Papers by Keyword: Quantum Dot (QD)

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Authors: Chun Li Hao
Abstract: Here we studied in vivo stability and biodistribution of quantum dots. Their distribution in vivo at various time points were determined by measuring the amount of cadmium ions and selenium ions in various organs by inductively coupled plasma-atomic emission spectrometry. The amount of cadmium ions was higher in liver than in other organs at all times. The amount of cadmium ions in kidney and spleen were increased gradually in time-dependent. There are also obviously increased cadmium ions in lung and heart at all times compared to the control. However the amount of selenium ions was high in all organs except for brain before the 3rd day.
Authors: M.A. Humayun, M.A. Rashid, F. Malek, A. Yusof, F.S. Abdullah, N.B. Ahmad
Abstract: This paper presents a comparative analysis of some of the important characteristics of the carriers of quantum well and quantum dot based laser. Among the characteristics of the carriers, confined carrier concentrations in the gain medium as well as the carrier concentrations at the threshold have been studied extensively by using InxGa1-xN based quantum well and InxGa1-xN based quantum dot in the active layer of the laser structure. The numerical results obtained are compared to investigate the superiority of the quantum dot over quantum well. It is ascertained from the comparison results that InxGa1-xN based quantum dot provides higher density of confined carrier and lower level of carrier concentration required for lasing action. This paper reports the enhancement of confined carrier density and minimization of carrier concentration at threshold of laser using InxGa1-xN based quantum dot as the active layer material. Hence, it is revealed that better performances of lasers have been obtained using InxGa1-xN based quantum dot than that of quantum well in the active medium of the device structure.
Authors: Chong Lin Luan
Abstract: An indirect competitive immunoassay using quantum dots (QDs) as the fluorescent label has been developed for detection of melamine in milk products. The method exhibited a response for melamine with IC50 value of 11.3 ng mL-1 and a detection limit of 0.27 ng mL-1. Milk and milk powder samples spiked with melamine have been analyzed, and the method provided recoveries ranging from 84.2% to 108.0%, and a CV of 12.8%. The implementation of QDs provides for at least 30 fold improvement of detection limit when compared with optically-based ELISA screening methods that have been reported. The analytical performance in combination with simplicity of sample and antibody preparation provides the basis for a practical method for melamine detection.
Authors: Su Wen Liu, Hai Zheng Zhang
Abstract: As advances are made in the lithographic patterning process and critical defect size continues to shrink, new filters are required to remove particles in the sub-10 nm size range. Membrane filtration separates unwanted particles from a fluid by retaining particles on the membrane surface and pores, in much the same manner as a sieve. One key parameter of membrane performance is pore size, usually expressed as pore diameter. However, for nanofiltration, especially for the membranes whose pore size measures under 30 nm, manufacturers may use different methods to rate the membranes pore. Considering the different chemical structures of membranes, the vast combination of materials, and the methods of manufacturing, it is highly unlikely that a universal method can be used for all combinations.
Authors: K. Ghosh, Y. Naresh, N. Srichakradhar Reddy
Abstract: In this paper, we present theoretical model and computations for tuning the photoluminescence (PL) emission of InAs/GaAs quantum dots at 1.3 -1.55 μm by optimizing its height and base dimensions through quantum mechanical concepts. Simulation on the annealing induced compositional change in the QDs was carried out using Fick’s diffusion model. Results from our computation illustrated that lower base size of 10 nm and larger height QDs of 5.1 nm can be effectively utilized for extending the PL emission to longer wavelengths with minimal blue-shift on annealing. This highlights the potential of our model and computation to assist in precisely engineering the optical properties of QD materials for specific device applications.
Authors: Peng He, Chong Wang, Jie Yang, Yu Yang
Abstract: The generation of quantum dots (QDs), the advantages and disadvantages of quantum dot infrared photodetector (QDIP) are briefly reviewed. Typical techniques for fabricating ordered Ge/Si QDs, the application of Ge/Si QDIP in optical communication and thermal imaging and the structure optimization are described. Finally, the key problems for improving the properties of Ge/Si QDs and Ge/Si QDIP, future trends and prospects are discussed.
