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7 May 2007

Volume 90, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 193501 (2007); http://dx.doi.org/10.1063/1.2737344 (3 pages)

Peter Modregger, Daniel Lübbert, Peter Schäfer, and Rolf Köhler
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2-phosphor-converted white light-emitting diodes using oxynitride/nitride phosphors

Rong-Jun Xie, Naoto Hirosaki, Naoki Kimura, Ken Sakuma, and Mamoru Mitomo

Appl. Phys. Lett. 90, 191101 (2007); http://dx.doi.org/10.1063/1.2737375 (3 pages) | Cited 129 times

Online Publication Date: 7 May 2007

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Green α-sialon:Yb2+ and red Sr2Si5N8:Eu2+ oxynitride/nitride phosphors have been demonstrated as potential downconversion luminescent materials for white light-emitting diodes (LEDs). In this letter, the authors attempt to fabricate white LEDs by combining α-sialon:Yb2+ and Sr2Si5N8:Eu2+ with a blue LED die and report their optical properties. These two phosphors lend themselves for use in 2-phosphor-converted white LEDs with promising properties: a wide range of tunable correlated color temperature (2700–6700 K), acceptable color rendering index (82–83), and luminous efficacy (17–23 lm/W). These LEDs are acceptable for general lighting.
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85.60.Jb Light-emitting devices
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.72.-g Optical sources and standards

Midinfrared doping-tunable extraordinary transmission from sub-wavelength Gratings

D. Wasserman, E. A. Shaner, and J. G. Cederberg

Appl. Phys. Lett. 90, 191102 (2007); http://dx.doi.org/10.1063/1.2737138 (3 pages) | Cited 15 times

Online Publication Date: 7 May 2007

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The authors demonstrate doping-tunable extraordinary transmission from subwavelength apertures in a periodic two-dimensional metallic grating deposited upon n-doped GaAs. By varying the doping of the underlying GaAs epilayer, they demonstrate wavelength tunability of ∼ 23 cm−1 or approximately 0.15 μm. The authors have achieved transmission peaks as narrow as 18 cm−1 with such gratings, which suggests that devices based on midinfrared extraordinary transmission gratings could be used in external cavity structures for quantum cascade lasers, or as tunable filters or modulators for midinfrared applications.
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42.79.Dj Gratings

Conductivity-dependency-free in-plane poling for Mach-Zehnder modulator with highly conductive electro-optic polymer

Reem Song, Andrew Yick, and William H. Steier

Appl. Phys. Lett. 90, 191103 (2007); http://dx.doi.org/10.1063/1.2737139 (3 pages) | Cited 7 times

Online Publication Date: 7 May 2007

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This letter presents the in-plane poling in electro-optic (EO) polymer modulators with conductivity dependency of core and claddings eliminated. A Mach-Zehnder (MZ) modulator with a highly conductive EO polymer, AJLS102/APC, is realized and poled by the in-plane coplanar waveguide poling electrode. Vπ of 7.7 V in a single-arm poled MZ (3.8 V for push-pull operation) is achieved and the evaluated r33 is 65 pm/V. Combined with the r33’s of the previously measured single layers and MZ modulators using two other EO polymers, this experiment proves that the r33 proportional to the single layer r33 can be achieved in an in-plane MZ device regardless of the material conductivities.
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42.79.Hp Optical processors, correlators, and modulators
42.82.Gw Other integrated-optical elements and systems

Two-photon absorption and Kerr coefficients of silicon for 850–2200 nm

Alan D. Bristow, Nir Rotenberg, and Henry M. van Driel

Appl. Phys. Lett. 90, 191104 (2007); http://dx.doi.org/10.1063/1.2737359 (3 pages) | Cited 76 times

Online Publication Date: 7 May 2007

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The degenerate two-photon absorption coefficient β and Kerr nonlinearity n2 are measured for bulk Si at 300 K using 200 fs pulses with carrier wavelength of 850<λ<2200 nm for which indirect gap transitions occur. With a broad peak near the indirect gap and maximum value of 2±0.5 cm/GW, the dispersion of β compares favorably with theoretical calculations of Garcia and Kalyanaraman [J. Phys. B 39, 2737 (2006) ]. Within our wavelength range, n2 varies by a factor of 4 with a peak value of 1.2×10−13 cm2/W at λ = 1800 nm.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.47.-p Spectroscopy of solid state dynamics
78.30.Am Elemental semiconductors and insulators

