Varian Associates

About: Varian Associates is a based out in . It is known for research contribution in the topics: Beam (structure) & Wafer. The organization has 2160 authors who have published 2591 publications receiving 46002 citations.

New epr methods for the study of very slow motion: application to spin‐labeled hemoglobin

Abstract: Nitroxide-radical spin labels have been widely used to study motion in biological systems. Smith l has recently reviewed the subject and provides access to the literature. The present work is concerned with the development of methodology that will permit studying slower motions than has previously been possible. Practically, the spin-label technique has been restricted to rotational correlation times T~ shorter than 3 x lo-; set.\" Theoretically, any motion affects the ordinary linear epr spectrum, but several problems arise as the motion becomes slow. ( 1 ) The effect of motion on the spectrum becomes less and less as the spectra asymptotically approach the line shape expected from a rigid powder. Hence, the signal-to-noise ratio of tne motional effects goes to zero. (2) Kreilick has observed temperature-dependent couplings of nitroxide radicals using nmr techniques. Thus, the inhomogeneous line width (i.e., the line width that would be observed in a single crystal, and arising from unresolved hyperfine couplings to protons of the radical) is temperature-dependent, and this affects the spectral shape. (3 ) It is necessary to know the theoretical line shape that is approached as the motion slows, but the expediency of freezing the sample fails because the dielectric constant of the solvent affects the hyperfine coupling and is itself generally temperature-dependent and changes markedly upon freezing. It has occurred to us that methods involving the nonlinear response of the spin system in which intense irradiating fields are employed and the observed spectrum depends to a considerable degree on relaxation to the lattice might permit determination of very slow motion. If the spin-state lifetime limiting line width is l/yTl,,, then the slowest motion that could in principle be measured by a nonlinear method would involve spectral diffusion by an amount I/yT,,. in a time T,,,. Here, y is the gyromagnetic ratio of the electron and T,,, is the electron longitudinal (or spin-lattice) relaxation time. Assuming that the anisotropy, AW. of the typical nitroxide radical is about 2s X loy rad (this being the spectral width swept out by the m, = -1 nuclear spin configuration as the radical undergoes isotropic rotational diffusion) and that TI, = 1 W sec, we can estimate a limiting maximum T : : T ? = T , < , ( A W T ~ , . ) ~ 0 4 sec. Success in extending the present range to times as long as 1W3 or lo--’ sec would be very useful. These slow times are relevant for many biological processes, and this is a time scale not readily accessible to other analytical methods.

Transesophageal Phased Array for Imaging the Heart

Abstract: A 3.5 MHz phased array has been developed for imaging the heart through the esophagus. The ultrasonic probe is fitted on the distal end of an Olympus gastroscope. Transesophageal images of the heart were obtained on ten patients. This paper describes the design and realization of the phased array and presents some clinical results obtained on patients.

Disk or wafer handling and coating system

Abstract: A system for handling and individually processing a plurality of thin substrates is described The system includes a main chamber, entrance and exit load locks, a plurality of processing stations, a load lock load/unload means, a vertical transport means, and a horizontal transport means In one embodiment the processing stations are deployed in a U-shaped configuration, allowing the entrance and exit load locks to be positioned at the same end of the machine Idle stations between processing stations may also be employed The substrates are vertically oriented and are raised and lowered into and out of load locks and processing stations by means of dedicated lift blades Substrates are transferred within the main chamber from lift blades of one station to lift blades of an adjacent station by means of substrate carriers affixed to a walking beam mechanism Substrates are transferred from the entrance load lock side of the machine to the exit load lock side by means of a reversing mechanism, which may be a rotating beam mechanism, or which may be a transverse motion mechanism which affects a rotationless substrate transfer A lift blade symmetrically engages a substrate nearer the lower half of its periphery, holding the substrate securely with the aid of gravity, and negligibly obscuring or eclipsing either surface of the substrate The lift blades carry the substrates into the processing stations and hold them in place during processing, or simultaneous processing of both sides of the substrates may be carried out

THE GROWTH OF MAGNESIUM-DOPED GaAs BY THE OM-VPE PROCESS

Abstract: Magnesium-doped GaAs has been grown by organometallic vapor phase epitaxy (OM-VPE). Bis (cyclopentadienyl) mag-nesium (Cp2Mg) is used as the organometallic precursor to Mg. The epitaxial layers have been characterized by resis-tivity and Hall measurements, photoluminescence spectro-scopy and optical microscopy. The material is of high electrical and optical quality; controllable doping over the range 1015 to 1019cm-3 is reproducibly attained. The ionization energy of the Mg acceptor is determined to be 30 ± 2.5 meV at 77K. Negligible compensation is observed, consistent with clean thermolysis of the Cp2Mg under growth conditions. GaAs diodes have been fabricated using Mg as the p-dopant and either Se, Si, or Sn as the n-dopant. The diodes show very low leakage currents under reverse bias, even at relatively high doping levels. Degenerately-doped junctions for interconnecting monolithic cascade concentrator solar cells have also been successfully grown, displaying forward conductivities as high as 19 amps V−1 cm-2 at 0.05V forward bias.