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8 Jan 2007

Volume 90, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 022501 (2007); http://dx.doi.org/10.1063/1.2430693 (3 pages)

V. Zakosarenko, N. Bondarenko, S. H. W. van der Ploeg, A. Izmalkov, S. Linzen, J. Kunert, M. Grajcar, E. Il’ichev, and H.-G. Meyer
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Polarization insensitive all-fiber mode-lockers functioned by carbon nanotubes deposited onto tapered fibers

Yong-Won Song, Keiyo Morimune, Sze Y. Set, and Shinji Yamashita

Appl. Phys. Lett. 90, 021101 (2007); http://dx.doi.org/10.1063/1.2431445 (3 pages) | Cited 28 times

Online Publication Date: 8 January 2007

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The authors demonstrate a nonblocked all-fiber mode locker operated by the interaction of carbon nanotubes with the evanescent field of propagating light in a tapered fiber. Symmetric cross section of the device with the randomly oriented nanotubes guarantees the polarization insensitive operation of the pulse formation. In order to minimize the scattering, the carbon nanotubes are deposited within a designed area around the tapered waist. The demonstrated passively pulsed laser has the repetition rate of 7.3 MHz and the pulse width of 829 fs.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
85.35.Kt Nanotube devices

Observation of Brillouin zone folding in photonic crystal slab waveguides possessing a superlattice pattern

Curtis W. Neff, Tsuyoshi Yamashita, and Christopher J. Summers

Appl. Phys. Lett. 90, 021102 (2007); http://dx.doi.org/10.1063/1.2431447 (3 pages) | Cited 2 times

Online Publication Date: 8 January 2007

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The optical properties of superlattice photonic crystal (PC) patterns in two-dimensional slab waveguides were investigated using coupled-resonance angular dependent reflectivity measurements. Additional features were found in the superlattice PC spectra in comparison to that of the triangular lattice, indicating Brillouin zone folding (BZF) due to the larger unit cell and reduced symmetry of the superlattice. Calculated band structures corroborate these measurements and confirm the BZF effect which was shown to extract portions of the triangular lattice guided bands into the waveguide radiating regime, making the dielectric bands excitable by an out-of-plane source.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Spatial coherence measurements in arrays of coupled vertical cavity surface emitting lasers

L. D. A. Lundeberg, G. P. Lousberg, D. L. Boiko, and E. Kapon

Appl. Phys. Lett. 90, 021103 (2007); http://dx.doi.org/10.1063/1.2431474 (3 pages) | Cited 7 times

Online Publication Date: 8 January 2007

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The spatial coherence and the optical phase distribution across a two-dimensional (2D) photonic crystal implemented with coupled arrays of vertical cavity surface emitting lasers (VCSELs) are experimentally characterized. This is achieved by performing Young’s interference experiments between pairs of array elements using a spatial light modulator arrangement. In contrast to far-field measurements that provide information only on the global spatial coherence, this approach can yield full mapping of the complex degree of spatial coherence. Examples of such analysis are presented for nominally uniform one-dimensional and 2D arrays of coupled VCSELs and possible mechanisms of the observed coherence degradation are discussed.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Subwavelength waveguide for visible light

J. Rybczynski, K. Kempa, A. Herczynski, Y. Wang, M. J. Naughton, Z. F. Ren, Z. P. Huang, D. Cai, and M. Giersig

Appl. Phys. Lett. 90, 021104 (2007); http://dx.doi.org/10.1063/1.2430400 (3 pages) | Cited 34 times

Online Publication Date: 8 January 2007

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The authors demonstrate transmission of visible light through metallic coaxial nanostructures many wavelengths in length, with coaxial electrode spacing much less than a wavelength. Since the light frequency is well below the plasma resonance in the metal of the electrodes, the propagating mode reduces to the well-known transverse electromagnetic mode of a coaxial waveguide. They have thus achieved a faithful analog of the conventional coaxial cable for visible light.
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42.79.Gn Optical waveguides and couplers

Time-resolved thermal characterization of semiconductor lasers

L. Lanco, S. Ducci, J.-P. Likforman, P. Filloux, X. Marcadet, M. Calligaro, G. Leo, and V. Berger

Appl. Phys. Lett. 90, 021105 (2007); http://dx.doi.org/10.1063/1.2430776 (3 pages) | Cited 3 times

