Showing papers by "Varian Associates published in 1979"

A Comparison of Noise and Dose in Conventional and Energy Selective Computed Tomography

Abstract: We compare the noise properties of conventional and energy selective X-ray computed tomography. The images produced by the systems are not directly comparable so we discuss their relationship and show that the conventional image is a subset of the energy selective data. We describe how to form a conventional image from the energy selective images and demonstrate that, if this is done at the optimal display energy, the resulting conventional image will have the same noise as that produced by a conventional system with the same dose. But the energy selective system also extracts all the energy dependent information so it produces more information for the same dose than a conventional system.

Wafer transfer system

Abstract: A system for the automated handling and transfer of wafers individually and repetitively to and between processing stations and cassettes. A track-like conveyor engages a cassette holding a plurality of wafers in vertically facing alignment, to move same horizontally past a loading station of a processing chamber. A vertically moveable blade passes between the conveyor tracks and through the cassette to engage a wafer edgewise from below and move same upwardly to the processing chamber entrance. Vacuum means mounted to the door of the chamber entrance engages and holds the wafer during insertion into the chamber by closure of the door. Clip means are mounted within the periphery of an aperture of a vertical support plate just within the chamber entrance, to engage edgewise the wafer and support it within the plate aperture while in the processing chamber. The wafer is removed after processing by operating the foregoing apparatus in reverse order. The processing chamber may be a vacuum chamber, and minimal-volume load lock means therefor are advantageously provided by the system with the aid of a sealing member within the chamber compressible against the wafer support plate and chamber wall while the chamber door is open, to seal off the entrance area from the remainder of the chamber. The wafer support plate is moveable within the processing chamber to various wafer processing stations once the door is closed and the sealing member withdrawn.

Apparatus for mechanically clamping semiconductor wafer against pliable thermally conductive surface

Abstract: An apparatus for providing active cooling for semiconductor wafers during implantation in an ion implantation chamber includes a housing incorporating a convexly curved platen. The platen has a coating of a pliable thermally conductive material adhered to the surface thereof. A clamping ring is mounted within the housing in slidable relationship with the convexly curved platen so that the travel of the clamping ring ranges between a receiving position wherein the clamping ring and the convexly curved platen define a slot for receiving a semiconductor wafer and a locked position wherein a semiconductor wafer is firmly pressed against the convexly curved platen by the contact of the clamping ring against the semiconductor wafer at its circumferential edge. In the locked position the wafer substantially conforms on its back side to the contour of the convexly curved platen. An active cooling means is provided for transferring thermal energy away from the platen.

Focusing apparatus for uniform application of charged particle beam

Abstract: An apparatus for performing double deflection scanning of charged particle beams utilizes a means for introducing variations in the angle of the charged particle beam in combination with the focal or optical properties of a sector magnet. The means for introducing angular variations receives a charged particle beam and varies the angle of, i.e., deflects, the beam in a plane to define a time modulated fan beam. Once the beam angle is varied the beam is introduced to the gap between the poles of a sector electromagnet operating in a direct current mode. The focal properties of the sector electromagnet translates the time modulated fan beam into a time modulated parallel beam. The parallel beam is double deflected and may be used, for example, as the substrate impinging beam in ion implantation equipment. Multiple sector magnets may be employed for multiple end stations.

Variable energy standing wave linear accelerator structure

Abstract: Variable energy selection is accomplished in a side cavity coupled standing wave linear accelerator by shifting the phase of the field in a selected side coupling cavity by π radians where such side coupling cavity is disposed intermediate groups of accelerating cavities. For an average acceleration energy of E 1 (MeV) per interaction cavity, and a total number of N interaction cavities, the total energy gain is E 1 (N-2N 1 ) where N 1 is the number of interaction cavities traversed beyond the incidence of the phase shift. The phase shift is most simply accomplished by changing the selected side cavity configuration mechanically in repeatable manner so that its resonant excitation is switched from TM 010 mode to either TM 011 or TEM modes. Thus, the total energy gain can be varied without changing the RF input power. In addition, the beam energy spread is unaffected.

