Chemical properties of the Bi-based superconducting whiskers studied by X-ray photoelectron spectroscopy

We investigated the chemical bond nature of the constituent elements in the surface of the as-grown Bi2Sr2Can−1CunOy (Bi-based) superconducting whiskers by a high-resolution X-ray photoelectron spectroscopy. From the results, we found that lots of the impurities, e.g. carbon, hydroxyl and so on were adsorbed or absorbed on the surface of the as-grown whiskers. Moreover, the valence of the Cu in CuO2 plane which is important for superconductivity has changed from divalent to less than divalent, which leads to the existence of the insulating layers in the surface of the Bi-based superconducting whiskers.