Showing papers by "John B Ketterson published in 1985"

Mechanical properties of composition modulated Cu‐Ni foils

Abstract: Measurements have been made of the Young’s, flexural, and torsional moduli of compositionally modulated Cu‐Ni foils. The average composition of the foils was 50‐at. % Ni and the wavelength of the modulation ranged from 8 to 80 A. At a wavelength of 20 A, the flexural modulus exhibited a maximum and had a value two times greater than that measured at shorter or longer wavelengths or that calculated from the bulk single‐crystal elastic constants of a homogeneous alloy. The Young’s and torsion moduli exhibited two maxima at 12 and 28 A. These results are consistent with earlier measurements of the biaxial modulus using a bulge tester. It was also observed that at a wavelength of 20 A there was a threefold increase in the breaking stress of the foils as compared with homogeneous bulk alloys.

Magnetic properties of V/Fe superlattices

Abstract: We have measured the magnetic and superconducting properties of V/Fe superlattices. It is observed that ultrathin Fe layers behave in a 2‐D fashion when isolated by thick V layers; however, on thinning the V layers a magnetic coupling between the Fe layers has been observed. No dead Fe layers were seen. When the V‐layer thicknesses were on the order of the BCS coherence length, superconductivity was observed. A 2‐D–3‐D crossover was observed in the temperature dependence of the parallel critical field when the Fe layers were only a few atomic planes thick, implying the coexistence of ferromagnetism and superconductivity.

Superconducting properties of layered Nb0.53Ti0.47/Ge structures prepared by dc sputtering

Abstract: Sandwich and superlattice structures composed of the high critical field superconducting alloy Nb053Ti047 (where the compositions refer to weight percent) and amorphous Ge were sputter‐deposited on sapphire substrates using a novel multi‐sputter‐gun system The thicknesses of both the superconducting Nb053Ti047 and the insulating Ge layers were varied over a wide range in order to study the two‐dimensional (2D) and three‐dimensional (3D) superconducting properties of these structures The observed suppression of the measured resistive superconducting transition temperature Tc with increasing sheet resistance is tentatively interpreted using the Maekawa–Fukuyama theory which incorporates contributions from localization and Coulomb interaction effects The upper critical fields, with the field both normal Hc2⊥ and parallel Hc2∥ to the film, were measured up to 50 kG Hc2∥ exhibited 2D behavior when the thickness of the superconducting layer was less than 200 A The zero temperature values of Hc2∥(0) wer

Determination of the viscosity of valinomycin monolayers as a function of surface density and a comment on conformation

Abstract: Determination de la viscosite surperficielle de la valinomycine etalee sur des supports aqueux tamponnes a pH 6,7±0,1 avec du triphosphate

New technique for excitation of bulk and surface spin waves in ferromagnets

Abstract: A meander‐line magnetic transducer is discussed in the context of bulk and surface spin‐wave generation in ferromagnets. The magnetic field created by the transducer was calculated in closed analytic form for this model. The linear response of the ferromagnet to the inhomogenous surface disturbance of arbitrary ω and k was obtained as a self‐consistent solution to the Bloch equation of motion and the Maxwell equations, subject to appropriate boundary condition. In particular, the energy flux through the boundary displays a sharp resonantlike absorption maximum concentrated at the frequency of the magnetostatic Damon–Eshbach (DE) surface mode; furthermore, the energy transfer spectrum is cut off abruptly below the threshold frequency of the bulk spin waves. The application of the meander line to the spin diffusion problem in NMR is also discussed.

Computer‐controlled four‐gun multisubstrate sputtering system for the preparation of composition‐modulated structures

Abstract: We describe a four‐gun sputtering system which has been used successfully to prepare composition‐modulated structures consisting of amorphous semiconductors and superconducting alloys or binary compounds. The substrates are mounted in ovens which can be individually heated to over 1000 °C. The ovens are mounted on a wheel which is driven by a computer‐controlled stepping motor. With appropriate programming of the movement of the stepping motor, the deposition sequence is determined.

Formation of ultrathin tungsten filaments via selective low‐pressure chemical vapor deposition

Abstract: A new technique for the formation of ultrathin tungsten filaments is described. It is based on the selective deposition of tungsten via the silicon reduction of WF6 along the sidewall of a photolithographically defined undoped polycrystalline silicon/SiO2 step. The width of the filament is determined by the tungsten deposition parameters and the thickness by the thickness of the polycrystalline film. Filaments with a cross section of 600×2000 A and 67.5, 140, and 265 μm lengths have been fabricated by this method. Initial low temperature resistance measurements of nonimplanted and Si‐implanted (1×1015 cm−2, 20 keV) filaments show localization/electron‐electron interaction behavior.

Coupling of rayleigh-like waves with zero-sound modes in normal3He

Abstract: The Landau kinetic equation is solved in the collisionless regime for a sample of normal3He excited by a surface perturbation of arbitrary ω andk. The boundary condition for the nonequilibrium particle distribution is determined for the case of specular reflection of the elementary excitations at the interface. Using the above solution, the energy flux through the boundary is obtained as a function of the surface wave velocity ω/k. The absorption spectrum and its frequency derivative are calculated numerically for typical values of temperature and pressure. The spectrum displays a sharp, resonant-like maximum concentrated at the longitudinal sound velocity and a sharp maximum of the derivative concentrated at the transverse sound velocity. The energy transfer is cut off discontinuously below the Fermi velocity. An experimental measurement of the energy transfer spectrum would permit a determination of both zero-sound velocities and the Fermi velocity with spectroscopic precision.

Method and apparatus for measuring shear modulus and viscosity of a monomolecular film

Abstract: Instrument for measuring the shear modulus of a monomolecular film comprises a circular trough having inwardly sloping sides containing a liquid for supporting the monolayer on the surface thereof; a circular rotor suspended above the trough such that the lower surface of the rotor contacts the surface of the liquid, positioned such that the axis of the rotor is concentric with the axis of the trough and freely rotable about its axis; apparatus for hydrostatically compressing the monolayer in the annular region formed between the rotor and the sides of the trough; and apparatus for rotating the trough about its axis Preferably, hydrostatic compression of the monolayer is achieved by removing liquid from the bottom of the trough (decreasing the surface area) while raising the trough vertically along its axis to maintain the monolayer at a constant elevation (and maintain rotor contact) In order to measure viscosity, a apparatus for rotating the rotor about its axis is added to the apparatus