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We report on a high energy ultrafast fibre laser architecture designed for high harmonics generation in solids. The laser delivering 50 fs pulses with 2.12 µJ at 1550 nm has enabled the generation of harmonics up to harmonic H5 from a magnesium oxide (MgO) bulk sample. To the best of our knowledge this is the first solid-state HHG source driven by a µJ-class few-cycle fiber laser in the mid-IR region.

The crystallographic dependence of electron emission properties from LaB6 single-crystal tips and its importance has been highlighted in several experimental and theoretical studies. Here, we report on the cold field electron emission from LaB6 nanotips in the ⟨ 310 ⟩ orientation under static (DC) and laser-assisted conditions for possible use as an ultrafast electron emitter. By changing the voltage and laser intensity, we observe different emission regimes such as the photo-field emission and the multiphoton photoemission. The field electron microscopy patterns change under ultrafast laser illumination and correspond to the region of a high laser field. The emission properties of LaB6 nanotips in the ⟨ 310 ⟩ orientation are compared with those of the ⟨ 100 ⟩ orientation. [ABSTRACT FROM AUTHOR]

Single crystal diamond needles are promising structures as point electron sources. However, the low electrical conductivity of diamond limits their application as high brightness electron sources. Here we study experimentally and numerically the field emission behavior of single crystal diamond needles, in order to better explain the link between the low electrical conduction, the non-homogeneous field distribution in the needle, the evolution of the field enhancement factor and the saturation of the Fowler–Nordheim plot. Field emission current and voltage loss were measured as a function of the applied voltage. Numerical modelling was used to solve conduction, emission and Laplace equations taking into account the real geometry of the field emitter and its environment. The combination of experimental and numerical results shows that the conduction behavior and the field enhancement factor depend on the diamond geometry. Moreover, the Fowler–Nordheim plot saturation is shown to be affected by the electrostatic environment which can limit the range of voltage losses that can appear along the diamond needle and hence limit the field emission current. At the same time, the increase of the emission current at high field, which is sometimes argued to be caused by the breakdown of the field emitter, is here presented as a simple consequence of the conduction properties of the field emitter as it was already shown for silicon field emitters. [ABSTRACT FROM AUTHOR]

Single crystal diamond nanotips reveal a new behavior for ultrafast laser-induced electron emission. Under tightly focused femtosecond laser illumination, electron yield shows a saturation with the laser intensity. When the DC bias is sufficient for dark field emission, large optical intensities can switch off the emission occurring between laser pulses during a few hundred μs, because of the low conductance of the diamond tip. We propose a macroscopic model to combine a capacitive effect with the different conduction and emission mechanisms. This study shows that non-metallic photocathodes offer different perspectives from the conventional metallic ones. [ABSTRACT FROM AUTHOR]

Nature 489, 414-18(2012); doi:10.1038/nature11439 In this Letter, the units of thermal conductivity on the y-axes of Fig. 2d and e should be W m 1K 1 and the y-axis label [...]

In an atom probe, molecular ions can be field evaporated from the analyzed material and, then, can dissociate under the very intense electric field close to the field emitter. In this work, field evaporation of ZnO reveals the emission of Zn2O22+ ions and their dissociation into ZnO+ ions. It is shown that the repulsion between the produced ZnO+ ions is large enough to have a measurable effect on both the ion trajectories and times of flight. Comparison with numerical simulations of the ion trajectories gives information on the lifetime of the parent ions, the energy released by the dissociation and repulsion, and also the dissociation direction. This study not only opens the way to a new method to obtain information on the behavior of molecular ions in high electric fields by using an atom probe, but also opens up the interesting perspective to apply this technique to a wide class of materials and molecules. [ABSTRACT FROM AUTHOR]

A single nanoscale object containinga set of InGaN/GaN nonpolarmultiple-quantum wells has been analyzed by microphotoluminescencespectroscopy (μPL), high-resolution scanning transmission electronmicroscopy (HR-STEM) and atom probe tomography (APT). The correlatedmeasurements constitute a rich and coherent set of data supportingthe interpretation that the observed μPL narrow emission lines,polarized perpendicularly to the crystal c-axis andwith energies in the interval 2.9–3.3 eV, are related to excitonstates localized in potential minima induced by the irregular 3D Indistribution within the quantum well (QW) planes. This novel methodopens up interesting perspectives, as it will be possible to applyit on a wide class of quantum confining emitters and nano-objects. [ABSTRACT FROM AUTHOR]

In situ measurements of the kinetics of the transient θ-Ni2Si phase formation have been obtained by x-ray diffraction and differential scanning calorimetry. A possible mechanism for the transient phase is proposed. It allows to simulate the growth and the consumption of the θ-Ni2Si during the growth of the δ-Ni2Si silicide. [ABSTRACT FROM AUTHOR]

In a previous work, the chemical elements necessary for the achievement of Niobium base superalloys were defined in order to get a structure equivalent to that of Nickel base superalloys, which contain ordered precipitates within a disordered solid-solution. It was especially emphasized that precipitation hardening in the Niobium matrix would be possible with the addition of Ni. The remaining question about the design of such Niobium superalloys concerned the achievement of ordered precipitates in crystalline coherence with the Nb matrix i.e., with a crystalline structure equivalent to the Nb crystal prototype and with a lattice parameter in coherency with that of the Nb matrix. In order to reduce the trial/error experimental work, a reasoning based on various data for the achievement of coherency is presented. Then, starting from the Nb-Hf-Ni ternary alloy thus defined, this paper demonstrates that the precipitation of an ordered Nb phase within a disordered Nb matrix can be achieved with lattice parameter coherency between the ordered precipitates and the disordered matrix. The chemistry and the crystallographic structure of the precipitates were characterized using Transmission Electron Microscopy and Atom Probe Tomography. These results can help to conceive a new family of Nb base superalloys. [ABSTRACT FROM AUTHOR]

Abstract: The redistribution of arsenic and nickel during the reaction of Ni thin films with arsenic doped Si(100) substrates is studied by a combination of transmission electron microscopy (TEM), atom-probe tomography (APT) and in situ X-ray diffraction (XRD). Ni was observed at the edges of a pseudo-hexagonal dislocation loop within As+-implanted (001)Si wafers, after recrystallisation of preamorphised Si and deposition of 100nm Ni. After an additional heat treatment at 280°C, the same concentration profiles were found with a maximum of ≈10% Ni at the edges of the dislocation loops, suggesting Cottrell atmospheres. In situ XRD showed the formation of a transient phase forming isolated grains at the δ-Ni2Si/Si interface. Clusters containing 10% of As are present only in the transient phase. The presence of As clusters in silicide used for contact on devices might have significant influences on devices properties. [Copyright &y& Elsevier]