Varian Associates

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

The iii-v photocathode: a major detector development

Abstract: Description of new (III-V) photocathodes which show improvements in sensitivity of as much as ten to a hundred times over conventional cathodes in the near infrared and useful improvements at shorter wavelengths. The development stems from a combination of basic knowledge of the photoemission process, gained in the 1950s, and the advancing understanding of the technology of III-V materials, in the 1960s. The superior performance of these cathodes is due to the fact that the vacuum level at the surface lies below the bottom of the conduction band in the bulk of the material. Consequently, the threshold of response is set by the III-V bandgap. The bandgap (and the threshold of response) can be varied by alloying different III-V materials together. A reduction in thermionic emission is realized with these cathodes. At present no semitransparent III-V cathodes with comparably interesting performance are available. The problems hindering further improvements, as well as the problems of placing these cathodes in practical multipliers and image tubes, are discussed briefly.

Analysis of creep transients in pure metals following stress changes

Abstract: The analysis of creep transients associated with stress change tests is reviewed, with an emphasis on using the results of these experiments to characterize the kinetics of deformation under conditions of nominally constant structure. In order to develop a common framework for the description of results obtained by various authors, operational definitions of the characteristic strain rates observed after stress changes are adopted. The data for aluminum reported by numerous investigators provide a consistent picture over a broad range of temperatures and initial creep stresses. These results show that transient creep after stress reductions occurs by two parallel processes of dislocation glide within subgrain interiors and dynamic recovery associated with subgrain boundary migration. Following relatively large stress reductions, the creep transient is dominated by the subgrain boundary migration processes. After relatively small changes in stress, thermally activated motion of dislocations within subgrain interiors is the predominant mechanism of deformation. In this regime, the creep transients can be described by a thermally activated rate law, thereby enabling various activation parameters to be evaluated from the data. In particular, the true activation areas are found to be equal to the dislocation spacing within subgrain interiors, hence are consistent with thermally activated cutting of forest dislocations. Limited results for other f.c.c. metals and related materials are shown to follow the trends established for aluminum. In particular. it is demonstrated that the data for pure copper and LiF at high temperatures and after small stress changes are also consistent with a description based on thermally activated glide. However, the true activation areas in copper are about five times greater than the dislocation spacing. This difference between copper and aluminum is attributed to the fact that the former has a substantially lower stacking fault energy. It is argued that the resulting wider separation of partials makes the thermally activated cutting of forest dislocations more difficult.

Package for push-pull semiconductor devices

Abstract: A semiconductor package for containing two individual devices such that they may be externally connected in a push-pull relationship. Two transistors, each having an input and output pad are formed on the same dielectric wafer, in a spaced relationship with each other and a ground plane so as to form two separate transmission line paths. The transistors are wired either in a grounded emitter or grounded base configuration. A shunt inductor is formed by a metallized strip or lead bond from the collector of one transistor to the collector of the other transistor. This inductor reduces the influence of the parasitic capacitance in the equivalent output circuit of the transistors. Since the collectors of both transistors are at the same DC level it is not necessary to include a DC blocking capacitor in series with the inductor. This increases the reliability and the reproducibility of the circuit because bonding wires necessary in prior devices to connect the blocking capacitor in series with the output inductance is not necessary. This packaging technique increases the output impedance, decreases the internal losses, and increases the bandwidth when wired as a push-pull circuit.

Three-terminal solar cell circuit

Abstract: Photovoltaic solar cells have improved efficiency when constructed in monolithic form with two different band gap energy junctions. Solar light goes first through an upper layer containing a high band gap energy junction which absorbs the short-wavelength components of light. Then the remaining long-wavelength components are absorbed in a second active layer containing a low band gap energy junction. The cell may comprise p-n-n-p type layers. According to the invention, each low band-gap, low-voltage junction is made to have 1/2 the voltage of the high band-gap high-voltage junctions. The junctions are then connected such that the high-voltage junctions are in parallel and the series connection of low-voltage junctions is also in parallel with them. The junction voltages are invariant so the parallel connection works for any light spectrum.