bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytoskeletal features of epithelia prepared by “extractive fixation“
Authors: Holy J. M. , Oaks J. A.
Published: June 2020

Techniques such as whole mount (high-voltage) electron microscopy of cultured cells (frequently extracted with non-ionic detergents), rapid-freezing (followed either by freeze-substitution or deep etching and rotary-replication), and reversible embedment of tissue have furnished novel insights into cytoskeletal architecture. Another approach in the examination of cytoskeletal morphology has been the modification of routine fixation and thin-section methods. Minimizing osmium exposure and including tannic acid in the primary fixative has been found to improve cytoskeletal preservation. Maupin and Pollard developed a fixation method in which a non-ionic detergent is added to the fixative to facilitate penetration of tannic acid into the cytoplasm. The images obtained by tannic acid fixation are frequently very electron-dense, however, and it is often difficult to clearly visualize the cytoplasmic filamentous system. This study describes results of an attempt to extract background material and reduce the density resulting from tannic acid fixation by reducing the concentration of aldehydes in the primary fixative.
Correlations of acid phosphatase activity and β-VLDL/colloidal gold conjugate localization in monocyte derived macrophages in culture: Intermediate voltage electron microscopy observations
Authors: Henson Dru A. , Lewis Jon C.
Published: June 2020

Lipid uptake by arterial cells is hallmark to atherosclerosis. Since in the progression from nascent to more advanced lesions lipid accumulation correlates with cell death and tissue necrosis, the relationship of lipid uptake to lysosomes is of interest. Recently, we reported the use of macrophage cultures to study lipoprotein uptake and to ultrastructurally correlate uptake with lipid accumulation and lysosomal activity. Although we have documented lipoprotein/gold tracer in lysosome-1ike organelles, simultaneous observation of both acid phosphatase reaction product and the β-VLDL gold tracer was limited by similarity of product and tracer electron densities. Reported is the use of IVEM to circumvent specimen contrast and simulaneously identify β-VLDL-gold within acid phosphatase positive lysosomes.

Pigeon monocytes, isolated from citrated whole blood were cultured in MEM-HEPES supplemented with 10% chicken serum, vitamins, L-glutamine, and antibiotics. Following 7 days in culture the monocyte/macrophages were incubated with pigeon β-VLDL conjugated to colloidal gold.
Biological specimen preparation for SEM by a method other than critical point drying
Authors: Adams J. L. , Battjes C. J. , Buthala D. A.
Published: June 2020

Quality sample preparation for SEM is important to observe fine details without artifacts, and good preparation requires proper fixation, dehydration, drying and coating, An alternative 5 min passage in hexamethyldisilazane (HMDS) can replace critical point crying (CPD) and gives satisfactory results on many biological samples. CPD procedure may take up to 1 h per sample to ensure adequate drying, therefore a brief rinse in HMDS followed by air drying requires less time and equipment yet provides excellent results.

Various biological samples were fixed in 3% glutaraldehyde; rinsed 3 times in Millonig's phosphate buffer for 10 min each; post-fixed in 1% osmium tetroxide for 1 h; rinsed as before; fixed again in 1% tannic acid (TA) for 30 min-1 h; rinsed well and partially dehydrated to 70% ethanol; placed in 1% uranyl-acetate (UA) in the dark, overnight: rinsed with 70% ethanol until UA cleared and then dehydrated through 100% ethanol.
Pectin's polygalacturonate single sugar chain helix visualized in Pt/C replicas
Authors: Ruben George C. , Bokelman Gordon H.
Published: June 2020

Pectic polysaccarides are 34% by weight of tobacco cell wall materials, more than any other cell wall component (cellulose, 18.7%; hemicellulose, 11.4%; protein, 21.6%; lignin, 4.1%). During cell growth, the cell wall is loosened by acidification which then enables it to elongate by its own turgor pressure. It has been suggested that the primary action of acidification is the loosening of a calcium pectate gel which at 34% by weight must permeate the wall and bind the cell wall together. This same work suggests that minimum Ca2+binding occurs at pH 3 and lower and maximum Ca2+ binding occurs at pH 6 and that Ca2+ binding capacity is lost by treatment with polygalacturonase. If the capacity for acid-induced wall loosening Is switched on, which is dependent on protein not carbohydrate synthesis, then the rate of wall loosening is proportional to the pH between 5.7 and 4.5.
Performance and applications of a field-emission gun TEM/STEM
Authors: Brock Judith M. , Otten Max T. , de Jong Marc. J.C.
Published: June 2020

A Field Emission Gun (FEG) on a TEM/STEM instrument provides a major improvement in performance relative to one equipped with a LaB6 emitter. The improvement is particularly notable for small-probe techniques: EDX and EELS microanalysis, convergent beam diffraction and scanning. The high brightness of the FEG (108 to 109 A/cm2srad), compared with that of LaB6 (∼106), makes it possible to achieve high probe currents (∼1 nA) in probes of about 1 nm, whilst the currents for similar probes with LaB6 are about 100 to 500x lower. Accordingly the small, high-intensity FEG probes make it possible, e.g., to analyse precipitates and monolayer amounts of segregation on grain boundaries in metals or ceramics (Fig. 1); obtain high-quality convergent beam patterns from heavily dislocated materials; reliably detect 1 nm immuno-gold labels in biological specimens; and perform EDX mapping at nm-scale resolution even in difficult specimens like biological tissue.

