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    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.
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    Environmental effects on photoinduced electron transfer and fluorescence blinking of single semiconducting nanocrystals in various matrices
    (2010-01-01)
    Ko, H. C.
    ;
    Yuan, C. T.
    ;
    Yu, Ping
    ;
    Huang, Jane
    ;
    Tang, Jau
    In this report we explore how the surrounding environments around a single semiconducting nancrystal affect the photoinduced electron transfer, charge trapping fluorescence lifetime and fluorescence blinking. Using the time-correlated single photon counting techniques combined with confocal microscopy, we investigated photoluminescence of single CdSe/ZnS quantum dots embedded in agarose gel and on conductive substrates as examples. Understanding of the underlying mechanisms would allow us to better control of the photoluminescence properties of nanoparticles and to improve their performance in biophotonics and optoelectronics applications such as fluorescence markers, single-photon sources, photovoltaics and quantum dot lasers.
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    Effect of atomic position on the spontaneous emission of a three-level atom in a coherent photonic-band-gap reservoir
    (2009-01-01)
    Cheng, Szu-
    ;
    Wu, Jing-Nuo
    ;
    Yang, Tzong-Jer
    ;
    Hsieh, Wen-Feng
    ;
    光電工程學系
    The effect of atomic position on the spontaneous emission and optical spectra of a three-level atom embedded in a photonic crystal was studied by considering the coherent two-band photonic-band-gap (PBG) reservoir. With the definite phase difference between the fields of the air band and dielectric band in this coherent PBG reservoir, we found that this coherent property grows stronger and results in the spectrum shift and the appearance of dark lines and kinks as the width of band gap gets smaller; and the variation of the atomic position leads to large shift of spectral peak. The averaged spectra of the system with an ensemble of atoms embedded in the dielectric region are blueshifted while those of atoms in the air region are redshifted. The spectra peaks can even shift more than 75% of the half width at half maximum. The feasible experimental systems composed of an ensemble of molecules (quantum dots or fluorescence dye) in photonic crystals are discussed.
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    0.7 anomaly due to the Rashba interaction in a nonuniform electric field
    (2009-01-01)
    Hsiao, J. H.
    ;
    Liu, K. M.
    ;
    Hsu, S. Y.
    ;
    Hong, T. M.
    ;
    電子物理學系
    We demonstrate that three conductance features, 0.5 and 0.7G(0) plateaus and a dip at 0.5G(0), observed in quantum point contacts (QPCs) can be consistently explained by the Rashba interaction in the nonuniform electric field created by the side gates along the transport direction. A quantity gamma is defined which depends on the extent of this nonuniformity and the electron density. A short QPC tends to have a small gamma. Only when gamma is large will the Rashba interaction produce a potential well deep enough to localize the electron. This provides the bound state that forms the Kondo resonance with the tunneling electrons. We propose to compare the medium/long QPC to small/large quantum dots, which are governed by the Kondo physics and the Coulomb blockade, respectively. The relation between 0.7 anomaly and the side-gate voltage, length of QPC, and temperature can all be determined to agree qualitatively with the experiments.
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    Quantum-dot exciton dynamics with a surface plasmon: Band-edge quantum optics
    (2009-03-01)
    Chen, Y. N.
    ;
    Chen, G. Y.
    ;
    Chuu, D. S.
    ;
    Brandes, T.
    ;
    電子物理學系
    We examine the spontaneous emission of a two-level emitter, quantum-dot exciton, into surface plasmons propagating on the surface of a cylindrical nanowire. The numerically obtained dispersion relations are found to influence the spontaneous emission rate strongly. At certain values of the exciton band gap, the emission rates can go to infinity due to the band-edge feature of the dispersion relations. Borrowing the idea from the photonic crystals, we model the quantum-dot exciton dynamics with a non-Markovian way and demonstrate that the decay can undergo an oscillatory behavior. In addition, we also show that the remote entangled states can be generated via super-radiance by using the one-dimensional propagating feature of the nanowire surface plasmons.
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    Detecting non-Markovian plasmonic band gaps in quantum dots using electron transport
    (2009-06-01)
    Chen, Yueh-Nan
    ;
    Chen, Guang-Yin
    ;
    Liao, Ying-Yen
    ;
    Lambert, Neill
    ;
    Nori, Franco
    Placing a quantum dot close to a metal nanowire leads to drastic changes in its radiative decay behavior because of evanescent couplings to surface plasmons. We show how two non-Markovian effects, band edge and retardation, could be observed in such a system. Combined with a quantum-dot p-i-n junction, these effects could be readout via current-noise measurements. We also discuss how these effects can occur in similar systems with restricted geometries, such as phononic cavities and photonic crystal waveguides. This work links two previously separate topics: surface plasmons and current-noise measurements.
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    Conjugated Polymer/Nanocrystal Nanocomposites for Renewable Energy Applications in Photovoltaics and Photocatalysis
    (2014-11-26)
    Su, Yu-Wei
    ;
    Lin, Wei-Hao
    ;
    Hsu, Yung-Jung
    ;
    Wei, Kung-Hwa
    ;
    材料科學與工程學系
    Conjugated polymer/nanocrystal composites have attracted much attention for use in renewable energy applications because of their versatile and synergistic optical and electronic properties. Upon absorbing photons, charge separation occurs in the nanocrystals, generating electrons and holes for photocurrent flow or reduction/oxidation (redox) reactions under proper conditions. Incorporating these nanocrystals into conjugated polymers can complement the visible light absorption range of the polymers for photovoltaics applications or allow the polymers to sensitize or immobilize the nanocrystals for photocatalysis. Here, the current developments of conjugated polymer/nanocrystal nanocomposites for bulk heterojunction-type photovoltaics incorporating Cd- and Pb-based nanocrystals or quantum dots are reviewed. The effects of manipulating the organic ligands and the concentration of the nanocrystal precursor, critical factors that affect the shape and aggregation of the nanocrystals, are also discussed. In the conclusion, the mechanisms through which conjugated polymers can sensitize semiconductor nanocrystals (TiO2, ZnO) to ensure efficient charge separation, as well as how they can support immobilized nanocrystals for use in photocatalysis, are addressed.