Single glass substrate liquid crystal device using electric field-enforced phase separation and photoinduced polymerization

Hongwen Ren, Shin-Tson Wu, and Yi-Hsin Lin

Appl. Phys. Lett. 90, 191105 (2007); http://dx.doi.org/10.1063/1.2737366 (3 pages) | Cited 7 times

Online Publication Date: 7 May 2007

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An in-plane switching liquid crystal (LC) cell using a glass substrate and a photoinduced polymer layer is demonstrated. The fabrication process is based on the electrodynamics of dielectric fluids. When the fringing field is present, the LC molecules tend to aggregate in the strong electric field regions while the monomers diffuse to the weak field regions. After photopolymerization, the LC molecules are confined by a thin polymer layer and polymer walls which define the cell gap. This approach enables single-substrate large panel display devices to be fabricated.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Ytterbium and chromium doped composite Y3Al5O12 ceramics self-Q-switched laser

Jun Dong, Akira Shirakawa, Ken-ichi Ueda, Hideki Yagi, Takagimi Yanagitani, and Alexander A. Kaminskii

Appl. Phys. Lett. 90, 191106 (2007); http://dx.doi.org/10.1063/1.2737361 (3 pages) | Cited 8 times

Online Publication Date: 7 May 2007

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Composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramics were fabricated by using vacuum sintering technique and nanocrystalline technology. Self-Q-switched composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramic lasers with pulse energy of 125 μJ and peak power of over 105 kW at repetition rate of 3.8 kHz have been demonstrated. Nearly diffraction-limited beam quality with M2 less than 1.35 was achieved in this composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramic self-Q-switched lasers.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Midinfrared, optically pumped, unstable resonator lasers

A. P. Ongstad, R. Kaspi, G. C. Dente, M. L. Tilton, and J. Chavez

Appl. Phys. Lett. 90, 191107 (2007); http://dx.doi.org/10.1063/1.2737426 (3 pages) | Cited 3 times

Online Publication Date: 7 May 2007

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The authors describe high-brightness, broad area midinfrared semiconductor lasers. These devices were fabricated in the authors’ laboratory using a commercial solid-source molecular beam epitaxial system. The laser structures incorporated 14 type-II quantum wells embedded in thick waveguide/absorber regions composed of In0.2Ga0.8As0.18Sb0.82. The optically pumped devices achieved higher brightness operation as unstable resonators. Each unstable resonator was realized by polishing a diverging cylindrical mirror at one of the facets. For an unstable resonator semiconductor laser operating at ∼ 4.6 μm, near 84 K, and at a peak power of 6.7 W, the device was observed to be nearly diffraction limited at 25 times threshold. In comparison, a standard Fabry-Pérot laser was observed to be many times diffraction limited when operated under similar conditions.
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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
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Dispersive phase response in optical waveguide-resonator system

Y.-S. Choi, M. Davanço, K. H. Lee, C.-F. Wang, J. Mack, D. Blumenthal, and E. L. Hu

Appl. Phys. Lett. 90, 191108 (2007); http://dx.doi.org/10.1063/1.2737913 (3 pages) | Cited 4 times

Online Publication Date: 8 May 2007

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The authors report on the dispersive phase response of light traversing a tapered optical fiber coupled to the whispering-gallery modes (WGMs) of GaAs microdisks with cavity Q factors of up to 3×105 at wavelengths of around 1.5 μm. The group delay of the coupled light, that is, a derivative of the phase shift, becomes positive (+10 ps) and then negative (−55 ps) near the high-Q WGM resonances, as compared with a reference group delay without evanescent-wave coupling. The chromatic dispersion becomes as high as ±8 ns/nm near WGM wavelengths.
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42.81.Dp Propagation, scattering, and losses; solitons
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Nonlocal effects in effective-medium response of nanolayered metamaterials

Justin Elser, Viktor A. Podolskiy, Ildar Salakhutdinov, and Ivan Avrutsky

Appl. Phys. Lett. 90, 191109 (2007); http://dx.doi.org/10.1063/1.2737935 (3 pages) | Cited 39 times

