We study a crystallographic etching process of graphene nanostructures where zigzag edges can be prepared selectively. The process involves heating exfoliated single-layer graphene samples with a predefined pattern of antidot arrays in an argon atmosphere at 820 • C, which selectively removes carbon atoms located on armchair sites. Atomic force microscopy and scanning electron microscopy cannot resolve the structure on the atomic scale. However, weak localization and Raman measurements -which both probe intervalley scattering at armchair edges -indicate that zigzag regions are enhanced compared to samples prepared with oxygen based reactive ion etching only.
. At the same time, the films are highly stable in the high-temperature methane/hydrogen atmosphere typically required to grow single wall carbon nanotubes. We characterize molybdenum rhenium alloy films deposited via simultaneous sputtering from two sources, with respect to their composition as function of sputter parameters and their electronic dc as well as GHz properties at low temperature. Specific emphasis is placed on the effect of the carbon nanotube growth conditions on the film. Superconducting coplanar waveguide resonators are defined lithographically; we demonstrate that the resonators remain functional when undergoing nanotube growth conditions, and characterize their properties as function of temperature. This paves the way for ultra-clean nanotube devices grown in situ onto superconducting coplanar waveguide circuit elements.
Cavity optomechanics allows the characterization of a vibration mode, its cooling and quantum manipulation using electromagnetic fields. Regarding nanomechanical as well as electronic properties, single wall carbon nanotubes are a prototypical experimental system. At cryogenic temperatures, as high quality factor vibrational resonators, they display strong interaction between motion and single-electron tunneling. Here, we demonstrate large optomechanical coupling of a suspended carbon nanotube quantum dot and a microwave cavity, amplified by several orders of magnitude via the nonlinearity of Coulomb blockade. From an optomechanically induced transparency (OMIT) experiment, we obtain a single photon coupling of up to g 0 = 2π ⋅ 95 Hz. This indicates that normal mode splitting and full optomechanical control of the carbon nanotube vibration in the quantum limit is reachable in the near future. Mechanical manipulation and characterization via the microwave field can be complemented by the manifold physics of quantum-confined single electron devices.
We study the selective preparation of graphene zigzag edges by crystallographically anisotropic etching processes. Exfoliated graphene on a set of substrates is heated at various temperatures in argon atmospheres with different oxygen concentrations in the ppm range. The removal of carbon atoms from armchair sites at predefined antidots is studied by scanning electron and force microscopy. The anisotropy of etching is determined by the choice of the substrate, graphene's layer thickness and sample conditioning. We show that under all experimental conditions, gaseous oxygen at low concentrations is responsible for graphene etching.
SEM image of anisotropically etched antidots in graphene and dependence of etch rate on added oxygen concentration.
With the objective of integrating single clean, as‐grown carbon nanotubes into complex circuits, we have developed a technique to grow nanotubes directly on commercially available quartz tuning forks using a high‐temperature chemical vapor deposition process. Multiple straight and aligned nanotubes bridge the >100 µm gap between the two tips. The nanotubes are then lowered onto contact electrodes, electronically characterized in situ, and subsequently cut loose from the tuning fork using a high current. First quantum transport measurements of the resulting devices at cryogenic temperatures display Coulomb blockade characteristics.
The in‐place growth of suspended carbon nanotubes facilitates the observation of both unperturbed electronic transport spectra and high‐Q vibrational modes. For complex structures integrating, e.g., superconducting rf elements on‐chip, selection of a chemically and physically resistant material that survives the chemical vapor deposition (CVD) process provides a challenge. We demonstrate the implementation of molybdenum–rhenium coplanar waveguide resonators that exhibit clear resonant behavior at cryogenic temperatures even after having been exposed to nanotube growth conditions. The properties of the MoRe devices before and after CVD are compared to a reference niobium device.
(a) Schematic of the CVD growth environment; a metal thin film is exposed to a CH4 /H2 atmosphere at 850 °C. (b) MoRe coplanar waveguides still display superconductivity after this treatment, with clear resonant behavior of a λ/4 structure.
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