The high brightness and small energy spread of the FEG also bring an advantage in high-resolution imaging by significantly improving both spatial and temporal coherence.
A high-resolution, wide-field, optically coupled, digital CCD camera for the JEOL 4000-EX intermediate-voltage electron microscope
Authors: Horn Edward , Metzger Gregory J. , Ashton Francis T. , Peachey Lee D.
Published: June 2020

We have designed and constructed a camera system for acquisition of digital images directly from a JEOL 4000-EX 400 kV transmission electron microscope. Our major goal was the ablity to sample and test images for suitability for various forms of image processing and analysis during a session on the microscope, rather than after processing and digitizing films, so that adjustments could be made while the specimens were still in place. Our design parameters were 1) good resolution, in terms of pixels in the image, 2) wide field, so low magnification images could be obtained, 3) no interference with normal operation of the microscope, including the film camera, and 4) minimal modification of the microscope.

Cameras positioned below the film camera have narrow fields of view because of increase in image size below the film camera and the small size of CCD targets relative to film. We chose a position above the microscope's fluorescent viewing screen, where there is a convenient port on the 4000-EX, and achieved a field width approximately equal to that on film.
Determination of mean inner potential and thickness in wedge shaped specimens by interferometry and electron holography
Authors: Herring R.A. , Tanji T. , Tonomura A.
Published: June 2020

Knowlege of a specimens' mean innner potential and thickness is important for many purposes including holography, analytical (AEM) and microstructural analysis. This paper shows that both electron interferometry and holography can easily be used to determine the mean inner potential, as well as, the thickness at every point within a TEM specimen. The relative fringe shift, Δs/s , in a hologram by an object is linearly proportional to the object's mean inner potential, V, and thickness, d, and is given by,

where C is considered a constant and described by the relativistic energy correction divided by the acceleration energy, E, and wavelength, λ, i.e. [(1 + eE/mc2)/(l + eE/2mc2)/2Eλ]. Inorder to separate d and V another holographic image is required to provide another image equation. This image equation is easily provided by rotating the specimen a known angle, Δθ, such that d becomes a function of Δθ.
The morphology of moth and butterfly wing scales which exhibit reflective diffraction phenomena
Authors: Lee M.E. , de Neijs E.O.
Published: June 2020

The butterfly and moth families illustrate how nature has used diffractive micro-relief structures to achieve unique optical effects. Whereas the majority of insects use pigments (absorption) or occasionally thin film multi-layer structures (interference) to create colour, the wings of many families of butterfly and moth have complex 2-D or 3-D arrangements of submicron grating structures which produce zero and higher order diffraction conditions.

The special properties of a diffraction grating can be understood by light incident perpendicularly on a transmission grating. The light is diffracted into a number of grating orders at angles θn given by the grating equation sin θn = n λ/d where λ is the wavelength of the light, n = 0, ± 1, --- and d is the grating period. The same conditions are valid for reflective diffraction structures. If the grating period is finer than the wavelength ie. d < λ, no first order diffraction exists for normal illumination.
Epitaxial growth of nanocrystalline lead sulfide particles at monolayers
Authors: Yang Jianping , Zhao Xiao Kang , Fendler Janos H.
Published: June 2020

Generation of size-quantized semiconductor particulate films (SQSPFs) from their precursors has been the subject of intense investigations in our laboratory during the past several years. Most recently, we have utilized monolayers as templates for SQSPFs. Semiconductor particles were generated in situ at the monolayer headgroup-aqueous subphase interface. An appropriate aqueous metal ion solution (1.0 × 10-3 M Pb(NO3)2, or CdCl2, or ZnCl2, or CuSO4, for example) constituted the subphase. Either a commercial Lauda Model P Langmuir film balance or a simple circular trough was used for monolayer formation and the subsequent generation of semiconductor particles. The Lauda film balance was enclosed in a plexiglass hood and placed on a Micro-g optical isolation table. The water surface was cleaned several times by sweeping with a teflon barrier prior to monolayer formation. The monolayer-forming surfactants were compressed at a rate of (2-5) 10-3 Å2 per molecule per second. Subsequent to five to 15 min of incubation at the desired surface pressure (typically 25 mN/m), H2S was slowly injected into the nitrogen-filled plexiglass hood covering the film balance. Semiconductor particle formation at the monolayer surface was visually observed and monitored by reflectivity measurements and Brewster-angle microscopy.
Molecular organization in phospholipid monolayer domains by electron diffraction
Authors: Hui S. W. , Yu H.
Published: June 2020

In the LC/LE phase of phospholipid monolayers at the air/water interface, solid and fluid domains may be visualized by epi-fluorescence microscopy. Supposedly, solid domains are distinguished by the absence of fluorescence due to the preferential partitioning of most fluorescent dyes to the surrounding fluid phase lipids. The size, shape and stability of these domains are governed by molecular dipole-dipole interaction and inter-phase line tension. While x-ray and neutron diffractions offer some global average molecular packing information on a large sampling area of monolayers, selected area electron diffraction may provide local structural information within and along individual domains.

