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...
We have developed a simple process to fabricate high-TC Josephson junctions by a combination of focused ion beam milling and 100 keV H2+ ion implantation. The resistively shunted junction-like current–voltage characteristics were observed in the temperature range of 48 to 4.2 K. The devices showed clear dc and ac Josephson effects. This technique is very promising in terms of simplicity and flexibility of fabrication and has potential for high-density integration.
Ion beam damage combined with nanoscale focused-ion-beam direct milling was used to create manufacturable superconductor–normal–superconductor type (SNS) Josephson junctions in 100-nm-thick MgB2 with TC of 38 K. The junctions show nonhysteretic current–voltage characteristics between 36 and 4.2 K. Experimental evidence for the dc and ac Josephson effects in MgB2 metal-masked ion damage junctions are presented. This technique is particularly useful for prototyping devices due to its simplicity and flexibility of fabrication and has a great potential for high-density integration.
Bone graft materials have been mainly developed based on inorganic materials, including calcium phosphate. However, these graft materials usually act as osteoconductive rather than osteoinductive scaffolds. To improve bone reconstruction, a combination of several materials has been proposed. However, there are still no alternatives that can completely replace the existing animal-derived bone graft materials. In this work, a marine-inspired biomineral complex was suggested as a potential bone graft material. The proposed biosilicified coccolithophorederived coccoliths using bioengineered mussel adhesive proteins show osteopromotive ability through the synergistic effects of osteoconductivity from calcium carbonate and osteoinductivity from silica. Its possibility of use as a bone substitute was determined by evaluating the in vitro osteogenic behaviors of multipotent mesenchymal stem cells and in vivo bone regeneration in a rat calvarial defect model. Therefore, the marine-inspired biomineral complex developed in this study could be successfully used for bone tissue engineering.
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