Blue phosphorene on Au(111) as a decoupling layer for organic epitaxially grown films

Blue phosphorene (BlueP) is considered as a promising two-dimensional (2D) material for future(opto)electronic applications. Monolayer BlueP is often fabricated on Au(111) single-crystal surfaces. It has been suggested that small P domains form a lateral network with Au adatoms. Previous studies attempting to use BlueP/Au(111) as a substrate for the deposition of fullerene indicated that the former is susceptible to structural deterioration, unlike most other 2D materials in this regard. Here, we investigate 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA) monolayers and multilayer films deposited on BlueP/Au(111). We monitor the film growth in real time using in situ optical differential reflectance spectroscopy with the substrate kept either at room temperature or at approximate to 120 degrees C. Furthermore, we examine the epitaxial alignment between PTCDA and BlueP by means of distortion-corrected low-energy electron diffraction and low-temperature scanning tunneling microscopy. Our data clearly reveal that PTCDA exhibits a highly ordered monolayer structure with a herringbone packing motif, whereas the domain orientations differ from all previously reported structures of PTCDA directly on Au(111). Importantly, we find no indications for adsorption-induced reordering or degradation of BlueP/Au(111). At elevated temperatures, PTCDA is observed to form multilayer islands covering only a fraction of the available PTCDA monolayer surface on BlueP/Au(111), and this Stranski-Krastanov growth mode bears similarities to literature results for PTCDA multilayers on pristine coinage metal surfaces.