Dipalmitoyl-monomethyl-phosphatidylethanolamine [DP(Me)PE] and dipalmitoyldimethyl-phosphatidylethanolamine [DP(Me)PE] monolayers were spread on an environmentally controlled Langmuir trough. The monolayers were adjusted to the LE/LC phase by a servo-motor-driven Teflon bar moving along the surface of the trough.
Fractal analysis with scanning probe microscopy
Authors: West Paul E. , Marchesse-Rugona Sid , Li Zhuoning
Published: June 2020

Surface roughness determined qualitatively by direct visualization can be correlated to several physical properties. However, finding a suitable method of quantifying surface roughness, until recently, has been difficult. The concept of Fractal Dimension, recently popularized by Mandelbrot(1982) has been extremely successful in quantifying surface roughness and relating it to such measurable physical properties such as; cleanability, catalytic activity, rate of corrosion, and even flavor.

Atomic Force Microscopes permit direct three dimensional measurements of surface microstructure. AFM images are obtained by measuring the motion of a sharp stylus as it is scanned across a surface. Because the AFM directly measures three dimensional topograms, it is ideally suited for two dimensional and three dimensional fractal analysis. Other microscope techniques such as the scanning electron or optical microscope give only two dimensional magnification and fractal measurements are not easily made.

The Atomic Force Microscope enables us to obtain the fractal dimension of surface profiles as well as surface areas. For surface profiles we use a box counting method (Mandelbrot 1986, Chesters et al. 1989).
An application protocol of 3-D variance estimation theory for significance assessment of reconstructions and detection of 3-D conformational changes
Authors: Liu Weiping , Frank Joachim , Boisset Nicholas
Published: June 2020

A theory has been developed for estimating the 3-D variance of the weighted back-projection reconstruction from a single-exposure random conical tilt series. The variance estimate provides a new dimension of information that would otherwise be buried due to the averaging nature of the 3-D reconstruction. By combining the analysis of 3-D variance with classification and 3-D reconstruction, the average 3-D structure as well as the significance and the variability of its local features can now be studied. Through its successful applications to the 50S ribosomal subunit depleted of L7/L12 proteins and the hemocyanin-Fab complex, an application protocol of 3-D variance is proposed as outlined in the following:

(I) If we have one homogeneous projection set:

*

compute the 3-D reconstruction

*

compute the 3-D variances corresponding to different low-pass filter cut-off frequencies.

From this we can obtain
In the beginning there were electrons
Authors: Watson John H. L.
Published: June 2020

Electrons have undoubtedly been around since the beginning of time, but not until the first quarter of the twentieth century, following the work of deBroglie on the dual nature of the electron, Busch's hypothesis that an electron beam could be focussed by an axially symmetric magnetic field, and Davisson & Germer's and Thomson's independent demonstrations of electron diffraction, did microscopists take seriously the possibility of a microscope utilizing electrons and magnetic fields. The first attempts at building electron microscopes were made in Europe but the resolution in the often blurred and distorted electron images was not much better than that achieved by light microscopy, so that a general opposition to funding the development of electron microscopes began to emerge. In 1935 E.F. Burton, Chairman of the Department of Physics at the University of Toronto began a program of electron optical research with his graduate student Cecil E. Hall, building emission microscopes.
“Freeze-etching”: A historical perspective
Authors: Steere Russell L. , Erbe Eric F.
Published: June 2020

In 1953, when I first developed the idea of preparing specimens by the procedure now known as “freeze-etching”, the major techniques required for this approach had already been developed and were in use in our laboratory. We were freeze-drying viruses using the methods reported by Williams. We were shadowing such specimens with chromium (Cr) as well as other heavy metals. We were evaporating silicon monoxide (SiO) to provide support films or replicas. We had already looked at freeze-dried tobacco mosaic virus (TMV) crystals in various ways. We also were well aware that some specimens, for example, the very fragile TMV crystals, within infected cells, could not be examined properly with the existing cytological methods. Since I had used all of these methods, it became clear to me that a new cytological approach could be developed for the examination of biological specimens in the electron microscope. The approach appeared to be very simple at the time: 1) freeze the sample; 2) fracture the sample while still frozen; 3) keep the sample at very low temperature while it was being evacuated;
Total etch dentin bonding systems: scanning electron microscopy of the resin-dentin hybrid layer
Authors: Perdigao Jorge
Published: June 2020

In 1955, Buonocore introduced the etching of enamel with phosphoric acid. Bonding to enamel was created by mechanical interlocking of resin tags with enamel prisms. Enamel is an inert tissue whose main component is hydroxyapatite (98% by weight). Conversely, dentin is a wet living tissue crossed by tubules containing cellular extensions of the dental pulp. Dentin consists of 18% of organic material, primarily collagen. Several generations of dentin bonding systems (DBS) have been studied in the last 20 years. The dentin bond strengths associated with these DBS have been constantly lower than the enamel bond strengths. Recently, a new generation of DBS has been described. They are applied in three steps: an acid agent on enamel and dentin (total etch technique), two mixed primers and a bonding agent based on a methacrylate resin. They are supposed to bond composite resin to wet dentin through dentin organic component, forming a peculiar blended structure that is part tooth and part resin: the hybrid layer.
Biodegradable polyester neuroprostheses promote the reconnection of separated peripheral nerve stubs
Authors: Giammara Beverly L. , Stevenson Jennifer S. , Yates Peggy E. , Gunderson Robert H. , Hanker Jacob S.
Published: June 2020

