Elimination of bubbles and improvement of the superconducting properties in MgB₂films annealed using electron beam

Abstract

MgB2 superconducting films can be readily obtained using the electron-beam annealing method. However, many bubbles existing in the film severely damage the surface morphology, which is known as the deleterious current-limiting mechanism. Based on morphology images and energy-dispersive spectroscopy spectra, we found that, during the annealing process, solid Mg-rich layers evaporate to form Mg vapour in the precursor film, resulting in bubbles in the film. By reducing the cycle thickness of the precursor film, we obtained MgB2 films with better properties. The root-mean-square surface roughness was 2.7 nm over a 10 × 10 μm area for a 100 nm-thick film, and the critical current density at 20 K was increased to 3.8 × 106 A cm−2. These MgB2 films are suitable for fabricating MgB2 superconducting devices.

Measurement and Evaluation of Local Surface Temperature Induced by Irradiation of Nanoscaled or Microscaled Electron Beams

“…The up-limit of local temperature T max in a SEM was also revealed with our experiments on annealing of [Mg-B] N multilayered thin films. The results showed that high-intensity e-beams could induce phase transition in amorphous [Mg-B] N multilayered thin films within 1 s. As a result, an amorphous multilayer was partially turned into a MgB 2 superconducting phase [5–7]. Figure 3 and Table 2 present some typical results.…”

“…For some applications, in e-beam lithography for instance, this e-beam-induced surface heat may cause distortion of designed patterns at the nanoscale in the e-beam writing process, thus resulting in failure of the final devices [1–3]. In some other applications, the local surface heating effect is utilized for thin film deposition [4], annealing [5–7], or even sculpting of nanomaterials [8, 9]. Yet to date, precise measurement and evaluation of the local surface temperatures under e-beam irradiation remain as a technical challenge [10–12].…”

“…With careful operation procedures, one could use an e-beam to make a bridge of single-atom chain of carbon from a continuous carbon thin film [9]. Using e-beams as in situ energy sources, one could obtain superconducting MgB 2 phase from a multilayered [Mg-B] n “superlattice” film [5–7].…”

Thermal Probing Techniques for a Single Live Cell

“…Heat dissipation through the substrate of TFTCs has been identified as a serious problem in the thermal probing of local temperature at micro-/nano-scales [ 31 ]. For example, in a transmission electron microscope (TEM) or SEM, a focused electron beam (e-beam) were used to melt metallic thin films or nanowires, or could even vaporize parts of them [ 86 , 87 ], indicating that the local temperature under the focal point of the incident e-beam was higher than the melting points or even vaporization points. However, when a micro-TFTC made on a SiO 2 /Si wafer was placed at the focal point of the incident e-beam, it recorded a much lower temperature.…”

Nanoscience and Nanotechnology

“…A number of techniques were applied for fabrication of practical MgB2 conductors during last 17 years. The chemical doping [8][9][10] , substitution [11,12] , evaporation [13,14] and changing preparation condition [15][16][17] have extensively been used to improve the mechanical, microstructural, superconducting and magnetic properties of the MgB2 material.…”