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

Abstract

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.

Electron‐Irradiation Promoted Exchange Reaction as a Tool for Surface Engineering and Chemical Lithography

“…The IPER-based lithography and nanofabrication represent an important tool, complementing a variety of other lithographic techniques, including those relying on EBL, such as electron beam induced deposition (EBID) and focused electron beam induced fabrication (FEBIF) [97][98][99][100][101][102][103] or in situ EBL. [104] IPER also served as an inspiration for an analogous approach utilizing ultraviolet light instead of electrons, which has several advantages, such as applicability in ambient and even liquid environments, but also drawbacks, such as a lower lateral resolution and less broad choice of commercial lithographic setups.…”

Thickness-Varied Carbon Nanomembranes from Polycyclic Aromatic Hydrocarbons

“…However, there are no fundamental obstacles for employing other compounds provided they are able to withstand exposure to a flood gun. Thus, the formation of CNMs has been demonstrated upon irradiating physisorbed tetraphenylporphyrin molecules that were evaporated in vacuum onto gold substrates . The bulky species were shown to lie flat and form compact multilayer films, and analogous to the conversion of SAMs, cross-linking was found to be accompanied by massive dehydrogenation, resulting in 1.5 nm thick CNMs.…”