P. R. Auvil

Scanning plasmon optical microscope

A new scanning near‐field optical microscopy based on the surface plasmon resonance is presented. Enhanced fields are localized at individual surface irregularities by the scattering of plasmons and the scattered plasmons produce a conical radiation. Variations in the conical radiation intensity caused by interactions between a raster‐scanned probe tip and the enhanced fields are recorded and related to the surface topography, providing an optical image with lateral resolution exceeding the diffraction limit. This technique is compared to complementary atomic force microscopy and scanning tunneling microscopy measurements and potential advantages are discussed.

Proximity effect coupled VCr superlattices

Abstract V m Cr n superlattices, where m and n denote the number of atomic planes of V and Cr in each layer, with m equal to 98, 147, 175 and 197 and n varying between 3 and 100 have been prepared. The films were grown in an ultra-high vacuum chamber (base pressure ≈1×10 −9 Torr) equipped with dual e-guns and a rotating substrate holder. Films were grown at 250°C on “c” cut sapphire substrates. The zero field transition temperature and parallel upper critical field of the films have been measured. A dimensional crossover in the parallel upper critical field is observed at n equal to about 80. The zero field transition temperature data has been modeled using the procedures and of Werthamer and Auvil and Ketterson. The magnetic scattering time, τ, in the Cr layers has been found to be dependent on the vacuum during deposition: 4.5×10 −14 sec for films deposited at ≤ 4×10 −7 Torr and 5.5×10 −14 sec for films deposited at ≤ 4×10 −8 Torr. For the V 175 Cr x series with n >- 80 the best fits occur for infinite scattering time τ.

Conical electromagnetic radiation in the Kretschmann attenuated total reflections configuration.

The polarization of the conical electromagnetic radiation produced by the scattering of surface plasmons by film roughness in the Kretschmann attenuated total reflection configuration was measured. The conical radiation was p polarized in the plane of observation. A tip of a scanning tunnel microscope was brought close to the film surface to act as a plasmon-scattering center. From a measurement of the conical radiation generated by this single-scattering center, it was found that plasmons tend to be forward scattered. Using a scanning plasmon optical microscope (SPOM), we imaged plasmon-scattering surface irregularities, which act in a first approximation as independent conical centers, along with interferences caused by these fixed conical radiation centers and the moving conical radiation center (the SPOM probe tip). The possibility of detecting localized surface plasmons with a SPOM is discussed.

Propagation and generation of Josephson radiation in superconductor/insulator superlattices alternately containing two different barriers

The sine-Gordon equation for a Josephson coupled superconductor/insulator superlattice is derived using a Lagrangian formalism. This equation has essentially the same form as that given eariler by Kulik for a single Josephson junction but with different parameters. For the case of S/I superlattices alternately containing two different barrier thicknesses, the behavior of the propagation and generation of the Josephson radiation is governed by two coupled sine-Gordon equations, which results in two photon branches separated by a frequency gap. Some potential applications of these structures, involving increased outputs of the Josephson radiation and two hand filters, are discussed.

Simple model for the observed plasmon conical radiation interference patterns in a Kretschmann configuration

In two previous papers we presented experimental results of measurements with a scanning plasmon optical microscope constructed in the Kretschmann configuration. The angular distribution of the conical radiation from the scanning tip was measured, and the multiple-scattering images of simple surface irregularities were detected. We make a simple model of the multiple-scattering images and compare it with our data, deriving excellent results.

Studies of static and dynamic properties of multilayered (stacked) Josephson junctions

We have studied the static I-V characteristics and vortex dynamics in stacked Nb/AlOx/Nb Josephson junctions. In josephson junction stacks consisting of two junctions having identical maximum Josephson supercurrent Ic,Ic versus H characteristics deviating from the Fraunhofer pattern have been observed, implying that a structural phase transformation to a triangular vortex lattice occurs with increasing H. Interjunction coupling leads to splitting of the Swihart mode; which manifest itself as Fisk steps with different voltage spacings. When subjected to microwave radiation, the I-V curves of the stacked Josephson junctions exhibit new features which are absent in single junctions.