifetime and reliability of these interconnections in IC devices are the individual microstructures, device layer combinations, electron migration, and stress migration that occur during their fabrication and their in-service application. There are many possible remedies for each of these factors. The use of bias sputtering or “planarization” has been shown to improve the quality of the interconnection greatly. Recently, some studies have revealed a new planarization technique involving sputter deposition of Al alloys at elevated temperature without any substrate bias, combined with a TiN precoating to reduce the migration of Al atoms. In this paper, the microstructure of Al-0.2Cu/TiN/SiO2/Si under optimum lifetime conditions is assessed, and a mechanism of void formation is proposed to explain the observations.

A representative TEM cross section image of Al-0.2% Cu sputtered at 100 V bias and at substrate temperature 450°C with a TiN/SiO2 prercoating is shown in Fig.l. The surface topography of the Al-Cu alloy is shown for comparison purposes in Fig.2.
The observation of defects on (100) CdTe surfaces by chemical etching
Authors: Lee M.E.
Published: June 2020

The crystalline perfection of bulk CdTe substrates plays an important role in their use in infrared device technology. The application of chemical etchants to determine crystal polarity or the density and distribution of crystallographic defects in (100) CdTe is not well understood. The lack of data on (100) CdTe surfaces is a result of the apparent difficulty in growing (100) CdTe single crystal substrates which is caused by a high incidence of twinning. Many etchants have been reported to predict polarity on one or both (111) CdTe planes but are considered to be unsuitable as defect etchants. An etchant reported recently has been considered to be a true defect etchant for CdTe, MCT and CdZnTe substrates. This etchant has been reported to reveal crystalline defects such as dislocations, grain boundaries and inclusions in (110) and (111) CdTe. In this study the effect of this new etchant on (100) CdTe surfaces is investigated.

The single crystals used in this study were (100) CdTe as-cut slices (1mm thickness) from Bridgman-grown ingots.
CVD process characterization using a selective delineation technique for quantitative SEM analysis
Authors: McAfee George H. , Dean Steven J.
Published: June 2020

The scanning electron microscope is one of the most universal and well-respected analytical tools in the semiconductor industry. The limitless potential of this tool serves as the basis for this article. As process geometries continue to shrink below the sub-micron level, precise characterization of the individual processing areas is of the utmost importance. One area of particular interest is the CVD (chemical vapor deposition)/thin film area.

Modern CVD reactors implement a triple injector configuration for film deposition. Each injector provides an individual contribution to the composite film thickness. In essence, the composite film is comprised of three separate thin film layers. These films have a very high surface tension and the interfaces of the three films form areas of high stress. From these two properties, surface tension and interfacial stress, it becomes possible to quantify and visually identify the individual contribution of each injector (in a multi-injector CVD reactor). This can be accomplished by using a selective etching technique in preparation for cross-sectional SEM analysis. Areas of high stress, by nature, have a higher etch rate than the bulk film itself.