An 11mm length of sciatic nerve was removed from 10 anesthetized adult rats and replaced by a biodegradable polyester Vicryl™ mesh sleeve which was then injected with the basement membrane gel, Matrigel™. It was noted that leg sensation and movement were much improved after 30 to 45 days and upon sacrifice nerve reconnection was noted in all animals. Epoxy sections of the repaired nerves were compared with those of the excised segments by the use of a variation of the PAS reaction, the PATS reaction, developed in our laboratories for light and electron microscopy. This microwave-accelerated technique employs periodic acid, thiocarbohydrazide and silver methenamine. It stains basement membrane or Type IV collagen brown and type III collagen (reticulin), axons, Schwann cells, endoneurium and perineurium black. Epoxy sections of repaired and excised nerves were also compared by toluidine blue (tb) staining. Comparison of the sections of control and repaired nerves was done by computer-assisted microscopic image analysis using an Olympus CUE-2 Image Analysis System.
Scanning electron microscopy and x-ray analysis of fossilized materials from calvert cliffs, md
Authors: Milburn Darolyn , Moses Melonie , Hammond Ernest
Published: June 2020

Diatoms are classified in the plant kingdom as Bacillariophyta. They are unicellular plants with cell walls of silica and are found in all types of fresh and salt waters. Some species have been found in different types of soils, as well. The oldest diatoms were marine and were from the Cretacious period. “No fresh water diatoms are known prior to the Miocene era.”

Several students went to the Calvert Cliffs located on the Western Shore of the Chesapeake Bay, near the confluent of the Patuxent River in southern Maryland. Fossils were collected and the scrapings were examined under the scanning electron microscope. Also, an x ray analysis was made and the objects were photographed for digital imaging processing. The x ray analysis revealed that the fossils contained large quantities of silicon, calcium, magnesium, iron and oddly enough, plutonium.

From the photographs and x ray analysis, the identification of the diatoms is narrowed down and eventually identified.
The use of scanning electron microscopy in interpreting chenopodium remains from three archaeological sites in northwestern Iowa
Authors: Jones Douglas William
Published: June 2020

Within the past 20 years, archaeobotanical research in the Eastern United States has documented an early agricultural complex before the dominance of the Mesoamerican domesticates (corn, beans, and squash) in late prehistoric and historic agricultural systems. This early agricultural complex consisted of domesticated plants such as Iva annua var.macrocarpa (Sumpweed or Marshelder), Hellanthus annuus (Sunflower) and Chenopodium berlandieri, (Goosefoot or Lasbsquarters), and heavily utilized plants such as Polygonum erectum (Erect Knotweed), Phalaris caroliniana (May grass), and Hordeum pusillum (Little Barley).

Recent research involving the use of Scanning Electron Microscopy (SEM) specifically on Chenopodium has established diagnostic traits of wild and domesticated species seeds. This is important because carbonized or uncarbonized seeds are the most commonly recovered Chenopodium material from archaeological sites. The diagnostic seed traits assist archaeobotanists in identification of Chenopodium remains and provide a basis for evaluation of Chenopodium utilization in a culture's subsistence patterns. With the aid of SEM, an analysis of Chenopodium remains from three Late Prehistoric sites in Northwest Iowa (Blood Run [Oneota culture], Brewster [Mill Creek culture], and Chan-Ya-Ta [Mill Creek culture]) has been conducted to: 1) attempt seed identification to a species level, 2) evaluate the traits of the seeds for classification as either wild or domesticated, and 3) evaluate the role of Chenopodium utilization in both the Oneota and Mill Creek cultures.
Factors influencing adhesive bonding at the bone/implant interface
Authors: Martini Julie A. , Doremus Robert H.
Published: June 2020

Tracy and Doremus have demonstrated chemical bonding between bone and hydroxylapatite with transmission electron microscopy. Now researchers ponder how to improve upon this bond in turn improving the life expectancy and biocompatibility of implantable orthopedic devices.

This report focuses on a study of the- chemical influences on the interfacial integrity and strength. Pure hydroxylapatite (HAP), magnesium doped HAP, strontium doped HAP, bioglass and medical grade titanium cylinders were implanted into the tibial cortices of New Zealand white rabbits. After 12 weeks, the implants were retrieved for a scanning electron microscopy study coupled with energy dispersive spectroscopy.