Zero reference and offset compensation circuit

Abstract: A zero reference and offset compensation circuit for an operational amplifier operating in the inverting mode in order to correct for both current and voltage offset errors. The zero reference and offset compensation circuit includes comparators for comparing the zero condition output of the operational amplifier with representations of lower and upper boundary signal levels, a pair of digital-to-analog converters having their respective analog outputs connected through appropriate scaling networks to the inverting input terminal and to the non-inverting input terminal of the operational amplifier, a microprocessor connected to the output of the comparators for providing an input to the associated digital-to-analog convertor so it produces an incremented digital signal whenever the comparators indicate the zero condition signal output exceeds either boundary signal level, the incremented digital signal being incremented in a direction to drive the associated digital-to-analog converter in a direction to bring said zero condition signal within the boundary which has been exceeded. The microprocessor has a current range selection capability so that the digital-to-analog converter connected to the inverting terminal is incremented for nanoampere range signal currents and the digital-to-analog converter associated with the non-inverting terminal is incremented for signal currents in the microampere range and above.

Effective use of dispersion shaping in broadband helix TWT circuits

Abstract: This paper presents the measured performance characteristics of four broadband TWTs which used various amounts and methods of circuit loading in order to control the helix dispersion. The tubes used identical guns, collectors, and focusing structures, so direct comparisons of the circuit performances could be made. The most heavily loaded circuit, with anomalous dispersion over a large part of the frequency range, performed well over more than two octaves, compared with one octave for a conventional unloaded circuit. The various circuits are described and some factors influencing the choice of a "best" circuit are presented.

Cooling structure for an oil sealed rotary vacuum pump

Abstract: An oil pool in a rotary vane, oil sealed mechanical vacuum pump casing is cooled by air drawn by a relatively low pressure and low speed laminar flow fan mounted on a motor shaft for the pump and positioned in a shroud between end plates for the motor and casing. The air pumped by the fan flows axially relative to the shaft through a horizotally extending slot at the bottom of the shroud and vertically extending slots on the sides of the shroud. The pumped air flows against vertically and horizontally extending fins respectively on the pump casing bottom and sides. The vertically extending fins at the bottom of the casing have bases slightly above the horizontal slot at the bottom of the housing so air flowing through that slot flows against the bases of the fins at a shallow angle. A vertical surface of the housing remote from the fan and the shroud has vertically extending fins that are aligned with the vertically extending fins on the bottom of the casing.

Lattice constant grading in the Aly Ca1-y As1-x Sbx alloy system

Abstract: Liquid phase epitaxy is employed to grow a lattice matched layer of GaAsSb on GaAs substrates through the compositional intermediary of the III-V alloy system AlGaAsSb which acts as a grading layer. The Al constituent reaches a peak atomic concentration of about 6% within the first 2.5μm of the transition layer, then decreases smoothly to about 1% to obtain a lattice constant of 5.74 A. In the same interval the equilibrium concentration of Sb smoothly increases from 0 to about 9 atomic percent to form a surface on which a GaAsSb layer having the desired energy bandgap of 1.1 ev for one junction of an optimized dual junction photovoltaic device. The liquid phase epitaxy is accomplished with a step cooling procedure whereby dislocation defects are more uniformly distributed over the surface of the growing layer.

Radiation therapy apparatus having retractable beam stopper

Abstract: A translation mechanism for linearly moving a beam stopper in radiation therapy apparatus includes first and second arms pivotally mounted to a support and third and fourth arms pivotally mounted to the first and second arms. The third and fourth arms are attached to the beam stopper and can comprise part of the beam stopper. In one embodiment, the third and fourth arms include disc shaped portions stacked in axial alignment with a drive motor attached to one disc portion ahd having a drive shaft axially aligned with and coupled to the other portion whereby relative rotation of the disc portions effects linear translation of the beam stopper.

