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DDC: 530 × Subject: Nanowires ×

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Now showing 1 - 10 of 22
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    Self-organized formation of unidirectional and quasi-one-dimensional metallic Tb silicide nanowires on Si(110)
    (Amsterdam [u.a.] : Elsevier, 2022) Appelfeller, Stephan; Franz, Martin; Karadag, Murat; Kubicki, Milan; Zielinski, Robert; Krivenkov, Maxim; Varykhalov, Andrei; Preobrajenski, Alexei; Dähne, Mario
    Terbium induced nanostructures on Si(110) and their growth are thoroughly characterized by low energy electron diffraction, scanning tunneling microscopy and spectroscopy, core-level and valence band photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy. For low Tb coverage, a wetting layer forms with its surface fraction continuously decreasing with increasing Tb coverage in favor of the formation of unidirectional Tb silicide nanowires. These nanowires show high aspect ratios for high annealing temperatures or on substrates already containing Tb in the bulk. Both wetting layer and nanowires are stable for temperatures up to 750°C. In contrast to the nanowires, the wetting layer is characterized by a band gap. Thus, the metallic nanowires, which show a quasi-one-dimensional electronic band structure, are embedded in a semiconducting surrounding of wetting layer and substrate, insulating the nanowires from each other.
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    Lattice parameter accommodation between GaAs(111) nanowires and Si(111) substrate after growth via Au-assisted molecular beam epitaxy
    (London : BioMed Central, 2012) Davydok, Anton; Breuer, Steffen; Biermanns, Andreas; Geelhaar, Lutz; Pietsch, Ullrich
    Using out-of-plane and in-plane X-ray diffraction techniques, we have investigated the structure at the interface between GaAs nanowires [NWs] grown by Au-assisted molecular beam epitaxy and the underlying Si(111) substrate. Comparing the diffraction pattern measured at samples grown for 5, 60, and 1,800 s, we find a plastic strain release of about 75% close to the NW-to-substrate interface even at the initial state of growth, probably caused by the formation of a dislocation network at the Si-to-GaAs interface. In detail, we deduce that during the initial stage, zinc-blende structure GaAs islands grow with a gradually increasing lattice parameter over a transition region of several 10 nm in the growth direction. In contrast, accommodation of the in-plane lattice parameter takes place within a thickness of about 10 nm. As a consequence, the ratio between out-of-plane and in-plane lattice parameters is smaller than the unity in the initial state of growth. Finally the wurtzite-type NWs grow on top of the islands and are free of strain.
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    Molecular beam epitaxy of GaAs nanowires and their suitability for optoelectronic applications – comparing Au- and self-assisted growth methods
    (Berlin : Humboldt-Universität zu Berlin, 2011) Breuer, Steffen
    In this work the synthesis of GaAs nanowires by molecular beam epitaxy (MBE) using the vapour-liquid-solid (VLS) mechanism is investigated. A comparison between Au- and self-assisted VLS growth is at the centre of this thesis. While the Au-assisted method is established as a versatile tool for nanowire growth, the recently developed self-assisted variation results from the exchange of Au by Ga droplets and thus eliminates any possibility of Au incorporation. By both methods, we achieve nanowires with epitaxial alignment to the Si(111) substrates. Caused by differences during nanowire nucleation, a parasitic planar layer grows between the nanowires by the Au-assisted method, but can be avoided by the self-assisted method. Au-assisted nanowires grow predominantly in the metastable wurtzite crystal structure, while their self-assisted counterparts have the zincblende structure. All GaAs nanowires are fully relaxed and the strain arising from the lattice mismatch between GaAs and Si of 4.1\% is accommodated by misfit dislocations at the interface. Self-assisted GaAs nanowires are generally found to have vertical and non-polar side facets, while tilted and polar nanofacets were described for Au-assisted GaAs nanowires. We employ VLS nucleation theory to understand the effect of the droplet material on the lateral facets. Optoelectronic applications require long minority carrier lifetimes at room temperature. We fabricate GaAs/(Al,Ga)As core-shell nanowires and analyse them by transient photoluminescence (PL) spectroscopy. The results are 2.5 ns for the self-assisted nanowires as well as 9 ps for the Au-assisted nanowires. By temperature-dependent PL measurements we find a characteristic activation energy of 77 meV that is present only in the Au-assisted nanowires. We conclude that most likely Au is incorporated from the droplets into the GaAs nanowires and acts as a deep, non-radiative recombination centre.
