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12 Jan 2009

Volume 94, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 94, 022101 (2009); http://dx.doi.org/10.1063/1.3065067 (3 pages)

Hong Li and Qing Zhang
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Transverse surface waves in a functionally graded piezoelectric substrate coated with a finite-thickness metal waveguide layer

Zheng-Hua Qian, Feng Jin, Tian-Jian Lu, and Kikuo Kishimoto

Appl. Phys. Lett. 94, 023501 (2009); http://dx.doi.org/10.1063/1.3070540 (3 pages) | Cited 5 times

Online Publication Date: 13 January 2009

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An analytical study on transverse surface waves propagating in a functionally graded piezoelectric substrate carrying a metal layer of finite thickness was carried out. Dispersion relations for the existence of the waves were obtained and the effects of material gradient on wave propagation were quantified. Numerical examples show that the presence of the material gradient affects significantly the fundamental mode but has only negligible effects on the higher order modes. Depending on whether the surface wave velocity is smaller or greater than the bulk shear wave velocity in the metal layer, three different types of the dispersion behavior are discussed.
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68.35.Iv Acoustical properties
43.35.Pt Surface waves in solids and liquids
62.65.+k Acoustical properties of solids

Miniature atomic magnetometer integrated with flux concentrators

W. Clark Griffith, Ricardo Jimenez-Martinez, Vishal Shah, Svenja Knappe, and John Kitching

Appl. Phys. Lett. 94, 023502 (2009); http://dx.doi.org/10.1063/1.3056152 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2009

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High permeability magnetic flux concentrators are used to enhance the sensitivity of an atomic magnetometer operating in the spin-exchange relaxation-free regime. The magnetometer uses a millimeter scale 87Rb vapor cell and either mu-metal or Mn–Zn ferrite flux concentrators. The measured sensitivity gives excellent agreement with calculations of thermal noise from the concentrator material. The mu-metal concentrators allow a sensitivity of 50 fT Hz−1/2, limited by thermal current magnetic noise. The ferrite concentrators are limited by thermal magnetization noise at low frequencies, and reach a sensitivity of 10 fT Hz−1/2 for frequencies above 125 Hz.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
07.55.Ge Magnetometers for magnetic field measurements

Valve-based flow focusing for drop formation

Adam R. Abate, Mark B. Romanowsky, Jeremy J. Agresti, and David A. Weitz

Appl. Phys. Lett. 94, 023503 (2009); http://dx.doi.org/10.1063/1.3067862 (3 pages) | Cited 23 times

Online Publication Date: 14 January 2009

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Microfluidic devices can produce highly monodisperse drops at kilohertz rates using flow-focus drop formation. We use single-layer membrane valves to control, in real time, the dimensions of the flow-focus drop makers. This allows drop size and frequency to be controlled in real time and without adjusting flow rates.
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47.55.db Drop and bubble formation
47.61.-k Micro- and nano- scale flow phenomena

Normal and reversed tunable magnetoresistance in a NiOx/p-doped silicon diode

Oscar Céspedes and Michel Viret

Appl. Phys. Lett. 94, 023504 (2009); http://dx.doi.org/10.1063/1.3070519 (3 pages)

Online Publication Date: 14 January 2009

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Nonstoichiometric NiOx thin films fabricated by heating in air nickel thin films sputtered on p-doped silicon substrates show a superparamagnetic magnetization and frustrated magnetism with transition temperatures of 200–300 K. Transport measurements across the magnetic/semiconductor bilayer have a rectifying I-V and voltage dependent magnetoresistance, with maximum ratios at 77 K and 2 T of 70% and −17%. The effect is explained in terms of field dependent polarization in granular NiOx and highly efficient spin filtering/injection.
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75.47.Pq Other materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
85.30.Kk Junction diodes
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Strongly localized acoustic surface waves propagating along a V-groove