Online Publication Date: 10 January 2007

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The authors propose and demonstrate a simple nondestructive technique that allows characterizing precisely the thermal properties of semiconductor lasers. The method consists of performing transmission measurements with a probe beam end fire coupled into one of the waveguide facets. Fabry-Perot oscillations occur as the cavity temperature varies, allowing for a time-resolved characterization of heating and dissipation processes. This leads to a very accurate knowledge of the thermal behavior of a third-order-mode semiconductor laser proposed for intracavity nonlinear processes.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.20.-n Thermal instruments and apparatus

Effect of annealing temperature and ambient gas on phosphorus doped p-type ZnO

Dae-Kue Hwang, Min-Suk Oh, Jae-Hong Lim, Chang-Goo Kang, and Seong-Ju Park

Appl. Phys. Lett. 90, 021106 (2007); http://dx.doi.org/10.1063/1.2430937 (3 pages) | Cited 34 times

Online Publication Date: 10 January 2007

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The authors report on the thermal activation of phosphorus doped p-type ZnO thin films grown by radio frequency magnetron sputtering. The p-type ZnO was produced by activating phosphorus doped ZnO thin films in N2, Ar, or O2 ambients. The hole concentration of the p-type ZnO, prepared in an O2 ambient, showed a lower hole concentration compared to samples annealed in N2 and Ar ambients. The activation energies of the phosphorus dopant in the p-type ZnO under different ambient gases indicate that phosphorus atoms replace oxygen atoms in the ZnO to form PO which acts as an acceptor.
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61.72.Cc Kinetics of defect formation and annealing
73.61.Ga II-VI semiconductors

Cooperative quantum cutting in one-dimensional (YbxGd1−x)Al3(BO3)4:Tb3+ nanorods

Q. Y. Zhang, C. H. Yang, and Y. X. Pan

Appl. Phys. Lett. 90, 021107 (2007); http://dx.doi.org/10.1063/1.2430942 (3 pages) | Cited 49 times

Online Publication Date: 10 January 2007

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Near-infrared (NIR) quantum cutting (QC) involving the emission of two NIR photons per absorbed photon via a cooperative downconversion mechanism in one-dimensional (1D) (YbxGd1−x)Al3(BO3)4:Tb3+ nanorods has been demonstrated. The authors have analyzed the measured luminescence spectra and decay lifetimes and proposed a mechanism to rationalize the QC effect. Upon excitation of Tb3+ with a blue-visible photon at 485 nm, two NIR photons could be emitted by Yb3+ through an efficient cooperative energy transfer from Tb3+ to two Yb3+ with optimal quantum efficiency as great as 196%. The development of 1D Tb3+–Yb3+ QC nanomaterials could open up a possibility to realize high efficiency silicon-based solar cells by means of downconversion of the green-to-ultraviolet part of the solar spectrum to ∼ 1000 nm photons with a twofold increase in the photon number.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.55.Hx Other solid inorganic materials

InGaAs/AlAsSb/InP quantum cascade lasers operating at wavelengths close to 3 μm

D. G. Revin, J. W. Cockburn, M. J. Steer, R. J. Airey, M. Hopkinson, A. B. Krysa, L. R. Wilson, and S. Menzel

Appl. Phys. Lett. 90, 021108 (2007); http://dx.doi.org/10.1063/1.2431035 (3 pages) | Cited 49 times

Online Publication Date: 10 January 2007

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The authors report the realization of short wavelength (3.05 μm ⩽ λ ⩽ 3.6 μm) InP lattice-matched In0.53Ga0.47As/AlAs0.56Sb0.44 quantum cascade lasers (QCLs). The highest-performance device displays pulsed laser action at wavelengths between 3.4 and 3.6 μm, for temperatures up to 300 K, with a low temperature (80 K) threshold current density of approximately 2.6 kA/cm2, and a characteristic temperature of T0 ∼ 130 K. The shortest wavelength QCL (λ ≈ 3.05 μm) has a higher threshold current density ( ∼ 12 kA/cm2 at T = 20 K) and operates in pulsed mode at temperatures up to 110 K.
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42.55.Px Semiconductor lasers; laser diodes

Free electron laser seeded by ir laser driven high-order harmonic generation

Juhao Wu, Paul R. Bolton, James B. Murphy, and Xinming Zhong

Appl. Phys. Lett. 90, 021109 (2007); http://dx.doi.org/10.1063/1.2431455 (3 pages) | Cited 6 times

