Browsing by Author "Parzefall, Markus"

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    Antenna-coupled light emission from two-dimensional materials
    (SPIE, 2017) Bharadwaj, Palash; Parzefall, Markus; Jain, Achint; Novotny, Lukas
    We have studied the ultrafast conversion of electrons localized in vertical Au-hBN-Au tunnel junctions to free-space photons, mediated by resonant slot antennas. We achieve polarized, directional and resonantly enhanced light emission from inelastic electron tunneling and establish a novel platform for studying the interaction of electrons with strong electromagnetic fields. Further, we show that plasmonic antennas made from a gold nanoparticle dimer coupled with a semiconducting 2D material (MoS2) offer control over emission directionality.
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    Minimizing residues and strain in 2D materials transferred from PDMS
    (IOP Publishing, 2018) Jain, Achint; Bharadwaj, Palash; Heeg, Sebastian; Parzefall, Markus; Taniguchi, Takashi; Watanabe, Kenji; Novotny, Lukas
    Integrating layered two-dimensional (2D) materials into 3D heterostructures offers opportunities for novel material functionalities and applications in electronics and photonics. In order to build the highest quality heterostructures, it is crucial to preserve the cleanliness and morphology of 2D material surfaces that come in contact with polymers such as PDMS during transfer. Here we report that substantial residues and up to ∼0.22% compressive strain can be present in monolayer MoS2 transferred using PDMS. We show that a UV-ozone pre-cleaning of the PDMS surface before exfoliation significantly reduces organic residues on transferred MoS2 flakes. An additional 200 ◦C vacuum anneal after transfer efficiently removes interfacial bubbles and wrinkles as well as accumulated strain, thereby restoring the surface morphology of transferred flakes to their native state. Our recipe is important for building clean heterostructures of 2D materials and increasing the reproducibility and reliability of devices based on them.