Following sacrifice and careful retrieval, the samples were dehydrated through a graduated series starting with 50% ethanol and continuing through 60, 70, 80, 90, 95, and 100% ethanol over a period of two days. The samples were embedded in LR White. Again a graduated series was used with solutions of 50, 75 and 100% LR White diluted in ethanol.
High-spatial-resolution microanalysis in the analytical electron microscope: a tutorial
Authors: Romig A. D. , Michael J. R.
Published: June 2020

High spatial resolution x-ray microanalysis in the analytical electron microscope (AEM) describes a technique by which chemical composition can be determined on spatial scales of less than 50 nm. Dependent upon the size of the incident probe, the energy (voltage) of the beam, the average atomic number of the material being analyzed, and the thickness of the specimen at the point of analysis it is possible to measure uniquely the composition of a region 2-20 nm in diameter. Conventional thermionic (tungsten or LaB6) AEMs can attain direct spatial resolutions as small as 20 nm, while field emission (PEG) AEM's can attain direct spatial resolutions approaching 2 nm. Recently, efforts have been underway to extract compositional information on a finer spatial scale by using massively parallel Monte Carlo electron trajectory simulations coupled with AEM measurements. By deconvolving the measured concentration profile with the calculated x-ray generation profile it is possible to extract compositional information at near atomic resolution.
STM imaging of the sample or the tip ? an in situ REM study
Authors: Lo W.K. , Spence J.C.H.
Published: June 2020

Image interpretation for Scanning Tunneling Microscopy (STM) is complicated by inadequate tip characterization. Tip and surface features can be difficult to separate, especially for rough surfaces. Figure 1, an STM image of a gold platelet deposited onto graphite, illustrates some of the possible problems. The doubled image of the platelet and step, for example, is a commonly encountered image artifact caused by tunneling from multiple tip asperities. The shape of the platelet(s) may also be an artifact since they are usually round. Ordinarily, to confirm the interpretation of such objects, experiments would be repeated using different tips and specimens to test for reproducibility. This is not an ideal procedure since the exact experimental conditions are difficult to duplicate. Alternatively, by comparing images of the same topography taken by STM and an independent imaging method, one can expose these artifacts.

STM image artifacts were studied using an STM operating inside a Philips EM 400T TEM. This allowed imaging of the same region by Reflection Electron Microscopy (REM) and STM, independently of each other.
Ultra-high sensitivity secondary ion and thermal ionisation mass spectrometry
Authors: O'Nions R.K.
Published: June 2020

In the earth and environmental sciences there is an increasing need for isotopic analysis at higher precision and on samples with a smaller number of atoms and often with high spatial resolution. For example, these are the requirements for problems involving climate change on the 102 to 105 year time scale to those of continental deformation on the 105 to 107 year scale. At one extreme measurements of seawater 87Sr/86Sr, now possible to a precision of 5ppm (lσ), provide information on the effects of climate change. At the other extreme an ability to measure the smallest number of atoms of 10Be or 26Al in the smallest volumes provides new information on cosmic ray fluxes at the surface. These challenges are being met using a variety of instrumentation, but prominent amongst them is a new generation of high sensitivity mass spectrometers able to accept ions produced thermally, by sputter ionisation and laser resonant ionisation.
Quantification of grain boundary segregation in TiO2 by STEM
Authors: Ikeda Jeri Ann S. , Chiang Yet-Ming , Garratt-Reed Anthony J.
Published: June 2020

A complete characterization of interfacial segregation involves knowing both the concentration of a solute or impurity and its spatial distribution, often at the subnanometer scale. In a number of materials problems, however, it is the segregation per unit area of interface that is of greatest interest. Problems involving charged interfaces are one example. In space-charge segregation at interfaces, the aliovalent solute density per unit area of interface is equivalent to the charge-density per unit area. Application of space-charge theory, in essence the application of Gauss' law and Poisson' equation allows the electrostatic potential to be deconvolved from segregation data.

We have developed a new technique for measuring the solute segregation density at interfaces, here applied to the quantification of space-charge segregation at grain boundaries in TiO2. Using the results of a recent study by Furdanowicz et al. showing that beam broadening in nanoprobe STEM is much less than predicted by many conventional models, we use the VG HB5 in scan mode to analyze a volume containing the grain boundary.
EELS in the High-Resolution STEM
Authors: Brown L. M.
Published: June 2020

The advent of efficient parallel recording systems for electron energy-loss spectra in electron microscopes, particularly those equipped with field emission guns which permit the formation of a useful nanometre probe, has transformed these instruments into remarkably versatile tools for solid state science. It is now possible in one's own laboratory to acquire spectra of quality comparable to those obtained from dedicated synchrotron sources, and in addition to record energy-filtered convergent-beam patterns and energy-selected images, in addition to the usual STEM outputs.

The system in use in our laboratory has been developed by McMullan and co-workers. Its main feature is the use of a charge-coupled device to record both spectra and convergent beam patterns. The system is under constant development, and in its latest version offers a choice of three detectors: a slow scan CCD camera for PEELS and microdiffraction (CBED from the probe optimised for best spatial resolution); a TV-rate CCD for rapid readout, instrument alignment and ‘super-resolution’ experiments; and a specialised scintillator-photomultiplier bright-field detector.
Electron energy loss spectroscopy of diamond-like carbon thin films
Authors: Kulik J. , Lifshitz Y. , Lempert G.D. , Rotter S. , Rabalais J.W. , Marton D.
Published: June 2020

Carbon thin films with diamond-like properties have generated significant interest in condensed matter science in recent years. Their extreme hardness combined with insulating electronic characteristics and high thermal conductivity make them attractive for a variety of uses including abrasion resistant coatings and applications in electronic devices. Understanding the growth and structure of such films is therefore of technological interest as well as a goal of basic physics and chemistry research. Recent investigations have demonstrated the usefulness of energetic ion beam deposition in the preparation of such films. We have begun an electron microscopy investigation into the microstructure and electron energy loss spectra of diamond like carbon thin films prepared by energetic ion beam deposition.