Online Publication Date: 10 January 2007

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Coherent x-ray production by a seeded free electron laser (FEL) is important for next generation synchrotron light sources. The authors examine the feasibility and features of FEL emission seeded by a high-order harmonic generation (HHG) of an infrared laser. In addition to the intrinsic FEL chirp, the longitudinal profile and spectral bandwidth of the HHG seed are modified significantly by the FEL interaction well before saturation. This smears out the original attosecond pulselet structure. The authors introduce criteria for this smearing effect on the pulselet and the stretching effect on the entire pulse. They discuss the noise issue in such a seeded FEL.
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41.60.Cr Free-electron lasers
42.60.By Design of specific laser systems
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.60.Fc Modulation, tuning, and mode locking

Method for measuring the three-dimensional distribution of a fluorescent dye in a cell membrane

Kazuya Yamamoto, Ichirou Ishimaru, Yoshiki Fujii, Toshiki Yasokawa, Shigeki Kuriyama, Tsutomu Masaki, Kaoru Takegawa, and Naotaka Tanaka

Appl. Phys. Lett. 90, 021110 (2007); http://dx.doi.org/10.1063/1.2428457 (3 pages)

Online Publication Date: 10 January 2007

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This letter reports on a method for accurately determining the component distribution in a cell membrane over the entire cell surface. This method involves exciting a fluorescent-dyed cell membrane using evanescent light and scanning the entire cell surface by rotating the cell using a noncontact technique, namely, proximal two-beam optical tweezers. To position the cell membrane in the thin evanescent field, the authors designed an optical system capable of precisely positioning the focal position. Using this method, they were able to measure the surface distribution of glycoprotein labeled by lectin in a breast cancer cell membrane.
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87.63.L- Visual imaging
87.16.D- Membranes, bilayers, and vesicles
87.14.E- Proteins
87.15.M- Spectra of biomolecules
33.50.Dq Fluorescence and phosphorescence spectra
37.10.Mn Slowing and cooling of molecules
37.10.Pq Trapping of molecules

Laser-scanning angle deviation microscopy

Ming-Hung Chiu, Bo-Yuan Shih, and Chih-Wen Lai

Appl. Phys. Lett. 90, 021111 (2007); http://dx.doi.org/10.1063/1.2430027 (3 pages) | Cited 4 times

Online Publication Date: 11 January 2007

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A microscope manifesting a dynamic range of several microns and an axial (or height) resolution of 1 nm is presented. It is based on the method of angle deviation due to nonfocal plane reflection and the application of surface plasmon resonance effect as well as the technique of heterodyne interferometry. The deviation angle and the induced phase difference between two rays are proportional to the departure from the focal plane. Using the common-path heterodyne interferometry to scan the specimen and measure the phase difference distribution, the surface profile would be obtained in real time.
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07.60.Pb Conventional optical microscopes
07.60.Ly Interferometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.62.-b Laser applications

High order mode formation of externally coupled hybrid photonic-band-gap cavity

Seok-Gy Jeon, Young-Min Shin, Kyu-Ha Jang, Seong-Tae Han, Jin-Kyu So, Young-Do Joo, and Gun-Sik Park

Appl. Phys. Lett. 90, 021112 (2007); http://dx.doi.org/10.1063/1.2431451 (3 pages) | Cited 4 times

Online Publication Date: 12 January 2007

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The electromagnetic field distribution obtained from a finite-difference-time-domain simulation shows that a hybrid photonic-band-gap (PBG) cavity enveloped by a dielectric lattice and three metallic walls provides a better field uniformity of a high order mode, TMmn0, than a conventional one does under an external coupling with the maintenance of a high quality factor of the metallic cavity. Experimentally measured reflection and transmission scattering matrices of a TM550 mode show that the hybrid PBG structure improves the field uniformity to within 10% compared with a larger variation reaching a few tens of a percent with the conventional cavity under critical coupling.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Experimental characterization of material nonlinearity using Lamb waves

Christian Bermes, Jin-Yeon Kim, Jianmin Qu, and Laurence J. Jacobs

Appl. Phys. Lett. 90, 021901 (2007); http://dx.doi.org/10.1063/1.2431467 (3 pages) | Cited 24 times

Online Publication Date: 8 January 2007

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The objective of this research is to develop an accurate and reliable procedure to measure the second order harmonic of a Lamb wave propagating in a metallic plate. There are two associated complications in measuring these nonlinear Lamb waves, namely, their inherent dispersive and multimode natures. To overcome these, this research combines a time-frequency representation with a hybrid wedge generation and laser interferometric detection system. The effectiveness of the proposed procedure is demonstrated by characterizing the inherent material nonlinearity of two different aluminum plates whose absolute nonlinearity parameters are known from longitudinal wave measurements.
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68.35.Iv Acoustical properties

