Publications by authors named "Jan N Kirchhof"

5 Publications

  • Page 1 of 1

The patterning toolbox FIB-o-mat: Exploiting the full potential of focused helium ions for nanofabrication.

Beilstein J Nanotechnol 2021 6;12:304-318. Epub 2021 Apr 6.

Corelab Correlative Microscopy and Spectroscopy, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.

Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.
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http://dx.doi.org/10.3762/bjnano.12.25DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8042487PMC
April 2021

Tunable Graphene Phononic Crystal.

Nano Lett 2021 Mar 23;21(5):2174-2182. Epub 2021 Feb 23.

Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.

In the field of phononics, periodic patterning controls vibrations and thereby the flow of heat and sound in matter. Bandgaps arising in such phononic crystals (PnCs) realize low-dissipation vibrational modes and enable applications toward mechanical qubits, efficient waveguides, and state-of-the-art sensing. Here, we combine phononics and two-dimensional materials and explore tuning of PnCs via applied mechanical pressure. To this end, we fabricate the thinnest possible PnC from monolayer graphene and simulate its vibrational properties. We find a bandgap in the megahertz regime within which we localize a defect mode with a small effective mass of 0.72 ag = 0.002 m. We exploit graphene's flexibility and simulate mechanical tuning of a finite size PnC. Under electrostatic pressure up to 30 kPa, we observe an upshift in frequency of the entire phononic system by ∼350%. At the same time, the defect mode stays within the bandgap and remains localized, suggesting a high-quality, dynamically tunable mechanical system.
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http://dx.doi.org/10.1021/acs.nanolett.0c04986DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7953378PMC
March 2021

Selective Functionalization of Graphene at Defect-Activated Sites by Arylazocarboxylic tert-Butyl Esters.

Angew Chem Int Ed Engl 2019 Mar 25;58(11):3599-3603. Epub 2019 Jan 25.

Institut für Chemie und Biochemie, Freie Universität Berlin, Takustraße 3, 14195, Berlin, Germany.

The development of versatile functionalization concepts for graphene is currently in the focus of research. Upon oxo-functionalization of graphite, the full surface of graphene becomes accessible for C-C bond formation to introduce out-of-plane functionality. Herein, we present the arylation of graphene with arylazocarboxylic tert-butyl esters, which generates aryl radicals after activation with an acid. Surprisingly, the degree of functionalization is related to the concentration of lattice vacancy defects in the graphene material. Consequently, graphene materials that are free from lattice defects are not reactive. The reaction can be applied to graphene dispersed in solvents and leads to bitopic functionalization as well as monotopic functionalization when the graphene is deposited on surfaces. As the arylazocarboxylic tert-butyl ester moiety can be attached to various molecules, the presented method paves the way to functional graphene derivatives, with the density of defects determining the degree of functionalization.
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http://dx.doi.org/10.1002/anie.201811192DOI Listing
March 2019

Microstructure and Elastic Constants of Transition Metal Dichalcogenide Monolayers from Friction and Shear Force Microscopy.

Adv Mater 2018 Sep 21;30(39):e1803748. Epub 2018 Aug 21.

Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489, Berlin, Germany.

Optical and electrical properties of 2D transition metal dichalcogenides (TMDCs) grown by chemical vapor deposition (CVD) are strongly determined by their microstructure. Consequently, the visualization of spatial structural variations is of paramount importance for future applications. This study demonstrates how grain boundaries, crystal orientation, and strain fields can unambiguously be identified with combined lateral force microscopy and transverse shear microscopy (TSM) for CVD-grown tungsten disulfide (WS ) monolayers, on length scales that are relevant for optoelectronic applications. Further, angle-dependent TSM measurements enable the fourth-order elastic constants of monolayer WS to be acquired experimentally. The results facilitate high-throughput and nondestructive microstructure visualization of monolayer TMDCs and insights into their elastic properties, thus providing an accessible tool to support the development of advanced optoelectronic devices based on such 2D semiconductors.
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http://dx.doi.org/10.1002/adma.201803748DOI Listing
September 2018

Detecting Ultrasound Vibrations with Graphene Resonators.

Nano Lett 2018 08 17;18(8):5132-5137. Epub 2018 Jul 17.

JARA-FIT and 2nd Institute of Physics , RWTH Aachen University , 52056 Aachen , Germany.

Ultrasound detection is one of the most-important nondestructive subsurface characterization tools for materials, the goal of which is to laterally resolve the subsurface structure with nanometer or even atomic resolution. In recent years, graphene resonators have attracted attention for their use in loudspeakers and ultrasound radios, showing their potential for realizing communication systems with air-carried ultrasound. Here, we show a graphene resonator that detects ultrasound vibrations propagating through the substrate on which it was fabricated. We ultimately achieve a resolution of ∼7 pm/[Formula: see text] in ultrasound amplitude at frequencies up to 100 MHz. Thanks to an extremely high nonlinearity in the mechanical restoring force, the resonance frequency itself can also be used for ultrasound detection. We observe a shift of 120 kHz at a resonance frequency of 65 MHz for an induced vibration amplitude of 100 pm with a resolution of 25 pm. Remarkably, the nonlinearity also explains the generally observed asymmetry in the resonance frequency tuning of the resonator when it is pulled upon with an electrostatic gate. This work puts forward a sensor design that fits onto an atomic force microscope cantilever and therefore promises direct ultrasound detection at the nanoscale for nondestructive subsurface characterization.
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http://dx.doi.org/10.1021/acs.nanolett.8b02036DOI Listing
August 2018
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