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30 May 2011

Volume 98, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 223101 (2011); http://dx.doi.org/10.1063/1.3595266 (3 pages)

Takahiro Ohori, Yasuhide Ohno, Kenzo Maehashi, Koichi Inoue, Yutaka Hayashi, and Kazuhiko Matsumoto
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Quantized characteristics in carbon nanotube-based single-hole memory with a floating nanodot gate

Takahiro Ohori, Yasuhide Ohno, Kenzo Maehashi, Koichi Inoue, Yutaka Hayashi, and Kazuhiko Matsumoto

Appl. Phys. Lett. 98, 223101 (2011); http://dx.doi.org/10.1063/1.3595266 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2011

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We have fabricated floating-gate carbon nanotube field-effect transistors (CNTFETs), in which Au floating dots are expected to act as charge storage nodes. The fabricated floating-gate CNTFETs clearly exhibited the memory effect, in addition to single-hole memory operation. A staircase relation between the gate threshold voltage and the charging voltage was obtained. Quantized shifts in the gate threshold voltage as a function of charging time and retention time were also observed. The quantized characteristics are attributed to the effect of single-hole charging in the Au floating dot.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Electric field induced crystallization in phase-change materials for memory applications

Krisztian Kohary and C. David Wright

Appl. Phys. Lett. 98, 223102 (2011); http://dx.doi.org/10.1063/1.3595408 (3 pages) | Cited 6 times

Online Publication Date: 31 May 2011

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Emerging electrical memory technologies based on phase-change materials capitalize on a fast amorphous-to-crystalline transition. Recent evidence from measurements of relaxation oscillations and switching statistics in phase-change memory devices indicates the possibility that electric field induced crystal nucleation plays a dominant role in defining the characteristic electrical switching behavior. Here we present a detailed kinetics study of crystallization in the presence of an electric field for the phase-change material Ge2Sb2Te5. We derive quantitative crystallization maps to show the effects of both temperature and electric field on crystallization and we identify field ranges and parameter values where the electric field effects might play a significant role.
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84.30.Sk Pulse and digital circuits
64.60.qj Studies of nucleation in specific substances
72.60.+g Mixed conductivity and conductivity transitions

Self-heating in piezoresistive cantilevers

Joseph C. Doll, Elise A. Corbin, William P. King, and Beth L. Pruitt

Appl. Phys. Lett. 98, 223103 (2011); http://dx.doi.org/10.1063/1.3595485 (3 pages) | Cited 3 times

Online Publication Date: 31 May 2011

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We report experiments and models of self-heating in piezoresistive microcantilevers that show how cantilever measurement resolution depends on the thermal properties of the surrounding fluid. The predicted cantilever temperature rise from a finite difference model is compared with detailed temperature measurements on fabricated devices. Increasing the fluid thermal conductivity allows for lower temperature operation for a given power dissipation, leading to lower force and displacement noise. The force noise in air is 76% greater than in water for the same increase in piezoresistor temperature.
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85.30.De Semiconductor-device characterization, design, and modeling
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
02.70.Bf Finite-difference methods
07.10.Cm Micromechanical devices and systems
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Surfactant-mediated Si quantum dot formation on Ge(001)

D. Pachinger, H. Groiss, M. Teuchtmann, G. Hesser, and F. Schäffler

Appl. Phys. Lett. 98, 223104 (2011); http://dx.doi.org/10.1063/1.3595486 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2011

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Stranski–Krastanow growth, modified by the presence of submonolayer coverages of carbon or antimony, is investigated for tensile strained silicon epilayers on Ge(001) substrates. We find a reduction in the wetting layer thickness from >10 monolayers without surfactant, to 7.5 and 4.5 monolayers, respectively, with Sb and C predeposition. Very small islands with an aspect ratio of 0.05 and a narrow size distribution were found for Sb-mediated growth. For both adatom species the wetting layer is free of dislocations, whereas the Si islands are almost completely strain relaxed, mainly via sessile 90° misfit dislocations. We show that early dislocation nucleation is an inherent property of a (001) oriented cubic heterosystem under tensile strain.
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81.05.Cy Elemental semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Electrochemically grown metallic nanocomb structures on nanoporous alumina templates

Savas Kaya and Erdem Atar

Appl. Phys. Lett. 98, 223105 (2011); http://dx.doi.org/10.1063/1.3596432 (3 pages)

Online Publication Date: 31 May 2011

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Electrochemical growth of metallic nanocomb structures on anodized alumina templates is described. Nanocombs originate from the orderly growth and merger of very thin (d = 15∓5 nm) metallic nanowires which do not completely fill much larger pores (d ∼ 100 nm) in the alumina template (t ≤ 3 μm). Instead, the nanowires prefer growing along the inner corners of the hexagonal pores, coalescing into a highly ordered structure as they emerge, resulting a metallic form reminiscent of the topology of the original template. We disclose here the typical processing conditions and the microstructure of this previously unknown material as observed with a scanning electron microscope (SEM) and energy dispersive x-ray (EDX) spectroscopy. It is shown that Au nanocombs have an anomalous EDX spectra and can emit electrons at a field of ∼ 1 kV/cm.
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81.07.Gf Nanowires
81.05.Bx Metals, semimetals, and alloys
81.16.Be Chemical synthesis methods
82.45.Qr Electrodeposition and electrodissolution
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Improving near-field confinement of a bowtie aperture using surface plasmon polaritons

