In-situ observation of the onset of plastic deformation by prismatic loop emission

We report direct observations on the incipient plasticity of dislocation-free single crystal Au [110] nanowires by in situ transmission electron microscopy nanomechanical testing. The diameter of the tested nanowires ranged from ~ 80 nm to 350 nm and the length-to-diameter ratio was larger than 5. The top end of all [110]-oriented Au nanowires is bound by two inclined {111} faces in a wedge shape, on the other hand the side faces consist of four large {111} and two small {100} planes, resulting in a truncated rhombic cross-section. In our deformation setup where the wedge-shaped growth end of nanowire was compressed with a flat diamond punch, the strain becomes localized to the region under the contact. Under such a strong strain gradient condition, the initial compressive deformation began with the emission of small prismatic loops from the top corner, which have a radius ranging from ~20 nm to 100 nm. The Burgers vector of these loops was determined to be 1/2[-1-10], which generates the vertical downward displacement of the inner area encompassed by the prismatic loops. Right after the nucleation, these prismatic loops glided immediately down to reach a certain position where it remained stationary until newly generated loops force to glide downward in jerky manner. After a certain number of closed loops being punched out (typically less than ten), there was a clear transition in the nucleation mechanism of the loops; open loops started to bulge out and then released from the contact area. Very different from the closed prismatic loops, the freely moving ends of the open loops intersected and swept across the top faces before being released, thereby relaxing the strain accumulated beyond the contact area. The stress field accumulated inside the nanowire is also released by escape of open loops through the free surface. More importantly, these loops can act as sources for ordinary dislocations which slip along the inclined {111} planes. Based on the direct observation of prismatic loops and supporting molecular dynamics simulations, detailed characteristics of the loops and their behaviors at the initial stage of deformation of nanowire will be presented

K*{\Lambda}(1116) photoproduction and nucleon resonances

In this presentation, we report our recent studies on the $K^*\Lambda(1116)$ photoproduction off the proton target, using the tree-level Born approximation, via the effective Lagrangian approach. In addition, we include the nine (three- or four-star confirmed) nucleon resonances below the threshold $\sqrt{s}_\mathrm{th}\approx2008$ MeV, to interpret the discrepancy between the experiment and previous theoretical studies, in the vicinity of the threshold region. From the numerical studies, we observe that the $S_{11}(1535)$ and $S_{11}(1650)$ play an important role for the cross-section enhancement near the $\sqrt{s}_\mathrm{th}$. It also turns out that, in order to reproduce the data, we have the vector coupling constants $g_{K^*S_{11}(1535)\Lambda}=(7.0\sim9.0)$ and $g_{K^*S_{11}(1650)\Lambda}=(5.0\sim6.0)$.Comment: 2 pages, 2 figures, talk given at International Conference on the structure of baryons, BARYONS'10, Dec. 7-11, 2010, Osaka, Japa

A Suspended Nanogap Formed by Field-Induced Atomically Sharp Tips

A sub-nanometer scale suspended gap (nanogap) defined by electric field-induced atomically sharp metallic tips is presented. A strong local electric field (\u3e109 V=m) across micro/nanomachined tips facing each other causes the metal ion migration in the form of dendrite-like growth at the cathode. The nanogap is fully isolated from the substrate eliminating growth mechanisms that involve substrate interactions. The proposed mechanism of ion transportation is verified using real-time imaging of the metal ion transportation using an in situ biasing in transmission electron microscope (TEM). The configuration of the micro/nanomachined suspended tips allows nanostructure growth of a wide variety of materials including metals, metal-oxides, and polymers. VC 2012 American Institute of Physics

Anisotropic Acoustic Plasmons in Black Phosphorus

Recently, it was demonstrated that a graphene/dielectric/metal configuration can support acoustic plasmons, which exhibit extreme plasmon confinement an order of magnitude higher than that of conventional graphene plasmons. Here, we investigate acoustic plasmons supported in a monolayer and multilayers of black phosphorus (BP) placed just a few nanometers above a conducting plate. In the presence of a conducting plate, the acoustic plasmon dispersion for the armchair direction is found to exhibit the characteristic linear scaling in the mid- and far-infrared regime while it largely deviates from that in the long wavelength limit and near-infrared regime. For the zigzag direction, such scaling behavior is not evident due to relatively tighter plasmon confinement. Further, we demonstrate a new design for an acoustic plasmon resonator that exhibits higher plasmon confinement and resonance efficiency than BP ribbon resonators in the mid-infrared and longer wavelength regime. Theoretical framework and new resonator design studied here provide a practical route toward the experimental verification of the acoustic plasmons in BP and open up the possibility to develop novel plasmonic and optoelectronic devices that can leverage its strong in-plane anisotropy and thickness-dependent band gap