J. B. Ketterson

Structural and thermoelectric transport properties of Sb2Te3 thin films grown by molecular beam epitaxy

We have studied the structural and transport properties of Sb2Te3 thin films prepared by molecular beam epitaxy as a function of the Te/Sb flux ratio during deposition. Both the crystallinity and the transport properties are found to be strongly affected by nonstoichiometry. The most stoichiometric sample (prepared with a Te/Sb ratio of 3.6) had a high degree of crystallinity, high thermopower, and high carrier mobility. However, Sb2Te3 films with excess Sb or Te had poorer crystallinity, reduced magnitude of the thermopower, and reduced mobility as a result of the formation of antisite defects. These antisite defects were able to be reduced by controlling the relative flow rate ratio of Te to Sb during growth.

Contact angle of lead stearate-covered water on mica during the deposition of Langmuir-Blodgett assemblies☆

Abstract We have measured the dynamic and static contact angles between the monolayer-covered water surface and a mica substrate during the deposition of successive monolayers of lead stearate. The substrate was suspended from a Cahn RG Electrobalance in order to measure the contact angle-dependent force during deposition of the film; both dynamic and static angles were calculated from the output of the balance. The difference between the dynamic contact angles of the film- covered subphase on clean mica and during polar deposition on a lead stearate multilayer is approximately 18°. The static contact angle on the upstroke (polar deposition, StPb/PbSt) averages 6° greater than the dynamic angle. On the other hand, there is very little difference on the downstroke (PbSt/StPb deposition) between the static and the dynamic angles. The contact angles appear to be independent of surface pressure in the range 15–24 dyn cm-1.

Study of in-plane structure in lead-fatty acid LB films using X-ray diffraction

Abstract We have observed several (11 l ) diffraction peaks in Langmuir-Blodgett films of lead myristate, lead stearate and lead behenate. We find that all three types of films appear to have the same in-plane structure, and that alternate planes of lead ions are shifted laterally by half of an in-plane lattice spacing (as in the structure proposed earlier for bulk lead stearate).

Verification of epitaxial growth and determination of chain positions in Langmuir—Blodgett films of lead stearate on mica

Abstract We have determined from X-ray diffraction that lead stearate, which like many hydrocarbon compounds does not form good crystals in bulk, can be grown epitaxially on mica using the Langmuir—Blodgett technique. The strong alternation in intensities of the (11 l ) peaks cannot be explained by considering the lead ions only, and imply that the hydrocarbon chains do not close-pack into a triangular array but reproduce the in-plane structure of the lead ions.

Effect of annealing on the transport properties of an epitaxial film of bismuth

Abstract We have studied the effect of annealing on the transport properties of an epitaxial bismuth film. By annealing close to the melting temperature, the helium temperature resistivity is found to decrease by a factor of 15. The results are potentially of importance in connection with quantum size effect (QSE) measurements and the combined Shubnikov-de Haas effect-QSE.

Fiber‐optic detection system for capillary waves: An apparatus for studying liquid surfaces and spread monolayers

Generating capillary waves with an alternating electric field gradient is a noncontact way to study the mechanical properties of monolayers. By studying capillary waves the surface tension can be calculated. In addition, the surface elasticity can be deduced and film inhomogeneity can be determined. We have incorporated a fiber‐optic detection system into a capillary wave apparatus. This makes the apparatus more compact, movable, versatile, and easier to use than detection systems currently in use.

Possible manifestation of Andreev bound states in double-barrier Nb/Al/AlOx/Al/AlOx/Nb tunnel junctions

Abstract We have experimentally investigated electron transport in double-barrier Nb/Al/AlO x /Al/AlO x /Nb devices. At low temperatures, the devices reveal a novel magnetic-field-sensitive subgap structure in the current-voltage characteristics, which is interpreted as a manifestation of Andreev bound states. A correlation between phase-coherent and nonequilibrium properties is suggested.

Hysteretic characteristics of low-field microwave absorption of a Co thin film

We have investigated the spin dynamics of a sputtered Co thin film using our broadband ferromagnetic resonance (FMR) spectrometer. From FMR spectra taken at frequencies of 4–20 GHz, we found that our Co film has a g-factor of 2.25 and a Gilbert damping factor of 4.5×108 s−1, indicating an enhanced spin-orbit interaction compared to bulk material or epitaxial films. Besides the normal FMR mode in the saturated state, we also observed the evolution of the low-field hysteretic behavior in the unsaturated state, which affects the FMR mode as the excitation frequency is lowered from 5.000 to 1.636 GHz. We found that the microwave absorption process persists in the unsaturated state for frequencies higher than 1.868 GHz such that the absorption minima occur at −12 Oe on a down-field sweep and at +12 Oe on a up-field sweep, respectively.

A wide temperature range hermetically sealed langmuir-blodgett apparatus

Abstract We have built a Langmuir-Blodgett system situated inside a double-walled enclosure through which water or refrigerant can be circulated. This permits the temperature to be varied over a wide range without temperature gradients or condensation on the sides of the enclosure. Since the enclosure can be hermitically sealed, oxygen-free or other selected environments may be introduced.

A qubit device based on manipulations of Andreev bound states in double-barrier josephson junctions

Abstract A qubit system exploiting manipulations of the Andreev bound state (ABS) levels in the SINIS junction by applying appropriate bias voltages and transport currents is suggested. The parameters of the SINIS setup may be chosen in such a way that only two ABS levels are present; this is in agreement with our experimental data obtained using Nb/Al double-barrier junctions. In the qubit Hamiltonian, H , the two ABS levels are presented as the ‘↑’ and ‘↓’ spin states, while the controlling physical parameters (voltage across one of the barriers and the transport current) are mapped to the ‘magnetic fields’ B x n and B z n . The phase decoherence time is estimated.