Photoluminescence characterization of solution and lec grown InP

Abstract: Low temperature photoluminescence and electrical measurements on bulk grown polycrystalline and single crystal InP indicate the purity and crystal perfection to be equivalent to that of LPE and VPE samples

Evidence of trapping in device-quality liquid-phase-epitaxial In1−xGaxAsyP1−y

Abstract: Traps have been identified in epitaxial n- and p-type In1−xGaxAsyP1−y for the first time. The activation energy, capture cross-section and density of several electron traps in the quaternary composition range from InP to In0.53Ga0.47As have been determined. An electron trap similar in some characteristics to the 0.83 eV electron trap present dominantly in bulk and v.p.e. GaAs was observed in an n-type In0.71Ga0.29As0.45P0.55(Eg=0.95 eV) layer. Hole traps were not observed.

Lock and elevator arrangement for loading workpieces into the work chamber of an electron beam lithography system

Abstract: In apparatus having a work chamber in which workpieces are treated under high vacuum, that improvement comprising an inner chamber having a capacity for a plurality of workpieces, an outer chamber, vacuum means for evacuating the inner and outer chambers, a first valve for sealing between the work chamber and the inner chamber, a second valve for sealing between the inner and outer chambers, a third valve for sealing between the outer chamber and the atmosphere, loading means for loading workpieces through the third valve into the outer chamber from the atmosphere, and transfer means for transferring individual workpieces through the second valve between the inner and outer chambers, and for transferring individual workpieces through the first valve between the inner chamber and the work chamber.

Walking drag line

Abstract: A walking drag line having an oxcillating wheel segment, a vertical axis roller slot coupling the wheel segment and the walking drag line, a shoe for stepping the walking drag line and a track frame assembly coupling the oscillating wheel segment and the shoe. The crankpin which is journalled into the wheel segment imparts a reciprocal motion in the wheel segment having both horizontal and vertical components. The wheel segment rotates about the axis of a roller axis pin journalled in the vertical axis roller slot and rotates on a track surface of the shoe on the curved outer surface of the wheel segment without slippage.

Cryogenic pumping apparatus with replaceable pumping surface elements

Abstract: Two-stage cryogenic pumping apparatus having individual plate members with cryosorbent coatings secured by removable fasteners to permit easy assembly and replacement of the plate members. The plate members are spaced apart to provide relatively unrestricted access to the cryosorbent material for the gases to be adsorbed thereon.

Low-noise microwave f.e.t.s fabricated by molecular-beam epitaxy

Abstract: The growth of m.b.e. GaAs suitable for f.e.t. fabrication is reported. The m.b.e. structure consists of an n+ = 2.5×1018 cm−3 contact layer on top of an n+ = 3.5×1017 cm−3 active layer. Using this material, f.e.t.s. have been fabricated that have a minimum noise figure of 1.5 dB with an associated gain of 15 dB at 8 GHz. These are the best results yet reported for low-noise m.b.e. GaAs f.e.t.s.

Collector for thermionic energy converter

Abstract: An improved collector is provided for a thermionic energy converter. The collector comprises a p-type layer of a semiconductor material formed on an n-type layer of a semiconductor material. The p-n junction is maintained in a forward biased condition. The electron affinity of the exposed surface of the p-type layer is effectively lowered to a low level near zero by the presence of a work function lowering activator. The dissipation of energy during collection is reduced by the passage of electrons through the p-type layer in the metastable conduction band state. A significant portion of the electron current remains at the potential of the Fermi level of the n-type layer rather than dropping to the Fermi level of the p-type layer. Less energy is therefore dissipated as heat and a higher net power output is delivered from a thermionic energy converter incorporating the collector.

