Martin E. Klausmeier-Brown

Superconductivity in epitaxial Bi2Sr2CuO6/Bi2Sr2CaCu2O8 superlattices: The superconducting behavior of ultrathin cuprate slabs

Utilizing atomic layer-by-layer molecular beam epitaxy (ALL-MBE), we have synthesized a series of high-quality superlattices in which ultrathin slabs (one-half unit cell thick) of the high-Tc superconductor Bi2Sr2CaCu2O8 alternate with up to five such layers of the low-Tc Bi2Sr2Cu1O6 phase. In all these superlattices we foundTc to be essentially equal to that of the high-Tc Bi2Sr2CaCu2O8 phase itself, which indicates that this cuprate is a 2D superconductor insofar as the interslab coupling plays at best a secondary role. Furthermore, it is demonstrated thatTc need not be reduced at heterostructure interfaces.

Flat panel imaging system for fluoroscopy applications

This paper describes a multi-mode, digital imager for real- time x-ray applications. The imager has three modes of operation: low dose fluoroscopy, zoom fluoroscopy, and high resolution radiography. These modes trade-off resolution or field-of-view for frame rate and additionally optimize the sensitivity of the imager to match the x-ray dose used in each mode. This large area sensing technology has a form factor similar to that of a film cassette, no geometric image distortion, no sensitivity to magnetic fields, a very large dynamic range which eliminates repeat shots due to over or under exposure, 12 bit digital output and the ability to switch between operating modes in real-time. The imager, which consists of three modules: the Receptor, the Power Supply and the Command Processor, is intended as a component in a larger imaging system. Preliminary characterization of the prototype imager in fluoroscopic mode at entrance exposure rates down to 2.5 (mu) R/frame, indicates that the DQE(f), MTF and low contrast resolution are comparable to that obtained with an image intensifier tube (IIT) coupled to a video camera.

Characterization of a third-generation multimode sensor panel

This paper describes a third-generation multi-mode x-ray imager whose applications include low-dose fluoroscopy, cine, spot films, and radiography. In addition, volumetric CT and applications whose environment includes a 2 tesla magnetic field are also in development. The VIP-9 is based on an amorphous silicon TFT/Photodiode array and x-ray conversion screen, which is optionally a deposited CsI(Tl) film or a removable Gd2O2S screen. There are three primary modes of operation: RAD for high resolution radiographs and spot films; Fluoro for video rate, low dose fluoroscopy as well as cine; Zoom for high resolution, limited field of view (FOV) fluoroscopy. Through improved electronics, the imager has greater sensitivity at low doses and far better rejection of correlated line noise than its predecessors. In addition, the VIP-9 incorporates many ease-of-use features absent from earlier prototype imagers. While previous reports have primarily focused on the imager construction and noise issues in large area sensing technology, in this paper the emphasis is on features which facilitate integration into a complete imaging system and measures of image quality.

Characterization of an amorphous-silicon fluoroscopic imager

This paper describes a dual-mode, flat panel imaging system capable of both fluoroscopy and radiography. Two generations of large area sensing technology are described. The general system architecture incorporates both the high sensitivity and data throughput required for fluoroscopy with the large signal capacity, spatial resolution and form factor necessary for radiography.

Amorphous silicon dual-mode medical imaging system

An amorphous silicon medical imaging system designed to operate in both radiographic and fluoroscopic modes is described. Images of medical phantoms are presented for both modes of operation. MTF and DQE measurements are also presented. The effect of recursive filtering on the DQE performance of the system operating in fluoroscopic mode is discussed.

Real-time image processing in a flat-panel solid state medical fluoroscopic imaging system

This paper describes a real-time image processing system for correction and enhancement of fluoroscopic (video X-ray) image data obtained from a large area, flat-panel, solid- state medical image sensor. The amorphous silicon sensor is 1536 X 1920 pixels, measuring 20 X 25 cm; for operation at 30 frames per second, the real pixel data rate is approximately 45 MB/sec.

Superconducting multilayer structures grown by ALL-MBE

Thin films of various Bi-Sr-Ca-Cu-O (2201, 2212, {hor ellipsis}, 2-2-11-12) compounds have been synthesized using atomic-layer-by-layer molecular beam epitaxy (ALL-MBE). Signal-crystal films with excellent transport properties, smooth surfaces and atomically sharp interfaces in multilayer structures have been obtained. That made it possible to deposit virtually perfect ultrathin layers and superlattices, and fabricate hysteretic Josephson junctions from SIS multilayers. 6 refs.

Real-time high-resolution camera with an amorphous silicon large-area sensor

To provide real-time imaging, x-ray diagnostic imaging relies entirely on the combination of the x-ray image intensifier and the high-performance television camera. Although these devices have been pushed to remarkable degrees of performance, they remain complex electro-optical assemblies with significant built-in errors, instabilities and degradation mechanisms. We describe a replacement for these systems utilizing as a sensor a large array of amorphous silicon photodiodes and thin-film switching transistors. Specially, the equipment described is a replacement for a 9-inch dual-mode x-ray image intensifier with a high-performance 2000-line digital tv camera capable of operating in both real-time video and high-performance spotfilm modes.

High T c Tri-Layers for Josephson Junctions

Atomic Layer-by-Layer Molecular Beam Epitaxy (ALL-MBE) of high T c superconducting films can be used to grow defect-free and flat multi-layer structures in which superconducting molecular layers are stacked with molecular layers having other electronic properties. In particular, tri-layers consisting of c-axis Bi 2 Sr 2 CaCu 2 O 8 base and counter electrode layers, each several hundred angstroms thick, have been grown separated by single molecular layers of metastable compounds such as Bi 2 Sr 2 Ca n-1 Cu n O 2+4 where n ranged from 5 to 11. Furthermore, the electronic properties of such barrier layers have been modified by doping with trivalent cations. Using such structures, tri-layer Josephson junctions have been fabricated which exhibit hysteretic I - V characteristics. Other doping schemes have given insulating layers which dominate c-axis transport, demonstrating the ability of this technique to grow thin, 25 A, single molecular layers that are free of pinholes.