Authors: Vladimir M. Lantratov, Sergey A. Mintairov, Sergey A. Blokhin, Nikolay A. Kalyuzhnyy, Nikolay N. Ledentsov, Maxim V. Maximov, Alexey M. Nadtochiy, Alexey S. Pauysov, Alexey V. Sakharov, Maxim Z. Shvarts
Abstract: We studied the different carrier kinetic mechanisms involved into the interband absorption of quantum dots (QDs) by photocurrent spectroscopy. It was shown that in vertically coupled InGaAs QDs an effective carrier emission, collection and separation take place due to minizone formation. The possibility for the incorporation of vertically-coupled QDs into solar cells (SC) without any deterioration of structural quality of the p-i-n-junction has been shown. Due to the additional absorption of solar spectrum in QD media and the subsequent effective separation of photogenerated carriers, an increase (~1%) in short-circuit current density (Jsc) for the QD SC-devices has been demonstrated. However the insertion of QDs into intrinsic region reduced the open circuit voltage (Voc) of such devices. Moving the QD array in the base layer as well as including the Bragg reflector (BR) centered on 920 nm resulted in increase of the Voc. Moreover an improved absorption in the QD media for SC with BR led to further increase of Jsc (~1%). The efficiency for QD SCs at the level of 25% (30 suns AM1.5D) has been demonstrated.
Authors: S.A. Shamsudin, Hirokazu Hasegawa, Mikihito Takenaka, Saijo Kenji
Abstract: Quantum dots (QDs) have a great potential to be applied as a biosensor to detect cancer cells because of their properties such as high photoluminescence, photo stability, narrow peak of luminescence, etc. However, cadmium sulphide (CdS) quantum dots are toxic and hydrophobic, making it impossible to be applied into biomaterials. A template is needed to make CdS QDs nontoxic and hydrophilic. The optical properties of these QDs are needed to be protected. To achieve this purpose, the template for CdS QDs has been designed by capping CdS QDs with apo-ferritin shells before aligning them onto cylindrical perpendicular PS-b-P2VP template, with the aim of locating CdS QDs appropriately in sequence. A host-guest system can be developed.
Authors: Shi Chao Xu, Yue Qian Yang, Yan Shan Liu, Heng Miao, Mei Dong, Juan Yang, Ji Mei Zhang, Zhao Dai, Guo Zheng, Bo Sun, Shu Qing Sun, Zhen Zhong Jiang
Abstract: The core-shell CdTe/ZnS quantum dots were prepared with an improved process in aqueous phase. CdTe QDs were synthesized under conditions of pH 9.1, 96 °C, refluxing for 5h, and which was used as core material; ZnS was formed as shell material to enhance the optical properties. Optical properties were characterized with fluorescence spectrum (FS), and morphology of QDs was investigated via transmission electron microscopy (TEM) method. Moreover, composition and formation of CdTe/ZnS core-shell QDs was characterized via x-ray diffraction (XRD) method. Optimum conditions were investigated to obtain the qualified CdTe/ZnS core-shell QDs, the results indicated QDs with high quantum yields and fluorescence intensity were achieved under conditions of pH 9.0, 45 °C, refluxing for 1h, and v/v/v ratio of CdTe/Na2S/ZnSO4 is 4/1/1. The TEM data indicated that average size of 5 nm CdTe core was prepared, and CdTe/ZnS core-shell QDs with average size of 11 nm were achieved under the optimum conditions. ca 30nm of red shift of a maximum emission wavelength from ca 530 nm (CdTe) to 560 nm (CdTe/ZnS) was observed via FS under the optimum conditions, which inferred the growth of QDs and formation of ZnS shells. Furthermore, the enhanced fluorescence intensity of CdTe/ZnS core-shell QDs was detected and over two times of fluorescence intensity was increased after formation of ZnS shell. The obtained QDs will have great potential application in biological researches and biosensing system based on fluorescence resonance energy transition (FRET).
Authors: T. Ogawa, H. Niwa, Hiroshi Okuda, Shojiro Ochiai
Abstract: Grazing-incidence small-angle scattering (GI-SAXS) technique was applied to self-assembled Ge islands capped with Si. GI-SAXS has a merit over TEM and AFM that the structure of islands buried in a cap layer for stabilization can be evaluated nondestructively. By analyzing the scattering patterns, the size of Ge islands was estimated to be about 5 nm in height and 26 nm in diameter, with the islands density of 4.2×1014/m2. From the best fitting of two-dimensional model intensity to the experiments, the shape of the islands was deduced
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