Superconducting MgB₂ flowers: Growth mechanism and their superconducting properties

We report for the first time the growth and the systematic study of the growth mechanism for flower-like MgB₂ structures fabricated on the substrates for solid-state electronics by the hybrid physical-chemical vapor deposition (HPCVD) technique. The MgB₂ flower has a width of 30 μm and a height of 10 μm. The superconductivity of MgB₂ flowers was confirmed by a magnetization measurement, and the transition temperature is 39 K, which is comparable with high-quality bulk samples. The excellent current-carrying capability was demonstrated by MgB₂ flowers. To understand the nucleation and growth mechanism of MgB₂ flowers a very systematic study was performed by a high-resolution transmission electron microscope (HRTEM) and atom probe (AP) microscopy. The HRTEM revealed that the seed grain of a MgB₂ flower has a [1010] direction, and the flower is composed of micro-columnar MgB₂ grains having pyramidal tips and which are grown along the (0001) plane. A clear understanding of the growth mechanism for MgB₂ flowers could lead to the growth of other low-dimensional MgB₂ structures for superconducting electronic devices.