Online Publication Date: 8 May 2007

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The authors analyze electromagnetic modes in multilayered nanocomposites and demonstrate that the response of a majority of realistic layered structures is strongly affected by the nonlocal effects originating from strong field oscillations across the system, and is not described by conventional effective-medium theories. They develop the analytical description of the relevant phenomena and confirm their results with numerical solutions of Maxwell equations. Finally, the authors use the developed formalism to demonstrate that multilayered plasmonic nanostructures support high-index volume modes, confined to deep subwavelength areas, opening a wide class of applications in nanoscale light management.
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42.70.-a Optical materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.68.+m Optical properties of surfaces

High-intensity C-shaped nanoaperture vertical-cavity surface-emitting laser with controlled polarization

Zhilong Rao, Joseph A. Matteo, Lambertus Hesselink, and James S. Harris

Appl. Phys. Lett. 90, 191110 (2007); http://dx.doi.org/10.1063/1.2737938 (3 pages) | Cited 10 times

Online Publication Date: 8 May 2007

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The authors designed and demonstrated a C-shaped nanoaperture (C aperture) vertical-cavity surface-emitting laser (VCSEL) with a maximum far-field power of 157 μW coming from a 70 nm C aperture. Simulation shows that the near-field full width at half maximum spot size at 30 nm away from the C aperture is 94×108 nm2 in X and Y directions. The authors estimate the peak near-field intensity from the C-aperture VCSEL to be as high as 19 mW/μm2. This high intensity and small spot size are promising for realizing near-field applications such as near-field imaging and ultradense near-field optical data storage.
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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

Determination of diffusion lengths for intermixed quaternary quantum well with polarized edge-emitting photoluminescence

C. D. Xu, T. Mei, and J. R. Dong

Appl. Phys. Lett. 90, 191111 (2007); http://dx.doi.org/10.1063/1.2737125 (3 pages) | Cited 4 times

Online Publication Date: 8 May 2007

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Diffusion lengths of the group III and V sublattices are quantitatively determined for intermixing of a quaternary InGaAs/InP quantum well using polarized edge-emitting photoluminescence. Diffusion-length loci are plotted on a contour diagram of wavelength shifts of electron-heavy-hole and electron-light-hole transitions and illustrate the time progression of intermixing clearly. The plasma-enhanced intermixing effect is investigated using this technique, showing the difference of intermixing development in the early and the late stages. It is seen that the calculated diffusion-length ratio may change with the annealing duration.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
78.67.De Quantum wells
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Periodic versus aperiodic: Enhancing the sensitivity of porous silicon based optical sensors

Luigi Moretti, Ilaria Rea, Luca De Stefano, and Ivo Rendina

Appl. Phys. Lett. 90, 191112 (2007); http://dx.doi.org/10.1063/1.2737391 (3 pages) | Cited 7 times

Online Publication Date: 8 May 2007

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The authors have compared the sensitivities of resonant optical biochemical sensors, based on both periodic and aperiodic porous silicon structures, such as the Bragg and the Thue-Morse multilayer. The shifts of the reflectivity spectra of these devices on exposure to several chemical compounds have been measured: the aperiodic multilayer is more sensitive than the periodic one. Adopting a simple theoretical model of the optical response of devices, they inferred that the aperiodic structure provide a higher filling capability with respect to the periodic one, due to the lower number of interfaces.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
87.80.-y Biophysical techniques (research methods)

980 nm Bi3Fe5O12/Sm3Ga5O12 magneto-optical photonic crystal

A. M. Grishin, S. I. Khartsev, and H. Kawasaki

Appl. Phys. Lett. 90, 191113 (2007); http://dx.doi.org/10.1063/1.2737933 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2007

