Polyfluorene as a model system for space-charge-limited conduction

Ethyl-hexyl substituted polyfluorene (PF) with its high level of molecular disorder can be described very well by one-carrier space-charge-limited conduction for a discrete set of trap levels with energy $\sim$ 0.5 eV above the valence band edge. Sweeping the bias above the trap-filling limit in the as-is polymer generates a new set of exponential traps, which is clearly seen in the density of states calculations. The trapped charges in the new set of traps have very long lifetimes and can be detrapped by photoexcitation. Thermal cycling the PF film to a crystalline phase prevents creation of additional traps at higher voltages.Comment: 13 pages, 4 figures. Physical Review B (accepted, 2007

Spacetime Dependent Lagrangians and Weak-Strong Duality : Sine Gordon and Massive Thirring Models

The formalism of spacetime dependent lagrangians developed in Ref.1 is applied to the Sine Gordon and massive Thirring models.It is shown that the well-known equivalence of these models (in the context of weak-strong duality) can be understood in this approach from the same considerations as described in [1] for electromagnetic duality. A further new result is that all these can be naturally linked to the fact that the holographic principle has analogues at length scales much larger than quantum gravity. There is also the possibility of {\it noncommuting coodinates} residing on the boundaries. PACS: 11.15.-q: 11.10/EfComment: Latex, 16 pages, article shortened, references added, minor typos correcte

Pressure-induced Superconductivity in CaLi2

A search for superconductivity has been carried out on the hexagonal polymorph of Laves-phase CaLi2, a compound for which Feng, Ashcroft, and Hoffmann predict highly anomalous behavior under pressure. No superconductivity is observed above 1.10 K at ambient pressure. However, high-pressure ac susceptibility and electrical resistivity studies to 81 GPa reveal bulk superconductivity in CaLi2 at temperatures as high as 13 K. The normal-state resistivity shows a dramatic increase with pressure.Comment: bulk superconductivity in CaLi2 now confirme

Permittivity enhancement of aluminum oxide thin films with the addition of silver nanoparticles

doi:10.1063/1.2425010Multilayer reactive electron-beam evaporation of thin aluminum oxide layers with embedded silver nanoparticles (Ag-nps) has been used to create a dielectric thin film with an enhanced permittivity. The results show a frequency dependent increase of the dielectric constant κ. Overall stack κ of the control sample was found to be 7.7-7.4 in the 1 kHz-1 MHz range. This is in comparison with κ = 16.7-13.0 over the same frequency range in the sample with Ag-nps. Capacitance-voltage and conductance-voltage measurements indicate the presence of charge capture resulting from the Ag-nps. The authors attribute this dielectric constant enhancement to dipole and space charge polarization mechanisms.The authors thank M. Othman for ellipsometry measurements. They are also grateful for the funding provided by the National Science Foundation Grant No. ECS0223

Room temperature ageing of Al–Ni–RE (RE = La, Gd, Er) metallic glasses

The effect of long-term ageing of Al–TM–RE (TM = Ni, Ag, Cu; RE = rare earth) amorphous alloys under ambient conditions, and at a slightly elevated temperature (100 °C), has been studied. The phase evolution and devitrification kinetics were studied using differential scanning calorimetry, X-ray diffraction and transmission electron microscopy techniques. Partial crystallization was observed in Al89Ni6La5, Al87Ni6La7, Al87Ni5(Ag/Cu)1La7 alloys after several years under ambient conditions (20–50 °C), and in Al88Ni4La8, Al88Ni4Gd2Er6 and Al88Ni4Er8 alloys following a 90 h anneal at 100 °C

Initial growth of interfacial oxide during deposition of HfO2 on silicon

doi:10.1063/1.1771457Interfacial chemistry of Hf∕Si, HfO2∕SiO2∕Si, and HfO2∕Si is investigated by x-ray photoelectron spectroscopy in order to understand the interfacial layer formation mechanism. Deposition of Hf and HfO2 films was carried out on Si wafers by electron-beam evaporation with oxygen backfill. We show that the interfacial layer formation takes place predominantly at the initial stage of the HfO2 film deposition. Temporary direct bonding between Hf metal and Si is proposed to be the source of the catalytic reaction resulting in formation of interfacial layer. Formation of interfacial layer was suppressed by chemically grown thin oxide blocking the direct Si-Hf bonding. We also demonstrate reduced interfacial layer after modified Shiraki surface etch, compared to the Radio Corporation of America clean. This indicates that a more complete hydrogen termination and atomically smoother surface can delay the onset of interfacial layer formation

Antimagnetic rotation and sudden change of electric quadrupole transition strength in 143Eu

Lifetimes of the states in the quadrupole structure in 143Eu have been measured using the Doppler shift attenuation method as well as parity of the states in the sequence has been firmly identified from polarization measurement using the Indian National Gamma Array. The decreasing trends of the deduced quadrupole transition strength B(E2) with spin, along with increasing J (2) /B(E2) values before band crossing, conclusively establish the origin of these states as arising out of antimagnetic rotation. The abrupt increase in the B(E2) values after the band crossing in the quadrupole band, a novel feature observed in the present experiment, may indicates the crossing of different shears configurations resulting in re-opening of shears structure. The results are well reproduced by numerical calculation within the framework of semi-classical geometric model.Comment: 6 pages, 4 postscript figure