The carbon films were deposited using the MEIRA ion beam facility at the Soreq Nuclear Research Center in Yavne, Israel. Mass selected C+ beams in the range 50 to 300 eV were directed onto Si {100} which had been etched with HF prior to deposition.
A conduction-cooled stage for high-resolution Cryo-SEM
Authors: Sheehan John G.
Published: June 2020

The goal is to examine with high resolution cryo-SEM aqueous particulate suspensions used in coatings for printable paper. A metal-coating chamber for cryo-preparation of such suspensions was described previously. Here, a new conduction-cooling system for the stage and cold-trap in an SEM specimen chamber is described. Its advantages and disadvantages are compared to a convection-cooling system made by Hexland (model CT1000A) and its mechanical stability is demonstrated by examining a sample of styrene-butadiene latex.

In recent high resolution cryo-SEM, some stages are cooled by conduction, others by convection. In the latter, heat is convected from the specimen stage by cold nitrogen gas from a liquid-nitrogen cooled evaporative heat exchanger. The advantage is the fast cooling: the Hexland CT1000A cools the stage from ambient temperature to 88 K in about 20 min. However it consumes huge amounts of liquid-nitrogen and nitrogen gas: about 1 ℓ/h of liquid-nitrogen and 400 gm/h of nitrogen gas. Its liquid-nitrogen vessel must be re-filled at least every 40 min.
In situTEM measurements of the electrical properties of interface dislocations
Authors: Ross F. M. , Hull R. , Bahnck D. , Bean J. C. , Peticolas L. J. , King C. A.
Published: June 2020

We describe an investigation of the electrical properties of interfacial dislocations in strained layer heterostructures. We have been measuring both the structural and electrical characteristics of strained layer p-n junction diodes simultaneously in a transmission electron microscope, enabling us to correlate changes in the electrical characteristics of a device with the formation of dislocations.

The presence of dislocations within an electronic device is known to degrade the device performance. This degradation is of increasing significance in the design and processing of novel strained layer devices which may require layer thicknesses above the critical thickness (hc), where it is energetically favourable for the layers to relax by the formation of misfit dislocations at the strained interfaces. In order to quantify how device performance is affected when relaxation occurs we have therefore been investigating the electrical properties of dislocations at the p-n junction in Si/GeSi diodes.
Ex situ and In situ TEM study of the relaxation of thin films by the modified frank-read mechanism
Authors: LeGoues F.K.
Published: June 2020

In recent papers, we have described a novel mechanism for strain relaxation of thin films. Because of its strong resemblance to the well known Frank-Read sources of dislocations, it was called the “Modified-Frank-Read” (MFR) mechanism. This process was first observed during the growth of compositionally graded SiGe/Si(001) thin films, where it results in dislocations pile-ups being injected deep into an initially perfect substrate, leaving the topmost part of the film relaxed and nominally defect free. This last observation opens the door to a wide range of electronic applications since it makes it possible to grow electronic grade buffer layers of arbitrary composition and lattice parameter.

The exact mechanism of the reproduction of dislocations was identified through tilting experiment and analysis of several compositionally graded SiGe/Si(001) structures. These also provided the important parameters controlling this mode of strain relaxation. We thus demonstrated that the MFR mechanism corresponds to the multiplication of “corner dislocations” (dislocations whose line forms a 90° angle) by simultaneous glide on two (111) planes.
Degradation of visible cathodoluminescence from porous silicon
Authors: Batstone J.L. , Tischler M.A. , Collins R.T.
Published: June 2020

Porous Si has recently been shown to luminesce efficiently in the visible region of the spectrum. This discovery has lead to much excitement at the prospect of developing Si-based optoelectronic devices. However, the mechanism of this visible luminescence from an indirect-gap semiconductor is still the subject of much debate. In addition, the peak wavelength and efficiency of the luminescence is extremely sensitive to the preparation conditions and subsequent treatment of the sample. In this paper, Cathodoluminescence (CL) data are presented to show the degradation of luminescence when the samples are exposed to an electron beam.

Porous silicon films were prepared by anodically etching p− Si(001) substrates in a solution of HF: H2O:C2H5OH at current densities of 1-20mA/cm2. Cathodoluminescence was excited by electron beam irradiation of the samples in a JEOL JSM6400 scanning electron microscope (SEM) equipped with an Oxford Instruments wavelength-dispersive CL system and liquid He cold stage. Monochromatic CL images were obtained in the wavelength range 600-800nm.
The morphology and microstructure of polycrystalline CdTe thin films for solar cell applications
Authors: Jones K.M. , Hasoon F.S. , Swartzlander A.B. , Al-Jassim M.M. , Chu T.L. , Chu S.S.
Published: June 2020

