Browsing by Author "Braeuninger-Weimer, Philipp"

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    Atomic layer deposited oxide films as protective interface layers for integrated graphene transfer
    (IOP Publishing: Hybrid Open Access, 2017-10-17) Cabrero-Vilatela, Andrea; Alexander-Webber, Jack; Sagade, Abhay; Aria, Adrianus Indrat; Braeuninger-Weimer, Philipp; Martin, Marie-Blandine; Weatherup, Robert; Hofmann, Stephan
    The transfer of chemical vapour deposited (CVD) graphene from its parent growth catalyst has become a bottleneck for many of its emerging applications. The sacrificial polymer layers that are typically deposited onto graphene for mechanical support during transfer are challenging to fully remove and hence leave graphene and subsequent device interfaces contaminated. Here, we report on the use of atomic layer deposited (ALD) oxide films as protective interface and support layers during graphene transfer. The method avoids any direct contact of the graphene with polymers and through the use of thicker ALD layers (≥100nm), polymers can be eliminated from the transfer-process altogether. The ALD film can be kept as a functional device layer, facilitating integrated device manufacturing. We demonstrate back-gated field effect devices based on single-layer graphene transferred with a protective Al2O3 film onto SiO2 that show significantly reduced charge trap and residual carrier densities. We critically discuss the advantages and challenges of processing graphene/ALD bilayer structures.
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    Bolometric detection of terahertz quantum cascade laser radiation with graphene-plasmonic antenna arrays
    (IOP Publishing, 2017-03-27) Degl'Innocenti, Riccardo; Xiao, Long; Kindness, Stephen J.; Kamboj, Varun S.; Wei, Binbin; Braeuninger-Weimer, Philipp; Nakanishi, Kenichi; Aria, Adrianus Indrat; Hofmann, Stephan; Beere, Harvey E.; Ritchie, David A.
    We present a fast room temperature terahertz detector based on graphene loaded plasmonic antenna arrays. The antenna elements, which are arranged in series and are shorted by graphene, are contacting source and drain metallic pads, thus providing both the optical resonant element and the electrodes. The distance between the antenna’s arms of approximately 300 nm allows a strong field enhancement in the graphene region, when the incident radiation is resonant with the antennas. The current passing through the source and drain is dependent on the graphene’s conductivity, which is modified by the power impinging onto the detector as well as from the biasing back-gate voltage. The incident radiation power is thus translated into a current modification, with the main detection mechanism being attributed to the bolometric effect. The device has been characterized and tested with two bound to continuum terahertz quantum cascade lasers emitting at a single frequency around 2 THz and 2.7 THz yielding a maximum responsivity of ~2 mA W−1.
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    Parameter space of atomic layer deposition of ultra-thin oxides on graphene
    (American Chemical Society , 2016-10-10) Aria, Adrianus Indrat; Nakanishi, Kenichi; Xiao, Long; Braeuninger-Weimer, Philipp; Sagade, Abhay A.; Alexander-Webber, Jack; Hofmann, Stephan
    Atomic layer deposition (ALD) of ultrathin aluminum oxide (AlOx) films was systematically studied on supported chemical vapor deposition (CVD) graphene. We show that by extending the precursor residence time, using either a multiple-pulse sequence or a soaking period, ultrathin continuous AlOx films can be achieved directly on graphene using standard H2O and trimethylaluminum (TMA) precursors even at a high deposition temperature of 200 °C, without the use of surfactants or other additional graphene surface modifications. To obtain conformal nucleation, a precursor residence time of >2s is needed, which is not prohibitively long but sufficient to account for the slow adsorption kinetics of the graphene surface. In contrast, a shorter residence time results in heterogeneous nucleation that is preferential to defect/selective sites on the graphene. These findings demonstrate that careful control of the ALD parameter space is imperative in governing the nucleation behavior of AlOx on CVD graphene. We consider our results to have model system character for rational two-dimensional (2D)/non-2D material process integration, relevant also to the interfacing and device integration of the many other emerging 2D materials.