Ultrathin Carbon Nanomembranes from 5,10,15,20-Tetraphenylporphyrin: Electron Beam Induced Fabrication and Functionalization via Focused Electron Beam Induced Processing

Two-dimensional (2D) materials are promising candidates as main components for future applications in electronics, optics, and magnetics due to their specific properties. One method to fabricate such 2D materials is electron-induced cross-linking of organic precursor molecules. In this work, we significantly expand the concept from wet chemically prepared self-assembled monolayers (SAMs) to physisorbed molecular layers of functional organic molecules prepared by thermal sublimation under (ultrahigh) vacuum. More specifically, 1.5 nm thick carbon nanomembranes (CNM) were fabricated from a porphyrin, namely 5,10,15,20-tetraphenylporphyrin (2H-TPP) molecules. The processes occurring on a molecular scale during electron-induced cross-linking of 2H-TPP molecules are analyzed by reflection absorption infrared spectroscopy (RAIRS) and electron stimulated desorption (ESD). ESD shows that beside hydrogen, no further fragments desorb during electron irradiation. In RAIRS, most of the significant bands resulting from C-H or N-H bonds have disappeared after electron irradiation. The resulting 2D nanomembranes can be functionalized by focused electron beam induced processing (FEBIP). Clean iron nanostructures are fabricated on top of the 2D material via either electron beam induced deposition (EBID) or electron beam induced surface activation (EBISA). The resulting hybrids consisting of metallic nanostructures and nonmetallic 2D material can be transferred onto either solid substrates or onto grids to obtain free-standing metal/CNM hybrid structures. This transfer process gives evidence of the flexibility and high mechanical stability of the CNM fabricated from 2H-TPP molecules. In this work, we thus demonstrate that porphyrins, which are of high scientific interest and play a crucial role in nature, can be used for the fabrication of stable 2D materials.