Periodic stacking of two dimensional Bismuth bi-layers in Bismuth stearate thin films

Abstract

Investigations of single and bi-layer of Bismuth are one of the most thrust areas of research in contemporary condensed matter physics and material sciences. This is because such ultrathin layers of Bismuth host interesting exotic electronic properties which are important from both fundamental science and future application perspectives. Many inorganic processes of synthesis of single and bi-layers of Bismuth are reported using physical and chemical vapor deposition techniques in the past. The ultrathin films deposited are found to interact electronically with the substrates due to their close vicinity to the substrate surface. We introduce a new and easy organic channel of synthesis of Bi multi-bilayers in ambient conditions. Bismuth stearate multi-bi-layer thin films are deposited on the hydrophobic silicon and hydrophilic glass substrates using the Langmuir-Blodgett technique. Optical absorption spectroscopy measurements in the infrared region provided information on various bond structures present in those Bismuth stearate thin films. Specular x-ray reflectivity experiments and their analysis of such thin films unambiguously show the highly periodic stacking of bismuth bi-layers along the surface-normal directions, within the multilayer film structure. Model-based micro-structural analysis of the x-ray reflectivity data further shows that each bi-layer of bismuth is well separated (≈ 3.5 nm) from other bismuth bi-layer by hydrocarbon chains. At these separations, the electronic states of the bismuth bi-layers are expected to be non-interacting with each other. Morphology of the surface obtained from field emission scanning electron microscopy supports the XRR analysis. A bandgap of 3.2 eV was obtained for such bismuth stearate thin films from the optical spectroscopy measurement in the UV-visible range. The large separations between the Bi-bilayers and between the substrate and the bi-bilayers are expected to minimize the electronic interactions between them.