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Heteroepitaxial all-garnet magneto-optical photonic crystal (MOPC) was fabricated to enhance Faraday rotation at 980 nm. MOPC was composed of alternating MO-active Bi3Fe5O12 and transparent Sm3Ga5O12 quarter-wavelength layers grown by rf-magnetron sputtering on Ca,Mg,Zr:Gd3Ga5O12(111) single crystal substrate. High MO performance at the resonance wavelength λ = 980 nm, specific Faraday rotation θF = −7.3°/μm, absorption coefficient α = 3350 cm−1, and MO figure of merit Q = 2∣θF∣/α = 43.6° demonstrates feasibility to use bismuth iron garnet MOPCs for application in pump laser diodes, optical amplifiers, modulators, and sensors.
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42.70.Qs Photonic bandgap materials
75.50.Gg Ferrimagnetics
78.20.Ls Magneto-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Influence of grain size on ultrafast carrier dynamics in thin nanocrystalline silicon films

Emmanouil Lioudakis, Andreas Othonos, A. G. Nassiopoulou, Ch. B. Lioutas, and N. Frangis

Appl. Phys. Lett. 90, 191114 (2007); http://dx.doi.org/10.1063/1.2738383 (3 pages) | Cited 11 times

Online Publication Date: 9 May 2007

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The ultrafast carrier dynamics in thin nanocrystalline silicon films (10 and 20 nm thick) on quartz over a broad spectral range using optical pumping at a moderate fluence of 2.5 mJ/cm2 were studied. The films were composed of randomly oriented silicon nanocrystals of various sizes and shapes. The authors probed a fast and a slow relaxation mechanism. The slow decay ( ∼ 300 ps) was attributed to bulk nanocrystal states similar to those of bulk silicon, while the faster one ( ∼ 3 ps) was attributed to surface states at grain boundaries, more dominant in the smaller nanocrystals due to their larger surface/volume ratio.
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78.66.Db Elemental semiconductors and insulators
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.47.-p Spectroscopy of solid state dynamics
68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states

Terahertz quantum cascade lasers with large wall-plug efficiency

Miriam S. Vitiello, Gaetano Scamarcio, Vincenzo Spagnolo, Sukhdeep S. Dhillon, and Carlo Sirtori

Appl. Phys. Lett. 90, 191115 (2007); http://dx.doi.org/10.1063/1.2737129 (3 pages) | Cited 23 times

Online Publication Date: 9 May 2007

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Improved optical power performance of bound-to-continuum quantum-cascade lasers operating at 2.83 THz is reported. Peak optical powers of 100 mW at 4 K and power conversion-efficiencies as high as ηw = (5.5±0.4)% in continuous wave at 40 K were measured. The ηw values were assessed via an experimental method based on the analysis of the local lattice temperature as extracted by microprobe photoluminescence versus electrical power. From the measured ηw values they extracted a slope efficiency value 0.41±0.11 W/A.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Superconducting single photon detectors made by local oxidation with an atomic force microscope

C. Delacour, J. Claudon, J.-Ph. Poizat, B. Pannetier, V. Bouchiat, R. Espiau de Lamaestre, J.-C. Villegier, M. Tarkhov, A. Korneev, B. Voronov, and G. Gol’tsman

Appl. Phys. Lett. 90, 191116 (2007); http://dx.doi.org/10.1063/1.2738195 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2007

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The authors present a fabrication technique of superconducting single photon detectors made by local oxidation of niobium nitride ultrathin films. Narrow superconducting meander lines are obtained by direct writing of insulating niobium oxynitride lines through the films using voltage-biased tip of an atomic force microscope. Due to the 30 nm resolution of the lithographic technique, the filling factor of the meander line can be made substantially higher than detector of similar geometry made by electron beam lithography, thus leading to increased quantum efficiency. Single photon detection regime of these devices is demonstrated at 4.2 K.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Characterization and optoelectronic properties of p-type N-doped CuAlO2 films

Ruei-Sung Yu, Shih-Chang Liang, Chih-Jung Lu, Du-Cheng Tasi, and Fuh-Sheng Shieu

Appl. Phys. Lett. 90, 191117 (2007); http://dx.doi.org/10.1063/1.2679233 (3 pages) | Cited 11 times

