Subsequent Scanning Electron Microscopy Research Articles

Microstructure and local brittle zone phenomena in high-strength low-alloy steel welds

This study is concerned with a correlation between the microstructure and the local brittle zone (LBZ) phenomena in high-strength low-alloy (HSLA) steel welds. The influence of the LBZ on toughness was investigated by means of simulated heat-affected zone (HAZ) tests as well as welded joint tests. Micromechanical processes involved in microvoid and cleavage microcrack formation were also identified using notched round tensile tests and subsequent scanning electron microscopy (SEM) analyses. The LBZ in the HAZ of a mUltipass welded joint is the intercritically reheated coarse-grained HAZ whose properties are strongly influenced by metallurgical factors such as an effective grain size and high-carbon martensitic islands: The experimental results indicated that Charpy energy was found to decrease monotonically with increasing the amount of martensitic islands, confirming that the martensitic island is the major microstructural factor controlling the HAZ toughness. In addition, microvoids and microcracks were found to initiate at the interface between the martensitic island and the ferrite matrix, thereby causing the reduction in toughness. These findings suggest that the LBZ phenomena in the coarse-grained HAZ can be explained by the morphology and the amount of martensitic islands.

Ultrastructure of plant chromosomes by high-resolution scanning electron microscopy

A technique is described for using standard squash preparations of mitotic and meiotic chromosomes for both light microscopy and subsequent high-resolution scanning electron microscopy for investigation of the same specimen. Depending on the microscope and conditions of preparation, a resolution of a few nanometers is routinely possible. Tilting of the specimen provides a three-dimensional insight into chromosomal structures. Combination of material-dependent signals of backscattered electrons with the secondary electron image allows an unambiguous localization of surface markers.

Photoemission Study of Low-Fluence, Non-Thermal Laser Damage of UHV-Cleaved Gallium Arsenide (110)

AbstractThe pulsed-laser induced photochemical production of metallic Ga islands on the surface of GaAs cleaved, irradiated, and studied in ultrahigh vacuum (UHV) is documented through photoelectron spectroscopy and subsequent scanning electron microscopy. Ga islands are detected for laser fluences as low as 1 mJ/cm2, far below those previously reported for modification of GaAs, and for which the temperature rise is negligible.

Improved procedure for surface analysis of explanted intraocular lenses by combined light microscopy and scanning electron microscopy

An improved surface characterization procedure for evaluating explanted intraocular lens (IOL) biocompatibility was developed. The technique combines aqueous hematoxylin-eosin staining for characterizing adherent cells and tissue with subsequent scanning electron microscopy of the same 1OL.

Excimer laser-assisted etching of polysilicon at 193 nm

Excimer laser-assisted etching of polysilicon at 193 nm was studied in the presence of CF3Br, CF2Cl2, and NF3. In the presence of 193 nm radiation, CF3Br showed some propensity to etch polysilicon, while CF2Cl2did not show any appreciable etching. In the presence of NF3, maximum etch rates of 0.6 Å/pulse were obtained for pressures greater than 500 Torr and fluences exceeding 200 mJ/(cm2pulse). The etch rate increased with both fluences and pressure to a limiting value of 0.6 Å/pulse. An adsorptive etch mechanism was proposed, where NF3molecules diffuse to the surface, adsorb, and then react after absorbing laser radiation. Thermal effects enhance this process and appear to dominate at lower pressures (<400 Torr) and higher fluences. Etching caused by the gas phase formation of F atoms is minimal due to the low absorption cross section of NF3at 193 nm. Etching of submicron profiles in polysilicon was also examined. Polysilicon samples masked by patterned SiO2were exposed to NF3and 193 nm ArF radiation. Subsequent scanning electron microscopy (SEM) analysis demonstrated directional etching with some surface roughening.

The isolated sinoatrial node cell in primary culture from the newborn rat.

We prepared primary cell cultures of the sinus node region from newborn rat hearts. Sinoatrial node cells were easily distinguished from the other cardiac muscle cells and nonmuscle cells in culture by size, configuration, and rapid, attenuated spontaneous contractions (185.0 +/- 8/min, mean +/- SEM). The spontaneously contracting sinoatrial node cells were extremely sensitive to acetylcholine and norepinephrine, responding to concentrations at least 1000-fold less than other cardiac muscle cells. These same sinoatrial node cells in culture were fixed and precisely relocated by either subsequent scanning or transmission electron microscopy. The ultrastructural features of these sinoatrial node cells in culture were similar to those observed in the cells of intact sinus node sections from the source hearts. This study is the first to present single, spontaneously active, neonatal sinoatrial node cells maintained in vitro with morphological and functional properties desirable for physiological investigations.

