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8 Oct 2007

Volume 91, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 91, 153101 (2007); http://dx.doi.org/10.1063/1.2793688 (3 pages)

B. J. Lee, K. Park, and Z. M. Zhang
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Mechanical deformation and failure of electrospun polyacrylonitrile nanofibers as a function of strain rate

Mohammad Naraghi, Ioannis Chasiotis, Harold Kahn, Yongkui Wen, and Yuris Dzenis

Appl. Phys. Lett. 91, 151901 (2007); http://dx.doi.org/10.1063/1.2795799 (3 pages) | Cited 15 times

Online Publication Date: 8 October 2007

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The mechanical deformation of 12 μm long electrospun polyacrylonitrile (PAN) nanofibers with diameters of 300–600 nm was investigated. The nanofibers were subjected to cold drawing in atmospheric conditions and at strain rates between 10−2 and 10−4 s−1. The ultimate strain of the PAN nanofibers was 60%–130% varying monotonically with the strain rate. On the contrary, the fiber tensile strength, ranging between 30 and 130 MPa, varied nonmonotonically with the slowest drawing rate resulting in the largest ductilities and fiber strengths. At the two faster rates, the large fiber ductilities originated in the formation of a cascade of ripples (necks), while at the slowest strain rate, the nanofibers deformed homogeneously allowing for the largest engineering strengths and extension ratios.
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62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
62.25.-g Mechanical properties of nanoscale systems
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Surface plasmon coupled fluorescence from copper substrates

Michael J. R. Previte, Yongxia Zhang, Kadir Aslan, and Chris D. Geddes

Appl. Phys. Lett. 91, 151902 (2007); http://dx.doi.org/10.1063/1.2794761 (3 pages) | Cited 4 times

Online Publication Date: 8 October 2007

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Previously, we reported the observation of metal enhanced emission from copper nanoparticles. In this letter, we report the observation of surface plasmon coupled fluorescence (SPCF) or emission from thin copper (Cu) continuous films. Using Fresnel calculations to theoretically calculate the reflectance curves for polymethyl methacrylate films doped with sulforhodamine 101, we correlated the minimum reflectance angles for both s- and p-polarized lights with maximum fluorescence emission. These observations reveal that we can achieve SPCF with copper substrates and possibly design inexpensive copper substrates for fluorescent sensing applications and potentially, fluorescent based electrical signals and circuits.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Hx Other solid inorganic materials
68.55.-a Thin film structure and morphology

Epitaxial growth mechanisms of AlN on SiC substrates at room temperature

Myunghee Kim, Jitsuo Ohta, Atsushi Kobayashi, Hiroshi Fujioka, and Masaharu Oshima

Appl. Phys. Lett. 91, 151903 (2007); http://dx.doi.org/10.1063/1.2795804 (3 pages) | Cited 6 times

Online Publication Date: 9 October 2007

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Epitaxial AlN films have been grown on atomically flat 6H-SiC (0001) and 4H-SiC (0001) substrates at room temperature (RT), and their growth mechanisms have been investigated. It has been revealed that the growth of AlN at RT proceeds in a layer-by-layer mode from the initial stage. During the growth, AlN nucei have an equilateral triangular shape probably due to the anisotropy in growth rates. The triangular AlN nuclei at the adjacent terraces formed on the 6H-SiC substrates are rotated by 60°, whereas the triangular AlN nuclei on the 4H-SiC were formed in the same direction on all of the terraces. This phenomenon can be explained by the difference in the arrangement of the atoms for the topmost layers.
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68.55.-a Thin film structure and morphology

Photochromism in yttrium hydride

Ayako Ohmura, Akihiko Machida, Tetsu Watanuki, Katsutoshi Aoki, Satoshi Nakano, and K. Takemura

Appl. Phys. Lett. 91, 151904 (2007); http://dx.doi.org/10.1063/1.2794755 (3 pages) | Cited 2 times

Online Publication Date: 12 October 2007

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Transparent orange yttrium hydride turns to black when illuminated by visible laser light at pressures of several gigapascals at room temperature. The marked reduction in optical transmittance extends over the infrared region, suggesting that illumination creates persistent free carriers. The opaque black sample returns to the transparent orange hydride during room-temperature annealing for a few hours. Photochromism is pronounced for the coexistent state of the metallic fcc-YH2 and the insulating hexagonal-YH3 state but is depressed for the single phase of hexagonal-YH3. The results indicate that light illumination can modify the optical and possibly electronic properties during a certain period of times.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments

Coherent anti-Stokes Raman scattering polarized microscopy of three-dimensional director structures in liquid crystals

A. V. Kachynski, A. N. Kuzmin, P. N. Prasad, and I. I. Smalyukh

Appl. Phys. Lett. 91, 151905 (2007); http://dx.doi.org/10.1063/1.2800887 (3 pages) | Cited 18 times

Online Publication Date: 12 October 2007

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We demonstrate three-dimensional vibrational imaging of director structures in liquid crystals using coherent anti-Stokes Raman scattering (CARS) polarized microscopy. Spatial mapping of the structures is based on sensitivity of a polarized CARS signal to the orientation of anisotropic molecules in liquid crystals. As an example, we study structures in a smectic material and demonstrate that single-scan CARS and two-photon fluorescence images of molecular orientation patterns are consistent with each other and with the structure model.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
63.50.-x Vibrational states in disordered systems
78.30.C- Liquids
78.55.Bq Liquids
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