Online Publication Date: 10 May 2007

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This letter reports a technique for increasing the carrier concentration and the conductivity of the p-type CuAlO2 through doping the material with nitrogen. The x-ray photoelectron spectroscopy and the optical band gap analyses suggested that the nitrogen atoms occupying the interstitial sites of the delafossite structure provided the p-type CuAlO2 with an impurity energy level in the energy gap. It was also found that the N-doped CuAlO2 film had its optimum conduction properties when the dopant level reached 1.1 at. %. Here, the carrier concentration was raised from 4.81×1016 in the undoped film to 2.13×1017 cm−3 in the doped film, and the corresponding film’s conductivity was increased from 3.8×10−2 to 5.4×10−2 (Ω cm)−1, as compared with the undoped CuAlO2 film.
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73.61.Le Other inorganic semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.55.Ht Other nonmetals

Electrically switchable computer-generated hologram recorded in polymer-dispersed liquid crystals

Y. J. Liu and X. W. Sun

Appl. Phys. Lett. 90, 191118 (2007); http://dx.doi.org/10.1063/1.2736270 (3 pages) | Cited 10 times

Online Publication Date: 10 May 2007

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A computer-generated hologram (CGH) designed using the iterative Fourier transform algorithm was recorded in a cell filled with a polymer-dispersed liquid crystal material under a collimated He–Ne laser beam operating at 543 nm. Due to the photopolymerization induced phase separation, an index modulation was formed between the polymer-rich and liquid-crystal-rich regions. The results showed a good reconstructed image. With a suitable voltage applied, the reconstructed image can be erased due to the index change between the polymer and liquid crystal. Such electrically switchable CGH is potentially useful in information storage and adaptive optical elements.
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42.40.Jv Computer-generated holograms
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
42.79.Vb Optical storage systems, optical disks
42.30.Wb Image reconstruction; tomography
42.30.Kq Fourier optics
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Stability and tunability of the gyrotron backward-wave oscillator

T. H. Chang, C. T. Fan, K. F. Pao, K. R. Chu, and S. H. Chen

Appl. Phys. Lett. 90, 191501 (2007); http://dx.doi.org/10.1063/1.2737135 (3 pages) | Cited 11 times

Online Publication Date: 7 May 2007

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To fulfill the broadband tunability of the gyrotron backward-wave oscillator (gyro-BWO), stability issues are studied and displayed in the form of stability maps. These maps serve as a guide for the identification and optimization of stable windows for broadband tuning. A Ka-band gyro-BWO experiment was conducted accordingly. In the case of a short interaction length, stable and smooth tunability of 1.3 GHz was demonstrated with a peak interaction efficiency of 29.8%. In the longer length case, piecewise-stable tuning curves were obtained, as predicted in theory.
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84.30.Ng Oscillators, pulse generators, and function generators
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)

On the hysteresis in E to H and H to E transitions and the multistep ionization in inductively coupled plasma

Min-Hyong Lee, Kyeong Hyo Lee, Dong-Seok Hyun, and Chin-Wook Chung

Appl. Phys. Lett. 90, 191502 (2007); http://dx.doi.org/10.1063/1.2734501 (3 pages) | Cited 14 times

Online Publication Date: 9 May 2007

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Plasma densities, E to H and H to E transition coil currents, and electron energy distribution functions (EEDFs) are measured at various argon pressures in an inductively coupled plasma. The measured plasma density versus coil current shows that the hysteresis during the E-H transition is clearly observed only when the pressure is sufficiently high. At low gas pressures the hysteresis is not obvious. The measured EEDFs show that when the hysteresis is obvious (high pressures), electrons whose energy is not sufficient for excitation or ionization of the ground state atom are strongly depleted in the H mode. This depletion may be caused by multistep ionization. However, for the case where the hysteresis is not obvious (low pressures), the depletion due to multistep ionization is also not present. These experimental results show that the multistep ionization is a dominant factor in the E-H transition hysteresis.
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52.50.Dg Plasma sources
52.25.Jm Ionization of plasmas
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements

Efficient extreme ultraviolet plasma source generated by a CO2 laser and a liquid xenon microjet target

Yoshifumi Ueno, Tatsuya Ariga, George Soumagne, Takeshi Higashiguchi, Shoichi Kubodera, Igor Pogorelsky, Igor Pavlishin, Daniil Stolyarov, Marcus Babzien, Karl Kusche, and Vitaly Yakimenko

Appl. Phys. Lett. 90, 191503 (2007); http://dx.doi.org/10.1063/1.2738190 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2007

