Browsing by Author "Yu, Pyng"

Now showing 1 - 13 of 13

2-D modeling of dual-mode acoustic phonon excitation of a triangular nanoplate
(2010-08-23)
Tai, Po-Tse
;
Yu, Pyng
;
Tang, Jau
;
光電工程學系
;
Department of Photonics
In this theoretical work, we investigated coherent phonon excitation of a triangular nanoplate based on 2-D Fermi-Pasta-Ulam lattice model. Based on the two-temperature model commonly used in description of laser heating of metals, we considered two kinds of forces related to electronic and lattice stresses. Based on extensive simulation and analysis, we identified two major planar phonon modes, namely, a standing wave mode related to the triangle bisector and another mode corresponding to half of the side length. This work elucidates the roles of laser-induced electronic stress and lattice stress in controlling the initial phase and the amplitude ratio between these two phonon modes. (C) 2010 Elsevier B.V. All rights reserved.
Antibunching Single-Photon Emission and Blinking Suppression of CdSe/ZnS Quantum Dots
(2009-10-01)
Yuan, C. T.
;
Yu, Pyng
;
Ko, H. C.
;
Huang, J.
;
Tang, Jau
We demonstrated that by property coupling to silver nanoprisms, single CdSe/ZnS semiconductor quantum dots (QDs) exhibited suppressed blinking behavior, an enhanced fluorescence intensity (similar to 2.5 fold), increased radiative decay rates (similar to 12.5,fold), and antibunching single-photon emission. All these modifications significantly promote the overall performance of the proposed single-photon sources based on colloidal semiconductor QDs.
Blinking Suppression and Anti-Bunching of Quantum Dots as Single-Photon Sources
(2010-01-01)
Yu, Pyng
;
Yuan, Chi-Tsu
;
Ko, Hsien-Chien
;
Huang, Jane
;
Tang, Jau
We report here our study on suppression of fluorescence blinking of colloidal CdSe/ZnS quantum dots (QDs) for potential applications as high performance single-photon sources. Blinking is an interesting property for single QDs, but it is undesirable for their applications. We have demonstrated that by coupling these QDs to adjacent silver nanoprisms, we could not only completely suppress the blinking but also enhance the fluorescence quantum yield, and also increase the fluorescence decay rates. These single QDs also exhibit anti-bunching behavior which is a signature for a single-photon emitter. In addition, we have also achieved blinking suppression by embedded the QDs in agarose gel. The electrostatic environment around QDs due to negatively charged fibers of gel might strongly affect the extent of blinking suppression. The mechanisms of blinking suppression will be discussed in the frame work of diffusion-controlled electron transfer model.
Blinking suppression of colloidal CdSe/ZnS quantum dots by coupling to silver nanoprisms
(2009-06-15)
Yuan, C. T.
;
Yu, Pyng
;
Tang, Jau
;
光電工程學系
;
Department of Photonics
Fluorescence blinking of quantum dots (QDs) is a common but annoying behavior for practical applications as fluorescent markers or single photon sources. We demonstrate here, by coupling colloidal CdSe/ZnS QDs to silver nanoprisms, fluorescence blinking behavior can be suppressed. For most of coupled QDs, two emissive states with different fluorescence intensities and lifetime were observed. We suggest that energy transfer could play an important role in suppressing blinking behavior.