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    Scanning single quantum emitter fluorescence lifetime imaging: Quantitative analysis of the local density of photonic states
    (Washington, DC : American Chemical Society, 2014) Schell, A.W.; Engel, P.; Werra, J.F.M.; Wolff, C.; Busch, K.; Benson, O.
    Their intrinsic properties render single quantum systems as ideal tools for quantum enhanced sensing and microscopy. As an additional benefit, their size is typically on an atomic scale that enables sensing with very high spatial resolution. Here, we report on utilizing a single nitrogen vacancy center in nanodiamond for performing three-dimensional scanning-probe fluorescence lifetime imaging microscopy. By measuring changes of the single emitter's lifetime, information on the local density of optical states is acquired at the nanoscale. Three-dimensional ab initio discontinuous Galerkin time-domain simulations are used in order to verify the results and to obtain additional insights. This combination of experiment and simulations to gather quantitative information on the local density of optical states is of direct relevance for the understanding of fundamental quantum optical processes as well as for the engineering of novel photonic and plasmonic devices.
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    Correction: Electrochemically deposited nanocrystalline InSb thin films and their electrical properties (Journal of Materials Chemistry C (2016) 4 (1345-1350) DOI: 10.1039/C5TC03656A)
    (London : RSC Publ., 2019) Hnida, K.E.; Bäßler, S.; Mech, J.; Szaciłowski, K.; Socha, R.P.; Gajewska, M.; Nielsch, K.; Przybylski, M.; Sulka, G.D.
    There was an error in eqn (3) which was reproduced from the literature and used for the interpretation of the results. The calculations (using the equations from an original work from 1987) were done according the correct version of eqn (3) presented below:. (Table Presented). © 2019 The Royal Society of Chemistry.
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    Wafer-level uniformity of atomic-layer-deposited niobium nitride thin films for quantum devices
    (New York, NY : Inst., 2021) Knehr, Emanuel; Ziegler, Mario; Linzen, Sven; Ilin, Konstantin; Schanz, Patrick; Plentz, Jonathan; Diegel, Marco; Schmidt, Heidemarie; Il’iche, Evgeni; Siegel, Michael
    Superconducting niobium nitride thin films are used for a variety of photon detectors, quantum devices, and superconducting electronics. Most of these applications require highly uniform films, for instance, when moving from single-pixel detectors to arrays with a large active area. Plasma-enhanced atomic layer deposition (ALD) of superconducting niobium nitride is a feasible option to produce high-quality, conformal thin films and has been demonstrated as a film deposition method to fabricate superconducting nanowire single-photon detectors before. Here, we explore the property spread of ALD-NbN across a 6-in. wafer area. Over the equivalent area of a 2-in. wafer, we measure a maximum deviation of 1% in critical temperature and 12% in switching current. Toward larger areas, structural characterizations indicate that changes in the crystal structure seem to be the limiting factor rather than film composition or impurities. The results show that ALD is suited to fabricate NbN thin films as a material for large-area detector arrays and for new detector designs and devices requiring uniform superconducting thin films with precise thickness control.
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    Edge states and topological insulating phases generated by curving a nanowire with Rashba spin-orbit coupling
    (College Park : American Physical Society, 2015) Gentile, Paola; Cuoco, Mario; Ortix, Carmine
    We prove that curvature effects in low-dimensional nanomaterials can promote the generation of topological states of matter by considering the paradigmatic example of quantum wires with Rashba spin-orbit coupling, which are bent in a nanoscale periodic serpentine structure. The effect of the periodic curvature generally results in the appearance of insulating phases with a corresponding novel butterfly spectrum characterized by the formation of finite measure complex regions of forbidden energies. When the Fermi energy lies in the gaps, the system displays localized end states protected by topology. We further show that for certain superstructure periods the system possesses topologically nontrivial insulating phases at half filling. Our results suggest that the local curvature and the topology of the electronic states are inextricably intertwined in geometrically deformed nanomaterials.
