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Three-Dimensional Composition and Electric Potential Mapping of III–V Core–Multishell Nanowires by Correlative STEM and Holographic Tomography
The nondestructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms of functional potentials is crucial for correlating device properties with their morphological/materials features, as well as for precisely tuning and optimizing their growth process. Electron holographic tomography (EHT) has been used in the past to reconstruct the total potential distribution in three-dimension but hitherto lacked a quantitative approach to separate potential variations due to chemical composition changes (mean inner potential, MIP) and space charges. In this Letter, we combine and correlate EHT and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography on an individual ⟨111⟩ oriented GaAs–AlGaAs core–multishell nanowire (NW). We obtain excellent agreement between both methods in terms of the determined Al concentration within the AlGaAs shell, as well as thickness variations of the few nanometer thin GaAs shell acting as quantum well tube. Subtracting the MIP determined from the STEM tomogram, enables us to observe functional potentials at the NW surfaces and at the Au–NW interface, both ascribed to surface/interface pinning of the semiconductor Fermi level.
Correction: Selective particle and cell capture in a continuous flow using micro-vortex acoustic streaming
The authors regret that a citation to a relevant paper was missed. The following sentence and reference (ref. 1 shown below) should be added in the Introduction after the sentence ending "...of the applied flow rate.5,37": "For example, Lee et al. acoustically oscillate air/liquid interfaces using a ∼50 kHz piezoelectric transducer to produce acoustic streaming fields for size-based separation of cells and particles".1 The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.
Theoretical Prediction of a Giant Anisotropic Magnetoresistance in Carbon Nanoscrolls
Snake orbits are trajectories of charge carriers curving back and forth that form at an interface where either the magnetic field direction or the charge carrier type are inverted. In ballistic samples, their presence is manifested in the appearance of magnetoconductance oscillations at small magnetic fields. Here we show that signatures of snake orbits can also be found in the opposite diffusive transport regime. We illustrate this by studying the classical magnetotransport properties of carbon tubular structures subject to relatively weak transversal magnetic fields where snake trajectories appear in close proximity to the zero radial field projections. In carbon nanoscrolls, the formation of snake orbits leads to a strongly directional dependent positive magnetoresistance with an anisotropy up to 80%.
Serrated flow of CuZr-based bulk metallic glasses probed by nanoindentation: Role of the activation barrier, size and distribution of shear transformation zones
We report on the effect of Al and Co alloying in vitreous Cu50Zr50 on local deformation and serrated flow as a model for relating the size and localization of shear transformation zones (STZ) to Poisson ratio and strain-rate sensitivity of metallic glasses. Alloying with Al results in significant variations in mechanical performance, in particular, in Young's modulus, hardness and strain-rate sensitivity. Increasing strain-rate sensitivity with increasing degree of alloying indicates a reduced tendency for shear localization. In parallel, a gradual transition from inhomogeneous to homogeneous plastic flow is observed. Using a statistical analysis of the shear stress associated with the initiation of the first pop-in in the load-displacement curve during spherical indentation, the activation volume for plastic flow at the onset of yielding is reported. This analysis is employed for experimental evaluation of the compositional dependence of activation barrier, size and distribution of STZs. It is demonstrated that the STZ size does not change significantly upon Al alloying and encompasses a local volume of around 22–24 atoms. However, the barrier energy density for the initiation of a single STZ progressively increases. The broader distribution of STZs impedes their accumulation into larger-size flow units, leading to a lower number and reduced size of serrations in the load-displacement curve. On the contrary, lower barrier energy densities enable a larger quantity of STZs to be activated simultaneously. These STZs can easily percolate into large flow units, promoting plastic flow through their interaction. We employ Poisson's ratio as an indicator for plasticity to shown that this interpretation can be transferred to other types of metallic glasses. That is, larger flow units were found for metallic glasses with higher Poisson ratio and more pronounced plasticity, while the flow units in alloys with very low Poisson ratio and high brittleness are significantly reduced in size and more homogeneously distributed throughout the material.
Phonon-Assisted Two-Photon Interference from Remote Quantum Emitters
Photonic quantum technologies are on the verge of finding applications in everyday life with quantum cryptography and quantum simulators on the horizon. Extensive research has been carried out to identify suitable quantum emitters and single epitaxial quantum dots have emerged as near-optimal sources of bright, on-demand, highly indistinguishable single photons and entangled photon-pairs. In order to build up quantum networks, it is essential to interface remote quantum emitters. However, this is still an outstanding challenge, as the quantum states of dissimilar “artificial atoms” have to be prepared on-demand with high fidelity and the generated photons have to be made indistinguishable in all possible degrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51 ± 5%) from remote strain-tunable GaAs quantum dots emitting on-demand photon-pairs. We achieve this result by exploiting for the first time the full potential of a novel phonon-assisted two-photon excitation scheme, which allows for the generation of highly indistinguishable (visibility of 71 ± 9%) entangled photon-pairs (fidelity of 90 ± 2%), enables push-button biexciton state preparation (fidelity of 80 ± 2%) and outperforms conventional resonant two-photon excitation schemes in terms of robustness against environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeaters and complex multiphoton entanglement experiments involving dissimilar artificial atoms.