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    磁場作用下之單一量子點分子能態
    (2008)
    張文豪
    ;
    CHANG WEN HAO
    ;
    國立交通大學電子物理學系(所)
    本計畫目的是研究由雙層堆疊之砷化銦鎵量子點所形成的單一量子點分子在 磁場作用下之耦合能態，擬研究主題包含:（1）量子點分子之激子轉換機制以及（2） 量子點分子在磁場作用下之耦合效應。本計畫將運用超快時間解析光譜量測技術， 研究激子能量轉換的動態行為，並以顯微螢光激發能譜探索選擇性激發QDM 激子 態的可能性。此外，我們也將設計極化解析之光子相干量測研究QDM 中雙激子- 激子之序列輻射中所隱含的按激子態。顯微磁光光譜技術，藉由外加垂直（Faraday） 及水平（Vogit）方向的磁場，可以用來偵測量子點的反磁能移及奇曼（Zeeman） 效應。我們將利用這樣的技術，研究量子點大小、形狀及應力分佈對於g 值的影響， 並探討QDM 在磁場作用下的能態耦合現象。探討議題包括g 值的操控、輕-重電洞 能帶混和及明-暗激子混和。
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    半導體奈米元件的軌道與電子自旋磁性
    (2008)
    霍斯科
    ;
    Voskoboynikov Oleksa
    ;
    國立交通大學電子工程學系及電子研究所
    現代的半導體技術已經發展到可以製作人造半導體介觀物質，利用數十奈米尺度 的微小物體來建構這些新的介物質。而這些奈米半導體介物質讓我們很有潛能在 一個非常廣的範圍內操縱電磁場，這可以應用在很多新的應用元件或基礎科學， 短期可能的偉大成就包含：大規模量子計算、光學的負折射率介物質、使用非磁 性物質來產生靜磁性或動態磁性，等等驚人的發展。 明顯的，奈米半導體介物質需要一個合適的半導體奈米材料組成，近年來，量子 點、量子環、量子線、量子點分子的物理特性大幅被瞭解，包括他們的傳輸、磁 場還有光學行為，他們會是很合適的候選人。但是，我們對這些奈米材料相對應 的動態靜態的軌道與自旋的磁學卻所知不多。 在我們先前的工作，我們已經在理論上成功驗證了，在非磁性半導體上獲得特殊 動態靜態磁性的機會。我們也成功驗證了量子環複合材料足以產生等效負介電常 數與透磁率。 在這個接續的計畫中，我們設計發展一個有力的理論基礎去描述半導體奈米材料 與介物質的磁場控制行為。包含兩方面: 1. 擁有少數可控制的電子(電洞)能階的半導體奈米材料的軌道與自旋磁學的量 化描述 2. 在一個包含兩個以上的奈米材料的系統中，這些奈米材料間的量子與電磁交 互作用 我們將發展一套方法去設計並控制非磁性半導體奈米材料(包含量子點，量子 環，量子點分子)的軌道與自旋磁性，這將提供我們對半導體介物質特殊磁性的 最重要的資訊。我們強調，這個方法將有與傳統半導體科技相容的優勢。
  • Thumbnail Image
    Item type:Item,
    半導體奈米元件的軌道與電子自旋磁性
    (2009)
    霍斯科
    ;
    Voskoboynikov Oleksa
    ;
    國立交通大學電子工程學系及電子研究所
    現代的半導體技術已經發展到可以製作人造半導體介觀物質，利用數十奈米尺度 的微小物體來建構這些新的介物質。而這些奈米半導體介物質讓我們很有潛能在 一個非常廣的範圍內操縱電磁場，這可以應用在很多新的應用元件或基礎科學， 短期可能的偉大成就包含：大規模量子計算、光學的負折射率介物質、使用非磁 性物質來產生靜磁性或動態磁性，等等驚人的發展。 明顯的，奈米半導體介物質需要一個合適的半導體奈米材料組成，近年來，量子 點、量子環、量子線、量子點分子的物理特性大幅被瞭解，包括他們的傳輸、磁 場還有光學行為，他們會是很合適的候選人。但是，我們對這些奈米材料相對應 的動態靜態的軌道與自旋的磁學卻所知不多。 在我們先前的工作，我們已經在理論上成功驗證了，在非磁性半導體上獲得特殊 動態靜態磁性的機會。我們也成功驗證了量子環複合材料足以產生等效負介電常 數與透磁率。 在這個接續的計畫中，我們設計發展一個有力的理論基礎去描述半導體奈米材料 與介物質的磁場控制行為。包含兩方面: 1. 擁有少數可控制的電子(電洞)能階的半導體奈米材料的軌道與自旋磁學的量 化描述 2. 在一個包含兩個以上的奈米材料的系統中，這些奈米材料間的量子與電磁交 互作用 我們將發展一套方法去設計並控制非磁性半導體奈米材料(包含量子點，量子 環，量子點分子)的軌道與自旋磁性，這將提供我們對半導體介物質特殊磁性的 最重要的資訊。我們強調，這個方法將有與傳統半導體科技相容的優勢。