Fengming Liu, Shasha Peng, Han Jia, Manzhu Ke, and Zhengyou Liu

Appl. Phys. Lett. 94, 023505 (2009); http://dx.doi.org/10.1063/1.3072346 (3 pages) | Cited 3 times

Online Publication Date: 14 January 2009

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Strongly localized acoustic surface waves propagating along an immersed V-groove are numerically analyzed and experimentally demonstrated. We analyze the dispersion relation and the distribution of displacements of such groove waves using the compact two-dimensional finite-difference time-domain method. It is shown that they are dispersionless and strongly confined in the lateral cross section. The variations in their velocities as a function of the apex angle are also presented. Furthermore, we implement experimental observation by the near-field detection of these predicted waves in the 30° polymethyl methacrylate groove. The experimental measurements of the wave velocities agree very well with the numerical results.
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43.35.Pt Surface waves in solids and liquids
62.60.+v Acoustical properties of liquids
02.70.Bf Finite-difference methods
43.20.Mv Waveguides, wave propagation in tubes and ducts

GaSb-based, 2.2 μm type-I laser fabricated on GaAs substrate operating continuous wave at room temperature

J. B. Rodriguez, L. Cerutti, and E. Tournié

Appl. Phys. Lett. 94, 023506 (2009); http://dx.doi.org/10.1063/1.3072596 (2 pages) | Cited 5 times

Online Publication Date: 14 January 2009

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We report on a Sb-based type-I laser grown on GaAs substrate, emitting continuous wave at room temperature around 2.2 μm. The device was grown using solid-source molecular beam epitaxy and comprised two GaInAsSb quantum wells embedded in AlGaAsSb barriers. Despite the large lattice mismatch, a good crystalline quality was obtained, and processed devices operated continuous wave up to 50 °C with threshold current densities in the range of 1.5–2.2 kA/cm2. An optical output power of 3.7 mW was obtained at 20 °C.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.82.Cr Fabrication techniques; lithography, pattern transfer

Ferroelectric tunable balanced right- and left-handed transmission lines

Aurélien Marteau, Gabriel Velu, Gregory Houzet, Ludovic Burgnies, Eric Lheurette, Jean Claude Carru, and Didier Lippens

Appl. Phys. Lett. 94, 023507 (2009); http://dx.doi.org/10.1063/1.3068495 (3 pages) | Cited 4 times

Online Publication Date: 15 January 2009

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The tuning of the dispersion characteristics of a balanced composite right- and left-handed transmission lines is demonstrated at centimeter and millimeter wavelengths. To this aim, coplanar waveguides, periodically loaded by interdigitated capacitances and stublike inductances, were fabricated onto a Ba0.5Sr0.5TiO3 ferroelectric thin film. The scattering parameter measurements show that the lines are left handed from 8 to 18 GHz and right handed above. The results are interpreted by the retrieval of the effective permittivity and permeability, which exhibit Drude-like dispersion characteristics with a magnetic plasma frequency, which can be tuned via the voltage-controlled permittivity variation in the BST thin film.
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84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Dependence of memory margin of Cap-less memory cells on top Si thickness

Ki-Ryoung Choi, Choong-Hyun Lee, Seong-Je Kim, Hirofumi Enomoto, Tae-Hun Shim, Won-Ju Cho, and Jea-Gun Park

Appl. Phys. Lett. 94, 023508 (2009); http://dx.doi.org/10.1063/1.3072600 (3 pages) | Cited 4 times

Online Publication Date: 16 January 2009

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We investigated the dependence of Cap-less memory on top of silicon with a thickness between 15.5 and 72.3 nm. It was confirmed that the memory margin depends on the impact ionization rate associated with the increased conduction current density and the decreased lateral electric field as the top silicon thickness increases. In particular, we observed that the maximum memory margin is 61 μA at a 45 nm top silicon thickness, where the impact ionization rate is maximized. Consequently, we obtained the optimal top silicon thickness of 45 nm for Cap-less memory cells operating in fully depleted silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices
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