Differential Capacitance of In-SrTiO_3-xContacts –Influence of the Electric-Field-Dependent Permittivity–

Abstract

The N = 88 nucleus "'Eu has been studied by Coulomb excitation with 1 6 0 beams, and from the decay of '"Gd using high-resolution y ray spectroscopy. A comprehen'sive level scheme including many new transitions, new levels and spin assignments is established. The results are compared with previous studies and with the predictions of a rotational-model calculation.NUCLEAR REACTIONS 151Eu('60, 160'y), E = 2 5 4 2 MeV: measured E.,; I,.i"/ coin, py coin, o(E;, OJ, DSA. ' 5 1 E~( r , T'), E = 10 MeV; measured c ( E J ; deduced levels, J , B ( E i ) , Tl,2, branching ratios, 6. Enriched targets, Ge(Li) detectors. RADIOACTIVITY '"Gd (from 15'Eu(p. n)); measured E.,, I ; , y y coin. Ge(Li) detectors. the 4ground state of '"Gd. Despite this selectivity many of the transitions known from p decay, and not previously seen in Coulomb excitation, have been observed in the present study, allowing an energy level scheme consistent with both decay processes to be deduced.Particle reaction studies of '"Eu have been reported by Straume er a1 (1976), Burke er al (1973), Taketani er a1 (1975) and Bernstein et a1 (1970). Experimental procedure Coulomb excitation of '"EuTargets of '"Eu metal (enriched to 97% in I5'Eu) were bombarded with beams of l60 ions from the ANU EN tandem accelerator at energies between 25 and 42 MeV. All of the coincidence measurements were made at 42 MeV. In addition, singles measurements were made with a beam of 4MeV protons. The targets were usually 15 to 20 mg cm-' foils on Pb backings. .le Singles y ray measurements.The energies and intensities of y rays were studied with a 60 cm3 coaxial Ge(Li) detector, a 10 cm3 planar Ge(Li) detector and a thin-windowed 3cm3 Ge(Li) x-ray detector. The resolution of the first two detectors was about 2.2 keV at 1333 keV, and for the x-ray detector, about 0.8 keV at 122 keV. A singles spectrum is shown in figure 1. Thick target excitation functions between 25 and 42 MeV l6O energy were measured with the coaxial detector. These agreed with previous measurements which were consistent with direct E2 excitation for most of the strong lines (Lewis and Graetzer 1971, Thun andMiller 1972). Gamma ray angular distributions were measured at 42 MeV, at seven angles between 0" and 90" to the beam direction. Most of the transitions were essentially isotropic. The energies of the transitions were determined by simultaneous measurement of a ls2Eu source and of the Coulomb excitation with l60 at 90". The ls2Eu source has accurately known y ray energies in the range 122 to 1409 keV (Aubin et al 1969). The energies of the strong '"Eu lines determined in this manner were used later to 1 2 3 L 5 6

Temperature-dependent polarity reversal inAu∕Nb:SrTiO3Schottky junctions

“…1͑b͒. As already reported, 14 1/C 2 changes almost linearly as a function of the bias voltage at 300 K, while it shows a U-like bending at low temperatures due to enhanced electric-field dependence of the permittivity of SrTiO 3 . By fitting 1 / C 2 =2͑V bi − V͒ / ͑q r 0 N D ͒ ͑Ref.…”

Temperature Dependent Polarity Reversal in Au/Nb:SrTiO3 Schottky Junctions

“…1 (b). As already reported, [14] 1/C 2 changes almost linearly as a function of the bias voltage at 300 K while it shows a U-like bending at low temperatures due to enhanced electric field dependence of the permittivity of SrTiO [15] to the data at 300 K, the built-in potential V bi is estimated to be 1.76 V, assuming a relative permittivity of ε r = 300. Here q is the elementary electric charge, N D is the donor density, and ε 0 is the vacuum permittivity.…”

Intrinsic electrical properties of Au/SrTiO3 Schottky junctions

“…This behavior may explain anomalous large tunneling currents observed at low temperature in In/ STO:Nb junctions using high-doping STO:Nb single crystals. 31,32 It is noted that compared with the experimental results, 28,33 the calculated doping dependence show rapid decrease of the SBH and gradual increase of the ideality factor with increasing space charge density. This may be due to doping dependency of the dielectric property of the ILP layer, and/or temperature-and field-dependent permittivity of the ILP layer.…”