Strain relaxation in nanopatterned strained silicon round pillars

C. Himcinschi, R. Singh, I. Radu, A. P. Milenin, W. Erfurth, M. Reiche, U. Gösele, S. H. Christiansen, F. Muster, and M. Petzold

Appl. Phys. Lett. 90, 021902 (2007); http://dx.doi.org/10.1063/1.2431476 (3 pages) | Cited 9 times

Online Publication Date: 8 January 2007

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Periodic arrays of strained Si (sSi) round nanopillars were fabricated on sSi layers deposited on SiGe virtual substrates by electron-beam lithography and subsequent reactive-ion etching. The strain in the patterned sSi nanopillars was determined using high-resolution UV micro-Raman spectroscopy. The strain relaxes significantly upon nanostructuring: from 0.9% in the unpatterned sSi layer to values between 0.22% and 0.57% in the round sSi pillars with diameters from 100 up to 500 nm. The strain distribution in the sSi nanopillars was analyzed by finite element (FE) modeling. The FE calculations confirm the strain relaxation after patterning, in agreement with the results obtained from Raman spectroscopy.
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68.35.Gy Mechanical properties; surface strains
78.40.Fy Semiconductors
78.30.Am Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

ZnIr2O4, a p-type transparent oxide semiconductor in the class of spinel zinc-d6-transition metal oxide

Matthijn Dekkers, Guus Rijnders, and Dave H. A. Blank

Appl. Phys. Lett. 90, 021903 (2007); http://dx.doi.org/10.1063/1.2431548 (3 pages) | Cited 19 times

Online Publication Date: 8 January 2007

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The authors report on the growth of spinel ZnM(d6)2O4 (M = Co, Rh, and Ir), a p-type wide band gap semiconductor by pulsed laser deposition. The band gap of these compounds is determined by the ligand field splitting in the subbands of the metallic d6 cation. Photoemission spectroscopy revealed that the valence band maximum is composed of occupied t2g6 states. The observed band gap is increasing for higher quantum numbers, being as large as ∼ 3 eV for ZnIr2O4, which is expected from theoretical predictions. Grown in polycrystalline phase, films of these materials display high conductivity, well above 2 S cm−1.
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81.15.Fg Pulsed laser ablation deposition
79.60.Dp Adsorbed layers and thin films
73.61.Le Other inorganic semiconductors
68.55.A- Nucleation and growth
71.20.Nr Semiconductor compounds

Nanoscale phase separation in amorphous immiscible copper-niobium alloy thin films

R. Banerjee, A. Puthucode, S. Bose, and P. Ayyub

Appl. Phys. Lett. 90, 021904 (2007); http://dx.doi.org/10.1063/1.2429017 (3 pages) | Cited 6 times

Online Publication Date: 8 January 2007

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While amorphous phases have been reported in immiscible alloy systems, there is still some controversy regarding the reason for the stabilization of these unusual amorphous phases. In this letter, using three-dimensional atom probe tomography, direct evidence of nanoscale phase separation within the amorphous phase forming in immiscible Cu–Nb alloy thin films has been presented. This evidence clearly indicates that the nanoscale phase separation is responsible for the stabilization of the amorphous phase in such immiscible systems since it substantially reduces the free energy of the undercooled liquid (or amorphous) phase, below that of the competing supersaturated crystalline phases.
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68.55.Nq Composition and phase identification
61.43.Dq Amorphous semiconductors, metals, and alloys
64.75.-g Phase equilibria
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Narrow UV emission from homogeneous GaN/AlGaN quantum wells

E. Feltin, D. Simeonov, J.-F. Carlin, R. Butté, and N. Grandjean

Appl. Phys. Lett. 90, 021905 (2007); http://dx.doi.org/10.1063/1.2429027 (3 pages) | Cited 8 times

Online Publication Date: 8 January 2007

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The authors report on the achievement of narrow ultraviolet emission using GaN/AlGaN quantum wells grown by metal organic vapor phase epitaxy. The origin of the inhomogeneous broadening of the emission is explained by means of micro-photoluminescence and atomic force microscopy measurements. The effect of the well/barrier interface roughness on the linewidth is found to be marginal, while the impact of Al composition fluctuations of the barriers is highly critical. Emission linewidths as small as 5 meV at 10 K are obtained by decreasing the aluminum concentration fluctuations in the AlGaN barrier.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)

