Strategies for Controlled Placement of Nanoscale Building Blocks

The capability of placing individual nanoscale building blocks on exact substrate locations in a controlled manner is one of the key requirements to realize future electronic, optical, and magnetic devices and sensors that are composed of such blocks. This article reviews some important advances in the strategies for controlled placement of nanoscale building blocks. In particular, we will overview template assisted placement that utilizes physical, molecular, or electrostatic templates, DNA-programmed assembly, placement using dielectrophoresis, approaches for non-close-packed assembly of spherical particles, and recent development of focused placement schemes including electrostatic funneling, focused placement via molecular gradient patterns, electrodynamic focusing of charged aerosols, and others

Model-independent measurement of t\boldsymbol{t}-channel single top quark production in ppˉ\boldsymbol{p\bar{p}} collisions at s=1.96\boldsymbol{\sqrt{s}=1.96} TeV

We present a model-independent measurement of $t$-channel electroweak production of single top quarks in \ppbar collisions at $\sqrt{s}=1.96\;\rm TeV$. Using $5.4\;\rm fb^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider, and selecting events containing an isolated electron or muon, missing transverse energy and one or two jets originating from the fragmentation of $b$ quarks, we measure a cross section \sigma({\ppbar}{\rargap}tqb+X) = 2.90 \pm 0.59\;\rm (stat+syst)\; pb for a top quark mass of $172.5\;\rm GeV$. The probability of the background to fluctuate and produce a signal as large as the one observed is $1.6\times10^{-8}$, corresponding to a significance of 5.5 standard deviations.Comment: 8 pages, 4 figures, submitted to Phys. Lett.

Mechanical properties, microstructure and crystallographic texture of magnesium AZ91-D alloy welded by Friction Stir Welding (FSW)

The objective of the study was to characterize the properties of a magnesium alloy welded by friction stir welding (FSW). The results led to a better understanding of the relationship between this process and the microstructure and anisotropic properties of alloy materials. Welding principally leads to a large reduction in grain size in welded zones due to the phenomenon of dynamic recrystallization. The most remarkable observation was that crystallographic textures appeared from a base metal without texture in two zones: the thermo-mechanically affected and stir welded zones. The latter zone has the peculiarity of possessing a marked texture with two components on the basal plane and the pyramidal plane. These characteristics disappeared in the TMAZ, which had only one component following the basal plane. These modifications have been explained by the nature of the plastic deformation in these zones, which occurs at a moderate temperature in the TMAZ and high temperature in the SWZ

Microstructure and hardness of fiber laser deposited Inconel 718 using filler wire

A continuous wave 5 kW fiber laser welding system was used to deposit INCONEL\uae alloy 718 (IN718) layers in conduction mode by applying filler wire with a composition similar to the parent metal, which was extracted directly from a scrapped, service-exposed IN718 aerospace component. The quality of the deposits was characterized in both the as-deposited and fully heat-treated conditions in terms of the macrostructure, defects, microstructure, and hardness. Integral deposits with no visible porosity were obtained using the fiber laser deposition technique. In the as-deposited clad zone, weld metal liquation cracking led to the presence of minor microcracks in the lower layer beads near the layer interface. The crack healing behavior observed after post-clad heat treatment of the IN718 deposits supports the marked potential of using the laser deposition technique by filler wire addition to manufacture and repair/remanufacture superalloy components for aerospace applications. \ua9 2013 Her Majesty the Queen in Right of Canada as represented by: National Research Council Canada.Peer reviewed: YesNRC publication: Ye

THE MICROSTRUCTURE OF THE PRECIPITATES IN A Ni-Be ALLOY, AS STUDIED WITH ATOM-PROBE FIM

The microstructure, chemistry and morphology of a decomposed Ni-12at%Be alloy were investigated with atom-probe FIM. The β-precipitates were revealed to be disc shaped. The orientation relationship between the α-matrix ( A1 ) and the β-precipitates (B2) was determined. Atom-probe analyses showed that the interphase boundaries are very sharp. On the interfaces some ledge were revealed. The results were interpreted in terms of Gibbs-Wulff theorem and growth ledge mechanism

Fiber laser deposition of nickel-based superalloys using filler wire feed

In this work, a continuous wave fiber laser welding system was used to deposit nickel-based superalloys Inconel 718 (IN 718) and Waspaloy using filler wire feed sources. The multi-bead and multi-layer deposits that were manufactured were characterized in terms of the macro- and microstructures, defects, and hardness in both the as-deposited and fully heat treated conditions. The tensile properties of the deposits in the heat treated condition were also determined and compared to the existing aerospace materials specifications. Using optimized laser processing parameters, high strength deposits could be manufactured, though minor weld metal liquation cracking for IN718 and strain-age cracking for Waspaloy were present, which compromised slightly the ductility as compared to wrought aerospace specifications for the two alloys. The successful development of the direct laser deposition process using wire feeding indicates the potential of employing the fiber laser technology to manufacture nickel-based superalloy aerospace components.Peer reviewed: YesNRC publication: Ye

THE COMPOSITION FLUCTUATION IN AN Fe46Ni31V1Si8B14 GLASS

The as quenched metallic glass Fe46Ni31VlSi8B14 has been investigated by atom probe field ion microscopy. The results have shown that the material had separated into a fine-scaled mixture of a boron and silicon-rich phase and an iron-enriched phase. Their chemical compositions have been determined. The composition profile of the specimen revealed that the characteristic length of the two-phase-structure was in the order of 10 nm. It is proposed that the observed structure originated from the nucleation and growth of molecular cluster-like zones in the material