Fabrication Of MgB Research Articles

The Fabrication of MgB<sub>2</sub> Film and Nano-Bridge by EB and FIB

100nm thin Mg/B precursor films were prepared on SiC substrates in ZZSX-500 vacuum coating machine. They were annealed by electron-beam(EB) which only took fractions of a second. In this paper the best annealing duration to fabricate the superconducting MgB2 thin films was investigated. Under the optimized annealing condition(accelerating voltage 15kV, electron beam current 5mA, annealing duration 0.7s), the superconducting MgB2 thin film with critical temperature Tconset~35.3 K and transition width ∆Tc~1K was fabricated. Besides that, a nano-bridge (about 100×200nm2) was etched on the superconducting MgB2 thin film by Focused Ion Beam (FIB). It’s a relative simple and efficient method. The nano-bridge exhibited the effect of Josephson junction with RSJ characteristics. At the same time a little loss of superconducting property was detected.

Fabrication of MgB$_2$ Thin Films at Various Temperatures by Using Laser-assisted Chemical Vapor Deposition

Fabrication of MgB$_2$ Thin Films at Various Temperatures by Using Laser-assisted Chemical Vapor Deposition

Sputtered magnesium diboride thin films: Growth conditions and surface morphology

Magnesium diboride (MgB 2) thin films were deposited on C-plane sapphire substrates by sputtering pure B and Mg targets at different substrate temperatures, and were followed by in situ annealing. A systematic study about the effects of the various growth and annealing parameters on the physical properties of MgB 2 thin films showed that the substrate temperature is the most critical factor that determines the superconducting transition temperature ( T c ), while annealing plays a minor role. There was no superconducting transition in the thin films grown at room temperature without post-annealing. The highest T c of the samples grown at room temperature after the optimized annealing was 22 K. As the temperature of the substrate ( T s ) increased, T c rose. However, the maximum T s was limited due to the low magnesium sticking coefficient and thus the T c value was limited as well. The highest T c , 29 K, was obtained for the sample deposited at 180 °C, annealed at 620 °C, and was subsequently annealed a second time at 800 °C. Three-dimensional (3D) AFM images clearly demonstrated that the thin films with no transition, or very low T c , did not have the well-developed MgB 2 grains while the films with higher T c displayed the well-developed grains and smooth surface. Although the T c of sputtered MgB 2 films in the current work is lower than that for the bulk and ex situ annealed thin films, this work presents an important step towards the fabrication of MgB 2 heterostructures using rather simple physical vapor deposition method such as sputtering.

Fabrication of MgB 2 thin films on r-Al 2O 3 substrates by rf sputtering and thermal evaporation

Superconducting MgB 2 thin films on the r-Al 2O 3 substrates have been grown by the combination of radio frequency magnetron sputtering of B and thermal evaporation of Mg, followed by in situ and ex situ annealing. The MgB 2 layers had ∼200 nm in average thickness and exhibited non-stoichiometry in Mg content. The Mg content in the grown MgB 2 layers could be controlled by the temperature of the evaporator and the opening diameter of the shutter. Superconducting transition temperatures have been measured and showed around ∼38 K depending on the Mg content and the annealing condition.

Fabrication of MgB 2 nanowire and its superconductivity

MgB 2 nanowires were synthesized on various kinds of substrates by chemical vapor transportation reaction and solid state reaction. The morphology examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) shows that the diameter and the length of the nanowires are approximately 50 nm and hundreds μm, respectively. The FFT pattern of the high-resolution transmission electron microscopy (HRTEM) image of MgB 2 illustrates that the nanowire has quasi-single crystal hexagonal structure. The low DC field magnetic response displays a perfect diamagnetism with onset superconducting transition temperature of 35 K. The superconducting hysteresis loop measurement indicates that the critical current density decreases with increasing applied magnetic field.

Fabrication of MgB 2 superconducting wires as low activation superconducting materials for an advanced fusion reactor application

Magnesium diboride (MgB 2) superconducting wires are interesting as alternative conductor of Nb-based superconducting wire applying for the advanced nuclear fusion reactor from viewpoint of decay time of induced radioactivity. However, J c property of MgB 2 wire is insufficient for alternative material of Nb-based superconductor, and it is necessary to improve further J c property. In order to improve J c property, we tried to fabricate the several trace amounts of Cu addition MgB 2/Fe-sheathed wires through PIT process using Mg 2Cu as Cu addition source. T c values of Cu addition samples were higher than those of non-Cu addition samples and they were improved with increasing amount of Cu addition. On the other hand, core J c value were decreased with increasing amount of Cu addition and the maximum core J c values were estimated to be over 100 A/mm 2 at 4.2 K under 8 T for 1 and 3 at% Cu addition sample.