Screw dislocation assisted martensitic transformation of a bcc Cu precipitate in bcc Fe

Jae-Hyeok Shim, Young Whan Cho, Sang Chul Kwon, Whung Whoe Kim, and Brian D. Wirth

Appl. Phys. Lett. 90, 021906 (2007); http://dx.doi.org/10.1063/1.2429902 (3 pages) | Cited 16 times

Online Publication Date: 8 January 2007

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Molecular dynamics simulations of the interaction between a screw dislocation and a coherent bcc Cu precipitate in bcc Fe indicate that the screw dislocation stress field assists a martensitic transformation into a close-packed structure for precipitate diameters larger than 1.8 nm, resulting in a stronger obstacle to dislocation glide. The observed martensitic transformation mechanism agrees with the Nishiyama-Kajiwara [Jpn. J. Appl. Phys. 2, 478 (1963) ] model. For coherent bcc Cu precipitates with diameter larger than 2.5 nm, the screw dislocation bypass mechanism becomes Orowan looping due to the coherency loss of the precipitates during the transformation.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
64.70.K- Solid-solid transitions
64.75.-g Phase equilibria

Surface enhancement of soft-mode transformation in Ni2MnGa

G. Landmesser, U. Klemradt, R. L. Johnson, and T. R. Finlayson

Appl. Phys. Lett. 90, 021907 (2007); http://dx.doi.org/10.1063/1.2431459 (3 pages) | Cited 3 times

Online Publication Date: 9 January 2007

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Ni2MnGa exhibits both shape memory behavior, owing to a diffusionless structural transformation, and ferromagnetism, leading to magnetic-field based actuator applications. The current interest in highly miniaturized mechanical devices raises the question whether the structural phase transformations of Ni2MnGa are affected by the presence of interfaces. Thermal diffuse scattering of x-rays from the soft phonon mode which drives the transformation was analyzed for depths from 3.5 nm to 6.4 μm beneath a clean (001) surface. The authors find an enhancement of the transition temperature by about 15 K in the near-surface region, but no evidence for a change of the soft-mode polarization.
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68.35.Rh Phase transitions and critical phenomena
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
64.70.K- Solid-solid transitions
64.60.Q- Nucleation
78.70.Ck X-ray scattering

Change in electrical resistance and thermal stability of nitrogen incorporated Ge2Sb2Te5 films

YoungKuk Kim, Uk Hwang, Yong Jai Cho, H. M. Park, M.-H. Cho, Pyeong-Seok Cho, and Jong-Heun Lee

Appl. Phys. Lett. 90, 021908 (2007); http://dx.doi.org/10.1063/1.2431462 (3 pages) | Cited 16 times

Online Publication Date: 9 January 2007

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Changes in the electrical resistance of nitrogen incorporated Ge2Sb2Te5 (NGST) films were investigated as a function of nitrogen content by four-point probe and ac two-point probe methods. Some nitrogen is initially located inside the cubic structure, resulting in a significant increase in crystalline temperature and electrical resistance. As the amount of incorporated nitrogen increases, excess nitrogen accumulates in the grain boundaries, which does not contribute substantially to the increase in electrical resistance and the crystallization temperature. The supersaturated nitrogen distorts the Ge2Sb2Te5 structure, resulting in a NGST film with a structure that is different from the metastable fcc structure. X-ray absorption spectroscopy revealed that Ge–N and N2 molecular states were present in the film and gradually increased in proportion to the amount of incorporated nitrogen. Moreover, the nitrogen states were very stably maintained even during the phase transition process.
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73.61.Le Other inorganic semiconductors
68.60.Dv Thermal stability; thermal effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra

Lamb waves in plates covered by a two-dimensional phononic film

Bernard Bonello, Christine Charles, and François Ganot

Appl. Phys. Lett. 90, 021909 (2007); http://dx.doi.org/10.1063/1.2431569 (3 pages) | Cited 30 times

Online Publication Date: 9 January 2007

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The propagation of Lamb waves in silicon plates coated by a very thin two-dimensional phononic film is studied experimentally. The dispersion curves are measured using a laser ultrasonics technique. The data are then compared to the calculated dispersion curves of the uncoated silicon plate. The overall shapes of the lower-order symmetric and antisymmetric Lamb modes are not altered by the thin phononic film, except by the appearing of frequency band gaps at the edges of both the first and the second Brillouin zone. The influence of the filling fraction on the magnitude of the gaps is investigated experimentally.
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68.47.Fg Semiconductor surfaces
68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
73.20.At Surface states, band structure, electron density of states
71.20.Mq Elemental semiconductors