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    Surface acoustic wave modulation of single photon emission from GaN/InGaN nanowire quantum dots
    (Bristol : IOP Publ., 2018) Lazić, S.; Chernysheva, E.; Hernández-Mínguez, A.; Santos, P.V.; van der Meulen, H.P.
    On-chip quantum information processing requires controllable quantum light sources that can be operated on-demand at high-speeds and with the possibility of in-situ control of the photon emission wavelength and its optical polarization properties. Here, we report on the dynamic control of the optical emission from core-shell GaN/InGaN nanowire (NW) heterostructures using radio frequency surface acoustic waves (SAWs). The SAWs are excited on the surface of a piezoelectric lithium niobate crystal equipped with a SAW delay line onto which the NWs were mechanically transferred. Luminescent quantum dot (QD)-like exciton localization centers induced by compositional fluctuations within the InGaN nanoshell were identified using stroboscopic micro-photoluminescence (micro-PL) spectroscopy. They exhibit narrow and almost fully linearly polarized emission lines in the micro-PL spectra and a pronounced anti-bunching signature of single photon emission in the photon correlation experiments. When the nanowire is perturbed by the propagating SAW, the embedded QD is periodically strained and its excitonic transitions are modulated by the acousto-mechanical coupling, giving rise to a spectral fine-tuning within a ~1.5 meV bandwidth at the acoustic frequency of ~330 MHz. This outcome can be further combined with spectral detection filtering for temporal control of the emitted photons. The effect of the SAW piezoelectric field on the QD charge population and on the optical polarization degree is also observed. The advantage of the acousto-optoelectric over other control schemes is that it allows in-situ manipulation of the optical emission properties over a wide frequency range (up to GHz frequencies).
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    On the electronic properties of a single dislocation
    (College Park : American Institute of Physics Inc., 2014) Reiche, M.; Kittler, M.; Erfurth, W.; Pippel, E.; Sklarek, K.; Blumtritt, H.; Haehnel, A.; Uebensee, H.
    A detailed knowledge of the electronic properties of individual dislocations is necessary for next generation nanodevices. Dislocations are fundamental crystal defects controlling the growth of different nanostructures (nanowires) or appear during device processing. We present a method to record electric properties of single dislocations in thin silicon layers. Results of measurements on single screw dislocations are shown for the first time. Assuming a cross-section area of the dislocation core of about 1 nm2, the current density through a single dislocation is J = 3.8 × 1012 A/cm2 corresponding to a resistivity of ρ ≅ 1 × 10-8 Ω cm. This is about eight orders of magnitude lower than the surrounding silicon matrix. The reason of the supermetallic behavior is the high strain in the cores of the dissociated dislocations modifying the local band structure resulting in high conductive carrier channels along defect cores.
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    Transition to the quantum hall regime in InAs nanowire cross-junctions
    (Bristol : IOP Publ., 2019) Gooth, Johannes; Borg, Mattias; Schmid, Heinz; Bologna, Nicolas; Rossell, Marta D.; Wirths, Stephan; Moselund, Kirsten; Nielsch, Kornelius; Riel, Heike
    We present a low-temperature electrical transport study on four-terminal ballistic InAs nanowire cross-junctions in magnetic fields aligned perpendicular to the cross-plane. Two-terminal longitudinal conductance measurements between opposing contact terminals reveal typical 1D conductance quantization at zero magnetic field. As the magnetic field is applied, the 1D bands evolve into hybrid magneto-electric sub-levels that eventually transform into Landau levels for the widest nanowire devices investigated (width = 100 nm). Hall measurements in a four-terminal configuration on these devices show plateaus in the transverse Hall resistance at high magnetic fields that scale with (ve 2 /h) -1 . e is the elementary charge, h denotes Planck's constant and v is an integer that coincides with the Landau level index determined from the longitudinal conductance measurements. While the 1D conductance quantization in zero magnetic field is fragile against disorder at the NW surface, the plateaus in the Hall resistance at high fields remain robust as expected for a topologically protected Quantum Hall phase. © 2019 IOP Publishing Ltd.