Investigation of Fretting Corrosion at Dissimilar Metal Interfaces in Socketed IC Device Applications

Gold has traditionally been the material of choice for separable connector contact surfaces in high reliability applications. With the rising cost of gold, major efforts have been focused on finding ways of reducing or altogether eliminating its use while still maintaining low and stable values of contact resistance. Currently in commercial semiconductor devices, gold-plated device leads are often not available. Tin and solder finishes are common. Recently early intermittent contact resistance failures were found when dissimilar metal (Au/Sn and Au/solder) interfaces were used in conjunction with socketed integrated circuit (IC) devices. Analysis of these failures indicated that fretting corrosion of tin had occurred. To better understand the phenomena of fretting corrosion in such applications, a laboratory study was conducted on a variety of dissimilar metal (socketed device) interfaces under conditions of mild vibration. The static resistance behavior of the samples was studied for a ten month period. The samples were then disassembled and the contact surfaces were examined using scanning electron microscope (SEM) and scanning Auger microprobe (SAM) techniques. The resistance data obtained indicated that, without lubrication, all metal interfaces except Au/ Au failed repeatedly. Subsequent SEM and SAM investigations showed that all interfaces of Sn and SnPb (solder) mated to themselves or to Au failed by tin fretting corrosion, resulting in high contact resistances (>100 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Omega</tex> .

In Situ AES Characterization of Rotating Electrical Contacts

The electrical contact resistance and surface chemical composition of a rotating copper slip ring in contact with two wire brushes were investigated in situ under ultrahigh vacuum (UHV) conditions as a function of the number of revolutions of the slip ring. The initial surface of the copper slip ring was examined by Auger electron spectroscopy (AES) techniques and found to be almost completely covered by surface impurities largely consisting of carbon. As the slip ring was rotated in contact with the brushes, the impurity concentration declined sharply to less than ten at% after several hundred revolutions. A corresponding decrease in electrical contact resistance and a sharp increase in friction and wear were also observed. Regardless of polarity, the brush with the higher contact pressure had the lower contact resistance. The in situ experiments were terminated when the motor turning the slip ring could no longer overcome the adhesive forces between the brushes and slip ring. Subsequent scanning electron microscopy observations of the brush and slip ring surfaces gave supplementary information on the mechanisms of friction, wear and surface cleaning during rotation. For a given experiment the change in contact resistance during rotation divided by the change in impurity concentration on the surface of the slip ring is approximately the same for the positive and negative interfaces. This parallelism of contact resistance and surface impurity concentration suggests that the former is caused to a significant extent by the latter. Since the surface impurities are mostly carbon atoms, it is concluded that carbon impurities are largely responsible for the observed contact resistance.

A practical method for the identification of particulate and crystalline material in paraffin--embedded tissue specimens.

The combination of light microscopy, low temperature micro-incineration of paraffin sections, and subsequent scanning electron microscopy (SEM), with X-ray energy spectroscopy (XES) has been shown to allow rapid and reliable identification of inorganic crystalline and particulate material in body tissues. Applications of this technique to hospital practice are illustrated and its potential in diagnosis and research are suggested.

American patents

An investigation has been carried out into the manufacture and field trial of alloy white iron beater plates used to process coal in a KSG coal pulveriser mill. The components were made by the cast bonding process, which involves casting a wear layer onto a steel substrate to form a bimetallic composite product. Four alloy white irons, containing primary and/or eutectic carbide volume fractions ranging from nominally 10 to 40%, were used as the cast overlay in the manufacture of the beater plates. Two replicates of each alloy composition were tested in a mill along with two standard austenitic manganese steel plates. All beater plates completed 3275 h of operation, with the best-performing alloys receiving an additional 3471 h of service in a second campaign. The results showed that increasing carbide volume fraction decreased the wear rate most markedly at sites of low-angle erosion, and that it had a smaller influence at higher angles of abrasive particle attack. Subsequent scanning electron microscopy examination of worn components revealed that the primary mode of material loss at the lower carbide volume fractions was microspalling, with sub-surface fractures occurring within the carbide particles and along carbide-matrix interfaces. Surface microgrooves were more evident in the alloy white iron beater plates with higher carbide volume fractions.