Superconducting MgB 2 thin films were prepared on Al 2 O 3 (0001) and MgO(100) substrates. Boron thin films were deposited by the electron-beam evaporation followed by post-annealing process with magnesium. Proper post annealing conditions were investigated to grow good superconducting MgB 2 thin films. The X-ray diffraction patterns showed randomly orientated growth of MgB 2 phase in our thin films. The surface morphology was examined by scanning electron microscope (SEM) and atomic force microscope (AFM).Critical current density (J c ) measured by transport method was about 10 7 A/cm 2 at 15 K, and superconducting transition temperature (T c ) was ~ 39 K in the MgB 2 thin films on Al 2 O 3 .PACS numbers: 74.25. Fy, 74.60.Jg, 74.70.Ad, 74.76.Db a) Corresponding author, e-mail: smoon@LG-Elite.com 2 The recent discovery of the superconductivity above 39 K in magnesium boride (MgB 2 ) material attracts many researchers in scientific as well as technical reasons. 1 This material seems to have conventional BCS type superconductivity, and it has the simple structure. 2 The possibility of making good superconducting MgB 2 wires with low-cost was reported by several groups, because the weaklink problem between grains does not seem to be the case in this material. [3][4][5] The possibility of the electronic device application is also wide open, since it becomes possible to operate devices made of MgB 2 thin films with a low-cost refrigerator because of the higher T c ~ 39 K than other conventional superconductors. In addition, it may be easy to make very reliable electronic devices and Josephson junctions with this material, because of its simpler crystal structure and longer coherence length compared with the oxide superconductors. To make electronic devices, MgB 2 thin films with good superconducting properties are essential. Several groups have reported MgB 2 thin films made by pulsed laser deposition (PLD) method or e-beam evaporation followed by post annealing. [6][7][8][9][10][11] In this paper, we report our results on the growth of MgB 2 thin films by the electron-beam evaporation method followed by post-annealing process. The evaporation method has an advantage to the PLD method to make large area thin films. We investigated optimum growth conditions to make good superconducting MgB 2 thin films on Al 2 O 3 (0001) and MgO(100) substrates. Some superconducting transport properties (T c and J c ) and surface morphology of the MgB 2 thin films were also investigated.To make MgB 2 thin films, we have started with the boron thin films deposited on the substrates, similar to the MgB 2 wire formation by Canfield et al. 4 The boron thin film was deposited by the electron beam evaporation from boron source in crucible. We have used two different substrate temperatures for the boron deposition, room temperature and 750 °C. The background pressure of the deposition chamber was below 1 x 10 -6 Torr. Typically 250 ~ 300 nm thick boron films were made with the deposition rate of ~ 2 Å /sec. The boron films as deposited...

Using an optimized bridge geometry we have been able to make accurate measurements of the properties of YBa 2 Cu 3 O 7-d grain boundaries above T c .The results show a strong dependence of the change of resistance with temperature on grain boundary angle. Analysis of our results in the context of band-bending at the boundary allows us to estimate the height of the potential barrier present at the grain boundary interface.

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The interface resistance of YBa 2 Cu 3 O 7 grain boundaries has been measured in the range 5-270 K by means of a Wheatstone bridge for 24 , 30 and 36 symmetric and 45 degree asymmetric, [001] tilt, thin film grain boundaries. A number of preliminary experiments have demonstrated the validity of the technique employed. Above, the grain boundary resistance decreases as the temperature is increased, and the temperature variation is more pronounced for higher angle boundaries. A number of possibilities for interpreting the data are considered.

Tunneling spectra of a polycrystalline bulk HgBa&Ca2Cu308+& with T, = 132 K have been measured by point-contact spectroscopy using a low-temperature scanning tunneling microscope. Unlike other high-T, superconductors the conductance of this material shows a BCS-like gap structure with a relatively small smearing parameter I'. Conductances with a linear density of states for IeVI ( b, and a small cusp at the gap are also observed. From a simple calculation based on the assumption that the surface is covered with a normal layer, we explained the linear dI/dV for IeVI ( 4 and obtained two distinctively different energy gaps 6 = 48 meV and 22 meV with the resultant 2A/k&T, = 8.5 and 3.9, respectively.

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We have investigated YBa 2 Cu 3 O 7−x (YBCO) ramp-edge Josephson junctions by reacting the ramp-edge interface with deionized water. YBa 2 Cu 3 O 7−x /PrBa 2 Cu 3 O x (YBCO/PBCO) films were deposited on SrTiO 3 (1 0 0) by on-axis KrF laser deposition. After patterning the bottom YBCO/PBCO layer, the ramp edge was cleaned by Br-in-ethanol and then reacted with deionized water. The top YBCO/PBCO layer was deposited and patterned by photolithography and ion milling. We measured the current-voltage (I-V ) characteristics, magnetic field modulation of the critical current and microwave response at 10 GHz. The 20-minute water-immersed junction showed resistively shunted junction (RSJ)-type I-V characteristics, while others exhibited flux-flow behaviour. The average values of I c , R n and I c R n of these RSJ-type junctions were 4 mA, 0.1 and 400 µV, respectively, and Shapiro steps were fitted well by the microwave characteristic parameter (= hf/2eI c R n ) = 0.18.