Pornsak Srisungsitthisunti, Okan K. Ersoy, and Xianfan Xu

Appl. Phys. Lett. 98, 223106 (2011); http://dx.doi.org/10.1063/1.3595412 (3 pages) | Cited 3 times

Online Publication Date: 1 June 2011

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Bowtie aperture is known to produce subdiffraction-limited optical spot with high intensity. In this work, we investigate integrating a bowtie aperture with circular grooves to reduce the divergence of the near-field produced by the bowtie aperture. Numerical results indicate that surface waves reflected from circular grooves improve the field confinement of a bowtie aperture along the polarization axis. These circular grooves with period near half the wavelength of surface plasmon polaritons reduce the spot size by as much as 40% at distances between 20 and 100 nm from the surface and create a more symmetrical optical spot.
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78.68.+m Optical properties of surfaces
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Electronic properties of hydrogenated silicene and germanene

M. Houssa, E. Scalise, K. Sankaran, G. Pourtois, V. V. Afanas’ev, and A. Stesmans

Appl. Phys. Lett. 98, 223107 (2011); http://dx.doi.org/10.1063/1.3595682 (3 pages) | Cited 17 times

Online Publication Date: 2 June 2011

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The electronic properties of hydrogenated silicene and germanene, so called silicane and germanane, respectively, are investigated using first-principles calculations based on density functional theory. Two different atomic configurations are found to be stable and energetically degenerate. Upon the adsorption of hydrogen, an energy gap opens in silicene and germanene. Their energy gaps are next computed using the HSE hybrid functional as well as the G0W0 many-body perturbation method. These materials are found to be wide band-gap semiconductors, the type of gap in silicane (direct or indirect) depending on its atomic configuration. Germanane is predicted to be a direct-gap material, independent of its atomic configuration, with an average energy gap of about 3.2 eV, this material thus being potentially interesting for optoelectronic applications in the blue/violet spectral range.
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81.05.Hd Other semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds

Modeling of solvent evaporation from polymer jets in electrospinning

Xiang-Fa Wu, Yury Salkovskiy, and Yuris A. Dzenis

Appl. Phys. Lett. 98, 223108 (2011); http://dx.doi.org/10.1063/1.3585148 (3 pages) | Cited 4 times

Online Publication Date: 2 June 2011

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Solvent evaporation plays a critical role in nanofiber formation in electrospinning. Here, we present a nonlinear mass diffusion-transfer model describing the drying process in dilute polymer solution jets. The model is used to predict transient solvent concentration profiles in polyacrylonitrile/N,N-dimethylformamide (PAN/DMF) jets with the initial radii ranging from 50 μm down to 100 nm. Numerical simulations demonstrate high transient inhomogeneity of solvent concentration over the jet cross-section in microscopic jets. The degree of inhomogeneity decreases for finer, submicron jets. The simulated jet drying time decreases rapidly with the decreasing initial jet radius, from seconds for microjets to single milliseconds for nanojets. The results demonstrate the need for further improved coupled multiphysics models of electrospinning jets.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.16.-c Methods of micro- and nanofabrication and processing
68.03.Fg Evaporation and condensation of liquids
61.25.he Polymer solutions

De-embedding parasitic elements of GaN nanowire metal semiconductor field effect transistors by use of microwave measurements

Dazhen Gu, T. M. Wallis, P. Blanchard, Sang-Hyun Lim, A. Imtiaz, K. A. Bertness, N. A. Sanford, and P. Kabos

Appl. Phys. Lett. 98, 223109 (2011); http://dx.doi.org/10.1063/1.3597408 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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We present a de-embedding roadmap for extracting parasitic elements of a nanowire (NW) metal semiconductor field effect transistor (MESFET) from full two-port scattering-parameter measurements in 0.1–25 GHz range. The NW MESFET is integrated in a microwave coplanar waveguide structure. A conventional MESFET circuit model is modified to include capacitors of small value that is non-negligible in NW devices. We follow a step-by-step removal of external elements and an iteration search for optimized model data. The fitted model indicates good agreement with experimental data. This letter reflects a significant step toward full circuit modeling of NW MESFETs under normal operating conditions.
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85.30.Tv Field effect devices
02.60.Pn Numerical optimization
84.32.Tt Capacitors
84.40.Az Waveguides, transmission lines, striplines
84.40.Lj Microwave integrated electronics
85.30.De Semiconductor-device characterization, design, and modeling
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