Pulse damper for high-pressure liquid chromatography

Abstract: A pulse damper for use in high-pressure liquid pumping applications, such as liquid chromatography, comprises a stainless steel cylindrical housing structure having threaded end caps to which inlet and outlet fittings are attached for coupling to a high-pressure liquid flow line. A spool made of a plastic material such as polytetrafluoroethylene or a perfluoroelastomer is fitted tightly within the housing structure, so that flow line liquid passes through the damper via the axial bore of the spool. The outer portion of the spool is configured to provide a cavity between the spool and the surrounding housing structure, and a compressible liquid fills this cavity. In operation, when a pressure pulse occurs in the flow line liquid, the relatively thin cylindrical wall of the spool expands radially outward in response, thereby causing a compression of the liquid in the surrounding cavity. Thus, the liquid in the cavity surrounding the spool serves as an energy-storing means for damping pulsations in the flow line.

Indirect detection of nuclear spins of low gyromagentic ratio coupled to spins of high gyromagnetic ratio

Abstract: In a heteronuclear system, the indirect detection of nuclei S, of weak gyromagnetic ratio, coupled to nuclei I, of strong gyromagnetic ratio, is accomplished by generation of zero and double quantum coherence between the I and S spin systems, during a preparatory period, t p . The zero and double quantum transitions are then interchanged at the midpoint of the evolution period, t 1 , producing an echo modulated only by S and I-I interactions at the end of the period t 1 , at which time the zero and double quantum coherence is then converted to I spin single quantum coherence yielding a free induction decay wave form S(t 2 ) for given t 1 . The period, t 1 , is then varied to obtain a two-dimensional function S(t 1 , t 2 ) which is then fully transformed to the frequency domain obtaining S(ω 1 , ω 2 ) whereby the chemical shift of the coupled S spin is obtained along the ω 1 axis and the chemical shift of the I spin is obtained along the ω 2 axis.

Gas ballast for oil sealed mechanical vacuum vane pump

Abstract: A gas ballast device for an oil sealed mechanical rotary vane vacuum pump prevents vapor condensation in the outlet port region of the low vacuum stage of the pump as a vane cyclically approaches the outlet port, whereby molecules of condensed vapor in the oil do not flow back to the inlet port of the low vacuum stage through the oil seal between the inlet and outlet ports. A flow path for atmospheric air leading to the outlet port region includes a tortuous, constricted fluid passageway. An outlet passage connecting the tortuous, constricted fluid passageway to the outlet port region is positioned so that an orifice thereof into the outlet port region is filled with and sealed by oil except during a small portion of each vane cycle immediately after the vane passes the orifice, whereby no movement of mechanical parts is employed to control air flow in response to the cyclical movement of the vanes past the orifice. The flow path for atmospheric air can be adjusted or closed at will, and includes a sleeve through which a portion of the passageway extends. The sleeve is spring biased in an upward direction to be normally urged against an air filter body, threadedly secured to a housing for the pump. The spring bias and turning of the air filter body move a plug relative to a seat in the outlet passage. The air filter body may be removed without removing the sleeve from the housing.

Slow-wave circuit for traveling-wave tubes

Abstract: In a travelling-wave tube for very high frequencies the slow-wave circuit is formed of four metal combs having teeth pointed toward the electron beam. The combs are arranged in two pairs. The teeth of the two combs in each pair extend inward from opposite sides of the beam and are axially aligned to form the electrical equivalent of a half-wave bar or ladder structure. They may or may not be joined at the tips because those are low-current points. The teeth of one pair are at right angles to those of the other pair and are displaced axially to interleave with them. Each comb is preferably made from a single piece of copper to provide better dimensional precision, low circuit loss, mechanical durability and high thermal capability.

Circular electric mode microwave window

Abstract: For conducting very high microwave power at very high frequencies, circular waveguide transmitting a circular-electric-field mode is used. The vacuum-tight window of an electron tube is often the element with lowest power-handling capability. The inventive window has two dielectric plates with a space between them. There is a gap in the waveguide inner wall through which a dielectric fluid is circulated between the plates to cool them. The gap leads to a region containing wave-absorbing material such as water to absorb modes other than the circular-electric-field mode.