Electron tunneling in tantalum surface layers on niobium
We have performed electron tunneling measurements on tantalum surface layers on niobium. The tunnel junctions comprise 2000-A-circle Nb base electrodes with 10--100-A-circle i-italicn-italic s-italici-italict-italicu-italic--deposited Ta overlayers, an oxide barrier, and Ag, Pb, or Pb-Bi alloy counterelectrodes. The base electrodes were prepared by ion-beam sputter deposition. The characteristics of these junctions have been studied as a function of Ta-layer thickness. These include the critical current, bound-state energy, phonon structure, and oxide barrier shape. We have compared our results for the product I-italic/sub c-italic/R versus tantalum-layer thickness with an extended version of the Gallagher theory which accounts for both the finite mean free path in the Ta overlayers and suppression of the I-italic/sub c-italic/R product due to strong-coupling effects. Excellent fits to the data yield a value of the intrinsic scattering probability for electrons at the Ta/Nb interface of r-italic/sup 2/ = 0.01. This is consistent with the value expected from simple scattering off the potential step created by the difference between the Fermi energies of Ta and Nb. We have found a universal empirical correlation in average barrier height phi-bar and width s-italic in the form phi-bar = 6 eV/(s-italic-10 A-circle) for measured junctions which holds both for our data and results for available data in the literature for oxide-barrier junctions. The latter are composed of a wide variety of base and counterelectrode materials. These results are discussed in the general context of oxide growth and compared with results for artificial tunnel barriers.
- Research Organization:
- Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556
- OSTI ID:
- 5661102
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 34:1; ISSN PRBMD
- Country of Publication:
- United States
- Language:
- English
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360104* -- Metals & Alloys-- Physical Properties
656102 -- Solid State Physics-- Superconductivity-- Acoustic
Electronic
Magnetic
Optical
& Thermal Phenomena-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BEAMS
BOUND STATE
CRITICAL CURRENT
CURRENTS
DATA
ELECTRIC CURRENTS
ELECTRONS
ELEMENTARY PARTICLES
ELEMENTS
ENERGY GAP
ENERGY LEVELS
EXPERIMENTAL DATA
FERMI LEVEL
FERMIONS
INFORMATION
ION BEAMS
LAYERS
LEPTONS
METALS
NIOBIUM
NUMERICAL DATA
PHONONS
QUASI PARTICLES
SPUTTERING
SUBSTRATES
TANTALUM
TRANSITION ELEMENTS
TUNNEL EFFECT