Carrier dynamics in InN nanorod arrays
(2012-01-16)
Ahn, Hyeyoung
;
Yu, Chih-Cheng
;
Yu, Pyng
;
Tang, Jau
;
Hong, Yu-Liang
In this report, we investigated ultrafast carrier dynamics of vertically aligned indium nitride (InN) nanorod (NR) arrays grown by molecular-beam epitaxy on Si(111) substrates. Dominant band filling effects were observed and were attributed to a partial bleaching of absorption at the probe wavelengths near the absorption edge. Carrier relaxation in nanorod samples was strongly dependent on the rod size and length. In particular, a fast initial decay was observed for carriers in NRs with a small diameter (similar to 30 nm), the lifetime of which is much shorter than the carrier cooling time, demonstrating the substantial surface-associated influence on carrier relaxation in semiconductor nanostructures. (C)2012 Optical Society of America
Dynamic study on the transformation process of gold nanoclusters
(2014-11-07)
Ma, Xiaoqian
;
Wen, Xiaoming
;
Toh, Yon-Rui
;
Huang, Kuo-Yen
;
Tang, Jau
In this paper, the transformation process from Au-8 to Au-25 nanoclusters (NCs) is investigated with steady state fluorescence spectroscopy and time-resolved fluorescence spectroscopy at various reaction temperatures and solvent diffusivities. Results demonstrate that Au-8 NCs, protected by bovine serum albumin, transform into Au-25 NCs under controlled pH values through an endothermic reaction with the activation energy of 74 kJ mol(-1). Meanwhile, the characteristic s-shaped curves describing the formation of Au-25 NCs suggest this process involves a diffusion controlled growth mechanism.
Optical properties of gold particle-cluster core-satellite nanoassemblies
(2013)
Yu, Pyng
;
Wen, Xiaoming
;
Toh, Yon-Rui
;
Lee, Yu-Chieh
;
Tang, Jau
Better understanding of core-satellite nanostructures is of great interest to researchers owing to their unusual properties and is key to their promising applications. The well-developed techniques based on protein-nanoparticle interactions were adopted to produce core-satellite nanoassemblies of similar to 10 nm core of Au nanoparticles (AuNPs) covered by Au-25@BSA or Au-10@histidine nanoclusters (NCs). The photoexcited dynamics in the core-satellite nanoassemblies were studied using steady-state and time-resolved spectroscopic measurements. Fluorescence quenching in AuNP-AuNCs core-satellite nanostructures was observed and confirmed as static quenching. The AuNPs alter neither radiative decay nor nonradiative decay in both nanoclusters. This indicates that the electron/energy transfer within the NP-NCs core-satellite nanoassemblies is absent, in contrast to the results involving other larger NP-NPs core-satellite nanoassemblies.
Photoinduced multimode coherent acoustic phonons of metallic nanoprisms and the effects of shape-induced anisotropic electronic stresses
(2011-05-14)
Tai, Po-Tse
;
Yu, Pyng
;
Tang, Jau
;
光電工程學系
;
Department of Photonics
In this work we reported experimental measurements of ultrafast structural dynamics in metallic nanoprisms induced by a femtosecond laser pulse. The main focus of this study of anisotropic heating in nanoprisms is about laser fluence effects on photoexcitation of two planar coherent acoustic phonon modes, namely, the breathing mode and the totally symmetric mode. We presented a combined two-temperature model and 2-D Fermi-Pasta-Ulam model to explain both the dependence of the initial phases and the mode weight on the excitation power. Our transient optical absorption data for both the initial fast monotonic decay and the subsequent coherent acoustic oscillations clearly indicate the presence of anisotropic thermal expansion in nanoprisms. (C) 2011 American Institute of Physics. [doi:10.1063/1.3590373]
Photoinduced Structural Dynamics in Laser-Heated Nanomaterials of Various Shapes and Sizes
(2008-11-06)
Yu, Pyng
;
Tang, Jan
;
Lin, Sheng-Hsien
;
應用化學系
;
Department of Applied Chemistry
We examined photoinduced ultrafast structural dynamics such as coherent acoustic waves in many shapes of fcc metallic nanomaterials. Experimental data of nanosized thin films, prisms, spheres, rods, disks and pyramids from transient optical absorption/reflectance measurements were analyzed based on a combined Fermi-Pasta-Ulam model and two-temperature model. This work elucidates the structural dynamics induced by femtosecond laser heating, its size and shape effects on the period and phase of the excited acoustic phonon modes.