Polycrystalline thin films of II-VI semiconductors on foreign polycrystalline (or amorphous) substrates have many applications in optoelectronic devices. In contrast to the extensive studies of the heteroepitaxial growth of compound semiconductors on single-crystal substrates, the nucleation and growth of thin films of II-VI compounds on foreign substrates have received little attention, and the properties of these films are often controlled empirically to optimize device performance. A better understanding of the nucleation, growth, and microstructure will facilitate a better control of the structural and electrical properties of polycrystalline semiconductor films, thereby improving the device characteristics. Cadmium telluride (CdTe) has long been recognized as a promising thin-film photovoltaic material. Under NREL's sponsorship, the University of South Florida has recently developed a record high efficiency (14.6% under global AM1.5 conditions) thin-film CdS/CdTe heterojunction solar cell for potential low-cost photovoltaic applications. The solar cell has the structure:

glass (substrate)/SnO2:F/CdS/CdTe/HgTe (contact)

The CdS films were grown from an aqueous solution, while the CdTe films were deposited by the closespaced sublimation method.
Characterization of defects resulting from the poly-buffered local oxidation isolation process
Authors: Staman J. W. , Hodges R. L. , Dixit G. A. , Bryant F. R. , Sundaresan R. , Wei C. C. , Liou F. T.
Published: June 2020

As device dimensions are being scaled down in today's advanced VLSI circuits, isolation has been one of the key technologies to achieve the submicron geometries. The conventional local oxidation (LOCOS) process results in a large bird's beak, rendering it ineffective for submicron technology. Poly buffered local oxidation (PBL) is a manufacturable process and can achieve a smaller bird's beak which makes it attractive for submicron device isolation. In PBL, a thin layer of poly silicon is sandwiched between the protective nitride and oxide. The polysilicon layer acts as a buffer to the nitride and oxidation induced stresses on the silicon substrate and thus a thicker nitride can be used to obtain a shorter bird's beak. Many papers have been published which describe the PBL process, however, very few of them have explored the physical and chemical nature of the defects associated with the PBL process. In this paper, we report the results of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) analysis of these defects and relate them to the traditional Kooi effect.
Interface morphology of thermal oxide grown on polycrystalline silicon by different processes
Authors: Yen H. , Kvam E. P. , Bashir R. , Venkatesan S. , Neudeck G. W.
Published: June 2020

Polycrystalline silicon, when highly doped, is commonly used in microelectronics applications such as gates and interconnects. The packing density of integrated circuits can be enhanced by fabricating multilevel polycrystalline silicon films separated by insulating SiO2 layers. It has been found that device performance and electrical properties are strongly affected by the interface morphology between polycrystalline silicon and SiO2. As a thermal oxide layer is grown, the poly silicon is consumed, and there is a volume expansion of the oxide relative to the atomic silicon. Roughness at the poly silicon/thermal oxide interface can be severely deleterious due to stresses induced by the volume change during oxidation. Further, grain orientations and grain boundaries may alter oxidation kinetics, which will also affect roughness, and thus stress.

Three groups of polycrystalline silicon films were deposited by LPCVD after growing thermal oxide on p-type wafers. The films were doped with phosphorus or arsenic by three different methods.
Formation of stacking-fault tetrahedra in low defect density oxygen-implanted silicon-on-insulator material
Authors: Lee June-Dong , Krause Stephen , Roitman Peter
Published: June 2020

Fabrication of integrated circuits on SOI (Silicon-On-Insulator) material is very attractive because it offers high component density, immunity to latch-up and radiation hardness. Among various SOI techniques SIMOX Separation by IMplantation of OXygen) provides the best material, with carrier mobilities and defect densities approaching bulk silicon values, Early SIMOX wafers were implanted at temperatures below 600°C and annealed at high temperature (>1300°C), which gave a high defect density (109cm−2), including threading dislocations and narrow stacking faults (SFs), as shown in Figure 1. Higher temperature (>600°C) implantation of SIMOX reduced defect densities to 106cm-2 with pairs of narrow SFs in the top silicon layer, as shown in Figure 2. This paper describes a further reduction of defect density in SIMOX material through various annealing conditions, which has resulted in a defect density less than 105cm−2. A new formation mechanism for stacking fault tetrahedra is also discussed.

Silicon (100) wafers were sequentially implanted (620°C) and annealed (at 1320°C for 5 hours) to doses of 0.5, 0.5, and 0.8×l018cm-2.
Effect of copper content on reaction compound formation in Al-Cu/Ti-W bilayers
Authors: Park M. , Krause S.J. , Wilson S.R.
Published: June 2020

In modern integrated circuits, a barrier layer of Ti-W is commonly used to reduce interdiffusion between Al-alloy interconnects and the Si substrate for multilevel metallization. Deterioration of the metallization layers may occur by the interaction of the Al-alloy film with the Ti-W sublayer during post-metallization thermal processing, resulting in the formation of aluminide reaction compounds, such as Al12W and Al5W. The reaction morphologies of the Al film with other transition metals, such as Ti4 and Hf5, have been studied. The morphologies of the compounds are planar for Al3Ti and spiked for Al3Hf, respectively. When Cu solute is added to Al, it has a significant effect on the growth and morphology of these reaction compounds. Although Al-Cu/Ti-W films are now extensively used for multilevel metallization, the effect of Cu content on the reaction growth and morphology of the compound has not been studied in detail. In this work, we report on the effect of Cu content on the reaction between the Al-Cu layer and Ti-W barrier layer, and the resulting morphology.
Characterization of stacked dielectric structures by TEM, electron holography and electron energy loss spectroscopy
Authors: Waytena G. , Weiss J.K. , Rez P.
Published: June 2020

