Pre-determining the location of electromigrated gaps by nonlinear optical imaging

In this paper we describe a nonlinear imaging method employed to spatially map the occurrence of constrictions occurring on an electrically-stressed gold nanowire. The approach consists at measuring the influence of a tightly focused ultrafast pulsed laser on the electronic transport in the nanowire. We found that structural defects distributed along the nanowire are efficient nonlinear optical sources of radiation and that the differential conductance is significantly decreased when the laser is incident on such electrically-induced morphological changes. This imaging technique is applied to pre-determined the location of the electrical failure before it occurs.Comment: 3 figure

Growth of high quality, high density single-walled carbon nanotube forests on copper foils

We demonstrate the growth of high quality single-walled carbon nanotube (SWCNT) forests on commercial Cu foils by cold-wall chemical vapor deposition. Time-of-flight secondary ion mass spectrometry was employed to study the effect of annealing on the catalyst evolution with or without an AlOₓ barrier layer. X-ray photoelectron spectroscopy was used to investigate the chemical states of the catalyst and the barrier layer. SWCNT forests can be reproducibly grown on Cu foils sputter-coated with Al and Fe layers as thin as 6 nm and 0.4 nm, respectively. Al transforms into AlOₓ on exposure to air and during annealing. Most importantly, such a thin AlOₓ barrier layer ensures not only the growth of SWCNTs but also an Ohmic contact between the as grown SWCNTs and the Cu base as measured by a two-point probe station. The as-grown SWCNTs exhibit a bimodal distribution of diameters ranging from 0.6 to 4.5 nm, with two peaks centered at 0.8 nn and 2.6 nm, respectively.This work supported by Honda Research Institute USA Inc. Sugime H. acknowledges a research fellowship from the Japanese Society for the Promotion of Science (JSPS).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.carbon.2015.11.04

Influence of Mo on the Fe:Mo:C nano-catalyst thermodynamics for single-walled carbon nanotube growth

We explore the role of Mo in Fe:Mo nanocatalyst thermodynamics for low-temperature chemical vapor deposition growth of single walled carbon nanotubes (SWCNTs). By using the size-pressure approximation and ab initio modeling, we prove that for both Fe-rich (~80% Fe or more) and Mo-rich (~50% Mo or more) Fe:Mo clusters, the presence of carbon in the cluster causes nucleation of Mo2C. This enhances the activity of the particle since it releases Fe, which is initially bound in a stable Fe:Mo phase, so that it can catalyze SWCNT growth. Furthermore, the presence of small concentrations of Mo reduce the lower size limit of low-temperature steady-state growth from ~0.58nm for pure Fe particles to ~0.52nm. Our ab initio-thermodynamic modeling explains experimental results and establishes a new direction to search for better catalysts.Comment: 7 pages, 3 figures. submitte

Interacting supernovae and supernova impostors. SN 2007sv: the major eruption of a massive star in UGC 5979

We report the results of the photometric and spectroscopic monitoring campaign of the transient SN 2007sv. The observables are similar to those of type IIn supernovae, a well-known class of objects whose ejecta interact with pre-existing circum-stellar material. The spectra show a blue continuum at early phases and prominent Balmer lines in emission, however, the absolute magnitude at the discovery of SN 2007sv (M_R = - 14.25 +/- 0.38) indicate it to be most likely a supernova impostor. This classification is also supported by the lack of evidence in the spectra of very high velocity material as expected in supernova ejecta. In addition we find no unequivocal evidence of broad lines of alpha - and/or Fe-peak elements. The comparison with the absolute light curves of other interacting objects (including type IIn supernovae) highlights the overall similarity with the prototypical impostor SN 1997bs. This supports our claim that SN 2007sv was not a genuine supernova, and was instead a supernova impostor, most likely similar to the major eruption of a luminous blue variable.Comment: Accepted for publication in MNRAS. 15 pages, 11 figures, 5 table

Sensor Development for Single-Photon Thermoelectric Detectors

As we reported earlier [1], thermoelectric detectors can be competitive as nondispersive energy resolving focal-plane instruments in X-ray/UV spectrum. The first generations of prototype devices demonstrated the viability of detector design and provided good agreement between theoretical expectations and experimental data. These devices exploited sensors made of gold with a small fraction of iron impurity. To get the projected high resolution one needs another type of material, namely, lanthanum-cerium hexaborides. We report on the first experimental tests of the feasibility of lanthanum-cerium films as sensor materials. Progress with thin films of these materials argues for the success of these thermoelectric detectors

Brillouin Light Scattering of Spin Waves Inaccessible with Free-Space Light

Micro-focus Brillouin light scattering is a powerful technique for the spectroscopic and spatial characterization of elementary excitations in materials. However, the small momentum of light limits the accessible excitations to the center of the Brillouin zone. Here, we utilize a metallic nanoantenna fabricated on the archetypal ferrimagnet yttrium iron garnet to demonstrate the possibility of Brillouin light scattering from large-wavevector, high-frequency spin wave excitations that are inaccessible with free-space light. The antenna facilitates sub-diffraction confinement of electromagnetic field, which enhances the local field intensity and generates momentum components significantly larger than those of free-space light. Our approach provides access to high frequency spin waves important for fast nanomagnetic devices, and can be generalized to other types of excitations and light scattering techniques.Comment: 6 pages, 4 figure