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  • Subscriber access provided by UNIV ULM

    ACS Nano is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

    Article

    A Universal Scheme to Convert Aromatic Molecular Monolayers into Functional Carbon Nanomembranes

    Polina Angelova, Henning Vieker, Nils-Eike Weber, Dan Matei, Oliver Reimer, Isabella Meier, Simon Kurasch, Johannes Biskupek, Dominik Lorbach, Katrin Wunderlich, Long Chen, Andreas

    Terfort, Markus Klapper, Klaus Mullen, Ute Kaiser, Armin Gölzhäuser, and Andrey Turchanin ACS Nano, Just Accepted Manuscript • DOI: 10.1021/nn402652f • Publication Date (Web): 26 Jun 2013

    Downloaded from http://pubs.acs.org on July 8, 2013

    Just Accepted

    “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

  • 1

    A Universal Scheme to Convert Aromatic Molecular Monolayers into

    Functional Carbon Nanomembranes

    Polina Angelova1, Henning Vieker1, Nils-Eike Weber1, Dan Matei1, Oliver Reimer1,

    Isabella Meier1, Simon Kurasch2, Johannes Biskupek2, Dominik Lorbach3,

    Katrin Wunderlich3, Long Chen3, Andreas Terfort4, Markus Klapper3, Klaus Müllen3,

    Ute Kaiser2, Armin Gölzhäuser1*, and Andrey Turchanin1

    1 Faculty of Physics, University of Bielefeld, 33615 Bielefeld, Germany

    2Central Facility of Electron Microscopy, University of Ulm, 89081 Ulm, Germany

    3Max Planck Institute for Polymer Research, 55128 Mainz, Germany

    4Institute of Inorganic and Analytical Chemistry, University of Frankfurt, 60438 Frankfurt, Germany

    Keywords: two-dimensional materials, carbon nanomembranes, graphene,

    molecular self-assembly, helium ion microscopy

    e-mail: ag@uni-bielefeld.de

    Tel.: +49-521-1065362

    Fax: +49-521-1066002

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  • 2

    Abstract

    Free-standing nanomembranes with molecular or atomic thickness are currently

    explored for separation technologies, electronics and sensing. Their engineering with

    well-defined structural and functional properties is a challenge for materials research.

    Here we present a broadly applicable scheme to create mechanically stable carbon

    nanomembranes (CNMs) with a thickness of ~0.5 to ~3 nm. Monolayers of

    polyaromatic molecules (oligophenyls, hexaphenylbenzene and polycyclic aromatic

    hydrocarbons) were assembled and exposed to electrons that crosslink them into

    CNMs; subsequent pyrolysis converts the CNMs into graphene sheets. In this

    transformation the thickness, porosity and surface functionality of the

    nanomembranes are determined by the monolayers, and structural and functional

    features are passed on from the molecules through their monolayers to the CNMs

    and finally on to the graphene. Our procedure is scalable to large areas and allows

    the engineering of ultrathin nanomembranes by controlling the composition and

    structure of precursor molecules and their monolayers.

    Table of contents graphic

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  • 3

    The creation of functional two-dimensional (2D) materials is a fast growing field within

    nanoscience. Nanomembranes,1 i.e. free-standing films with a thickness of a few

    nanometers, have been predicted to possess a superior performance in the

    separation of materials where they should allow a faster passage of the selected −

    gas or liquid − molecules than any conventional filter.2 Nanomembranes were

    integrated in stretchable electronics3 and have been applied as mechanical

    resonators in nano-electro-mechanical systems;4 further, hybrids of nanomembranes

    with fluid lipid bilayers were built as biomimetic interfaces for molecular recognition

    and sensing.5

    Diverse strategies have been developed to build nanomembranes. Since the 1990's

    the so-called Layer-by-Layer (LbL) technique is employed to fabricate membranes for

    corrosion protection, sensing and drug delivery.6-7 In the LbL process, an electrically

    charged surface is sequentially dipped into positively and negatively charged

    polyelectrolytes, leading to the formation of polymeric membranes of well-defined

    molecular composition with thicknesses from ~15 nm to several 100 nm. Much

    thinner membranes can be made by exfoliating single sheets out of a layered

    material.8 Graphene, consisting of a few (~1- 5) layers of carbon atoms, was initially

    made by exfoliation9 and is nowadays produced by a variety of techniques,10 allowing

    researchers to gain new insights into physics and chemistry in two dimensions.

    However, the surface of graphene is homogeneous and chemically inert, which

    makes an efficient functionalization with other molecules difficult. On the contrary,

    covalent organic frameworks11-12 (COFs) and related two-dimensional systems13-16

    are nanomembranes with heterogeneous, chemically reactive surfaces. The first step

    in their creation is the synthesis of organic molecules of well-defined size and shape

    with functionalities at defined positions. When brought into proximity, adjacent

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  • 4

    molecules form multiple covalent bonds and assemble − like Wang tiles − in a 2D

    lattice. COF nanomembranes look very aesthetic; however, their fabrication is time-

    consuming and requires high skill in organic synthesis.

    In this article, we present a modular and broadly applicable construction scheme to

    efficiently fabricate ultrathin carbon nanomembranes (CNMs) that unite the thinness

    of graphene with the chemical functionality of a COF and the ease of fabrication of

    LbL films. It was found earlier17 that self-assembled monolayers (SAMs) of 1,1’-

    biphenyl-4-thiol (BPT) are laterally cross-linked by low-energy electrons and can be

    removed from the surface forming 1 nm thick CNMs. When these CNMs are

    pyrolized at ~1000K, they transform into graphene.18-19 Motivated by these findings,

    we applied similar protocols to a variety of other polyaromatic molecules. Our

    scheme (Fig. 1a-c) utilizes a sequence of (i) molecular monolayer assembly on a

    solid surface, (ii) radiation induced two-dimensional crosslinking, and (iii) a lift-off of

    the network of crosslinked molecules. The product is a free-standing CNM, whose

    thickness, homogeneity, presence of pores and surface chemistry are determined by

    the nature of the initial molecular monolayer. We investigated three types of thiol-

    based precursors: non-fused oligophenyl derivatives (Fig. 1d: 1a-c) which possess

    linear molecular backbones providing an improved structural ordering of the formed

    SAMs; condensed polycyclic precursors like naphthalene (NPTH), anthracene

    (ANTH) and pyrene (MP) mercapto derivatives (Fig. 1d: 2a-f) which are more rigid

    and should result in a higher stability and an increased carbon density of the

    monolayers; “bulky” molecules, like the noncondensed hexaphenylbenzene

    derivative with a propeller-like structure (Fig. 1d: 3a) and extended disc-type

    polycyclic aromatic hydrocarbons such as hexa-peri-benzocoronene (HBC)

    derivatives (Fig. 1d: 3b-c).20-21 The former are specially functionalized with lo

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