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18 Feb 2013

Volume 102, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 073101 (2013); http://dx.doi.org/10.1063/1.4790646 (4 pages)

V. Reboud, J. Romero-Vivas, P. Lovera, N. Kehagias, T. Kehoe, G. Redmond, and C. M. Sotomayor Torres
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Single and multi-particle passive microrheology of low-density fluids using sedimented microspheres

P. Domínguez García and M. A. Rubio

Appl. Phys. Lett. 102, 074101 (2013); http://dx.doi.org/10.1063/1.4792742 (5 pages)

Online Publication Date: 19 February 2013

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We present a technique of passive microrheology based on tracking micron-sized particles which are denser than the surrounding fluid and therefore they sediment into a quasi two-dimensional layer. Theoretical corrections for the diffusion coefficient of polystyrene, magnetic, and melamine resin microspheres, situated at different average heights above the bottom of the container cell, allow to unify the corresponding results for the zero-shear viscosity and the dynamic modulus on low-density fluids, such as low-concentration mixtures of glycerol and poly(ethylene oxide) in water and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. Limitations of the experimental and data analysis methodology are discussed by developing experimental-like simulations of Brownian fluids.
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81.07.Bc Nanocrystalline materials
66.20.-d Viscosity of liquids; diffusive momentum transport
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
66.10.Ed Ionic conduction
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Physisorption of functionalized gold nanoparticles on AlGaN/GaN high electron mobility transistors for sensing applications

M. S. Makowski, S. Kim, M. Gaillard, D. Janes, M. J. Manfra, I. Bryan, Z. Sitar, C. Arellano, J. Xie, R. Collazo, and A. Ivanisevic

Appl. Phys. Lett. 102, 074102 (2013); http://dx.doi.org/10.1063/1.4791788 (5 pages)

Online Publication Date: 19 February 2013

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AlGaN/GaN high electron mobility transistors (HEMTs) were used to measure electrical characteristics of physisorbed gold nanoparticles (Au NPs) functionalized with alkanethiols with a terminal methyl, amine, or carboxyl functional group. Additional alkanethiol was physisorbed onto the NP treated devices to distinguish between the effects of the Au NPs and alkanethiols on HEMT operation. Scanning Kelvin probe microscopy and electrical measurements were used to characterize the treatment effects. The HEMTs were operated near threshold voltage due to the greatest sensitivity in this region. The Au NP/HEMT system electrically detected functional group differences on adsorbed NPs which is pertinent to biosensor applications.
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85.30.Tv Field effect devices
87.85.-d Biomedical engineering

Broadband flattened Luneburg lens with ultra-wide angle based on a liquid medium

Lingling Wu, Xiaoyong Tian, Huifeng Ma, Ming Yin, and Dichen Li

Appl. Phys. Lett. 102, 074103 (2013); http://dx.doi.org/10.1063/1.4793206 (4 pages)

Online Publication Date: 19 February 2013

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A two-dimensional flattened Luneburg lens with an ultra-wide viewing angle has been realized based on a liquid medium approach in our present work. A field-of-view angle up to 180° is achieved over the microwave regime. The transformed lens is realized by using a low-loss liquid medium and a large variation of refractive index from 1 to 4.18 is achieved. The non-resonant property of the liquid ensures a broadband and low-loss performance of the lens from 12.4 GHz to 18 GHz. The high directivity and relatively low loss of the proposed lens were demonstrated by simulation and experimental results.
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42.79.Bh Lenses, prisms and mirrors

Defect study of molecular beam epitaxy grown undoped GaInNAsSb thin film using junction-capacitance spectroscopy

Muhammad Monirul Islam, Naoya Miyashita, Nazmul Ahsan, and Yoshitaka Okada

Appl. Phys. Lett. 102, 074104 (2013); http://dx.doi.org/10.1063/1.4793430 (5 pages)

Online Publication Date: 21 February 2013

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Defects in undoped GaInNAsSb thin film (i-GaInNAsSb) were investigated by junction-capacitance technique using admittance and transient photocapacitance (TPC) spectroscopy. An electron trap D2 was identified at 0.34 eV below the conduction band (EC) of i-GaInNAsSb using admittance spectroscopy. Optical transition of valance band (EV) electrons to a localized state OH1 (EV + 0.75 eV) was manifested in negative TPC signal. Combined activation energy of OH1 and D2 defect corresponds to the band-gap of i-GaInNAsSb, suggesting that OH1/D2 acts as an efficient recombination center. TPC signal at ∼1.59 eV above EV was attributed to the nitrogen-induced localized state in GaInNAsSb.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Evidence for hydrogen generation in laser- or spark-induced cavitation bubbles

Takehiko Sato, Marc Tinguely, Masanobu Oizumi, and Mohamed Farhat

Appl. Phys. Lett. 102, 074105 (2013); http://dx.doi.org/10.1063/1.4793193 (4 pages) | Cited 1 time

Online Publication Date: 21 February 2013

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The growing use of focused lasers or electric sparks to generate cavitation bubbles raises concerns about the possible alteration of gas content during the initiation process and its effect on bubble dynamics. We provide experimental evidence that hydrogen molecules are produced for such plasma-induced bubbles. We performed spectral analysis of the light emitted by the plasma and monitored the dissolved hydrogen concentration in water. The mass of dissolved hydrogen was found proportional to the potential energy of the rebound bubble for both laser and spark methods. Nevertheless, hydrogen concentration was found 2.7 times larger with the spark.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Wq Discharge in liquids and solids

Growth and band alignment of Bi2Se3 topological insulator on H-terminated Si(111) van der Waals surface

Handong Li, Lei Gao, Hui Li, Gaoyun Wang, Jiang Wu, Zhihua Zhou, and Zhiming Wang

Appl. Phys. Lett. 102, 074106 (2013); http://dx.doi.org/10.1063/1.4792237 (4 pages)

Online Publication Date: 21 February 2013

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The van der Waals epitaxy of single crystalline Bi2Se3 film was achieved on hydrogen passivated Si(111) (H:Si) substrate by physical vapor deposition. Valence band structures of Bi2Se3/H:Si heterojunction were investigated by X-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. The measured Schottky barrier height at the Bi2Se3-H:Si interface was 0.31 eV. The findings pave the way for economically preparing heterojunctions and multilayers of layered compound families of topological insulators.
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68.55.aj Insulators
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.Rv Passivation

Nanochemical effects in femtosecond laser ablation of metals

A. Y. Vorobyev and Chunlei Guo

Appl. Phys. Lett. 102, 074107 (2013); http://dx.doi.org/10.1063/1.4793521 (5 pages)

Online Publication Date: 22 February 2013

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We study chemical energy released from the oxidation of aluminum in multipulse femtosecond laser ablation in air and oxygen. Our study shows that the released chemical energy amounts to about 13% of the incident laser energy, and about 50% of the ablated material is oxidized. The ablated material mass per laser pulse is measured to be on the nanogram scale. Our study indicates that femtosecond laser ablation is capable of inducing nanochemical reactions since the femtosecond laser pulse can controllably produce nanoparticles, clusters, and atoms from a solid target.
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79.20.Eb Laser ablation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
81.65.Mq Oxidation
82.50.Bc Processes caused by infrared radiation
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