Epitaxial Y1Ba2Cu3O7 thin films on CeO2 buffer layers on sapphire substrates

Pulsed laser deposition has been used to deposit Y1Ba2Cu3O7 layer on CeO2 buffer layers on (1102) sapphire. Both layers are epitaxial with the (110) direction of the CeO2 layer aligned with the direction of the sapphire substrate. The c-axis Y1Ba2Cu3O7 layer has its direction aligned with the direction of the CeO2. Cross-sectional transmission electron microscopy shows the epitaxy to be coherent and the interfaces to be abrupt at an atomic level. The best films have a critical current of 9 e6 A/cm2 at 4.2 K and lower microwave surface resistance than copper at 77 K and at a frequency of 31 GHz.Comment: 3 pages, 2 figures, journal articl

Charge carrier induced barrier height reduction at organic heterojunctions

In order to provide an accurate theoretical description of current density voltage (J-V) characteristics of an organic heterojunction device over a wide range of electric fields at various temperatures, it is proposed that an accumulation of charge carriers at the heterojunction will lead to a reduction in the barrier height across the heterojunction. Two well-known hole transporting materials, 4,4,4-Tris(N-3-methylphenyl-N-phenyl-amino) triphenylamine (MTDATA) and N,N-diphenyl-N,N-bis(1-naphthyl)(1,1-biphenyl)-4,4diamine (NPB) were used to fabricate unipolar heterojunction devices. It is found that the J-V characteristics depends strongly on applied bias. The simulated J-V characteristics of the heterojunction device, with the modified injection model, are found to be in excellent agreement with the experimental data.Comment: 4 pages, 4 figures, published in Phys. Rev. B Vol. 78, No. 8, http://link.aps.org/abstract/PRB/v78/e08130

An accurate calculation of spreading resistance

The spreading resistance of a round ohmic contact was calculated by solving the Laplace equation using analytic, numerical, and finite element methods. From this, formulas were found to calculate accurate values (better than 0.1%) of the spreading resistance over the entire range of contact size to substrate thickness ratio. I

Epitaxial CeO2\mathrm{CeO_2} buffer layers and cross-overs for YBa2Cu3O7\mathrm{YBa_2Cu_3O_7} thin films

We have grown epitaxial trilayer structures of YBa2Cu3O7/CeO2/YBa2Cu3O7 using pulsed laser deposition. The thin films were grown on a CeO2 buffer layer deposited on R-plane sapphire. The crystal quality and orientation of the CeO2 and the YBa2Cu3O7 layers has been determined using x-ray diffraction and transmission electron microscope cross-sections. All of the constituent films of the trilayer structure grow epitaxially and have sharp interfaces at an atomic level. The films have Tc above 88K, resistance ratioss between 2.5 and 3.0 and surface resistances at 31 GHz and 77K, which are lower than that of copper