Multi-beam Technique Research Articles

Revealing all types of threading dislocations in GaN with improved contrast in a single plan view image

In this letter, we demonstrate a transmission electron microscope based technique which reveals all types of threading dislocations (TDs) in GaN with high contrast over a relatively large area, even if the specimen is bent. This method uses a bright-field image with the crystal oriented at the ⟨1–21–3⟩ zone axis, taken using multi-beam diffraction conditions. Such an image reveals all screw, edge, and mixed types of threading dislocations. The multi-beam imaging technique described here for GaN is more generally applicable to counting the total dislocation density in a wide range of materials and structures.

Fabrication of fine-pitch TiO2-organic hybrid dot arrays using multi-photon absorption of femtosecond pulses

TiO2-organic hybrid dot arrays were produced from TiO2-organic hybrid films by a multi-beam laser interference technique of femtosecond laser pulses. The hybrid films were prepared from titanium alkoxide and β-diketonate by the sol–gel method. Films were exposed to interference light from femtosecond pulses which have an intensity distribution over the pitch of the order of a micron. The chemical structures of the hybrid film were changed by multi-photon absorption from femtosecond pulses, and made chemical patterning possible after the development process. The precursor arrays of the TiO2-organic hybrid material were calcined at 450 °C. TiO2-organic hybrid dot arrays with a refractive index of 2 were obtained.

Great solar bursts of October 19, 22 and 23, 1989

Itapetinga measurements at 48 GHz with the multibeam technique are used to determine the relative position of solar burst centroid of emission with high spatial accuracy and time resolution. For the Great Bursts of October 19,22, 1989, with a large production of relativistic particles, and October 23, it is suggested that, at 48 GHz, the bursts might have originated in more then one source in space and time. Additionally the October 19 and 22 Ground Level Events exhibited very unusual intensity-time profiles including double component structures for the onset phase. The Bern observatory spectral radio emission data show a strong spectral flattening typical for large source inhomogeneties. The interpretation for this is that large solar flares are a superposition of a few strong bursts (separated both in space and time) in the same flaring region.

A multi-beam intensity-based approach for lubricant film measurements in non-conformal contacts

Studies of elastohydrodynamic lubrication (EHL) frequently utilize the phenomenon of optical interference which is exhibited when an illuminated steel ball is in contact with a partially Cr-coated glass disc in conjunction with a lubricant layer of known refractive index. The use of the steel and chromium surfaces enables lubricants having similar refractive indices to glass to be examined. The EHL contact is composed of two microscopically thin layers: the Cr coating and the lubricant film, bounded by the glass disc and the steel ball. That the two-beam interference method frequently used in optical EHL research may induce significant errors in the measurement of film thickness is reported in this paper. A theoretical analysis which includes consideration of the effects of both multi-beam interference and optical absorption within the Cr film and the steel surface is presented. The analysis is used to devise a multi-beam intensity-based test technique which has been validated for a wide range of lubricant film thickness measurements at a resolution of 1 nm and offers a practical minimum detectable film thickness as thin as 1 nm.

Evaluation of juvenile salmon behavior at Bonneville Dam, Columbia River, using a multibeam technique

In recent years, with increased effort to bypass and guide fragile stocks of juvenile salmon in the Columbia Basin past hydroelectric projects, it has been increasingly important to obtain fine-scale fish behavior data in a non-intrusive manner. The Dual-Head Multibeam Sonar is an emerging technology for fisheries applications that addresses that requirement. It has two principal advantages over traditional hydroacoustic techniques: 1) it allows for simultaneous large-volume coverage of a region of interest, and 2) it affords three-dimensional tracking capability. The use of Dual-Head Multibeam Sonar in this study resulted in an unprecedented insight into fine-scale smolt behavior upstream of a prototype surface collector at the Bonneville Dam first powerhouse in 1998. Our results indicated that outmigrant juvenile salmon had an increased likelihood of milling or holding. This discovery will lead to better design criteria for future bypass and collector systems. Future fisheries multibeam sonar systems will likely be fully integrated systems with built-in real-time tracking capability. These systems may be used to track targets relative to physical guidance structures or other behavior-modifying stimuli such as light, turbulent flow, electrical/magnetic fields, or low-frequency sound and vibration. The combination of fine-scale fish behavior data and environmental parameters will yield better design criteria for the safe passage of listed or endangered species of Pacific salmon.