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We demonstrated efficacy of a CO2-laser-produced xenon plasma in the extreme ultraviolet (EUV) spectral region at 13.5 nm at variable laser pulse widths between 200 ps and 25 ns. The plasma target was a 30 μm liquid xenon microjet. To ensure the optimum coupling of CO2 laser energy with the plasma, they applied a prepulse yttrium aluminum garnet laser. The authors measured the conversion efficiency (CE) of the 13.5 nm EUV emission for different pulse widths of the CO2 laser. A maximum CE of 0.6% was obtained for a CO2 laser pulse width of 25 ns at an intensity of 5×1010 W/cm2.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.50.Dg Plasma sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Soft-mold-induced self-construction of polymer patterns under microwave irradiation

Fu-Hsiang Ko, Chia-Tien Wu, Mei-Fen Chen, Jem-Kun Chen, and Tieh-Chi Chu

Appl. Phys. Lett. 90, 191901 (2007); http://dx.doi.org/10.1063/1.2737364 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2007

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In this study, the authors used a soft-mold-induced self-construction method to fabricate three-dimensional patterns under microwave irradiation for 1 min. The authors estimated the actual pattern growth temperature using a fluorescence probe technique. The temperature at which pattern growth originated was, by necessity, higher than the glass transition temperature of the novolak resist. Electrostatic forces and surface tension effects under the electromagnetic field contributed significantly to the pattern growth, and the use of an antisticking agent allowed easy demolding.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining
78.60.-b Other luminescence and radiative recombination
68.03.Cd Surface tension and related phenomena

Galvanic corrosion induced degredation of tensile properties in micromachined polycrystalline silicon

David C. Miller, Brad L. Boyce, Ken Gall, and Conrad R. Stoldt

Appl. Phys. Lett. 90, 191902 (2007); http://dx.doi.org/10.1063/1.2737370 (3 pages) | Cited 4 times

Online Publication Date: 7 May 2007

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Immersion of polycrystalline silicon in hydrofluoric acid-based solutions is often utilized in microsystem fabrication to liberate mechanical structures. The authors demonstrate, using microfabricated tensile specimens, that such etching can cause a catastrophic reduction in tensile strength and elastic modulus in silicon galvanically coupled to a metallic layer, such as commonly used gold. Galvanically corroded silicon exhibits grain-boundary attack leading to intergranular fracture and/or generalized material removal. The severity of damage and corresponding losses in strength and modulus depend on etch duration and etch chemistry. In contrast, without a metallic layer, uncorroded silicon fails transgranularly and independent of etch duration or chemistry.
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81.65.Cf Surface cleaning, etching, patterning
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
61.72.Mm Grain and twin boundaries

Mechanical strengths of silicon nitrides studied by ab initio calculations

R. F. Zhang, S. H. Sheng, and S. Veprek

Appl. Phys. Lett. 90, 191903 (2007); http://dx.doi.org/10.1063/1.2737376 (3 pages) | Cited 27 times

Online Publication Date: 7 May 2007

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The stress-strain relationships under tensile and shear loads are calculated for hcp(β)-Si3N4 and fcc(NaCl)-SiN by means of ab initio density functional theory. The ideal shear strengths for fcc-SiN are much lower than those for hcp-Si3N4. This is in agreement with experiments which show that the interfacial fcc-SiN can strengthen the TiN/SiN heterostructures only when its thickness is about 1–2 ML. Based on the calculated electronic density of states, the physical origin of the mechanical strengths is addressed.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

Metamaterials with dendriticlike structure at infrared frequencies

Hui Liu and Xiaopeng Zhao

Appl. Phys. Lett. 90, 191904 (2007); http://dx.doi.org/10.1063/1.2737382 (3 pages) | Cited 8 times

Online Publication Date: 7 May 2007

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The authors present a planar medium composed of the copper dendriticlike structure and silver film at infrared frequencies. The dendriticlike copper, which has quasiperiodic hexagonal cells, and silver film were prepared using the electrochemical deposition method. It is shown that the transmission spectra of the copper dendriticlike structure and the planar medium appear to have a stop band and a passband in the range of 1.28–2.5 μm. A clear image is also observed at the wavelength near 1.92 μm, as expected, with our lens composed of copper dendritic cells and silver film.
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42.70.-a Optical materials
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