Atomic View of Metal Atoms Intercalation into Black Phosphorous
Woei Wu Pai1*, Yi Jeng Tzeng2, Horng Tay Jeng3
1Center for condensed matter sciences, National Taiwan University, Taipei, Taiwan
2Institute of nuclear energy research, N/A, TaoYuan, Taiwan
3Department of Physics, National Tsing Hua University, Hsin Chu, Taiwan
* presenting author:Woei Wu Pai,
Black phosphor(BP) is a promising material for electronics due to its non-zero band gap and good ambipolar carrier mobility. One important issue for applications is the properties of metal-BP contact and how it modifies the band gap of BP. BP subjected to ambient exposure is often p-doped and a high work function metal, such as platinum, is then a preferred choice of contact material. We studied the initial stage of Pt deposition on in-situ vacuum-cleaved BP surface at either 300 K or 78 K. In both cases, Pt atoms do not stay atop the BP surface. Instead, peanut-like protrusions with overlayed BP atomic lattice was observed. We interpreted this as Pt atoms intercalating into the van der Waals gap between the first and second BP layers. Ab-initio calculations indicate significant energy gain of intercalated Pt versus non-intercalated Pt, with >1 eV gain per Pt atom. Molecular dynamics simulations also reveal significant BP deformation upon Pt adsorption – which could lead to possible paths of intercalation. For pristine in-situ vacuum-cleaved BP surface, we found a band gap value ~0.3-0.4 eV close to its bulk band gap value. This is in contrast to a recent report claming a bulk BP surface has a ~2 eV band gap of a single BP layer. Incrreasing strain applied to BP surface also induces significant reduction in BP’s band gap value, eventually leads to metallic behavior. In contrast to a BP surface cleaved in air showing strongly p-doped character, in-situ vacuum-cleaved BP is nearly intrinsic. The band gap of BP slightly increases by ~0.2 eV near the Pt-intercalation sites and is consistent with theoretical calculations. Our results show that BP-metal interaction can be unexpectedly significant and can have substantial effect on BP band gap.

Keywords: black phosphor, intercalation, scanning tunneling microscopy, band gap