Observation of magnetic multilayers by electron holography.

Magnetic structures of Co/Cu multilayers in cross section are observed by two kinds of electron holography: a Fourier method and a phase-shifting method, which is introduced briefly. The Fourier method can easily reconstruct wave functions and is applied to many specimens, whereas the phase-shifting method requires longer time for processing, but has a higher spatial resolution that permits us to discuss fine structures. Magnetization vectors in Co layers aligning parallel and separating into two blocks with antiparallel alignment are observed. Magnetic blurring on the boundary between Co and Cu in the reconstructed phase images is larger than the estimated atomic roughness.

Serous retinal detachment and cystoid macular edema in hypotony maculopathy.

PURPOSE: To report the foveal structural findings of hypotony maculopathy imaged with optical coherence tomography. METHODS: Case report of a 39-year-old white woman with a 20 year history of uveitis, who underwent pars plana vitrectomy and pars plana Baerveldt implant for intractable glaucoma. Four months postoperatively, decreased vision and hypotony maculopathy ensued. Optical coherence tomographic (OCT) images were taken horizontally through the macula. RESULTS: OCT demonstrated large intraretinal cysts, serous macular detachment, and choroidal folds, which resolved upon resolution of hypotony. CONCLUSION: Cystic macular changes and serous macular detachment can be prominent features of hypotony maculopathy.

Hologram simulation for off-axis electron holography

Hologram simulation for electron holography using an electron biprism is described. An electron hologram is superimposed by Fresnel fringes originating from the electron biprism, which affects both the amplitude and the phase of the object wave and the reference wave. In this simulation, we consider the effects of Fresnel diffraction as well as the electron-wave phase shift due to the electromagnetic field produced by the specimen. We also take into account the phase shift due to the inner potential of the specimen, the amplitude modulation due to the absorption of the incident electrons by the specimen, reference-wave distortion caused by the electromagnetic fields, coherency of the electron wave, and quantum noise of the detected electrons. Simulated and experimentally obtained holograms and reconstructed images are compared for the cases of a charged latex spherical particle and a single magnetic-domain spherical particle placed on a carbon film.

Improvement of light collection efficiency of lens-coupled YAG screen TV system for a high-voltage electron microscope.

A new lens coupling television (TV) system using a YAG (Yttrium Aluminum Garnet: Y(3)Al(5)O(12) : Ce(3+)) single crystal screen has been developed for a high-voltage electron microscope (HVEM), and its performance is examined. The system, using a combination of YAG and lenses, is less damaged by high-energy electron irradiation and reduces the influence of X-rays on the image. YAG screens have not been used for lens-coupling systems, because the high refractive index (n = 1.84) of YAG results in a low light collection efficiency for emitted light. This disadvantage is overcome by combining a thin YAG disk screen (thickness; 100 microm) with a glass hemisphere whose refractive index is 1.81. We found that the light intensity is almost the same as that obtained with a conventional P22 powder screen and lenses system. The resolution is about 55 microm on the YAG screen, and this value is 1.3 times higher than that measured by the conventional system. Shading and distortion do not affect TV observation. Detection quantum efficiency, obtained after correction of the channel mixing effect, is about 0.1.

High precision phase-shifting electron holography

Today's information-oriented society requires high density and high quality magnetic recording media. The quantitative observation of fine magnetic structures by electron holography is greatly anticipated in the development of such new recording materials. However, the magnetic fields around particles <50 nm have not been observed, because the fields are too weak to observe in the usual way. Here we present a highly precise phase measurement technique: improved phase-shifting electron holography. Using this method, the electric field around a charged polystyrene latex particle (100 nm in diameter) and the magnetic field around iron particles (30 nm in diameter) are observed precisely. A precision of the reconstructed phase image of 2pi/300 rad is achieved in the image of the latex particle.

Biocompatibility response to modified Baerveldt glaucoma drains.

Glaucoma implants are designed to increase fluid outflow from the eye in order to decrease intraocular pressure and prevent damage to the optic nerve. The implant consists of a silicone tube that is inserted into the anterior chamber at one end and is attached at the other end to a silicone plate that is sutured to the outside of the globe beneath the conjunctiva. The glaucoma "implant" becomes a "drain" over the first 3 to 6 postoperative weeks as the silicone plate is enclosed by a fibrous capsule that allows a space to form into which fluid can drain and from which fluid can be absorbed by the surrounding tissues. Ideally, the size and thickness of the capsule (the filtering bleb) that surrounds the plate is such that the amount of fluid that passes through the capsule is identical to the amount of fluid produced by the eye at an intraocular pressure of 8 to 14 mmHg. The most common long-term complication of these implants is failure of the filtering bleb 2 to 4 years after surgery due to the formation of a thick fibrous capsule around the device. Micromovement of the smooth drainage plate against the scleral surface may be integral to the mechanism of glaucoma implant failure by stimulating low-level activation of the wound healing response, increased collagen scar formation, and increased fibrous capsule thickness. To test this hypothesis, we modified seven Baerveldt implants by adding porous cellular ingrowth material to the posterior surface of the drainage plate. Seven modified and five unmodified implants were placed in adult rabbit eyes. After 6 months, we found that the fibrous capsule around the modified implants was significantly thinner than the capsule surrounding the unmodified implants (p < 0.05), particularly on the surface between the porous ingrowth material and the sclera (p < 0.05). Although type I collagen predominated in the fibrous capsules around both types of implants, the amount of type III collagen in the capsules around the modified implants was significantly less than the amount around the unmodified implants (p < 0.05). We believe that these data suggest a reduction in the wound healing response to the modified implants, with greater stability of capsule thickness. Long-term studies are needed to verify that the stability of the capsules around the modified implants persists over a period of years, in which case this type of modification may prove useful in prolonging the functional life of these devices in the surgical treatment of glaucoma.