Direct phase determination for macromolecular crystals using the multiple-diffraction technique and an in-house X-ray source

This paper reports the first attempt at using a rotating-anode X-ray source and the multibeam diffraction technique to determine the phases of X-ray reflections from macromolecular crystals. Invariant phases of structure-factor triplets of lysozyme are determined unambiguously via four-beam diffractions.

Atomic scale structure of microtwins in single crystal Si grown by lateral solid phase epitaxy

Structural study of microtwins in single-crystal Si grown by lateral solid phase epitaxy has been done using high-resolution cross-sectional transmission electron microscopy. Microtwins with a few {111} atomic planes grow from the Si/SiO2 interface and extend to 20–30 nm in length. Using multibeam interference technique near the Scherzer focus, a structure image of a microtwin with a thickness of four {111} atomic planes was obtained. Lattice fringes of the matrix on both sides of the microtwin are shifted each other by one third of the {111} planar distance. From the analysis of a structural model of the microtwins, the growth mechanism of microtwins and the appearance of moire fringes are discussed. Consequently, the fact that the microtwins which originate from the Si/SiO2 interface are localized near the interface is shown clearly.

Multi-beam pattern measurement of the MU radar antenna by satellite OHZORA.

After finishing a series of tests, an antenna pattern monitoring system for the MU radar using satellite OHZORA has been put into the operational stage. We describe a multi-beam measurement technique, with which about 10 of the various MU radar antenna patterns can be measured simultaneously in one pass of the satellite, to make the best use of the limited number of chances for experiments. We also show the results of a preliminary attempt to synthesize a three-dimensional antenna pattern by integrating the data for different satellite passes.

An analysis of a satellite multibeam altimeter

Since the GEOS-3 and SEASAT-1 radar altimeters measured altitude over a narrow swath along the satellite subtrack, ocean current and mesoscale feature maps could only be generated after a large number of satellite revolutions. The present paper analyzes a new multibeam altimeter technique that has the potential to cover wide swaths. The multibeam altimeter uses two antenna elements, simple parabolic dishes with offset feeds, deployed cross-track on singly hinged booms into a fixed measurement geometry to generate an interferometer pattern over the desired swath extent. Range gating allows the isolation of a single interferometeric lobe, and the desired altitude measurements are extracted by using a modified altitude tracker design. Implementing this sensor on future altimetry missions would allow the timely generation of ocean current and mesoscale feature maps for the first time.

High‐Resolution Electron Microscopy of Chemically Vapor‐Deposited β‐Si3N4‐TiN Composites

Microstructures of Si3N4‐TiN composites prepared by chemical vapor deposition (CVD) were investigated by the multibeam imaging technique using a 1 MV electron microscope. High‐resolution images showed a number of fibrous TIN crystallites dispersed in the matrix of CVD β‐Si3N4. Crystallographic orientation relations between β‐Si3N4 and TiN were determined directly from the observed images in the subcell scale. The fibrous axis of TiN is parallel to the (110) direction of the NaCl structure and lies along the c axis of the hexagonal β‐Si3N4 crystal. Domain boundaries, planar faults, nonplanar faults, and dislocations were found in the CVD β‐Si3N4 matrix near the TiN crystallites. The origin of the structure defects is briefly discussed in connection with the formation of TiN crystallites in the matrix.

High resolution transmission electron microscopy investigation of adsorption and growth of Au on ZnTe surfaces

The monolayer adsorption and the epitaxial growth of Au on the surfaces of ZnTe crystals have been examined by means of a multi-beam lattice imaging technique in a 200 kV electron microscope with a pole piece of C s =1.2 mm and by simulation using the multi-slice method. Au was vacuum-deposited to an average thickness of 0.5 nm onto 10 nm thick ZnTe films. It has been found that Au atoms are adsorbed on the Zn atoms of the (001)ZnTe surface to build a 1 × 1 monolayer structure. From the lattice images of the Au island particles together with those of the ZnTe substrates, the epitaxial relations and more precisely the positions of the Au lattice with respect to the substrate ZnTe lattice have been established.