Interfacial viscoelasticity of thin polymer films studied by nanoscale dynamic mechanical analysis

J. Zhou and K. Komvopoulos

Appl. Phys. Lett. 90, 021910 (2007); http://dx.doi.org/10.1063/1.2429941 (3 pages) | Cited 9 times

Online Publication Date: 9 January 2007

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The interfacial viscoelastic behavior of thin polymer films deposited on silicon substrate was investigated by nanoscale dynamic mechanical analysis involving modulation of the nanoindentation load in the frequency range of 10–200 Hz. Significant differences were observed between interfacial and bulk viscoelastic properties. Both the storage modulus and the loss modulus increased with the indentation depth due to the effect of the substrate stiffness. In the low-frequency range, the interfacial viscous behavior was greatly suppressed, presumably due to changes in the molecular chain conformation at the film/substrate interface and/or dynamic confinement of the molecular chains between the indenter and the substrate. Both effects significantly restricted small-scale mobility of the main chains. In the high-frequency range, main chain rearrangement was inhibited and short-range side group relaxation was the dominant mode.
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68.35.Gy Mechanical properties; surface strains
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
62.20.M- Structural failure of materials
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Anisotropic actuation in electroclinic liquid crystal elastomers

Christopher M. Spillmann, Banahalli R. Ratna, and Jawad Naciri

Appl. Phys. Lett. 90, 021911 (2007); http://dx.doi.org/10.1063/1.2420780 (3 pages) | Cited 28 times

Online Publication Date: 9 January 2007

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The macroscopic mechanical response of a freestanding, electroclinic liquid crystal elastomer to an applied electric field is described. Contraction strains and shearing were observed upon e-field application when 60-μm-thick elastomer films were tested normal and parallel to smectic layers, respectively. The anisotropic response observed in the two orthogonal directions with respect to the smectic layers correlate calculated from mechanical studies with the induced tilt of the molecules. The electrostrictive and electroclinic coefficients agree well with the values calculated from optical tilt angle measurements.
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68.15.+e Liquid thin films
68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.10.+s Mechanical properties of liquids
61.30.Vx Polymer liquid crystals
77.65.Bn Piezoelectric and electrostrictive constants

Electron-beam induced recrystallization in amorphous apatite

In-Tae Bae, Yanwen Zhang, William J. Weber, Mikio Higuchi, and Lucille A. Giannuzzi

Appl. Phys. Lett. 90, 021912 (2007); http://dx.doi.org/10.1063/1.2430779 (3 pages) | Cited 11 times

Online Publication Date: 10 January 2007

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Electron-beam induced recrystallization of irradiation-induced amorphous Sr2Nd8(SiO4)6O2 is investigated in situ using transmission electron microscopy with 200 keV electrons at room temperature. Epitaxial recrystallization is observed from both the amorphous/crystalline interface and the surface, and the recrystallization is more pronounced with increasing electron-beam flux. Since the temperature increase induced by electron-beam irradiation is estimated to be less than 7 K and maximum energies transferred to target atoms are below the displacement energies, ionization-induced processes are considered to be the primary mechanisms for the solid-phase epitaxial recrystallization observed in the present study.
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61.80.Fe Electron and positron radiation effects
61.43.Er Other amorphous solids

Stress in tungsten carbide-diamond like carbon multilayer coatings

B. R. Pujada, F. D. Tichelaar, and G. C. A. M. Janssen

Appl. Phys. Lett. 90, 021913 (2007); http://dx.doi.org/10.1063/1.2430905 (3 pages) | Cited 7 times

Online Publication Date: 10 January 2007

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Tungsten carbide-diamond like carbon (WC-DLC) multilayer coatings have been prepared by sputter deposition from a tungsten-carbide target and periodic switching on and off of the reactive acetylene gas flow. The stress in the resulting WC-DLC multilayers has been studied by substrate curvature. Periodicity and microstructure have been studied by transmission electron microscopy. It has been observed that compressive stress in the multilayers decreases when the bilayer thickness is reduced. Results show a minimum compressive stress for bilayer thickness of around 5 nm. This behavior is discussed in terms of interface stress and mixing between layers.
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81.05.U- Carbon/carbon-based materials
68.65.Ac Multilayers
68.37.Lp Transmission electron microscopy (TEM)
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