Journal of Electron Microscopy - current issue

The development and characteristics of a high-speed EELS mapping system for a dedicated STEM

Isakozawa, S., Kaji, K., Jarausch, K., Terada, S., Baba, N. — 2008-03-05

A new EELS (electron energy loss spectroscopy) real-time elemental mapping system has been developed for a dedicated scanning transmission electron microscope (STEM). The previous two-window-based jump-ratio system has been improved by a three-window-based system. It is shown here that the three-window imaging method has less artificial intensity in elemental maps than the two-window-based method. Using the new three-window system, the dependence of spatial resolution on the energy window width was studied experimentally and also compared with TEM-based EELS. Here it is shown experimentally that the spatial resolution of STEM-based EELS is independent of the energy window width in a range from 10 eV to 60 eV.

Back-etch method for plan view transmission electron microscopy sample preparation of optically opaque films

Yao, B., Coffey, K. R. — 2008-03-05

Back-etch methods have been widely used to prepare plan view transmission electron microscopy (TEM) samples of thin films on membranes by removal of the Si substrate below the membrane by backside etching. The conventional means to determine when to stop the etch process is to observe the color of the light transmitted through the sample, which is sensitive to the remaining Si thickness. However, most metallic films thicker than 75 nm are opaque, and there is no detectable color change prior to film perforation. In this paper, a back-etch method based on the observation of an abrupt change of optical reflection contrast is introduced as a means to determine the etch endpoint to prepare TEM samples for these films. As the acid etchant removes the Si substrate material a rough interface is generated. This interface becomes a relatively smooth and featureless region when the etchant reaches the membrane (film/SiO₂). This featureless region is caused by the mirror reflection of the film plane (film/SiO₂ interface) through the optically transparent SiO₂ layer. The lower etch rate of SiO₂ (compared with Si) gives the operator enough time to stop the etching without perforating the film. A clear view of the morphology and control of Si roughness during etching are critical to this method, which are discussed in detail. The procedures of mounting wax removal and sample rinsing are also described in detail, as during these steps damage to the membrane may easily occur without appropriate consideration. As examples, the preparation of 100-nm-thick Fe-based amorphous alloy thin film and 160-nm-thick Cu-thin film samples for TEM imaging is described.

Characterization of the charging effect in a ZrO2 sintered body by Ga ion beam irradiation

Kim, K. H., Kim, J. J., Suzuki, T., Shindo, D. — 2008-03-05

The charging effect in a ZrO₂ sintered body was investigated by using scanning ion microscope (SIM) images. In this study, we report interesting features caused by the charging effect in the ZrO₂ sintered body during the Ga ion beam irradiation: a bright contrast with a distorted net shape appears around the positively charged specimen. From this feature in the SIM image, it is clarified that the Ga ion beam is strongly deflected and the wide area of the internal parts of the focused ion beam machine is irradiated by the Ga ion beam, depending on the extent to which the specimen is charged. We discuss the mechanism of the characteristic charging effect through observing SIM images by varying the intensity of the Ga ion beam.

Regeneration of muscle fibers in the extensor digitorum longus muscle of the aged rat

Desaki, J. — 2008-03-05

Regeneration of muscle fibers was observed in the extensor digitorum longus (EDL) muscle of aged (24 and 27 months) Wistar rats. The aged muscles consisted almost exclusively of medium-sized muscle fibers. In addition to degenerating and/or atrophied muscle fibers, very small muscle fibers <10 µm in diameter were observed in some muscle bundles which sporadically distributed in the muscle. In the degenerating muscle fibers, satellite cells mostly appeared to be normal, possibly surviving within the scaffold of basal lamina to form new (regenerating) muscle fibers. However, some of the satellite cells were degenerated and destroyed, suggesting the decrease in number of muscle fibers. On the other hand, very small muscle fibers existed between small and/or medium-sized muscle fibers or in the wide interstitial spaces between them solitarily or in small groups. In addition, immature muscle cells having a centrally located nucleus and sporadically distributed myofilaments were observed among the small and/or medium-sized muscle fibers and partially lacked a layer of basal lamina. These immature muscle cells were often closely apposed to fibroblasts with some slender cytoplasmic processes and/or to each other without an interposing basal lamina. These findings suggest that in addition to satellite cells within the basal lamina tubes, some of the regenerating muscle fibers in the aged EDL muscle may be originated from mesenchymal cells such as fibroblasts in the interstitial spaces.

Effect of Hydrofiber(R) wound dressings on bacterial ultrastructure

Hobot, J., Walker, M., Newman, G., Bowler, P. — 2008-03-05

Ionic silver has well-proven bactericidal properties, and silver-containing wound dressings are now widely used to aid in the creation of an antimicrobial environment in wounds. The effect of silver ions on bacterial ultrastructure can best be studied by viewing bacterial cells under a transmission electron microscope (TEM). Bacterial cells of Pseudomonas aeruginosa were incubated within a control dressing (e.g. a non-antimicrobial Hydrofiber® dressing) (Hydrofiber® is a registered trademark of E.R. Squibb and Sons, L.L.C.) and a silver-containing Hydrofiber® dressing, followed by processing for TEM. Liquid cultures, with and without silver, were prepared for comparison. The addition of silver to growing bacterial cultures stopped growth of the cells very quickly. Ultrastructurally, the presence of silver was found to affect both the shape of the bacterial nucleoid and the organization of bacterial DNA. X-ray microanalysis of bacteria from liquid cultures showed the presence of silver within silver-treated cells and the absence of calcium. It is suggested that the presence of available silver ions within the Hydrofiber® dressing could lead to the loss of cellular ions, vital for maintaining the structural integrity of the nuclear area.

Novel muscle spindles containing muscle fibers devoid of sensory innervation in the extensor digitorum longus muscle of aged rats

Desaki, J., Nishida, N. — 2008-03-05

We examined the structural features of muscle spindles at the equatorial and juxtaequatorial regions in the extensor digitorum longus muscle of adult (12 months) and aged (25 months) rats. In aged muscle spindles, the lamellated layers of the spindle capsule were a little increased in number compared to those in the adult ones. Two novel muscle spindles were observed in the aged muscle. In one muscle spindle, the spindle capsule contained four thin intrafusal muscle fibers invested by the inner capsule and two muscle fibers between the layers of the spindle capsule. Serial semithin sections revealed that the latter lacked the investment of the spindle capsule at the polar region. The other muscle spindle contained four intrafusal muscle fibers: two thin sensory-innervated muscle fibers invested by the inner capsule and two thick muscle fibers similar in structural features to neighboring extrafusal muscle fibers and lacking sensory innervation within the wide periaxial space. These findings suggest that two muscle fibers between the layers of the spindle capsule may be invested by the newly formed capsular cells during aging, while two thick fibers within the periaxial space may fail to receive the sensory innervation during the early development and follow the course of extrafusal fiber differentiation.