Quantum Confined Stark Effect in Au-8 and Au-25 Nanoclusters
(2013-02-21)
Wen, Xiaoming
;
Yu, Pyng
;
Toh, Yon-Rui
;
Tang, Jau
;
光電工程學系
The quantum confined Stark effect is investigated for the first time in bovine serum albumin (BSA) protected Au-8 and Au-25 nanoclusters. We observed a red-shift of 63 meV in Au-8 nanoclusters upon an increase in pH from 2.14 to 12.0. Such behavior could be well explained in terms of the presence of a linear polar component and a quadratic polarizable component. In contrast, Au-25 nanoclusters exhibit more complicated Stark shifts due to their specific core/semiring structure. A plateau of the Stark shift was observed in both absorption and fluorescence, showing an offset of 30 meV. The lifetime measurements confirm that the plateau is due to the screening effect of the semirings in Au-25@BSA. Moreover, the dual fluorescent bands of Au-25 nanoclusters exhibit two different Stark shifts of 79 and 52 meV, respectively. The experimental data indicate that the Stark shift in both Au-8@BSA and Au-25@BSA has a significant linear polar component due to their asymmetric structure. This study suggests that gold nanoclusters can become a potentially useful candidate in probing local electric fields and also in pH-sensing in nanoscale environment of biological systems.
Selective acoustic phonon mode excitation of multi-mode silver nanoprisms
(2010-08-30)
Tai, Po-Tse
;
Yu, Pyng
;
Huang, Jane
;
Tang, Jau
;
光電工程學系
Nanoprisms are known to exhibit two major planar phonon modes in ultrafast experiments, namely, a stronger mode related to the bisector height and a weaker mode related to half of the edge length. In this work we demonstrated photoacoustic excitation of a specific acoustic phonon mode in silver nanoprisms using two properly timed pump pulses. Using this technique, we could selectively excite only the weak totally symmetric mode while suppressing the dominant breathing mode. Via direct observation of such a mode, which is hardly detectable directly with the conventional single pump pulse technique, we could elucidate the roles of hot electrons in photoinduced ultrafast structural dynamics in laser-heated nanoparticles. (C) 2010 Elsevier B.V. All rights reserved.
Sound Wave Propagation Anisotropy in Silver Nanoprisms: Characterization of Photoinduced Multiple Modes Using the Symmetric Molecular Dynamics Method
(2013-07-04)
Ng, Ming-Yaw
;
Yu, Pyng
;
Tang, Jau
;
Chang, Yia-Chung
;
光電工程學系
We present both theoretical and experimental studies of the sound velocity anisotropy and laser-induced multiple acoustic phonon oscillations in silver nanoprisms. A large-scale simulation method based on molecular dynamics and group theory for nanoprisms with C-3v symmetry was developed. We observed the most prominent planar modes and the less studied vertical modes and found that the anisotropic vibrational properties of silver nanoprisms strongly depend on the particle's aspect ratio (bisector length over thickness). For the case of a smaller aspect ratio, we identified these modes as the A, modes with a larger in phase radial atomic displacement These modes can be classified into three main types: breathing modes and totally symmetric modes which are planar modes and thickness-related vertical modes. Due to the strong coupling with laterally confined modes, a broad band of thickness-related modes is found (in contrast to a single sharp peak for thin films), which leads to a fast decaying component in the oscillation spectrum. The calculated results and the sound velocity anisotropy along different crystal axes are in good agreement with our transient optical absorption experiments.
Synthesis of Silver Nanoprisms and Nanodiscs an Applications in Fluorescence Blinking Suppression
(2010)
Yu, Pyng
;
Huang, Jane
;
Yuan, Chi-Tsu
;
Tang, Jan
;
光電工程學系
In this work we investigated the influence of reagents in the synthesis of triangular silver nanoprisms through direct chemical reduction. We identified the chemical role of each reagent, i e H(2)O(2), poly(vinylpyrrolidone) (PVP) and NaBH(4), by systematically varying one reagent concentration while keeping the concentration of other reagents constant We also discuss the applications of nanoprisms in blinking suppression of single semiconductor quantum dots. In addition, we also investigated the synthesis of silver nanodiscs through the reconstruction of triangular nanoprisms using halide ions. The results from different halide ions presented the different face-selective etching rates on the well-identified facet in the silver nanoprism.