Fabrication of MgB 2 superconducting films by different methods*

Abstract MgB2 superconducting films have been successfully fabricated on single crystal MgO (111) and c-AL2O3 substrates by different methods. The film deposited by pulsed laser deposition is c-axis oriented with zero resistance transistion temperature of 38.4K, while the other two films fabricated by chemical vapor deposition and electrophoresis are c-axis textured with zero resistance transistion temperature of 38 K and 39 K, respectively. Magnetization hysteresis measurements yield critical current density J c of 107 A/ cm2 at 15K in zero field for the thin film and of 105 A/ cm2 for the thick film. For the thin film deposited by chemical vapor deposition, the microwave surface resistance at 10 K is found to be as low as 100µΩ, which is comparable with that of a high-quality high-temperature superconducting thin film of YBCO. * Supported by the Major State Basic Research Development Program of China (Grant No. 1999064604)

Nanofabrication of superconducting MgB 2 neutron detector

We report on the fabrication of MgB 2 neutron detector based on 10B enriched superconducting MgB 2 thin films. The MgB 2 thin films were prepared by a multiple targets sputtering system. To increase the nuclear reactions of MgB 2 with neutrons, we used a 10B-enriched target (97.0%). The MgB 2 meander lines with SiO protect layer and Al electrodes were fabricated by e-beam lithography, conventional etching and deposition techniques. The meander line width was 1.0 μm and the total length reached 47.3 cm. The DC characteristics measurements showed that the superconducting DC characteristics of fabricated MgB 2 meander lines were almost the same with the unprocessed film.

Fabrication of MgB 2 superconducting wire by in situ PIT method

We have fabricated the MgB 2 superconducting wire with a copper sheath by using an in situ synthesis powder in tube (PIT) method. The diameter of MgB 2 wire was reduced down to 0.5 mm. MgB 2 coil with 27 mm∅ inner diameter and 3.5 m length was made using this wire. In the first current raising process, the critical current ( I c) of the coil was 76 A at 4.2 K in self-field which corresponded to J c≈170,000 A/cm 2 and J e≈40,000 A/cm 2 was achieved in magnetic field of H≈0.14 T. In the second run, the coil did not quench at the maximum current of 200 A, which corresponded to J c≈440,000 A/cm 2, J e≈100,000 A/cm 2 and H≈0.37 T.

Fabrication of MgB 2 superconducting wire by suspension spinning

The suspension spinning of commercially available MgB 2 powder was examined to fabricate a long superconducting MgB 2 wire. The MgB 2 powder was suspended in a mixed poly(vinyl alcohol) solution of dimethylsulfoxide and hexamethylphosphoric triamide. The viscous suspension solution was extruded as a filament into a precipitating medium of methyl alcohol and coiled on a drum. The as-drawn filaments were pressed and pyrolyzed to remove volatile components. The filaments were then cold pressed, enveloped by an iron sheet with a pellet of mixed powder of Mg and B, and vacuum sealed in a fused quartz tube and sintered. The effect of the J c on the starting materials and sintering conditions of the filamentary MgB 2 superconductors was examined. The J c of the sample was strongly dependent on the staring materials. The optimum sintering condition was sample to sample. The maximum J c value of more than 10 4 A/cm 2 at 4.2 K and self-field was attained.

Fabrication of MgB 2 superconducting thick films by electrophoresis technique

MgB 2 superconducting thick films of about 40 μm were fabricated successfully by a simple and low-cost approach. Boron films were prepared on Ag/Al 2O 3 substrates using the electrophoresis technique followed by a post-annealing process with excessive magnesium. Resistance measurements of the MgB 2 thick films show T con of 39 K and ΔT c of 0.6 K. The X-ray diffraction analysis reveals that most part of the films consist of c-oriented crystalline MgB 2. The images of surface morphology and cross-section profiles by scanning electron microscopy show well structured grain boundary MgB 2 films and a well-defined compact layer.