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26 Apr 2010

Volume 96, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 96, 173501 (2010); http://dx.doi.org/10.1063/1.3409475 (3 pages)

Seoung-Ki Lee, Houk Jang, Musarrat Hasan, Jae Bon Koo, and Jong-Hyun Ahn
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Brownian motion induced dynamic near-field interaction between quantum dots and plasmonic nanoparticles in aqueous medium

Lina Xu, Bong Jae Lee, Willard L. Hanson, and Bumsoo Han

Appl. Phys. Lett. 96, 174101 (2010); http://dx.doi.org/10.1063/1.3415498 (3 pages) | Cited 2 times

Online Publication Date: 26 April 2010

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Metal-enhanced fluorescence has been studied over the past three decades in order to improve fluorescence sensing and imaging techniques in microfluidics and medical diagnostics. However, most of previous studies were performed while precisely maintaining the distance between fluorophore and plasmonic nanoparticles. In the present study, we investigate the enhanced fluorescence from quantum dots (QDs) that are mixed with plasmonic nanoparticles, such as gold nanoshell (GNS), in the aqueous medium without confining the interparticle distance. Although the near-field interaction could not occur based on the estimated interparticle distance according to particle concentrations, the experimental results indicate that the QD fluorescence can be greatly enhanced. A Monte Carlo simulation revealed that there exists considerable probability that QDs can reach the near-field region of GNS due to the thermally induced Brownian motion.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Bz Metals and metallic alloys
78.67.Hc Quantum dots

Concurrent structural and mechanical characterization of forming colloidal film by ultrasound and light

Timo Karppinen, Heikki Pajari, Jonne Haapalainen, Ivan Kassamakov, and Edward Hæggström

Appl. Phys. Lett. 96, 174102 (2010); http://dx.doi.org/10.1063/1.3387814 (3 pages) | Cited 1 time

Online Publication Date: 27 April 2010

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We combined noninvasive ultrasonic and optical measurements to estimate the mechanical properties of forming colloidal films. Light reflection measurements determined the stage of drying and film structure. A concurrent ultrasound measurement quantified the film stiffness. The main finding was that compressing capillary forces induced a temporal peak in film stiffness when air began to enter the pores in the film. We believe that empirically observing such a stiffening event has not been reported before. This finding advances the understanding of the physics of consolidating suspensions.
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68.15.+e Liquid thin films
82.70.Dd Colloids
62.10.+s Mechanical properties of liquids
78.66.Qn Polymers; organic compounds
68.60.Bs Mechanical and acoustical properties
62.60.+v Acoustical properties of liquids

Low-frequency ac electro-flow-focusing microfluidic emulsification

Peng He, Haejune Kim, Dawei Luo, Manuel Marquez, and Zhengdong Cheng

Appl. Phys. Lett. 96, 174103 (2010); http://dx.doi.org/10.1063/1.3424791 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2010

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Applications of electric field, using either dc or high-frequency ac field, have shown many advantages in emulsification. We further develop this technique by a detailed study on low-frequency ac electro-flow-focusing (EFF) microfluidic emulsification. Counter-intuitively, the droplet size variation is not monotonic with the electric field, in contrary to the dc-EFF emulsification. This phenomenon originates from a relaxation oscillation of flow rate through the Taylor cone. Particularly, a continuous droplet size decrease was obtained at the voltage ramp-up stage. This emulsification process was modeled in analog to the accumulation and release of charges in an RC electric circuit with an adjustable resistor.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.61.-k Micro- and nano- scale flow phenomena
47.85.Np Fluidics
47.55.D- Drops and bubbles
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Strong size-dependent photoacoustic effect on gold nanoparticles by laser-induced nanobubbles

Martín G. González, Xiangjiang Liu, Reinhard Niessner, and Christoph Haisch

Appl. Phys. Lett. 96, 174104 (2010); http://dx.doi.org/10.1063/1.3387890 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2010

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In this paper we propose a mathematical model and an approximate equation to explain the behavior found on the photoacoustic effect generated by laser-induced nanobubbles in colloidal gold solutions. To obtain the equation, we developed a simulation program based on the widely known Rayleigh–Plesset model. A set of measurements was carried out to assess its accuracy on real samples. The equation gives a good approximation for spherical gold nanoparticles with sizes between 10 and 80 nm, and laser fluences larger than the fluence threshold for bubble formation.
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78.20.Pa Photoacoustic effects
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.70.Dd Colloids
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