Polarity and inversion twins in ZnSe crystals observed by high-resolution electron microscopy

Abstract Zinc selenide crystals (zinc-blende structure) with (110) surface planes, produced by a solid–solid reaction, have been examined by means of a multi-beam lattice-imaging technique in a 200 kV electron microscope with a pole piece of C s = 1·2 mm, and by simulaton using the multi-slice method. In the experimental images the columns of Zn and fie atoms have been positoned so that the crystallographic polarity, as well as the stacking sequence, can be determined. Inversion twins, the components of which have opposite senses of polar axes across the boundary, have been found parallel to (111). It is concluded that the lattice on one side of the twin boundary is displaced from that on the other side by α/8[110] and that the formal charge at the two types of (111) boundary, positive and negative, is compensated by removing or supplying Zn atoms. It has been observed that layers with a wurtzite-type stacking sequence ere also formed by the introduction of similar growth stacking defects.

Observation of [110) tilt boundary structures in gold by high resolution HVEM

Abstract Tilt boundaries in evaporated gold foils with a [110] rotation axis perpendicular to the foil surface have been examined by a multi-beam lattice imaging technique in a JEM 1250 kV transmission electron microscope and various boundary structures, small-angle, twin, coincidence-related and near-coincidence tilt boundaries, analysed.

Elimination of Speckle Noise in Holograms with Redundancy

Holograms made of diffusely reflecting or diffusely illuminated objects can be scratched, spotted with dirt, and even broken into pieces without serious loss of information. This remarkable property is due to the redundancy introduced by diffuse illumination which, in effect, spreads information all over the hologram. Unfortunately, an unwanted by-product of diffuse illumination is speckle noise. This noise becomes more severe as hologram size is reduced. We show that, in order to obtain an acceptably high signal-to-noise ratio, the area of this type hologram must be more than 100 times the area needed to achieve a desired image resolution, making it prohibitively large for most data storage applications. In this paper we described a multibeam recording technique that produces redundant holograms that yield speckle free images of transparencies. We show that (1) achievable redundancy is equal to the ratio of actual hologram area to that area which just satisfies resolution requirements, (2) a two-dimensional phase grating provides a simple, efficient means for generating multiple beams, an optimized grating producing nine equally intense beams with 81% efficiency, (3) an optimized phase grating having a spatial period just equal to desired image resolution yields fourfold redundancy in holograms that are just large enough to encompass both side bands of the central (or zero order) beam, and (4) holograms having fourfold redundancy give reasonably good immunity to dust and scratches.

Elimination of speckle noise in holograms with redundancy

Holograms made of diffusely reflecting or diffusely illuminated objects can be scratched, spotted with dirt, and even broken into pieces without serious loss of information. This remarkable property is due to the redundancy introduced by diffuse illumination which, in effect, spreads information all over the hologram. Unfortunately, an unwanted by-product of diffuse illumination is speckle noise. This noise becomes more severe as hologram size is reduced. We show that, in order to obtain an acceptably high signal-to-noise ratio, the area of this type hologram must be more than 100 times the area needed to achieve a desired image resolution, making it prohibitively large for most data storage applications. In this paper we described a multibeam recording technique that produces redundant holograms that yield speckle free images of transparencies. We show that (1) achievable redundancy is equal to the ratio of actual hologram area to that area which just satisfies resolution requirements, (2) a two-dimensional phase grating provides a simple, efficient means for generating multiple beams, an optimized grating producing nine equally intense beams with 81% efficiency, (3) an optimized phase grating having a spatial period just equal to desired image resolution yields fourfold redundancy in holograms that are just large enough to encompass both side bands of the central (or zero order) beam, and (4) holograms having fourfold redundancy give reasonably good immunity to dust and scratches.