Fascia lata patch graft in glaucoma tube surgery.

PURPOSE: To determine if using human cadaveric fascia lata grafts to cover glaucoma implant tubes is safe and effective. METHODS: All patients who underwent glaucoma implant surgery at the Doheny Eye Institute between July 1993 and September 1993 received a fascia lata patch graft to cover the subconjunctival portion of the tube. These patients were followed prospectively for clinical signs of conjunctival breakdown, graft melt, tube erosion, graft-related inflammation, infection, and graft-related complications. RESULTS: Twenty-two eyes of 21 patients were followed for a mean of 19 months. All eyes tolerated the fascia lata grafts well without clinical evidence of graft-related conjunctival, scleral, or intraocular inflammation. No tube erosion or melting of the graft was observed in the study group. CONCLUSION: Preserved donor fascia lata was well tolerated as a grafting material in glaucoma implant surgery. No clinical signs of graft rejection, foreign body reaction, tube erosion, or graft melt were observed in the study group during the follow-up period.

Three-dimensional reconstruction of electric-potential distribution in electron-holographic interferometry.

A method of reconstructing the three-dimensional electric-potential distribution of a microscopic object with electron-holographic interferometry is presented. A sequence of processing techniques is developed to obtain the projected phase proportional to the potential distribution. A modified backprojection algorithm is used to reconstruct a three-dimensional potential distribution from the projected potentials obtained at different projection directions. In an experiment this method is applied to reconstruct three-dimensional latex particles.

Perfluoroperhydrophenanthrene (Vitreon) as a short-term vitreous substitute after complex vitreoretinal surgery.

Forty-one eyes underwent surgery for complex vitreoretinal disease, with perfluoroperhydrophenanthrene (Vitreon) used as an intraoperative tool and postoperative vitreous substitute. Postoperative use of Vitreon ranged from 3 days to 9 weeks (mean, 3.3 weeks). All retinas were reattached intraoperatively; 73% remained attached after the initial surgery. The final macular attachment rate was 100% after additional surgery. Four eyes that received a combination of Vitreon and silicone oil for simultaneous superior and inferior tamponade were successfully reattached after the initial procedure. Visual acuity improved or remained stable in 80% of the eyes. No toxic effects directly attributable to Vitreon were observed. Mean follow up was 9 months.

Real-time electron-holographic interference microscopy with a liquid-crystal spatial light modulator.

An electron-holographic interference microscope that produces a time-sequential interference micrograph at a TV rate is developed. In this system, the electron off-axis hologram detected with a TV camera is transferred to a liquid-crystal spatial light modulator as a video signal. The liquid-crystal spatial light modulator can function as a thin amplitude hologram or a thin phase hologram. Time-sequential interference micrograph is obtained at a TV rate by superimposition of a plane reference wave onto the reconstructed object wave. Experimental results for observing a dynamic domain-wall motion in thin Permalloy film are demonstrated.

Scanning image detection (SID) system for conventional transmission electron microscope (CTEM) images.

A new image detection system has been developed to display transmission electron microscope (TEM) images on a CRT without a video camera system. Deflection coils placed in both the upper space of an objective lens and in the lower space of the first intermediate lens scan a small electron probe simultaneously. The electrical signal acquired through an improved scintillator and a photomultiplier is synchronized with the scanning signal and displayed in a similar fashion to a conventional scanning TEM (STEM) instrument. A preliminary system using a 100 kV conventional TEM (CTEM) equipped with a hairpin-type electron gun, produced an image with a spatial resolution of 1 nm.

Studies of refractory carbides, nitrides, and borides as the thermionic emitters for electron microscopy.

Thermionic emission properties of several kinds of refractory carbides, nitrides, and borides of the transition metals in the form of powder were investigated with a newly developed measuring device and evaluated by the figure of merit defined as the ratio of the effective work function to the working temperature at which the vapor pressure becomes 1 x 10(-5) Torr. There are several materials whose thermionic emission properties are better than those of tungsten or compatible to those of tungsten among the carbides and borides, such as TaC, HfC, ZrC, LaB6, and CeB6, as judged by the figure of merit. New preparation methods for carburization, nitriding, and boriding of the wires of matrix metals and alloys were successfully developed for using these materials as the cathode of the electron microscope. Other necessary techniques such as spot welding and electrolytic etching were also developed. From the brightness characteristics, it was found that some of carbides, carbide solid solutions, and borides such as HfC, ZrC (Ta0.8-0.7Hf0.2-0.3)C, TaB2, and HfB2 are very good emitters comparable to LaB6. It is emphasized that the work functions of the carbide-solid solutions (Ta0.8Hf0.2)C and (Ta0.7Hf0.3)C, which have low rates of evaporation at high temperature, show no remarkable rise as compared with that of HfC, so that their figures of merit are better than that of HfC. Feasibility of providing good cathodes with HfC and (Ta0.8Hf0.2)C tips was demonstrated by taking high-resolution electron micrographs.