Thinner gate oxide regions, less than 100Å wide, are needed as MOS devices are scaled down in size to improve performance and increase the number of devices per chip. Triple layer dielectrics, in which a Si3N4 film is embedded between two SiO2 layers, are being investigated since the nitride layer provides a better diffusion barrier against dopants, metals and impurities as well as higher effective dielectric constant than a single layer of SiO2. To minimise atom diffusion, low temperature growth techniques such as Remote Plasma Enhanced Chemical Vapour Deposition (RPECVD) are being considered. As low temperature growth is not an equilibrium process non-stochiometric compositions can be formed. The aim of this work is to investigate structural characterisation of these layers in cross section by TEM and compositional analysis by PEELS.

Two oxide-nitride-oxide (ONO) structures, both with nominally 50Å of nitride sandwiched between 10Åoxide layers in one specimen (10-50-10), and 30Å oxide layers in the second specimen (30-50-30) were grown by RPECVD at Research Triangle Institute. Cross section TEM specimens were prepared in according to standard procedures.
Antiphase boundaries and misfit dislocations in gaAs grown on ge(001)
Authors: Guelton N. , Saint-Jacques R.G. , Lalande G. , Cossement D. , Dodelet J.P.
Published: June 2020

This work reports TEM investigation of the GaAs/Ge (100) heterojonction grown by close-spaced vapor transport (CSVT). It confirms that i) in layers deposited by this technique, the antiphase boundary (APB) density can be strongly reduced by using annealed misoriented substrates and that ii) the <011> misfit dislocations are mainly of the 60° type. It has been found that they are confined within 150 nm from the interface.

The CSVT is an efficient and cost effective technique that allows the growth of epitaxial layers of semiconductors. A temperature gradient is maintained between the closely spaced (1mm) solid source and substrate. A transporting agent (water vapor) is used to react with the source and form volatile compounds which are subsequently decomposed at the surface of the substrate to form a thin film of the source material. Prior to initiation of deposition, the Ge substrate is heated at 825°C for 30 min in H2 atmosphere while the source temperature is maintained at 775°C, i.e. at a lower temperature to avoid any deposition on the substrate. This procedure allows elimination of oxydes and leads to step doubling.
Direct phase determination in electron crystallography: Linear polymers
Authors: Dorset Douglas L.
Published: June 2020

Perhaps no other class of organic molecule has been the subject of quantitative electron crystallographic structure analyses than the linear polymers. Given the real restrictions to crystallization of these materials, the reason for this is very clear, since one can at least obtain single crystal electron diffraction patterns from the chain-folded lamellae for determination of unit cell dimensions and symmetry and for measurement of diffracted intensities. The usual methodology for crystal structure analysis with the observed intensity data is based on the procedure used in fiber X-ray analyses. That is, one determines the X-ray crystal structures of representative monomer and/or oligomer segments of the polymer chain to see what part of the repeat can be held conformationally rigid. These rigid units are concatenated through “linkage bonds”, around which conformational twists are allowed and the search for the stable chain structure is based on the simultaneous minimization of the crystallographic R-factor and an internal energy calculated from nonbonded atomatom potential functions.
Some characteristics of edge fringes in diffraction contrast images of grain boundaries
Authors: Cheng S. C. , Sheinin S. S.
Published: June 2020

The methods used to characterize interfaces from diffraction contrast images are normally based on the contrast exhibited by the edge fringes in these images. In one approach to this problem, Amelinckx et al. have characterized the edge fringes due to a displacement at an interface as being α fringes and the edge fringes which are due to a difference in orientation across the boundary as being δ fringes. The general properties of so called symmetrical δ fringes can be summarized as follows: bright field images are asymmetrical (i.e. one edge fringe is dark while the other is bright) while dark field fringes are symmetrical. Of particular interest in the generation of δ fringes are situations in which the reflections, g and h in Fig. 1b (and therefore 0 and g - h in the same figure) are very close. Under these circumstances both bright and dark field images will be formed with two reflections (either 0 and g-h or g and h) passing through the objective aperture.
A RHEED study of Cu3Au (110) surface
Authors: Huang Yi , Cowley John M.
Published: June 2020

In recent years the Cu3Au (110) surface has been studied by many authors to reveal its ordering structure and order-disorder transition phenomena. A 2×1 structure which corresponds to an ideal truncation of the ordered bulk crystal and a 4×1 reconstructed structure have been observed. Using ion scattering methods, McRae et al have determined the Au fractions in the first and the second layer at room temperature, which deviate from the ideal bulk value and indicate the segregation of Au to the surface. But the question how the atoms are rearranged in the 4×1 structure and why some of the Au stays in the second layer have not been answered. Another important question about Cu3Au (110) surface is whether the long period ordering structure (LPS) exists on the surface. In present work the Cu3Au (precise composition Cu71.7Au28.3) (110) surface is studied with Auger electron Spectroscopy (AES) and Reflection High Energy Electron Diffraction (RHEED) which have not been used to study the Cu3Au surface before.