Phase Transitions of the BlueP-Au Network by Intercalation of Potassium

In 2014, a new elemental semiconductor was postulated: Blue Phosphorene (BlueP) offers a layer thickness-dependent band gap and high charge carrier mobility. However, the synthesis of a highly ordered and stable monolayer of BlueP remains a challenge, and on Au(111) only a gold phosphorus network could be achieved so far. This undesirable coupling, which leads to a change in electronic properties, could be mitigated by the intercalation of potassium, with the goal of realizing a quasi-free-standing monolayer of BlueP. Here, the effects of substrate temperature during K deposition and the sequence of the deposition of P and K on Au(111) are investigated. Structural properties are characterized by LEED and RHEED, chemical properties are characterized by XPS, and electronic properties are characterized by ultraviolet photoelectron spectroscopy methods (UPS and ARUPS). At a temperature of 250 C-degrees, the BlueP-Au network transforms under the influence of potassium deposition and partial desorption of phosphorus into various intermediates. In the end, a (2 x 2) superstructure is obtained that exhibits the most promising electronic properties, which are very close to those of free-standing BlueP. The K:P ratio is between 1.5 and 2. However, no indications of highly ordered free-standing BlueP with a lattice constant of 3.15 could be found by LEED measurements. Therefore, we assume that K and P together form the basis of the (2 x 2) superstructure, since the reactive bonds of potassium are most likely saturated and stabilized by phosphorus.