5,982 research outputs found
Enhanced resistance of single-layer graphene to ion bombardment
We report that single-layer graphene on a SiO_2/Si substrate withstands ion bombardment up to ~7
times longer than expected when exposed to focused Ga^+ ion beam. The exposure is performed in
a dual beam scanning electron microscope/focused ion beam system at 30 kV accelerating voltage
and 41 pA current. Ga^+ ion flux is determined by sputtering a known volume of hydrogenated
amorphous carbon film deposited via plasma-enhanced chemical vapor deposition
Cathodoluminescence of enstatite from chondritic and achondritic meteorites and its selenological implications Technical report, 1 Sep. 1967 - 1 Jul. 1968
Cathodoluminescence of enstatite from chondritic and achondritic meteorites and selenological implication
Microstructure versus Size: Mechanical Properties of Electroplated Single Crystalline Cu Nanopillars
We report results of uniaxial compression experiments on single-crystalline Cu nanopillars with nonzero initial dislocation densities produced without focused ion beam (FIB). Remarkably, we find the same power-law size-driven strengthening as FIB-fabricated face-centered cubic micropillars. TEM analysis reveals that initial dislocation density in our FIB-less pillars and those produced by FIB are on the order of 10^(14) m^(-2) suggesting that mechanical response of nanoscale crystals is a stronger function of initial microstructure than of size regardless of fabrication method
Applications of luminescence techniques to the study of the lunar surface
Optical fluorescence spectra of rock-forming minerals for identifying mineral grains found on lunar surfac
In Situ Nanomechanical Measurements of Interfacial Strength in Membrane-Embedded Chemically Functionalized Si Microwires for Flexible Solar Cells
Arrays of vertically aligned Si microwires embedded in polydimethylsiloxane (PDMS) have emerged as a promising candidate for use in solar energy conversion devices. Such structures are lightweight and concurrently demonstrate competitive efficiency and mechanical flexibility. To ensure reliable functioning under bending and flexing, strong interfacial adhesion between the nanowire and the matrix is needed. In situ uniaxial tensile tests of individual, chemically functionalized, Si microwires embedded in a compliant PDMS matrix reveal that chemical functionality on Si microwire surfaces is directly correlated with interfacial adhesion strength. Chemical functionalization can therefore serve as an effective methodology for accessing a wide range of interfacial adhesion between the rigid constituents and the soft polymer matrix; the adhesion can be quantified by measuring the mechanical strength of such systems
Independent particle descriptions of tunneling from a many-body perspective
Currents across thin insulators are commonly taken as single electrons moving
across classically forbidden regions; this independent particle picture is
well-known to describe most tunneling phenomena. Examining quantum transport
from a different perspective, i.e., by explicit treatment of electron-electron
interactions, we evaluate different single particle approximations with
specific application to tunneling in metal-molecule-metal junctions. We find
maximizing the overlap of a Slater determinant composed of single particle
states to the many-body current-carrying state is more important than energy
minimization for defining single particle approximations in a system with open
boundary conditions. Thus the most suitable single particle effective potential
is not one commonly in use by electronic structure methods, such as the
Hartree-Fock or Kohn-Sham approximations.Comment: 4+ pages, 4 figures; accepted to Phys. Rev. B Rapid Communication
Developments in quantitative luminescence techniques
Developments in quantitative luminescence technique
Mechanical Response of Hollow Metallic Nanolattices: Combining Structural and Material Size Effects
Ordered cellular solids have higher compressive yield strength and stiffness compared to stochastic foams. The mechanical properties of cellular solids depend on their relative density and follow structural scaling laws. These scaling laws assume the mechanical properties of the constituent materials, like modulus and yield strength, to be constant and dictate that equivalent-density cellular solids made from the same material should have identical mechanical properties. We present the fabrication and mechanical properties of three-dimensional hollow gold nanolattices whose compressive responses demonstrate that strength and stiffness vary as a function of geometry and tube wall thickness. All nanolattices had octahedron geometry, a constant relative density, ρ ∼ 5%, a unit cell size of 5–20 μm, and a constant grain size in the Au film of 25–50 nm. Structural effects were explored by increasing the unit cell angle from 30 deg to 60 deg while keeping all other parameters constant; material size effects were probed by varying the tube wall thickness, t, from 200 nm to 635 nm, at a constant relative density and grain size. In situ uniaxial compression experiments revealed an order of magnitude increase in yield stress and modulus in nanolattices with greater lattice angles, and a 150% increase in the yield strength without a concomitant change in modulus in thicker-walled nanolattices for fixed lattice angles. These results imply that independent control of structural and material size effects enables tunability of mechanical properties of three-dimensional architected metamaterials and highlight the importance of material, geometric, and microstructural effects in small-scale mechanics
Development of Ocular Inserts for Cattle
Ring shaped ocular inserts have been developed to administer a therapeutic level of tylosin tartrate throughout a five day period to treat pinkeye in cattle. The inserts are based on polyvinyl chloride rings which are dip coated with a copolymer containing the antibiotic (tylosin tartrate). Scanning electron microscope (SEM) characterization of surfaces has been of value to evaluate the presence and extent of surface flaws in the hydrogel coating, and to contribute to improvement in fabrication of the rings to insure the establishment of satisfactory seals at joints, uniformity of microporosity and cross sections, and the absence of significant cracking or flaking. In vitro release rates were determined using-thin layer chromatography techniques, and rates were seen to be above a few micrograms of antibiotic per hour for experiments as long as nine days at simulated tear rates as high as 2 milliliters per hour
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